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AMPERE Newsletter Issue 88 March 31, 2016

1

Issue 88 March 31, 2016

In this Issue:

Prospects in RF and microwave application on medical diagnosis and treatment Yoshio Nikawa 2

Looking while cooking in a microwave oven Raymond L. Boxman, Edi Ya’ari, Sergei Shchelkunov 5

The microwave materials processing group at KIT Guido Link 8

Microwave technology in manufacturing and research at Corning Incorporated Rebecca L. Schulz 12

Field assisted processing of advanced ceramics: A research perspective Bala Vaidhyanathan 14

Microwave discharges Yuri A. Lebedev 18

The International Scientific Committee (ISC) on Microwave Discharges Yuri A. Lebedev 20

Ricky's afterthought: A “corrugated” conundrum A. C. (Ricky) Metaxas 22

Recently published journal papers 24

Upcoming Events 25

Call for Papers:

- Special Issue on Solid-State Microwave Heating

- Regular issues 25

Previous issues of AMPERE Newsletter are available at http://www.ampereeurope.org/index-3.html

AMPERE Newsletter Trends in RF and Microwave Heating ISSN 1361-8598

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AMPERE Newsletter Trends in RF and Microwave Heating

www.AmpereEurope.org

ISSN 1361-8598

AMPERE Newsletter Issue 88 March 31, 2016

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Prospects in RF and Microwave Applications on Medical Diagnosis and Treatment

Yoshio Nikawa

Department of Health and Medical Engineering, School of Science and Engineering, Kokushikan University, 4-28-1 Setagaya, Setagaya-ku, Tokyo 154-8515, Japan

Email: [email protected]

RF and microwave are non-ionizing radiation

energies. They are safe in application to the

human body hence applicable in medicine,

especially in noninvasive diagnosis and

treatment. For this reason, RF and microwave

energies contribution in the field of medicine

and healthcare is significantly expected.

One of the current technologies most

contributing in diagnosis is the magnetic

resonance imaging (MRI). Magnetic resonance

(MR) equipment applying an RF pulse is used

for obtaining a cross-sectional image of human

body for detecting hidden disease by measuring

longitudinal relaxation time of proton T1, as

well as the horizontal relaxation time T2.

Technology advancement makes it possible to

measure the phase shift of the longitudinal

relaxation signal. Thus, the cross-sectional

distribution of temperature elevation can be

obtained1. This new technique for obtaining

noninvasive temperature elevation inside the

human body is very useful not only for

treatment using RF and microwave energies,

such as hyperthermia treatment of cancer, but

also for treatment in the field of oriental

medicine such as moxibustion therapy which is

a heat treatment. Temperature distribution in

the anatomical transverse plane of leg at

acupuncture point ST 36 is shown in Fig. 1.

The results show that this kind of temperature

stimulation on skin will increase the

subcutaneous temperature, and can discover the

heat effects against human body2.

Furthermore, the MR equipment can also be

applied for RF heating device for application of

treatment inside the medium such as

hyperthermia application treatment of cancerous

tissues. To localize the RF energy at the treat-

ment area, the applicator design is essential in

the field of medical heating3-5.

In developing and applying these effects,

knowing the electromagnetic (EM) properties of

the human tissue is essential6. To measure

detailed complex permittivity, especially in the

millimeter wave region, EM transmission and

reflection data can be utilized for obtaining

detailed biological information such as blood

glucose level noninvasively7. Figure 2 shows

experimental results of the return loss versus

frequency for various blood glucose concent-

rations. The change of reflection coefficient was

measured in vivo as a parameter of blood

glucose level. The result shows that by measur-

ing the change of reflection coefficient, the

change of blood glucose level might be

estimated non-invasively8.

Not only for research but also for education,

an EM field sensor will be one of the most

important devices in this area. The tri-axial field

sensor is shown in Fig. 3. This sensor array is

useful to know the microwave field distribution.

The sensor can be used to show the spatial

distribution of the magnetic field not only in the

free space but also in the medium9. The LED

visualization of the microwave field especially

in the heating medium is very useful in order to

establish the SAR distribution and will be

applicable beforehand for medical usage of

microwaves especially for safety checking.

Application of RF and microwaves energies

on medical diagnosis and treatment will be more

and more significant and it is expected more

researchers will join the field of medicine and

healthcare.

Research brief

AMPERE Newsletter Issue 88 March 31, 2016

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Figure 2. Experimental results of return loss vs. frequency as a parameter of blood glucose concentration.

Figure 3. LED visualized microwave field distribution from a microwave surgical knife.

Microwave surgical knife

Figure 1. Temperature distribution of a human leg at acupuncture point ST36: (a) T1 enhanced MRI; (b) temperature elevation mapping by phase change of T1 enhanced MRI; (c) initial temperature distribution; and (d) temperature elevation at 12 minutes after moxa ignition.

Research brief

(a) (b)

(c) (d)

1.0⁰C

0

10cm

AMPERE Newsletter Issue 88 March 31, 2016

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For further reading:

[1] Y. Nikawa and A. Ishikawa, “Microwave and RF

heating for medical application under noninvasive

temperature measurement using magnetic

resonance,” Jour. Korean Inst. Electromagnetic Eng.

Sci. 10 (2010) 244.

[2] S. Nakamura, M. Nakamura, E. Maeda, Y. Nikawa,

“Study on temperature measurement using MRI

during acupuncture and moxibustion,” IEEJ Trans.

Electronics, Information & Systems 135 (2015)

1205.

[3] Y. Nikawa, M. Kikuchi, T. Terakawa, T. Matsuda,

“Heating system with a lens applicator for 430 MHz

microwave hyperthermia,” Int’l Jour. Hyperthermia

6 (1990) 671.

[4] T. Matsuda, S. Takatsuka, Y. Nikawa, M. Kikuchi,

“Heating characteristics of a 430 MHz microwave

heating system with a lens applicator in phantoms

and miniature pigs,” Int’l Jour. Hyperthermia 6

(1990) 685.

[5] T. Michiyama and Y. Nikawa, “Simulation of SAR

in the human body to determine effects of RF

heating,” IEICE Trans. Communication E92-B

(2009) 440.

[6] S. Gabriel, R.W. Lau, C. Gabriel, “The dielectric

properties of biological tissues: III. Parametric

models for the dielectric spectrum of tissues," Phys.

Med. Biol. 41 (1996) 2271.

[7] Y. Guan, Y. Nikawa, E. Tanabe, “Study of simulat-

ion for high sensitivity non-invasive measurement of

blood sugar level in millimeter waves,” IEICE

Trans. Communication E86-C (2003) 2488.

[8] Y. Nikawa and T. Michiyma, “Blood-sugar

monitoring by reflection of millimeter wave,” Proc.

Asia-Pacific Microwave Conf. Proc. III (2007) 1581.

[9] Y. Nikawa, Y. Kudo, S. Nakamura, “Development

of miniature diode sensor to visualize EM field

distribution”, Proc. 14th Int'l Conf. Microwave &

High Freq. Heating (2013) 296.

About the Author:

Yoshio Nikawa received the B.E., M.E. and Ph.D. degrees in electrical engineering from Keio University, Japan, in 1981, 1983, and 1986, respectively. He joined The National Defense Academy in 1986 as a Research Associate. From 1987 to 1988, he was a Visiting Scholar at the University

of Texas at Austin. He became an Associate Professor at The National Defense Academy in 1991. In April 1999, he joined Kokushikan University, Tokyo as a Professor in the Department of Electrical and Electronics Engineering. From 2007, he is a Head in the Department of Health

and Medical Engineering, Kokushikan University. From 2014, he is a Dean in the School of Science and Engineering, Kokushikan University.

Prof. Nikawa is awarded in recognition of distinguish-ed service as Associate Editor, IEEE Transactions on Microwave Theory and Techniques in 2008. He was the recipient of Electronics Society Award from the Electronics Society of the Institute of Electronics, Information and Communication Engineers (IEICE) in 2008. His research activities include microwave and millimeter-wave measurements and applications, microwave and millimeter-wave heating and processing for medical and industrial applications.

Research brief

AMPERE Newsletter Issue 88 March 31, 2016

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Looking while Cooking in a Microwave Oven

Raymond L. Boxman1, 2, *, Edi Ya'ari2, and Sergey Shchelkunov3

(1) Clear Wave Ltd., Herzliya, Israel, (2) Tel Aviv University, Tel Aviv, Israel, (3) Yale University, New Haven CT, U.S.A.

* E-mail: [email protected]

Cooks like to look while cooking. Visual

observation, together with sound, smell and

taste, give them essential feedback on the

cooking progress: e.g. the need to adjust the

heat flow, to stir, and in particular, an indication

that the cooking is complete. Recently,

transparent lids have become popular on pots

and pans for this purpose. Visual observation

during microwave cooking is particularly

critical, since even 10 or 20 seconds of

overcooking can convert a tasty meal into a

platter of “dog food”.

Today, conventional domestic microwave

oven doors are equipped with a window, which

employs a metallic grid. Apertures in the grid

allow some degree of visibility of the oven

contents, while sufficiently blocking microwave

leakage to meet current safety standards.

However, the visibility is very poor. The eye

focuses on the grid, and the easily discernable

details of the state of the oven contents is

insufficient to provide good cooking feedback.

This article describes a transparent window,

which provides excellent food visibility, while

attenuating microwave leakage even better than

conventional grid windows1. The window is

based on a pair of transparent conductive oxide

coatings, applied to glass substrates, and spaced

a quarter-wavelength apart. The basic idea has

been around for over 50 years2. However,

presently transparent microwave oven windows

are not commercially available.

Transparent conductive oxides are wide

band-gap semiconductors. Their band gaps are

typically a bit above 3 eV, which allows

transmission of visible light but causes

absorption of ultra-violet light. Electrical

conduction is provided by n-doping the oxide,

but only to an extent that their plasma frequency

is in the infra-red region of the spectrum.

Frequencies below the plasma frequency,

including microwave frequencies, are generally

reflected, while frequencies above the plasma

frequency are transmitted.

Quantitatively, the reflectance r iS S , trans-

mission t iS S and absorption a iS S of a single

conductive coating is determined by its sheet

resistivity R d , where is the resistivity of

the transparent oxide coating material and d is

the coating thickness (Fig. 1).

0.0

0.2

0.4

0.6

0.8

1.0

0 100 200 300 400

R [Ω]

Sa /Si

Sr /Si

St /Si

Figure 1. Reflectance

r iS S , transmission t iS S

and absorption a iS S of a conductive coating as a

function of the sheet resistivity R.

While in principle the microwave trans-

mission can approach 0 if R is sufficiently

small, in practice R cannot economically be

made small enough to satisfy safety require-

ments: the resistivity is limited by the doping of

the film, while very thick coatings tend to

absorb light and delaminate. To overcome this

difficulty, two coatings are employed, spaced a

quarter-of-wavelength apart. Figure 2 shows the

transmission as a function of the spacing

between 10- coatings for normal incidence. At

the optimal 4 spacing (or at odd integer

multiples thereof), attenuation of –57 dB is

obtained. However, if the wave is obliquely

incident, the attenuation depends on the angle of

incidence and the polarization, as shown in

Fig. 3. For increasing angle of incidence, the

Research brief

AMPERE Newsletter Issue 88 March 31, 2016

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transmission of TE waves is decreased, while

the transmission of TM waves is increased.

Figure 2. Transmission of a pair of 10 coatings spaced a distance L apart in air (normal incidence).

Figure 3. Transmission (dB) of TE and TM waves for pair of coatings at oblique incidence as a function of

incidence angle (with R between 2 to 12 ).

In a microwave oven, typically multiple

cavity modes are excited, each with its own

polarization and angle of incidence at the

window. The amplitude of each mode depends

on the excitation strength, geometry and

frequency, and on the load, whose properties

change during heating. Furthermore, the

properties of the load affect the magnetron

frequency and power. Thus for real food loads,

the transmission cannot be accurately predicted.

Figure 4 shows measurements of the band-

pass power leaking from a 20-litre microwave

oven with various loads, equipped with its

standard grid window, and with a ClearWaveTM

etalon window using 5 coatings separated by

12.6 mm of glass. It may be seen that under all

conditions, the leakage via the etalon window is

considerably less than the standard window.

Figure 4. Band power under the following conditions: (1) empty oven, after 20 s operation, (2) 300 ml water load, after 20 s operation, and (3) 300 ml water load, after 55 s operation

Figure 5 is a photograph of a lentil and

tomato mini-casserole being cooked in a 20-litre

microwave oven equipped with an etalon

window. Video clips of various foods cooking

in microwave ovens and photographed through

the ClearWaveTM etalon window may be

viewed at YouTube3. It may be seen that the

transparent etalon window provides except-

ional food visibility.

Figure 5. Lentil-tomato mini-casseroles during cooking in a 20-litre microwave oven, photo-graphed via a ClearWaveTM etalon window (see www.youtube.com/channel/UCiZLxQCzAqdYXUFuDUhWkdA).

Research brief

AMPERE Newsletter Issue 88 March 31, 2016

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The main challenge in developing this

window was finding an appropriate combination

of techniques and materials that would allow

safe operation under exceptional conditions

(e.g. empty oven operation), while having an

affordable price. The cost of the coated glass

used in the present implementation is about $2.5

for the 20-litre oven, in large quantities, and

thus should be affordable in mid-range and

luxury domestic ovens.

For further reading:

[1] R. Boxman, V. Dikhtyar, E. Gidalevich, V.

Zhitomirsky, "Microwave oven window," US Patent

8772687, July 2014.

[2] D. B. Haagensen, Microwave Ovens, U.S. patent

2,920,174, 5 Jan. 1960.

[3] www.youtube.com/channel/UCiZLxQCzAqdYXUFuDUhWkdA

About the Authors:

Raymond L. Boxman received his S.B. and S.M. degrees in Electrical Engineering in 1969, and his Ph.D. from M.I.T. in 1973. He worked as a Senior Research Engineer at GE from 1973 to 1975, at which time he took up a position on the Faculty of Engineering at Tel Aviv

University. Prof. Boxman is the co-founder of the Electrical Discharge and Plasma Laboratory at TAU, which he currently directs. His teaching included electro-magnetic fields, plasma, and thin film courses. He served as Head of the Department of Interdisciplinary Studies,

Coordinator of the Materials Engineering Program, Associate Dean for Research in the Faculty of Engineering, and Incumbent of the Kranzberg Chair for Plasma Engineering. He received the Joffee Foundation Award and the Walter Dyke Award, and is a Fellow of the IEEE. Prof. Boxman is the Founder and CEO of Clear Wave Ltd. He served as Chairman of the Technical Program Committee for the International Microwave Power Institute Conference in 2014 and 2015. He has presented over 480 scientific papers at conferences and in technical journals, as well as eleven patents. He also teaches short courses in scientific writing and is now completing a textbook on this subject.

Sergey V. Shchelkunov received his B.S. in Physics from Novosibirsk State University in 1994. He received subsequently his two M.S. degrees from Novosibirsk State University in 1996, and Columbia University, New York, in 2004. He received his Ph.D. (in Applied Physics and Math) from Columbia University in 2005. He worked from

1996 to 1999 as a teaching assistant in Novosibirsk State University, and also as a Junior Research Scientists in Budker Institute of Nuclear Physics (Novosibirsk, Russia). After having received his Ph.D., he pursued a career of accelerator scientists working first at Columbia University, and later at Yale University (from 2008). He

presently works as a Research Scientists at Yale University, and as a Senior Research Scientists at Omega-P, R&D, Inc. in New Haven. He has over 50 publications in journals and conference proceedings in the areas of RF engineering and high-gradient acceleration research. His latest synergetic activities include reviewing the articles submitted to Physics Review, Special Topics (PR-STAB) and Nuclear Instruments and Methods in Physics Research, Section A (NIM-A); participating as an invited speaker/presenter in meetings organized to assess the state of, and advise on possible direction of development in the fields of structure-based dielectric-wakefield accelerators and high-gradient acceleration research; and supervising and mentoring summer students at Yale University.

Research brief

AMPERE Newsletter Issue 88 March 31, 2016

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The Microwave Materials Processing Group at KIT

Guido Link

Institute for Pulsed Power and Microwave Technology Karlsruhe Institute of Technology, Karlsruhe, Germany

E-mail: [email protected]

As "The research university in the Helmholtz

Association", the Karlsruhe Institute of

Technology (KIT) is a pioneer in the German

science system, and it maximizes its synergies.

In the coming years, the tasks of national large-

scale research and a state university will be

merged step by step. In future, KIT will bring

the topics of energy, mobility and information

even more into focus. This aligns the KIT

traditional and major research fields at long-

term challenges of the society with the aim to

develop sustainable solutions to urgent

questions of the future. The perfect match in

basic and applied research is essential, for

example for the success of the energy

transition.

Within this political frame, the KIT

Institute for Pulsed Power and Microwave

Technology is - since more than 20 years now -

active in the field of microwave materials

processing. Besides program oriented funding

by the Helmholtz Association, further funds

have been raised in numerous cooperative

research and development activities with

partners from research and industry.

As well known in the microwave

community, heating by microwave may offer

advantages with respect to energy and time

saving, as compared to conventional heating.

This is based on microwave specific features,

including volumetric heating, selective heating,

and the potential of heating in a cold applicator

without temperature limit. During the last

decades, there have been motivating

investigations and developments all over the

globe in numerous applications. Similar

changes occurred at KIT, resulting in

substantial experience in fields like

debindering, sintering and calcination of

ceramics, metal powder sintering, melting,

welding and annealing of glasses, as well as

processing of glass and carbon fibre reinforced

composites, microwave assisted foaming of

polymers, microwave assisted gluing, and

microwave assisted chemistry, beside others.

When those activities have been started in

1993, as a spin off from nuclear fusion

research, a compact 30 GHz, 15 kW gyrotron

system was installed in close collaboration with

the Institute of Applied Physic, RAS Nizhny

Novgorod. While systematic investigation on

high temperature processes, like sintering of

functional and structural ceramics1-3 as well as

metal powder compacts4, 5, were performed, the

system was continuously improved and

extended. Meanwhile, it is a versatile system

that allows in-situ dilatometry and/or in-situ

resistivity measurement during mm-wave

sintering. Furthermore, those diagnostic tools

can be combined with a hybrid heating

module6.

Although high-frequency microwave

processing at 30 GHz using gyrotrons may have

significant benefits to processes with respect to

heating efficiency and heating uniformity, in

particular in applicators with hexagonal

geometry7, a real technology transfer into

industrial applications so far has not been

possible. Therefore, more than 10 years ago,

additional activities have been started at the

standard ISM Band frequencies (915 MHz,

2.45 GHz and 5.8 GHz) with a major focus on

2.45 GHz for applications in the field of

processing of fibre reinforced plastics. Initiated

by the former colleague Lambert Feher, a

modular large scale applicator technology has

been developed and successfully licensed to a

major industrial partner Vötsch Industrie-

technik GmbH, Germany. In collaboration with

automotive and avionic industries, significant

energy and time saving have been demonstrated

as comparted to regular heating technologies.8, 9

Research brief

AMPERE Newsletter Issue 88 March 31, 2016

9

Meanwhile, this so called HEPHAITOS

technology has been further improved and

upgraded. Now, this unique system technology

can be offered with features like hybrid heating

for temperatures up to 200°C, to improve

temperature uniformity in processes such as

curing of thick wall composites or foaming of

polymers. Furthermore, a conveyor belt can be

mounted that allows demonstrating continuous

processing, and a rotary feedthrough can be

installed for curing of filament winding part

(see Fig. 1).

Beside this, various process specific

microwave systems have been developed for

applications such as pultrusion of carbon fibre

reinforced composite10, microwave assisted

heterogeneous11, and homogeneous catalysis or

hydrothermal synthesis. Further investigation

has been successfully started in the field of

microwave assisted ablation of concrete that

could be used for the decommissioning of

nuclear power plants, what will be an exigent

problem in coming years, in particular in

Germany where nuclear technology has been

abandoned12 (see Fig. 2).

Figure 1. Modular hybrid HEPHAISTOS system with conveyor belt for continuous processing (left); with filament winding tool (middle), and microwave cured high precision filament winding parts (right).

Figure 2. Carbon-fiber reinforced polymer (CFRP) profiles successfully produced by microwave assisted pultrusion (left), pilot reactor for high temperature dry reforming and RWGS (middle), and concrete surface after microwave ablation (right).

In parallel to those system and process

developments, the implementation of in-situ

diagnostics was always of special interest in

terms of more fundamental investigations on

how microwave can influence processes. So

applicators have been developed that can be

combined with IR, RAMAN and X-ray absorp-

tion spectroscopy13,14, as well as thermogravi-

metry.

For a successful system and process design,

the detailed knowledge of the dielectric proper-

ties of materials is imperative. This information

is the essential input in any electromagnetic and

multi-physics simulation that allows design

studies and process optimization. Dielectric

materials of interest typically cover a wide

range of permittivity and all states of

aggregation. Furthermore, such permittivity

may change significantly with frequency and

Research brief

AMPERE Newsletter Issue 88 March 31, 2016

10

temperature as well as with phase transitions or

chemical reactions. To cover all those aspects, a

large variety of dielectric test-sets is needed.

Meanwhile, various test-sets based on resonant

and non-resonant methods are available in our

Institute, that cover a frequency range from 50

MHz to 24 GHz, and a temperature range from

room temperature up to 1000°C14-16. For

investigations of chemical reactions, test sets

for in-situ dielectric measurements at 2.45 GHz

have been developed based on the transmission-

reflection method18 (see Fig. 3) as well as the

cavity perturbation method. The latter allows

collecting calorimetric data to get qualitative

information about reaction enthalpy19.

In-house equipment and expertise can be

offered to interested partners from industry and

research for feasibility studies or more long-

term collaboration in research and development

of novel microwave applications.

0 50 100 150 200 250 3000.0

0.3

0.6

0.9

1.2

1.5

r"

Time in minutes

meas @80°C

meas @70°C

model

0

20

40

60

80

100

Te

mp

era

ture

in

°C

Figure 3. Dielectric loss factor of DGEBA based epoxy resin at 2.45 GHz during curing at differ-ent temperatures.

For further reading:

[1] Link, G.; Feher, L.; Thumm, M.; Ritzhaupt-Kleissl,

H. J.; Böhme, R.; Weisenburger, A.; Sintering of

advanced ceramics using a 30-GHz, 10-kW, CW

industrial gyrotron. Research Workshop of the Israel

Science Foundation on Cyclotron Resonance Masers

and Gyrotrons, Kibbuz Ma'ale Hachamisha, IL, May

18-21, 1998 IEEE Transactions on Plasma Science,

27(1999) S.547-54.

[2] Rybakov, K. I.; Semenov, V. E.; Link, G.; Thumm,

M.; Preferred orientation of pores in ceramics under

heating by a linearly polarized microwave field.

Journal of Applied Physics, 101(2007) S.84915/1-5. http://dx.doi.org/10.1063/1.2723187

[3] Paul, F.; Menesklou, W.; Link, G.; Zhou, X.; Haußelt,

J.; Binder, J. R.; Impact of microwave sintering on

dielectric properties of screen printed Ba₀ ̣₆Sr₀ ̣₄TiO₃ thick films. Journal of the European Ceramic Society,

34(2014) pp.687-694. . http://dx.doi.org/10.1016/j.jeurceramsoc.2013.09.009

[4] Takayama, S.; Link, G.; Miksch, S.; Sato, M.;

Ichikawa, J.; Thumm, M.; Millimetre wave effects on

sintering behaviour of metal powder compacts.

Powder Metallurgy, 49(2006) S.274-80. http://dx.doi.org/10.1179/174329006X110835

[5] Mahmoud, M. M.; Link, G.; Thumm, M.; The role of

the native oxide shell on the microwave sintering of

copper etal powder compacts. Journal of Alloys and

Compounds, 627(2015) pp.231-237. . http://dx.doi.org/10.1016/j.jallcom.2014.11.180

[6] Link, G.; Ichikawa, J.; Thumm, M.; Millimeter wave

sintering of metal powder compacts utilizing a

modified dilatometer for resistivity measurements. 1st

Global Congress on Microwave Energy Applications,

Otsu, J, August 4-8, 2008 Proc.S.561-64 Tokyo:

Japan Society of Electromagnetic Wave Energy

Applications, 2008 ISBN 978-4-904068-04-5.

[7] Feher L.; Link G.; Microwave resonator for the high

temperature treatment of materials; DE19633245;

US6072168

[8] Link, G.; Kayser, T.; Köster, F.; Weiß, R.; Betz, S.;

Wiesehöfer, R.; Sames, T.; Boulkertous, N.; Teufl,

D.; Zaremba, S.; Heidbrink, F.; Maus, M.; Ghomeshi,

R.; Küppers, S.; Milwich, M. (2015). Faserverbund-

Leichtbau mit Automatisierter Mikrowellenprozess-

technik hoher Energieeffizienz (FLAME):

Schlussbericht des BMBF-Verbundprojektes (KIT

Scientific Reports ; 7701). http://dx.doi.org/10.5445/KSP/1000047509

[9] Link, G. et al.; Innovative, modulare Mikrowellen-

technologie zur Herstellung von Faserver-

bundstrukturen. Schlussbericht für das BMBF-

Verbundprojekt Förderkennzeichen: 01RI05133,-135-

140, -282 Laufzeit: 01.09.2006 - 31.05.2011

Eggenstein-Leopoldshafen, 2011.

[10] Kayser, T., Link, G., Seitz, T., Nuss, V., Dittrich, J.,

Jelonnek, J., Heidbrink, F., Ghomeshi, R.; An

applicator for microwave assisted pultrusion of

carbon fiber reinforced plastic; (2014) IEEE MTT-

S Int'l Microwave Symp. Digest, art. no. 6848325

[11] Kayser T., Soldatov S., Melcher A.; Link G.;

Jelonnek J.; A microwave applicator for high

homogeneous high temperature heating of catalysts;

(2013) IEEE MTT-S Int'l Microwave Symp. Digest,

art. no. 6697418.

Research brief

AMPERE Newsletter Issue 88 March 31, 2016

11

[12] Lepers B., Seitz T., Link G., Jelonnek J., Zink M.;

Development of a 10 kW microwave applicator for

thermal cracking of lignite briquettes; Frontiers in

Heat and Mass Transfer (FHMT), 6, 20 (2015) http://dx.doi.org/10.5098/hmt.6.20

[13] Link, G.; Heissler, S.; Faubel, W.; Weidler, P.;

Miksch, S.; Thumm, M.; Novel methods to

investigate microwave specific effects. 1st Global

Congress on Microwave Energy Applications, Otsu,

J, August 4-8, 2008 Proc.S.275-78 Tokyo : Japan

Society of Electromagnetic Wave Energy

Applications, 2008 ISBN 978-4-904068-04-5.

[14] Link, G.; Thumm, M.; Faubel, W.; Heissler, S.;

Weidler, P. G.; Raman spectroscopy for

experimental investigation of microscale selective

microwave heating. Materials Science and

Technology Conf. and Exhibition (MS&T 2010),

Houston, Tex., October 17-21, (2010), p.2936.

[15] Akhtar, M. J.; Tiwari, N. K.; Devi, J.; Mahmoud,

M. M.; Link, G.; Thumm, M.; Determination of

effective constitutive properties of metal powders at

2.45 GHz for microwave processing applications.

Frequenz, 68(2014) pp.69-81. http://dx.doi.org/10.1515/freq-2013-0083

[16] Soldatov, S.; Kayser, T.; Link, G.; Seitz, T.; Layer,

S.; Jelonnek, J.; Microwave cavity perturbation

technique for high-temperature dielectric

measurements. IEEE MTT-S International

Microwave Symposium Digest (IMS'13), Seattle,

Washington/USA, June 2-7, (2013), pp. 1-4. http://dx.doi.org/10.1109/MWSYM.2013.6697793

[17] Link, G.; Measurement and modelling of intrinsic

dielectric properties of ionic crystals at microwave

frequencies. Tao, J. [Hrsg.] Microwave and RF

Power Applications : Proc.of the 13th

Internat.Conf.on Microwave and High Frequency

Heating (AMPERE 2011), Toulouse, F, September

5-8, (2011) pp.115-118 ISBN 978-2-85428-978-7.

[18] Prastiyanto, D.; Link, G.; Arnold, U.; Thumm, M.;

Jelonnek, J.; Time- and temperature-dependent

dielectric measurements of thermosetting resins.

Multiphysics Models and Material Properties; 16th

Seminar Computer Modeling in Microwave Power

Engineering, Karlsruhe, May 12-13, (2014)

Proceedings pp.47-51.

[19] Ramopoulos, V.; Soldatov, S.; Link, G.; Kayser, T.;

Jelonnek, J.; System for in-situ dielectric and

calorimetric measurements during microwave

curing of resins. German Microwave Conference

(GeMic 2015), Nürnberg, March 16-18, (2015)

pp.29-32 ISBN 978-3-9812668-6-3.

About the Author:

Guido Link received the Dipl.-Phys. and Dr. rer. nat. degree in physics from the Technical University Karlsruhe, Germany in 1990 and 1993, respectively. His diploma thesis and graduate research was devoted to the frequency and temperature dependent dielectric

characterization of low loss ceramics and ionic crystals. Since 1993, he has been working at the Karlsruhe Institute of Technology, Germany (former Forschungszentrum Karlsruhe) in the field of high power microwave and millimeter-wave processing of materials as a team leader at the Institute for Pulsed Power and Microwave Technology.

The microwave materials processing group in 2015

Research brief

Research brief

AMPERE Newsletter Issue 88 March 31, 2016

12

Microwave Technology in Manufacturing and Research at Corning Incorporated

Rebecca L. Schulz

Corning Incorporated, Corning, NY 14830 E-mail: [email protected]

The interest in microwave technology at

Corning Incorporated (Corning) has spanned

the last six decades. In the late 1950’s,

Corning Glass Works (CGW) became involved

in material selection, design and fabrication of

guided missile radomes as well as radomes for

aircraft. Starting in the late 1960’s, CGW was

developing materials for the manufacture of

microwave integrated circuits, highly stable

resonator cavities (silver-coated glass

ceramics) and high temperature/high intensity

Luneburg lenses (borosilicate and high silica

content foamed glass (Vycor)) and other

dielectric devices and antennae. In addition to

material development and forming, Corning

scientists were advancing the theoretical

understanding of dielectric properties in

conjunction with material properties.

In the 1970’s, Corning pioneered some of

the first susceptors for home microwave use.

These browning devices were comprised of tin-

antimony slurries that were applied to either to

the exterior under-surface or interior bottom

surface of Corning Ware casseroles, pizza

plates, skillets and other devices. Some of this

cookware was designed expressly for

microwave manufacturers and often came with

a small cookbook with microwave-specific

recipes. The main drawback of these early

browning devices was that they had to be pre-

heated in the microwave prior to use in order to

fully optimize the browning effects. Likely due

to the added time element, the products were

not readily accepted by consumers. Today,

even with advent of many consumer

susceptors, browning and the appearance of

microwave-cooked foods remains a challenge

for the frozen/processed food industries.

Microwave generated plasma chemical-

vapor deposition method was investigated for

the production of optical fiber preforms. This

method used a 2.45 GHz microwave to

generate non-isothermal plasma. One of the

key features of this methodology was the

ability to laydown fully consolidated layers, as

opposed to laying down soot layers and then

consolidating. Research into this process resul-

ted in improved understanding of applicator

heads, plasma stability and methods for charac-

terizing the plasma, the uniformity and density

of the glass layers and what parameters

affected the quality of the preform, as well as

numerical modeling of the processes.

Figure 1. Vintage cookware produced by Corning with tin-antimony susceptor coatings.

Also in the mid-1970’s, Corning began a

new venture to produce air pollution abatement

equipment in the form of catalytic converters,

and expanded into the production of auto-

motive and diesel filters (light and heavy duty

vehicles). Initially, these products were hot-air

dried, but, as this was very time-consuming,

research was carried out to determine if an

alternate drying method could improve process

time and product quality.

During this work, the cement and part

compositions were systematically altered to

produce a material that would adhere to the

walls of the unfired filter channels, dry with

minimal shrinkage, survive the subsequent

firing process, and meet customer

requirements. At the same time, the various

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AMPERE Newsletter Issue 88 March 31, 2016

13

compositions were subjected to several

different drying methods to determine what

method would provide a high quality part and

maintain production rates. Initially, most work

was carried out at a lab scale with small parts

and batch curing. As microwave drying was

much more rapid than other methods, it quickly

rose to the forefront. However, to successfully

implement microwave processing on an

industrial level, it was key that composition

work and process development be undertaken

simultaneously. This was necessary as very

minor adjustments in either path could result in

failures down the line.

An example of a successful collaboration

can be found in a study undertaken to eliminate

post-firing cracks in plugged diesel filters.

Different drying methods were tested in

conjunction with varying the depth of the plug

material, the geometry and part size. No

method was completely successful in

eliminating cracked parts. However, micro-

wave drying did result in fewer cracks when

compared to the other methods.

Large scale experiments were carried out

on the production lines. In one experiment, two

different compositions (A and B) were plugged

under identical conditions with the same batch

cement and the same plug depth. The samples

were dried at three different microwave drying

schedules. The results showed that slow drying

at low powers resulted in the greatest number

of cracks in both compositions. However,

Composition A had significantly more cracks

than B regardless of power level. Thermal

images show a very different heating profile for

the two compositions, as shown in Fig. 2.

Composition A absorbed the microwave

energy primarily at the ends, while B was

warm throughout the piece. This shows that

for Composition A, water in the wet cement

was the primary absorber and for B, the entire

composition absorbed the microwave energy.

Figure 3. Thermal profiles for compositions A (Left) and B (Right) after microwave drying at similar power levels and times.

As industry continues to push the envelope

of innovation with advanced materials and

processes, in order to meet the demands of an

ever-changing electronic society, microwave

technology will remain a processing tool to be

used when appropriate. While this option may

not always be applicable, it is anticipated that

with continued research, advances in process

control systems, and applicator design,

microwave energy may be able to replace many

fossil-fuel dependent processes and will no

longer be viewed as a novel technique.

About the Author:

Rebecca Schulz received her PhD in Materials Science and Engineer-ing from the University of Florida under the supervision of David C. Clark in 1998. During her doctoral studies, she developed and demonstrated the use of micro-wave energy as a remediation

technique in the destruction of electronic circuitry from weapons components. As part of this work she design-ed, constructed, and successfully demonstrated a micro-wave off-gas system for waste circuitry work. Rebecca was awarded an Oak Ridge Institute of Science and Education (ORISE) Fellowship to complete her studies at Westinghouse Savannah River Company (WSRC). Following graduation, she was employed by WSRC

where she continued research on microwave remed-iation of transuranic wastes, tires, and medical waste. In 2001, Dr. Schulz was recruited by Corning Incor-porated where she worked on various projects related to microwave technology. In 2002, she was promoted to Senior Scientist III and in 2007 to Development Associate. Rebecca was the conference chair for the 2012, 2nd Global Congress on Microwave Energy Applications (2GCMEA) and is on the technical comm-ittee for 3GCMEA (2016). Rebecca has over 40 technical publications, served as co-editor for conference proceedings, co-authored several invited book chapters, authored 30 internal technical reports, and holds 9 pat-ents with 5 applications in prosecution. She is currently serving as President of the Microwave Working Group.

Research brief

A B

AMPERE Newsletter Issue 88 March 31, 2016

14

Field Assisted Processing of Advanced Ceramics:

A Research Perspective

Bala Vaidhyanathan

Department of Materials, Loughborough University, Loughborough, Leicestershire, LE11 3TU, United Kingdom

E-mail: [email protected]

Advanced ceramic materials are being increase-

ingly used in a wide range of applications,

including aerospace, defence, electronics,

transport and energy. The global market for

advanced ceramics is projected to exceed $75B

by 2020, driven by resurgence in global

manufacturing activity, legislation of strict

environmental regulations, technology innova-

tions and expanding application areas1.

Both electronics and structural ceramics

markets are predicted to grow at >7% annually

for the foreseeable future2. For existing

applications, growth will come predominantly

from performance enhancement, whilst for new

applications advanced ceramics are delivering

performances previously not feasible1. All these

products however require densification/sintering,

a high temperature process (e.g. 1000 – 2000oC)

that in industry can take days. The amount of

energy needed, and CO2 emitted, is therefore

very significant; energy can account for 30% of

costs (one factory spent £1.9M pa on energy and

released 353.5 t of CO2 equivalent3). Thus energy

efficient, eco-friendly sintering methods such as

Spark Plasma Sintering (SPS)4, Microwave

Assisted Sintering (MAS)5,6, Flash Sintering

(FS)7,8 and Hybrid methods like Flash-SPS

(FSPS), Microwave-FS (MFS) are continuously

being developed. These approaches are together

referred as Field Assisted Sintering Techniques

(FAST), and in all these cases application of

electric, magnetic and/or electro-magnetic field

were demonstrated to have a positive effect on

ceramic densification.

For example, the recently invented DC

(direct current) flash sintering method, for

reasons that are far from fully understood, has

yielded full densification in very short periods at

very low temperatures, e.g. 5 s at 850oC for

zirconia7, and at a surprisingly low temperature

of 325oC for Co2MnO4 spinel8 ceramics. Thus

the associated time and energy advantage is

estimated to be staggering, as well as the ability

to tailor the required micro/nano structure and in

turn the performance9,10. Figure 1 shows the

comparative energy needs of the FAST and

conventional sintering methods for the

processing of advanced ceramics.

Though electric sparks and plasmas at

particle-particle contacts, joule heating,

additional driving force provided by the E/H

fields, and temperature-gradient-driven diffusion,

have been proposed as explanations for field-

enhanced sintering of materials. However, a clear

understanding of the underlying atomistic

mechanisms still remains clouded.

In this research brief, let us have a closer look at

two of the FAST methods, namely Microwave

Assisted Sintering and Flash Sintering – one a

well established and other a newly emerging

densification method. Whilst MAS received

significant research attention due to its ability to

reduce processing times from days to

hours/minutes11, the FS method was

demonstrated to achieve full densification within

seconds7! The MAS method can be suitable for

the processing of various simple and complex

shaped engineering components12, the early use

of FS method was restricted to dog-bone shaped7

ceramic specimens – that are both difficult to

make and do not have much industrial

applicability. However, the recent developments

at Loughborough University (LU) and elsewhere

have demonstrated that FS can be used to sinter

different sample shapes. LU recently constructed

the unique controlled gradient flash sintering

(GFS) facility with atmospheric capability and

the ability to be used in a hybrid flash sintering /

conventional mode. The latter allows the strength

of the electric field to be varied whilst the

Research brief

AMPERE Newsletter Issue 88 March 31, 2016

15

conditions remain otherwise identical. This is

particularly helpful for determining the

operational mechanism(s). Results have

demonstrated that the flash sintering effect is

genuine and a perspective is now starting to be

gained into how the process works and,

importantly, how it can be manipulated

desirably13.

Figure 1. Schematic showing the time and energy savings associated with the FAST methods

The use of MAS and FS at LU have been

demonstrated to produce genuinely

nanostructured, fully dense zirconia based

ceramics (see Fig. 2) for a number of applications

including ceramic armour, Solid Oxide Fuel cells

(SOFCs), petro-chemical valve and pump seats

etc. However, in particular, significant

performance advantage was gained when the

nanostructured zirconia based ceramics was

found to exhibit more than 500 times

improvement on the hydro-thermal ageing

(HTA) resistance14. Whilst the conventional

zirconia ceramic render itself into a pile of damp

powder (due to a tetragonal to monoclinic phase

transformation that is accelerated in the presence

of moisture, temperature and pressure) at 2450C

and 4 bar pressure, the longevity of these LU

made nanostructured ceramics against HTA is

extended up to the extreme conditions of >300oC

and in excess of 65 bar pressure – an accelerated

ageing time equivalent to >1800 years in ambient

conditions - essentially showing complete

immunity against HTA whilst retaining excellent

mechanical properties. HTA degradation is the

Achilles-heel for the use of zirconia based

ceramics in the biomedical sector. This was the

reason behind the well-publicised failure of

zirconia hip replacements around year 2000.

Thus, when HTA is countered, numerous

opportunities opened up. Interestingly we also

demonstrated that the HTA immunity can be

achieved even with 90% density nano zirconia

specimens, a trait that can be further exploited in

implant situations. For example if the fabrication

of completely HTA immune, all-ceramic, graded,

acetabular cups with a porous outer nanostructure

for direct bonding with natural bone and a dense

core to align with the femoral head can be

achieved - this could pave the way for a

functionally gradient, hierarchically structured

implants. Indeed this could be achieved by using

nanoceramic suspensions, granulation, compact-

ion and FAST firing methods. Based on this, a

new research project funded by the Engineering

and Physical Sciences Research Council, UK

(EPSRC Grant reference: EP/L024780/1) is

looking at the manufacture of functionally

graded, all-ceramic implants (see Fig. 3) using

GFS and MAS methods for ever-lasting hip and

knee prosthesis.

Figure 2. Microstructure of the fully dense nano-structured (a) and commercial (b) zirconia ceramics, fabricated at LU using the FAST methods

Figure 3. Schematic of the novel functionally gradient all-ceramic implant (a) and the functionally graded microstructure (b) fabricated using FAST methods

The FS process was further adapted for the

use of AC as well as Pulsed electric fields at LU

(b)

Research brief

AMPERE Newsletter Issue 88 March 31, 2016

16

that led to the achievement of homogeneous

temperature distribution inside ceramic

specimens and hence uniform microstructure

both are vital for consistency and large scale

production needs. The MAS and FS methods

have been successfully extended to the

processing of a number of technologically

important advanced ceramic materials such as

Zinc Oxide for varistors, Barium Titanate (BT)

and Calcium Copper Titanate for capacitors,

Lead Zirconium Titanate (PZT) for transducers,

Silicon Carbide and Zirconia based ceramics for

armour, Silicide’s and Chalcogenides for thermo-

electrics, Li/Na phosphates for batteries, Ultra

High Temperature (UHT) Carbides and Borides

for hypersonic aviation applications to name a

few. There were also some interesting similarities

noted and comparisons derived between the two

field assisted sintering methods described here,

namely MAS and FS (see Table 1), suggesting

that similar underpinning mechanisms may be

operative in these processing scenarios. Further

detailed investigations are underway.

Table 1: Similarities between MAS and FS methods for the processing of advanced ceramics

Materials Microwave Assisted Processing Flash Processing Yttria stabilised zirconia (YSZ) 8YSZ is a better microwave absorber

and easy to sinter compared to 3 YSZ. 8 YSZ easy to flash than 3 YSZ.

Zirconia toughened alumina (ZTA) Sintering temperature decreases with increasing Z content.

FS field and on-set temperature decreases with increasing Z content

Barium Calcium Zirconium Titanate, Barium Zirconium Titanate, Barium Titanate etc.

The ease of sintering follows BCZT < BZT <BT in that order

Very similar behaviour in terms of FS field and on-set temperature

Chalcogenides During processing photo-emission noticed in some cases

During FS process also photo-emission noticed in some cases

Dielectrics High loss materials are easier to process compared to low loss materials

High loss dielectrics (zirconia) are easier to flash than low loss dielectrics (e.g. alumina)

However in terms of the use of field assisted

sintering techniques for advanced ceramics, the

optimisation of process parameters (e.g. heating

rate, sintering time, sintering temperature,

applied field, applied power etc) is often

achieved mainly by a laborious and expensive

trial and error approach rather than through

informed judgement. This is where FAST

process modelling could be of vital significance

towards developing predictive capabilities that

are validated through in-situ field and

temperature mapping for a wide variety of

advanced ceramic materials. This can not only

help to enhance the understanding of the

operative mechanisms that are common to field

assisted sintering methods in general and also to

improve the ability to achieve the required

properties through microstructural tailoring.

Ability to predict whether a ceramic will be

amenable to FAST processes or not and if so at

what conditions would be a great advantage to

catapult industrial take-up of these advanced

manufacturing processes for the rapid fabrication

of these materials. LU is also developing a hybrid

microwave-FS capability that could lead to

contactless flash sintering of complex ceramic

parts where 3D-printing and FS/MAS methods

are innovatively combined to gain significant

advantages. This opens up new horizons for

advanced ceramics manufacturing where some of

the demanding needs of ceramics production

such as complex shape fabrication, near-net

shape manufacturing, reducing raw-material

usage, co-sintering of dissimilar materials etc.

can be looked at holistically to develop

sustainable engineering solutions.

Research brief

AMPERE Newsletter Issue 88 March 31, 2016

17

For further reading:

[1] Advanced Ceramics: A global strategic business

report, MCP1001, Global Industrial Analysts Inc,

(2014).

[2] Advanced Ceramics - Demand and Sales Forecasts,

Report 3091, The Freedonia Group Ltd, (2011).

[3] http://www.ceram.com/industries/ceramics/energy-

reducing-firing-technology

[4] Ning H, Mastrorillo GD, Grasso S, Du B, Mori T, Hu

C, Xu Y, Simpson K, Maizza G and Reece MJ, Jour.

Materials Chemistry A Vol. 3, (33) 17426-32 (2015).

[5] Vaidhyanathan B, Annapoorani K, Binner JGP,

Raghavendra R, Jour. Am. Ceram. Soc. 93(8),

pp.2274-2280 (2010).

[6] Binner JGP, Ketharam A, Paul A, Santacruz I,

Vaidhyanathan B, Jour. Euro. Ceram. Soc, 28 (5), pp.

973-977, (2008).

[7] Cologna M, Rashkova B, Raj R, Jour Am. Ceram.

Soc., 93 (11) 3556-9 (2010).

[8] Prette ALG, Cologna M, Sglavov V, Raj R, Jour.

Power Sources 196, 2061-2065 (2011).

[9] Binner, JGP and Vaidhyanathan, B, J. Euro. Ceram.

Soc, 28 (7), pp.1329-1339, (2008).

[10] Binner, JGP, Vaidhyanathan, B, Paul, A,

Annapoorani, K, Raghupathy, B, Int. J. Appl. Ceram.

Technol, 8(4), pp.766-782, (2011).

[11] Vaidhyanathan, B, Agrawal, DK, Roy, R, J. Am.

Ceram. Soc, 87(5), pp.834-839, (2004).

[12] Gadevanishvili, S, Vaidhyanathan, B, Agrawal, DK,

Roy, R, US Patent 6,512,216, (2003).

[13] Vaidhyanathan, B, Invited Paper, AMPERE 2015

Meeting, Krakow, Poland, (2015).

[14] Paul, A, Vaidhyanathan, B, Binner, JGP, J. Am.

Ceram. Soc, 94(7), pp.2146-2152, (2011).

About the Author:

Bala Vaidhyanathan (Vaidhy) is a Professor of Advanced Materials and Processing and the Associate Dean for Enterprise at Loughborough University, UK. Prior to this, he was a Lead Scientist at GE, Global Research Corporation and a member of

Research Faculty at The Pennsylvania State University, USA. He was born in Salem, India and obtained his PhD from Indian Institute of Science, Bangalore. He specializes in nanostructured functional materials and non-conventional field assisted processing with an emphasis to Energy, Electronic and Healthcare applications. He has published over 150 peer-reviewed articles (h-index: 29), 6 book chapters, holder of 14 patents and has delivered >50 key note and invited presentations across the globe. He has held/holds >40 Government/Industry sponsored projects worth >£8.2M. With 20 years of experience, Vaidhy is one of the leading exponents in the field of microwave-

assisted materials processing, pioneered the development of hybrid two stage sintering methods and was the first to set up an atmosphere controlled, gradient flash sintering facility for the processing of advanced functional oxide/non-oxide nanomaterials and devices. He is a member of ACerS, ECerS, ICS (life member), MRS, AMPERE (management team), DCERN, IOM3and is a Fellow of the IoN. He is also the fellow of Higher Education Academy, UK. He is an invited ‘Visiting Professor’ at two international institutions, Editor of Advances in Applied ceramics, Editorial Board member for 4 international materials’ journals, Session Chair and Organizing Committee Member for >10 International Materials Conferences and Symposia. He won numerous awards and prizes including the prestigious ‘Glory of India’ Award for his contribution to Science, Technology and Education in 2010 and Verulam Medal and Prize for his significant contributions to the field of ceramics by the Institute of Materials, Minerals and Mining (IOM3), UK in 2015.

Research brief

AMPERE Newsletter Issue 88 March 31, 2016

18

Microwave Discharges

Yuri A. Lebedev

Topchiev Institute of Petrochemical Synthesis of the Russian Academy of Sciences, Moscow, Russia E-mail: [email protected]

Microwave discharges (MD) are electrical

discharges generated by electromagnetic waves

with frequencies exceeding 300 MHz (the wave

length in free space [cm] = 30/f [GHz], where f

is the microwave frequency)1-29. The used

wavelengths of microwaves lie in the range from

millimeters up to several tens of centimeters and

should correspond to the permitted microwave

bands for industrial, medical and scientific (ISM)

applications16.

The starting point in the development of MD

and microwave induced plasma (MIP) was

related with successes in radar technologies. For

example, the antenna switches are microwave

plasma devices which use high-power micro-

wave pulse for plasma generation, in order to

prevent the damage of high sensitivity micro-

wave receiver as this pulse passes through the

microwave circuit.

Further development of microwave tech-

niques created the necessary prerequisites for

application of microwave devices in different

areas of science and technology, and in particular

for generation of microwave-induced plasma

(MIP). Quasi-equilibrium and non-equilibrium

microwave plasma is applied in many areas. The

low-temperature plasma is used for instance in

light and ion sources, in processes of plasma

chemical deposition of organic and inorganic

films, for coating (amorphous and nanocristalline

silicon, nitrides, oxides, diamond film), diamond

growth, formation of fullerenes, nanotubes,

graphene, for surface cleaning, polymer surface

functionalization for biomaterial applications,

etching organic and inorganic materials, planar-

ization, microwave plasma sterilization, in analy-

tical chemistry, for generation of the active

medium in gas discharge lasers, creation of

artificial ionized areas in the Earth’s atmosphere,

recovering of the Earth’s ozone layer, etc.

One could pose the question: “Why does

MIP attract the attention of scientists and

engineers?” There are several reasons for this

attention:

• MD's are interesting topics for fundamental

studies as they unite phenomena of electro-

dynamics, plasma kinetics and plasma

chemistry, in non-equilibrium and non-

homogeneous conditions;

• Wide range of operating pressures (from 10-2

Pa up to pressures exceeded the atmospheric

pressure);

• Wide range of plasma absorbed powers (0.1 –

10 W/cm3);

• Possibility of control of the internal structure

of plasma by means of changing the

electrodynamic characteristics of the

microwave-to-plasma applicator;

• Possibility for plasma generation both in

small and large volumes, including free space;

• Providing joint action of plasma and electro-

magnetic field on the treated substances (e.g.,

powders) to increase the energy efficiency of

plasma chemical processes;

• Possibility of plasma generation in the

electrode discharge systems without

contamination of the gas phase or treated

samples by products from electrode erosion;

• Possibility to treat large gas chambers or

processing of large area surfaces (e.g.,

cleaning) by scanning the small plasma region

over the chamber by means of electro-

magnetic optics;

• MIP produces little electrical interference;

• MD present no dangerous high voltage, hence

could be safer than other types of plasma;

• Numerous designs of developed high efficacy

microwave plasma devices permit to choose a

required construction for any application.

New designs of MD appear every year.

Research brief

AMPERE Newsletter Issue 88 March 31, 2016

19

MD can be generated in the pulse and

continuum wave regimes, at incident microwave

powers ranging between several watts and

hundreds of kW. The power absorbed by the

plasma can be high enough, and it may run up to

90% of the incident power. The electron density

in microwave-induced plasma usually exceeds

the critical density,

2-3 10cm 1 24 10 GHzecn . f ,

which corresponds to the electron density when

the electron plasma frequency e is equal to the

microwave frequency 2 f .

It is worth to note some general

dependences of plasma parameters on the gas

pressure. The decrease of the gas pressure from

1 atmosphere leads to the decrease of the

electron collision frequency with heavy particles.

This in turn decreases the efficiency of energy

exchange between electrons and heavy particles,

and leads to the decrease of the gas temperature

and increases the mean electron energy. As a

consequence, the degree of plasma non-

equilibrium is increased. The role of resonance

phenomena in plasma is increased with

decreasing the collision damping of the electron

energy (as the pressure decreases).

Typical experimental arrangement for

microwave plasma generation includes several

elements: the microwave power source (usually

the magnetron generator), elements for

protecting the magnetron from the reflected

power (a nonreciprocal device, e.g., isolator), a

standing-wave-ratio meter (such as a directional

coupler), a matching circuit, a microwave-to-

plasma applicator, and the plasma chamber.

The main element of the microwave plasma

generator is the microwave-to-plasma applicator

because it provides the input of microwave

energy to the plasma, and defines the type of

microwave discharge. It determines the energy

efficiency of the plasma generator (the portion of

the incident power absorbed by the plasma), the

levels of minimal and maximal plasma powers,

the system bandwidth, the electromagnetic field

structure in the plasma, its uniformity or non-

uniformity, and the size of the plasma. It is

difficult though to classify the microwave-to-

plasma applicators uniquely since the researchers

design their plasma devices to meet the

conditions of their own tasks.

Following16 all microwave discharges were

separated into two broad groups. The first group

unites discharges sustained inside the microwave

applicator (with a localized discharge zone). For

description of such applicators, the quasi-static

approach can be used as the phase incursion of

microwave field between two points in the

plasma is negligible. The second group unites the

microwave discharges with dimensions larger

compared to the wavelength. These discharges

were denoted as the travelling-wave discharges.

Microwave-to-plasma applicator can enclose a

short part of the discharge tube or covers all

length of the discharge.

At low pressures, when the effects resulting

from the field intensification in the plasma-

resonance region appear to have a dominant

effect on the dynamics of the discharge, these

were called plasma-resonance discharges. The

numerous microwave plasma devices can be

illustrated in the form of a tree of microwave

discharges, as shown below.

Information about the physics, chemistry

and applications of MD's are presented in

numerous books, papers, and in the Proceedings

of many plasma conferences. The Proceedings of

the specialized International Workshops on

Microwave Discharges: Fundamentals and App-

lications (1992, 1994, 1997, 2000, 2003, 2006,

2009, 2012, and 2015) contain comprehensive

data on microwave discharges.

Research brief

AMPERE Newsletter Issue 88 March 31, 2016

20

For further reading:

[1] Golant B E 1959 Soviet Physics-Uspekhi 23 958

[2] The Applications of Plasmas to Chemical Processing

1967 ed R. F. Baddour and R. S. Timmins, Cambridge,

Mass.: MIT Press

[3] MacDonald A D 1966 Microwave Breakdown in Gases

John Willey&Sons, NY, London, Sydney

[4] Ginzburg V L 1967 Propagation of electromagnetic

waves in plasma Moscow, Nauka (in Russian)

[5] Microwave Power Engineering 1968 ed E. Okress,

New York: Acad. Press

[6] Techniques and Applications of Plasma Chemistry

1974 J.R. Hollahan, A.T. Bell Eds. John Willey&Sons,

NY, London, Sydney, Toronto

[7] Wightman J P 1974 Proc IEEE 62 4

[8] Ginzburg V L, Rukhadze A.A. 1975 Waves in

Magnitoactive Plasma Moscow: Nauka (in Russian)

[9] Gekker I R 1978 Interaction of Strong

Electromagnetic Fields with Plasma Moscow:

Atomizdat (in Russian)

[10] Lebedev Yu A, Polak L S 1980 High Energy Chem.

13 331

[11] Zander A T and Hieftje G M 1981 Applied

Spectroscopy, 35 357

[12] Rusanov V D, Fridman A A 1984 Physics Chem.

Active Plasmas. Moscow: Nauka, (in Russian)

[13] Musil J 1986 Vacuum 36 161

[14] Batenin V M, Klimovskii I I, Lusov G V, Troitskii V

N 1988 Generators of Microwave Plasma, Moscow:

Energoatomizdat (in Russian)

[15] Moisan M and Zakrzewski Z 1991 J. Phys. D:

Appl.Phys. 24 1025

[16] Microwave Excited Plasmas 1992 ed M Moisan and J

Pelletier, Amsterdam: Elsevier.

[17] Physics and chemistry of gas discharges in

microwave beams. 1994 L.M. Kovrizhnykh, Ed.

Proceedings of IOFAN, 47 140 p (Nauka, Moscow)

[18] Wertheimer M R and Moisan M 1994 Pure &Appl.

Chern., 66 1343

[19] Zakrzewski Z and Moisan M 1995 Plasma sourses

Sci Technol. 4 379

[20] Lebedev Yu A Chemistry of Nonequilibrium

Microwave Plasma /Plasma Chemistry ed L S Polak,

Yu A Lebedev (1998): Cambridge Interscience

[21] Ohl A 1998 J. Phys. IV France 08 Pr7-83

[22] Sugai H, Ghanashev I, Nagatsu M 1998 Soursec

Sci.Technol. 7 192

[23] Marec J, Leprince P 1998 J. Phys. IV France 8 Pr7-1

[24] Moisan M and Zakrzewski Z 1986 Radiative

Processes in Discharge Plasmas eds. Proud J M,

Luessen L H, Plenum Publ. (p. 381)

[25] Lebedev Yu A 2010 J. of Phys.: Conf. Series, 257

012016.

[26] Conrads H and Schmidt M 2000 Plasma Sources Sci.

Technol. 9 441

[27] Asmussen J, Grotjohn T A, Mak P, Perrin M A, 1997

IEEE Trans on Plasma Science, 25 1196

[28] Moisan M, Pelletier J 2012 Phys. Collisional Plasma.

Intro. to High-Frequency Discharges, Springer

[29] Lebedev Yu A, Plasma Sources Sci. Technol., 2015

24, 053001

The International Scientific Committee on Microwave Discharges

The International Scientific Committee (ISC)

was organized and first elected in 1994 during

the International Workshop on Microwave Dis-

charges: Fundamentals and Applications in

Zvenigorod, Russia. The Constitution of the

Workshop was also accepted in 1994. It was

decided to organize meetings every three years

alternatively in Russia and elsewhere. It was

decided also to begin the numbering of the

Workshop from the NATO ARW Workshop

“Microwave Discharges: Fundamentals and

Applications” held in Portugal in 1992.

The ISC defines the next Workshop place,

and its main topics and plenary speakers. The

ISC staff are appointed and renewed on ISC

meetings during the Workshops. Several

rotations have already been done for different

countries. The tradition is that the representative

of the country of the next Workshop is also the

Chairman of ISC for the next period. The ISC

elected in 2015 contains representatives from 11

countries, including Profs. Asmusen (USA),

Awakowicz (Germany), Benova (Bulgaria),

Dias (Portugal), Gamero (Spain), Jerby (Israel),

Lebedev (the ISC Chairman, Russia), Lacoste

(France), Moisan (Canada), van der Mullen

(The Netherlands), and Nagatsu (Japan).

The principal aim of the Workshop is the

generalization of results of researches obtained

in the previous three years and identification of

promising directions of investigations. Very

important task is intensification of collaboration

MD presentation

AMPERE Newsletter Issue 88 March 31, 2016

21

of scientists from different countries in the

various fields of basic studies and applications

of microwave discharges. The latter promotes

the development of this perspective area of

science and technology. To increase the

effectiveness of mutual contacts of participants,

no parallel sections are conducted. Thus, all

participants could attend and discuss all reports.

The scientific program covers all modern

aspects of microwave discharges connecting

fundamental research and applications. The

main topics of the MD Workshops are:

Methods of microwave plasma generation.

High and low pressure MD's.

CW and pulsed microwave discharges.

Interaction of microwaves with plasma.

Discharge modeling and diagnosis.

Applications of microwave plasmas (surface

treatment, etching, film deposition, growth of

structures, ecology, improvement of burning

processes, light sources, plasma medicine,

analytical chemistry, etc).

Selected topics of closely related gas dis-

charge problems can also be discussed. The Int'l

Workshop on “Microwave Discharges:

Fundamentals and Applications” is usually

attended by 70-100 participants. The previous

meetings include the following:

1992, May 11-15: NATO ARW Workshop,

Vimeiro, Portugal. Director C.M. Ferreira.

1994, September 5-8: Zvenigorod, Russia.

Chairman A.A. Rukhadze.

1997, April 20-25: Fontenvraud, France.

Chairman J. Marec

2000, September 18-22: Zvenigorod, Russia.

Chairman Yu.A. Lebedev

2003, July 08-12: Greifswald, Germany.

Chairman A. Ohl

2006, September 11-15: Zvenigorod, Russia.

Chairman Yu. A. Lebedev

2009, September 23-27: Hamana-Like, Japan,

Chairman M. Kando

2012, September 10-14: Zvenigorod, Russia.

Chairman Yu. A. Lebedev

2015, September 7-11: Cordoba, Spain,

Chairman A. Gamero

The next MD Workshop will be held in 2018 in

Russia.

About the Author:

Yuri A. Lebedev was born in USSR. His education includes engineer in electronics (1968) and physicist (1974). He obtained his PhD degree in 1977 and degree of Doctor of Sciences in plasma physics in 1993. He has over 45 years of research experience in low temperature

plasma, electric gas discharges, microwave plasma, plasma chemistry, plasma diagnostics and modeling. He is a member of editorial boards of several journals and published over 350 papers, editor and co-author of 9 books. He is a member and one of the founders of the International Scientific Committee on Microwave

Discharges: Fundamentals and Applications (Chairman 1997-2000, 2003-2006, 2009-2012, 2015-2018), Deputy Chairman of the Scientific Council of the Russian Academy of Sciences on Physics of Low Temperature Plasma, Member of the Executive Boards of the United Physical Society of the Russian Federation and of the Moscow Physical Society, the Chairman/Member of Advisory and Program Committees of various conferences and schools on Low temperature Plasma Physics and Plasma Chemistry. His affiliation since 1971 is the Topchiev Institute of Petrochemical Synthesis of the Russian Academy of Sciences, Moscow, Russia. Since 1996 he is a head of the Laboratory of Plasma Chemistry and Physical Chemistry of Pulse Processes.

MD presentation

AMPERE Newsletter Issue 88 March 31, 2016

22

Ricky's Afterthought:

A “Corrugated” Conundrum A. C. (Ricky) Metaxas

AC Metaxas and Associates, Cambridge, UK E-mail: [email protected]

A recent report stated that the corrugated

packaging industry is booming. For example, if

the predicted annual rises of about 4% do

materialize the digital print industry packaging,

which relies heavily on corrugated paper, will in

2019 amount to some 115 million tonnes of

converted material worth an estimated $176

million. These are staggering amounts and

focus the mind to efficient ways of producing

the parts of corrugated paper in the first place

before any printing is applied.

The essential part of the corrugated paper is

the flute, which is a thin planar material which

is ultimately sandwiched between two heavier

papers (or indeed board). This flute starts as a

slurry and then is dried in various stages to

produce a thin paper of around 8% moisture, its

equilibrium value. The final stages of drying

often entails pressing the flute over steam

heated cylinders or drums, these being a few

metres in diameter and up to several metres in

length, as the product travels at around 400

m/min. These drums are cascaded over the

length of the entire dryer, which could be some

100 metres long.

There are drawbacks with such an

operation, for example, the moisture content

across the broadloom flute is not even when it

emerges from the last drum but could vary by at

least 2% from its mean. To remedy this, one

way is to over-dry down to say 5% and let the

flute idle for a few days to regain its equilibrium

moisture of 8%. This is wasting energy, as

every 1% of over-drying requires 3% additional

energy. Further, under-drying and then letting

the flute attain its equilibrium moisture is not

viable, as the wetness of the flute will damage

its structure.

Given the staggering amounts of flute

currently required for the production of

corrugated paper, we can assume that

manufacturers of the flute medium would

welcome novel ways of increasing production

rates from current machines without having to

install another conventional dryer. So one

solution would be to use a compact RF system

at the end of the existing drying line, where

conventional energy is inefficient, and increase

the throughput by say 20%.

The slide above shows the main parts of

such an application for a broadloom flute of

around 3-4 m in width. The addition of the RF

at the dry end of the gas fired drum dryer allows

one to increase the speed of operation and using

900 kW of RF could increase the speed from

334 to 400 m/min (that is a 20% increase). As

can be observed, essentially the RF will dry the

last 5% of moisture (dry basis), from say 13±2%

(red line on the diagram shown on the right)

down to the equilibrium at 8±0.5% (blue line).

Further, wet planar materials, such as the flute

for example, exhibit excellent moisture levelling

characteristics at around 27 MHz. Therefore, the

additional benefit of using RF would be that the

flute exiting at the dry end would be “moisture

levelled” down to the required equilibrium

value requiring no over-drying.

A cost benefit analysis of such an

application, taking into account both capital and

running costs as well as the interest on any

Ricky's afterthought

5 10 15

M

Dry basis

%

Distance in the dryer

RF drying

Speed = 400 m/min

Steam heated cylinder drying

13%

8%

13

8

%

M

Web width

.

Existing steam cylinder bank

Moving web

Wet end

RF dryer

Dry end

10 m 120 m

AMPERE Newsletter Issue 88 March 31, 2016

23

borrowed capital to purchase the RF source,

resulted in a payback period of just under 2

years.

An experimental system, which tested the

essential elements of such an industrial

application, is shown in the photo above where

an RF dryer was connected at the end of a

cascade of drum dryers the latter of which

removed the bulk of the moisture from the flute.

There is, however, a distinct lack of industrial

systems worldwide being applied to such an

operation contrary to the several thousands of

RF textile dryers and paper converters (drying

the glue, for example) operating very

successfully in the past 40 years.

One has to probe the scarcity of such

applications for the flute particularly given the

appropriateness of using a self-excited Class C

RF source coupled to a strayfield type of

applicator. The higher the moisture of the flute

entering the wet end of the RF dryer, the better

the coupling of RF energy into it, and

conversely, the lower the moisture content, the

less the power coupled to it. Indeed, it is

fascinating to observe what happens when the

last bit of material, say the flute in this case,

enters the dryer. Progressively as less and less

load fills the applicator the power lowers down

to its standby conditions. I cannot think of a

more suitable application than drying a wet

material through an RF system operating under

Class C conditions.

The following questions are bound to be

asked: are conventional paper, board or flute

dryers that efficient requiring no assistance from

an RF source. How is moisture levelling

effected with present equipment or could it be

that the latter is no big deal given the low gas

energy costs involved in their operations?

Indeed, a new gas plant came on stream in

February 2016 in the Shetland Islands north

west of Scotland run by the giant energy

company Total. The plant pumps gas from two

fields 125 km to the north west of the Shetlands

islands. It is also well known that gas costs for

large industrial users are four times cheaper than

electricity costs (2.5p/kWh as compared to

10p/kWh with reference to 2015 energy data).

But no one is advocating using electricity to dry

the flute when it is very wet! RF will be inserted

near the dry end when conventional energy

becomes very inefficient. One has to preserve

gas, an exhaustible energy resource, and use it

where it is very efficient, in this case from a

very wet flute down to moistures of around

15%.

Drum dryers

RF end dryer

Ricky's afterthought

AMPERE Newsletter Issue 88 March 31, 2016

24

Recently Published Journal Papers Microwave heating of heavy oil reservoirs: A critical analysis D. Oloumi and K. Rambabu Microwave and Optical Technology Letters Vol. 58, pp. 809-813, April 2016

Abstract: In this article, microwave heating of the heavy oil reservoir, oil-sand, is critically studied. The study is carried out based on full wave and multiphysics simulations that are performed at 2.45 GHz using both CST Microwave studio and COMSOL. It is demonstrated that most of the microwave power is deposited in bitumen rather in sand due to the dielectric properties of bitumen. Thermal analysis showed that most of the heat is generated in bitumen and is conducted to sand. Although microwave power is selectively deposited into bitumen of the oil-sand, the temperature gradient between the bitumen and sand is not able to maintain due to high thermal conductivity of the oil-sand medium. Microwave heating can play very important role to reduce the tailing ponds and protect the environment by minimizing water usage in the recovery process.

Microwave heat treatment of natural ruby and its characterization S. Swain, S. K. Pradhan, M. Jeevitha, P. Acharya, M. Debata, T. Dash, B. B. Nayak, B. K. Mishra Applied Physics A: Materials Science and Processing Vol. 122, Art. No. 224, pp. 1-7, March 2016

Abstract: Natural ruby (in the form of gemstone) collected from Odisha has been heat-treated by microwave (MW). A 3-kW industrial MW furnace with SiC susceptors was used for the heat treatment. The ruby samples showed noticeable improvements (qualitative), may be attributed to account for the improvement in clarity and lustre. Optical absorption in 200–800 nm range and photoluminescence peak at 693 nm (with 400 nm λex) clearly show that subtle changes do take place in the ruby after the heat treatment. Further, inorganic compound phases and valence states of elements (impurities) in the ruby were studied by X-ray diffraction, micro-Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). The valence states of the main impurities such as Cr, Fe, and Ti, in the untreated and MW heat-treated ruby, as revealed from XPS, have been discussed in depth. The overall results demonstrate for the first time the effect of fast heating like MW on the microstructural properties of the gemstone and various oxidation states of impurity elements in the natural ruby.

Thermodynamics model based temperature tracking control in microwave heating Y. Yuan, S. Liang, Q. Xiong, J. Zhong, Z. Wang Journal of Thermal Science and Technology Vol. 11, Paper No.15-00102, January 2016

Abstract: Microwave heating technology has been widely used in both domestic and industrial applications. Temperature control technique is significant in improving the performance of microwave heating. A generalized numerical thermodynamics model associating with the temperature-dependent thermal and physical properties of material for the microwave heating process is proposed in this paper. Experimental data is applied to estimate the microwave power coefficients. Two controllers, sliding mode controller (SMC) and proportional-integral-differential (PID) controller, are presented as the easily implementable and efficient on-line controllers to track the desired temperature profile while acting on the microwave power and the heated material’s temperature. The effectiveness of the proposed thermodynamics numerical model is verified by simulations and experiments, which shows that SMC controller has better dynamic control performance than PID controller.

Enhanced reduction of copper oxides via internal heating, selective heating, and cleavage of Cu-O bond by microwave magnetic-field irradiation J. Fukushima and H. Takizawa Materials Chemistry and Physics Vol. 172, pp. 47-53, April 2016

Abstract: The reduction behavior of copper (II) oxide (CuO) covered with boron nitride (BN) powder under microwave H-field irradiation was investigated to understand the mechanism of enhanced reduction of CuO in microwave processing. Internal heating using microwave irradiation resulted in a unidirectional diffusion of oxygen from inside the CuO pellet to its outside, and selective heating prevented the oxidization of the BN powder near the CuO pellet. A quantum chemical interpretation of this phenomenon revealed that the microwave H-field couples to the Fermi level electrons of CuO, and the copper-oxygen bond may be cleaved by both microwave energy and thermal energy. As a result, microwave H-field irradiation resulted in a more effective reduction of CuO to copper metal compared to conventional heating.

Recently published

AMPERE Newsletter Issue 88 March 31, 2016

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Upcoming Events 3rd Global Congress on Microwave Energy Applications (GCMEA) July 25-29, 2016, Cartagena, Spain

http://cpcd.upct.es/3gcmea

50th IMPI’s Annual Microwave Power Symposium

June 21-23, 2015, Florida, USA

http://impi.org/symposium-short-courses

Call for Papers Special Issue on Solid-State Microwave Heating

AMPERE Newsletter is planning a Special Issue on the various aspects of solid-state technologies of RF and microwave heating, to be published on June 30, 2016. Authors who wish to contribute to this issue are kindly requested to contact the Editor before April 30, 2016 in order to coordinate the contents of their articles.

Regular issues

AMPERE Newsletter welcomes submissions of articles, briefs and news on topics of interest for the RF-and-microwave heating community. These may include: • Research briefs and discovery reports. • Review articles on R&D trends and thematic issues. • New inventions and patents. • Technology-transfer and commercialization. • Safety, RFI, and regulatory aspects. • Technological and market forecasts. • Comments, views, and visions. • Interviews with leading innovators and experts. • New projects, openings and hiring opportunities. • Tutorials and technical notes. • Social, cultural and historical aspects.

• Economical and practical considerations. • New products and services. • Upcoming events, new books and papers.

AMPERE Newsletter is an ISSN registered

periodical publication hence its articles are citable as references. However, the Newsletter's publication criteria may differ from that of common scientific Journals by its acceptance (and even encouragement) of news in more premature stages of on-going efforts. We believe that this seemingly less-rigorous editorial approach may accelerate the circulation of new ideas and discoveries among the AMPERE community; and consequently enrich our common knowledge, and excite new ideas, findings, and developments.

Please send your submission to the Newsletter

or any question, comment or suggestion in this regard directly to the AMPERE-Newsletter Editor:

Eli Jerby Faculty of Engineering Tel Aviv University, Israel E-mail: [email protected]

AMPERE Disclaimer

The information contained in this Newsletter is given for the benefit of AMPERE members. All contributions are believed to be correct at the time of printing and AMPERE accepts no responsibility for any damage or liability that may result from information contained in this publication. Readers are therefore advised to consult experts before acting on any information contained in this Newsletter. AMPERE is a European non-profit association devoted to the promotion of microwave and RF heating techniques for research and industrial applications.

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