Microwave Drilling: Future Possibilities and Challenges Based on ... · Microwave Drilling: Future Possibilities and Challenges Based on Experimental Studies Titto John George# *,

Microwave Drilling: Future Possibilities and

Challenges Based on Experimental Studies Titto John George

#*, Apurbba Kumar Sharma

*, Pradeep Kumar

*,

Shantunu Das$, Rajesh Kumar

$

#Department of Mechanical Engineering, Viswajyothi College of Engineering and Technology

Muvattupuzha, Kerala, India *Department of Mechanical and Industrial Engineering, Indian Institute of Technology Roorkee, India

[email protected],

[email protected],

[email protected]

$Reactor Control Division, Baba Atomic Research Centre, Mumbai, India

[email protected]

Abstract— Microwave material processing is getting more

importance due to environmental concerns energy scarcity. It’s

an energy efficient process in which microwaves are used to heat

the materials for different applications which provides the

advantage of volumetric heating, selective heating based on the

material-microwave interaction rather than the conventional

heating which uses conductive and radiative heat transfer

methods. This paper gives a brief report of the works carried out

in applying microwave energy in machining area and intends to

check the feasibility of microwave machining, especially in

drilling of materials. Some studies were conducted using a setup

developed for drilling of materials inside a microwave oven along

with plasma formation in open atmosphere. This paper explains

development of equipment for concentrating microwave to a

small area like a beam and heating that area to produce a hole.

This was tested in wood, glass and in aluminium specimens. The

concept was also successfully used in drilling of raw animal bones

obtained as a food-waste with an aim to use for medical

applications. Details of the microwave drilling experiments

conducted along with the results were discussed in the paper and

it concludes with exploring the future possibilities and scope of

further research in this process.

Keywords—Microwaves, Selective heating, Drilling, Material

Processing

I INTRODUCTION

Microwaves belong to the portion of the electromagnetic

spectrum with wavelengths from 1mm to 1m with

corresponding frequencies between 300 MHz and 300 GHz.

For microwave heating, two frequencies 0.915 and 2.45 GHz

were reserved by the Federal Communications Commission

(FCC) for industrial, scientific, and medical (ISM) purposes

are commonly used for microwave heating. The theoretical

analysis of each of these microwave components is governed

by appropriate boundary conditions and the Maxwell

equations [1]-[3].

Significant research has been carried out to explore the

possibilities of using microwave in applications like heating,

sintering, bonding, welding, cladding and other areas of

material processing. In the recent years, application of

microwave in machining of materials has also been attempted.

Due to its special properties microwave processing has given

better results in comparison to conventional methods in all

fields where it was applied. The studies done with microwave

drilling has proved its ability in differentiating the materials

and drill accordingly which is even impossible by any other

techniques including laser drilling. This paper discuss the

possibilities and challenges in developing a drilling process

using microwave energy based on experimental studies

conducted in various materials.

II SIGNIFICANCE OF MICROWAVE PROCESSING

Microwaves have some special properties in material

interaction energy transfer which makes it useful in processing

different types of materials.

Energy is transferred to materials by interaction of the

electromagnetic fields at the molecular level, and the

dielectric properties ultimately determine the effect of the

electromagnetic field on the material. Two fundamental

mechanisms for energy transfer are dipole rotation and the

ionic conduction. The interaction of microwaves with

materials can be classified into three categories as shown in

Fig. 1. Absorbing materials with properties ranging from

conductors to insulators are usually high dielectric loss

materials, which absorb electromagnetic energy readily and

convert it to heat. Transparent materials are low dielectric loss

materials or insulating materials, such as glass, ceramics and

air which allow microwaves to pass through easily with little

attenuation. Opaque materials are typically conducting

materials with free electron, such as metals, that reflects

microwave at room temperature [1]-[4].

Fig. 1 Schematic of microwave material interaction

Microwave heating possess some special characteristics

like penetrating radiation, rapid heating, controllable field

distributions, selective heating of materials and self-limiting

which are not usually possible with conventional heating

techniques. The term ‘microwave effects’ has been proposed

to describe anomalies that cannot be predicted or easily

explained with present understanding of the electromagnetic

theory [1]-[2]. For experimental works two different methods

of microwave heating are generally used: direct microwave

heating (DMH), and microwave hybrid heating (MHH).

III BACKGROUND OF MICROWAVE DRILLING

A method for drilling/cutting using microwave discharge

was suggested by Kozyrev et al. [5] but further studies were

not reported. A novel method for drilling hard non-conductive

materials by localized application of microwave energy was

introduced by Jerby et al. [6]-[8]. Titto et al. [9], [10] made

some feasibility studies on drilling of metals with microwave

hybrid heating. Highlights of these initial attempts are briefly

discussed in this section and the latest studies were given in

the remaining sections.

A. Microwave Discharge Machining

Kozyrev et al. [5] studied the combined action of

microwave electric field and focused laser radiation on

dielectrics to develop discharge technique for machining of

certain kind of dielectrics. The concept was based on the local

absorption of microwave power by dielectrics followed by its

damage due to intensive heating. Localization of microwave

absorption was made by heating a small area using thermal

pulse such as laser. The basis of the process is dependence of

microwave absorption coefficient by dielectrics on its

temperature. Some experiments were performed and it was

proved that application of microwave field increased the

volume of removed material at least 8 times at 1 min exposure.

However, the profile was not good and the complexity of set

up may be the hindrance in conducting more studies in that.

B. Microwave Drilling of Non Conducting Materials with a

Near Field Concentrator

The concentration of the microwave energy into a small

spot is the key principle underlying the microwave-drill

invention [6]-[8]. The near field microwave radiator illustrated

in Fig. 2 is constructed as a coaxial waveguide ended with an

extendable monopole antenna, which functions also as the

drill bit with a movable centre conductor sustaining high

temperatures. Initially, the microwave energy deposition rate

is high at the material near the antenna. The subsurface tends

to increase to a slightly higher temperature than the

spontaneously cooled surface. A hot spot is created, and the

material becomes soft or molten. The coaxial centre electrode

is then inserted into this molten hot spot and shapes its

boundaries. Finally, the electrode is pulled out from the hole,

while the material cools down in its new shape.

This microwave drill was effective for drilling and cutting

in a variety of hard non-conductive dielectric materials, but

not in metals due to reflection of microwaves [6]-[8]. It was

also useful to insert and join metallic or ceramic nails into

these materials.

1) Application on Drilling of Ceramic Thermal-Barrier

Coatings: Its the inherent material selectivity makes

microwave drill ideally suited for the controlled removal of

ceramic coatings from underlying metallic substrates. TBC

consists of two layers: a metallic oxidation-resistant bond coat

and a thermally insulating layer. When the applicator is

brought into contact with a metal, the microwave energy is

reflected and little or no localized heating is obtained. Thus,

the process has the inherent feature of materials selectivity.

Drilling was stopped after reaching the surface of the metal

plate. In all holes examined, the microwave drill process did

not affect the microstructure of the underlying substrate [11].

Fig. 2 Scheme illustrating the principle of microwave drilling [6]

IV FEASIBILITY STUDIES AND FABRICATION OF

SETUP

Some initial trials were conducted to study the possibility

of drilling metallic materials through microwave heating. It is

a known fact that bulk metals reflect microwaves at room

temperature. The heating of metals has been achieved by

using microwave hybrid heating technique by using a suitable

susceptor and for non metallic materials microwave generated

plasma was used. From the results of initial feasibility study a

modified setup was made with which drilling of metals and

non metals were performed.

A. Fabrication of a Setup for Drilling Inside Microwave Oven

The schematic diagram of the setup developed to perform

microwave drilling inside a microwave oven is shown in Fig.

3. A spring of required stiffness was fixed to the bolt at the top

of setup. The drill bit was fixed at the bottom end of the spring

as shown in the schematic diagram. The spring and the drill

bit were covered by microwave friendly materials to avoid

reflection of microwave by metallic materials. The strength of

the beam structure which is holding the spring should be

sufficient to withstand the load. The specimen was placed at

the base of the setup and was covered at the top by susceptor

material in case of metallic materials. The fixture was made in

such a way that once the whole setup was put inside the

microwave cavity and power is switched on the specimen

becomes heated by microwave. The drill bit attached to the

spring will apply a small force on the specimen which will be

in a softened state due to heating. The preset force can be

increased or decreased by adjusting the height of the base

plate on which specimen was placed. All experiments were

performed at 2.45 GHz frequency inside a multimode cavity

of a domestic microwave oven.

Fig. 3 Schematic diagram of microwave drilling setup for drilling inside oven

B. Setup for Drilling with Concentrated Microwave Energy

Based on the results of the previous setup for drilling, a

new setup was made to perform drilling of both metallic and

non metallic materials outside microwave oven by

concentrating the microwave energy at the tip of the drill bit.

The schematic block diagram of the setup with circuit is given

in Fig. 5 and the various components are explained below.

1) Magnetron and its Circuit: A Panasonic (Model

2M211AM2) magnetron was used as a source of generating

microwave at a constant a frequency of 2.45 GHz. Magnetron

need a high voltage for accelerating the electron particles

which was given using a circuit having a capacitor and a step

up transformer. The output power of magnetron and the time

of heating were controlled by an electronic circuit.

2) Waveguide Launcher: The output waves from magnetron

will come to the atmosphere were collected and directed to

flow in a required direction using a waveguide launcher which

is also a rectangular waveguide of WR 340 standard for

frequency of 2.45 GHz. This launcher was designed to match

with the size of magnetron. The launcher was made of

stainless steel sheet of 3mm thickness with the rectangular

cross section of size 43 mm X 86 mm and the length of wave

guide was 90mm.

3) Rectangular to Coaxial Adapter: This was a standard

waveguide of WR 340 standard used to convert the

rectangular wave guide to coaxial waveguide/adapter.

4) Cooling Fan: The magnetron use to get heated up during

operation and is prone to damage if the temperature goes

beyond certain level. So to provide proper cooling to the

magnetron, a cooling fan of 20 W power was put near the

magnetron and it was connected to the magnetron circuit by

using another circuit containing a transformer to adjust

voltage and diodes to make it working in AC.

5) Coaxial Cable with Monopole Antenna: The microwaves

coming out from the coaxial adapter is transmitted to the

applicator by a coaxial cable. These cables were good for

using in low power and non heating applications, but for

getting flexibility and ease of fabrication of setup, coaxial

cables were used temporarily. The applicator, which emits

microwave to the object to be heated, was a unidirectional

monopole antenna made of copper and was attached to the end

of the coaxial cable and this acts as the drill bit too. The length

of antenna was 32.5 mm which was the standard size antenna

for transmitting microwave of 2.45 GHz frequency and the

diameter of the tip was 1.5 mm and 2 mm in all cases.

Photograph of antenna used is given in Fig. 4.

Fig. 4 Photograph of the antenna attached to the coaxial cable

The components were assembled in a similar way as shown

in the schematic block diagram given in Fig. 5. Coaxial cable

was connected to the adapter by a male connector attached to

it. Magnetron was place above the launcher and the cooling

fan was placed near to the magnetron. The coaxial cable of

length 1m was fixed into the metallic box where experiments

were done to prevent human exposure to microwave in case of

leakage. But the cable was free to move up and down. Proper

earthing was provided to whole setup. There was a provision

for inserting a thermocouple wire, in case of working with

metallic materials. The photograph of the assembled setup is

given in Fig. 6.

Fig. 5 Connection diagram of the concentrated microwave drilling setup

Fig. 6 Photograph of the assembled setup to perform microwave drilling by

concentrating microwave energy

V EXPERIMENTAL PROCEDURE

A. Drilling of Metals inside Microwave Oven

Trials were conducted to study drilling of metallic material

through MHH. The specimen was placed at the base of the set

up and was covered at the top by a concrete plate and with

graphite sheets as required to prevent reflection of

microwaves by the metallic specimen. The force was applied

by lifting the specimen above its position against the spring

pressure on tungsten rod which, in turn, will apply force on

the workpiece. The charcoal powder susceptor was directly

placed above the workpiece where we want to drill. Once the

whole set up was put inside the microwave cavity, the

exposure was initiated as per the parameters described in

Table 1. The red hot susceptor supplies heat to the metal

beneath it by conventional mode of heat transfer, and at high

temperature, metal starts absorbing microwave. Once the

metal gets softened, the drill feature is pushed downwards due

to force applied by the spring and a hole is formed in the

workpiece. Experiments were performed with an Al sheet of 1

mm thickness, Cu and MS sheets of 0.5 mm thickness. The

drill bit used was tungsten rod of 2 mm in all cases. Also,

stainless steel rod of 0.8 mm diameter was used for drilling

another aluminium specimen. All specimens were exposed to

microwave of frequency 2.45 GHz in a multimode applicator

with 900 W power.

TABLE I

PARAMETERS USED IN THE MICROWAVE DRILLING TRIALS

Material Thickness

(mm)

Output

power of

microwave

Time of

exposure

(s)

Drill

Feature

(diameter

in mm)

Aluminium

1

1 900 W 120 Tungsten

(2)

Copper 0.5 900 W 150 Tungsten

(2)

Mild steel 0.5 900 W 240 Tungsten

(2)

Aluminium

2

1 900 W 60 SS (0.8)

The specimens were then cut along the drilled hole using a

‘Baincut Low Speed Saw’ and then polished with emery

papers of fine grades and alumina powder. Then it was etched

with proper acid solutions. Later the drilled specimens were

characterized in scanning electron microscope (SEM) to see

the micro structure.

B. Drilling of Glass and Bone Inside Microwave Oven

The procedure was almost same as that followed for

metals. Here specimens were not covered to prevent reflection

as non metals will not reflect microwaves. Also susceptor was

not needed as a metallic drill touches the glass in presence of

microwave a spark initiates and it continues to become a

plasma formation. Here the tungsten rod itself will acts as a

receiving and transmitting antenna for microwaves so that all

the charge will concentrate at the tip of the drill feature. The

temperature due to plasma is sufficient to drill the glass

without any preloaded force from the spring. Self weight of

the drill bit is sufficient to deform the glass. Experiments were

performed with microwaves of frequency 2.45 GHz at 700 W

power for glass and 600 W power for bone in a multimode

applicator. Experiments were done with borosilicate glass of

1.5 mm and 4 mm thickness and the hole was drilled in 3 and

6 seconds respectively. Bone used was rib bone of cow which

is taken from food waste, is about 6 mm in thickness and it

took 10 seconds to make a hole in the bone. When the time or

power is more, the glass breaks due to high temperature or

thermal shock. The photograph of plasma formed in glass

drilling is given in Fig. 7.

Fig. 7 Plasma formation in drilling glass inside oven

C. Drilling with the Setup to Concentrate Microwave

In this setup, microwave generated in the magnetron will

pass through the rectangular waveguide and enter the coaxial

adapter from which it is transferred through a coaxial cable

and come out through the monopole antenna attached to the

end of the cable. The microwave coming out from the tip of

monopole antenna will be propagating in a single direction.

To avoid complexity of the setup microwaves tuners were not

used in the experiment for impedance matching. Microwaves

were concentrated to a point on the specimen to be drilled and

the spread will be more if the distance between the specimen

and tip of antenna is more. The specimen will get heated up

by microwave. First trials were performed in open atmosphere

by putting the specimens in a flat surface, but microwaves

were leaking and the side spread of microwaves was more due

the absence of impedance matching. Later the experiments

were conducted inside a metallic box to protect the operator

from exposing to microwave.

Experiments with the concentrated microwave drilling

setup were performed on borosilicate glass, wood (deodar)

and animal bone. Also drilling in Aluminium was tried with

microwave hybrid heating by covering the metal with charcoal

powder around the point of contact with antenna to prevent

reflection and to start initial heating. A spark was observed

similar to the plasma formation in drilling of glass with

previous setup, at the point of contact between the drill bit

(antenna) and the specimen in case of non metals. This spark

was sufficient to heat the specimen to a molten or burning

stage and the drill bit was pushed downward manually to

complete the hole. The parameters used in drilling with

concentrated microwave setup and the time taken to form hole

is given in Table 2. Also some trials were performed after

soaking the specimen in water to reduce the burnt area or the

heat affected zone in case of wood and bone.

As coaxial cable is not suitable for using in microwave

heating applications, due to easiness of design and fabrication

in comparison with coaxial wave guide it was used. Coaxial

cable provides flexibility in moving the applicator to any

position as needed. During experiments the covering of the

cable was burned due to high temperature so that the

experiments were difficult to perform continuously for more

than 15 seconds.

TABLE II

PARAMETERS USED IN DRILLING WITH CONCENTRATED

MICROWAVE

Material Thickness

(mm)

Power

(W)

Time (s)

Borosilicate

glass

1.5 360 8

Glass 8 500 4

Bone 6 500 12

Bone (wet) 6 500 15

Wood 2 500 5

Wood (wet) 2 500 5

Wood (wet) 5 700 10

Aluminium 1 700 5

VI RESULTS AND DISCUSSIONS

A. Drilling of Metals inside Microwave Oven

The first Al specimen was drilled with 2 mm tool was

melted and burned partially due to overheating. But a hole

was formed and is given in Fig. 8(a). The time was 2 minutes

but the charcoal started complete coupling in 30 s. The Al

plate no 1 shows overheating on the area near to hole. This is

due to low melting temperature of Al (about 650 0C) and non

uniformity in placing the charcoal at the target area. The mild

steel specimen was pierced partially with 2 mm diameter tool.

Even after 4 minutes of exposure, though it got red hot, yet the

temperature rise was not sufficient to form a hole. The

photograph of the partially drilled mild steel specimen is

given in Fig. 8 (b). The photograph of the drilled copper strip

is given in Fig. 9 (b). Aluminium specimen 2 was drilled with

a stainless steel rod of 0.8 mm diameter was drilled with

heating in 60 seconds which is shown in Fig. 9 (a). SEM

image of the 0.8 mm hole drilled in Aluminium specimen is

given in Fig. 10. The profile of the hole is having good finish

and shape.

Fig. 8 (a) Al specimen partially burnt, with a 2 mm diameter hole. (b) Partially drilled stainless steel specimen.

Fig. 9 (a) Aluminium with 0.8mm hole (b) Copper strip with 2 mm diameter

hole

In order to study the surface microstructure, SEM

micrographs of the specimens were taken before and after

drilling. No variation was observed in the surface structure of

Aluminium and the SEM image of surface before and after

microwave drilling is given in Fig. 11. Very small variation in

grain size of copper as per Fig. 12 was observed where as the

increase in grain size comparatively more in case of mild steel

as given in Fig. 13. This may be due to overall heating of the

specimen with charcoal and the time of heating was more in

case of copper and mild steel. This can be minimized by

proper concentration of microwave to the drilling point and

reducing the amount of susceptor to be used.

Fig. 10 SEM image of a 0.8mm diameter hole drilled in Aluminium of

1mm thickness

Fig. 11 SEM micrograph showing surface structure of Aluminium

specimen (a) before microwave drilling (b) after microwave drilling

B. Drilling of Non Metallic Materials inside Oven

Photograph of a drilled glass specimen is given in Fig.

14(a). The plasma formation was very large and sudden in

case of drilling of glass. Most of the specimens were broken

suddenly after exposing to microwave along with applying a

load by the drill feature. The surface finish is not good and

some cracks were visible around the hole. These problems can

be reduced by optimizing the parameters like power, time and

by selecting a drill bit of suitable metal. As glass is very brittle

the application of force on the glass must be minimized to

prevent the breakage. SEM image of the edge of a hole drilled

on glass specimen is given in Fig. 14(b).

Fig. 12 SEM micrograph of the copper specimen (a) before microwave

drilling (b) after drilling (grain coarsening)

Fig. 13 SEM micrograph showing surface structure of MS specimen (a)

before microwave drilling (b) after microwave drilling (grain coarsening)

In case of drilling bone the plasma formation was

comparative less than that in glass but it result in burning of

the specimen in fire. The holes formed were not of good finish

and the heat affected zone was much more in this case due to

the fire caused by plasma. The photograph of bone drilled

with this setup is given in Fig. 15.

Fig. 14 (a) Photograph of the drilled glass specimen (b) SEM image of the edge of hole

Fig. 15 Photograph of the hole drilled in bone

C. Results of Drilling with Concentrated Microwave

Trials were conducted in open atmosphere and inside a

metallic box also. There was no difference in the hole drilled

in both cases. The temperature inside the closed box was very

high and this resulted in more damage of coaxial cable in the

form of melting of the covering. The tendency of the cable

and specimen to catch fire was also large inside the closed box.

Due to this reason it was difficult to drill for more than 10

seconds continuously inside the metal box. The time taken in

drilling was less than that in the previous setup for drilling

inside microwave oven for the same power. But the overall

efficiency was much less due transmission through various

lengthy components in comparison with microwave oven.

Also lack of tuning and spread of microwave were responsible

for less efficiency.

1) Drilling of Glass: During drilling of borosilicate glass at

high power the glass was broken suddenly after switching on

the power. So the power used was 360 W in further trials. So

it takes approximately 8 seconds to drill a glass plate of

thickness 1.5 mm and the plasma formation was very less. The

picture of a drilled hole in borosilicate glass is given in Fig. 16.

In some cases, the portion which is drilled stick to the drill

feature due to high temperature and melting. Such a drilled

hole is removed from the drill bit after cooling and the SEM

image of that drilled hole is given in Fig. 17. In case of the

trials with glass of 8 mm thickness no spark was coming at

360 W so the power used was 500 W. In all the trials the

specimen was split in to two pieces instead of forming a hole

by localized heating.

Fig. 16 Hole drilled on a borosilicate glass by concentrated microwave setup

Fig. 17 SEM image of the 1.5 mm diameter hole drilled on glass

2) Drilling of Bone: In case of drilling bones, some trials

were performed with dry bones. In this case, the heat affected

zone was much higher but less than that in comparison with

that of the bones drilled with the previous setup. Then the

experiments were conducted with wet bone by soaking the

bone in water for 10 seconds. This is more similar to the real

life situation where bones are always wet with blood. In this

case the burning around the drilled hole was much less than

previous case. The photographs of the drilled bone in dry and

wet conditions were given in Fig. 18 and the SEM image of

drilled hole in bone is given in Fig. 19.

Fig. 18 Photograph of the hole drilled in bone without and with wetting

3) Drilling of Wood: During drilling of wood the plasma

formation was almost absent and there was no fire in the

specimen. But the specimen was burnt only at the portion

which is in contact with the drill and it was easy to make the

hole by inserting the drill bit. In case of drilling dry wood, the

heat affected zone was more than that in case of wet wood.

But it was less compared to bone in corresponding cases. The

photograph of 5 mm thick wood with a 2 mm diameter hole

drilled with and without wetting is given in Fig. 20. The SEM

image of the hole made in woods shown good finish of the

edges and is given in Fig. 21.

Fig. 19 SEM image of drilled bone

Fig. 20 Photograph of the hole drilled in wood without and with wetting

Fig. 21 (a) SEM image of the 2 mm diameter hole drilled in a wet wood (b) enlarged view of the edge

4) Drilling of Aluminium: In case of drilling Aluminium the

specimen was covered with charcoal powder around the point

of contact with antenna to prevent reflection. Here also small

spark was developed at the point of contact and an indentation

mark was formed in Aluminium specimen. Due to high

temperature at the drill bit, the coaxial cable in was burned

after 5 seconds of operation. The photograph of the

indentation mark on specimen is given in Fig. 22(a) and its

SEM image is given in Fig. 22(b). This gives the possibility of

drilling metals with this setup with a coaxial cable which can

sustain high temperature or with a coaxial wave guide.

Fig. 22 (a): Photograph of the Aluminium specimen having small deformation

due to microwave concentrated drilling (b) SEM image of the indentation

made my microwave drill in Aluminium specimen

VIII. CONCLUSIONS

Drilling of metals by microwave hybrid heating and

prosthetic load was done inside oven.

Microwave drilling of glass and bone was done with

microwave generated plasma inside an oven. A setup capable

of concentrating microwave to a small area was developed for

microwave drilling. Microwave drilling of engineering

materials such as glass and wood were done by concentrating

microwave to a small area along for localized heating along

with formation of plasma. Drilling of biological materials like

bone was performed by concentrating microwave which can

be applied for medical applications. Feasibility of drilling

metallic materials with concentrated microwave energy was

proved.

Drilling of wood and bone was performed in dry and wet

conditions in which the latter gives better results. Material

destruction was much reduced in wet materials. In both the

drilling setups plasma ball formation was observed in normal

atmosphere, which heats up the material locally to a high

temperature. Even though microwave drilling and heating is

competitive with laser in many aspects like cost, efficiency

and simplicity of operational equipment, it is lacking accuracy

and precision in comparison with laser. Use of concentrated

microwave for drilling is limited to millimetre range where as

laser can be easily focused to microns and the accuracy of

microwave drilling is very less.

IX SCOPE OF FUTURE WORK

The present studies show less accuracy and efficiency due

to leakage and spreading of microwave. This can be rectified

to certain extent by proper tuning and impedance matching.

This can be achieved by adding a three stub tuner and

reflection measuring equipments to the present system. Also,

the antenna and coaxial wave guide/cable design need to be

improved in order to get accurate focusing of microwave.

Usage of an EH tuner will help in processing materials with

separate electric and magnetic fields depending on their

properties as materials have different characteristic in heating

with electric and magnetic part of microwave. A model of

such a setup by modifying the present one is given in Fig. 23.

Fig. 23 Suggested setup for microwave drilling and concentrated heating

Drilling inside the microwave oven shows the feasibility of

developing this technique for gang/multiple drilling. Cutting

of hard and brittle materials can also be made possible by

further development of plasma formation in drilling. The

device for concentrating microwave is having the potential to

be developed as a heat source similar to a welding electrode in

process like joining, cladding, and hardfacing.

The plastic deformation observed during drilling of metals

opens up the beginning of a new technology of ‘microwave

assisted metal forming’. A setup which can be used in a

production line where continuous flow of materials along with

microwave heating for metal forming is given in Fig. 24.

Concentrated microwave drill with coaxial cable can be

developed further for medical applications like concentrated

heating of small points to destroy the cells of tumours or

cancer inside the flesh. Heating profile of such an application

is given in Fig. 25.

Fig. 24 Microwave assisted metal forming system

Fig. 25 Microwave heating of tumour inside flesh

ACKNOWLEDGEMENT

The financial support received for the present works from

the BRNS, Govt. of India vide Project Grant No. 2010/36/60-

BRNS/2048 has been duly acknowledged. Authors gratefully

acknowledge the inputs received from Dr. K P Ray of

SAMEER institute Mumbai and research students Amit

Bansal and Manjot Singh Cheema.

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