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Overview

September 2004

The Institute of Electronics, Communications and

Information Technology

A tutorial - Millimetre Wave imaging

European Microwave Conference

Defence and Security Forum

Prof Roger Appleby

Timetable

08.30: TITLE: Millimetre Wave Imaging – A Tutorial Introduction

SPEAKER: Roger Appleby, Queen’s University Belfast

0910: TITLE: A Terahertz Imaging Radar for Concealed Object

Detection at Long Standoff Ranges

SPEAKER: Ken Cooper, JPL, NASA

0945: TITLE: Passive Technology – The Application of Passive Sub-

millimetre Wave Technology to Weapon and IED Detection

SPEAKER: Arttu Luukanen, Millimetre Wave Laboratory of Finland –

MilliLab

1020: Coffee

10:40: TITLE: Ultra-wideband Radar for the Detection of Buried

Targets

SPEAKER: David Daniels, Cobham Technical Services

Acknowledgements

• QinetiQ

Outline

1. Introduction

– Atmosphere

– Materials properties

2. Architectures

– Performance – Spatial resolution

– Sensitivity

– Active

– Passive

3. Summary

Introduction Section 1

Introduction

EM spectrum

Cm-1 1 1000 100 10

Terahertz

Standoff Detection

• An instrument with aperture D

• Positioned at Range Rm

• Aim: to detect and recognise an object under clothing

• Airport, checkpoint, embassy, public event

7

D

Rm

Performance affected by:

1. Target (explosives) signature

2. Atmospheric transmission

(relates to range and

location)

3. Target concealment

4. General environment

• Laser sources at frequencies of less than 1 THz

used to image weapons under clothing

Barker, D.H., et al., T.S., “Far infrared imagery,”

Proceedings of SPIE, vol. 67, 1975.

Atmospheric Attenuation

Wallace Zuffrey Masters Thesis 1972

Stand-off detection of weapons and contraband in the 100-1000GHz region, R Appleby and BR Wallace,

IEEE Trans on Antennas and Propagation, Special Issue on, Optical and Antenna Technology, Vol. 55, No. 11, Nov

2007.

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

100 1000 10000

Frequency GHz

Ro

un

d T

rip

Tra

ns

mis

sio

n

Hot Dry Atmosphere Humid Hot Coastal Atmosphere

0.1-10THz Atmospheric

Transmission 100m path

9

Coastal areas of Gulf, highest

water content 40C, 63% RH

400GHz appears to be the upper

frequency limit

Extreme Hot/Dry 44C, 4%

RH, is a good case for THz,

1THz is the practical limit

Wallace’s Atmospheric Effects Model

>300GHz there is structure

and variability due

to atmospheric conditions

0.1 0.3 0.6 1 2 10

THz

Materials properties

t = Transmission

r = Reflectivity

= Emissivity

(Absorption A= )

rt1

t

r

Millimetre wave imaging

• Clothes transparent (t=1)

• Paper transparent (t=1)

• Body =0.6 r= 0.4

• Metal r=1 (specular)

• Sky very cold

• Resolution poor (3mrad)

• 94GHz passive

Contrast?

Scattering

• Particles large compared to wavelength – Irregular reflection

• Particles similar size to wavelength – Resonant scattering

– Mie scattering

• Particles smaller than wavelength – Rayleigh Scattering

– proportional to 1/4

99.8%

Att

en

uati

on

/ d

B p

er

km

Tra

nsm

issio

n o

ver

1km

10GHz 100GHz 1THz 10THz 100THz 1000THz

1

10

100

1000

0.1

0.01

10%

80%

98%

10 %-8

10 %

mm-wave

submm-wave

Infra-red

Vis. UVmicro-wave

94GHz

35GHz

Fog

(50m vis)

Heavy rain

(25 mm/hr)

Drizzle

(0.25 mm/hr)

Atmospheric Attenuation

Aerosols

3 0.03 0.3

mm

Scattering

Explosives

• Typically 150µm crystals in a binder

• Dense Medium Scattering Calculations • (Zurk et al JOSA (B) Vol 24 No 9 Sept 2007)

• Analysis of two polythene samples with different grain sizes

• SGPE~ 50µm and LGPE~ 150µm

• Clothing

• Phase Distribution model applied to clothing

• Fletcher et al. SPIE 5999 2005

13

SGPE LGPE

HMX

THz – Explosives signature

• Most spectra reported for thin

or diluted materials

• Thick (~5mm) explosive

opaque above 500GHz

Reflectance Spectrum of RDX (90%)

Diffuse 10-100 less

Baker, C., et al. SPIE, vol. 5790, pp. 1-10, 2005

Transmission/ Absorption Spectrum of thin RDX

Explosives

0

10

20

30

40

50

60

70

80

90

100

83 197 310 423

GHz

Tra

ns

mis

sio

n

PE4

Semtex

Sample A

Transmission Spectrum

5mm thick Semtex - C4

QinetiQ

Sample B

Zhang et.al NATO, MP-SET-129, May 2008.

Measured

Calculated

Measured

Calculated

Measured

Calculated

HMX spectrum

• Spectrum can be destroyed by scattering

• Dependence on: • Angle

• Microstructure

• Good fit to theory

15

Calculated

Measured

Reflectivity of HMX at 10 and 60º

(Ortolani et al, APPLIED PHYSICS LETTERS 93, 081906, 2008)

Clothing

Sweatshirt

0

0.2

0.4

0.6

0.8

1

0 0.5 1 1.5 2

THz

Tra

nsm

issio

n

Tee shirt

0

0.2

0.4

0.6

0.8

1

0 0.5 1 1.5 2

THz

Tra

nsm

issio

n

Leather

0

0.2

0.4

0.6

0.8

1

0 0.5 1 1.5

THz

Tra

nsm

issio

n

Sweater

0

0.1

0.2

0.3

0 0.5 1 1.5

THz

Tra

nsm

issio

n

QinetiQ

Gatesman et al. SPIE 6212 2006 Dickinson et al. SPIE 6212 2006

Bjarnason, et. Al. Appl. Phys. Lett. 85(4) 2004.

t=0.75mm

Skin

Reflectivity of water and skin

0

0.1

0.2

0.3

0.4

0.5

0 100 200 300 400 500 600 700 800 900 1000 1100

GHz

Refl

ew

cti

vit

y

Skin(30) Skin(0) Water(0)

Skin 35GHz(0) Pulsed THz(0)

Stand-off detection of weapons and contraband in the 100-1000GHz region, R Appleby and BR Wallace,

IEEE Trans on Antennas and Propagation, Special Issue on, Optical and Antenna Technology, Vol. 55, No. 11, Nov

2007.

Dielectric on water 100 and 500GHz

Dielectric (n=1.6)

Water (n =3.7, k=2.24 (100GHz)

Dielectric (n=1.6 k=0.02)

Water (n =2.37, k=0.75 (500GHz)

Baker

100GHz 500GHz

Baker, C., et al. Proceedings of SPIE, vol. 5790, pp. 1-10, 2005. Appleby,R., Coward,P., and Sinclair,G. Detection of Illegal Objects

Ed R Miles et al. Terahertz Frequency Detection and Identification

of Materials and Objects, 225-240, 2007 , Springer.

Summary Section 1

• Clothing, plastics and some other materials are transparent

• There is transmission through the atmosphere, so standoff is possible • above 450GHz dependent on the water vapour

• Scattering is an issue at higher frequencies

• Explosives have characteristic spectral signatures in the THz range – Difficult to exploit

Introduction Section 2

Architectures

Passive

Active

Spatial resolution

Spot size S at range R: S R D 122.

D

R

S

Resolution x3

(3D or R/3or /3)

90GHz

Resolution x1

90GHz

Note: Pistol images are schematics only

Passive

emission

reflection

horn

Lens

Represents dish or lens

Receiver

Signal broad band white noise

Typical Architectures

• System – Quasi-optic

– Aperture synthesis

• Detector Technology – RF Solid state

• Super heterodyne

• Direct detection

– Bolometer

• Cooled

Total power radiometer

(super heterodyne)

Direct Detection receiver

LNA 15dB gain <5dB NF

80 to 100GHz bandwidth

Diode detector

WG to MS transition

Horn Antenna

Line Driver

Barnes A.R., Munday P.D., Jennings R., Black M., Appleby R., Anderton R.N., Sinclair G.N., and Coward

P.R, “MMIC Technology and its applications in mm-wave imaging systems”. In 3rd

ESA Workshop on

mm-Wave Technology and Applications, pp 543-547, 2003.

Amp LNA LNA LNA

Bolometer

• Power P from an incident signal is absorbed by the bolometer

• Heats up a thermal mass with heat capacity C and temperature T.

• Thermal mass is connected to a reservoir of constant temperature

through a link with thermal conductance G.

• Temperature increase is ΔT = P/G.

• Change in temperature is read out with a resistive thermometer. The

intrinsic thermal time constant is τ = C/G.

http://en.wikipedia.org/wiki/Bolometer

Infrared bolometer Sang-Baek Ju. et al. SPIE 3698 1999

Active (Radar)

reflection

Lens

Transmitter

horn

Receiver

Signal narrow band coherent

Typical Architectures

• System – Quasi-optic

– Phased array

– Coherent / Incoherent

• Transmitter and receiver technology – RF Solid state

• Super heterodyne receiver

• Multiplied transmitter

– Tube for transmitter

• Solid state receiver

Radar Equation

• PR Power receiver

• PT Power transmitted

• GT gain of transmit antenna

• AR area receiver antenna

• RT transmitter to subject range

• RR receiver to subject range

• σ radar scattering cross-section area of target

2224 TR

RTTR

RR

AGPP

1. F.T. Ulaby, R.K. Moor, and A.K. Fung. Microwave Remote Sensing - Active and Passive, Vol. II, Radar Remote

Sensing and Surface Scattering and Emission Theory. Artech House, 1982.

2. Mark A. Richards, Fundamentals of Radar Signal Processing by, P 62-63, McGraw-Hill 2005,

TR

RTTR

RR

AGPP

24

For beam limited case (Ref 2)

i.e. All the beam falls on the target For general case (Ref 1)

Radar

• Narrow Bandwidth improves signal to

noise ratio

• Transmitter tends to be spatially and

temporally coherent

• Possibility of range gating – C speed of light

– RF bandwidth

RF

cR

2

RF

Radar Architecture

• Low frequency

source multiplied

• Clean source

s x2

PLO SPDT

x2 x2 x2

648GHz out

13.3GHz

27GHz54GHz 108GHz 216GHz

x3s x2

PLO SPDT

x2 x2 x2

648GHz out

13.3GHz

27GHz54GHz 108GHz 216GHz

x3100MHz ref

s x3

PLO SPDT

100MHz refx2 x2 x2

Reflected

640GHz in13.3GHz

40GHz 80GHz 160GHz 320GHz

IF output

IF output

s x3

PLO SPDT

100MHz refx2 x2 x2

Reflected

640GHz in13.3GHz

40GHz 80GHz 160GHz 320GHz

IF output

IF output

s x3

PLO SPDT

100MHz refx2 x2 x2

Reflected

640GHz in13.3GHz

40GHz 80GHz 160GHz 320GHz

IF output

IF output

Transmitter

Receiver

Active v Passive

Active

• Transmitter

– Monostatic, Bistataic,

Opportunity

• Coherent illumination

– Speckle

– High angular dependence

– Synthetic aperture

– Range gating

• More dynamic range

Passive

• Naturally emitted or reflected

radiation

• Less angular dependant

• More weather dependant

• Natural imagery

• Less processing

640GHz

Jacobs et al. SPIE 6212 2006

94GHz Passive

QinetiQ

Summary

• Materials and atmosphere

described

• Architectures – Active and Passive compared

Future

• Active systems at 300 and

600GHz

• Passive systems < 500GHz