(CAMERA)

https://ntrs.nasa.gov/search.jsp?R=20080031712 2018-06-16T17:21:01+00:00Z

M.T. Ghasr, M.A. Abou-Khousa, S. Kharkovsky, R. Zoughi,

and D. Pommerenke

Applied Microwave Nondestructive Testing Laboratory (amntl)

Electrical and Computer Engineering Department

Missouri University of Science and Technology

- (Formerly University of Missouri - Rolla)

Blla, MO 65409

I Acknowledgment

This works was supported by a grant f r -: n NASA .A-A.drshall

Space Flight Center (MSFC), Huntsville, AL, USA.

I

I Microwave Imaging - - C- '

I besign and specific aspects 1 B! I + Results &

<

*Real -Time Imaging'

Transmission Mode

Reflection Mode

Image Processing . Summary

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Microwave imaging is based on measuring the relative scattered field from an object over a known two-dimensional (20) space.

Objective is t o obtain the coherent electric field distribution (magnitude and phase) over a known 2 0 space (i . e . , mapping the field).

Two available imaging methods: f ndividual scanning probe

An array of probes

Original MST paper\: J J. H. Richmond, "A modulated scatterin technique for

measurement of field distributions," I E l? E Transactions on M77, vol. 3, no. 4, pp. 13-15, July 1955.

Imaging system "camera" Supelec:

A. Franchios, A. Joisel, C. Pichot, and J. -C. Bolomey, "Quantitative microwave imaging with a 2.45-GHz planar microwave camera," IEEE Transactions Medical Imaging, vol. 17, no. 4, pp. 550-561, August 1998.

Imaging system by PNNL, . . . . . 4 1 s t dimension: Linear switched antenna array

2nd dimension: Mechanically scanned

Others Passive imaging

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a I p I.! L ---- ---- - n 5d

$ .i An array of modulated probes provides fo r 7 :!Y '.$ , -4 coherent electric field distribution k;? tkq

measurement over a desired 2 0 space. g-,i

Modulated probes tag the scattered signal, %; t '

rendering specific - - spatial , measur , r . -4.:gyi -,

capability. I. < A & _

Traditional , minimally perturbing elements (e.9., sub- resonant dipoles) result in a compact array fo r field sampling and measurement, however they suffer from several drawbacks :

f nef f iciency of the sub- resonant dipoles, places their scattered signal very close t o the noise floor.

Mutual coupling among the dipoles can significantly l imit system dynamic range.

- * ' -7 4 .yt* *= 3 5:-; ; - : . = : ~ A s & L ~

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These problems become even more significant and challenging t o overcome at higher frequencies . An alternative approach is the use of high-Q compact resonant slots loaded with a PIN diode

tial or para or tagging can be implemented while operating at relatively high frequencies.

Large dynamic range

Eff ic ier etnents

Large modulation depth

D I O D E OFF: SIM

18 19 20 21 22 23 24 25 26 27

' d n A Rhnnnnnn+ 1 ---I- 1 111 - - 1 = = - = = 1 1 Slot

Strong Modulation- -1 0 I I I

17 dB w - I -

%kE "1

r L_ 2 - I I I I

0 20 40 60 80 100 120 140 160 180 200

'I'

Retina 4 Absorber

Open-ended ! \.I waveguide 1

collector slot

~alibraiion reference plane

Matched load

1 11 &

1

I n m a _-__-__-_--_-__I-~-~ J n

Retina is used as a receiver.

Object placed between retina and transmitter.

PI fi.4; ' k ~ b j e c t bLim is illuminated by a transmitter such as an open- ended waveguide.

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- - -

nn h I -II-IIII-I-II -I- --I-- rmnnnl

Object - .

4 mm-diameter metallic sphere

I) Distance of object to I Magnitude (dB) retina

5 m m Low intensity \ bistance o f transmitter

t o retina

80 mrn

x20 super-sampled

I Phase (deg)

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3 -- P

4 Objecr .-.+

c- P mm diameter metallic ,%*a

sphere lit: . Distance of object t o Magnitude (dB)

retina

12 rnrn

e(. -!'" Distance o f transmitter t o retina

+

80 rnrn I+.

+ x20 super-sampled

Phase (deg)

b - d - .-

Measurement

Object 10 mm-diameter metallic sphere + Oistance t o retina

4 0 mrn x10 super-sampled

SAF Magnitude

4

RAW Magnitude I

@-% (T!fI Synthetic Aperture Focused

\*J I Raw Magnitude & Phase

1) A novel 2b microwave imaging system a t 24 GHz based on MST techniques.

Enhanced sensitivity and SNR by utilizing PIN diode- e- &;. 7.i + loaded resonant slots. ' +

Specific slot and array design t o increase transmission and reduce cross -coupling.

Real-time imaging a t a rate in excess of 30 images per second.

Reflection as well transmission mode capabilities.

Utility and application for electric field distribution mapping related to:

Nondestructive Testing (NDT)

Imaging applications (SAR, Holography)

Antenna pattern measurements