(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 &
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*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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$ .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.
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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.
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Strong Modulation- -1 0 I I I
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0 20 40 60 80 100 120 140 160 180 200
Retina 4 Absorber
Open-ended ! \.I waveguide 1
collector slot
~alibraiion reference plane
Matched load
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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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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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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 - .-
Object 10 mm-diameter metallic sphere + Oistance t o retina
4 0 mrn x10 super-sampled
SAF Magnitude
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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