Transcript Northumbria University: Rising to the challenges

Presentation to Calgary University - October 2005
Microwave Imaging using Indirect
Synthetic Reference Beam
Holography
Dr. M. Elsdon
CEIS, Northumbria University, Newcastle-upon-Tyne, NE1 8ST, UK
Introduction
 Overview of Northumbria University Imaging Group
 Overview of Holographic Imaging
 Describe Northumbria University’s Imaging
Technique – Indirect Holography
 Applications of this technique:
Antenna fields
Concealed Metal Objects
Dielectric Objects,
Breast Cancer Detection
ABOUT ME
 Dr. Michael Elsdon
 BEng (Hons) Electronic and Communication
Engineering
 PhD ‘Compact Microstrip Antennas’
 July 2005: Post-Doctoral Researcher
Microwave Imaging Research Group,
Northumbria University, UK
Project: ‘Microwave Imaging of Breast
Cancer’
Research Overview
Work of group based upon patented invention of
Northumbria University: ‘Synthetic Reference Beam
Holography’
Exploits the advantage of NOT requiring direct
measurement of phase.
Mathematical Reconstruction enables phase to be
‘deduced’
VNA replaced with Diode Detector – LOW COST
Applications:
Antenna Radiation Pattern Measurement
Airport Security
Medical Imaging
Holographic Approach For Imaging
1. DIRECT HOLOGRAPHY:

Measure amplitude and phase of scattered signal
Object
Sampling
Antennas
Tx
Rx

Position
Control
Vector
Network
Analyser
Reconstruct Image using Mathematical Techniques
Requires VNA - EXPENSIVE
2. INDIRECT HOLOGRAPHY:


3D Images can be reconstructed from Amplitude of
scattered signal
Requires only SCALAR measurements
Requires Only Simple Diode Detector
- INEXPENSIVE
Indirect Holography
Two Stage Process:
Stage 1:
Illuminate Object with reference wave to
form Hologram (Intensity Pattern)
Stage 2:
Reconstruct Image of Original Object
using post-processing software
Stage 1: Formation of Intensity Pattern
 Illuminate object with coherent reference
wave
 Combine reflected signal with reference
signal
 Form Intensity Pattern – Hologram
 Record Intensity of Hologram
Intensity Pattern Formation –
Experimental Arrangement for Data Collection
RX Probe
TX Probe
Hybrid
Tee
Object
Synthetic
Reference
Wave
Position
Control
Directional
Coupler
Variable
Attenuator
Power
Meter
Phase
Shifter
Microwave
Source
Controller
Intensity Pattern
I (x,y)
Stage 2: Image Reconstruction
 Take Fourier Transform of Recorded
Intensity Pattern
 Filter Fourier Transform to remove
unwanted terms
 Take Inverse Fourier Transform
 Perform Back-propagation and IFT to
produce image at selected depth
1. Intensity Pattern
I ( x, y )  E ( x, y )  R ( x, y )
-Xm
2
+Xm
2. Fourier Transform

F I ( x, y )  F E ( x, y )
2
 F R( x, y) 
2


Direct Wave
Image 2
Image 1
-Km


 F E( x, y) F R  ( x, y)  F E  ( x, y)  FR( x, y)
+km
-Km
+km
Problem:
Difficult to produce sufficient offset to separate terms of
Fourier Transform
Synthesized Reference Wave separates required
term from origin
Required Term
ky
kx
Spectral Representation of Off-axis Hologram:
3. Filter off Unwanted Terms
Direct Wave
Image 1
-Km
Image 2
+km
-Km
+km
4. Re-centre remaining term
Image 2
-Km
+km
Measurement Plane Image
5. Back-propagate to selected depth and perform IFT
Image 2
-Km
+km
ORIGINAL IMAGE
At Object Plane
History of Microwave Imaging
Research at Northumbria
1. Imaging of Antenna Radiation Characteristics
2. Imaging of Concealed Metal Objects
3. Imaging of Plastic Objects
4. Breast Cancer Detection
1. Antenna Radiation Characteristics
Parabolic Dish
Data Collection System
Antenna under
Test
A.U.T.
Data
Output
Microwave
mixer and
Detector
Phase Shifter
Microwave Source
Variable
Attenuator
P.C
Reconstructed Near-Field
Magnitude
Phase
2. Imaging of Concealed Metal Objects
Uncovered Triangle:
Triangle Covered with Cloth:
Intensity Pattern Formation –
Experimental Arrangement for Data Collection
RX Probe
TX Probe
Hybrid
Tee
Object
Synthetic
Reference
Wave
Position
Control
Directional
Coupler
Variable
Attenuator
Power
Meter
Phase
Shifter
Microwave
Source
Controller
Intensity Pattern
I (x,y)
Typical Intensity Pattern
Linear Phase Shift Applied to Synthetic Reference Wave
Plane Wave Spectrum
0
0

0

0
  0

0
0

0
0

120 240 0 120 240 0 120 240 
120 240 0 120 240 0 120 240 
120 240 0 120 240 0 120 240 

120 240 0 120 240 0 120 240 
120 240 0 120 240 0 120 240 

120 240 0 120 240 0 120 240 
120 240 0 120 240 0 120 240 

120 240 0 120 240 0 120 240 
120 240 0 120 240 0 120 240 
Reconstructed IMAGE
Problem of Previous Example:
Terms in PWS overlap if object is tilted, can’t separate terms
Can only image objects that are FLAT
ky
+ve y
TILT
-ve x
TILT
+ve x
TILT
-ve y
TILT
+ve x
TILT
-ve x
TILT
kx
-ve y
TILT
+ve y
TILT
SOLUTION:
Apply 2D phase shift to reference wave
 0
120

240

 0
  120

240
 0

120
240

120 240
0
120 240
0
240 0 120 240 0 120
0 120 240 0 120 240
120 240
0
120 240
0
240 0 120 240 0 120
0 120 240 0 120 240
120 240
0
120 240
0
240 0 120 240 0 120
0 120 240 120 120 240
120 240
240 0 
0 120 

120 240
240 0 

0 120 
120 240

240 0 
0 120 
PWS with 2D Phase Shift
-ve y
TILT
ky
+ve x
TILT
-ve x
TILT
+ve y
TILT
kx
+ve y
TILT
-ve x
TILT
+ve x
TILT
-ve y
TILT
Tilted Objects do not cause terms to overlap
3. Imaging of Dielectric Objects
Recorded Intensity Pattern
F.T of Intensity Pattern
Reconstructed IMAGE
Immersion
Medium
 r 2 
Illuminating
Antenna
Receiving
Antenna
4. Imaging of Breast Cancer - Crude Phantom
h
Tumor
 r 1 
d1
εr1 = 30, εr2 = 2, d1 = 35mm, h = 10cm, x = y = 40cm,
dx = dy = 1cm, f = 8.6GHz
Photo of Breast Phantom
Photo of Experimental Setup
Recorded Intensity Pattern
F.T of Intensity Pattern
Reconstructed IMAGE
Benefits of Northumbria University’s Technique
 Provides 3D Holographic Image from “Single –
View” 2D Scan
 Employs Patented Synthetic Reference Beam
Electronically
 Hologram “Created” in Software
 Compact Microwave Network Compared to External
Offset Reference Beam Antenna Geometry
 Low-Cost
 Simple Square-Law Detector in Lieu of Vector
Analyser
 Phase Retrieval via Mathematical Reconstruction
Process
Microwave Imaging Research Group
Northumbria University
 Dr David Smith, Team Leader & Inventor of
Synthetic Reference Beam Holography
 Dr Michael Elsdon, Post - Doctoral Researcher
 Dr Mark Leach, Post - Doctoral Researcher
 Prof. Stephen J Foti, Consultant
 Mr M. Joy, PhD Student
Acknowledgements
 Engineering and Physical Science Research Council
(EPSRC)
 Wellcome Trust
 Newcastle University Medical School
 Prof. T. Lennard (Royal Victoria Infirmary)
 Mr Peter Elsdon, Technical Consultant