Microwave Imaging using Indirect Synthetic Reference Beam Holography

1
Microwave Imaging using Indirect Synthetic
Reference Beam Holography
Presentation to Calgary University - October
2005
Dr. M. Elsdon CEIS, Northumbria University,
Newcastle-upon-Tyne, NE1 8ST, UK
2
Introduction

• Overview of Northumbria University Imaging Group
• Overview of Holographic Imaging
• Describe Northumbria Universitys Imaging
  Technique Indirect Holography
• Applications of this technique
• Antenna fields
• Concealed Metal Objects
• Dielectric Objects,
• Breast Cancer Detection

3
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

4
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

5
Holographic Approach For Imaging

• 1. DIRECT HOLOGRAPHY
• Measure amplitude and phase of scattered signal

• Reconstruct Image using Mathematical Techniques
• Requires VNA - EXPENSIVE

6

• 2. INDIRECT HOLOGRAPHY
• 3D Images can be reconstructed from Amplitude of
  scattered signal
• Requires only SCALAR measurements
• Requires Only Simple Diode Detector
• - INEXPENSIVE

7
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

8
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

9
Intensity Pattern Formation Experimental
Arrangement for Data Collection
10
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

11
1. Intensity Pattern
2. Fourier Transform
12
Problem Difficult to produce sufficient offset
to separate terms of Fourier Transform
Synthesized Reference Wave separates required
term from origin

13
3. Filter off Unwanted Terms
4. Re-centre remaining term
Measurement Plane Image
14
5. Back-propagate to selected depth and perform
IFT
ORIGINAL IMAGE At Object Plane
15
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

16
1. Antenna Radiation Characteristics
Parabolic Dish
Data Collection System
17
Reconstructed Near-Field
Magnitude
Phase
18
2. Imaging of Concealed Metal Objects
Triangle Covered with Cloth
Uncovered Triangle
19
Intensity Pattern Formation Experimental
Arrangement for Data Collection
20
Typical Intensity Pattern
21
Linear Phase Shift Applied to Synthetic
Reference Wave
Plane Wave Spectrum
22
Reconstructed IMAGE
23
Problem of Previous Example Terms in PWS
overlap if object is tilted, cant separate
terms Can only image objects that are FLAT
24
SOLUTION Apply 2D phase shift to reference
wave
25
PWS with 2D Phase Shift
Tilted Objects do not cause terms to overlap
26
3. Imaging of Dielectric Objects
27
Recorded Intensity Pattern
F.T of Intensity Pattern
28
Reconstructed IMAGE
29
4. Imaging of Breast Cancer - Crude Phantom
er1 30, er2 2, d1 35mm, h 10cm, x y
40cm, dx dy 1cm, f 8.6GHz
30
Photo of Breast Phantom
31
Photo of Experimental Setup
32
Recorded Intensity Pattern
F.T of Intensity Pattern
33
Reconstructed IMAGE
34
Benefits of Northumbria Universitys 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

35
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

36
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