Microwave Imaging using Indirect Synthetic Reference Beam Holography 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 Reconstruct Image using Mathematical Techniques Requires VNA - EXPENSIVE

Requires Only Simple Diode Detector 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 Object RX Probe Controller TX Probe Power Meter Intensity Pattern I (x,y) Microwave Source Directional Coupler Variable Attenuator Phase Shifter Position Control Synthetic Reference Wave Hybrid Tee

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 2. Fourier Transform

Synthesized Reference Wave separates required term from origin Problem: Difficult to produce sufficient offset to separate terms of Fourier Transform Synthesized Reference Wave separates required term from origin Spectral Representation of Off-axis Hologram:

3. Filter off Unwanted Terms 4. Re-centre remaining term Measurement Plane Image

5. Back-propagate to selected depth and perform IFT ORIGINAL IMAGE At Object Plane

History of Microwave Imaging Research at Northumbria Imaging of Antenna Radiation Characteristics Imaging of Concealed Metal Objects Imaging of Plastic Objects Breast Cancer Detection

1. Antenna Radiation Characteristics Parabolic Dish Data Collection System

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 Object RX Probe Controller TX Probe Power Meter Intensity Pattern I (x,y) Microwave Source Directional Coupler Variable Attenuator Phase Shifter Position Control Synthetic Reference Wave Hybrid Tee

Typical Intensity Pattern

Linear Phase Shift Applied to Synthetic Reference Wave Plane Wave Spectrum

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

SOLUTION: Apply 2D phase shift to reference wave

PWS with 2D Phase Shift Tilted Objects do not cause terms to overlap

3. Imaging of Dielectric Objects

Recorded Intensity Pattern F.T of Intensity Pattern

Reconstructed IMAGE

4. Imaging of Breast Cancer - Crude Phantom 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