Microwave Imaging using Indirect Microwave Imaging using Indirect Synthetic Reference Beam Synthetic Reference Beam

Holography Holography

Dr. M. Elsdon

CEIS, Northumbria University, Newcastle-upon-Tyne, NE1 8ST, UK

Presentation to Calgary University - October 2005

IntroductionIntroduction

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 MEABOUT 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 OverviewResearch Overview

Work of group based upon patented invention of Northumbria Work of group based upon patented invention of Northumbria University: ‘Synthetic Reference Beam Holography’University: ‘Synthetic Reference Beam Holography’

Exploits the advantage of NOT requiring direct Exploits the advantage of NOT requiring direct measurement of phase. measurement of phase.

Mathematical Reconstruction enables phase to be Mathematical Reconstruction enables phase to be ‘deduced’‘deduced’

VNA replaced with Diode Detector – LOW COSTVNA replaced with Diode Detector – LOW COST

Applications: Applications:

Antenna Radiation Pattern MeasurementAntenna Radiation Pattern Measurement

Airport SecurityAirport Security

Medical ImagingMedical Imaging

Holographic Approach For ImagingHolographic Approach For Imaging

1. DIRECT HOLOGRAPHY:

Measure amplitude and phase of scattered signal

Reconstruct Image using Mathematical Techniques

Requires VNA - EXPENSIVE

VectorNetworkAnalyser

PositionControl

SamplingAntennasObject

Tx

Rx

2. INDIRECT HOLOGRAPHY:

3D Images can be reconstructed from Amplitude of scattered signal Requires only SCALAR measurements

Requires Only Simple Diode Detector

- INEXPENSIVE

Indirect HolographyIndirect Holography

Two Stage Process:Two Stage Process:

Stage 1:Stage 1:

Illuminate Object with reference wave to Illuminate Object with reference wave to form Hologram (Intensity Pattern)form Hologram (Intensity Pattern)

Stage 2:Stage 2:

Reconstruct Image of Original Object Reconstruct Image of Original Object using post-processing softwareusing post-processing software

Stage 1: Formation of Intensity PatternStage 1: Formation of Intensity Pattern

Illuminate object with coherent reference Illuminate object with coherent reference wavewave

Combine reflected signal with reference Combine reflected signal with reference signalsignal

Form Intensity Pattern – HologramForm Intensity Pattern – Hologram

Record Intensity of HologramRecord Intensity of Hologram

Intensity Pattern Formation – Intensity Pattern Formation – Experimental Arrangement for Data CollectionExperimental Arrangement for Data Collection

Object

RX ProbeRX Probe

Controller

TX ProbeTX ProbePower Meter

Intensity PatternI (x,y)

MicrowaveSource

DirectionalCoupler

Variable Attenuator

Phase Shifter

PositionControl

SyntheticSyntheticReference Reference

WaveWave

HybridTee

Stage 2: Image ReconstructionStage 2: Image Reconstruction

Take Fourier Transform of Recorded Take Fourier Transform of Recorded Intensity PatternIntensity Pattern

Filter Fourier Transform to remove Filter Fourier Transform to remove unwanted termsunwanted terms

Take Inverse Fourier TransformTake Inverse Fourier Transform

Perform Back-propagation and IFT to Perform Back-propagation and IFT to produce image at selected depthproduce image at selected depth

1. Intensity Pattern

2. Fourier Transform

22),(),(),( yxRFyxEFyxIF ),(),(),(),( yxRFyxEFyxRFyxEF

+Xm-Xm

+km-Km-Km +km

Direct Wave

Image 2Image 1

2),(),(),( yxRyxEyxI

kx

ky

Required Term

Spectral Representation of Off-axis Hologram:

Synthesized Reference Wave separates required term from origin

Problem:Problem: Difficult to produce sufficient offset to separate terms of Fourier Transform

3. Filter off Unwanted Terms

4. Re-centre remaining term

+km-Km-Km +km

Direct Wave

Image 2Image 1

Measurement Plane Image

+km-Km

Image 2

5. Back-propagate to selected depth and perform IFT

ORIGINAL IMAGE ORIGINAL IMAGE

At Object PlaneAt Object Plane

+km-Km

Image 2

History of Microwave Imaging History of Microwave Imaging Research at NorthumbriaResearch 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 Characteristics1. Antenna Radiation Characteristics

Microwave SourceVariable

Attenuator

Phase Shifter

Microwavemixer andDetector

P.C

Antenna underTest

A.U.T.Data

Output

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 – Intensity Pattern Formation – Experimental Arrangement for Data CollectionExperimental Arrangement for Data Collection

Object

RX ProbeRX Probe

Controller

TX ProbeTX ProbePower Meter

Intensity PatternI (x,y)

MicrowaveSource

DirectionalCoupler

Variable Attenuator

Phase Shifter

PositionControl

SyntheticSyntheticReference Reference

WaveWave

HybridTee

Typical Intensity PatternTypical Intensity Pattern

Linear Phase Shift Applied to Synthetic Reference Wave

240120024012002401200

240120024012002401200

240120024012002401200

240120024012002401200

240120024012002401200

240120024012002401200

240120024012002401200

240120024012002401200

240120024012002401200

Plane Wave Spectrum

Reconstructed IMAGEReconstructed IMAGE

Problem of Previous Example:Problem of Previous Example:

Terms in PWS overlap if object is tilted, can’t separate terms

Can only image objects that are FLAT

kx

ky

+ve xTILT

+ve xTILT

-ve xTILT

-ve xTILT

-ve yTILT

-ve yTILT

+ve yTILT

+ve yTILT

SOLUTION:SOLUTION:

Apply 2D phase shift to reference wave

12002401201202401200240

024012002401200240120

240120024012002401200

120024012002401200240

024012002401200240120

240120024012002401200

120024012002401200240

024012002401200240120

240120024012002401200

kx

ky

+ve xTILT

+ve xTILT

-ve xTILT

-ve xTILT

-ve yTILT

-ve yTILT

+ve yTILT

+ve yTILT

PWS with 2D Phase Shift

Tilted Objects do not cause terms to overlap

3. Imaging of Dielectric Objects3. Imaging of Dielectric Objects

Recorded Intensity Pattern

F.T of Intensity Pattern

Reconstructed IMAGEReconstructed IMAGE

4. Imaging of Breast Cancer - Crude Phantom4. Imaging of Breast Cancer - Crude Phantom

Illum

inat

ing

Ante

nna

Rece

ivin

gAn

tenn

a

h

d1Tumor

1r

ImmersionMedium

2r

εr1 = 30, εr2 = 2, d1 = 35mm, h = 10cm, x = y = 40cm, dx = dy = 1cm, f = 8.6GHz

Photo of Breast PhantomPhoto of Breast Phantom

Photo of Experimental SetupPhoto of Experimental Setup

Recorded Intensity Pattern

F.T of Intensity Pattern

Reconstructed IMAGEReconstructed IMAGE

Benefits of Northumbria University’s TechniqueBenefits of Northumbria University’s Technique

Provides 3D Holographic Image from “Single –Provides 3D Holographic Image from “Single –View” 2D ScanView” 2D Scan

Employs Patented Employs Patented SyntheticSynthetic Reference Beam Reference Beam ElectronicallyElectronically Hologram “Created” in SoftwareHologram “Created” in Software

Compact Microwave Network Compared to External Compact Microwave Network Compared to External Offset Reference Beam Antenna GeometryOffset Reference Beam Antenna Geometry

Low-CostLow-Cost Simple Square-Law Detector in Lieu of Vector Simple Square-Law Detector in Lieu of Vector

AnalyserAnalyser

Phase Retrieval via Mathematical Reconstruction Phase Retrieval via Mathematical Reconstruction ProcessProcess

Dr David SmithDr David Smith, Team Leader & Inventor of , Team Leader & Inventor of Synthetic Reference Beam Holography Synthetic Reference Beam Holography

Dr Michael ElsdonDr Michael Elsdon, Post - Doctoral Researcher, Post - Doctoral Researcher

Dr Mark LeachDr Mark Leach, Post - Doctoral Researcher, Post - Doctoral Researcher

Prof. Stephen J FotiProf. Stephen J Foti, Consultant, Consultant

MrMr M. JoyM. Joy, PhD Student, PhD Student

Microwave Imaging Research Group Microwave Imaging Research Group Northumbria UniversityNorthumbria University

AcknowledgementsAcknowledgements

Engineering and Physical Science Research CouncilEngineering and Physical Science Research Council

(EPSRC)(EPSRC)

Wellcome TrustWellcome Trust

Newcastle University Medical SchoolNewcastle University Medical School

Prof. T. Lennard Prof. T. Lennard (Royal Victoria Infirmary)(Royal Victoria Infirmary)

Mr Peter ElsdonMr Peter Elsdon, Technical Consultant, Technical Consultant