Design of a 3 D Microwave Imaging System

Design of a 3 D Microwave Imaging System Drew Jaworski Advisor: Dr. Yong Zhou Fall 2011 – Senior Design I

Why Microwave Imaging? n Electromagnetic Imaging Systems ¡ Vision n ¡ X-Ray n ¡ Expensive Microwave n n Limited to surfaces MRI (quantum mechanics) n ¡ Ionizing radiation Infrared (“thermal”) n ¡ Nature doesn’t always know best! Non-ionizing, penetrating, less expensive! Applications ¡ ¡ Medical imaging (cancerous tumors, etc) Industrial scanning (forging defects, etc)

Project Specifications n Design of a 3 -dimensional microwave imaging system ¡ ¡ Vector network analyzer signal analysis Automated data acquirement and processing Biomedical focus, but adaptable for other imaging applications Multiplexed antenna array

Project Constraints n Size ¡ n Budget ¡ n $300 from department + personal funds FCC Regulations ¡ n Entire system less than 1[m]*1[m] Medical device band: 3. 1[GHz]– 10. 6 [GHz] Many others related to trying to manage the above constraints

Electromagnetic Overview n Plane-wave approximation ¡ ¡ n Imaging subject located in far-field of antenna array, perpendicular to propagation of waves Simplifies analysis at expense of system size Scattering through media ¡ A result of multiple layers of diffraction and refraction, in the case of the complex human body. Images courtesy of: http: //en. wikipedia. org/wiki/File: Linear. Polarization. Linearly. Polarized. Light_plane. wave. svg http: //commons. wikimedia. org/wiki/File: Huygens_brechung. png

Vector Network Analyzer n Measures a Two Port Network ¡ Returns S-Parameters (Scattering Parameters) n n n S 11 – Return Loss S 21 – Insertion Loss Parallel antennas connected to VNA ports ¡ ¡ ¡ Calibrate response Place object between antennas Result is how the object affected the electromagnetic radiation between the two antennas n Results can be manipulated with software algorithms to give dielectric properties of the object!

Inverse Scattering Solution n Repeat with multiple antennas (4 x 4 array, in this case) ¡ ¡ Rotate object between antenna arrays Result is a set of matrixes of scattering parameters for a 32 -port network (for a range of frequencies!) n n Can be manipulated to produce a discretized graphical representation of the dielectric properties in different regions between antenna arrays Inverse Scattering Problem – Microwave Tomography ¡ ¡ ¡ We know the forward transmitted radiation (aka Incident Fields) We have information about the received fields (aka Scattered Fields) Now we want to know what made them change! n n Very complex calculations that are demanding of computing resources Fortunately, much research has been published that has mathematically and/or computationally simplified the solution process (relatively)

Automated Data Analysis n Labview ¡ ¡ Automate collection of data Several colleagues have worked out the details n n n Rotation mechanism – Juan Nava, Miguel Rivera TTL communication (for multiplexer) – Julio Vasquez Matlab ¡ ¡ Process data Numerous published algorithms can be implemented and tested

Frequency Selection n n Often limited by hardware technology (switch/antenna bandwidth) Biomedical focus – human tissues Estimates vary, best to come up with your own and justify accordingly Begin with what spectrum is available ¡ ¡ FCC “Medical Systems: These devices must be operated in the frequency band 3. 1 -10. 6 GHz. A medical imaging system may be used for a variety of health applications to “see” inside the body of a person or animal. Operation must be at the direction of, or under the supervision of, a licensed health care practitioner. ” n n http: //transition. fcc. gov/Bureaus/Engineering_Technology/Orders/2002/fcc 02 048. pdf Begin with properties of human body ¡ Database of dielectric properties of numerous types of tissue available from Italian National Research Council site: n http: //niremf. ifac. cnr. it/tissprop/

Dielectric Properties Database n Skin (wet and Dry), Muscle, Fat, and Bone ¡ Major constituents most body parts Highest λ Highest alpha Lowest λ Lowest alpha intersection

Antenna Array Multiplexer n Julio Vasquez’s RF multiplexer design intended for this project ¡ n Overlapping semesters meant his prototype was not yet completed and could not be used immediately Microstrip antenna array with integrated multiplexer switch hierarchy ¡ ¡ ¡ Avoids requirement of numerous expensive and tangled SMA patch cables Integrates network of SPDT switches into antenna array 4 x 4 microstrip antenna array n n 1 SMA connector (patched to VNA) 15 SPDT RF switches (operating up to 8[GHz]) 16 microstrip patch antennas 8 TTL-level (5 V) control lines

Antenna Array with Multiplexer

RF Layout Guidelines n Line Widths ¡ 3. 08[mm] n n Curves ¡ ¡ n Ideally smooth curves radius >= 3*line. Width Ground fills ¡ Not completely necessary n n 50Ω impedance Relatively noise-free environment Noise reducing padding around experiment setup Not feasible for hand-produced prototype Tapered impedance tranformers ¡ ¡ Linear (“triangular”) is best for wideband operation (Pozar) λ/4 ~ λ used in design (as long as could be reasonably fit)

Multiplexer versus Switch Network n Fully featured DC-12[GHz] multiplexer ¡ n $700 ~ $1700 Single SPDT RF switch IC ¡ ¡ $1 ~ $3 M/A-COM technology solutions n n MASW-007107 Pros ¡ ¡ n Large variety of models available Distributed by Mouser Cons ¡ Small package size (Ga. As DIE ~ 4[mm]*4[mm]

MASW-007107 Obtained from IC Datasheet: http: //www. macomtech. com/Data. Sheets/MASW-007107. pdf

MASW-007107 (continued)

Switch Network Hierarchy

UWB Microstrip Antenna n Two-port network theory (one-port input network, in this case) ¡ S 11 measures “return-loss” [d. B] n n n Lower is better, -10[d. B] indicates half of the input power is lost in the network Return Loss is power radiated from antenna (hopefully) and other losses. Bandwidth is measured where S 11 crosses the -10[d. B] point ¡ Design is UWB when (BW / Fcenter) >= 25%

UWB Microstrip Antenna n There are many published designs for UWB microstrip antennas n Most use complex ground geometries n n (continued) Usually explain it as something to keep the phase response level across the useable band After trying several designs, I began modifying the geometries in an attempt to find something new

UWB Microstrip Antenna n n n (continued) BW = 979[MHz] Fcenter = 5. 595[GHz] -10[d. B] BW => 17. 52% (close, but not UWB)

UWB Microstrip Antenna n (continued) Fractal and/or self-symmetry based designs n Intended to induce multiple resonance frequencies Inspired by: Miniaturized UWB Monopole Microstrip Antenna Design by the Combination of Guisepe Peano and Sierpinksi Carpet Fractals, IEEE AWPL, 2011

Budget (proposed) n Double-sided FR-4 boards (2 x) ¡ n MASW 007107 RF Switches (50 x) ¡ n $37. 50 + shipping Commercially Manufactured PCBs ¡ n $12. 66 + shipping $150 All other supplies already in possession

Gantt Chart – SD 1 9/19/15 Select Frequency Operation Range Decide Switching Design/Product Learn HFSS Decide Antenna Design Layout Array PCB Design Simulate Design Explicitely Modify PCB Design Accordingly Produce Protoype Board 9/169/30 10/15 10/1610/31 11/15 11/1611/30 12/1512/30

Gantt Chart – SD 2 (proposed) 1/11/15 Layout Final Design Send Layout Out for Manufacturing Test New Boards Establish Mathematics of System Program Algorithms Test System and Collect Data Prepare for Research Symposium Final Report and Presentation 1/151/31 2/12/15 2/162/29 3/13/15 3/163/31 4/14/30 5/15/31

Future Work n n Finalize UWB antenna candidate design RF Layout of antenna array ¡ ¡ Produce a prototype (using materials on hand) Export Gerber file and have it manufactured commercially n n Develop mathematics of Imaging System ¡ n $1 per square inch (min. 150 square inch order) Microwave Imaging (2011), Matteo Pastorino Begin making microwave images!