Full Wave Modeling of Body Area Path Loss and Related Antenna Modeling S. Makarov & G. Noetscher Ant. Lab ECE Dept., WPI, MA

Task #1 Compare performance of in-house MATLAB FDTD and FEM simulator Ansoft/ANSYS HFSS Establish how important the effect of internal body composition is on the performance of out-of-body wireless link Establish how important the effect of body shape variation is on the performance of out- of-body wireless link

Typical Simulation Results Case 04_05: Antenna position: X = 156.5mm, Z = mm. Adaptive Step Mesh Size (elements) Z-matrix, ΩS-Matrix Received voltage amplitude, mV Ansoft/ANSYS (top) FDTD (bottom) ANSOFT Runtime (HH:MM:SS) 1 400,193 Z 11 = ° Z 22 = ° Z 21 = ° S 11 = ° S 22 = ° S 21 = 4.187e-4 118° :10: ,239 Z 11 = ° Z 22 = ° Z 21 = ° S 11 = ° S 22 = ° S 21 = 1.378e-4 136° :46: ,290 Z 11 = ° Z 22 = ° Z 21 = ° S 11 = ° S 22 = ° S 21 = e-5 141° :05: ,549 Z 11 = ° Z 22 = ° Z 21 = ° S 11 = ° S 22 = ° S 21 = e-5 143° :19: ,863 Z 11 = ° Z 22 = ° Z 21 = ° S 11 = ° S 22 = ° S 21 = e-5 143° :26: ,836 Z 11 = ° Z 22 = ° Z 21 = ° S 11 = ° S 22 = ° S 21 = e-5 143° :21: ,134,472 Z 11 = ° Z 22 = ° Z 21 = ° S 11 = ° S 22 = ° S 21 = 6.675e-5143° :49: ,361,367 Z 11 = ° Z 22 = ° Z 21 = ° S 11 = ° S 22 = ° S 21 = e-5 143° :57:

Relative error comparison Case Number Estimated Relative Error of Received Voltage: FDTD vs. the finest FEM mesh Ansoft/ANSYS HFSS Runtime (HH:MM:SS) FDTD Runtime (MM:SS) 123%23:29:1010:57 221%24:53:0815:22 327%27:55:0128:01 46%29:32:1628:12 56%27:57:1527:51 614%25:08:1715:12 712%25:47:5327:45

Testing different body shapes Case Designation Received Voltage (mV) WPI Male A0.119 WPI Male B0.119 Ansys Mesh0.119

Conclusions: out-of-body networks at 402 MHz Performed code-to-code validation Established that FDTD is superior to FEM w.r.t. CPU time Established that: –Out-of-body wireless link weakly depends on internal body composition –Out-of-body wireless link weakly depends on body shape –Critical diffraction parameters include path length and body area projected onto a plane perpendicular to path

1x8 dipole array Homogeneous body Near-field scanning array task: ~2λ x 2λ x 2λ domain Task #2-In-body to on-body link

Task#3-In-body Antenna Design Independent of  r as long as  r >200 Induced voltage is found using Faraday’s law (  reff >~10-20)

Antenna matching and tuning Series matching for low input impedance Input impedance is on the order of several ohms (loss resistance)

Antenna challenges += Small impedance bandwidth: R/(2  L) High loss and low efficiency A 3D coil antenna is a must Direct measurements are difficult to perform Suggested: signal strength measurements with passive RFID SAW sensors and the calibrated reader antenna