The EM wave propagates through the waveguide and irradiates the breast model. Absorption of the incident microwaves leads to transient heating and thermoelastic expansion. The power transmission efficiency from the waveguide to the breast model can be enhanced with proper impedance matching. A matching layer is designed to maximize the available microwave power deposited in the breast model so that maximum acoustic signal is generated. Considering the geometry of the waveguide and breast model,aplanarmatchinglayerissuitable.Thetransversedimensionofthematchinglayeris10cm×10 cm,which is the same as the breast model and much larger than the waveguide aperture.Because the high-power microwave pulse signal generator represents the most demanding component in a TAI system, employing a matching layer is beneficial to meliorating the efficiency of the power utilized in real experiments and thus
2784 IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING, VOL. 59, NO. 10, OCTOBER 2012
alleviates the critical device requirement. This is not only economically meaningful, but also valuable to increase the SNR in the harvested acoustic pressures. Unfavorable matching conditions will cause much of the power unused and reflected back to the power source.