Broadband Wide-Angle Absorber for Microwave Imaging of Tissue

A broadband wide-angle absorbing structure for the non-reflective termination of tissue is proposed for enclosures needed in microwave tissue imaging. A prototype consisting of 10 x 10 unit cells is fabricated and experimentally tested using breast-tissue phantoms. Through simulations and measurements, it is demonstrated that the proposed absorbing structure achieves a reflection coefficient better than -20 dB for TE polarization and better than -12 dB for TM polarization for incidence angles from 0 degrees to 80 degrees and within the frequency band from 3 GHz to 8 GHz. The design principles are delineated, enabling the development of other absorbing structures suitable for any tissue of interest. A calibration method and procedure are also developed and employed with the reported measurements, which allow for de-embedding the effect of the lossy tissue medium and extracting the intrinsic reflection coefficient of the absorber. The proposed structure demonstrates superior absorption compared to prior designs and provides a much-needed solution for the construction of non-reflective enclosures for microwave biomedical imaging applications.