Evanescent Field Applicator for Contactless Microwave Breast Diagnostics in Air

In this paper, we present an air-based approach to irradiate the female breast with electromagnetic microwave radiation by means of contactless evanescent near-field coupling for medical applications. A suitable transducer, so-called applicator, is presented, designed to create a TE-polarized evanescent field at approximately 4 GHz, reducing stray radiation and other unwanted first-order interactions at the breast surface without the need for a dielectric bolus liquid. Initial numerical investigations showed that the applicator setup achieves a 20 dB higher signal-to-clutter ratio (SCR) than a comparable bolus-based setup when applied to a simple high-adipose breast phantom. In the case of a low-adipose test load, the SCR could not be readily attributed to the presence of a tumor, yet it was found that under realistic conditions, the applicator setup achieves a significantly higher power transmission effectiveness into the load of up to 80% compared to the bolus-based setup that achieved less than 0.1% effectiveness. Experimental measurements of the applicator show a change of resonance frequency of less than 2% for load permittivities ranging from 1 to 80, enabling the applicator to be used for a wide span of patient-specific dielectric breast properties.