Dual-Mode Resonant Sensor for Depth Spectroscopy

Microwave spectroscopy holds great potential for the development of non-invasive biomedical sensors capable of penetrating tissues and detecting changes in biomarker permittivity. However, the surrounding tissue can interfere with the signal, reducing selectivity when targeting subcutaneous volumes. Depth spectroscopy, using sensors such as open-ended coaxial probes (OCPs), has been proposed to access different tissue layers. Despite their promise, OCPs face challenges in practical, out-of-lab applications. In this paper, we present a sensor interface with tunable sensing volume. Through dual-mode excitation, we demonstrate that the sensor can detect two distinct depths: 0.62 mm and 1.4 mm, highlighting the suitability of this technique for developing sensor interfaces for depth spectroscopy.