The limited penetration depth of electromagnetic (EM) waves into biological tissues is a significant challenge for the use of microwave sensors in medical diagnostics. This study proposes a sensor based on a complementary split-ring resonator (CSRR) for the non-invasive detection of carotid atherosclerotic plaques, designed to be placed on the patient's neck.

The sensor employs a widened feed line and an optimized sensing area to concentrate the electric field and store a significant amount of energy within the biological tissue. Validation includes EM simulations and ex-vivo measurements on fresh animal tissues using monolayer and multilayer configurations to simulate human neck anatomy. A three-dimensional carotid artery model is also introduced to extend the analysis to deeper tissue layers and simulate different degrees of stenosis between 25% and 75%.

The sensor demonstrates a sensitivity of 0.72% and a detection resolution of 14 MHz for a dielectric constant range from 1 to 52 in material measurements, which has contributed to enhancing the EM penetration depth in neck tissues. Simulation results for atherosclerotic plaques in the carotid artery revealed a frequency shift difference induced by stable and vulnerable plaques of around 1 to 2 MHz.

These findings highlight the sensor's potential for future use in the in- vivo diagnosis of carotid artery atherosclerosis.