A Tuned Microwave Resonant Sensor for Skin Cancerous Tumor Diagnosis

In this work, a planar microwave sensor based on a flexible polyimide substrate has been developed to distinguish if a skin lesion is malignant or benign. The sensor is a tuned loop resonator operating in the industrial, scientific, and medical (ISM) band at 2.465 GHz, providing a localized high-intensity electric field that penetrates into tissues with sufficient spatial and spectral resolutions. The loop resonator with a radius of 5.4 mm was tuned by a concentric metal pad to the desired resonant frequency with a sufficiently high quality factor of 98.7 and a reflection coefficient of $-$63.98 dB. The sensor is based on the detection of electromagnetic resonance change and sequential frequency shift that is susceptible to the dielectric property difference between cancerous and benign tissues. Basal Cell Carcinoma (BCC) and Seborrheic Keratosis (SK), the most commonly found malignant and benign skin lesions with close visual similarities, were selected to demonstrate the sensing concept. Tissue-mimicking materials were fabricated to have similar dielectric properties to those of healthy skin, SK, and BCC tissues in the literature. Simulations and measurements were conducted. Significant frequency shifts of 759 MHz and 415 MHz were observed between BCC and SK phantoms in simulations and measurements, respectively, when the size of the tumor phantom was a cuboid of 12 mm × 12 mm × 4 mm underneath and among healthy skin. Simulations were conducted for different cuboid side lengths from 2 to 16 mm while the thickness remained at 4 mm. Malignant lesions could be distinguished with a cuboid side length as small as 2 mm. Corresponding measurements for cuboid side lengths of 6, 8, 10, and 12 mm were conducted and matched the trend well with the simulation results. The promising results in simulations and measurements validate the sensing principle, showing great potential for skin cancer detection in a noninvasive, efficient, and lower-cost way.