Low-Cost UWB CPW Microwave Tattoo Sensor for Respiratory Monitoring in Epilepsy Detection

This paper presents a flexible, ultra-thin, and transparent tattoo-based CPW slot microwave sensor designed for epilepsy detection based on respiratory monitoring and wearable biomedical applications. The sensor is fabricated using gold leaf on transparent PVC, enabling excellent skin conformity and long-term comfort. The proposed microwave sensor achieves an ultra-wide operating bandwidth of 2.4–17 GHz. Mechanical reliability is confirmed through bending and crumpling tests, where the sensor maintains stable impedance characteristics. In addition to respiratory monitoring, the proposed sensor is highly relevant for epilepsy detection, as epileptic seizures are often accompanied by abnormal respiratory patterns such as apnea, irregular breathing, or sudden changes in breathing rate. Continuous monitoring of respiration can therefore provide an indirect, non-invasive indicator of seizure onset and progression. Experimental measurements demonstrate clear respiratory-phase detection with an average breathing rate of approximately 27 breaths per minute (BPM), corresponding to a normal adult subject under non-pathological conditions. Safety evaluation shows that the SAR values remain well below international exposure limits. The maximum simulated SAR values of 0.946 W/kg (1 g) and 0.258 W/kg (10 g) occur at 6 GHz and a transmitted power of 20 dBm, while significantly lower SAR levels are observed at lower frequencies and power levels. With its wide bandwidth, flexibility, skin transparency, and confirmed electromagnetic safety, the proposed sensor demonstrates strong potential for continuous healthcare monitoring, epilepsy-related respiratory assessment, and future integration into unobtrusive wearable systems.