Flexible Passive Sensor Patch with Contactless Readout for Measurement of Human Body Temperature

• Published in: Biosensors (Basel) 2023-05, Vol.13 (6), p.572
• Main Authors: Zini, Marco, Baù, Marco, Nastro, Alessandro, Ferrari, Marco, Ferrari, Vittorio
• Format: Article
• Language: English
• Subjects: Biomedical engineering; Biosensors; Body Temperature; body temperature sensor; Capacitance; coil-coupled sensor; Coils; Communication; contactless; Design and construction; Electric Capacitance; Embedding; Humans; Interrogation; Measurement; Measurement techniques; Methods; passive sensor; Questioning; Resonant frequencies; RLC circuits; RLC resonator; Sensors; Skin; Skin temperature; Temperature; Temperature measurement; Temperature measurements; time-gated technique; Upper Extremity
• ISSN: 2079-6374; 2079-6374
• DOI: 10.3390/bios13060572

A passive flexible patch for human skin temperature measurement based on contact sensing and contactless interrogation is presented. The patch acts as an RLC resonant circuit embedding an inductive copper coil for magnetic coupling, a ceramic capacitor as the temperature-sensing element and an additional series inductor. The temperature affects the capacitance of the sensor and consequently the resonant frequency of the RLC circuit. Thanks to the additional inductor, the dependency of the resonant frequency from the bending of the patch has been reduced. Considering a curvature radius of the patch of up to 73 mm, the maximum relative variation in the resonant frequency has been reduced from 812 ppm to 7.5 ppm. The sensor has been contactlessly interrogated by a time-gated technique through an external readout coil electromagnetically coupled to the patch coil. The proposed system has been experimentally tested within the range of 32-46 °C, giving a sensitivity of -619.8 Hz/°C and a resolution of 0.06 °C.