Wearable UHF-RFID Sensor for Wetness Detection

The use of wearable textile Radio Frequency Identification (RFID) sensors is becoming widespread in many different application areas because of their technical utilization advantages. In this study, a textile-based Ultra High Frequency (UHF) RFID sensor that can be used to detect wetness has been developed and fabricated with a pad printing machine using silver conductive ink. The overall physical dimension of the proposed sensor structure is 75.0 mm
$\times38.0$
mm
$\times0.12$
mm. Two different types of Received Signal Strength Indicator (RSSI) measurement setups in near field region and at practical separation distances emulating more realistic environmental conditions have been carried out to test and validate the applicability of the proposed sensor. Water, saline and urine solutions have been used to evaluate different wetting conditions in the near field RSSI measurements by dropping different solutions on the RFID sensor integrated diaper. A permissible signal difference of at least 17 dBm has been detected between the wet and dry states of the proposed wetness detection sensor. The performance of the proposed RFID sensor has been evaluated using different separation distances of 32 cm, 40 cm and 50 cm with the practical result of maximum reading range to be 50 cm for the reliable determination of the binary wetness states. In addition, the performance of the RFID wetness sensor against different bending and deformation conditions is almost robust. It is concluded that the proposed sensor structure can be integrated onto the patient’s diapers to facilitate the reliable detection of wetness states in cases such as urinary incontinence in remote health monitoring systems.