Design and fabrication of implantable pressure sensing resistor sensor for human bladder monitoring system

Many aging people and patients have difficulties in bladder control. Recent methods have been studied for non-invasive measuring for bladder information. It must be improved to a more convenient and real time measurable system for accurately analyzing and controlling individual bladder information. This paper presents the pressure sensor for the invasive bladder monitoring system. The system has the pressure sensing resistor sensor (PSRS) which is set-up inside the bladder. The PSRS consists of a flexible and contactable diaphragm which deforms towards an underlying substrate while a range of pressure is applied. The flexible diaphragm has a thin metal film which acts as a switch and the underlying substrate has interdigitated electrodes which serve as a variable resistor. The PSRS initially exhibits infinite electrical resistance with no external pressure applied since the metal switch is not contact with the interdigitated electrodes. As the applied pressure increases above a threshold, the contact area increases thus the resistance of the PSRS decreases. Based on the finite element analysis, proper ranges for the diaphragm size and gap distance are determined. The sensor, the diaphragm size of which is 2.6 × 2.6 mm 2 , has been fabricated through MEMS technology. The change of the electrical resistance is 0.5 Ω for the range of human bladder pressure (0–10 kPa). This PSRS will be effectively used for reliability and stability of the research for the improvement of bladder management. It can also be utilized for the future application.