Investigation into the pressure sensing properties of PVDF and PVB thick film capacitors

This paper examines the sensitivity of polyvinylidene fluoride (PVDF) and polyvinyl butyral (PVB) capacitors to pressures ranging from 0-100 kPa. The capacitors were formed by screen-printing onto flexible substrates and have an active area of 2 times 3 mm². There are no moving parts and as a result the complexity of sensor design, fabrication and packaging issues may be reduced. After fabrication, sensors were adhered to planar and cylindrical surfaces and interfaced with an AD7746 24-bit capacitance to digital converter. This allowed precise measurements to be taken. It has high linearity and accuracy and can accept up to 17 pF absolute capacitance. The pressure was applied by housing the sensor in an airtight container and pumping air into the system to increase the pressure. It was found that PVDF devices on planar surfaces exhibited the largest response to the application of pressure. This was further increased for devices placed on cylindrical surfaces. It is thought that this is due to cracking of the thick film upon bending of the substrate. The results suggest that PVDF and PVB are suitable candidate materials for use in a pressure monitoring system.