Thermal flow sensors on flexible substrates for minimally invasive medical instruments

We present a flexible polyimide-based calorimetric thermal flow sensor featuring two thermopiles and a heating element perpendicular to the flow direction, connected to a rigid silicon chip containing the bondpads for standard wire bonding. After measurement of the temperature coefficient of resistance of the heater (TCR) and the Seebeck coefficient of the thermopiles of the sensor, the devices are mounted on a printed circuit board (PCB) flow channel and tested in constant power (CP) mode under both steady and dynamic flow conditions. The obtained results are in good agreement with previous research on similar, less flexible, flow sensors. The presented device can then potentially be wrapped around catheters or guidewires for intravascular blood flow assessment.