A wirelessly powered and interrogated blood flow monitoring microsystem fully integrated with a prosthetic vascular graft for early failure detection

This paper presents an implantable blood flow monitoring microsystem embedded in a prosthetic graft for early graft failure detection. The microsystem consists of two MEMS pressure sensors, an inductively powered wireless sensor interface ASIC, two miniature coupling coils, and a flexible cable connecting them. The implantable microsystem is powered and configured by an external monitoring device using 13.56-MHz carrier frequency. The blood flow rate information is sensed in the form of an oscillation frequency and transmitted to the external monitoring device through backscattering. The ASIC fabricated in 0.18-μm CMOS process occupies a total area of 0.5 × 3.3 mm² including pads and consumes a total power of 12.6 μW. With the high-efficiency design of coupling coils, rectifier and LDO, the wireless power link achieves an overall power efficiency of 2% through 5-cm-thick tissue. With the ultra low power consumption and high-efficiency power transfer, the ASIC can be powered by transmitting only 630-μW RF carrier from the external device. The measured performance of the blood flow monitoring microsystem demonstrates a 0.17-psi pressure resolution.