An Inductively Powered Implantable Blood Flow Sensor Microsystem for Vascular Grafts

Abstract

Monitoring blood flow rate inside prosthetic vascular grafts enables an early detection of the graft degradation, followed by the timely intervention and prevention of the graft failure. This paper presents an inductively powered implantable blood flow sensor microsystem with bidirectional telemetry. The microsystem integrates silicon nanowire (SiNW) sensors with tunable piezoresistivity, an ultralow-power application-specific integrated circuit (ASIC), and two miniature coils that are coupled with a larger coil in an external monitoring unit to form a passive wireless link. Operating at 13.56-MHz carrier frequency, the implantable microsystem receives power and command from the external unit and backscatters digitized sensor readout through the coupling coils. The ASIC fabricated in 0.18-μm CMOS process occupies an active area of 1.5 × 1.78 mm (2) and consumes 21.6 μW only. The sensors based on the SiNW and diaphragm structure provide a gauge factor higher than 300 when a small negative tuning voltage (-0.5-0 V) is applied. The measured performance of the pressure sensor and ASIC has demonstrated 0.176 mmHg/√Hz sensing resolution.

Efficient ultra low power rectification at 13.56 MHz for a 10 µA load current

“…Our PCE is higher than in other comparable but more complex works, e.g. a 66% rectifier PCE for a 21.6 µW load [3]. …”

Continuous wireless pressure monitoring and mapping with ultra-small passive sensors for health monitoring and critical care

“…The smallest wireless pressure monitoring device to date is a battery-powered wireless sensor that researchers have fit into a 1-mm 3 package for intraocular applications 19 . Several groups have been able to successfully reduce the integrated circuit (IC) chip size down to 2.5-4.5 mm 2 for actively powered wireless pressure devices, but they still require a separate 5-6 mm diameter antenna coil [20][21] . Recently, microfabrication techniques and microelectromechanical system technology have been applied to reduce device footprints in passive wireless sensing of intraocular pressures [18][19][20][21][22] .…”

“…Several groups have been able to successfully reduce the integrated circuit (IC) chip size down to 2.5-4.5 mm 2 for actively powered wireless pressure devices, but they still require a separate 5-6 mm diameter antenna coil [20][21] . Recently, microfabrication techniques and microelectromechanical system technology have been applied to reduce device footprints in passive wireless sensing of intraocular pressures [18][19][20][21][22] . However, with all the sensors operating below a few hundred MHz, none has been able to miniaturize below a few mm 3 in volume [3][4][5][6][7][8][9][10][22][23][24][25][26] .…”

Microelectromechanical Systems and Nephrology: The Next Frontier in Renal Replacement Technology

“…Cheong et al have designed a MEMS based pressure sensor for monitoring blood flow in prosthetic vascular grafts. 104 The implantable device uses a silicon nanowire sensor with tunable piezoresistivity to monitor blood flow illustrated in Figure 19. The MEMS fabricated device uses a stack of silicon nitride and silicon oxide layers to form a membrane and a nanowire serves as the sensing element.…”