Implantable Flow Sensors

Inductively powered implantable blood flow sensors

        The inductively powered implantable blood flow sensors 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 13.56MHz
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 0:18microm CMOS process occupies an active area of 1:51:78mm2
and consumes 21.6microW only. The sensors based on the SiNW and diaphragm structure.

Integrated laser Doppler blood flowmeter

Integrated laser Doppler blood flowmeter that consists of two silicon cavities
with a photo detector(PD) and laser diode inside each cavity. A silicon lid formed with a
converging microlens completes the package. This structure, which was achieved using
micromachining techniques, features reduced optical power loss in the sensor, resulting
in its small size and significantly lowpower consumption.

Volumetric-flow velocity measurement using CMUT array

Volumetric-flow velocity measurement using an implantable capacitive micromachined
ultrasonic transducer (CMUT) array is comprised of multiple-concentric
CMUT rings for ultrasound transmission and an outmost annular CMUT array for ultrasound
reception. Microelectromechanical-system (MEMS) fabrication technology
allows reception CMUT on this flowmeter to be implemented with a different membrane
thickness and gap height than that of transmission CMUTs, optimizing the performance
of these two different kinds of devices. The silicon substrate of this 2-mmdiameter
CMUT ring array was bulk micromachined to approximately 80 to 100 m
thick, minimizing tissue disruption. The blood-flow velocity was detected using pulse
ultrasound Doppler by comparing the demodulated echo ultrasound with the incident
ultrasound. The demodulated ultrasound signal was sampled by a pulse delayed in time
domain from the transmitted burst, which corresponds to detecting the signal at a specific
distance. The flow tube/vessel diameter was detected through the time-flight delay
difference from near and far wall reflections, which was measured from the ultrasound
pulse echo. The angle between the ultrasound beam and the flow was found by using
the cross-correlation from consecutive ultrasound echoes.

Smart catheter flow sensor

Smart catheter flow sensor (SCF) for continuous monitoring of regional cerebral
blood flow (CBF). The SCF employs a periodic heating technique rather than continuous
heating and calibrates itself every 5 seconds. SCF is based on thermal difffusion
flowmetry which allows the direct and quantitative assessment of regional cerebral
perfusion represents a promising monitoring tool in the management of head injured
patients SCF consists of a temperature sensor located outside the thermal influence area
for temperatre compensation and a flow sensor.