Darrin J. Young

A Wireless and Batteryless 10-Bit Implantable Blood Pressure Sensing Microsystem With Adaptive RF Powering for Real-Time Laboratory Mice Monitoring

An implantable real-time blood pressure monitoring microsystem for laboratory mice has been demonstrated. The system achieves a 10-bit blood pressure sensing resolution and can wirelessly transmit the pressure information to an external unit. The implantable device is operated in a batteryless manner, powered by an external RF power source. The received RF power level can be sensed and wirelessly transmitted along with blood pressure signal for feedback control of the external RF power. The microsystem employs an instrumented silicone cuff, wrapped around a blood vessel with a diameter of approximately 200 ¿m, for blood pressure monitoring. The cuff is filled by low-viscosity silicone oil with an immersed MEMS capacitive pressure sensor and integrated electronic system to detect a down-scaled vessel blood pressure waveform with a scaling factor of approximately 0.1. The integrated electronic system, consisting of a capacitance-to-voltage converter, an 11-bit ADC, an adaptive RF powering system, an oscillator-based 433 MHz FSK transmitter and digital control circuitry, is fabricated in a 1.5 ¿m CMOS process and dissipates a power of 300 ¿W. The packaged microsystem weighs 130 milligram and achieves a capacitive sensing resolution of 75 aF over 1 kHz bandwidth, equivalent to a pressure sensing resolution of 1 mmHg inside an animal vessel, with a dynamic range of 60 dB. Untethered laboratory animal in vivo evaluation demonstrates that the microsystem can capture real-time blood pressure information with a high fidelity under an adaptive RF powering and wireless data telemetry condition.

High-temperature single-crystal 3C-SiC capacitive pressure sensor

Single-crystal 3C-silicon carbide (SiC) capacitive pressure sensors are proposed for high-temperature sensing applications. The prototype device consists of an edge-clamped circular 3C-SiC diaphragm with a radius of 400 /spl mu/m and a thickness of 0.5 /spl mu/m suspended over a 2-/spl mu/m sealed cavity on a silicon substrate. The 3C-SiC film is grown epitaxially on a 100-mm diameter <100> silicon substrate by atmospheric pressure chemical vapor deposition. The fabricated sensor demonstrates a high-temperature sensing capability up to 400/spl deg/C, limited by the test setup. At 400/spl deg/C, the device achieves a linear characteristic response between 1100 and 1760 torr with a sensitivity of 7.7 fF/torr, a linearity of 2.1%, and a hysterisis of 3.7% with a sensing repeatability of 39 torr (52 mbar). A wide range of sensor specifications, such as linear ranges, sensitivities, and capacitance values, can be achieved by choosing the proper device geometrical parameters.

Personal Navigation via High-Resolution Gait-Corrected Inertial Measurement Units

In this paper, a personal micronavigation system that uses high-resolution gait-corrected inertial measurement units is presented. The goal of this paper is to develop a navigation system that uses secondary inertial variables, such as velocity, to enable long-term precise navigation in the absence of Global Positioning System (GPS) and beacon signals. In this scheme, measured zero-velocity duration from the ground reaction sensors is used to reset the accumulated integration errors from accelerometers and gyroscopes in position calculation. With the described system, an average position error of 4 m is achieved at the end of half-hour walks.

Monolithic high-performance three-dimensional coil inductors for wireless communication applications

An on-chip three-dimensional RF coil inductor is proposed as a key component to implement monolithic wireless transceivers. The device achieves a substantially superior performance compared to conventional spiral inductors, and is amenable to monolithic integration in a standard IC process due to its low thermal budget. Experimental devices fabricated on a standard silicon substrate (10 /spl Omega/-cm) achieve a 2.6 nH inductance with a peak quality-factor (Q) of 13 at 900 MHz. The Q-factor is limited by a lossy adhesive used in the fabrication. In a modified process without adhesive in the coil area, a 4.8 nH inductor achieves a peak Q-value of 30 at 1 GHz. High-Q 8 nH and 13.8 nH inductors have also been fabricated.

Wireless Batteryless Implantable Blood Pressure Monitoring Microsystem for Small Laboratory Animals

A novel, wireless, batteryless, implantable blood pressure monitoring microsystem for small laboratory animals is developed for advanced biological and system biology research. The system employs an instrumented elastic circular cuff, wrapped around a blood vessel, for real-time blood pressure monitoring. The elastic circular cuff is made of soft bio-compatible silicone material, which is filled with bio-compatible insulating fluid with an immersed microelectromechanical systems (MEMS) pressure sensor and integrated electronic system to detect a down-scaled vessel blood pressure waveform. This technique avoids vessel penetration and substantially minimizes vessel restriction due to the soft cuff elasticity, thus attractive for long-term monitoring. A large-model engineering experiment is first developed to verify and demonstrate the concept. A miniature prototype monitoring cuff is then fabricated and implanted in two laboratory rats to evaluate its functionality. A wireless and batteryless monitoring microsystem is then implanted and characterized in a laboratory rat. The measured in vivo blood pressure waveform by the microsystem and a reference waveform recorded by a commercial catheter-tip transducer are closely matched in shape with a constant scaling factor, demonstrating a blood pressure signal with high fidelity can be wirelessly obtained by the implantable monitoring microsystem. The overall implant dissipates 300 ¿W, which is powered by an external adaptive RF powering source.

A High-Performance MEMS Capacitive Strain Sensing System

This paper describes a high-performance strain sensing microsystem. The system consists of four parallel differential MEMS capacitive strain sensors with a nominal capacitance value of 440 fF, converting an input strain to a capacitance change with a sensitivity of 265 aF per microstrain (muepsiv), and low-noise integrated sensing electronics, which employ a differential continuous-time synchronous detection architecture converting the capacitive signal to an output voltage for further signal processing. Based on system noise characterization, the prototype design shows a capability of measuring a strain resolution of 0.9 nepsiv/radicHz, while demonstrating a maximum dc input stain range of 1000 muepsiv. The overall system consumes 1.5 mA dc current from a 3-V supply

A micromachine-based RF low-noise voltage-controlled oscillator

A voltage-controlled oscillator (VCO) employs an aluminum micromachined variable capacitor for frequency tuning. Unlike conventional varactor diodes, the capacitor is fabricated on a silicon substrate and thus amenable to monolithic integration with a standard IC process. Experimental capacitors achieve a 16% tuning range with a nominal capacitance value of 2 pF and a quality factor above 60 at 1 GHz. A prototype VCO exhibits -107 dBc/Hz phase-noise at 100 kHz offset frequency from the carrier. The center frequency of 714 MHz and 14 MHz tuning range are limited by the test setup.

Remote RF powering system for wireless MEMS strain sensors

A reliable remote radio frequency (RF) powering system is developed for industrial wireless microelectromechanical systems (MEMS) strain-sensing applications. The prototype system is insensitive to mechanical rotation and produces a stable DC voltage of 2.8 V with a 2-mA current supply capability from a 50-MHz RF power source with a power conversion efficiency of 11%. An improved efficiency can be expected with an optimized power transmitter design. The CMOS power converter electronics are fabricated in a 1.5-/spl mu/m CMOS process occupying an area of approximately 1 /spl times/1 mm. The achieved DC power is adequate for supplying a high-performance wireless MEMS strain-sensing system.

Wireless powering and data telemetry for biomedical implants

Wireless powering and data telemetry techniques for two biomedical implant studies based on (1) wireless in vivo EMG sensor for intelligent prosthetic control and (2) adaptively RF powered implantable bio-sensing microsystem for real-time genetically engineered mice monitoring are presented. Inductive-coupling-based RF powering and passive data telemetry is effective for wireless in vivo EMG sensing, where the internal and external RF coils are positioned with a small separation distance and fixed orientation. Adaptively controlled RF powering and active data transmission are critical for mobile implant application such as real-time physiological monitoring of untethered laboratory animals. Animal implant studies have been successfully completed to demonstrate the wireless and batteryless in vivo sensing capabilities.

In vivo RF powering for advanced biological research.

An optimized remote powering architecture with a miniature and implantable RF power converter for an untethered small laboratory animal inside a cage is proposed. The proposed implantable device exhibits dimensions less than 6 mmtimes6 mmtimes1 mm, and a mass of 100 mg including a medical-grade silicon coating. The external system consists of a Class-E power amplifier driving a tuned 15 cmtimes25 cm external coil placed underneath the cage. The implant device is located in the animals abdomen in a plane parallel to the external coil and utilizes inductive coupling to receive power from the external system. A half-wave rectifier rectifies the received AC voltage and passes the resulting DC current to a 2.5 kOmega resistor, which represents the loading of an implantable microsystem. An optimal operating point with respect to operating frequency and number of turns in each coil inductor was determined by analyzing the system efficiency. The determined optimal operating condition is based on a 4-turn external coil and a 20-turn internal coil operating at 4 MHz. With the Class-E amplifier consuming a constant power of 25 W, this operating condition is sufficient to supply a desired 3.2 V with 1.3 mA to the load over a cage size of 10 cmtimes20 cm with an animal tilting angle of up to 60deg, which is the worst case considered for the prototype design. A voltage regulator can be designed to regulate the received DC power to a stable supply for the bio-implant microsystem