Nattapon Chaimanonart

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.

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

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.

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

A wireless and batteryless 130mg 300µW 10b implantable blood-pressure-sensing microsystem for real-time genetically engineered mice monitoring

Genetic engineering of mice DNA sequences, together with in vivo real-time blood pressure measurement is crucial for identifying an animals genetic variation susceptibility to cardiovascular-related diseases. However, there is no adequate solution for long-term in vivo blood pressure monitoring to date. Due to the small size of laboratory mice, a miniature, light-weight, wireless, batteryless, implantable microsystem is highly critical to capture accurate biological signals from an untethered animal in its natural habitat, thus eliminating stress and post-implant trauma-induced information distortion. Furthermore, miniaturization of a packaged system is essential for interfacing with a mouses arteries, which exhibit a small diameter of only 200εm, and is crucial for achieving a reliable sensor-artery contact for accurate measurement. The small artery renders intra-vascular stent-based blood-pressure-sensing techniques infeasible. Remote RF powering has been widely used for biomedical implants [1,2]. However, the proposed microsystem is implanted in a freely moving laboratory mouse, thus resulting in continuously changing magnetic coupling, which demands adaptive control for RF powering.

Low-noise CMOS integrated sensing electronics for capacitive MEMS strain sensors

This paper describes a high-performance strain sensing microsystem. A MEMS capacitive strain sensor converts an input strain to a capacitance change with a sensitivity of 26.5 aF per 0.1 /spl mu//spl epsiv/. Low-noise integrated sensing electronics, employing a continuous time synchronous detection architecture, convert the capacitive signal to an output voltage for further signal processing. The prototype microsystem achieves a minimum detectable strain of 0.09 /spl mu//spl epsiv/ over a 10 kHz bandwidth with a dynamic range of 81 dB. The sensing electronics consume 1.5 mA from a 3 V supply.

Adaptive RF power control for wireless implantable bio-sensing network to monitor untethered laboratory animal real-time biological signals

A wireless implantable adaptive RF power converter system for monitoring real-time biological signals of an untethered small laboratory animal inside a housing cage is developed. The overall prototype sensing system exhibiting a dimension of 6 mm times 6 mm times 2 mm and a weight less than 100 mg can be implanted in the animal abdomen. The implant unit consisting of a tuned 20-turn spiral coil is inductively coupled a 4 MHz RF energy source from an external power amplifier driving a tuned 25 cm times 15 cm, 4-turn RF coil. An on-chip rectifier and linear regulator circuit convert the received AC voltage to a stable 2 V DC supply with 1 mA driving capability. Due to animalpsilas different positions and tilting angles (up to 60 degrees) inside the cage with a 1 cm nominal separation distance between internal and external coils, a large varying RF coupling strength is produced and can be detected by a power sensing circuit. The received RF power level is quantized and processed with other biological data before wireless transmission using frequency shift keying (FSK) scheme. The external power source can adaptively adjust its RF power strength based on the received one-bit power sensing data to achieve a stable and reliable voltage supply for the overall bio-implant microsystem with an optimal power coupling efficiency.

A Wireless Strain Sensing Microsystem with External RF Power Source and Two-Channel Data Telemetry Capability

A wireless strain sensing microsystem is powered by a 50MHz signal and can simultaneously telemeter both digitized strain and temperature data over the RF powering link using passive PSK and ASK modulations, respectively. The prototype system achieves a minimum detectable strain of 0.87muepsiv over a 10kHz bandwidth with a maximum input signal of plusmn1000muepsiv. The temperature sensor resolution is 0.02Cdeg rms with a 100Hz BW. The chip is fabricated in 1.5mum CMOS and dissipates 6mW

Wireless power recharging for implantable bladder pressure sensor

This paper presents a wireless power recharging system design for implantable bladder pressure chronic monitoring application. The power recharging system consists of an external 4-turn 15-cm-diameter powering coil and a silicone-encapsulated implantable spiral coil with a dimension of 7 mm × 17 mm × 2.5 mm and 18 turns, which further encloses an ASIC with a programmable charging current and logic control capability, a 3-mm-diameter 12-mm-long rechargeable battery, and two ferrite rods. The ferrite rods are employed to improve the quality factor of the implantable coil. For a constant charging current of 100 µA, an RF power of 2.4 mW needs to be coupled into the implantable microsystem through tuned coil loops. With the two coils aligned coaxially or with a tilting angle up to 30°, an external RF power of 7W or 25W is required, respectively, for a large coupling distance of 20 cm at an optimal frequency of 3 MHz.

A wireless batteryless in vivo EKG and body temperature sensing microsystem with adaptive RF powering for genetically engineered mice monitoring

A wireless, batteryless, and implantable EKG and core body temperature sensing microsystem with adaptive RF powering for untethered genetically engineered mice real-time monitoring is designed, implemented, and in vivo characterized. A packaged microsystem, exhibiting a total size of 9 mm x 7 mm x 3 mm with a weight of 400 mg including a pair of stainless steel EKG electrodes, is implanted in a mouse abdomen for real-time monitoring. A low power 2 mm x 2 mm ASIC, consisting of an EKG amplifier, a PTAT temperature sensor, an RF power sensing circuit, an RF-DC power converter, an 8-bit ADC, digital control circuitry, and a 433 MHz FSK transmitter, is powered by an adaptively controlled external RF energy source at 4 MHz to ensure a stable 2V supply with 156μA current driving capability for the overall microsystem.