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This paper presents the design, fabrication, and characterization results of a paper-based, low-cost, easy-to-use, comfortable and wearable tactile sensor array for human health monitoring applications. Paper substrate and spray-deposited metallic electrodes and traces are employed to achieve a low fabrication cost. Capacitive sensing scheme employing a deformable triangular PDMS sensing membrane is chosen due to its high sensitivity and zero DC power dissipation. Trade-offs among different sensor array designs are investigated to achieve an optimal design, which consists of a $1\times 5$ sensor array occupying an area of 10 mm $\times10$ mm. Each sensor in the array achieves a nominal capacitance value and sensitivity of approximately 1 pF and 30 fF/mmHg, respectively. Fabricated sensor array can be comfortably attached to an individual’s temporal region and ankle area to monitor real-time blood pressure (BP) pulse waveform with high fidelity, from which heart rate and heart rate variability information can be accurately obtained. In addition, the prototype sensor array demonstrates its capability of detecting atrial fibrillation (AFib) from BP pulse waveform measured from an AFib patient. [2020-0179]

A wireless inductive sensing technology with a robust packaging scheme is proposed and demonstrated for future implantable hydrogel-based glucose monitoring applications. A prototype wireless glucose sensor employs a glucose-sensitive hydrogel embedding a parylene-coated metallic sensing plate as a key sensing element. The hydrogel changes its volume responding to glucose change; thus displacing the metallic sensing plate that can be sensed by a nearby sensing coil through the coil inductance change. An ultra-low-power tunnel diode oscillator is designed to convert the inductance change to an oscillator frequency change, which can be wirelessly detected by a nearby receiver. The entire sensing system can be energized by RF powering, thus achieving a wireless and battery-less operation. The proposed sensing scheme allows the sensing electronics to be fully encapsulated in a hermetically sealed package, critical for long-term implantable applications. In vitro characterization demonstrates that the prototype sensor operated around 40 MHz can be wirelessly powered by a 2.77 mW 5 MHz power source with a distance of 2 cm, and achieves a sensing resolution of 0.05 mM and 0.3 mM within a glucose range from 0 mM to 2 mM and 8 mM to 10 mM, respectively, limited by the oscillator frequency drift and fluctuation. Furthermore, a hydrogel pillar-based design is promising to substantially shorten the system response time.

Efficient water use is a must for sustainable agriculture, driving the need for affordable soil moisture sensors to guide irrigation timing. Sensors are limited by cost, maintenance and the need for wires for data capture and charging. We are developing low-cost, long-life, wireless in-situ soil sensing networks, which can potentially enable a much higher sensor density for large farmland or intense research plot monitoring. This custom soil sensor is made from off-the-shelf electronics and consumes approximately 10x less energy per measurement, compared to commercially available sensors. Here we present our new sensor technology, while also investigating its repeatability and accuracy in controlled conditions and comparing it to that of commercially available soil moisture sensors. The final application of the custom soil moisture sensor is an underground in-situ sensing network, which will be enabled through wireless powering and telemetry systems implemented on autonomous vehicles, both ground and aerial.

This paper describes two selected research projects on “middle ear implantable microphone for future fully implantable cochlear prosthesis” and “brain sensing technology with embedded DSP”. The projects present strong ambitious research and development efforts from university research laboratory and industry, respectively, with a focus on advancing biomedical implantable technologies Encouraging research performances have been demonstrated in both projects. The achieved results pave the way for realizing future high-performance human prosthetic systems and bran machine interface systems.

Bio-implantable medical devices need a reliable and stable source of power to perform effectively. Although batteries are typically the first candidate to power implantable devices, they have a limited lifetime and must be periodically replaced or recharged. To alleviate this issue, ultrasonic power transfer systems can wirelessly power bio-implantable devices. Diaphragm structures which use piezoelectric materials (also known as piezoelectric micromachined ultrasonic transducers) can be fabricated on a small scale suitable for implantable devices. Diaphragms can be fabricated by deposition of lead zirconate titanate (PZT) films on a non-piezoelectric material. However, current deposition techniques cannot provide PZT thicknesses more than about 6 μm. We numerically investigate the performance of a square ultrasonic PZT receiver with inner and outer electrodes. Using COMSOL simulations, we optimize the piezoelectric film thickness for a 2 mm × 2 mm diaphragm with a silicon substrate of 50 μm and find the optimal thickness to be 20 μm for a maximum output power delivered to an optimal load. We fabricate a micromachined ultrasonic power-generating receiver capable of providing sufficient power for implantable medical devices using bulk PZT. We show that when a transmitter is generating an input power intensity of 322 mW/cm 2 at 88 kHz, less than Food and Drug Administration limit of 720 mW/cm 2 , the receiver delivers a power of 0.7 mW to an optimal resistive load of 4.3 kΩ when the distance between the transmitter and the receiver is 20 mm. Furthermore, the process developed can be used to fabricate devices that are significantly smaller than the one characterized, which enables further miniaturization of bio-implanted systems.

This paper presents an evaluation study of a wearable MEMS tactile sensors array in comparison to a commercial photoplethysmography (PPG) sensor for potential atrial fibrillation (AFib) detection through monitoring heart rate (HR) and heart rate variability (HRV) from an individual's foot under a sitting condition. The foot is chosen as the monitoring site over other body locations such as the wrist due to its less movement under a sitting environment, which is measured to be less than 0.3g during a one-hour testing period. The PPG sensor exhibits strong motion artifacts (MA) likely due to the toes residual movement when the foot is in a stationary position. The MEMS tactile sensors array is less susceptible to motion artifacts and can accurately obtain HR and HRV under a 0.5g motion, which is suitable for AFib monitoring under a sitting condition.

This paper presents the characterization results of RF coils in loamy soil with a goal to develop low-cost, long-life, wireless, in-situ sensing technologies for monitoring soil health to ensure future sustainable agriculture. Two types of RF coil exhibiting 6 cm-Φ / 9-turn and 12 cm-Φ / 9-turn are employed for the study. The characterization results reveal that coils maximum quality factor takes place around 1 MHz limited by the loamy soil loss. A small gap on the order of 1-2 cm between a coil and surrounding soil can help improve the quality factor significantly. Wireless power transfer efficiency estimation reveals that a sufficient amount of power can be transferred across a soil depth of 30 cm to energize an underground wireless soil sensing network. Further optimized designs are expected to achieve an enhanced performance and extended power transfer distance underground.

Due to copyright restrictions, the access to the full text of this article is only available via subscription. A personal inertial navigation system (PINS) assisted by a microelectromechanical systems (MEMS)-based 13 × 26 ground reaction sensor array (GRSA) and a low-power interface application-specified integrated circuit (ASIC) has been designed and demonstrated for GPS-denied environment. The GRSA operating in a contact mode achieves a sensitivity of approximately 3.7 fF/kPa at each sensor node. An electronic interface system, consisting of a capacitance-to-voltage (C/V) converter followed by a correlated double sampling stage, is designed to convert the GRSA capacitance change to an analog output voltage. The analog output voltage is then digitized by a 12-bit cyclic analog-to-digital converter (ADC). Switch capacitance compensation technique is employed to ensure the ADC performance. The ASIC is fabricated in 0.35-μm CMOS process and dissipates a power of 3 mW. The prototype system incorporates a GRSA, an ASIC, and a commercial nine degreeof-freedom (DOF) inertial measurement unit (IMU) in the heel region of a boot. The GRSA can determine an accurate foot-onground timing based on the pressure profiles detected during walking, thus enabling an accurate position calculation and a precise zero velocity update. Furthermore, a system calibration procedure measures the IMU inherent directional drift and scaling factor errors, and compensates them for the navigation data to achieve a superior performance. The prototype system demonstrates a position accuracy of approximately 5.5 m over a navigation distance of 3100 m. The prototype system also achieves a consistent performance over different field tests with various distances and random paths. System characterization results further indicate a tradeoff between sensor array size and system resolution for a given navigation performance requirement, thus providing a design guideline for future system optimization. Utah Science Technology and Research ; University of Utah ; University of London

An accurate personal inertial navigation system under GPS-denied environment is highly critical for demanding applications such as firefighting, rescue missions, and military operations. Location-aware computation for large-area mixed reality also calls for accurate personal position tracking. Position calculation can be accomplished by using an inertial measurement unit (IMU) composed of a 3-axis accelerometer, 3-axis gyroscope, and 3-axis magnetometer. A gyroscope and magnetometer together can provide the orientation information, while the displacement can be obtained by integrating the acceleration data over time. A MEMS-based IMU is attractive for its small size, low power and low cost. However, such devices exhibit a limited accuracy, large offset, and time drift, which can result in an excessive position error over time. To achieve high-performance navigation, it is critical to accurately reset the IMU time-integration during each step when the foot contacts the ground. Furthermore, correcting the IMU inherent inaccuracy, bias, and time drift becomes important for improving system performance.

This paper presents a RF powering system that can wirelessly transfer power to an array of 10 × 10 1.5 mm-diameter micro coils positioned at 2 cm away from a powering coil. Under 10 W external RF power, the micro coils can receive 5 mW and 0.6 mW at the center and edge of the array, respectively, enabling spherical particle-based neural recording applications. Presence of saline solution between the powering coil and micro coils array causes a power transfer reduction, which can be compensated by improving the quality factor of the micro coils in the array.

We report the fabrication and wireless power coupling for a neural probe, not based on the needle geometry but a much less intrusive minimum-radius spherical pill. The pills 1.3 mm in diameter, consist of two parylene hemispherical halves which can be bonded together to enclose a bio-telemetry circuit. The two hemispheres contain feedthrough electrodes and micro coils patterned along the shell surface respectively. A 1.2 mm diameter hemispherical coil can receive 24.5 mW with a peak-peak AC voltage output of 5.8 V, sufficient to power bio-telemetry circuits, from an external 10 W RF power source placed 1 cm away.

A prototype skin-coupled personal wearable ambulatory pulse wave velocity (PWV) monitoring system is proposed and demonstrated. The system employs two packaged silicone-coated microelectromechanical systems (MEMS) pressure sensors for detecting blood pressure waveforms through skin surface contact in a non-invasive and continuous manner. The sensors are placed at two adjacent measurement points of the body, for example, the wrist or the neck, to measure blood pressure waveforms simultaneously. The measured waveforms are recorded by a data acquisition unit for signal processing and analysis. Analyzing the two waveforms can obtain the delay time between them, thus determining the local PWV. An application-specific signal processing algorithm is developed to accurately obtain the PWV. The PWV and detailed blood pressure waveforms are critical for monitoring human health condition. The prototype personal wearable monitoring system demonstrated its capability of detecting PWV of approximately 5.3 m/s at the wrist and 5.1 m/s at the neck from a volunteer. Similar tests were performed on two additional volunteers, obtaining PWV of 5.9 and 6.7 m/s, respectively, measured at the wrist.

Implantable medical devices (IMDs) can be powered wirelessly using acoustics with no need for a battery. In an acoustic power transfer system, which consists of a transmitter, medium, and a receiver, the power that the receiver generates is a function of its position (depth, orientation, and alignment relative to the transmitter). The power delivered to the implant should remain stable and reliable even with possible uncertainties in the location of the implant. In this paper, we compare two common designs for piezoelectric ultrasonic transducers that can be used for acoustically powering IMDs, and study their generated power sensitivity to any change in their location. Although commercial off-the-shelf (COTS) transducers are widely being used in the literature, they may not be the best candidate for powering small implants since they may not be able to provide sufficient power in the presence of location uncertainties. Piezoelectric micromachined ultrasonic transducers (pMUTs) are diaphragm structures and are also suitable for wirelessly powering implants. We present a pMUT receiver and study the sensitivity of the generated power of the pMUT to changes in its position. We then perform a comparative study between power generation capability of our pMUT and a COTS transducer with the same lateral dimensions as the pMUT. We observed that the generated power from a pMUT structure is less sensitive to misorientation and misalignment of the device. The average percentage improvement in the generated power from pMUT compared to COTS are 86%, 917%, and 111% for depth, alignment, and orientation, respectively.

This paper describes a high-performance interface electronics system design for a high-density flexible biomechanical ground reaction sensor array (GRSA). The prototype system can be incorporated into a personal boot heel to measure real-time ground force, shear strain, and sole deformation associated with a human bipedal locomotion, thus providing zero-velocity correction to an inertial measurement unit placed in a close proximity. This approach can greatly reduce inertial error accumulation and improve positioning accuracy. The sensing electronics consist of a front-end multiplexer that can sequentially connect individual sensing nodes from a 13 × 13 GRSA to a capacitance-to-voltage converter followed by a 12-bit algorithmic ADC with a sampling rate of 66.7 k-samples/s. The entire sensor array can be scanned within 10 ms. The GRSA employs capacitive sensing scheme and is fabricated using PDMS deformable dielectric layer. The integrated sensing electronics are fabricated in XFAB 0.35 μm CMOS process and dissipate 3 mW power. The overall system sensing resolution is limited by electrical interferences coupled through long interconnect traces between a GRSA and an electronic sensing module. Dynamic and static pressure testing shows the prototype system functionality achieving a gait ground velocity sensing resolution of 100 μm/s.

This paper presents the design and characterization of a microelectromechanical system (MEMS)-based intraoperative monitoring system for improving lumbar surgery safety. A MEMS pressure-sensing module is designed and incorporated into a nerve root retractor tip to directly monitor pressure exerted on a nerve root during a lumbar surgery. Animal experiments are conducted for intraoperative pressure monitoring to investigate effects of nerve root retraction during a surgery. Amplitude and latency of electrophysiological response of a nerve root are measured during different time intervals after retraction under various retraction magnitude and duration conditions. Correlation between exerted pressure on a retracted nerve root and its electrophysiological response is investigated. The relationship between intraoperative pressure and alteration of neural tissue structure is analyzed by morphological observation. Experimental results indicate that a nerve root injury is strongly related to the magnitude and duration of its retraction. The prototype MEMS-based intraoperative monitoring system can potentially alert surgeons about risk factors associated with nerve root injury during a lumbar surgery as well as provide critical surgical guidelines. The system can also serve as a basis for implementing an intelligent robotically controlled closed-loop lumbar surgical operating system in the future.

This paper presents a hydrogel-based glucose sensor for future implantable applications employing an inductive sensing technique. The prototype system is based on an ultra-low power tunnel diode oscillator employing a 2 mm-diameter/10-turn sensing coil enclosed in a 3D-printed sealed sensor package. A 3 mm × 3 mm × 80 μm metallic sensing plate embedded in a 3 mm × 3 mm × 400 μm glucose-sensitive hydrogel slab is positioned at 130 μm away from the sensing coil by using an adjustable platform in the prototype design. The small gap is critical for a high sensitivity. The oscillator achieves a 38 MHz nominal frequency while dissipating 40 μW. Under a stable DC power supply, the sensor demonstrates a sensing accuracy around 0.2 mM in human physiological glucose range.