Michael McKnight

Low-Power Wearable Systems for Continuous Monitoring of Environment and Health for Chronic Respiratory Disease.

We present our efforts toward enabling a wearable sensor system that allows for the correlation of individual environmental exposures with physiologic and subsequent adverse health responses. This system will permit a better understanding of the impact of increased ozone levels and other pollutants on chronic asthma conditions. We discuss the inefficiency of existing commercial off-the-shelf components to achieve continuous monitoring and our system-level and nano-enabled efforts toward improving the wearability and power consumption. Our system consists of a wristband, a chest patch, and a handheld spirometer. We describe our preliminary efforts to achieve a submilliwatt system ultimately powered by the energy harvested from thermal radiation and motion of the body with the primary contributions being an ultralow-power ozone sensor, an volatile organic compounds sensor, spirometer, and the integration of these and other sensors in a multimodal sensing platform. The measured environmental parameters include ambient ozone concentration, temperature, and relative humidity. Our array of sensors also assesses heart rate via photoplethysmography and electrocardiography, respiratory rate via photoplethysmography, skin impedance, three-axis acceleration, wheezing via a microphone, and expiratory airflow. The sensors on the wristband, chest patch, and spirometer consume 0.83, 0.96, and 0.01 mW, respectively. The data from each sensor are continually streamed to a peripheral data aggregation device and are subsequently transferred to a dedicated server for cloud storage. Future work includes reducing the power consumption of the system-on-chip including radio to reduce the entirety of each described system in the submilliwatt range.

Sensing textile seam-line for wearable multimodal physiological monitoring

This paper investigates a novel multimodal sensing method by forming seam-lines of conductive textile fibers into commercially available fabrics. The proposed ultra-low cost micro-electro-mechanical sensor would provide, wearable, flexible, textile based biopotential signal recording, wetness detection and tactile sensing simultaneously. Three types of fibers are evaluated for their array-based sensing capability, including a 3D printed conductive fiber, a multiwall carbon nanotube based fiber, and a commercially available stainless steel conductive thread. The sensors were shown to have a correlation between capacitance and pressure; impedance and wetness; and recorded potential and ECG waveforms.

A low-power wearable substance monitoring device

Alcohol and illicit drug abuse has become a major problem in recent years. According to US Census, there are approximately 40 million teenagers between the age of 10-19, and 20% of them have used an illegal substance at least once in their lifetime. Therefore, by extrapolation, there are potentially 8 million drug abuse cases across the board. This opens up a major requirement for drug monitoring and devices capable of monitoring drug abusers or helping addicts recover. Previous research has shown that certain quantifiable physiological parameters become altered following illicit drug or alcohol consumption. A solution that addresses the problem of detecting drug abuse is the core focus of this research. Initial steps have been focused on developing a device in the form of a wrist-watch that is capable of measuring selected physiological parameters using commercially available sensors. An Android application with algorithms capable of determining if the user is under the influence of alcohol or drugs has been developed and tested.

Microfabricated impedance sensors for concurrent tactile, biopotential, and wetness detection

Several biomedical applications require concurrent measurement of movement of the subject, sensing of the biopotentials and detection of wetness caused by bodily fluids. This paper presents the use of flexible capacitive tactile sensing arrays for concurrent monitoring of biopotential and wetness. This has been enabled by designing the cross-section of the capacitive sensor in a specific “H” shape where the movement of the capacitive plates is used for estimating the presence and the value of tactile forces. The capacitive plates act as biopotential sensors when coupled to the skin and the presence of conductive fluids in-between the plates can be sensed through impedance spectroscopy. We have designed a preliminary miniaturized circuit front-end using commercial-of-the-shelf components to interface the sensors and wirelessly transmit the data through a Bluetooth low energy link. Using the designed circuitry, the force applied to the pixel in the array has been estimated through capacitive sensing with a linear change in the capacitance with the applied force. Same sensor was used to detect EKG waveforms and sense the presence of wetness and salinity using impedance characterization.

Soft, flexible 3D printed fibers for capacitive tactile sensing

This study presents our latest efforts towards developing a force sensor array by weaving 3D printed functionalized polymer fibers. Silicone was used as the base polymer and carbon fillers were used to impart electrical conductivity. Two “H”-shaped fiber cross-sections oriented orthogonally acted as a parallel plate capacitor and were used for detecting normal forces. In this article, we present the fabrication method of the unique “H”-shaped fiber cross-section along with the investigation of the relation between applied force and measured capacitance. We also report the sensor response to variation in temperature. The sensing crossover was found to have a stable mechanical and electrical response in the force range of 0–6 N and the performance of this soft sensor was not significantly affected by temperature.

A finger touch force detection method for textile based capacitive tactile sensor arrays

The use of touch-based technology to interact with electronic devices pre-dates modern day multi-touch technology and even the personal computer. It has recently been growing in popularity in wearable computing devices especially in the form of textile based tactile sensor. These sensors often target the detection of not only touch but also force applied. A significant problem arises here in differentiating inputs from an intended finger touch and just a bend of the sensor or other objects touching the sensor. In this work, we present our initial efforts to differentiate between a finger and an insulated object touch event on a custom textile based tactile sensor we developed before. Our experiments show that the two cases could be differentiated using the capacitance change of the neighboring cross-over points.

Silver nanowire based wearable sensors for multimodal sensing

We present multifunctional sensors based on highly stretchable silver nanowire conductors, which can be conformally attached to human skin for multimodal sensing. The wearable sensors were integrated with an interface circuit with wireless capability in the form of a chest patch. The capabilities of electrocardiography, strain/motion sensing and skin impedance sensing were demonstrated. Additionally, the impedance sensor with the interface circuit was packaged into a wrist watch for skin impedance monitoring.

Towards paper based diaper sensors

This paper presents our initial efforts towards the development of screen printed sensors on folded paper substrates for multi-modal sensing of biopotentials, wetness, and pressure. These sensors contain three layers of sensing stripes forming a 16-pixel array where various layers are utilized for different sensing modalities. The performance of the paper-based sensors was assessed. The sensors were shown to exhibit a linear capacitive response to changes in force, as well as a decrease in impedance in the presence of wetness. We discuss the integration of these low-cost and partially disposable paper-based sensors into a wearable diaper system for Bluetooth-based wireless heart rate monitoring, respiratory rate tracking and urination frequency and amount detection.

In vitro electrochemical assessment of electrodes for neurostimulation in roach biobots

Biobotics investigates the use of live insects as biological robots whose locomotion can be controlled by neurostimulation through implanted electrodes. Inactivity in the biobots (biological robots) can sometimes be noticed following extended neurostimulation, partly owing to incompatibility of implanted electrodes with the biobotic application or gradual degradation of the tissue-electrode interface. Implanted electrodes need to sufficiently exhibit consistent, reliable, and stable performance during stimulation experiments, have low tissue-electrode impedance, facilitate good charge injection capacity, and be compact in size or shape. Towards the goal of finding such electrodes suitable for biobotic applications, we compare electrochemical performances of five different types of electrodes in vitro with a saline based electrolytic medium. These include stainless steel wire electrodes, microfabricated flexible gold electrodes coated with PEDOT:PSS conductive polymer, eutectic gallium indium (EGaIn) in a tube, and “hybrid” stainless steel electrodes coated with EGaIn. We also performed accelerated aging of the electrodes to help estimate their longitudinal performance. Based on our experimentation, microfabricated electrodes with PEDOT:PSS and stainless steel electrodes coated with EGaIn performed remarkably well. This is the first time conductive polymer and liquid metal electrodes were studied comparatively for neurostimulation applications. These in vitro comparison results will be used in the future to provide a benchmark for subsequent in vivo tests with implanted electrodes in cockroach biobots.