James Dieffenderfer

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.

Wearable wireless sensors for chronic respiratory disease monitoring

We present a wearable sensor system consisting of a wristband and chest patch to enable the correlation of individual environmental exposure to health response for understanding impacts of ozone on chronic asthma conditions. The wrist worn device measures ambient ozone concentration, heart rate via plethysmography (PPG), three-axis acceleration, ambient temperature, and ambient relative humidity. The chest patch measures heart rate via electrocardiography (ECG) and PPG, respiratory rate via PPG, wheezing via a microphone, and three-axis acceleration. The data from each sensor is continually streamed to a peripheral data aggregation device, and is subsequently transferred to a dedicated server for cloud storage. The current generation of the system uses only commercially-off-the-shelf (COTS) components where the entire electronic structure of the wristband has dimensions of 3.1×4.1×1.2 cm3 while the chest patch electronics has a dimensions of 3.3×4.4×1.2 cm3. The power consumptions of the wristband and chest patch are 78 mW and 33 mW respectively where using a 400 mAh lithium polymer battery would operate the wristband for around 15 hours and the chest patch for around 36 hours.

Solar powered wrist worn acquisition system for continuous photoplethysmogram monitoring

We present a solar-powered, wireless, wrist-worn platform for continuous monitoring of physiological and environmental parameters during the activities of daily life. In this study, we demonstrate the capability to produce photoplethysmogram (PPG) signals using this platform. To adhere to a low power budget for solar-powering, a 574nm green light source is used where the PPG from the radial artery would be obtained with minimal signal conditioning. The system incorporates two monocrystalline solar cells to charge the onboard 20mAh lithium polymer battery. Bluetooth Low Energy (BLE) is used to tether the device to a smartphone that makes the phone an access point to a dedicated server for long term continuous storage of data. Two power management schemes have been proposed depending on the availability of solar energy. In low light situations, if the battery is low, the device obtains a 5-second PPG waveform every minute to consume an average power of 0.57 mW. In scenarios where the battery is at a sustainable voltage, the device is set to enter its normal 30 Hz acquisition mode, consuming around 13.7 mW. We also present our efforts towards improving the charge storage capacity of our on-board super-capacitor.

Social facilitation of insect reproduction with motor-driven tactile stimuli

Tactile stimuli provide animals with important information about the environment, including physical features such as obstacles, and biologically relevant cues related to food, mates, hosts and predators. The antennae, the principal sensory organs of insects, house an array of sensory receptors for olfaction, gustation, audition, nociception, balance, stability, graviception, static electric fields, and thermo-, hygro- and mechanoreception. The antennae, being the anteriormost sensory appendages, play a prominent role in social interactions with conspecifics that involve primarily chemosensory and tactile stimuli. In the German cockroach (Blattella germanica) antennal contact during social interactions modulates brain-regulated juvenile hormone production, ultimately accelerating the reproductive rate in females. The primary sensory modality mediating this social facilitation of reproduction is antennal mechanoreception. We investigated the key elements, or stimulus features, of antennal contact that socially facilitate reproduction in B. germanica females. Using motor-driven antenna mimics, we assessed the physiological responses of females to artificial tactile stimulation. Our results indicate that tactile stimulation with artificial materials, some deviating significantly from the native antennal morphology, can facilitate female reproduction. However, none of the artificial stimuli matched the effects of social interactions with a conspecific female.

Towards a sweat-based wireless and wearable electrochemical sensor

The analysis of biomarkers within sweat is advantageous for both being a non-invasive diagnostic method as well as the physiological relevance of the present biomarkers. Due to these advantages, having a wearable system that can continually perform sweat analytics holds potential for various applications. In order to create a wearable system that operates efficiently, both the electrochemical sensor and the front-end electronic system need to be optimized. In this paper, we present our work on the electronic interface portion for use with skin adhered biosensors. For proof of concept, we focused on the sensing of lactate; the conjugate base of lactic acid. Our system was shown to calibrate itself using cyclic voltammetry and measure concentrations of lactate from 0.1 mM to 0.75 mM. The system can wirelessly transmit readings to a peripheral smart-phone data aggregator, and continuously operate for over 36 hours.

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.

Shedding light to sleep studies

This paper presents our efforts in the development of a small wireless, flexible bandage sized near-infrared spectroscopy (NIRS) system for sleep analysis. The current size of the system is 2.8 cm × 1.7 cm × 0.6 cm. It is capable of performing NIRS with 660nm, 940nm and 850nm wavelengths for up to 11 hours continuously. The device is placed on the forehead to measure from the prefrontal cortex and the raw data is continuously streamed over Bluetooth to a nearby data aggregator such as a smartphone for post processing and cloud connection. In this study, we performed traditional polysomnography simultaneously with NIRS to evaluate agreement with traditional measures of sleep and to provide labelled data for future work involving learning algorithms. Ultimately, we expect a machine learning algorithm to be able to generate characterization of sleep states comparable to traditional methods based on this biophotonics data. The system also includes an inertial measurement unit and the features that can be extracted from the presented system include sleep posture, heart rate, respiratory rate, relative change in oxy and deoxy hemoglobin concentrations and tissue oxygenation and cerebral arterial oxygen extracted from these. Preliminary proof of concept results are promising and demonstrate the capability to measure heart rate, respiratory rate and slow-wave-sleep stages. This system serves as a prototype to evaluate the potential of a small bandage-size continuous-wave NIRS device to be a useful means of studying sleep.

Room temperature sensing of VOCs by atomic layer deposition of metal oxide

This work demonstrates room temperature sensing of volatile organic compound (VOC) — acetone via an ultrathin film metal oxide sensing layer. Atomic layer deposition (ALD) enables a high quality ultrathin film with precise thickness control. The 14nm ultrathin SnO2 thin film was deposited by ALD resulting in VOCs sensing at room temperature. The ultra-low power consumption (less than 50nW) and the room temperature operation of these devices make them compatible with wearable devices for real-time health and environment monitoring.

Nanocellulose electrodes for interfacing plant electrochemistry

The study of plant bioelectricity has provided a unique perspective to understand how plants sense their environment and adjust their morphology, physiology, and phenotype accordingly. In this study, we present nanocellulose based novel dry electrodes suitable for use as non-invasive bioelectrical plant interfaces. These electrodes were specifically designed to monitor plant electrochemistry without significantly disturbing their physiology. Using electrochemical impedance spectroscopy enabled us to construct an equivalent circuit model to evaluate the performance of the electrodes. The preliminary characterization of the electrodes in vitro and in vivo using Arabidopsis thaliana provided promising results.