We present our efforts towards enabling a wearable sensor system that allows for the correlation of individual environmental exposures to 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 towards 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 sub-milliwatt system ultimately powered by the energy harvested from thermal radiation and motion of the body with the primary contributions being an ultra-low 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 milliwatts respectively. 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. Future work includes reducing the power consumption of the system-on-chip including radio to reduce the entirety of each described system in the sub-milliwatt range.
challenge, however, is to engender electrical functionalities in textiles while preserving the desirable textile qualities such as softness, comfort, flexibility, and texture that arise from its hierarchical structure through the complex interaction of inherent fiber material properties and the characteristic textile structural features at multiple length scales. To this end, among all the different potential routes of incorporating electronic functionalities into textiles, integration of textile fibers performing as electrical devices, on its own or when assembled, seems to provide the most obvious, unobtrusive, and practical means. Appropriately designed flexible fiber-based electronics are fundamentally transformational; they present very attractive possibilities of ease of manufacturing using standard fiber-extrusion, roll-to-roll textile processing technologies, and enable high spatial sensing density with redundancy within the textile structure. The utility of fiber-based electronics has been recognized as a key step for truly mass-produced e-textiles. Accordingly, the constituents (e.g., fibers or yarns) of textile products have been directly fashioned into electrical devices by incorporating appropriate functional design and materials. These include "fiber"shaped photovoltaic devices, [1,2] transistors, [3][4][5] logic circuits, [6,7] sensors, [8,9] actuators, [10][11][12] other electronic/optical devices [13][14][15] in addition to "fabric"-based devices. [16,17] Modulation of resistance and/or capacitance have been the two most common strategies to sense various physical stimuli, such as applied forces [8,18] and moisture. [19,20] Piezoresistive sensors in the form of fibers/yarns and printed layers on fabrics have been proposed for monitoring motion, posture, and various physiological signals for patient monitoring and rehabilitation. [21,22] For pressure measurements, multicore fibers consisting of layers of soft dielectric and conductive polymers or thin metal films, [23,24] sets of orthogonal fibers, [25,26] or fabric-like structures with soft dielectric and conductive fibers [27] have been employed to form capacitive structures. While remarkable progress has been made in e-textiles, practical real-life products in e-textiles remain elusive. Arguably, the most difficult challenge has been the development of truly textile/fiber-compatible materials/devices and practical Soft polymer-based sensors as an integral part of textile structures have attracted considerable scientific and commercial interest recently because of their potential use in healthcare, security systems, and other areas. While electronic sensing functionalities can be incorporated into textiles at one or more of the hierarchical levels of molecules, fibers, yarns, or fabrics, arguably a more practical and inconspicuous means to introduce the desired electrical characteristics is at the fiber level, using processes that are compatible to textiles. Here, a prototype multimodal and multifunctional sensor array formed within a woven fabr...
The unique potential of e‐textiles for unobtrusive and ubiquitous monitoring and their innovative interfacing with electronic devices has garnished great attention. Sensors are one of the few essential devices or components necessary for most functional e‐textile applications. Ideally, any e‐textile based sensor should be soft, easily integrated in textile manufacturing processes, and tunable for the desired applications. Here, an easy‐to‐manufacture, tunable, fully‐textile sensor system with capability of detecting pressure, humidity, or wetness is presented. Capacitive pressure sensors are formed via a traditional sewing process with two commercially available conductive sewing yarns (silver‐plated polyamide (silver) and stainless steel (SS)) with cotton knit, polyethylene‐terephthalate (PET) knit and elastomeric meltblown textile dielectrics. The relationship between the sensor's physical, mechanical, and electromechanical properties including hysteresis, sensitivity, response, and relaxation time is evaluated. In addition, the same sensor configuration is assessed for its humidity and wetness sensing performance. Results indicate that pressure, relative humidity (RH), and wetness sensing performance are easily tunable using different combinations of the conductive and dielectric textile materials. Finally, proof of concept deployment demonstrations as human‐machine interfaces within a pressure sensing mat and a smart glove capable of remotely controlling a drone are provided.
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.
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