Ruya Li
Published: 2016
Total Pages:
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Currently, wearable sensing is an attractive focus of research in the sensing field. Flexible sensors thrive along with the development of wearable technologies because they provide unique features for wearable applications through their compliance and comfort. Resistive, parallel-plate capacitive, and piezoelective based flexible pressure sensors have been investigated over the years for flexible pressure sensing. However, the intrinsic defects of these sensors prevent their application in medical devices, as most applications require high sensitivity, accuracy, and a fast mechanical response. In this dissertation, several types of novel, ion-based pressure sensing devices, referred to as iontronic pressure sensors have been developed with ultrahigh sensitivity, fast mechanical responses, and high flexibility for hemodynamic monitoring applications. Using ultrahigh electrical double layer interfacial capacitance and ionic material resistance, highly sensitive pressure sensing devices are designed and fabricated. Different working modes, resistive and capacitive, are tuned to fit different use scenarios. Parameters that influence device performance, such as sensitivity and mechanical response, are modelled and investigated. A microfluidic film based pressure sensing device that can achieve 0.45 kPa−1 sensitivity within a response time of milliseconds is designed and fabricated for large-area pressure distribution mapping in transparent and flexible package. A novel ionic gel material is implemented with improved device performance using the electrical double layer capacitive mode for sensing. An ionic gel droplet based pressure sensor can achieve a sensitivity of 0.2 nF/mmHg and measures pressure distribution in an array configuration. Further integration of the novel ionic gel within textile generates a new type of ionic pressure sensor that can achieve pressure sensing in all-fabric structures. This novel all-fabric ionic pressure sensor has 0.62 nF/mmHg sensitivity and remains stable when placed on a curved surface with radii decreased to 25 mm. Well-developed iontronic pressure sensors are applied in non-invasive pulse waveform monitoring and chronic venous disorder management. In non-invasive pulse waveform monitoring application, the microfluidic based flexible pressure sensor captures radial arterial pulse waveforms with a matrix configuration when worn on the wrist. Hemodynamic parameters can be calculated based on the waveform acquired to indicate arterial condition of the tested individual. In chronic venous disorder management application, an ionic droplet pressure sensing matrix is integrated into a commercial compression garment to monitor pressure distribution on limbs in a wireless and real-time manner. The iontronic pressure sensors presented offer a highly-transformative solution for wearable health monitoring applications which may benefit patients and clinicians in disease diagnosis, treatment, and rehabilitation.