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A novel temperature transduction method using the high-frequency electrochemical impedance between a pair of microelectrodes exposed to aqueous solution is reported. The solution resistance of an aqueous ionic solution is highly temperature dependent, and the electrochemical impedance between two microelectrodes is dominated by solution resistance when measured at the appropriate frequency. Therefore, precise measurements of electrochemical impedance at the proper frequency in a two-electrode system can be used to transduce solution temperature. To demonstrate this method, a temperature sensor composed of two thin-film platinum electrodes on a freestanding Parylene C substrate was designed and fabricated. A platinum resistance temperature detector was co-fabricated to provide a simple means of benchmarking against an existing standard. Transduction via electrochemical impedance was achieved by measuring the real part of impedance at the frequency where phase was minimized. Fluid temperature was transduced between 15°C and 50°C with high sensitivity (−1.21%/°C) and resolution (0.02°C). A $4\times $ improvement in sensitivity and resolution over the conventional platinum resistance temperature detector was achieved. The sensor design described here features flexible construction with inert materials which facilitates future use in biomedical or microfluidic applications. [2019-0190] [ABSTRACT FROM AUTHOR]

A kirigami-based strategy was investigated for strain transduction, using serpentine gold traces embedded in thin-film Parylene C. Multiple kirigami slit designs were evaluated via COMSOL simulation and mechanical force testing; sensors having tightly packed slits stretched up to 17.5 mm (350% strain) before mechanical failure and 9 mm (180% strain) before electrical failure. Strain transduction was achieved by monitoring DC resistance changes during stretching. DC resistance linearly increased with strain, with sensitivities up to 0.16 $\Omega$ /mm (gauge factor = 0.007) and minimal hysteresis. High-frequency trace impedance and inter-trace capacitance were also investigated during strain cycling. Capacitance increased with strain and high-frequency impedance show a nonlinear strain relationship. The biocompatible construction and extremely low profiles (20 $\mu \text{m}$ thick) of these sensors are attractive for minimally invasivein vivostrain sensing applications. [2018-0130] [ABSTRACT FROM AUTHOR]

A novel electrochemical-thermal flow sensor was developed for use in physiological liquids. The sensor was constructed out of a platinum resistive heater and platinum sensing electrodes on a Parylene C substrate, rendering it flexible and fully biocompatible. During heating, changes in electrochemical impedance across the sensing electrodes were used to detect changes in temperature, and highly sensitive flow measurements were achieved with overheat temperatures of only 1 °C. The sensor’s biocompatibility and low overheat temperature make it an ideal candidate for chronic in vivo applications. [2016-0170] [ABSTRACT FROM PUBLISHER]