A resistive flexible humidity sensor based on multi-walled carbon nanotubes (MWCNTs) was designed and fabricated. Screen and gravure printing processes were used for monolithically fabricating the humidity sensor containing interdigitated electrodes (IDE), a sensing layer and a meandering conductive heater. An average thickness and surface roughness of 0.99 μm and 0.23 μm, respectively, was registered for the printed MWCNTs sensing layer. The capability of the printed sensor, with heater, was investigated by subjecting it to relative humidity (RH) ranging from 10% to 90%. The response demonstrated an overall resistance change of 55% when the sensor was subjected to 90% RH, when compared to 10% RH. A maximum hysteresis of 5.1%, at 70% RH, was calculated for the resistive response of the sensor. The printed sensors can be bend with radius of curvature of 1.5 inch with literally no effect.

A printed strain gauge based on metal/non-metal composite was successfully fabricated and tested for micro-strain (μƐ) detection. A silver ink was blended with a carbon ink to achieve a silver-carbon (Ag/C) composite ink. The composite ink was then screen printed on a polyimide substrate in a meandering pattern to achieve a desired resistance of ~350 Ω. The printed strain gauge was bonded on to a flat aluminum beam. The capability of the printed strain gauge to detect linear strain was investigated by applying varying tensile and compressive loads on the aluminum beam, to simulate μƐ. Corresponding linear gauge factors for tensile and compressive loads were calculated as 2.26 and 1.47, respectively. In addition, transverse gauge factors for tensile and compressive loads were calculated as 1.18 and 0.43, respectively. The strain gauge has a temperature coefficient resistance of 0.26 %/°C. The screen-printed Ag/C composite strain gauge was also compared to a commercial strain gauge of similar gauge resistance. The results demonstrate that a strain gauge with screen-printed Ag/C and encapsulation ink on a polyimide substrate can be utilized for μƐ detection. The electromechanical response of the fabricated strain gauge as a function of resistance is investigated and presented in this paper.

A flexible capacitive force sensor was developed for force sensing applications. The force sensor consists of two electrodes and a dielectric layer. The electrodes were fabricated by depositing conductive silver (Ag) ink on a flexible polyimide platform using screen-printing process. The dielectric layer was prepared by mixing the contents of polydimethylsiloxane (PDMS) (pre-polymer and curing agent) in a 16:1 ratio. Then the PDMS dielectric layer was sandwiched between the screen-printed Ag electrodes. The capability of the fabricated force sensor was investigated by recording its capacitive response for varying applied forces of 100 N. It was observed that the capacitance increased from 5.83 pF to 6.36 pF as the force was increased from 0 N (no load) to 100 N. A sensitivity and correlation coefficient of 0.081%N ⁻¹ and 0.998 were calculated for the force sensor. In addition, a response time and recovery time of 3.7 seconds and 5.7 seconds was measured for the fabricated force sensor. The relative humidity (% RH) tests performed from 20% RH to 80% RH, in steps of 20% RH, revealed that there was a minimal effect of RH on the base capacitance of the force sensor at room temperature.

Most of the resistive sensors have a large baseline resistor and a relatively small incremental change in the resistor value due to the measurand. A half-bridge-based versatile Δ R/Rₛ measurement system for a wide range of resistive sensors is reported in this article. A four-phase auto-calibration-based differential and ratiometric operation is used to compensate for the baseline resistance of the sensor and the mismatches due to the non-ideal circuit parameters. A low-noise application-specific current generator and low noise, high CMRR current-mode instrumentation amplifier is designed and fabricated in UMC 180-nm technology. A prototype board of the Δ R/Rₛ measurement system is developed and tested. The experimental results show that the proposed system is able to detect even smaller ppm level of about 72 ppm of Δ R/Rₛ for the base resistor Rₛ value as high as 0.5 MΩ with a relative error of less than ±1%. The effect of the parasitic capacitors on the sensor response is also tested experimentally. Finally, the proposed system is tested with an in-house fabricated displacement sensor.

A novel pulsometer was successfully developed using microelectromechanical systems (MEMS) based silicon-on-glass (SOG) technology for biomedical applications. The sensor was modelled and simulated in COMSOL Multiphysics^® for pressures ranging from 0 to 40 mmHg. The capability of the fabricated pulsometer to detect movements in x and z-axis directions was investigated. The simulation results demonstrated displacement changes as high as of 98% and 36% in the x and z-axis directions, respectively for 40 mmHg, which correspond to typical radial blood pressure (rBP) on the wrist. In addition, an average capacitance change of 1 nF was experimentally obtained in the x-axis direction, from −5 V to 5 V. The response of the pulsometer is analyzed and presented in this paper.

In this study, voltage distribution and surface dielectric barrier discharge (DBD) of a microplasma discharge device (MDD) were modeled in 2-D domain using finite-element analysis (FEA). Initially, the voltage distribution across comb-, H-tree-, and honeycomb-structured MDD was analyzed. Then, the cross section of an MDD consisting of a polyimide-based dielectric sandwiched between two copper electrodes was used for modeling the microplasma discharge characteristics in an argon environment. A sinusoidal voltage was applied to one of the copper electrodes while the other electrode was grounded. The spatial distributions of electron temperature (ET) across the electrodes for varying input voltages were simulated to demonstrate the importance of breakdown voltage. A detailed analysis on the effect of varying electrode and dielectric barrier thicknesses on electron density and ET was also performed to understand the importance of optimizing device configurations for microplasma discharge. Moreover, MDD was also simulated in varying ambient temperature and pressure conditions to evaluate their effect on ET and density across the electrodes. The results from these simulations provide a better understanding of parameters such as varying input voltage, electrode, and dielectric thickness on ET and electron density. This enables us to optimize design parameters for fabricating MDDs and the operating conditions for effective sterilization applications.