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.

A novel flexible capacitive pressure sensor based on hybrid micro-structured (HM) polydimethylsiloxane (PDMS) dielectric layer was developed. The HM-PDMS with M-tooth structured patterns was fabricated using a laser engraved acrylic master mold. The top and bottom electrodes were fabricated by depositing silver (Ag) on flexible polyethylene terephthalate PET) substrate using additive screen-printing process. The pressure sensor was assembled by sandwiching two HM-PDMS based dielectric layers between the top and bottom electrodes. The capability of the developed pressure sensor to detect a wide range of pressure was investigated by applying varying pressure from 0 to 1 kPa, 1 to 10 kPa, and 10 kPa to 40 kPa. A sensitivity of 51.36% kPa ⁻¹ , 8.37% kPa ⁻¹ , and 2.46% kPa ⁻¹ was obtained for the pressure ranges of 0 to 1 kPa, 1 to 10 kPa, and 10 to 40 kPa, respectively. The capacitive pressure sensor response, hysteresis, and repeatability of the fabricated pressure sensor is investigated and presented in this paper. To demonstrate the wide sensing range of the pressure sensor, the sensor was attached to face mask for breath monitoring applications that require low pressure sensing of ~20 Pa, and to the hand glove for fingertip pressure monitoring applications that require relatively high pressure sensing of ~3 kPa.

A multi-channel stethograph system was designed and developed as an electronic auscultation system for graphic recording of heart, lung, and trachea (HLT) sounds non-invasively through a set of 16 acoustic sensors. The multi-channel stethograph system was fabricated by placing 16 microphone based acoustic sensor in a CNC machined DelrinⓇhousing cases that are covered using diaphragms. Among the 16 acoustic sensors, 14 were positioned in a memory foam pad, and two were placed directly on the heart and trachea to acquire sounds simultaneously from the lungs, heart, and trachea. The sounds acquired from the 16 acoustic sensors were processed through a custom designed and fabricated 16-channel PCB for signal conditioning. A National Instruments (NI) 9205 data acquisition device (DAQ) along with a NI 9191 wireless chassis was used to acquire and wirelessly transmit the data from the 16-channel PCB to a Wi-Fi enabled device such as a PC/tablet. A custom LabVIEW program was developed on a Wi-Fi enabled PC/tablet to record the data from the DAQ. In addition, a MATLAB program was developed to convert the recorded data from the acoustic sensors into 16 audio files (for audio playback) and plot the waveforms in time and frequency domain as well as spectrogram for visual examination of any abnormal patterns in inhalation and exhalation. This provides critical information on the presence of crackles, rhonchi and wheeze sounds as well as abnormal heartbeat and respiration rate which helps in analyzing the condition of heart and lungs. The graphically displayed HLT sounds will help physicians in the clinical diagnosis and monitoring of lung and heart disorders, particularly chronic obstructive pulmonary disease (COPD), asthma, pneumonia, and congestive heart failure by providing objective evidence.

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.