Cheng-Wen Ma

A flexible capacitive tactile sensing array with floating electrodes

In this work, we present the development of a capacitive tactile sensing array realized by using MEMS fabrication techniques and flexible printed circuit board (FPCB) technologies. The sensing array, which consists of two micromachined polydimethlysiloxane (PDMS) structures and a FPCB, will be used as the artificial skin for robot applications. Each capacitive sensing element comprises two sensing electrodes and a common floating electrode. The sensing electrodes and the metal interconnect for signal scanning are implemented on the FPCB, while the floating electrode is patterned on one of the PDMS structures. This special design can effectively reduce the complexity of the device structure and thus makes the device highly manufacturable. The characteristics of the devices with different dimensions are measured and discussed. The corresponding scanning circuits are also designed and implemented. The tactile images induced by the PMMA stamps of different shapes are also successfully captured by a fabricated 8 × 8 array.

A Passive Inertial Switch Using MWCNT–Hydrogel Composite With Wireless Interrogation Capability

This paper presents the development of a passive inertial switch using multiwall carbon nanotube (MWCNT)-hydrogel composite integrated with an inductor/capacitor (L -C) resonator. The device consists of a polydimethylsiloxane (PDMS) microfluidic chip containing MWCNT-hydrogel composite and water droplet and a glass substrate with a capacitor plate and an inductor coil. When the acceleration exceeds the designed threshold level, the water passes through the channel to the hydrogel cavity. The hydrogel swells and changes the capacitance of the integrated L-C resonator, which, in turn, changes the resonant frequency that can be remotely detected. Each sensor unit does not require onboard power and circuitry for operation, so the proposed device is disposable and is suitable for low-cost applications. All PDMS structures were fabricated using soft lithography. The L-C resonator was fabricated using a lift-off process to pattern metal layers on a glass substrate. The response time of the device is considerably reduced by introducing MWCNTs into the hydrogel composites. The dimensions of the device are 15 mm × 10 mm × 1.5 × mm. The characterization of the proposed device was also demonstrated. The threshold g-values, which differ for various applications, were strongly affected by the channel widths. The phase-dip measurement shows that the resonant frequencies shift from 164 to approximately 148 MHz when the device is activated by acceleration.

Highly Sensitive Tactile Sensing Array Realized Using a Novel Fabrication Process With Membrane Filters

This paper presents a highly sensitive tactile sensing array. Sensing elements of the array comprise multiwall carbon nanotubes and polydimethylsiloxane polymer. A novel lithography process is proposed for fabricating an SU-8 mold for shaping the sensing cells in the array. In addition, a nylon membrane filter is proposed to serve as a mold for numerous microdome patterns, which were transferred onto a conductive polymer film. The proposed device features advantages, such as ultra-high sensitivity, flexibility, and a simple fabrication process. Tunneling piezoresistive effects of interlocked microdome structures fabricated using membrane filters with different pore sizes were observed. The measured maximum sensitivity and typical response time were approximately -7.73 kPa-1 and 4 ms, respectively. In addition, the measured results show that the patterned polymer composite arranged in a row-column array can effectively eliminate the crosstalk effect. Moreover, measurements for various tactile sensing applications were demonstrated.

A paper-like micro-supercapacitor with patterned buckypaper electrodes using a novel vacuum filtration technique

This study reports a paper-like micro-supercapacitor (SC) with in-plane interdigital buckypaper electrodes on a filter membrane substrate. A vacuum filtration method assisted by lithography techniques is proposed for patterning buckypaper. The proposed micro-SC features advantages including a flexible structure, simple fabrication, easy chip integration, and high specific capacitance. Increasing the aspect ratio of the patterned buckypaper electrodes effectively enhances the specific capacitance of the SC. The specific capacitance measured by cyclic voltammetry was 107.27 mF/cm2 at a scan rate of 20 mV/sec. The measured charge-discharge behaviors at various discharge rates show the electrochemical stability of the device.

A flexible tactile and shear sensing array fabricated by novel buckypaper patterning technique

In this work, we present a flexible tactile and shear sensing array utilizing patterned buckypaper as the sensing elements. A novel fabrication process for patterning buckypaper with high aspect ratio was proposed. The fabricated sensing device possesses the advantages such as anisotropic sensing capability, flexibility, simple fabrication, and low cost. The measured resistance vs. applied shear force on a single sensing element shows that the element exhibits different sensitivities along different directions. This anisotropic sensing capability can be employed for better shear sensing. The sensing elements also give good sensitivity and repeatability.

Polymer-based disposable microneedle array with insertion assisted by vibrating motion

This work presents a disposable polymer-based microneedle array that carries out insertions by mimicking the vibrating motion of a mosquitos proboscis. The proposed device, which comprises a 10:1 high-aspect-ratio parylene microneedle array and a chamber structure, was monolithically realized using a novel fabrication process. The vibrating motion of the microneedles was generated using a piezoelectric actuator. This device can be potentially applied to extract and collect blood by puncturing the dermis layer of human skin. The fabricated device is advantageous because of its biocompatibility, simple fabrication process, and low associated costs. Additionally, the graph of the measured extraction flow rate versus the pressure drop that is presented shows an agreement with the results predicted by analytical models. A 40% reduction of insertion force was demonstrated when the microneedle insertion was assisted by actuator-induced vibratory motions. Buckling analyses for estimating the maximum loads that the microneedle can sustain before failure occurs were also evaluated. Finally, the relationship between the insertion force and the vibration frequency was demonstrated in this study.

Tunneling piezoresistive tactile sensing array fabricated by a novel fabrication process with membrane filters

In this work, a highly-sensitive tactile sensor array using the tunneling piezoresistive effect is presented. The sensing element, which is made of multi-wall carbon nanotubes and polydimethylsiloxane (MWCNT and PDMS) conductive polymer, was patterned with microdome structures by a novel fabrication process on a membrane filter substrate. The fabricated sensing device features advantages such as ultra-high sensitivity, flexibility, and simple fabrication process. The tunneling piezoresistive effects of the interlocked microdome structures with different MWCNT concentrations are demonstrated. The resistance change of the sensor array due to different elbow-bending motion was measured. Force images were also obtained by using an 8×8 sensing array with different patterns.

Sea-urchin-like ZnO nanoparticle film for dye-sensitized solar cells

We present novel sea-urchin-like ZnO nanoparticles synthesized using a chemical solution method. Solution approaches to synthesizing ZnO nanostructures have several advantages including low growth temperatures and high potential for scaling up. We investigated the influence of reaction times on the thickness and morphology of sea-urchin-like ZnO nanoparticles, and XRD patterns show strong intensity in every direction. Dye-sensitized solar cells (DSSCs) were developed using the synthesized ZnO nanostructures as photoanodes. The DSSCs comprised a fluorine-doped tin oxide (FTO) glass with dense ZnO nanostructures as the working electrode, a platinized FTO glass as the counter electrode, N719-based dye, and I-/I3-liquid electrolyte. The DSSC fabricated using such nanostructures yielded a high power conversion efficiency of 1.16% with an incident photo-to-current efficiency (IPCE) as high as 15.32%. Electrochemical impedance spectroscopy was applied to investigate the characteristics of DSSCs. An improvement in the electron transport in the ZnO photoanode was also observed.

A capacitive immunosensor using on-chip electrolytic pumping and magnetic washing techniques for point-of-care applications

This work presents a capacitive immunosensor using on-chip electrolytic pumping and magnetic washing techniques. The proposed device possesses the advantages such as simple operation, low power consumption, and portability. The proposed device was fabricated using typical micromachining process, and is suitable for mass-production. We also demonstrated the detection of N-Terminal pro-brain-Type natriuretic peptide (NT-proBNP) using the fabricated device integrated with a CMOS capacitance sensing chip. The proposed device potentially can be used as a portable system for point-of-care applications.

Micromachined Planar Supercapacitor with Interdigital Buckypaper Electrodes

In this work, a flexible micro-supercapacitor with interdigital planar buckypaper electrodes is presented. A simple fabrication process involving vacuum filtration method and SU-8 molding techniques is proposed to fabricate in-plane interdigital buckypaper electrodes on a membrane filter substrate. The proposed process exhibits excellent flexibility for future integration of the micro-supercapacitors (micro-SC) with other electronic components. The device’s maximum specific capacitance measured using cyclic voltammetry was 107.27 mF/cm2 at a scan rate of 20 mV/s. The electrochemical stability was investigated by measuring the performance of charge-discharge at different discharge rates. Devices with different buckypaper electrode thicknesses were also fabricated and measured. The specific capacitance of the proposed device increased linearly with the buckypaper electrode thickness. The measured leakage current was approximately 9.95 µA after 3600 s. The device exhibited high cycle stability, with 96.59% specific capacitance retention after 1000 cycles. A Nyquist plot of the micro-SC was also obtained by measuring the impedances with frequencies from 1 Hz to 50 kHz; it indicated that the equivalent series resistance value was approximately 18 Ω.