We describe the design, fabrication, and calibration of a highly compliant artificial skin sensor. The sensor consists of multilayered mircochannels in an elastomer matrix filled with a conductive liquid, capable of detecting multiaxis strains and contact pressure. A novel manufacturing method comprised of layered molding and casting processes is demonstrated to fabricate the multilayered soft sensor circuit. Silicone rubber layers with channel patterns, cast with 3-D printed molds, are bonded to create embedded microchannels, and a conductive liquid is injected into the microchannels. The channel dimensions are 200 μm (width) × 300 μm (height). The size of the sensor is 25 mm × 25 mm, and the thickness is approximately 3.5 mm. The prototype is tested with a materials tester and showed linearity in strain sensing and nonlinearity in pressure sensing. The sensor signal is repeatable in both cases. The characteristic modulus of the skin prototype is approximately 63 kPa. The sensor is functional up to strains of approximately 250%.

Design and Fabrication of Soft Artificial Skin Using Embedded Microchannels and Liquid Conductors

Relaxor-based ferroelectric single crystals: growth, domain engineering, characterization and applications.

A new method for fabricating textile integrable capacitive soft strain sensors is reported, based on multicore-shell fiber printing. The fiber sensors consist of four concentric, alternating layers of conductor and dielectric, respectively. These wearable sensors provide accurate and hysteresis-free strain measurements under both static and dynamic conditions.

Capacitive Soft Strain Sensors via Multicore–Shell Fiber Printing

A highly stretchable, low-cost strain sensor was successfully prepared using an extremely cost-effective ionic liquid of ethylene glycol/sodium chloride. The hysteresis performance of the ionic-liquid-based sensor was able to be improved by introducing a wavy-shaped fluidic channel diminishing the hysteresis by the viscoelastic relaxation of elastomers. From the simulations on visco-hyperelastic behavior of the elastomeric channel, we demonstrated that the wavy structure can offer lower energy dissipation compared to a flat structure under a given deformation. The resistance response of the ionic-liquid-based wavy (ILBW) sensor was fairly deterministic with no hysteresis, and it was well-matched to the theoretically estimated curves. The ILBW sensors exhibited a low degree of hysteresis (0.15% at 250%), low overshoot (1.7% at 150% strain), and outstanding durability (3000 cycles at 300% strain). The ILBW sensor has excellent potential for use in precise and quantitative strain detections in various areas,...

Highly Stretchable, Hysteresis-Free Ionic Liquid-Based Strain Sensor for Precise Human Motion Monitoring.

A novel soft strain sensor capable of withstanding strains of up to 100% is described. The sensor is made of a hyperelastic silicone elastomer that contains embedded microchannels filled with conductive liquids. This is an effort of improving the previously reported soft sensors that uses a single liquid conductor. The proposed sensor employs a hybrid approach involving two liquid conductors: an ionic solution and an eutectic gallium-indium alloy. This hybrid method reduces the sensitivity to noise that may be caused by variations in electrical resistance of the wire interface and undesired stress applied to signal routing areas. The bridge between these two liquids is made conductive by doping the elastomer locally with nickel nanoparticles. The design, fabrication, and characterization of the sensor are presented.

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A Soft Strain Sensor Based on Ionic and Metal Liquids

This paper presents two-dimensional membrane-type ultrasonic transducer arrays based on thick piezoelectric film and micromachining. The transducer array can be used to generate ultrasound in air or water. Individual array element consists of a thick piezoelectric film and a periphery clamped rectangular membrane. The vibrating membranes, which are the radiating elements of the transducer, are excited by thick piezoelectric film. A composite coating technique based on chemical solution deposition and high-energy ball milled powders has been employed to fabricate thick PZT film on platinum coated silicon wafer. High yield micromachining of the integrated transducer array on silicon or SOI wafer using such thick PZT films with thickness of up to 10 μm has been successfully demonstrated. The directivities of the array have also been measured and reported.

Micromachined thick film piezoelectric ultrasonic transducer array

Ferroelectric microelectromechanical systems (MEMS) has been a growing area of research in past decades, in which ferroelectric films are combined with silicon technology for a variety of applications, such as piezoelectric micromachined ultrasonic transducers (pMUTs), which represent a new approach to ultrasound detection and generation. For ultrasound-radiating applications, thicker PZT films are preferred because generative force and response speed of the diaphragm-type transducers increase with increasing film thickness. However, integration of 4- to 20-/spl mu/m thick PZT films on silicon wafer, either the deposition or the patterning, is still a bottleneck in the micromachining process. This paper reports on a diaphragm-type pMUT. A composite coating technique based on chemical solution deposition and high-energy ball milled powder has been used to fabricate thick PZT films. Micromachining of the pMUTs using such thick films has been investigated. The fabricated pMUT with crack-free PZT films up to 7-/spl mu/m thick was evaluated as an ultrasonic transmitter. The generated sound pressure level of up to 120 dB indicates that the fabricated pMUT has very good ultrasound-radiating performance and, therefore, can be used to compose pMUT arrays for generating ultrasound beam with high directivity in numerous applications. The pMUT arrays also have been demonstrated.

Fabrication and characterization of piezoelectric micromachined ultrasonic transducers with thick composite PZT films

A novel fluidic strain sensor is proposed with the use of a mixture of glycerin with aqueous sodium chloride encapsulated within an elastomer as a mean for piezoresistive large strain measurement. Electrochemical impedance spectroscopy (EIS) is conducted for strain response measurement and equivalent circuit analysis is applied for explaining the strain-affected ion transportation behavior of the sensor. The applied strain has caused an increase in both the resistance to charge transfer (Rct) and the resistance of the salt solution which is reflected in an increase in the resistance of the system (Rsys). A parabolic relationship between the real part of the impedance (Zre) and the true strain (ɛ) for an applied strain of up to about 30% is verified. In addition, a novel fluid encapsulation technique by applying oxygen plasma surface modification is introduced. Aqueous sodium chloride is successfully encapsulated within an elastomeric casing with a pattern and this sensor is capable of measuring large strain of even up to about 40%. This method is suggested as an industrial fabrication technique for the strain sensor. The use of ionic liquids for green chemistry has been suggested for years and its use as an electrical conductive media in large strain sensor technology is found to be direct and environmentally friendly.

A novel fluidic strain sensor for large strain measurement

This letter reports on a membrane-type piezoelectric micromachined ultrasonic transducer (pMUT). It consists of 3.5 or 7μm thick composite lead zirconate titanate (PZT) film on a multilayered membrane and works as an ultrasonic transmitter. The ultrasound-radiating performance of the transmitter, in response to a continuous ac driving voltage, has been tested systematically. The generated sound pressure level at resonance frequency of the transmitter varies with the applied dc bias and driving voltage and can exceed 110dB at a measuring distance of 12mm. For a given square membrane with the same multilayer structure and thickness, the resonance frequency of the transmitter is inversely proportional to the area of the membrane, and can be further tuned by control of the poling conditions of the PZT film or the applied dc bias.

Ultrasound radiating performances of piezoelectric micromachined ultrasonic transmitter

A novel liquid strain sensor was developed by using ldquoroom-temperature ionic liquidrdquo as the piezoresistive gauge material. Polydimethylsiloxane, with microchannels, was used to form gauge structures, and carbon fibers were used as electrodes. The strain performance was examined by electrochemical impedance spectroscopy at room temperature, and curve fitting was applied for explaining the strain response. The results show that a maximum true strain of up to 55% can be measured with good repeatability. A parabolic relationship between the real part of the impedance (Zre) and the true strain (epsiv) is observed, mainly due to the resistance change of the electrolyte. The demonstrated ionic-liquid-based strain sensor is of low cost, is environmentally friendly, and is promising for a wide variety of applications.

Chen Chao

Papers

Micromachined thick film piezoelectric ultrasonic transducer array

Fabrication and characterization of piezoelectric micromachined ultrasonic transducers with thick composite PZT films

A novel fluidic strain sensor for large strain measurement

Ultrasound radiating performances of piezoelectric micromachined ultrasonic transmitter

A Novel Ionic-Liquid Strain Sensor for Large-Strain Applications