Electroactive polymer patches for wearable haptic interfaces

Monitoring Flexions and Torsions of the Trunk via Gyroscope-Calibrated Capacitive Elastomeric Wearable Sensors

Reliable, easy-to-use, and cost-effective wearable sensors are desirable for continuous measurements of flexions and torsions of the trunk, in order to assess risks and prevent injuries related to body movements in various contexts. Piezo-capacitive stretch sensors, made of dielectric elastomer membranes coated with compliant electrodes, have recently been described as a wearable, lightweight and low-cost technology to monitor body kinematics. An increase of their capacitance upon stretching can be used to sense angular movements. Here, we report on a wearable wireless system that, using two sensing stripes arranged on shoulder straps, can detect flexions and torsions of the trunk, following a simple and fast calibration with a conventional tri-axial gyroscope on board. The piezo-capacitive sensors avoid the errors that would be introduced by continuous sensing with a gyroscope, due to its typical drift. Relative to stereophotogrammetry (non-wearable standard system for motion capture), pure flexions and pure torsions could be detected by the piezo-capacitive sensors with a root mean square error of ~8° and ~12°, respectively, whilst for flexion and torsion components in compound movements, the error was ~13° and ~15°, respectively.

Nonlinearly Frequency-Adaptive, Self-Powered, Proton-Driven Somatosensor Inspired by a Human Mechanoreceptor

In the human skin, it has been well known that several mechanoreceptors uniquely sense external stimuli with specific frequencies and magnitudes. With regard to sensitivity, the output response shows nonlinearity depending on the frequency magnitude of the stimulus. We demonstrate a self-powered proton-driven solid-state somatosensor, which mimics a unique nonlinear response and intensity behavior of human mechanoreceptors. For this, a solid-state sensor is fabricated by combining a piezoelectric film and a proton generation device. The proton injection electrode and the Nafion layer conjugated with sulfonated graphene oxide are used for proton generation and transport. Two types of nonlinear signals from the sensor are similar to the Merkel/Ruffini (low deviation of threshold intensity), and in contrast, the behavior of Pacinian/Meissner (high deviation of threshold intensity) is simultaneously shown. The region of the most responsive frequency is also discriminated according to proton conduction. Moreover, it is asserted that unique signal patterns are obtained from the stimuli of various frequencies, such as respiration, radial artery pulse, and neck vibration, which naturally occur in the human body.

Refreshable Tactile Display Based on a Bistable Electroactive Polymer and a Stretchable Serpentine Joule Heating Electrode

The demand for tactile interactive devices has been growing exponentially as the sense of touch enriches the human-machine interaction experience. However, the tactile devices reported so far cannot offer high-quality performance, compact form factor, and relatively simple system architecture for low-cost production. We report the fabrication of a 4 × 4 pneumatic tactile display with Braille standard resolution using a bistable electroactive polymer (BSEP) thin film and a serpentine-patterned carbon nanotube electrode. The BSEP is a variable stiffness material that exhibits a stiffness change of 3000-fold within the narrow temperature range of 43 ± 3 °C. The carbon nanotube electrode was patterned on the polymer film via a P3R process, Prestretch-Pattern-Protect-Release, which leads to a serpentine-patterned composite electrode that is highly stretchable, retains its high electrical conductivity up to an ∼200% area strain, and provides a fast Joule heating rate of 31 °C/s. The tactile pixels are diaphragm actuators that can be individually controlled to produce 0.7 mm out of plain deformation and greater than 50 g of blocking force by application of local heating and pneumatic pressure. The device can operate under low voltage supply (30 V) and has a lifetime of over 100 000 cycles without much performance degradation. This work could open a path to building compact, user-friendly, and cost-effective tactile devices for a variety of important applications.

Experimental Research on Fluid Coupling Flexible Actuator

In the field of micromechanics, piezoelectric actuator has attracted great attention for its high-frequency response, high displacement resolution, and high output force. However, its prospect of practical application has been largely limited by the displacement of micrometer. A fluid coupling flexible actuator was proposed, which utilizes resonance to enlarge the output displacement. The actuator uses a piezoelectric oscillator as an excitation source, fluid as the transmission medium and a flexible diaphragm for the displacement output. On the condition that the fluid is inviscid and incompressible, mathematical formulation of the membrane vibration theory has been analyzed. Then, the prototype is made. The displacement is amplified 21 times to 1.106 mm when driving frequency is 127 Hz. The flexible diaphragm appears the largest displacement output when driving frequency is close to one of the system's natural frequency. Then, the points with zero amplitude form a circle on the surface of flexible diaphragm and the movement direction of the flexible diaphragm is opposite on different sides of the circle. In fact, rather than vibrates at the first resonance frequency, the membrane in the essay is vibrating at a certain higher-order resonance frequency. The experimental results are mainly consistent with the theoretical analysis.