The very simple and cost-effective elastomer-based device is made up of a layer of microstructured dielectric elastomer (polydimethylsiloxane or PDMS) sandwiched between two PET films each sporting an indium tin oxide (ITO) electrode. The microstructures consist of pyramidal shapes obtained from casting the uncured elastomer solution into an inverted pyramid silicon mold (fabricated via an anisotropic wet etching technique).
Applying a biased positive sinusoidal voltage across the ITO electrodes compresses the microstructures, subject to the coulomb forces and electrostatic attraction. As the amplitude of the biased sinusoidal voltage decreases, the microstructures return to their original shape (through elastic force) and generate a perceivable reaction force in the thickness direction.
In a paper titled “High-pressure endurable flexible tactile actuator based on microstructured dielectric elastomer” published in Applied Physics Letters, the researchers explain that for a given pyramid height, the compressibility of the actuator can be tuned, as well as its resonance frequency by changing the interspacing between the micro-pyramids.
They reported and tested several dielectric elastomer actuators (DEAs) using pyramidal microstructured PDMS layers with a fixed pyramid height of 300μm and different pitches of 500, 600, and 700μm, all on a 300μm thick substrate, showing that the device becomes more compressible as the spatial distance between the micropyramids is increased.
Operating in the frequency range of 100 to 200Hz, which is the most sensitive to vibration acceleration for human finger pads, the device is able to generate perceivable vibration acceleration even under pressure loads up to 25 kPa (approximately 0.255kgf/cm2), which is in the range of typical pressures exerted by fingers when manipulating objects.
What’s more, the transparent device was tested over 250 000 cycles, showing little performance degradation a consistent response under 2ms. All these attributes make the thin flexible actuator a good candidate for unobtrusive and conformable haptics in wearables.
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