People rely on a highly tuned sense of touch to manipulate objects, but injuries to the skin and the simple act of wearing gloves can impair this ability. Surgeons, for example, find that gloves decrease their ability to manipulate soft tissues. Astronauts are also hampered by heavy spacesuits and find it difficult to work with equipment while wearing heavy gloves.
In this week’s issue of Applied Physics Reviews (“Visually aided tactile enhancement system based on ultrathin highly sensitive crack-based strain sensors”), scientists report the development of a new tactile-enhancement system based on a highly sensitive sensor. The sensor has remarkable sensitivity, allowing the wearer to detect the light brush of a feather, the touch of a flower petal, water droplets falling on a finger and even a wire too small to be seen.
The crack-based sensor used in this device was inspired by a spider’s slit organ, an idea first proposed by other researchers. This pattern of cracks in the exoskeleton allows the spider to detect small movements. In the same way, the ultrathin crack-based strain sensor, or UCSS, uses cracks formed in a thin layer of electrically conductive silver.
The UCSS is fabricated from several layers of flexible polymer film coated with silver. The entire system is draped and stretched over a curved surface, causing the silver to crack, and generating parallel channels that conduct electricity and are sensitive to movement.
The investigators found thinner layers of both the flexible film and the silver yielded sensors with higher sensitivity, while thicker ones exhibited a larger sensing range. To achieve a balance of these two effects, UCSSs with 15-micron thick polymer layers and 37-nanometer thick silver layers were the best choice.
The investigators also designed a visually aided tactile enhancement system, VATES, by connecting one or more UCSSs to a signal acquisition unit and visual readout device. They attached UCSSs to gloves, either on the fingertips or on the back of the hand, producing a type of electronic skin, or e-skin. Tiny movements, as small as a person’s pulse moving the tip of a finger, could be monitored.
The investigators suggest UCSSs could be used in a variety of ways: as highly sensitive electronic whiskers, which can be used to map wind flow patterns; as wearable sensors for heartbeat and pulse detection; or as sensors on prosthetics to enhance the sense of touch.
They also demonstrated their use when applied to various parts of the body. UCSSs were able to detect movement due to smiling, frowning and eye blinking.
Co-author Caofeng Pan said, “These results demonstrate the wide applications of our ultrathin strain sensor in e-skin and human-machine interfaces.”
Source: American Institute of Physics
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Read moreThe new method of making mixed halide-perovskites results in solar cells with improved stability and performance. The new method results in better control over perovskite crystallization rates. This means the crystal structure is more ordered, in part due to researchers understanding and taking advantage of the faster crystallization of bromide relative to iodide.
The result is a material with fewer defects and less halide migration and thus less segregation of the bromide and iodide. This in turn means uniform mixing of bromide and iodide across the material, which allows the material to absorb light evenly. The end result is that solar cells made using the new method will perform better under real-world conditions.
Typical halide perovskite solution deposition uses an anti-solvent drip procedure to initiate crystallization of the halide film. The standard anti-solvent method for producing bromide-iodide mixed halide perovskite films often leads to excessive defect formation (e.g., bromide vacancies) owing to the rapid crystallization of bromide vs. iodide-perovskite phases. Simulations show that halide migration is enhanced in the presence of a large population of halide vacancies. This limits the stability of bromide-iodide mixed halide perovskites under light and heat.
In comparison to the anti-solvent approach, the gentler gas-quench method better controls crystallization, first producing a bromide-rich surface layer that then induces top-down columnar growth to form a gradient structure with less bromide in the bulk than in the surface region. The anti-solvent method does not produce such a gradient structure.
In this study, researchers from the National Renewable Energy Laboratory, the University of Toledo, and the University of Colorado Boulder demonstrated that the gas-quench method also produces fewer bromide vacancies and results in materials with a higher quality opto-electronic performance. Solar cells made using the gas-quench method retain desirable light absorption properties and provide enhanced performance in the form of a higher charge carrier mobility, higher open circuit voltage, and enhanced stability.
