Optical pressure detector could improve robot skin

The pressure sensor consists of a series of waveguides running alongside one another (top). Where the gap between the waveguides narrows, light from the first channel can jump into the second channel (bottom). Higher pressure makes the gap narrower, allowing more light to move out of channel 1 and into channel 2. Image Credit: Suntak Park, Electronic and Telecommunications Research Institute, Daejeon, South Korea

A new type of pressure sensor based on light could allow the creation of sensitive artificial skins to give robots a better sense of touch, wearable blood-pressure monitors for humans and optically transparent touch screens and devices.

In the Optical Society (OSA) journal Optics Letters, researchers report on a sensor that detects pressure by analyzing changes in the amount of light traveling through tiny tunnels embedded in polydimethylsiloxane (PDMS), a common type of silicone. The flexible, transparent device is sensitive to even gentle pressure and is less prone to failure compared to previous types of pressure sensors. It also should be feasible to incorporate the embedded optical sensors across a large surface area, researchers say.

“The silicone sheet can be placed on display panels to enable touch screens, or can be wrapped on robot surfaces as an artificial skin layer for tactile interactions,” says Suntak Park, Electronic and Telecommunications Research Institute, Daejeon, South Korea. “Considering that PDMS is a very well-known bio-compatible, non-toxic material, the sensor sheet may even be applied on or inside the human body, for example, to monitor blood pressure.”

Measuring pressure distribution over a curved surface can be important in research areas such as aerodynamics and fluid dynamics. Park says the sensors could be useful for studying pressure-related effects on the surfaces of aircraft, automobiles, and ships.

Avoiding interference
Most existing pressure sensors are based on electronics. Piezoresistive sensors, for instance, which are often used as accelerometers, flow meters, and air-pressure sensors, change their electrical resistance when subjected to mechanical strain. The problem with electronic systems is that they can be subject to electromagnetic interference from power sources, nearby instruments and charged objects. They also contain metal components, which can block light and be subject to corrosion.

“Our approach is almost free from such problems because the sensing device is embedded in the middle of a sheet made of silicone rubber,” says Park. “When compared to electrical approaches, our optical approach is particularly suitable for applications that take advantage of large-area feasibility, resistance to electromagnetic interference, and high visual transparency.”

Sensing pressure with light
The device works by measuring the flow of light through a precisely arranged pair of minuscule tubes known as a photonic tunnel-junction array. “The pressure-sensitive photonic tunnel-junction array consists of light-guiding channels where external pressure changes the brightness of the light transmitted through them,” Park says. “This is similar to how a valve or faucet works at a flow-splitting node.”

Read more: Optical pressure detector could improve robot skin

thumbnail courtesy of osa.org

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