In the Optical Society (OSA) journal Optics Letters, researchers report on a new type of optical pressure detector.  The sensor is based on light and could allow the creation of sensitive artificial skins to give robots a better sense of touch and wearable blood-pressure monitors for humans. “The silicone sheet can be placed on display panels to enable touch screens. Or it 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.”

Putting it to the test

To test the device the researchers placed a “pressing stub” on top of the sensor and gradually increased the pressure. In a sensor that was 5 mm long embedded in a 50-µm thick sheet of PDMS, the researchers measured a change in optical power of 140% at a pressure of approximately 40 kilopascals (kPa). This proof-of-concept demonstration suggests the device is capable of sensing pressure as low as 1 kPa, roughly the same level of sensitivity as a human finger. The change in blood pressure between heartbeats is about 5 kPa.

Park says several steps are needed to move the sensor from a laboratory demonstration to a practical device. One is to develop a simpler way to attach the optical fibers that move light into and out of the sensor. In developing their prototype, the research team used precision alignment tools, which would be too expensive and time-consuming to use in most commercial applications. An alternative approach, known as pigtail fibers, which telecommunications companies use to couple fibers in their systems, should make the process easier.

In addition, the team tested their approach with a 1-dimensional sensor, whereas most applications would require a 2-dimensional array of sensors. That can probably be accomplished by rotating a one-dimensional sheet 90 degrees and placing it on top of another, creating a cross-hatched array. The size of the sensors and the spacing between them would also likely need to be optimized for different applications.

Source: Optical Society of America