Now a touch of science news. Researchers who build robots look at our fingertips with great wonder. That's because of all the five senses touch is the most difficult to replicate in mechanical form. But scientists have developed a new kind of robotic skin that's surprisingly sensitive. NPR's Nell Boyce has more.

NELL BOYCE reporting:

You never think about it, but your fingertips are amazing sensors. They constantly register temperature, vibrations, texture. Ravi Saraf says that one thing a fingertip does really well is measure pressure.

Mr. RAVI SARAF (University of Nebraska): When you touch somebody, or when you - when you try to feel a texture of an object, you have a pressure distribution on your finger. And what the human body does is it measures a special distribution and from there it deciphers the texture.

BOYCE: Saraf works at the University of Nebraska. He says touch a smooth surface like glass and your fingertip feels an even distribution of pressure. Touch a rough surface, like sandpaper, and you feel lots of little pressure points. Now, mechanical pressure sensors have been around for years, but none are as good as a fingertip. And Saraf says they're also hard to make.

Mr. SARAF: And I was thinking about it and I came up with a different way of doing these things.

BOYCE: His team built a sensor that's more like skin. It's a thin film and it's easy to make in sheets. The film is no thicker than a human hair but inside it looks like a layer cake. Each layer is made of a different kind of nanoparticle, gold or a semiconductor. Between the layers is a thin plastic. When something touches the film the nanoparticles are pushed closer together. That changes a small electric current running through the film and causes some of the nanoparticles to emit light.

Mr. SARAF: And so the area that is pressed more, more light comes out, and the area that is pressed less, less light comes out.

BOYCE: The light is captured by a camera. So put, say, a penny on this mechanical fingertip and the pressure created by the penny produces an amazingly detailed image. Saraf says you can even see the wrinkles in President Lincoln's clothing and the letters T-Y in liberty.

Mr. SARAF: We were very surprised by this device. We knew in principle it would work. We just didn't think we would get so much light.

BOYCE: Saraf's team describes their work in the Journal of Science. They say there's a lot to do before a robot could wear this skin. For example, they need to replace the camera with some other kind of detector. Allison Okamura is a robotics researcher at Johns Hopkins. She says the device's sensitivity is impressive, but it deals with texture in a way that's not at all like a fingertip.

Dr. ALLISON OKAMURA (Department of Mechanical Engineering, Johns Hopkins University): For example, if you took your finger and pressed it down on a - on a penny, you would not feel the word liberty on that penny. In fact, humans could only feel that word if they slide their finger back and forth over the surface. So it - it's not operating at all like a person does.

BOYCE: Still, Saraf's team hopes their mechanical fingertip could one day help a robot sense the world more like a human, even if it does it in a total alien way. Nell Boyce, NPR News.

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