Stanford’s Rubber Based Artificial Skin

The same issue of Nature Materials that features Berkeley’s touch sensitive semiconductor based artificial skin we wrote about earlier today, also profiles another artificial skin from Stanford. This one is based on a rubber membrane stretched between two electrodes, similar to how electrostatic microphones and stethoscopes work.
Details from a Stanford press announcement:

Previous attempts at building a sensor of this type using a smooth film encountered problems.
“We found that with a very thin continuous film, when you press on it, the material does not have room to expand,” said Stefan Mannsfeld, a former postdoctoral researcher in chemical engineering and a coauthor. “So the molecules in the continuous rubber film are forced closer together and become entangled. When pressure is released, they cannot go back to the original arrangement, so the sensor doesn’t work as well.”
“The microstructuring we developed makes the rubber behave more like an ideal spring,” Mannsfeld said. The total thickness of the artificial skin, including the rubber layer and both electrodes, is less than one millimeter.
The largest sheet of sensors that Bao’s [Zhenan Bao, associate professor of chemical engineering] group has produced to date measures about seven centimeters on a side. The sheet exhibited a great deal of flexibility, indicating it should perform well when wrapped around a surface mimicking the curvature of something such as a human hand or the sharp angles of a robotic arm.
The sensors have from several hundred thousand up to 25 million pyramids per square centimeter. Under magnification, the array of tiny structures looks like the product of an ancient Egyptian micro-civilization obsessed with order and gone mad with productivity.
But that density allows the sensors to perceive pressures “in the range of a very, very gentle touch,” Bao said. By altering the configuration of the microstructure or the density of the sensors, she thinks the sensor can be refined to detect subtleties in the shape of an object.
The team also invented a new type of transistor in which they used the structured, flexible rubber film to replace a component that is normally rigid in a typical transistor. When pressure is applied to their new transistor, the pressure causes a change in the amount of current that the transistor puts out. The new, flexible transistors could also be used in making artificial skin, Bao said.