Human touch: Sensor lets robots 'feel'

Robots do not look human just yet, but soon they may get the “human touch.” Researchers say they have developed a flexible sensor able to detect temperature, pressure and humidity simultaneously, and more accurately than currently existing devices.

In addition to improving robotics, the sensor could one day be embedded into the “electronic skin” of prosthetics, to help amputees sense environmental changes.

The sensor is “a huge step towards imitating the sensing features of the human skin,” said study author Hossam Haick, a professor of chemical engineering and nanotechnology at the Technion-Israel Institute of Technology in Haifa. The device is about 10 times closer to how real human skin senses the environment, compared with other designs.

To make the device, the researchers integrated gold nanoparticles covered with organic connector molecules, called ligands, into the surface of a plastic commonly used to make water bottles. The system has a flowerlike arrangement, with a layer of gold in the center, and the ligands forming the “petals.”

When the plastic is bent or pressed upon, the nanoparticles inside shift, and the distances between them change. This shift affects how quickly electrons can pass between the particles, altering the electrical characteristics of the sensor. [Bionic Humans: Top 10 Technologies]

In other words, a change in pressure affects how well the compound conducts electricity. “By measuring the electrical resistance, we can know how much pressure was applied on the sensor,” Haick said.

Temperature and humidity also affect the distance between the nanoparticles in a similar way, he added. “By using a combination of software and hardware operations, it is possible to isolate the values for humidity, temperature and touch making the sensor 3-in-1.”

The researchers also found that by altering the thickness and material of the plastic surface, they could control the sensitivity of the sensor.

Changing the properties of the plastic “allows measuring a large range of loads, ranging from tens of milligrams to tens of grams,” Haick said.

This means that in addition to being used in prosthetics and giving a humanlike “sense of touch” to robots, the sensor could be used in an early warning system to detect abnormal temperatures and tiny cracks in airplanes, bridges and other structures. Another possible application could be to monitor people’s health.

Of course, to function as a real artificial skin, the signals received by a tactile prosthetic limb would have to be transmitted to the brain. To do so, the sensor would have to be connected to the human nervous system, and the technology for such a connection does not exist.

“Until complete implementation of this vision, an intermediate development would be the integration of e-skin with a computer system,” Haick said.

The study is detailed in the June issue of the journal Applied Materials & Interfaces.