Using gold nanoparticles on top of a PVC substrate, researchers at the Technion-Israel Institute of Technology have built a new type of cheap, flexible sensor that simultaneously detects pressure, humidity and temperature with surprising accuracy. The sensor could be used to monitor cracks in bridges, create a better artificial skin to benefit amputees, or even to give robots that special "human touch."
Previous designs have been able to sense pressure almost as accurately as a human finger; others are attractive because they draw very little power; but, sophisticated as they may be, they are limited in that, unlike human skin, they can only sense pressure.
The sensor developed here does much more. According to Prof. Hossam Haick, who led the research, the device "is at least 10 times more sensitive in touch than the currently existing touch-based e-skin systems" and can also precisely measure temperature (with a resolution lower than 1°C) and humidity (with a 9 percent error margin).
The flexible sensor draws very little power, is cheap to manufacture, and showed consistent performance even after a very large number of bending cycles.
At the core of the sensor are monolayer-capped gold nanoparticles five to eight nanometers in diameter and surrounded by protective connector molecules called ligands (black in the picture above). The substrate of the structure consists of PET – the inexpensive, very common plastic used for plastic bottles.
When the circuit is bent, the geometry of the material changes and some particles move close to others, which affects the speed at which electrons can pass through the device. The sensor measures these changes and can detect a large range of pressures, from milligrams to the order of tens of grams.
The researchers have also found that by changing the thickness and material of the substrate, they can control how sensitive the sensor is. This could mean the sensor may find use in more heavy-duty applications, such as monitoring strain on bridges and detecting cracks developing within an engine.
A paper describing the research was published in the June issue of the journal Applied Materials & Interfaces.