Researchers have developed a single sensor that combines the ability to measure pressure, temperature, and humidity simultaneously. The sensor has applications such as monitoring patients at home, robotics, electronic skin, functional textiles, surveillance, and security.
The team developed an elastic aerogel of polymers that conducts both ions and electrons, and subsequent exploitation of the thermoelectric effect. A thermoelectric material is one in which electrons move from the cold side of the material towards the warm side, and in this way create a voltage difference.
When nanofibers of cellulose are mixed with the conducting polymer PEDOT:PSS in water and the mixture is freeze-dried under vacuum, the resulting material has the same structure as aerogel. Adding a substance known as polysilane causes the sponge to become elastic. Applying an electrical potential across the material gives a linear current increase, typical of any resistor. But when the material is subject to a pressure, its resistance falls and electrons flow more readily through it.
Since the material is thermoelectric, it is also possible to measure temperature changes. The larger the temperature difference between the warm and cold sides, the higher the voltage developed. The humidity affects how rapidly the ions move from the warm side to the cold one. If the humidity is zero, no ions are transported.
The researchers found a way to separate the three signals from each other such that each can be simply read individually.