In this paper the sensor which has a simple structure, flexibility and also has the function of displaying the pressure distribution is proposed, and measured results are shown.
The sensor consists of four layers. First and third layers are patterned electrodes. Second layer is the pressure conductive rubber whose resistance varies with pressure. Last layer is the liquid crystal whose color varies with temperature.
The theory of measurement is as follows: the distributed pressure(p) on the sensor causes a drop in the resistance (r_p) of the pressure conductive rubber: as a voltage is applied between two patterned electrode layers. the electric current(i) passes through the rubber in proportion to the r_p: then this electric current produces heat(q) and the temperature(θ) rises as the result. Consequently this changes the color of liquid crystal at the position. In a word, this sensor converts the intensity of pressure into the difference of temperature and displays it using liquid crystal. The following equations show these relations: θ∝q∝i²r_p=v²/r_p∝v²p∝p(ifr_p∝p^-1).
However, the heat diffusion occuring in the rubber and the electrodes causes the measurement errors. Therefore the ways of preventing heat from diffusion are necessary. Hence these methods are proposed; (1) the electrodes are constructed of a lot of small square electrodes which are connected with narrow channels each other. In order to decide the sizes of the patterned electrode, the simulation is carried out. (2) the heat produced in the rubber is controlled by using a heat controller.
This sensor is useful for the measuring the contact pressure between the soft materials, such as between human body and a seat.