A new optical waveguide pressure sensor using evanescent field

The sensor is primary used as pressure sensor or as a touch sensor. It consists of one flexible optical waveguide. Its optical attenuation depends strongly on the local pressure and takes advantage of the evanescent field properties. The optical waveguide core is similar to a normal plastic optical fiber. There is a light-absorptive layer in the optical cladding. The transmitter is placed on one side of the sensor with a signal source, such as an LED and there is a receiver on the other side with one photosensitive element, such as a PIN diode. In the normal state (no pressure), there is a total reflection at the boundary between the core and the cladding. The optical rays do not reach the absorptive layer. Under pressure, since the optical ray is skin-deep in the optical coating, the light will absorb in the absorptive layer. This results in a strong rise of optical attenuation.