1. Field of the Invention
The present invention relates to a sensor for detecting the magnitude of an applied force, and in particular a sensor that measures capacitive coupling to provide an indication of the magnitude of an applied force.
2. Description of the Related Art
Sensors that provide an output signal indicative of the magnitude of an applied force are well known in the art. Resistive sensors include piezoresistive materials whose resistivity changes in dependence upon their degree of compression due to an applied force. A problem encountered with such designs is that they are usually inflexible, as any change in the geometry of the piezoresistive material making up the sensor will cause a change in the output signal, even if no force is applied.
Additionally, many capacitive sensor types have been proposed that provide an output in dependence upon the capacitance between two electrically active plates. As capacitance is proportional to the distance between plates in the convention parallel-plate capacitor, it is relatively easy to measure the distance between plates as one is brought closer to the other under compression. However, such designs are often prone to stray capacitance from other electrical networks in close proximity, and therefore conventional capacitive sensors tend to provide inaccurate and noisy output signals.