Force and load sensors have a variety of applications in an automobile. They may be used to detect the weight of a passenger (to determine airbag inflation force) or to sense whether contact is securely made between two mechanical parts. Typically, these sensors measure small deflections in a rigid object. This can be done using piezoresistive materials, magneto-elastic materials or structures with variable capacitance.
Piezoresistive
In a piezoresistive acceleration sensor, a piezoresistive material is positioned so that it is deformed by the position of the mass changing its resistance. This type of acceleration sensor generally has a small size, large signal amplitude and good linearity, but it can be sensitive to variations in temperature. Piezoresistive sensors can be used to measure both steady-state and dynamic accelerations.
Magneto-elastic
Magneto-elastic materials are magnetic materials with properties that change in response to an applied force. Sensors utilizing these materials sense a change in an applied magnetic field in response to small deflections in the magneto-elastic material.
Variable Capacitance
A variable capacitance sensor uses changes in capacitance caused by a structural displacement to detect an applied force. The sensing element usually employed is an air-damped, opposed plate capacitor. These types of sensors generally have good sensitivity, linear output, good DC response, low power dissipation and low temperature sensitivity. One drawback of variable capacitance sensors is that they can be susceptible to electromagnetic interference.
