Manufacturing
There are two common methods used to manufacture accelerometers. One is based upon the principles of piezoresistance and the other is based on the principles of piezoelectricity. Both methods ensure that unwanted orthogonal acceleration vectors are excluded from detection.
Manufacturing an accelerometer that uses piezoresistance first starts with a semiconductor layer that is attached to a handle wafer by a thick oxide layer. The semiconductor layer is then patterned to the accelerometer's geometry. This semiconductor layer has one or more apertures so that the underlying mass will have the corresponding apertures. Next the semiconductor layer is used as a mask to etch out a cavity in the underlying thick oxide. A mass in the cavity is supported in cantilever fashion by the piezoresistant arms of the semiconductor layer. Directly below the accelerometer's geometry is a flex cavity that allows the mass in the cavity to flex or move in direction that is orthogonal to the surface of the accelerometer.
Accelerometers based upon piezoelectricity are constructed with two piezoelectric transducers. The unit consists of a hollow tube that is sealed by a piezoelectric transducer on each end. The transducers are oppositely polarized and are selected to have a specific series capacitance. The tube is then partially filled with a heavy liquid and the accelerometer is excited. While excited the total output voltage is continuously measured and the volume of the heavy liquid is microadjusted until the desired output voltage is obtained. Finally the outputs of the individual transducers are measured, the residual voltage difference is tabulated, and the dominate transducer is identified.
In 1943 the Danish company Brüel & Kjær launched Type 4301 - the world's first charge accelerometer.
Read more about this topic: Piezoelectric Accelerometer