Pressure sensors detect types of pressure, such as air pressure or loads, and convert it into an electrical signal. Alps Alpine makes silicon semiconductor devices for pressure sensors using MEMS* processes. Here we introduce the sensing principles behind Alps Alpine's pressure sensors.
※Micro-electromechanical systems (MEMS) technology refers to micromachining technology involving application of semiconductor manufacturing techniques.
Types of Pressure Sensor
Pressure sensors come in various forms. Alps Alpine's pressure sensors are the piezoresistive type, employing silicon semiconductor devices, and we will explain them here.
Other kinds of pressure sensor include the metal thin-film type, which uses a metal strain gauge, and the capacitive type, which ascertains changes in capacitance.
Sensing Principles of Alps Alpine Pressure Sensors
A piezoresistive pressure sensor works using the piezoresistive effect - when mechanical strain is applied to a semiconductor crystal (silicon), the internal energy structure changes, causing a change in electron mobility and, in turn, electrical resistance.
As shown in the diagram to the right, electrical resistance changes depending on the direction of the strain applied to the piezoresistive element.
Four such piezoresistive elements are placed at points in each direction along intersecting perpendicular axes on a diaphragm that bends when pressure is applied. When the diaphragm bends, the piezoresistive elements also strain, causing a change in resistance in a bridge circuit and changes in output voltage (Vout 1, Vout 2), as shown below.
In this way, pressure is converted into an electrical signal.
Alps Alpine's Air Pressure Sensors
Pressure occurs in various forms, but here we will explain sensing of air pressure.
Air pressure is pressure exerted by air. Atmospheric pressure (generally often referred to as just "air pressure") is pressure exerted by the weight of the atmosphere.
Altitude and Air Pressure
The diagram on the right shows the relationship between altitude and air (atmospheric) pressure. The higher you go, the less air there is on top of you, so the air pressure falls. Air pressure can be used to measure altitude.
Absolute Pressure and Gauge Pressure
Alps Alpine's air pressure sensors are absolute pressure sensors. Absolute pressure is zero-referenced against an absolute vacuum. This is in contrast with gauge pressure, which is zero-referenced against atmospheric pressure. Pressure higher than atmospheric pressure is referred to as positive pressure, pressure lower than atmospheric pressure as negative pressure.
Besides air pressure, there are various other kinds of pressure, too. Alps Alpine's product lineup has a variety of sensors for detecting air pressure, water pressure and loads using the sensing principles detailed above.
