Resistive pressure sensors utilize the piezoresistive effect of monocrystalline silicon. A monocrystalline silicon wafer is used as the elastic element. Using integrated circuit technology, a set of equivalent resistors are diffused onto the monocrystalline silicon wafer in a specific direction, and these resistors are connected in a bridge circuit. The monocrystalline silicon wafer is placed inside the sensor cavity. When the pressure changes, the monocrystalline silicon undergoes strain, causing the strain resistors diffused directly on it to change in a manner proportional to the measured pressure. The corresponding voltage output signal is then obtained through the bridge circuit.
Piezoresistive sensors are ideal for this purpose. For example, they are used to measure airflow pressure distribution on helicopter wings, test dynamic distortion at engine inlets, pulsating pressure in blade cascades, and wing flutter. In measuring the center pressure of aircraft jet engines, specially designed silicon pressure sensors are used, with operating temperatures exceeding 500°C. Boeing passenger aircraft air data measurement systems employ matching silicon pressure sensors with an accuracy of up to 0.05%.
In scaled-down wind tunnel model tests, piezoresistive sensors can be densely installed at wind tunnel inlets and in engine intake duct models. A single sensor has a diameter of only 2.36 mm, a natural frequency as high as 300 kHz, and nonlinearity and hysteresis of ±0.22% across the full range. In biomedicine, piezoresistive sensors are also ideal detection tools. Injection needle-type piezoresistive pressure sensors with diffused silicon films as thin as 10 micrometers and outer diameters of only 0.5 mm have been fabricated, along with sensors capable of measuring pressure in the cardiovascular system, intracranial cavity, urethra, uterus, and intraocular region.
Piezoresistive sensors are also effectively used in measuring explosion pressure and shock waves, vacuum measurement, monitoring and controlling automobile engine performance, and in weaponry measurements such as measuring gun barrel pressure and detecting emitted shock waves. Furthermore, piezoresistive sensors are widely used in oil well pressure measurement, drilling direction finding, detecting faults in underground sealed cables, and flow and level measurements. With the further development of microelectronics and computers, the application of piezoresistive sensors will continue to expand rapidly.
A resistance strain gauge pressure sensor is a type of resistance pressure sensor that measures pressure by detecting changes in the resistance of a strain gauge bonded to an elastic element. It is used to measure force, torque, tension, displacement, angle, velocity, acceleration, and amplitude. The basic principle behind resistance strain gauge pressure sensors is the strain effect of resistance: when a conductor is subjected to mechanical deformation, its resistance changes, a phenomenon known as the "strain effect."
A strain gauge consists of three parts: a strain-sensitive element, a substrate and a cover layer, and lead wires. The strain-sensitive element is generally composed of metal wire or metal foil (a material with a high resistivity), which converts mechanical strain into a change in resistance. The substrate and cover layer serve to fix and protect the sensitive element, transmit strain, and provide electrical insulation.
