Sapphire is al Ψ o three Its melting point is 2040 ℃, and it has good optical and insulating properties. It has good mechanical properties at 1500 ℃. At present, there are two main categories of sapphire sensors.
1. Strain type pressure sensor based on SOS (silicon on
sapphire High temperature pressure sensor It is a kind of strain resistance type working principle. It adopts silicon sapphire as semiconductor pressure sensor and has good metrological characteristics. Sapphire is composed of single crystal insulator elements, which generally will not occur hysteresis, fatigue and creep; sapphire is stronger than silicon, with higher hardness, and is not afraid of deformation; sapphire has very good elastic and insulating properties (within 1000 ℃), so, semiconductor pressure sensitive components made of silicon sapphire are not sensitive to temperature changes, even under high temperature conditions, The pressure sensor also has good working characteristics; sapphire has good radiation resistance; in addition, silicon sapphire semiconductor pressure sensor has no p-n drift, so the manufacturing process is basically simplified, the repeatability is improved, and the high yield is ensured.
The high temperature pressure sensor made of silicon sapphire semiconductor sensor can work normally under the worst working conditions, and has high reliability, good accuracy and small temperature error, but generally it is not cost-effective. It should be specially pointed out that this kind of high temperature pressure sensor generally needs to be imported exclusively from Russia, so it faces certain risks in after-sales service.
Sapphire gauge pressure sensor consists of two diaphragms: titanium alloy measuring diaphragm and titanium alloy receiving diaphragm. Sapphire chip printed with heteroepitaxial strain sensitive bridge circuit is welded on titanium alloy measuring diaphragm. The measured pressure is transmitted to the receiving diaphragm (the receiving diaphragm and the measuring diaphragm are firmly connected by a pull rod). Under the action of the silicon bridge, the change of the output pressure is proportional to that of the pressure sensing element.
The circuit of sapphire high temperature pressure sensor can ensure the power supply of strain bridge circuit, and convert the unbalance signal of strain bridge into industrial standard electrical signal output (such as 4-20mA signal). In the absolute pressure sensor and transmitter, sapphire flake is connected with the ceramic base glass solder, which acts as an elastic element and converts the measured pressure into strain gauge deformation, so as to achieve the purpose of pressure measurement.
2. Sapphire fiber optic high temperature pressure sensor
Optical fiber sensor has the advantages of high measurement accuracy, anti electromagnetic interference, anti radiation, high working temperature, easy networking and multi parameter measurement. It is suitable for application in high temperature and harsh environment such as gas turbine, aviation / aerospace engine, etc. at present, it has become a hot research direction of high temperature pressure sensor. European and American countries began to study optical fiber pressure under high temperature and harsh environment 20 years ago There are two kinds of force sensing technology: optical shed fiber and Fabry Perot interference fiber. Light shed optical fiber pressure sensor has low sensitivity and is suitable for high-pressure measurement fields such as highway and railway safety monitoring, bridge and tunnel safety monitoring, petrochemical industry and other high-pressure measurement fields. F-P interference fiber optic high temperature pressure sensor is shown in Fig. 1. The principle of F-P interference pressure measurement is shown in the figure. When the laser passes through the F-P cavity, multiple reflected light is formed. The length of the cavity is inversed by using the interference characteristics of the reflected light. The pressure measurement is realized through the relationship between the cavity length and the pressure. Pressure sensors with different ranges can be prepared by adjusting the thickness of the pressure sensitive film.
With the development of sapphire micromachining technology, optical fiber sensor based on all sapphire F-P cavity has become an important research direction of high temperature sensor. Oxsensis, located in oxsens, oxsens, UK, has been developing a fiber optic high temperature pressure sensor based on Fabry Perot cavity interference principle since 2005 (as shown in Fig. (b)). It has developed from a single pressure sensor product to a multi parameter measurement system, which can simultaneously measure pressure, temperature, vibration, flow and other parameters. The company's temperature, pressure and working temperature of vibration products are up to 1000 ℃, and has extensive cooperation with Alstom, Siemens, SNECMA and other gas turbine manufacturers. In 2015, oxsensis, together with GE company, proposed the development plan of compressor active stability management system based on ultra-high temperature optical fiber sensor. The system includes several sensors and micro actuators, which breaks the situation that traditional measurement system only carries out passive monitoring. Wang Anbo of Virginia University of technology and others used the ICP dry etching of sapphire and the hot pressing bonding process of sapphire to fabricate a full sapphire structure F-P cavity, as shown in figure (c). The packaged pressure sensor is shown in figure (d). The maximum operating temperature of the sensor reaches 1500 ℃. In addition, research institutes such as sheplak mark research group of University of Florida, Luna innovation company of the United States, European Aviation Administration and other research institutions have carried out research on ultra-high temperature sensor based on sapphire F-P cavity. The research content focuses on the new method of F-P cavity preparation, low stress packaging of sensor and further improvement of sensor working temperature. The research on sapphire optical fiber pressure sensor is still less in China. Rao Yunjiang research group of University of Electronic Science and technology has developed the sensor prototype, but only carried out the normal temperature pressure test, and the high temperature pressure sensor prototype has not been reported. This article comes from Zetian sensor, please keep it.