Super! Comprehensive summary of sensor knowledge

Sensor, also known as Sensor or Transducer in English, is defined in the New Webster Dictionary as: "A device that receives power from one system and usually sends power to a second system in another form." According to this definition, the function of a sensor is to convert one form of energy into another form of energy, so many scholars also use "transducer" to refer to "sensor".

A sensor is a detection device, usually composed of sensitive elements and conversion elements, which can measure information and allow users to perceive information. Through transformation, the data or value information in the sensor is converted into an electrical signal or other required form of output to meet the requirements of information transmission, processing, storage, display, recording and control.

01. History of sensor development

In 1883, the world's first thermostat was officially launched, and it was created by an inventor named Warren S. Johnson. This thermostat can maintain the temperature to a certain degree of accuracy, which is the use of sensors and sensing technology. At that time, it was a very powerful technology.

In the late 1940s, the first infrared sensor came out. Subsequently, many sensors were continuously developed. Until now, there are more than 35,000 types of sensors in the world, which are very complex in number and use. It can be said that now is the hottest period for sensors and sensor technology.

In 1987, ADI (Analog Devices) began to invest in the research and development of a new sensor. This sensor is different from others. It is called MEMS sensor, which is a new type of sensor manufactured using microelectronics and micromachining technology. Compared with traditional sensors, it has the characteristics of small size, light weight, low cost, low power consumption, high reliability, suitable for mass production, easy integration and intelligentization. ADI is the earliest company in the industry to do MEMS research and development.

In 1991, ADI released the industry's first High-g MEMS device, which is mainly used for automobile airbag collision monitoring. After that, many MEMS sensors were widely developed and used in precision instruments such as mobile phones, electric lights, and water temperature detection. As of 2010, there were about 600 units in the world engaged in the research and development and production of MEMS.

02. Three stages of sensor technology development

Phase 1: Before 1969

Mainly manifested as structural sensors. Structural sensors use changes in structural parameters to sense and convert signals. For example: resistance strain sensors, which use changes in resistance when metal materials undergo elastic deformation to convert electrical signals.

Phase 2: About 20 years after 1969

Solid-state sensors, which began to develop in the 1970s, are composed of solid components such as semiconductors, dielectrics, and magnetic materials, and are made using certain properties of materials. For example: using thermoelectric effect, Hall effect, and photosensitivity effect to make thermocouple sensors, Hall sensors, and photosensors, respectively.

In the late 1970s, with the development of integration technology, molecular synthesis technology, microelectronics technology, and computer technology, integrated sensors emerged.

Integrated sensors include 2 types: integration of the sensor itself and integration of the sensor and subsequent circuits. This type of sensor mainly has the characteristics of low cost, high reliability, good performance, and flexible interface.

Integrated sensors are developing very rapidly and now account for about 2/3 of the sensor market. They are developing in the direction of low price, multi-function and serialization.

The third stage: generally refers to the end of the 20th century to the present

The so-called intelligent sensor refers to its ability to detect, self-diagnose, process data and adapt to external information. It is the product of the combination of microcomputer technology and detection technology.

In the 1980s, intelligent sensors just began to develop. At this time, intelligent measurement was mainly based on microprocessors. The sensor signal conditioning circuit, microcomputer, memory and interface were integrated into a chip, giving the sensor a certain degree of artificial intelligence.

In the 1990s, intelligent measurement technology was further improved, and intelligence was realized at the first level of the sensor, making it have self-diagnosis function, memory function, multi-parameter measurement function and networking communication function.

03. Types of sensors

At present, there is a lack of international standards and norms in the world, and no authoritative standard types of sensors have been formulated. They can only be divided into simple physical sensors, chemical sensors and biosensors.

For example, physical sensors include: sound, force, light, magnetism, temperature, humidity, electricity, radiation, etc.; chemical sensors include: various gas sensors, acid-base pH value, ionization, polarization, chemical adsorption, electrochemical reaction, etc.; biological sensors include: enzyme electrodes and mediator bioelectricity, etc. The causal relationship between product use and formation process is intertwined, and it is difficult to strictly classify them.

Based on the classification and naming of sensors, there are mainly the following types:

(1) According to the conversion principle, they can be divided into physical sensors, chemical sensors and biological sensors.

(2) According to the detection information of the sensor, they can be divided into acoustic sensors, light sensors, thermal sensors, force sensors, magnetic sensors, gas sensors, humidity sensors, pressure sensors, ion sensors and radiation sensors.

(3) According to the power supply method, they can be divided into active or passive sensors.

(4) According to their output signals, they can be divided into analog output, digital output and switch sensors.

(5) According to the materials used in sensors, they can be divided into: semiconductor materials; crystal materials; ceramic materials; organic composite materials; metal materials; polymer materials; superconducting materials; optical fiber materials; nanomaterials and other sensors.

(6) According to energy conversion, they can be divided into energy conversion sensors and energy control sensors.

(7) According to their manufacturing process, they can be divided into mechanical processing technology; composite and integrated technology; thin film and thick film technology; ceramic sintering technology; MEMS technology; electrochemical technology and other sensors.

There are about 26,000 types of sensors that have been commercialized worldwide. my country already has about 14,000 types, most of which are conventional types and varieties; more than 7,000 types can be commercialized, but there are still shortages and gaps in special varieties such as medical, scientific research, microbiology, and chemical analysis, and there is a large space for technological innovation.

04. Functions of sensors

The functions of sensors are usually compared to the five major sensory organs of humans:

Photosensitive sensors - vision

Acoustic sensors - hearing

Gas sensors - smell

Chemical sensors - taste

Pressure-sensitive, temperature-sensitive, fluid sensors - touch

①Physical sensors: based on physical effects such as force, heat, light, electricity, magnetism and sound;

②Chemical sensors: based on the principles of chemical reactions;

③Biological sensors: based on molecular recognition functions such as enzymes, antibodies, and hormones.

In the computer age, humans solved the problem of brain simulation, which is equivalent to using 0 and 1 to digitize information and use Boolean logic to solve problems; now is the post-computer age, and we are beginning to simulate the five senses.

But simulating the five senses of a person is just a more vivid term for sensors. The relatively mature sensor technology is still the physical quantities such as force, acceleration, pressure, temperature, etc. that are often used in industrial measurements. For real human senses, including vision, hearing, touch, smell, and taste, most of them are not very mature from the perspective of sensors.

Vision and hearing can be considered as physical quantities, which are relatively good, while touch is relatively poor. As for smell and taste, since they involve the measurement of biochemical quantities, the working mechanism is relatively complex and is far from the stage of technical maturity.

The market for sensors is actually driven by applications. For example, in the chemical industry, the market for pressure and flow sensors is quite large; in the automotive industry, the market for sensors such as rotation speed and acceleration is very large. Acceleration sensors based on micro-electromechanical systems (MEMS) are now relatively mature in technology, and have contributed greatly to the demand for the automotive industry.

Before the concept of sensors "emerged", there were actually sensors in early measuring instruments, but they appeared as a component in the whole set of instruments. Therefore, before 1980, the textbook introducing sensors in China was called "Electrical Measurement of Non-Electrical Quantities".

The emergence of the concept of sensors is actually the result of the gradual modularization of measuring instruments. Since then, sensors have been separated from the entire instrument system and studied, produced, and sold as a functional device.

05. Common professional terms for sensors

As sensors continue to grow and develop, we have a deeper understanding of them. The following 30 common terms are summarized:

1. Range: the algebraic difference between the upper and lower limits of the measurement range.

2. Accuracy: the degree of consistency between the measured result and the true value.

3. Usually composed of sensitive elements and conversion elements:

Sensitive elements refer to the part of the sensor that can directly (or respond to) the measured value.

Conversion elements refer to the part of the sensor that can convert the measured value sensed (or responded) by the sensitive element into an electrical signal for transmission and (or) measurement.

When the output is a specified standard signal, it is called a transmitter.

4. Measuring range: the range of measured values within the allowable error limit.

5. Repeatability: the degree of consistency between the results of multiple consecutive measurements of the same measured quantity under all the following conditions:

Same measurement party, same observer, same measuring instrument, same location, same use conditions, and repetition within a short period of time.

6. Resolution: The minimum change in the measured quantity that the sensor can detect within the specified measurement range.

7. Threshold: The minimum change in the measured quantity that can cause the sensor output to produce a measurable change.

8. Zero position: The state that makes the absolute value of the output the minimum, such as the equilibrium state.

9. Linearity: The degree to which the calibration curve is consistent with a certain limit.

10. Nonlinearity: The degree to which the calibration curve deviates from a certain specified straight line.

11. Long-term stability: The ability of the sensor to maintain the tolerance within a specified time.

12. Natural frequency: The free (no external force) oscillation frequency of the sensor when there is no resistance.

13. Response: The characteristic of the measured quantity changing during output.

14. Compensated temperature range: The temperature range compensated for the sensor to maintain zero balance within the range and specified limits.

15. Creep: The change in output within a specified time when the environmental conditions of the measured machine remain constant.

16. Insulation resistance: If not otherwise specified, it refers to the resistance value measured between the specified insulation parts of the sensor when the specified DC voltage is applied at room temperature.

17. Excitation: The external energy (voltage or current) applied to make the sensor work properly.

18. Maximum excitation: The maximum value of the excitation voltage or current that can be applied to the sensor under indoor conditions.

19. Input impedance: The impedance measured at the input end of the sensor when the output end is short-circuited.

20. Output: The amount of electricity generated by the sensor that is a function of the external measured quantity.

21. Output impedance: The impedance measured at the output end of the sensor when the input end is short-circuited.

22. Zero output: The output of the sensor when the applied measured quantity is zero under urban conditions.

23. Hysteresis: The maximum difference in the output when the measured value increases and decreases within the specified range.

24. Delay: The time delay of the output signal change relative to the input signal change.

25. Drift: The amount of change in the sensor output that is not related to the measurement within a certain time interval.

26. Zero drift: The change in zero output at a specified time interval and under indoor conditions.

27. Sensitivity: The ratio of the increment of the sensor output to the corresponding increment of the input.

28. Sensitivity drift: The change in the slope of the calibration curve caused by the change in sensitivity.

29. Thermal sensitivity drift: The sensitivity drift caused by the change in sensitivity.

30. Thermal zero drift: The zero drift caused by the change in ambient temperature.

06. Application fields of sensors

Sensors are a widely used detection device, which is used in environmental monitoring, traffic management, medical health, agriculture and animal husbandry, fire safety, manufacturing, aerospace, electronic products, and other fields. It can sense the information being measured and can transform the sensed information into electrical signals or other required forms of information output according to certain rules to meet the requirements of information transmission, processing, storage, display, recording and control.

①Industrial control: industrial automation, robotics, testing instruments, automotive industry, shipbuilding, etc.

Industrial control applications are widely used, such as various sensors used in automobile manufacturing, product process control, industrial machinery, special equipment, and automated production equipment, etc., which measure process variables (such as temperature, liquid level, pressure, flow, etc.), measure electronic characteristics (current, voltage, etc.) and physical quantities (motion, speed, load and intensity), and traditional proximity/positioning sensors are developing rapidly.

At the same time, smart sensors can break through the limitations of physics and materials science by connecting humans and machines, and combining software and big data analysis, and will change the way the world works. In the vision of Industry 4.0, end-to-end sensor solutions and services are revived in the production site. It promotes smarter decision-making, improves operational efficiency, increases production, improves engineering efficiency and greatly improves business performance.

②Electronic products: smart wearables, communication electronics, consumer electronics, etc.

Sensors are mostly used in smart wearables and 3C electronics in electronic products, and mobile phones account for the largest proportion in the application field. The substantial growth in mobile phone production and the continuous increase in new mobile phone functions have brought opportunities and challenges to the sensor market. The increasing market share of color screen mobile phones and camera phones has increased the proportion of sensor applications in this field.

In addition, ultrasonic sensors used in group phones and cordless phones, magnetic field sensors used in magnetic storage media, etc. will see strong growth.

In terms of wearable applications, sensors are essential components.

For example, fitness trackers and smart watches are gradually becoming a daily lifestyle device that helps us track our activity level and basic health parameters. In fact, there is a lot of technology in those tiny devices worn on the wrist to help people measure activity levels and heart health.

Any typical fitness bracelet or smart watch has about 16 sensors built in. Depending on the price, some products may have more. These sensors, together with other hardware components (such as batteries, microphones, displays, speakers, etc.) and powerful high-end software, constitute a fitness tracker or smart watch.

Today, the application field of wearable devices is expanding from external watches, glasses, shoes, etc. to a wider field, such as electronic skin, etc.

③ Aviation and military: aerospace technology, military engineering, space exploration, etc.

In the aviation field, the safety and reliability of installed components are extremely high. This is especially true for sensors used in different places.

For example, when a rocket takes off, the air creates tremendous pressure and forces on the rocket surface and the body of the rocket due to the very high takeoff speed (over Mach 4 or 3000 mph), creating an extremely harsh environment. Therefore, pressure sensors are needed to monitor these forces to ensure that they remain within the design limits of the body. During takeoff, the pressure sensors are exposed to the air flowing over the surface of the rocket, thereby measuring data. This data is also used to guide future body designs to make them more reliable, tight and safe. In addition, if something goes wrong, the data from the pressure sensors will become an extremely important analysis tool.

For example, in aircraft assembly, sensors can ensure non-contact rivet hole measurement, and there are displacement and position sensors that can be used to measure the landing gear, wing components, fuselage and engines of aircraft missions, which can provide reliable and accurate determination of measurement values.

④ Home life: smart home, household appliances, etc.

The gradual popularization of wireless sensor networks has promoted the rapid development of information appliances and network technology. The main equipment of home networks has expanded from a single machine to multiple home appliances. The smart home network control node based on wireless sensor networks provides a basic platform for the connection of internal and external networks in the home and the connection of information appliances and equipment between internal networks.

Embedding sensor nodes in home appliances and connecting them to the Internet through wireless networks will provide people with a more comfortable, convenient and more humane smart home environment. The remote monitoring system can be used to remotely control home appliances, and the family safety can be monitored at any time through image sensing devices. The sensor network can be used to establish a smart kindergarten, monitor the early education environment of children, and track the activity trajectory of children.

⑤ Traffic management: transportation, urban transportation, smart logistics, etc.

In traffic management, the wireless sensor network system installed on both sides of the road can be used to monitor the road conditions, water accumulation conditions, and road noise, dust, gas and other parameters in real time to achieve the purpose of road protection, environmental protection and pedestrian health protection.

Intelligent Transportation System (ITS) is a new type of transportation system developed on the basis of the traditional transportation system. It integrates information, communication, control and computer technology and other modern communication technologies into the transportation field, and organically combines "people-vehicle-road-environment". Adding a wireless sensor network technology to the existing transportation facilities will be able to fundamentally alleviate the problems of safety, smoothness, energy saving and environmental protection that plague modern transportation, and at the same time improve the efficiency of transportation work.

⑥ Environmental monitoring: environmental monitoring and forecasting, weather testing, hydrological testing, energy environmental protection, earthquake testing, etc.

In terms of environmental monitoring and forecasting, wireless sensor networks can be used to monitor crop irrigation conditions, soil air conditions, livestock and poultry environment and migration conditions, wireless soil ecology, large-area surface monitoring, etc., and can be used for planetary exploration, meteorological and geographical research, flood monitoring, etc. Based on wireless sensor networks, rainfall, river water level and soil moisture can be monitored through several sensors, and flash floods can be predicted to describe ecological diversity, thereby conducting ecological monitoring of animal habitats. Population complexity can also be studied by tracking birds, small animals and insects.

As humans pay more attention to environmental quality, in the actual environmental testing process, people often need analytical equipment and instruments that are easy to carry and can realize continuous dynamic monitoring of multiple test objects. With the help of new sensor technology, the above needs can be met.

For example, in the process of atmospheric monitoring, nitrides, sulfides, etc. are pollutants that seriously affect people's production and life.

Among nitrogen oxides, SO2 is the main cause of acid rain and acid mist. Although traditional methods can measure the content of SO2, the method is complicated and not accurate enough. Recently, researchers have found that specific sensors can oxidize sulfites, and part of the oxygen will be consumed during the oxidation process, which will cause the electrode dissolved oxygen to decrease and generate a current effect. The use of sensors can effectively obtain the sulfite content value, which is not only fast but also highly reliable.

For nitrides, nitrogen oxide sensors can be used for monitoring. The principle of nitrogen oxide sensors is to use oxygen electrodes to generate a specific bacteria that consumes nitrites, and calculate the content of nitrogen oxides by calculating the change in dissolved oxygen concentration. Because the generated bacteria use nitrate as energy, and only use this nitrate as energy, therefore, it is unique in the actual application process and will not be affected by the interference of other substances. Some foreign researchers have conducted more in-depth research using the principle of membranes, and indirectly measured the very low concentration of NO2 in the air.

⑦ Medical health: medical diagnosis, medical health, health care, etc.

Many medical research institutions at home and abroad, including internationally renowned medical industry giants, have made important progress in the application of sensor technology in the medical field.

For example, the Georgia Institute of Technology in the United States is developing an in-body embedded sensor with pressure sensors and wireless communication circuits. The device is composed of conductive metal and insulating film, which can detect pressure changes according to the frequency changes of the resonant circuit, and will dissolve in body fluids after playing its role.

In recent years, wireless sensor networks have been widely used in medical systems and health care, such as monitoring various physiological data of the human body, tracking and monitoring the actions of doctors and patients in hospitals, and drug management in hospitals.

⑧ Fire safety: large workshops, warehouse management, airports, stations, docks, safety monitoring of large industrial parks, etc.

Due to the continuous repair of buildings, there may be some safety hazards. Although occasional small tremors in the earth's crust may not cause visible damage, potential cracks may be generated in the pillars, which may cause the building to collapse in the next earthquake. Inspections using traditional methods often require the closure of the building for several months, while smart buildings equipped with sensor networks can tell management departments their status information and automatically perform a series of self-repair work according to priority.

With the continuous progress of society, the concept of safe production has been deeply rooted in the hearts of the people, and people's requirements for safe production are getting higher and higher. In the construction industry where accidents are frequent, how to ensure the personal safety of construction workers and the preservation of construction materials, equipment and other property on the construction site is the top priority of construction units.

⑨Agriculture and animal husbandry: agricultural modernization, animal husbandry, etc.

Agriculture is another important area for the use of wireless sensor networks.

For example, since the implementation of the "Precision Management System for the Production of Advantageous Crops in the Northwest", special technical research, system integration and typical application demonstration have been carried out mainly for the dominant agricultural products in the western region, such as apples, kiwis, salvia miltiorrhiza, melons, tomatoes, and other major crops, as well as the characteristics of the dry and rainy ecological environment in the west, and the wireless sensor network technology has been successfully applied to precision agricultural production. This advanced technology of the sensor network that collects crop growth environment in real time is applied to agricultural production, providing new technical support for the development of modern agriculture.

⑩Other fields: complex machinery monitoring, laboratory monitoring, etc.

Wireless sensor network is one of the hot topics in the current information field, which can be used to collect, process and send signals in special environments; the wireless temperature and humidity sensor network is based on the PIC microcontroller, and the hardware circuit of the temperature and humidity sensor network node is designed using the integrated humidity sensor and the digital temperature sensor, and communicates with the control center through the wireless transceiver module, so that the system sensor node has low power consumption, reliable data communication, good stability, and high communication efficiency, which can be widely used in environmental detection.