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IntroductionDefinition: A ceramic capacitor is a capacitor that has a ceramic dielectric as its dielectric material. Multi-layer ceramic capacitors and ceramic disc capacitors are the two most common types. The dielectric in a ceramic capacitor is ceramic. Ceramics, a well-known insulator, is one of the first materials used in the manufacture of capacitors. Ceramic capacitors come in a variety of geometric forms, some of which have been phased out due to size, parasitic effects, or electrical characteristics, such as ceramic tubular capacitors and barrier layer capacitors. Multi-layer ceramic capacitor, also known as ceramic multi-layer chip capacitor (MLCC), and ceramic disc capacitor are the two types of ceramic capacitors most widely used in modern electronics.                                                                                                                                             Typical Multilayer Ceramic Capacitor With a production volume of about 1000 billion devices per year, MLCCs are the most widely used capacitors. Due to their small size, they are commonly used and manufactured using SMD (surface-mounted) technology. Ceramic capacitors are usually made with very small capacitance levels, ranging from 1nF to 1F, with a maximum capacitance of 100F. Ceramic capacitors are thin, and their maximum rated voltage is low. Since they lack polarity, they can be safely linked to AC electricity. Due to low parasitic effects including resistance and inductance, ceramic capacitors have excellent frequency response. Ceramic capacitors have the following advantages over other capacitors: small size, large capacity, good heat resistance, mass production suitability, and low price.CatalogIntroductionCatalogⅠThe Origin of Ceramic CapacitorsⅡ Classification of Ceramic Capacitors  2.1 Semiconductor Ceramic Capacitors  2.2 High Voltage Ceramic CapacitorsⅢ Characteristics  3.1 Precision and Tolerance  3.2 Size Advantages  3.3 High Voltage and High PowerⅣ Ceramic Dielectric TypesⅤ Construction and Properties of Ceramic Capacitors  5.1 Ceramic Disc Capacitors  5.2 Multi-layer Ceramic Capacitor (MLCC) Ⅵ Advantages and Disadvantages  6.1 Advantages  6.2 DisadvantagesⅦ Applications for Ceramic CapacitorsⅧ How to read ceramic capacitor value?Ⅸ How to Test Ceramic Disc CapacitorⅩ FAQⅠThe Origin of Ceramic CapacitorsLombardi from Italy invented ceramic dielectric capacitors in 1900. It was discovered in the late 1930s that by adding titanate to ceramics, the dielectric constant can be doubled, resulting in cheaper ceramic dielectric capacitors. Ceramic capacitors were first used in military electronic equipment around 1940, following the discovery of the insulation properties of BaTiO3 (Barium titanate), the primary raw material for today's ceramic capacitors. Around 1960, ceramic laminate capacitors became commercially available. It had become an essential part of electronic devices by 1970, thanks to the rapid growth of hybrid IC, computers, and portable electronic devices. Ceramic dielectric capacitors currently account for approximately 70% of the overall capacitor market.                                                                                                             Historic Ceramic CapacitorsⅡ Classification of Ceramic Capacitors2.1 Semiconductor Ceramic Capacitors(1)Surface Layer Ceramic CapacitorThe miniaturization of capacitors, that is, the capacitor obtains the largest possible capacity in the smallest possible volume, which is one of the development trends of capacitors. For the separation of capacitor components, there are two basic approaches to miniaturization: ①Make the dielectric constant of the dielectric material as high as possible; ②Make the thickness of the dielectric layer as thin as possible. Among ceramic materials, the dielectric constant of ferroelectric ceramics is very high, but when ferroelectric ceramics are used to manufacture ordinary ferroelectric ceramic capacitors, it is difficult to make the ceramic dielectric very thin. Firstly, due to the low strength of ferroelectric ceramics, it is difficult to carry out actual production operations because it is easy to fracture when it is thin. Secondly, when the ceramic medium is fragile, it is easy to cause various structural defects and the production process will be challenging.(2)Grain Boundary Layer Ceramic CapacitorThe surface of BaTiO3 semiconductor ceramics with sufficiently developed grains is coated with appropriate metal oxides (such as CuO or Cu2O, MnO2, Bi2O3, Tl2O3, etc.), and heat treatment is performed under oxidizing conditions at appropriate temperatures. Then the substance will form a low eutectic solution phase with BaTiO3, rapidly diffuse and penetrate into the ceramic along with the open pores and grain boundaries, forming a thin solid solution insulating layer on the grain boundaries. The resistivity of this thin solid solution insulating layer is very high (up to 1012~1013Ω·cm). Although the ceramic grain interior remains as semiconductor, the entire ceramic body is shown as the dielectric constant of 2×104 to 8×104 dielectric medium. Capacitors made with this kind of porcelain are called boundary layer ceramic capacitors, or BL capacitors for short.2.2 High Voltage Ceramic CapacitorsThe ceramic materials of high-voltage ceramic capacitors are barium titanate-based and strontium titanate-based. Barium titanate-based ceramic materials have the advantages of high dielectric coefficient and good AC withstand voltage characteristics, but also have the shortcomings of capacitance change rate with the increase of medium-temperature and decrease of insulation resistance. The Curie temperature of strontium titanate crystal is -250℃, and it is a cubic perovskite structure at room temperature.  It is a para-electric body, and there is no spontaneous polarization phenomenon. Under high voltage, the dielectric coefficient of strontium titanate ceramic material changes little. The dielectric loss tangent value (tgδ) and capacitance change rate are small, which makes it a high-voltage capacitor dielectric. 2.3 Multilayer Ceramic CapacitorsMultilayer ceramic capacitors are the most widely used type of electronic component. They are stacked alternately in parallel with the internal electrode material and ceramic body and fired into a whole, also known as chip monolithic capacitors. It has the characteristic of small size, high specific volume and high precision. It can be mounted on a printed circuit board (PCB) and hybrid integrated circuit (HIC) substrates. It can effectively reduce the volume and weight of electronic information terminal products (especially portable products), and also improve product reliability.                                                             Multilayer ceramic capacitors conform to the IT industry's development direction of miniaturization, lightweight, high performance, and multifunction. The outline of the national vision goal for 2010 clearly puts forward that new components such as surface-mounted components should be the development focus of the electronic industry. It is not only simple packaging, good sealing, and can effectively isolate the opposite electrode. MLCC can store charge, block DC, filter merge, distinguish different frequencies and tune the circuit in the electronic circuit.  It can partially replace organic film capacitors and electrolytic capacitors in high-frequency switching power supplies, computer network power supplies and mobile communication equipment. What's more, it can greatly improve the filtering performance and anti-interference performance of high-frequency switching power supplies.                                                Ⅲ Characteristics3.1 Precision and ToleranceCeramic capacitors are currently available in two classes: class 1 and class 2. When high stability and low losses are needed, Class 1 ceramic capacitors are used. They are extremely precise, and the capacitance value remains constant regardless of applied voltage, temperature, or frequency. Within a total temperature range of -55 to +125 °C, the capacitance thermal stability of the NP0 series of capacitors is 0.54%. The nominal capacitance value's tolerances can be as poor as 1%. Class 2 capacitors have a large capacitance per volume and are used in less sensitive applications. Their thermal stability in the operating temperature range is usually 15%, and nominal value tolerances are about 20%.3.2 Size AdvantagesMLCC devices outclass other capacitors when high component packing densities are needed, as is the case in most modern printed circuit boards (PCBs). The “0402 multi-layer ceramic capacitor package” measures just 0.4 mm x 0.2 mm to demonstrate this point. There are 500 or more ceramic and metal layers in such a box. As of 2010, the minimum ceramic thickness was on the order of 0.5 microns.3.3 High Voltage and High PowerCeramic capacitors that are physically bigger and can withstand even higher voltages are known as power ceramic capacitors. These are much larger than the ones used on PCBs, and they have specialized terminals for connecting to a high-voltage supply safely. Ceramic capacitors with a power specification of much more than 200 volt-amperes can withstand voltages ranging from 2 kV to 100 kV. Printed circuit boards use smaller MLCCs that are rated for voltages ranging from a few volts to several hundreds of volts, depending on the application.Ⅳ Ceramic Dielectric TypesUnlike other capacitor types such as tantalum capacitors and electrolytic capacitors, ceramic capacitors may use a variety of dielectrics. These various dielectrics give capacitors very different properties, so in addition to deciding on a ceramic capacitor, a second decision about the type of dielectric may be needed. Popular ceramic capacitor dielectrics, such as C0G, NP0, X7R, Y5V, Z5U, and many others, are frequently listed in distributors' lists. However, determining which form is best necessitates a little more study. Ceramic Capacitor Dielectric ClassesSome industry organizations have identified a range of ceramic dielectric application classes to make selecting capacitors with the appropriate dielectric easier. These application groups divide the various ceramic capacitor dielectrics into separate classes based on the anticipated application.     International bodies such as the IEC (International Electrotechnical Commission) and the EIA (Electronic Industries Alliance) have standardized these ceramic capacitor classes.Ⅴ Construction and Properties of Ceramic Capacitors5.1 Ceramic Disc CapacitorsCeramic disc capacitors are made by coating a ceramic disc on both sides with silver contacts. These devices can be constructed from several layers to achieve higher capacitances. Ceramic disc capacitors are usually through-hole components that have lost popularity due to their large scale. If capacitance values allow, MLCCs are used instead. Ceramic disc capacitors have capacitance values ranging from 10pF to 100pF and voltage ratings ranging from 16 volts to 15 kV and beyond.                                                                    5.2 Multi-layer Ceramic Capacitor (MLCC)MLCCs are made by combining finely ground granules of paraelectric and ferroelectric materials and layering the mixture with metal contacts alternately. Following the layering, the device is heated to a high temperature and the mixture sintered, yielding a ceramic substance with the desired properties. The capacitance of the resulting capacitor is increased by connecting several smaller capacitors in parallel. MLCCs are made up of 500 layers or more, with a minimum layer thickness of 0.5 microns. As technology advances, layer thickness decreases, allowing for higher capacitances in the same volume.Ⅵ Advantages and Disadvantages6.1 AdvantagesThe following are some of the benefits of using a ceramic capacitor:• This capacitor's physical structure is very compact.• It is well suited for the application of AC signals due to its non-polarized nature.• Signal interference suppression, such as radiofrequency suppression and electromagnetic interference suppression, is improved with these capacitors.• This capacitor is reasonably priced, and it can withstand voltages of up to 100 volts.6.2 DisadvantagesThe following are the drawbacks of using these capacitors:• The capacitance value of these capacitors is less than one microfarad.• These components are also responsible for the Microphonic effect in circuits.• It is unable to withstand high voltages. Since it can easily impact the dielectric present in it. As a consequence, there is a breakdown.Ⅶ Applications for Ceramic CapacitorsGiven that MLCCs are the most commonly manufactured capacitor in the electronics industry, it should come as no surprise that they have a wide range of applications. A resonant circuit in transmitter stations is an interesting high-precision, high-power application. High-voltage laser power supplies, power circuit breakers, and induction furnaces all use Class 2 high-power capacitors. Small-form SMD (surface mount) capacitors are commonly used in printed circuit boards, and capacitors the size of a grain of sand are used in high-density applications. They're also used in DC-DC converters, where high frequencies and high levels of electrical noise put a lot of strain on the components. Since ceramic capacitors are non-polarized and come in a wide range of capacitances, voltage ratings, and sizes, they can be used as a general-purpose capacitor. Ceramic disc capacitors, which are used throughout brush DC motors to reduce RF noise, are familiar to many hobbyists, especially in the field of robotics.Ⅷ How to read ceramic capacitor value?Ceramic capacitors normally have three digits for their values, such as 102, 103, and 101, and the values are in Pico farads. The numbering scheme is simple to understand if you note that picofarads, not microfarads, are used.The worth of a ceramic capacitor with three digits – ABC is AB*10^C Pico Farad. The digit 104 means 10*104pF = 100000pF = 100nF = 0.1uF if ABC is 104. The first two digits of the printed code correspond to the first two digits of the capacitor value, while the third digit indicates the number of zeroes that must be applied to convert the capacitor value to Pico Farad. If we calculate in Nano Farad for values ending with 4, then the reading becomes easy like 104 is 100nF. If we calculate in Nano Farad for values ending with 3, then the reading becomes easy like 103 is 10nF.Some ceramic capacitors are polarized, meaning they have both positive and negative terminals. The capacitor can be identified by its tolerance in addition to its capacitance value. There is many tolerance marking schemes in use, with one and two alphabets being the most common. You don't need to recall them unless you're dealing with a precise circuit. We only looked at ceramic capacitors in direct current (DC) circuits with voltages ranging from 12V to near zero in this short article. Hobbyists are familiar with this collection. It is also useful to be familiar with the tolerance marking scheme for professional purposes. Ⅸ How to Test Ceramic Disc CapacitorCeramic disc capacitors are units used in the computer industry to control voltage for various dielectric functions. Ceramic layers aim to dissipate heat generated by high voltage while also protecting the environment — both internal and external — from damage. Volumetric efficiency is inversely proportional to stability and accuracy with these capacitors, making testing difficult.Step 1 Ceramic capacitors must be tested since they will short out if they are exposed to high voltage. Your monitor can blink or go blank if this happens. This issue can be resolved by removing all of the ceramic capacitors. Ceramic capacitors, on the other hand, can be tested if you have the right tools. Step 2To measure a ceramic capacitor, use a wireless multimeter. The capacitor works properly when the voltage is constant. However, you won't be able to accurately calculate it if the ohmmeter's output and digital capacitance don't match the capacitor's voltage, so the second option is preferable. Step 3To locate the short circuit or assess cases where optical capacitance meters fail to produce shortened readings, use an analog insulation tester. In order to obtain a 12-volt output, set the analog meter to 10 Kohm. This phase is needed for the ceramic capacitor to be tested. You may also use both methods to improve measurement precision if you do want to stop removing the capacitor and test it aboard.Related recommendation: How to Test a Start Capacitor?                                             How to Discharge a Capacitor? Ⅹ FAQ1. What is Ceramic Capacitor?A fixed value type of capacitor where the ceramic material within the capacitor acts as a dielectric is the Ceramic Capacitor. This capacitor consists of more alternating layers with ceramic and also a metal layer which acts as an electrode. The composition of this ceramic material in this capacitor tells about the electrical behavior along with its applications. We can define a ceramic capacitor as A fixed-value capacitor where the ceramic material acts as the dielectric. 2. What are the advantages of ceramic capacitors?Following are the advantages of ceramic capacitors:Manufacturing cost is lessHigh-frequency performance is exhibitedThe stability of the capacitor is dependent on the ceramic dielectric 3. What is the capacitance range for a ceramic capacitor?The typical capacitance range for a ceramic capacitor is 10 pF to 0.1 μF. 4. Can I replace all electrolytic capacitors with ceramic ones?If you can find ceramic capacitors of the correct value, you can certainly do this. Ceramic capacitors are more stable, have a longer useful lifetime, have higher voltage ratings and are not polarized. Be prepared to find that there will be a substantial size difference. 5. What are the differences between electrolytic, tantalum and ceramic capacitors?Ceramic capacitors don't have polarity, their terminals can be interchanged. They are suitable for both ac and dc. They don't have any chemical reaction involved in their work. They have a lesser capacity for the same given size. Electrolytic capacitors have polarity (i.e. they have fixed positive and negative terminal), Suitable for dc only. A chemical reaction involves the formation of aluminum oxide on the electrode. ( Consists of aluminum electrodes in a solution of Ammonium borate).Higher capacity. A tantalum electrolytic capacitor, a member of the family of electrolytic capacitors, is a polarized capacitor whose anode electrode (+) is made of tantalum on which a very thin insulating oxide layer is formed, which acts as the dielectric of the capacitor. A solid or liquid electrolyte that covers the surface of the oxide layer serves as the second electrode (cathode) (-) of the capacitor. 6. What is the time constant for the discharge of the capacitors in (figure 1)?figure 1The equivalent resistance:R= 2*1× 10∧3 = 2000 i©=> the time constant: T= R*C = 2000*1× 10∧-6 = 2×10∧-3s = 2ms 7. How do you read a ceramic capacitor value?The first two digits, in this case, the 10 give us the first part of the value. The third digit indicates the number of extra zeros, in this case, 3 extra zeros. So the value is 10 with 3 extra zeros, or 10,000. Ceramic disc capacitor codes are always measured in pico Farads or pF. 8. How can you tell if a ceramic capacitor is bad?Use the multimeter and read the voltage on the capacitor leads. The voltage should read near 9 volts. The voltage will discharge rapidly to 0V because the capacitor is discharging through the multimeter. If the capacitor will not retain that voltage, it is defective and should be replaced. 9. Do ceramic capacitors degrade over time?Among ceramic capacitors, the capacitance, especially of capacitors classified as a high dielectric constant (B/X5R, R/X7R characteristics), decreases over time. ... When the capacitor cools down below the Curie point, aging starts again. 10. How do you tell the positive and negative of a ceramic capacitor?In general, the ceramic capacitor has no positive and negative poles, and the capacity is generally small. It is often used for signal source filtering, and the polarity is only temporary behavior. This is a kind of non-polar electrolytic capacitor, so it is not polar. 

In the article today, we will introduce you 7 commonly used sensor technologies.CatalogI. IntroductionII. Seven Commonly Used Sensor Technologies2.1 Physical Sensor2.2 Optical Fiber Sensor2.3 Bionic Sensor2.4 Infrared Sensor2.5 Electromagnetic Sensor2.6 Magneto-optic Effect Sensor2.7 Pressure SensorFAQI. IntroductionThe sensor is a common but very important device, it is a device that feels the specified amount of measurement and converts it into a useful signal according to a certain law. For the sensor, according to the state of the input, the input can be divided into static and dynamic quantities. We can obtain the static characteristics of the sensor according to the relationship between the output and the input in the stable state of each value.The main indexes of the static characteristics of the sensor are linearity, hysteresis, repeatability, sensitivity, and accuracy. The dynamic characteristics of the sensor refer to the response characteristics of the input, which changes with time. The dynamic characteristics are usually described by automatic control models such as transfer function and so on. Usually, the signal received by the sensor has a weak low-frequency signal, sometimes the amplitude of external interference can exceed the measured signal, so eliminating the serial noise has become a key sensor technology.II. Seven Commonly Used Sensor Technologies2.1 Physical SensorA physical sensor is a sensor that detects physical quantities. It is a device that uses some physical effects to convert the measured physical quantity into a signal in the form of energy that is easy to process. There is a definite relationship between the output signal and the input signal. The main physical sensors are photoelectric sensor, piezoelectric sensor, piezoresistive sensor, electromagnetic sensor, thermoelectric sensor, optical fiber sensor, and so on. As an example, let's take a look at the more commonly used photoelectric sensors. The sensor converts the optical signal into an electrical signal, which directly detects radiation information from the object, and can also convert other physical quantities into optical signals.The main principle is the photoelectric effect: when light shines on the material, the electrical effect on the material changes, where the electrical effect includes electron emission, conductivity, and potential current. Obviously, devices that can easily produce such an effect have become the main components of photoelectric sensors, such as photoresistors. In this way, we know that the main workflow of the photoelectric sensor is to receive the corresponding light, convert the light energy into electric energy through devices such as photoresistors, and then process it by amplifying and removing noise. Thus you will get the electrical signal you need to output. The output electrical signal here has a certain relationship with the original optical signal, usually close to a linear relationship, so that the calculation of the original optical signal is not very complex. The principle of other physical sensors can be analogous to photoelectric sensors.The application of physical sensors is very extensive. For example, let’s take a look at the application of physical sensors from the perspective of biomedicine. It is not difficult to speculate that physical sensors also have important applications in other aspects.Blood pressure measurement, for example, is one of the most conventional medical measurements. Our usual blood pressure measurements are indirect, through the relationship between the blood flow and pressure detected on the body surface, so as to measure the blood pressure in the pulse tube. The sensors needed to measure blood pressure usually include an elastic diaphragm that converts the pressure signal into the deformation of the diaphragm and then converts it into a corresponding electrical signal according to the strain or displacement of the diaphragm. We can detect the systolic blood pressure at the peak of the electrical signal. After the inverter and the peak detector, we can get the diastolic pressure through the shape of the sensor, and we can get the average pressure through the integrator.Next, let's take a look at respiration measurement. Respiratory measurement is an important basis for clinical diagnosis of pulmonary function and is essential in surgery and patient monitoring. For example, when a thermistor type sensor for measuring respiratory frequency is used, the resistance of the sensor is mounted on the outer side of the front end of a clip. And then clamp the clip on the nasal wing. When the respiratory airflow flows through the surface of the thermistor, the frequency of breathing and the state of the hot gas can be measured by thermistors.Here is another example. Although the most common body surface temperature measurement process seems easy, there is a complex measurement mechanism. Body surface temperature is determined by many factors, such as local blood flow, heat conduction of lower tissue, and heat dissipation of the epidermis. So, many effects should be taken into account in measuring skin temperature. Thermocouple sensors are widely used in temperature measurement, usually, there are rod thermocouple sensors and thin-film thermocouple sensors. Because the size of the thermocouple is very small and the precision is high enough to reach the micron level, the temperature at a certain point can be measured more accurately. Coupled with the later analysis and statistics, a more comprehensive analysis result can be obtained. This is incomparable to the traditional mercury thermometer, and also shows the broad prospects for the application of new technology to the development of science.From the above introduction, it can be seen that physical sensors have a variety of applications in biomedicine alone. The development direction of sensors is multi-functional, image-based, and intelligent sensors. Sensor measurement, as an important means of data acquisition, is an indispensable device in industrial production and even family life. And the physical sensor is the most common sensor family. Flexible use of the physical sensors is bound to create more products and bring better benefits.2.2 Optical Fiber SensorIn recent years, sensors are developing in the direction of sensitivity, accuracy, adaptability, small size, and intelligentization. In this process, the optical fiber sensor, a new member of the sensor family, is very popular. Optical fiber has many excellent properties. For example, the performance of resistance to electromagnetic interference and atomic radiation, the mechanical properties of fine diameter, soft and lightweight, the electrical properties of insulation and non-induction, the chemical properties of water resistance, high-temperature resistance and corrosion resistance, etc., It can play the role of human eyes and ears in places that are not accessible to people (such as high-temperature zones) or harmful areas (such as nuclear radiation areas). It can also go beyond the physiological boundaries of people and receive external information that cannot be felt by people's senses.Optical fiber sensor is a new technology in recent years, which can be used to measure a variety of physical quantities, such as sound field, electric field, pressure, temperature, angular velocity, acceleration, and so on. It can also complete the measurement tasks that are difficult to be completed by the existing measurement technology. In a narrow space, strong electromagnetic interference, and high voltage environment, optical fiber sensors have shown a unique ability. At present, there are more than 70 kinds of optical fiber sensors, which are roughly divided into optical fiber self-sensors and optical fiber sensors.The so-called optical fiber self-sensor is that the optical fiber itself directly receives the measurement from the outside world. The external measured physical quantity can cause the change of the length, refractive index, and diameter of the measuring arm, which makes the light transmitted in the optical fiber change in amplitude, phase, frequency, polarization, and so on. The light transmitted by the measuring arm interferes (compares) with the reference light of the reference arm so that the phase (or amplitude) of the output light changes. According to this change, the measured change can be detected. The phase transmitted in the optical fiber is highly sensitive to the influence of the outside. The physical quantity corresponding to the small phase change of the negative fourth power radian of 10 can be detected by using interferometry. By using the winding and low loss of the fiber, the very long fiber disk can be formed into a small optical fiber ring, in order to increase the utilization length and obtain higher sensitivity.An optical fiber acoustic sensor is a kind of sensor that uses optical fiber itself. When the optical fiber is subjected to a very small external force, it will produce micro-bending, and its light transmission ability will change greatly. Sound is a kind of mechanical wave, its effect on optical fiber is to force and bend the optical fiber, and it can get strong and weak sound through bending. A gyroscope is also a kind of optical fiber self-sensor. Compared with laser gyro, the gyroscope has the advantages of high sensitivity, small size, and low cost. It can be used in the high-performance inertial navigation systems of aircraft, ships, missiles, and so on.Another large class of optical fiber sensors is the sensor that uses optical fiber. The structure is roughly as follows: the sensor is located at the end of the optical fiber, the optical fiber is only the transmission line of light, which transforms the measured physical quantity into the amplitude, phase, or amplitude change of the light. In this kind of sensor system, the traditional sensor and optical fiber are combined. The introduction of optical fiber makes it possible to realize probe telemetry. The sensor transmitted by optical fiber has a wide range of applications and is easy to use, but the accuracy is slightly lower than that of the first kind of sensor.Optical fiber is a rising star in the sensor family. It has been widely used because of its excellent performance, and it is a kind of sensor worthy of attention in production practice.2.3 Bionic SensorThe bionic sensor is a new type of sensor that adopts a new detection principle. It uses immobilized cells, enzymes, or other bioactive substances to combine with the transducer to form the sensor. This kind of sensor is a new type of information technology developed by the mutual penetration of biomedicine, electronics, and engineering in recent years. This kind of sensor is characterized by high function and long life. Among the bionic sensor, the biological simulation sensor is more commonly used.Bionic sensors can be divided into enzyme sensors, microbial sensors, organelle sensors, tissue sensors, and so on according to the medium used. In the figure, we can see that bionic sensors are closely related to all aspects of biological theory, which is the direct result of the development of biological theory. In the biological simulation sensor, the urea sensor is a recently developed sensor. The following is an example of a urea sensor to introduce the application of a bionic sensor.Urea sensor is mainly composed of a biological membrane and its ion channel. The biological membrane can feel the effect of external stimulation, and the ion channel can receive the information of the biological membrane and then amplify and transmit it. When the sensory part of the membrane is affected by external stimulants, the permeability of the membrane will change, so that a large number of ions flow into the cell, forming the transmission of information. Among them, the component of the biological membrane is the membrane protein, which can produce the change of the conformal network, change the permeability of the membrane, transmit and amplify the information. The ion channel of the biological membrane, which is composed of amino acid polymers, can be replaced by   L-glutamic acid, PLG, which is easy to synthesize in organic chemistry and has better chemical stability than enzymes.PLG is water-soluble and is not suitable for motor modification, but PLG and polymers can synthesize block copolymers to form induction films used in sensors. The principle of the ion channel of the biological membrane is basically the same as that of the biological membrane. After the block copolymer membrane is fixed at the electrode, if the substance sensing the change of the PLG retention network is added, the permeability of the membrane will change, resulting in the change of the current. By the change of current, the irritant substance can be detected. The urea sensor has been proved to be a kind of biological analog sensor with good stability. The detection limit is 10 of the order of minus 3, and the irritant can also be detected, but by now it is not suitable for the measurement of the biological body for the time being.At present, although many bionic sensors have been developed successfully, the stability, reproducibility, and batch productivity of bionic sensors are obviously insufficient, so bionic sensing technology is still in its infancy. In the future, in addition to continuing to develop a new series of bionic sensors and improve the existing series, the immobilization technology of bioactive membrane and the solid-state of bionic sensors are worthy of further study.In the near future, bionic sensors simulating the functions of the living body, such as smell, taste, hearing, and touch will appear, and it may exceed the sensitivity of human facial features. At the same time, it will improve robots’ vision, taste, touch, and ability to operate objects. We can see the broad prospects for the application of biomimetic sensors, but these need the further development of biotechnology. Let’s wait and see the arrival of this day.2.4 Infrared SensorUp to now, infrared technology has been well known. This kind of technology has been widely used in modern science and technology, national defense, industry and agriculture, and other fields. An infrared sensing system is a measurement system with an infrared medium, which can be divided into five categories according to its functions:（1）Radiometer for radiation and spectral measurement;（2）Searching and tracking system for searching and tracking infrared targets so as to determine its spatial position and track its motion;（3）The thermal imaging system can generate the distribution image of the whole target infrared radiation;（4）The infrared ranging and communication system;（5）Hybrid system refers to the combination of two or more of the above types of systems.The core of the infrared system is the infrared detector. According to the different detection mechanisms, it can be divided into two categories: a thermal detector and a photon detector. The following is an example of a thermal detector to analyze the principle of the detector.The thermal detector makes use of the radiation thermal effect to cause the temperature to rise after the detector receives the radiation energy, and then causes the performance which depends on the temperature in the detector to change. Radiation can be detected by detecting changes in one of these properties. In most cases, radiation is detected through thermoelectric changes. When the element receives radiation and causes the physical change of the non-electric quantity, the corresponding electric quantity change can be measured after the appropriate transformation.2.5 Electromagnetic SensorThe magnetic sensor is the oldest sensor; a compass is the earliest application of a magnetic sensor. However, as a modern sensor, in order to facilitate signal processing, magnetic sensors are needed to convert magnetic signals into electrical signals. The earliest application is the magnetoelectric sensor made according to the principle of electromagnetic induction. This magnetoelectric sensor has made outstanding contributions in the field of industrial control, but today it has been replaced by a new type of magnetic sensor based on high-performance magnetic sensitive materials.Among the electromagnetic effect sensors used today, the magnetic rotation sensor is an important one. The magnetic rotation sensor is mainly composed of semiconductor magnetoresistive elements, permanent magnet, retainer, shell, and so on. The typical structure is that a pair of magnetoresistive elements are installed on the stimulation of a permanent magnet, the input and output terminals of the elements are connected to the fixator, and then installed in a metal box. Next, seal it with engineering plastic to form a closed structure. This structure has good reliability. The magnetic rotation sensor has many advantages over the shape of an electromagnetic sensor. In addition to high sensitivity and large output signal, it has a strong speed detection range, which is due to the development of electronic technology. In addition, the sensor can also be used in a wide temperature range. It has a long working life, strong resistance to dust, water, and oil, so it can withstand a variety of environmental conditions and external noise. Therefore, this kind of sensor has been paid more and more attention in industrial applications.The magnetic rotation sensor is widely used in factory automation systems because it has satisfactory characteristics and does not need to be maintained. It is mainly used in the rotation detection of machine tool servo motor, the positioning of factory automated robot arm, the detection of hydraulic stroke, the position detection of factory automation related equipment, the detection unit of a rotary encoder, and various rotating detection units, and so on. Modern magnetic rotation sensors mainly include four-phase sensors and single-phase sensors. In the working process, the four-phase differential rotation sensor uses one pair of detection units to realize differential detection, and the other pair to realize reverse differential detection. In this way, the detection ability of the four-phase sensor is four times that of a single element. The two-element single-phase rotation sensor also has its own advantages, that is, small, reliable, and low cost. At the same time, it has a large output signal, strong ability of anti-environmental impact and anti-noise and it can detect low-speed motion. Therefore, single-phase sensors will also have a good market.Magnetic rotation sensors also have great application potential in household appliances. In the reversing mechanism of a cassette recorder, a magnetoresistive element is available to detect the endpoint of the tape. Most of the household video recorders have variable speed and high-speed playback functions, which can also use a magnetic rotation sensor to detect and control the spindle speed to obtain a picture of high quality. The positive and negative rotation and high and low-speed rotation functions of the motor in the washing machine can be detected and controlled by a servo rotation sensor. This switch can sense the metal object entering its own inspection area and control the opening or closing of its own internal circuit. The switch itself produces a magnetic field. When a metal object enters the magnetic field, it causes a change in the magnetic field. This change can be converted into an electrical signal through the internal circuit of the switch.2.6 Magneto-optic Effect SensorModern electrical measurement technology is becoming more and more mature. Because of its high precision and convenience for microcomputer connection to achieve automatic real-time processing, it has been widely used in the measurement of electrical and non-electrical quantities. However, the electrical measurement method is easy to be interfered with. In AC measurement, the frequency response is not wide enough and has certain requirements for voltage and insulation. With the rapid development of laser technology today, it has been able to solve the above problems.Magneto-optic effect sensor is a high-performance sensor developed by laser technology. Laser is another new technology developed rapidly in the early 1960s. Its appearance indicates that people have entered a new stage of mastering and utilizing light waves. In the past, the single chromaticity of the ordinary light source is low. Therefore, many important applications are limited. With the emergence of laser, radio technology and optical technology are advancing by leaps and bounds, permeating and complementing each other. Now, many sensors have been made by using laser, which has solved many technical problems that cannot be solved before and makes it suitable for dangerous and flammable places such as coal mine, oil, natural gas storage, and so on.For example, the optical fiber sensor made of laser can measure the parameters of crude oil injection and crack of large oil tanks. In the measured location, there is no need for a power supply, which is especially suitable for petrochemical equipment groups with strict requirements for safety and explosion-proof measures. It can also be used to realize the telemetry chemical technology of optical methods in some links of large iron and steel mills.The principle of the magneto-optical effect sensor is to realize the function of the sensor by using the polarization state of light. When polarized light passes through a medium, if there is an external magnetic field in the direction of beam propagation, then the light will rotate an angle through the polarization surface, which is the magneto-optic effect. That is, the external magnetic field can be measured by rotating the angle. In a specific experimental device, the deflection angle is proportional to the output light intensity. The digital light intensity can be obtained by irradiating the laser diode LD, with the output light, which can be used to measure specific physical quantities.Since the end of the 1960s, RCLecraw has put forward the research report on the magneto-optic effect, which has attracted everyone's attention. Japan, the Soviet Union, and other countries have carried out research, domestic scholars have also explored. The magneto-optic effect sensor has characteristics of excellent electrical insulation performance, anti-interference, frequency response width, quick response, safe explosion-proof, and so on. Therefore, it has a unique effect on the measurement of electromagnetic parameters on some special occasions. Especially in the measurement of high voltage and current in power systems, it shows its potential advantages. At the same time, by developing the software and hardware of the processing system, the automatic real-time measurement of welding machines and robot control systems can also be realized.In the use of a magneto-optic effect sensor, the most important thing is to select a magneto-optical medium and laser. Different devices have different abilities in sensitivity and working range. With the emergence of high-performance lasers and new magneto-optical medium in recent decades, the performance of magneto-optical effect sensors is getting stronger and stronger, and the application is more and more extensive. As a special purpose sensor, the magneto-optical effect sensor can play its own function in a specific environment, and it is also a very important industrial sensor.2.7 Pressure SensorThe pressure sensor is the most commonly used sensor in industrial practice, and the pressure sensor we usually use is mainly made of piezoelectric effect, which is also called a piezoelectric sensor.We know that crystals are anisotropic and amorphous crystals are isotropic. When some crystal medium is deformed by a mechanical force in a certain direction, it produces a polarization effect; when the mechanical force is removed, it will return to the state of being uncharged, that is when it is subjected to pressure. Some crystals may produce the effect of electricity, which is called the polarization effect. Based on this effect, some scientists have developed pressure sensors.+The main piezoelectric materials used in piezoelectric sensors include quartz, potassium sodium tartrate, and dihydroamine phosphate. Quartz (silica) is a kind of natural crystal in which the piezoelectric effect is found. Within a certain temperature range, piezoelectric properties always exist. But after the temperature exceeds this range, the piezoelectric properties disappear completely (this high temperature is the so-called "Curie point"). Because the electric field changes slightly with the change of stress (that is to say, the piezoelectric coefficient is relatively low), quartz is gradually replaced by other piezoelectric crystals. Potassium sodium tartrate has high piezoelectric sensitivity and piezoelectric coefficient, but it can only be used at room temperature and in an environment with low humidity. Dihydroamine phosphate is an artificial crystal, which can withstand high temperature and high humidity, so it has been widely used. Nowadays, the piezoelectric effect is also used in polycrystals, such as piezoelectric ceramics, including barium titanate piezoelectric ceramics, PZT, niobate piezoelectric ceramics, lead magnesium niobate piezoelectric ceramics, and so on.The piezoelectric effect is the main working principle of the piezoelectric sensor. The piezoelectric sensor cannot be used for static measurement because the charge after external force can only be preserved when the loop has infinite input impedance. This is not the case, so it determines that piezoelectric sensors can only measure dynamic stress.Piezoelectric sensors are mainly used in the measurement of acceleration, pressure, and force. A piezoelectric accelerometer is a commonly used accelerometer. It has the advantages of simple structure, small volume, lightweight, long service life, and so on. The piezoelectric accelerometer has been widely used in aircraft, automobile, ship, bridge, the vibration of building and impact measurement, especially the shape of the piezoelectric sensor has its special position in the field of aviation and aerospace. It can also be used to measure the internal combustion pressure and vacuum of the engine. Moreover, it can be used in the military industry, for example, to measure the change in chamber pressure and the shock wave pressure at the muzzle of a gun bullet fired in the bore.It can be used not only to measure large pressure but also to measure small pressure. Piezoelectric sensors are also widely used in biomedical measurements. For example, ventricular catheterized microphones are made of piezoelectric sensors. Because the measurement of dynamic pressure is so common, piezoelectric sensors are widely used. In addition to piezoelectric sensors, there are piezoresistive sensors made by piezoresistive effect, strain sensors using strain effect, etc. These different pressure sensors can play their unique uses in different situations by using different effects and materials.FAQ1. What sensor means?a device that responds to a physical stimulus (such as heat, light, sound, pressure, magnetism, or a particular motion) and transmits a resulting impulse (as for measurement or operating a control) .2. What is the purpose of a sensor?A sensor converts the physical action to be measured into an electrical equivalent and processes it so that the electrical signals can be easily sent and further processed. The sensor can output whether an object is present or not present (binary) or what measurement value has been reached (analog or digital).3. How do sensors work?Put simply, a sensor converts stimuli such as heat, light, sound and motion into electrical signals. These signals are passed through an interface that converts them into a binary code and passes this on to a computer to be processed.4. What can sensors detect?Broadly speaking, sensors are devices that detect and respond to changes in an environment. Inputs can come from a variety of sources such as light, temperature, motion and pressure.5. What are the importance of sensors in our daily life?Intelligent sensor systems are omnipresent in our everyday lives. They provide security, save lives and improve our quality of life. As more and more areas of life are automated and networked, the importance of innovative sensor technologies will also increase in the future.6. How do we classify sensors?Classification of Sensors:Active and Passive Sensors. Contact and Non-Contact Sensors.Absolute and Relative Sensors.Analog and Digital Sensors.Miscellaneous Sensors.7. How are sensors used to collect data?With a sensor, a machine observes the environment and information can be collected. A sensor measures a physical quantity and converts it into a signal. Sensors translate measurements from the real world into data for the digital domain.8. What is the difference between sensor and transducer?The main difference between sensor and transducer is that a transducer is a device that can convert energy from one form to another, whereas a sensor is a device that can detect a physical quantity and convert the data into an electrical signal.9. Why do we need a temperature sensor?Within our homes, temperature sensors are used in many electrical appliances, from our refrigerators and freezers to help regulate and maintain cold temperatures as well as within stoves and ovens to ensure that they heat to the required levels for cooking, air confectioners/heaters.10. How sensors are connected?A sensor device directly connected to a computer. A connected sensor is a sensor that also has a way to send data to either a local network or the Internet. Diagram of a sensor receiving waves on the left and broadcasting a wireless signal on the right to a router. A sensor device wirelessly connected to a network.11. Can a transducer be a sensor?A Sensor is defined as a device which measures a physical quality (light, sound, space) and converts them into an easily readable format. If calibrated correctly, sensors are highly accurate devices. Not all transducers are sensors but most sensors are transducers.12. What is the difference between active and passive sensors?Active sensors have its own source of light or illumination. In particular, it actively sends a pulse and measures the backscatter reflected to the sensor. But passive sensors measure reflected sunlight emitted from the sun. When the sun shines, passive sensors measure this energy.13. What are the basic characteristics considered in the process of sensor selection?Sensor selection criteria include temperature, size, protection class, and whether the sensor requires a discrete or analog input. Also consider sensor repetition accuracy, sensor response speed, and sensing range.14. What are the applications of sensors?Sensors are central to industrial applications being used for process control, monitoring, and safety. Sensors are also central to medicine being used for diagnostics, monitoring, critical care, and public health.15. How do you check the accuracy of a sensor?To find out the accuracy of sensor you have to take several readings by your sensor on that particular one input parameter (like. temperature). after accumulating those sensor output values evaluate the standard deviation as per law, which indicate the accuracy level of your sensor.