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Classification and Application of UV Sensor
Alan   utmel.com   2021-10-21 17:36:58

Topics covered in this post:

What is a UV sensor?

Structural classification of UV sensors

Applications of the UV sensor

What is a UV sensor?

The UV sensor is also called the ultraviolet photosensitive tube, which is a photoelectric tube that uses the photoelectron emission effect. Its characteristics are that it only responds to ultraviolet radiation below 300nm, has high sensitivity, high output, high response speed, etc... And it has strong anti-interference ability, stability and reliability, long life, and low power consumption.

UV Sensors.jpg

UV Sensors

With the widespread application of electronic computers, various sensing technologies serving computers have received more and more attention. The UV sensor can detect ultraviolet rays that are not detectable by the human senses and can avoid the interference of sunlight, lights, and other common light sources. It is very useful for the detection of fires, flameout protection, and photoelectric control in special places.

Structural classification of UV sensors

UV sensors can be divided into spherical, wire-shaped, and flat-shaped structures according to the shape of the cathode. They are all the electrode structure forms of diodes. The shape and material type of the housing are designed for user requirements.

1. Wire electrode structure

The electrode of this type of UV sensor is generally composed of two or more symmetrical metal wires. This is an early structure of ultraviolet sensors. High-purity tungsten wires or platinum wires are often used. The parallel lines near the distance are the working area.

Since the UV sensor relies entirely on the photoelectron emission effect on the electrode surface and then uses gas multiplication to obtain a stronger signal, its spectral response range depends on the work function of the cathode material.

The characteristic of this kind of UV sensor is that it can work in an AC state, the working current is large, the circuit is simple, and the impurities on the electrode surface can be removed by appropriate processing. But, the viewing angle sensitivity is relatively large, and the working area is prone to uneven emission.

2. Spherical cathode structure

In order to fully avoid the tip effect and make the photoelectron emission more stable and uniform, it is necessary to fix the working area on the cathode, because the UV sensor relies on photoelectron emission and gas multiplication to complete the conversion of optical signals into electrical signals and amplify them. In the near area, the utilization rate of light emission is the highest. Therefore, an ultraviolet sensor with a dot structure spherical cathode is designed, and its structure is shown in the figure.

No matter from which angle the photons radiate to the hemispherical cathode, the discharge area is always on the hemispherical vertex close to the anode. Because the effective area of the cathode is small, the working current of the tube is generally less than 0.3mA, but its viewing angle is wider and the viewing angle sensitivity is relatively uniform, which is especially suitable for fire forecasting places.

3. Flat cathode structure

The sensitivity of the UV sensor depends on the number of photons received from the far-ultraviolet radiation on the cathode. The larger the area of the cathode, the higher the probability of reception, so that more electrons on the cathode will escape and be accelerated under the action of an external high-voltage electric field. And it will collide with the gas molecules in the tube to ionize the gas molecules, and the electrons generated after ionization collides with the gas molecules, so that the cyclic motion will eventually discharge the gas in the tube. The chance of this avalanche discharge depends on the photoelectron emission effect on the cathode. In order to improve the sensitivity, a kind of UV sensor with a flat cathode structure has been developed in recent years.

Various structures of UV sensors.jpg

Various structures of UV sensors

Applications of the UV sensor

UV(Ultraviolet) is the general term for radiation with wavelengths from 10nm to 400nm in the electromagnetic spectrum. According to different wavelengths, ultraviolet rays are generally divided into three bands: A, B, and C, as follows: UVA is 400-315 nm, UVB is 315-280 nm, and UVC is 280-100 nm. Corresponding to different wavelengths, specific applications are different.

In UVLED market applications, UV-A has the largest market share, up to 90%. Its main application market is curing, which involves nail art, teeth, ink printing and other fields. In addition, UV-A also introduces commercial lighting, which can make white clothes look whiter. As for UV-B and UV-C, they are mainly used in sterilization, disinfection, medical light therapy, etc. Among them, UV-B is mainly used for medical treatment, and UV-C is used for sterilization and disinfection. UV LED has been applied to photoresin hardening, insect trapping, printing from banknote recognition, and the development of biomedical, anti-counterfeiting, air purification, data storage, and military aviation fields towards sterilization and disinfection markets, etc...

A UVB ultraviolet sensor.jpeg

A UVB ultraviolet sensor

1. Application fields in the light-curing system

Typical applications of the UVA band are UV curing and UV inkjet printing. The representative wavelengths are 395nm and 365nm. UV LED light curing applications to include the curing of UV adhesives in the display, electronic medical, instrumentation, and other industries. Among them, the UV LED decorative panel industry has become a hot spot. The biggest advantage is that it can produce zero-formaldehyde environmentally friendly panels and save 90% of energy. It has the advantages of large output, coin scratch resistance, comprehensive benefit, and economy. This means that the UV LED curing market is an all-around and full-cycle application product market.

Microelectronics industry-UV curing applications

Mobile phone component assembly (camera lens, earpiece, microphone, housing, liquid crystal module, touch screen coating, etc.), hard disk head assembly (gold wire fixing, bearing, coil, chip bonding, etc.), DVD/digital camera (lens, lens adhesion Connection, circuit board reinforcement), motor and component assembly (wire, coil fixing, coil end fixing, PTC/NTC component bonding, transformer core protection), a semiconductor chip (anti-moisture protective coating, wafer mask, wafer Pollution inspection, UV tape exposure, wafer polishing inspection), sensor production (gas sensor, photoelectric sensor, fiber optic sensor, photoelectric encoder, etc.).

LEDUV curing application in the PCB industry

Components fixing(capacitors, inductors, various plug-ins, screws, chips, etc.), moisture-proof potting and core circuit, chip protection, anti-oxidation coating protection, circuit board conformal (corner) coating, ground wire, flying wire, coil Fixed, wave soldering through-hole mask.

Light resin hardening application

At present, UV-curable resins are mainly used for wood floor coatings, plastic coatings (such as PVC decorative boards), photosensitive inks (such as plastic bag printing), electronic product coatings (marking and circuit board printing), printing and glazing (such as paper, playing card polishing), metal parts (such as motorcycle parts) coating, optical fiber coating, photoresist and precision parts coating, etc.

2. Medical field

Skin treatment

An important application of the UVB band is the treatment of skin diseases, that is, the application of ultraviolet light therapy. Scientists have found that ultraviolet rays with a wavelength of about 310nm have a strong dark spot effect on the skin, which can accelerate skin metabolism and improve skin growth. Therefore, in the medical industry, ultraviolet light therapy is currently more and more used.

Compared with traditional light sources, the spectrum of UV-LED is pure, which can guarantee the treatment effect to the greatest extent. UVB band can also be used in the field of health care. UVB band irradiation can cause photochemical and photoelectric reactions of the human body and produce a variety of active substances in the skin. It is currently used to regulate advanced nerve functions, improve sleep, and lower blood pressure.

Studies have shown that the UVB band can accelerate the production of polyphenols in certain leaf vegetables (such as red lettuce). These polyphenols are claimed to have anti-cancer, anti-cancer spread, and anti-cancer mutation properties.

Medical instruments

UV glue bonding makes the economical and automated assembly of medical devices easier. Now, the advanced LED UV light source system, which can cure UV glue without solvent in a few seconds, and the dispensing system, make the medical device assembly process form an effective and economical method of consistent and repetitive bonding.

The optimization and control of UV light sources are very important for the manufacture of reliable medical devices. The use of UV-curing glue provides many advantages, such as lower energy requirements, saving curing time and location, increasing productivity, and easier automation.

UV glue is generally used to bond and seal medical devices, which require very high quality and best reliability. UV glue curing is typically used in the assembly of medical devices, such as bonding 1) different materials (or different mechanical properties) 2) the material is not thick enough to use welding methods 3) pre-production of components.

3. Field of sterilization and disinfection

Due to the short wavelength and high energy of UVC band ultraviolet rays, it can destroy the molecular structure of DNA (deoxyribonucleic acid) or RNA (ribonucleic acid) in microbial organisms (bacteria, viruses, spores, and other pathogens) in a short time. UVC band products can be widely used for sterilization and disinfection of water and air.

Because UV-LED has the advantages of small size, it can be used as the light source of a complete set of UV (ultraviolet) sterilization equipment, which is suitable for the pre-packaging process of mass production of various shapes and structures, and materials. It can be used as an indoor air killer. The UV (ultraviolet) light source of the bacteria machine: suitable for indoor air sterilization and disinfection in households, public places, etc...

4. Flame detection field

UV flame detectors detect fires by detecting ultraviolet rays generated by the burning of substances. In addition to ultraviolet flame detectors, there are infrared flame detectors on the market, which are termed linear beam smoke detectors. Ultraviolet flame detectors are suitable for places that are prone to open flames when a fire occurs. UV flame detectors can be used in places where there is strong flame radiation or no smoldering stage when a fire occurs. The flame detection ultraviolet sensor requires the sensor itself to be resistant to high temperatures.

5. Arc detection field

High-voltage equipment will produce arc discharge due to insulation defects, which will be accompanied by a large amount of light radiation, which contains rich ultraviolet light. By detecting the ultraviolet light radiation generated by arc discharge, the safe operation of high-voltage power equipment can be judged. Ultraviolet imaging is an effective arc discharge detection method, which is intuitive and has good detection and positioning capabilities. However, the signal of ultraviolet light is relatively weak and there are some difficulties in detection.

6. Banknote recognition

Ultraviolet recognition technology mainly uses fluorescent or UV sensors to detect the fluorescent imprinted anti-counterfeiting marks of banknotes and the matte response of banknotes. This type of identification technology can identify most counterfeit currency (such as washed, bleached, and pasted banknotes). This technology is not only used in the recognition of deposits in ATM machines, but also in financial machines such as currency counters and currency detectors. Under normal circumstances, fluorescence and UV are used to carry out all-round reflection and transmission detection of banknotes. According to the different absorption and reflectivity of banknotes and other papers to ultraviolet light, the authenticity can be distinguished. Quantitative identification can also be performed on banknotes with fluorescent imprints.

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