After nearly 10 years of slow natural growth, fingerprint recognition technology is about to usher in a golden period of leapfrog development. Experts conservatively estimate that in the next five years, my country will have a market worth nearly 10 billion yuan waiting for enterprises to explore. At present, fingerprint recognition is mainly used in fields such as time attendance, access control, safes and cabinets. I believe that with the improvement of fingerprint recognition technology, it will be widely used in more fields such as ID cards, motor vehicles, and household appliances. So what are the main technologies for fingerprint recognition image acquisition?
Fingerprint recognition technology is a high-tech that uses the uniqueness and stability characteristics of fingerprints and integrates Sensor technology, biological technology, digital image processing, pattern matching, and electronic technology.
Development Trend of Fingerprint Recognition TechnologyThe huge market prospect of fingerprint recognition technology will have a huge impact on the international and domestic security industry. Smaller companies will face relentless competition from newcomers in traditional industries. In the face of these giants, it is difficult to say that the existing small and medium-sized companies have too much competitiveness. The industry reshuffle is inevitable. Mergers and exits may become the helpless choice of most small and medium-sized companies. Eventually, a situation where companies or large capitals in traditional industries dominate the biometric identification industry in a relatively short period of time may be formed. Of course, it is not ruled out that some companies with core competitiveness have grown into emerging large companies in the way of "fast fish eating slow fish". "Big fish" and "fast fish" coexist, which is also the inevitable result of every emerging market. The result of competition will form a new big industry.
The civilian market opportunity of fingerprint recognition technology already exists, so is there a time for large-scale application? It depends on whether the fingerprint product's consumer awareness, product stability and price can be resolved. That is to say, whether fingerprint recognition technology can be applied on a large scale in the civilian field requires three conditions: sufficient audience awareness, stable product quality and good service and guarantee, and the profit of the product is large enough.
The consumer awareness of fingerprint products here mainly refers to people's understanding of the application of fingerprint recognition technology. People here include manufacturers, distribution agents, engineering companies and direct users. An interesting example is that fingerprints are required for access control, and more than 80% are direct user requirements. Most of the access control manufacturers, distribution agents, engineering companies and other middlemen do not actively recommend products. This is fingerprint recognition. The biggest problem that cannot be applied on a large scale is a manifestation of low consumer awareness.
The stability of the product requires fingerprint manufacturers to have a deeper understanding of the security industry, and the fingerprint products developed must comply with usage specifications and meet most of the requirements and service guarantees.
Product price is very important, especially in the product development stage. Some users will say that even if the product is stable and the price is not appropriate, don’t use it! The results of the analysis, take the mid-range route, maximize the strengths and avoid weaknesses, and give full play to the absolute competitive advantage of the product in the market terminal. This is the foundation of invincibility in the civilian market .
Fingerprint recognition technology typeThere are four main types of fingerprint image acquisition technologies: optical scanning devices (such as micro-prism matrix), temperature-sensitive fingerprint sensors, semiconductor fingerprint sensors, and ultrasonic fingerprint scanning.
Optical recognition technologyUsing optical technology to collect fingerprints is the oldest and most widely used technology. Place your finger on the optical lens, and use a prism to project your finger on the charge coupled device (CCD) under the illumination of the built-in light source to form ridges (the lines with a certain width and direction in the fingerprint image) that are black and valleys. The line (the concave part between the lines) is a white digitized multi-gray fingerprint image that can be processed by the fingerprint device algorithm.
The optical fingerprint collection technology has obvious advantages: it has been tested for a long time, adapts to temperature variation to a certain extent, can reach a higher resolution of 500DPI, etc. The most important thing is its low price. There are also obvious shortcomings: due to the requirement of a sufficiently long optical path, a sufficiently large size is required, and too dry and too greasy fingers will also deteriorate the effect of optical fingerprint products.
The limitations of optical fingerprint sensing are reflected in potential fingerprints (potential fingerprints are left after the finger is pressed on the platen), which will not only reduce the quality of the fingerprint image, but may also cause the overlap of the two fingerprints in severe cases. Obviously, it is difficult to satisfy Actual application needs. In addition, the platen coating and the CCD array will wear out over time, which may cause the quality of the captured fingerprint image to decrease. However, it has disadvantages such as inability to perform live fingerprint identification and poor applicability to wet and dry fingers.
Since the optical fingerprint recognition system cannot penetrate the surface of the skin (dead skin layer), it can only scan the surface of the finger skin, or scan the dead skin layer, but cannot penetrate deep into the dermis. In this case, the cleanliness of the finger surface directly affects the recognition effect. If a lot of dust is stuck on the user's finger, there may be an error in recognition. And if people follow their fingers and make a fingerprint
For example, in the case of the prison escape in Inner Mongolia at the end of last year, the escaped prisoner cut off the guard’s finger to verify the optical fingerprint machine to open the prison entrance. Recently, the major media have rushed to report that you can buy silicone fingerprints for about 100 yuan on Taobao. It can be easily verified through the optical fingerprint machine, and office workers use it to print fingerprints and attendance.
In addition, there is a prism in the optical sensor, and its volume is relatively large, generally several times or even 10 times the size of a semiconductor, which limits its application in small devices. There is no problem of size limitation when used on large devices such as attendance machines and access control, but when used on U disks, mobile hard drives, and handheld devices, the size becomes the biggest obstacle. Low cost has always been regarded as the biggest advantage of optical sensors, but because the consistency of its manufacturing process is difficult to guarantee, with the large-scale development of semiconductor sensors represented by capacitive sensors, the cost advantage of optical sensors is no longer obvious. Although most companies are still using optical sensors, their development trend is novel, high-quality semiconductor capacitive fingerprint sensors.
Temperature difference induction type recognition technologyThe temperature difference sensing recognition technology is made based on the principle of temperature sensing. Each pixel is equivalent to a miniaturized charge sensor, which is used to sense the temperature difference between the finger and the image area of ​​the chip to generate a representative image information. Electrical signal.
Its advantage is that the fingerprint image can be obtained within 0.1s, and the sensor has the smallest volume and area, that is, the currently commonly referred to as sliding fingerprint identification device adopts this technology. The disadvantage is: subject to temperature limitations, after a long time, the finger and the chip are at the same temperature.
Semiconductor silicon sensing technology (capacitive technology)In the late 1990s, the technology based on the semiconductor silicon capacitor effect became mature. The silicon sensor becomes one plate of the capacitor, and the finger is the other plate. The capacitance difference between the ridge and valley of the fingerprint line of the hand and the smooth silicon sensor is used to form an 8-bit grayscale image. The capacitive sensor sends out an electronic signal, which will pass through the surface of the finger and the dead skin layer to reach the living body layer (dermis layer) of the finger's skin, and directly read the fingerprint pattern. As it goes deep into the dermis, the sensor can capture more real data, is less susceptible to the influence of dust on the surface of the finger, improves the recognition accuracy, and effectively prevents recognition errors.
Semiconductor fingerprint sensors include semiconductor pressure-sensitive sensors, semiconductor temperature-sensing sensors, etc. Among them, semiconductor capacitive fingerprint sensors are the most widely used.
The semiconductor capacitance sensor judges which position is the ridge and which position is the ridge according to the difference between the ridge and ridge of the fingerprint and the capacitance formed by the semiconductor capacitive sensing particles. Its working process is to pre-charge the capacitive sensing particles on each pixel to a certain reference voltage. When the finger touches the fingerprint performance of the semiconductor capacitor, because the ridge is convex and the ridge is concave, according to the relationship between the capacitance value and the distance, different capacitance values ​​will be formed at the ridge and the ridge. Then use the discharge current to discharge. Because the ridge and yu have different capacitance values, their discharge speeds are also different. The pixels under the ridge (high capacitance) discharge more slowly, and the pixels under the ridge (low capacitance) discharge faster. Depending on the discharge rate, the positions of the ridges and ridges can be detected to form fingerprint image data.
Unlike optical equipment that uses manual adjustment to improve image quality, capacitive sensors use automatic control technology to adjust fingerprint image pixels and the sensitivity of the fingerprint's local range, and combine feedback information to generate high-quality images in different environments. Due to the local adjustment capability, even images with poor contrast (such as areas where the fingers are lightly pressed) can be effectively detected, and the sensitivity of these pixels can be increased at the moment of capture to generate high-quality fingerprint images.
The semiconductor capacitive fingerprint sensor has the advantages of good image quality, generally no distortion, small size, and easy integration into various devices. The electronic signal sent out will pass through the surface of the finger and the dead skin layer, reach the living body layer (dermis layer) of the finger skin, and directly read the fingerprint pattern, thereby greatly improving the security of the system.
The most important advantage of semiconductor silicon sensing technology is that it can achieve live fingerprint recognition. It can also obtain better image quality than optical technology on a smaller surface, and a resolution of 200-300 lines can be obtained on a surface of 1cm×1.5cm (the smaller surface also leads to a reduction in cost and can be integrated into more In a small device). Small size, low cost, high imaging accuracy, and low power consumption, so it is very suitable for use in security and high-end consumer electronic products, known as the second generation of fingerprint recognition technology after optics.
Semiconductor capacitive fingerprint sensors have complex manufacturing processes, many sensing units per unit area, including high-end, IC design technology, large-scale integrated circuit manufacturing technology, IC chip packaging technology, etc., so capacitive fingerprint sensors are almost all developed in countries where IC technology is developed. Or regions, such as the United States, Europe, Taiwan and other places design and manufacture. At present, only a few domestic manufacturers have the ability to produce semiconductor fingerprint sensors.
However, the semiconductor silicon sensor technology also has a disadvantage, that is, it will be interfered by static electricity, but it can be solved by grounding during installation. In the past, the cost was relatively expensive. In recent years, the cost has dropped significantly, and the cost of optical sensors is getting closer and closer. It is currently the most ideal fingerprint recognition technology. For example, the security access control system of high-risk security places such as bank vaults and prisons. The fingerprint machine using semiconductor silicon sensor recognition technology is used for the front-end live fingerprint recognition of the access control, instead of the traditional password, card swiping, and optical fingerprint machine, so as to truly achieve the uniqueness of identity recognition. , To ensure foolproof.
Ultrasonic technologyUltrasonic fingerprint collection is a new type of technology. Its principle is to use the ability of ultrasonic waves to penetrate materials and generate echoes of different sizes depending on the material (when ultrasonic waves reach the surface of different materials, they are absorbed, penetrated and reflected to different degrees ). Therefore, by using the difference in acoustic impedance between the skin and the air, the location of the fingerprint ridge and ridge can be distinguished. The ultrasonic frequency used by the ultrasonic technology is 1×104Hz-1×109Hz, and the energy is controlled to the extent that it does not damage the human body (the same intensity as the medical diagnosis). Ultrasonic technology products can achieve the best accuracy. It has low requirements for the cleanliness of fingers and surfaces, but its collection time will be significantly longer than the aforementioned two types of products, and it is expensive and cannot achieve live fingerprint recognition. Used sparsely.
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