Refers to a special instrument made according to the characteristics of fingerprints. The characteristics of fingerprints are that they are all different and lifelong. The foot fingerprint, the palm print, the palm print, the lip print, and the texture of the retina at the bottom of the pupil also have the above characteristics. But there is no fingerprint accuracy, such as palm print is easy to wear and aging. This feature of the fingerprint can be used as an "identity card" for the person. In addition to distinguishing criminals, it can be used for credit cards to prevent counterfeiting; a magnetic card can be used as a pass, and it can be used in a confidential place where cards are released. In the thousands of fingerprint cards, the fingerprints of specific people are checked. The international level is 3,000 cards per person per day, and the electronic computer is used overnight.
Currently, there are three types of fingerprint acquisition devices commonly used, such as optical, capacitive/inductive, and bio-RF. Among them, the optical fingerprint collector is the earliest fingerprint collector, which is the most commonly used, and there is also a collector that replaces the prism and the lens system with a grating lens. Some of the photoelectric conversion CCD devices have been replaced with CMOS imaging devices, thereby omitting the image acquisition card to directly obtain digital images.
1. The optical fingerprint collector has a long use time; it collects a fingerprint surface texture image. The finger contacts the surface of the prism, the light-emitting diode provides a light source, and the image is acquired by a charge coupled device integrated circuit. The optical fingerprint sensor is reliable and the price is very cheap, but the fingerprint image recognition rate of the cover on the dirty finger and the dry finger surface is very low, and the adaptability to environmental factors such as temperature is poor. However, due to the limitation of the optical path, the distortion-free collector is large in size. There are usually more serious optical distortions; the surface of the collection window often has traces left behind. CCD devices may be aging due to their age, and have defects such as reduced image quality and false fingerprints.
Due to the limitation of the fingerprint collection principle, the optical fingerprint collector is difficult to collect clear fingerprint images on the dry fingers, which causes the problem that the recognition rate of the dry finger is low (the rejection rate is high). The more dry your fingers, the more prominent the problem. In northern winter weather conditions, dry fingers can cause many people's fingers to be unrecognizable. This problem is particularly prominent in the northern region.
Applying a film on the surface of the glass can improve the problem of dry fingers, but the film itself is not very durable, and the use of the film makes the problem of false fingerprints more serious.
Because of the cost advantage, the fingerprint-based attendance attendance machine based on optical principle is quite popular in China (the difference between access control and attendance is only in the management software), and even can be said to account for most of the market share. However, due to the existence of artificial fingerprints, its use in financial systems, especially in Treasury, is not safe. Some of the fingerprint products of the early installation of the banking system are optical fingerprint collectors. At that time, people still didn't know enough about the seriousness of artificial fingerprints, and there were not many examples of fake fingerprints in the early days of fingerprint products. However, with the popularity of fingerprint technology, the use of fake fingerprints by criminals will also increase. Fingerprint projects in the financial system generally exclude optical fingerprinting technology, and some banks even explicitly banned use. However, some banking systems still use fingerprint control of some optical technologies for a variety of reasons: 1) The winter in the south is not very cold, the fingers are not very dry, and the problem of dry fingers is not very prominent. 2) Price factor 3) Insufficient understanding of optical technology 4) Human factors of the project.
2. The second evolutionary stage is the thermal sensor. The basis of the fingerprint surface image is that the fingerprint ridges and grooves change with the heat of the emitted heat. In a typical thermal sensor, a small heating element is directly attached to a set of thermal sensing elements. Because the "read" fingerprint is the first element, the ridges and grooves are heated. The heat sensing has no difference in detecting the temperature of the ridge and groove and the composite fingerprint composite image. Although cheap and small, it consumes more energy than other competing technology thermal sensors, and image collection is unclear in hot environments or hot weather.
Capacitive sensor technology uses alternating commands and arrays and sensor boards. The alternating plates are in the form of two capacitive plates, and the valleys and ridges of the fingerprint become the dielectric between the plates. A sensor of constant dielectric between the two detects changes to generate a fingerprint image. Manufacturing DC capacitive sensors uses the same procedures and silicon materials as standard integrated circuits to reduce thickness and power requirements. Capacitive technology provides better image quality over a wider operating range than thermal sensors. Because its collection range is relatively large, the cost of capacitor technology is higher than the previous two technologies. Since the surface of the capacitive sensor is made of a dielectric material, it is easily damaged and has poor sensitivity to dirty fingers.
3, bio-radio fingerprint identification technology, RF sensor technology is to emit a small amount of radio frequency signal through the sensor itself, penetrate the skin layer of the finger to control the texture of the inner layer to obtain the best fingerprint image. Therefore, the fingers of dry fingers, Chinese fingers, dry fingers, etc. can pass up to 99.5%, and the ability of anti-counterfeiting fingerprints is strong. The recognition principle of fingerprint sensors only responds to human skin, which fundamentally eliminates the problem of artificial fingerprints. Warm zone: Suitable for areas that are particularly cold or particularly hot. Because RF sensors produce high quality images, RF technology is the most reliable and powerful solution. In addition, high-quality images allow for the reduction of sensors without sacrificing the reliability of authentication, thereby reducing costs and allowing the application of RF sensor ideas to any field where mobility and size are unconstrained. RF sensor: It works very well. It consists of an array of RF and sensitive components. Each member is actually an equivalent small antenna that transmits waves through the human finger to the inner layer of the skin (the dermis). . The receiving part of the component demodulates the phase of the returned wave, and the phase difference reflects the fingerprint texture. In a sense, its principle is similar to that of radar, so it is called RF sensor. Moreover, it automatically adjusts internal electrical parameters to accommodate changes in finger dryness, finger pressure, age, and more. Due to its unique working principle, the fingerprint image collected corresponds to the living fingerprint of the finger inside the finger, which is not directly sensitive to the outer skin of the finger surface, and some dirt, oil stains, dust and other substances on the surface. Has the ability to penetrate. Its special working principle makes it possible to capture ideal images for all types of fingers under various conditions of use, thus providing significant superior performance. Dry fingers are a common problem encountered with other types of sensors, but this sensor can be a good solution to this problem.
Because it only works on living skin, this sensor has a good ability to identify artificial fingerprints. It is the best anti-counterfeiting fingerprint in all fingerprint sensors in the world. The popularity of such fingerprint sensors in foreign countries is quite high, and it has been applied in the built-in fingerprint technology of computers and mobile phones, advanced fingerprint locks, and banking systems in China. (Note that some of the built-in fingerprint collectors on the computer are capacitive, and the performance differs greatly from the RF principle.
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