Optical imaging equipment has the longest history, which can be traced back to the 1970s. Optical imaging equipment is based on the principle of total reflection (FTIR) of light. Light shines on the glass surface with fingerprints, and the reflected light is obtained by CCD. The amount of reflected light depends on the depth of ridges and valleys of the fingerprint pressed on the glass surface, as well as the grease and moisture between the skin and the glass. After hitting the valley through the glass, the light is totally reflected at the interface between the glass and the air, and the light is reflected to the CCD, while the light hitting the ridge is not totally reflected, but is absorbed or diffusely reflected to other places by the interface between the ridge and the glass, thus forming a fingerprint image on the CCD.
Crystal sensor has only recently appeared in the market, although it has appeared in the technical introduction article for nearly 20 years. These planes containing microcrystals draw fingerprint images by various techniques. The most common silicon capacitive sensor is designed to capture fingerprints by electronic metering. About 100000 capacitance sensors can be combined on the semiconductor metal array, and the outer surface is an insulating surface. When the user's finger is placed on it, the skin forms the other side of the capacitive array. The capacitance of the capacitor decreases due to the distance between the conductors, which refers to the distance between the ridge (near) and the valley (far) relative to the other pole. Another kind of crystal sensor is pressure sensitive, and the top layer of its surface is elastic pressure sensitive dielectric material, which is converted into corresponding electrical signals according to the external morphology (concave and convex) of the fingerprint. Other crystal sensors include temperature sensors, and fingerprint images can be obtained by sensing the temperature difference between ridges pressed on the equipment and valleys far away from the equipment.
Ultrasonic scanning is considered as a very good fingerprint imaging technology. Much like optical scanning laser, ultrasonic waves first scan the fingerprint surface. Then, the receiving device obtains its reflected signal, measures its range and obtains the depth of the ridge. Different from optical scanning, the dirt and grease accumulated on the skin have little influence on the image obtained at supersonic speed, so such an image is a true reflection of the actual ridge shape (concave and convex), which is more convenient for application.
In a word, each technology has its own advantages and disadvantages.
Dalian Xiaguang Electronic Engineering Technology Co., Ltd. was established in 1998, and won unanimous praise from customers with its professional service and technical team. Mainly engaged in attendance machine, fingerprint attendance machine, rice vending machine, fingerprint access control, monitoring system, hotel wireless ordering system, human resource management software, financial software, salary software, and various industry membership software. Secondary development can be carried out according to customer requirements. Long-term trade-in service saves unnecessary expenses for customers. Sales service hotline: 0411-3983358-818819.