Fingerprint locks are more and more widely used on doors. As part of fingerprint locks, fingerprint sensors have three types: optical fingerprint sensor, semiconductor fingerprint sensor, scratching fingerprint sensor.
Optical Fingerprint Sensor
Optical fingerprint sensor is a mature sensor with relative long history. It casts fingerprint image into CMOS image sensing chip through triple prism and convex glass, then after electric signal treatment, the image data is turned into electric signal. Then it extracts the characteristic value by unique arithmetic. The matching and calculating of the fingerprint is made according to the unique arithmetic and with the characteristic value.
Optical fingerprint sensor needs lighting when collecting fingerprint. This is why we see the light when fingerprint sensor is working. The light usually is red, green or blue. Some people think blue is good, red is not good, etc, actually it has no relation to what color, but the image resolution and arithmetic. While the image resolution has relation to the quality of hardware and chip, and the arithmetic of North Korea is best. Among the manufacturers of the module, some directly use the arithmetic of North Korea, and some buys the arithmetic authority of other factories. Only few manufacturers develop sensors by themselves.
Optical fingerprint sensor is widely used because its good applicability, and recognition rate for unclear fingerprint is higher(depends on different factories), and cost is in middle level. But its shortage is big volume and thickness so that the front lock body cannot be thin.
Semiconductor Fingerprint Sensor
Semiconductor fingerprint sensor, no matter capacitance or inductance, share the same principle, on a pad which integrated with thousands of semiconductor devices, when a finger is touching the pad, it forms the other side of the capacitance (inductance). Because a finger surface is rough and uneven, and the bump and pit have different distance to the pad, so it will create different capacitance or inductance value. On basis of this theory, the device collects the different value and finish the fingerprint collection.
Generally, semiconductor fingerprint sensor adopts capacitance sensing technology. While inductance type sensor is easily be shot through by static electricity, and it gradually dies out. Capacitance type sensor, because of its small volume and thin features, it can be used on small equipment, also on fingerprint lock.
This kind of fingerprint sensor has better adaptability to a finger. and the fingerprint recognition capability, each has its own merits compared with that of optical sensor. The cost will be much higher than optical sensor and generally used on high class fingerprint lock. The advantage is that it can make the front plate of the fingerprint lock be thin and of small volume. The disadvantage is surface is fragile and easy to be broken.
Scratching Fingerprint Sensor
Scratching fingerprint sensor is the smallest fingerprint sensor, which requiring user to scratch his finger on sensor surface slightly and gain the fingerprint data. Because of its small volume, it is used on mobile, notebook, PAD etc.
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