Before the popularization of mobile phone fingerprint unlocking technology, as long as it is mentioned that “fingerprint scanning”, people’s mind is the picture of “007 going deep behind the enemy to perform secret task unlocking mechanism”. Nowadays, it seems that everyone, from heads of state to ordinary people, has a smart phone that can unlock fingerprints (fingerprint unlocking is divided into two types, one is capacitive and the other is optical sensing). But how does fingerprint sensor work in fingerprint unlocking and how does it spread to consumer mobile devices?
In fact, the working principle of ordinary fingerprint recognizer is actually very simple. It relies on capacitive sensing, just like touch panel and touch screen. Their working principle is to detect the charge difference between your skin and the mobile phone screen when the conductive bottom layer of your skin touches the screen. Fingerprint sensors use this idea for identity recognition.
In fact, under their surface, there are a lot of micro capacitor plates, which are thinner than the ridges of fingerprints. When you press your fingertip on the recognizer, the sensor can recognize your finger ridge, which part is pressed and which part is not. Because these small “gullies” are farther away from the sensor, the capacitance detected by the wechat capacitor board will become lower. The recognizer can form a virtual image of the ridge through the difference in these capacitances.
For fingerprint technology, in fact, fingerprint scanners have appeared on mobile phones since 2007, but it began to catch fire after Apple released touch ID on iphone5s in 2013. However, there are other types of fingerprint recognizers on the market, such as optical scanners, which capture your fingerprint image in the same way as the traditional visible light. However, these devices are rare on portable devices because they are bulky.
In addition, there is an ultrasonic fingerprint recognizer, which may be the next dark horse. Its working principle is somewhat similar to the echo location of bats. This is how bats recognize the shape of objects in the dark. The recognizer will send out ultrasonic pulses, which will then hit your fingerprint ridge. Then, through the difference of reflected signals, the recognizer can scan a scanning image.
The advantage of ultrasonic sensor is not only that it has a loud name suitable for marketing, but also that it can work through other materials. Therefore, the ultrasonic fingerprint recognizer can be seamlessly embedded under the surface of the mobile phone, so that your mobile phone appearance fingerprint unlock is full of high-tech feeling. It is so handsome that there are no friends. Another more practical point is that it can penetrate the dirt and water on your hand during scanning, providing higher accuracy for fingerprint unlocking, which is much stronger than capacitive sensor.