Xiaomi Mi 15 will be standard on all series! Ultrasonic fingerprint science

There are currently two mainstream biometric unlocking methods for mobile phones: face recognition and fingerprint unlocking. Android generally chooses a wide variety of fingerprint unlocking: capacitive fingerprint unlocking, short-throw fingerprint unlocking, ultra-thin fingerprint unlocking and ultrasonic fingerprint unlocking. So what are the differences between these four types of fingerprint unlocking? What are the advantages and disadvantages of each? Optical fingerprint recognition uses light to capture an image of a fingerprint. A light source illuminates the finger, and then a camera captures the reflected light, creating an image of the fingerprint. There are two types of optical fingerprints: short-focus fingerprint unlocking and ultra-thin fingerprint unlocking.

1. Short-focus fingerprint unlocking

Since short-focus fingerprints are thicker than ultra-thin fingerprints, in order to increase battery capacity, the fingerprints are usually placed lower on the phone, making it uncomfortable to unlock with your thumb.

2. Optical fingerprint unlocking

Optical fingerprint unlocking will fill in the light, which will produce dazzling light when unlocking the phone at night, making the experience poor.

3. Capacitive Fingerprint Unlock

Capacitive fingerprint detects the ridges and valleys of the fingerprint through a capacitive sensor to generate a fingerprint image. The initial fingerprint recognition used capacitive fingerprints, but now mobile phones integrate fingerprint recognition on the power button, and the use of capacitive fingerprints is gradually reduced.

4. Types of mobile phones unlocked by capacitive fingerprint

There are two main types of mobile phones unlocked by capacitive fingerprint: equipped with LCD screen and folding screen. The LCD screen is thick and has low light transmittance, making it impossible to unlock with an under-screen fingerprint. In order to reduce the thickness of the folding screen, capacitive fingerprints are also used, because optical fingerprint unlocking still has thickness under the screen.

5. Disadvantages of capacitive fingerprint unlocking

Consumers think that capacitive fingerprints are low-cost, not high-end enough, and are easy to accidentally touch when placed in their trouser pockets.

6. Ultrasonic fingerprint unlocking

Ultrasonic fingerprint unlocking can solve the shortcomings of the above fingerprint unlocking methods, but the current technology cost is high and few manufacturers adopt it on a large scale.

Ultrasonic technology uses sound waves to detect the 3D details of fingerprints. Ultrasound waves pass through the surface layer of the skin and the reflected signals are picked up by the sensor to create an accurate fingerprint model. The thickness of Fenye's ultrasonic fingerprint is only 0.17mm, which is much thinner than traditional ultra-thin fingerprints, and the recognition speed has also been improved. However, the recognition area of ​​Goodix's single-point ultrasonic fingerprint unlocking is much smaller than that of many ultra-thin fingerprints. .

In addition, ultrasonic signals may not be able to effectively penetrate thicker screen protectors, especially tempered glass films. The thickness of these films (usually 300 to 400 microns) is enough to prevent ultrasonic signals from reaching the fingerprint, thus affecting recognition performance.

It is undeniable that ultrasound will be a standard feature of future flagships. After the cost drops, it will gradually be decentralized to sub-flagships.

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