Xiaomi Mi 15 comes standard with ultrasonic fingerprint unlocking? Analysis of the differences between the four fingerprint unlocking methods

Zhongguancun Online

2024-06-28 12:02Zhongguancun Online Official Account

At present, there are 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 is the difference 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-throw fingerprint unlocking and ultra-thin fingerprint unlocking.

Since the short-throw fingerprint is thicker than the ultra-thin fingerprint, in order to increase the capacity of the battery, the position of the battery is often avoided and the fingerprint is placed at the bottom of the phone. This makes the thumb unlock uncomfortable. Many mobile phones are equipped with short-throw fingerprints, mostly to save costs and increase battery capacity.

And the optical fingerprint will be filled with light when unlocking, and unlocking the phone at night will have a very dazzling light, and the experience is not good.

Capacitive sensors to detect the ridges and valleys of fingerprints. When a finger is placed on a sensor, the electrodes on the sensor come into contact with the skin, forming tiny capacitances. Different parts of the fingerprint (ridges and valleys) are different at different distances from the sensor, forming different capacitance values, which allows the fingerprint image to be generated.

Capacitive fingerprint is the first fingerprint recognition, and now mobile phones integrate fingerprint recognition on the power button, but more and more mobile phones no longer use capacitive fingerprints, why is this happening?

There are two types of mobile phones that can be unlocked with a capacitive fingerprint: those with an LCD screen and those with a folding screen. The LCD screen is thick, the light transmittance is not high, and it cannot be unlocked with an under-screen fingerprint; The folding screen is also to reduce the thinness, after all, the optical fingerprint unlock still has a thickness under the screen, and the inner and outer screens of the folding screen each have a fingerprint unlock, it is better to do a capacitive fingerprint directly, which does not increase the thickness of the screen, and can also solve the unlocking of the inner and outer screens with a capacitive fingerprint.

There is a disadvantage, many consumers think that the cost of capacitive fingerprints is low, not high-end enough, and it is easy to touch it by mistake when it is in the trouser pocket.

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

Ultrasonic technology uses sound waves to detect 3D details of fingerprints. The ultrasound waves pass through the surface layer of the skin, and the reflected signal is picked up by the sensor, creating an accurate fingerprint model.

In addition, the thickness of ultrasonic is only 0.17mm, which is much thinner than traditional ultra-thin fingerprints, and the recognition speed has also been improved, but the recognition area of Goodix's single-point ultrasonic fingerprint unlocking is much smaller than that of many ultra-thin fingerprints.

In addition, the ultrasonic signal may not be effective in penetrating thicker screen protectors, especially tempered glass films. The thickness of these films (typically 300 to 400 microns) is sufficient to prevent the ultrasound signal from reaching the fingerprint, affecting the recognition performance. However, I don't know if the current ultrasonic fingerprint unlocking will be improved.

It is undeniable that ultrasonic will be the standard configuration of the flagship in the future, and after the cost drops, it will gradually be degraded to the sub-flagship.

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