The patent number granted to Apple by the US Patent and Trademark Office is NO. 9,772,721,named "pressure sensing and touch sensing based on ultrasonic wave". According to the description of the patent certificate, this is a method to measure the input pressure by emitting and detecting ultrasonic pulses. More precisely, the system can measure the interaction between the above pulse and the user's finger.
In some examples, the pressure sensors may be ultrasonic elements arranged in rows and columns, or a plurality of independent sensors arranged in a preset arrangement, which may generate and receive ultrasonic waves.
Ultrasonic waves are first emitted to a screen area or an interactive surface that a user's finger may touch. Ultrasonic waves or pulses first pass through the sensing layer or information input panel, and then are reflected by the user's fingers or other objects in contact with the surface.
The reflected pulse can be used to judge the distance between the finger (or other object for inputting information) and the sensor, and then used to calculate the pressure. Attenuation, that is, the number of pulse signals absorbed by the touching object, can also be used to judge the pressure.
For example, when the finger presses the screen harder, the contact surface will increase and a larger proportion of pulse information will be absorbed. These data can be used to improve the calculation accuracy of input pressure.
According to Apple's patent, this pressure sensor array can be used with other sensing devices (such as capacitive touch sensors), and these devices may also act as reflective surfaces. In addition to detecting the input position, the capacitive layer can also be used to detect the pressure parameters of multiple simultaneous pressing operations.
More importantly, this pressure sensing device can be placed below or above the display screen of the equipment. For example, putting the ultrasonic sensor on the screen can be made transparent or placed in a place that will not block the user's line of sight. This method is different from the 3D touch pressure sensing system currently used by Apple in iPhone, which stacks multiple component layers under the display screen of smart phone.
The current 3D touch system can measure and locate the subtle capacitance changes between the iPhone glass panel and the hard metal sensor layer embedded in the iPhone backlight array. When the user presses the glass panel, the distance between the system and the sensor will decrease, resulting in a decrease in capacitance.
In addition, a single multi-touch capacitive sensor located above the display screen improves the accuracy of 3D touch. When the user clicks on the screen or uses gestures, the sensor can detect the position where the finger presses the screen. The precise vibration generated by the tactile feedback module Taptic Engine further enhances the sensitivity of 3D Touch.
Although 3D Touch can produce extremely accurate results, its design is very complicated and takes up valuable internal space of the device. Due to space considerations, Apple did not use the off-screen fingerprint identification system on the iPhone X.
Before the release of iPhone X, there were rumors that Apple wanted to keep the fingerprint reader as a backup authentication method when the face recognition scheme failed. But now it seems that the company completely canceled the touch ID and switched to the Face ID.
But in any case, the patent obtained by Apple today can solve the technical obstacles faced by off-screen fingerprint identification, and it seems to be more accurate and powerful than thin film.