The principle of surface acoustic wave touch screen

The principle of surface acoustic wave touch screen

1. Surface Acoustic Wave

Surface acoustic wave, a type of ultrasonic wave, is a wave of mechanical energy that propagates shallowly on the surface of a medium (such as glass or metal and other rigid materials). Through the wedge-shaped triangular base (strictly designed according to the wavelength of the surface wave), directional, small-angle surface acoustic wave energy emission can be achieved. The surface acoustic wave performance is stable, easy to analyze, and has very sharp frequency characteristics in the process of transverse wave transmission. In recent years, it has developed rapidly in the direction of non-destructive flaw detection, imaging and de-wave. The theoretical research of surface acoustic wave, semiconductor materials, acoustics Technologies such as guiding materials and testing technology are quite mature. The touch screen part of the surface acoustic wave touch screen can be a flat, spherical or cylindrical glass plate, which is installed in front of the CRT, LED, LCD or plasma display screen. The upper left corner and the lower right corner of the glass screen are respectively fixed with vertical and horizontal ultrasonic transmitting transducers, and the upper right corner is fixed with two corresponding ultrasonic receiving transducers. The four peripheries of the glass screen are engraved with very precise reflection stripes with 45° angles ranging from sparse to dense.

2. Working principle of surface acoustic wave touch screen

Take the X-axis transmitting transducer as an example: The transmitting transducer converts the electrical signal sent by the controller through the touch screen cable into sound wave energy and transmits it to the left surface, and then the sound wave energy is transferred by a set of precision reflection stripes under the glass plate Reflected into an upward uniform surface, the sound wave energy passes through the surface of the screen, and then is gathered into a rightward line by the upper reflection fringe and propagates to the X-axis receiving transducer. The receiving transducer changes the returned surface acoustic wave energy into electric signal. When the transmitting transducer emits a narrow pulse, the sound wave energy arrives at the receiving transducer through different paths. The one on the far right is the earliest to arrive, and the one on the far left is the last to arrive. The early and late sonic energy is superimposed into one With a wider waveform signal, it is not difficult to see that the received signal gathers all the acoustic energy returning from different paths in the X-axis direction. The distance they travel on the Y-axis is the same, but on the X-axis, the farthest The closest one traveled twice the maximum distance on the X axis. Therefore, the time axis of this waveform signal reflects the position before the superposition of the original waveforms, which is the X-axis coordinate. Waveforms of transmitted signal and received signal When there is no touch, the waveform of the received signal is exactly the same as the reference waveform. When a finger or other object that can absorb or block sound wave energy touches the screen, the sound wave energy going up on the X axis through the finger part is partially absorbed, reflecting that there is an attenuation gap in the received waveform, that is, the waveform at a certain moment. The received waveform attenuates a notch corresponding to the signal at the part blocked by the finger. The touch coordinate is obtained by calculating the position of the notch. The controller analyzes the attenuation of the received signal and determines the X coordinate by the position of the notch. After that, the same process on the Y axis determines the Y coordinate of the touch point. In addition to the X and Y coordinates that a general touch screen can respond to, the surface acoustic wave touch screen also responds to the third axis Z coordinate, that is, it can sense the magnitude of the user's touch pressure. The principle is calculated from the attenuation at the attenuation of the received signal. Once the three axes are determined, the controller transmits them to the host.

3. Features of surface acoustic wave touch screen

High clarity and good light transmittance. High durability, good scratch resistance (have a surface film relative to resistance, capacitance, etc.). Responsive. Not affected by environmental factors such as temperature and humidity, high resolution, long life (50 million times under good maintenance); high light transmittance (92%), can maintain clear and bright image quality; no drift, just install it One-time calibration; there is a third axis (ie pressure axis) response, which is currently used more in public places. Surface acoustic wave screens need frequent maintenance, because dust, oil stains or even beverage liquid contaminates the surface of the screen, which will block the wave guide groove on the surface of the touch screen, causing the wave to not be emitted normally, or the waveform changes and the controller cannot recognize it, thus affecting For normal use of the touch screen, the user shall strictly pay attention to environmental hygiene. The surface of the screen must be wiped frequently to keep the screen smooth and clean, and a thorough erasure should be done regularly.