Surface acoustic waves are a type of ultrasound, which is a wave of mechanical energy that propagates shallowly on the surface of a medium such as a rigid material such as glass or metal. Through a wedge-shaped triangular base (strictly designed according to the wavelength of the surface wave), directional, small-angle surface acoustic energy emission can be achieved.
Surface acoustic wave performance is stable, easy to analyze, and has very sharp frequency characteristics in the shear wave transmission process, in recent years in non-destructive testing, contrast and wave canceler applications have developed rapidly, surface acoustic wave related theoretical research, semiconductor materials, acoustic guide materials, detection and other technologies have been quite mature.
1. Structure
The screen body portion of the surface acoustic wave touch screen may be a flat, spherical or cylindrical glass plate, mounted in front of the CRT, LED, LCD or plasma display screen. This glass plate is just a pure piece of tempered glass, which distinguishes it from other touch screen technology without any foil and overlay.
The upper left and lower right corners of the glass screen are fixed vertically and horizontally ultrasonic emission transducers, and the upper right corner is fixed with two corresponding ultrasonic receiving transducers. The four periphery of the glass screen has a very precise reflection strip at an angle of 45° from sparse to dense. This is shown in Figure 2.1. The reflective stripes of early sonic screens were grooves engraved on the screen body, which had shortcomings such as easy dust accumulation on the stripes, difficult to clean, and large signal attenuation. The reflective stripes of the current wave screen are designed to bulge on the surface of the screen body, which well overcomes the shortcomings of the early sound wave screen.
2. Working principle
Taking the X-axis transmitting transducer in the lower right corner as an example, the transmitting transducer converts the electrical signal sent by the controller through the touch screen cable into sound wave energy to the left surface, and then reflects the sound wave energy into an upward uniform surface by a set of precision reflection stripes under the glass plate, and the sound wave energy passes through the surface of the screen body, and then the upper reflection stripe gathers into a sound wave propagating to the right to the X-axis receiving transducer, and the receiving transducer turns the returned surface sound wave energy into an electrical signal.
When the transmitting transducer emits a narrow pulse, the sound wave energy travels through different paths to reach the receiving transducer, taking the far right to arrive first, the far left to arrive late, and these sound wave energies that arrive early and arrive late are superimposed into a wide waveform signal. It is not difficult to see that the received signal gathers all the sound wave energy that has gone through different lengths and paths in the axis direction, and they travel the same distance on the y-axis, but on the x-axis, the farthest travels twice as much as the nearest x-axis maximum distance. Therefore, the time axis of this waveform signal reflects the position of each original waveform before superposition, that is, the X-axis coordinates.
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 that the X axis passes through the finger part upward is partially absorbed, and the waveform is reflected in the receiving waveform, that is, there is an attenuation gap in the waveform at a certain moment.