Surface acoustic waves are a type of ultrasonic waves, which are mechanical energy waves that propagate shallowly on the surface of a medium (such as rigid materials such as glass or metal). 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.
Surface acoustic wave has stable performance, easy to analyze, and has very sharp frequency characteristics in the process of transverse wave transmission. In recent years, it has developed rapidly in non-destructive testing, imaging and de-wave applications. Surface acoustic wave related theoretical research, semiconductor materials, acoustics, etc. Technologies such as guiding materials and testing are already quite mature.
1. Structure
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. This glass plate is just a piece of pure strengthened glass, which is different from other types of touch screen technology in that there is no film or covering layer.
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 perimeters of the glass screen have very precise reflection stripes with 45 degree angles ranging from sparse to dense. As shown in Figure 2.1. The reflection fringes of early acoustic wave screens were grooves engraved on the screen. This kind of screen has the disadvantages of easy dust accumulation on the fringes, difficult to clean, and large signal attenuation. The reflection stripes of the current wave screen are all designed to be raised on the surface of the screen, which has overcome the disadvantages of the early acoustic wave screen.
2. Working principle
Take 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 and transmits it to the left surface, and then a set of precision reflection stripes under the glass plate The sound wave energy is reflected into an upward uniform surface to be transmitted. The sound wave energy passes through the surface of the screen, and then is gathered by the upper reflection stripe into a rightwardly propagating sound wave to the X-axis receiving transducer. The receiving transducer changes the returned surface acoustic wave energy For electrical signals.
When the transmitting transducer emits a narrow pulse, the sound wave energy reaches the receiving transducer through different paths. The sound wave energy arrives at the earliest by going to the far right, and arrives at the latest by going to the far left. The sound wave energy that arrives early and arrives late is superimposed into one. Wider waveform signal. It is not difficult to see that the received signal is a collection of all the acoustic energy returned through different long and short paths in the axis direction. They travel the same distance on the y axis, but on the x axis, the farthest one travels twice as much as the nearest one. The maximum distance on the x-axis. Therefore, the time axis of this waveform signal reflects the position before each original waveform is superimposed, which is the X-axis coordinate.
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.
