The structure of the surface elastic wave touch screen is that X, y light-emitting units and light-receiving units are installed on the corners of the transparent glass, and a reflective array is formed on 4 sides. Usually X, y light-emitting units are located at the opposite corners. The reflector array is installed at an angle of 45°. The spacing of the reflective arrays shown in Figure 3>4 is relatively equal, but in actual situations, the spacing of the reflective arrays changes according to a certain rule. This is done to reduce the attenuation of the signal. A short-time pulse signal is input to the transmitter (the input signal sensor), so that ultrasonic waves (surface elastic waves) are generated in the side direction of the glass, which are reflected in the direction of the glass surface through the reflective array, and the reflective array in the opposite direction is used to make it Reflected to the other side, the receiver (receiving sensor) is used to receive and convert it into an electrical signal. Because the waveform of the electrical signal of the touch is attenuated, the position of the touch is detected through the attenuation time.
For the surface elastic wave touch screen, the way it detects the degree of absorption based on the touch, while the bending wave touch screen detects the vibration generated by the touch panel or the friction vibration generated by the drag operation. Acoustic waves are propagated by mixing longitudinal waves and transverse waves, so it seems that the entire panel is vibrating, which can be transmitted over long distances. The time that the bending wave travels in the glass is proportional to its distance. The vibration wave during touch expands outward with concentric circles centered on the touch. Using the characteristic of different arrival times of the vibration of the touch, the position of the touch where the vibration occurs can be checked. The pressure sensor receives the vibration of each touch position, and converts the pulse signal into electronic signal data through the converter. According to the manufacturer, it can be divided into Acoustic Pulse Recognition (APR) and vibration detection (Dispersive Signal Technology, DST). Both methods use bending waves, but the detection principles are different.
APR type is that the pressure sensor is unevenly arranged outside, so that the arrival time of the bending wave is different. But according to the vibration frequency, the propagation speed will be different, so the position cannot be accurately selected, so the reference waveform corresponding to the touch position must be prepared in advance and compared with the actual waveform to detect the accurate position.
The DST type also uses the difference in vibration arrival time. The principle of detection is the same as that of GPS, which uses triangulation detection. In this way, the natural vibration of the glass will be specified as the frequency generated by the touch, and everything else will be regarded as noise, so it can cancel the error input other than the touch. Bending waves propagate inside glass, etc., so unlike surface elastic waves, they are rarely affected by scratches and foreign objects. However, the problem of incorrect input caused by falling objects or residual problems in the performance of software, touchpad, and dragging operations need to be resolved urgently. And because of the characteristics of its detection method, this method is not suitable for small machines.
