The principle of surface acoustic wave touch screen

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 for transmission. The sound wave energy passes through the surface of the screen, and then is gathered into a rightward line by the upper reflection fringe to propagate to the X-axis receiving transducer, and the surface acoustic wave that the transducer will return The energy becomes an electrical 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 left is the last to arrive. The energies of the sound waves arriving early and arriving late are 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 ratio is 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 capable of absorbing or blocking 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 by the attenuation at the attenuation of the received signal. Once the three axes are determined, the controller transmits them to the host.

Surface acoustic wave touch screen features

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 normally, thus affecting For the 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.

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. This glass plate is just a piece of pure strengthened glass, which is different from other types of touch screen technology in that it does not have any film or overlay. 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 reflective stripes with a 45° angle ranging from sparse to dense. 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. A set of precise reflection fringes under the glass plate reflects the sound wave energy into an upward uniform surface for transmission. 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 converts the returned surface acoustic wave energy into an electrical signal.

When the waveforms of the transmitted signal and the received signal are not touched, the waveform of the received signal is exactly the same as the reference waveform. When a finger or other object capable of absorbing or blocking 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 by the attenuation at the attenuation of the received signal.