Principle of surface acoustic touch screen

1Surface Acoustic Waves

Surface acoustic waves, a type of ultrasonic waves, in the media ( Rigid materials such as glass or metal ) Mechanical energy waves transmitted from the superficial layer. Through the wedge-shaped triangular pedestal (strictly designed according to the wavelength of the Surface Wave), it can realize oriented and small-angle surface acoustic energy emission. The surface acoustic wave is stable, easy to analyze, and has sharp Frequency Characteristics in the Process of transverse wave transfer. In recent years, the applications of non-destructive flaw detection, angiogram and wave return devices have developed rapidly, surface acoustic wave-related theoretical research, semiconductor materials, acoustic materials, testing technology and other technologies have been quite mature. The Touch Screen part of the surface acoustic touch screen can be a flat, spherical, or cylindrical glass panel installed on CRT , LED , LCD Or the front of the plasma display screen. In the upper left and lower right corner of the glass screen, the vertical and horizontal ultrasonic transmitters are fixed, and the two corresponding ultrasonic receivers are fixed in the upper right corner. The four surrounding areas of the glass screen are engraved 45 ° Angle from sparse to dense interval very precise reflection stripes.

 

2Working principle of surface acoustic touch screen

In the lower-right corner X- The shaft transmitter is used as an example: The transmitter converts the electrical signal sent by the Controller through the touch screen cable into acoustic energy to transmit to the left side surface, and then the acoustic energy is reflected into an upward uniform surface by a set of precise reflection stripes under the glass plate, the acoustic energy passes through the screen surface, and then the reflection stripes on the top converge to the right line for transmission. X- The receiving transducer of the shaft converts the returned surface acoustic energy into an electrical signal. When the transmitter emits a narrow pulse, the acoustic energy goes through different ways to receive the transducer, the earliest arrival at the rightmost, And the last arrival at the leftmost, these acoustic waves that arrive early and arrive late are combined into a wide waveform signal. It is not hard to see that the received signal is a collection of all X Returns the acoustic energy from different paths in the axial direction. Y The path traveled by the axis is the same, X On the axis, the farthest is twice the most recent X Maximum axis distance. Therefore, the timeline of the waveform signal reflects the position before the superposition of the original waveform, that is X Axis coordinate. Transmit and receive Signal Waveforms When there is no touch, the waveform of the received signal is exactly the same as that of the reference waveform. When you touch the screen with your fingers or other objects that can absorb or block acoustic energy, X The acoustic energy of the shaft passing through the finger is partially absorbed, and the response shows an attenuation gap in the waveform at a certain point of time. The signal at the finger block corresponding to the received waveform degrades a gap, and the touch coordinate is obtained when the gap position is calculated. The Controller analyzes the attenuation of the received signal and determines the position of the gap. X Coordinates. After Y The same process of the Axis determines the touch point Y Coordinates. Except for touch screens X , Y In addition to coordinates, the surface acoustic touch screen also responds to the third axis. Z Axis coordinates, that is, the user's touch pressure value. The principle is calculated by the attenuation at the attenuation of the received signal. Once the three axes are determined, the controller sends them to the host.

 

3Surface acoustic touch screen features

High Definition and good light transmittance. High Durability, good Scratch Resistance ( Surface Film relative to resistance, capacitance, etc. ) . Responsive. It is not affected by temperature, humidity, and other environmental factors. It features high resolution and long service life (under good maintenance ). 5000 10 thousand times); high light transmittance ( 92% ), Can maintain a clear and translucent image quality; no drift, only one correction at installation time; has a third-axis (I .e., pressure axis) response, currently used in public places more. The surface acoustic screen must be maintained frequently. Because the dust, oil stains, and even the liquid of the beverage are stained on the screen surface, the Guided Wave slots on the touch screen surface will be blocked, so that the waves cannot be normally transmitted, otherwise, the controller cannot recognize the waveforms, which affects the normal use of the touch screen. Users must pay close attention to the environmental sanitation. The screen surface must be wiped regularly to keep it clean and permanently erased on a regular basis.