Touch screen (touch screen), also known as "touch screen", "touch panel, touch is a kind of can receive the first input signal of induction type liquid crystal display device, when contact with the graphic buttons on the screen, the screen of the tactile feedback system according to the program of pre-programmed drive all kinds of connecting device, can be used to replace the mechanical button panel, and liquid crystal display screen by creating vivid audio effect.
 
Touch screen gives the multimedia with brand-new appearance, is very attractive new multimedia interactive devices. Mainly used in the public information query, leadership office, industrial control, military command, electronic games, so I take your order, multimedia teaching, real estate open to booking, etc.
 
 The main types:
From the technical principle to distinguish the touch screen, can be divided into five basic categories: vector pressure sensing technology, touch screen, resistance touch screen technology, capacitive touch screen technology, infrared technology, touch screen and surface acoustic wave touch screen technology.
The vector pressure sensing technology touch screen has become relics;
Accurate resistance technology, touch screen, but its price is quite high, vulnerability and fear;
Capacitive touch screen technology design is reasonable, but the image distortion problem is very difficult to get the fundamental solution;
Infrared technology touch screen price is low, but the casing outside the fragile, easy to produce light interference, surface condition distortion;
Surface acoustic wave touch screen solved all kinds of flaws of the touch screen, clear and not easily damaged, suitable for various occasions, the disadvantage is that if there are water droplets and dust can make the screen surface touch screen has become dull, don't even work.
A brief description of the various types of touch screen to introduce:
Resistive touch screens
Using pressure sensor to control the touch screen. Resistive touch screen is a main part of the surface is very match the resistance of the film and display screen, it is a kind of multilayer composite films, it with a piece of glass or hard plastic flat as grassroots, surface coated with a layer of transparent metal oxide transparent conductive resistance of the conductive layer, the above with a layer of surface hardening treatment, smooth and rubbing the plastic layer, its inner surface is coated with a layer of coating, among them there are many small (less than 1/1000 of an inch) of transparent isolation point separates two conductive layer of insulation. Resistance touch screen is the key to material science and technology, the commonly used transparent conductive coating materials are: ITO, indium oxide, pervious to light at a rate of 80%, if you go on thin light transmittance drop instead, to the thickness of 300 and up to 80%.
 

The limits of resistive screen

Resistive touchscreen common faults because the outer layer of the composite membrane with plastic materials, people who do not know too hard or the use of sharps touch may scratch the touch screen to scrap. Scratches within limits, however, will only hurt the conductive layer and the conductive layer of scratch for five line resistance touch screen has nothing to do, and for 4-wire resistive touch screen is fatal.
Capacitive touch screen is to use the working current of induction of human body. Capacitive touch screen is a four layer composite glass screen, the inner surface of the glass and laminated coated with a layer of ITO, the outermost layer is a thin layer of silica glass coating, laminated ITO coating as the working face, four corners raises four electrodes, inner ITO for shield to ensure good working environment. When the fingers on the metal layer, the electric field due to the human body, the user and the touch screen surface formed by a coupling capacitance, for high frequency current, capacitance is directly conductor, so the fingers from the point of contact suck a small current. The current points out from the touch screen on the four corners of the electrode, the four electrodes and the current is proportional to the finger to the four corners, the controller based on the four current ratio of precise calculation, it is concluded that the location of the touch point.

The defects of capacitive touch screen

Capacitive touch screen of light transmittance and clarity is better than that of 4 line resistance screen, of course also cannot and surface acoustic screen compared with five line resistance screen. Capacitance screen reflection is serious, and the capacitance technology of four layer composite touch screen for each wavelength of light transmittance is not uniform, has the problem of color distortion, due to the reflection light between the layers, also caused the image fuzzy characters.
 
Infrared touch screen
Early ideas, the low resolution, the infrared touch screen touch restricted and influenced by environmental interference and technical limitations, such as false action once out of the market. Since the second generation of infrared screen part solved the problem of the light interference, third and fourth generation also improved in raising resolution and stability, but did not have a qualitative leap on key indicators or comprehensive performance. But, understand knows that touch screen technology, infrared touch screen is not affected by current, voltage and electrostatic interference, suitable for harsh environment conditions, the development trend of infrared technology is a touch screen products eventually. Using acoustics and other materials science technology touch-screen has its formidable barriers, such as the damage to the single sensor, aging, touch interface afraid of contaminated, destructive use, maintenance is multifarious, and so on. Infrared touch screen as long as truly achieve high stability and high resolution, will replace other technology products and become a mainstream touch-screen market.
 
Surface acoustic wave touch screen
 
1, the surface acoustic wave

A kind of surface acoustic wave, ultrasonic wave, in the medium (e.g., rigid material such as glass or metal) surface shallow mechanical energy wave propagation. Through the wedge triangular base (strictly designed according to the wavelength of surface wave), can be directed, small Angle of surface acoustic wave energy emission. Surface acoustic wave, stable performance, easy to analysis and in the process of shear wave transmission has a very sharp frequency characteristic, 2013 in nondestructive flaw detection, imaging and annealing wave direction on application development soon, surface acoustic wave related theory research, semiconductor materials, acoustic materials, testing technology and technology already quite mature. Touch screen part of the surface acoustic wave touch screen can be a piece of plane and spherical or cylindrical glass plate, mounted on a CRT, LED, LCD or plasma display in the front of the screen. Glass screen for fixed on the upper left and lower right of the vertical and horizontal direction of ultrasonic transmitting transducer, the top right corner is fixed for two corresponding ultrasonic receiving transducer. The ultrasonic transmitting and receiving transducers are made of piezoelectric ceramic. Four around the glass screen is engraved with 45 ° Angle from sparse to dense spacing is very sophisticated reflection stripe.
 
2, the working principle of the surface acoustic wave touch screen

Touch screen and around corners or placement of piezoelectric ceramic piece, as a touch screen and the support of sensing point. When external forces hit a touch screen, produce forces at contact, the location of the contact point is different, the different proportion of voltage that generates four ceramic chip. Ceramic surface charge or voltage produced by the principle is based on the piezoelectric effect of piezoelectric ceramic materials. Create a voltage measuring four ceramic, the location of the contact point can be calculated, at the same time can know the size of the force. Formed by the voltage waveform on the ceramic rise along the falling edge and the change, can get the force change of speed or acceleration force. By determining the location of the contact point and contact strength, eventually achieve the goal of a touch, and the effect of this new touch produce different from the traditional touch, can not only accurate perception of contact position, also can the size of the perception and acceleration, tactility dimension increase.
 
3, surface acoustic wave touch screen features

High resolution and good light transmittance. Highly durable, good scratch resistance (relative to the degree of membrane resistance, capacitance, etc have surface). Responsive. Is not affected by environmental factors such as temperature, humidity, high resolution, long service life, maintenance good cases 50 million); High light transmittance (92%), can maintain a clear and transparent image quality; There is no drift, when need to install a correction; There is a third axis (that is, the pressure axis) response, is widely used in public places. Surface acoustic wave screens require constant maintenance, because of the dust, oil and even drink liquid contamination on the surface of the screen, can block the touch screen on the surface of the guided wave trough, wave will not launch properly, or make the waveform change and controller cannot normal recognition, which affect the normal use of touch screen, the user must strictly pay attention to sanitation.