Working principle and characteristics of four kind of commonly used touch screen:

1. Resistive screen

basic principle:
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. 
 
When fingers touching the screen, two conductive layers in touch point location had contact, resistance to change, produced in the X and Y directions signal, and then send a touch screen controller.Controller to detect the contact and to calculate the position (X, Y), according to simulation the mouse operate.This is the most basic principle of resistance technology of touch screen.

Commonly used materials
A:ITO, indium oxide, weak electrical conductor, the feature is that when the thickness of the drop to 1800 el (Mr = 10-10 meters) below will suddenly become transparent, light transmittance was 80%, the light transmittance drop instead, if you go on thin to 300 when Mr Thickness and up to 80%.ITO is all resistance touch screen technology and capacitive touch screen using the main material, in fact the resistance and capacitance touch screen working face is ITO coating technology.


B: nickel and gold coatings, five line of resistance touch screen outer conductive layer using a good ductility nickel gold coating material, conductive layer due to frequent touch, good ductility of nickel alloy material in order to extend the service life, but the process cost is relatively high.Nickel gold conductive layer while the ductility is good, but can only be transparent conductor and doesn't fit as working face of resistive touch screens, because of its high conductivity, and the thickness of metal is not easy to do it is very uniform, unfavorable for voltage distribution layer, only as a agent layer.

Four wire resistance screen and five line resistance screen:
4-wire resistive touch - a 4-wire resistive analog technology both layer transparent metal work each layer increased 5 v constant voltage: a vertical and a horizontal direction.A total of four cables.Features: high resolution, high speed transfer reaction.Surface hardness processing, reduce the scratch, scratch and chemical treatment.With smooth surface treatment and fog.A correction, high stability, never drift.


Five line resistance screen - five line resistance touch screen technology base the voltage field of two direction by precision resistor network is added in conductive glass, we can simply understood as voltage field in two directions and at the same time work, and the outer conductor used as more than just pure nickel gold conductive layer, a touch after the time-sharing testing inner ITO contact point X axis and Y axis voltage method measured the position of the touch point.Five inner ITO need four lead wire resistance touch screen, outer only just a conductor, touch screen have to lead a total of 5.


Features: high resolution, high speed transfer reaction.High surface hardness, reduce the scratch, scratch and chemical treatment.With the point contact 30 million can be used.Conductive glass substrate of the medium.A correction, high stability, never drift.
L resistance screen limitations:
Whether 4-wire resistive touch screen or five line resistance touch screen, they are a completely isolated to the outside environment, does not fear the dust and water vapor, it can use any object to touch, can be used to write drawing, more suitable for industrial control field and the use of the limited people in the office.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.


With the passage of use, the surface scratch, light transmittance drop, the precision of data drift and decline, has become a fatal wound of resistive screen.Resistive screen now due to the use fixed number of year and surface scratch, gradually withdraw from the market, only used on some low-end products.

1. Sound wave screen 

Acoustic screen in the one horn of the glass installation has an energy converter, it put the controller through the touch screen cable from the electrical signals into acoustic energy transferred through the glass surface, and then by a set of precise reflection stripe at the bottom of the glass plate acoustic energy is reflected into the uniform surface upward transmission, acoustic energy through the screen surface, again by the reflective stripes above to spread to the right line to X axis receiving transducer, receiving transducer will return to the surface of the acoustic energy into electrical signals.
 
When launched a narrow pulse transmitting transducer, acoustic energy through different approaches to receiving transducer, most the right side of the first walk, walk the most on the left side of the late arrival, arriving early and late of the superposition of acoustic energy into a wide waveform signal, it is not hard to see, the received signal collection all through different path length in the X direction regression acoustic energy, they are on the Y axis through the path is the same, but on the X axis, the farthest walked two times more than the latest X axis maximum distance.So this time waveform signal reflect the original waveform former position, is the X coordinate. 
 
Transmitting and receiving signal waveform at the time of no touch, received signal waveform and reference waveform are exactly the same.When your fingers or other objects can absorb or halt the acoustic energy when touching the screen, the X axis passing through finger parts going up acoustic energy absorbed by the part of reaction on the received waveform that has a position at a certain moment wave attenuation gap.Receiving waveform corresponding finger block parts signal attenuation a gap, gap position for a quick touch coordinate controller analysis to the received signal attenuation and by the gap position determine the X coordinate.Y the same process after determine the Y coordinate of touch point.In addition to touch screen can respond to the X, Y coordinates, surface acoustic wave touch screen response also third axis Z axis coordinate, namely can perceive the user touch pressure values.Its principle is calculated by the attenuation of received signal attenuation.Three axis once established, the controller will pass them to the host, will identify the location of the touch point.

advantages and disadvantages:
High resolution and good light transmittance.Highly durable, good scratch resistance (relative to the degree of membrane resistance, capacitance, etc have surface).Responsive.But affected by temperature, humidity, wind speed, glass surface dust, environmental factors, such as ambient noise, high resolution, long service life (good maintenance cases 50 million times);High light transmittance (92%), can maintain a clear and transparent image quality;There are some drift, only need to install a correction;There is a third axis (that is, the pressure axis) response, now 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.Must often wipe the surface of the screen to keep the screen surface is bright and clean, and makes a thorough erasing regularly.

1. Capacitive

Basic principle:
Mainly by the special material for the SENSOR, the sampling capacitance change caused by the current change position.The touch screen is capacitive touch screen using the working current of the human body induction, on the glass surface with a layer of transparent conductive material special metal, when conducting objects touch, can change the contact capacitance, which can detect the location of the touch.But with a gloved hand or handheld non-conducting objects touch when no response, this is because increased more insulating medium.
 
L the advantages and disadvantages:
Current is given priority to with small and medium size, there is also a company trying to develop in the direction of large size, but the cost is very high.Can realize multi-touch, may replace resistive touch products in the future.Investment in equipment in more than 20 million.Advantages: high resolution, small installation appearance, size, high sensitivity, more.Defect: (longer than resistive screen), short service life of light transmittance is not high, explosion-proof, anti-dazzle, easy damaged, fear of electromagnetic interference, etc.Applications: mobile phone (apple), portable devices, games, gambling.

1. IR touch frame

basic principle:
Infrared touch screen is the use of X, Y direction with infrared ray matrix to detect and locate the user's touch.Infrared touch screen in front of the display to install a circuit board frame, circuit boards and around the screen configuration of infrared transmitting tube and infrared receiving tube, one to one correspondence form somehow cross infrared matrix.Users in the touch screen, the finger will block after the location of the relation of two infrared, which can determine the location of the touch point on the screen.Any touch objects can change the infrared on the contact and touch screen operation.


L infrared development course, advantages and disadvantages of various 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.