Ever since Apple has launched the first iPhone in 2007, the industry of mobile phones has entered a new era as touch screen became wildly popular after the release. Soon after, the presence of touchscreen technology has increased so rapidly that it became a large part of our everyday lives.
The most common and commercially used touchscreens can be summarized into the following four types.
Resistive senor
A resistive sensor is made of two electrically resistive layers. The top layer is made of a flexible material and the bottom layer, on the opposite, is very rigid. The surfaces inside are coated with conducting materials that allow a voltage gradient when voltage is applied. When pressure is applied on a point of the screen, the top layer touch the bottom layer and cause a voltage change. This change is detected by a controller and it signals the computer that the user has touched the screen. This type of screen is not costly to make and the touchscreen can be very thin and sense any types of material. Therefore, it is mostly widely used. However, the flexible top layer of are sensitive to scratches.
Examples of a resistive touchscreens: old PDA, Nintendo 3DS
Structure of a Resistive Touchscreen
Photo credit : via Wikipedia
Surface Acoustic Wave (SAW) Sensor
This type of touchscreen is much more resistant to dirt than the other types.The screen is made purely of regular glass, which means that it is the strongest of all types and has the highest light transmittance. The corners of the screen are equipped with ultrasonic wave generators which evenly pass waves over the touchscreen. When the screen is touched, a portion of those waves is absorbed and this change is detected by a controller just like all the other types of screens.
Examples of SAW touchscreen: ATM and public places where dirt-resistance is required
Infrared Sensor
This type is also made of pure glass but the difference is that this screen is surrounded by LED projector and receiver instead of sound wave generator and receiver. The mechanism of receiving signals is similar to SAW touchscreen. The controller senses the location where LED light is blocked, and thus calculates the exact place that is been touched.
Example of infrared sensor: Electronic Whiteboard

Wave Can be Very Useful.
Photo credit : via Wikipedia
Capacitive Sensor
Now let’s talk about the type of screens that can be found in smart phones. The surface of this screen is made of a material that can store electrical charges. This allows the screen to detect any micro current. Our body generates electric impulses to communicate with motor and sensory cells through neurons. And there is an impulse-generating tissue called sinoatrial node. It is located in the heart and signals the heart to pump every second. In fact almost all of our cells are capable of generating electricity. Therefore, the touchscreen on smart phone is actually detecting the electric impulses that are generated by our body. And as a result, the screen does not work when you have gloves on.
Examples of a capacitive sensing screen: iPhones and most current smartphones and Tablets.
By William Yang

Most Touchscreen Now are Capacitive
Photo credit : via Wikipedia
Here is a video for the comparison of two most common touchscreens.
[youtube]https://www.youtube.com/watch?v=FyCE2h_yjxI&src_vid=5fOI-EQCOOQ&feature=iv&annotation_id=annotation_558874[/youtube]

