Resistive Touchscreens Resistive touchscreens use a thin, flexible membrane separated from a glass or plastic substrate by insulating spacers (Figure 1). The substrate surface and the facing membrane surface have transparent metallic coatings that meet when the user’s finger or a stylus presses on the screen, thus closing an electrical circuit. Four- and five-wire designs are available for sensing the position of the touch.
	In a four-wire-resistive touchscreen, electrode arrays at opposite sides of the substrate can establish a 1-D voltage gradient across the substrate’s resistive indium-tin-oxide (ITO) coating. Similar electrodes can establish an orthogonal gradient across the membrane’s ITO coating.Both sets of electrodes also allow the ITO coatings to act as high-impedance probes.
Figure 1	When a user touches a four-wire-system screen, the controller establishes a gradient across the
substrate. The controller then measures the voltage at the point of touch using the membrane as a probe. Similarly, the controller establishes a gradient across the membrane and uses the substrate as a probe. The two voltages provide the x and y coordinates of the touch point.

Advantages	Disadvantages
High touch resolution Pressure sensitive, works with any stylus Not affected by dirt, dust, water, or light Affordable touchscreen technology	75 % clarity Resistive layers can be damaged by a sharp object Less durable then 5-Wire Resistive technology

In a five-wire system, the substrate has a resistive ITO coating and electrodes on all four sides. The membrane has a single electrode and a conductive coating. When a user touches the screen, the controller establishes first an x-axis and then a y-axis gradient across the substrate. The controller uses the membrane as a probe at all times. The two voltages that the probe senses reflect the point’s x and y coordinates.

Advantages	Disadvantages
High touch resolution Pressure sensitive, works with any stylus Not affected by dirt, dust, water, or light More durable then 4-Wire Resistive technology	75 % clarity Resistive layers can be damaged by a sharp object

Capacitive Touchscreens Capacitive touchscreens use resistive-ITO sensor coatings but have no membrane. The ITO coating lies below a protective layer of glass Figure 2. With analog-capacitive screens, electrodes at the corners establish an ac field on the coating, while the controller monitors the current flow through each electrode. A user touches the screen with his or her finger or a conductive stylus, and capacitive coupling between the coating and the finger or stylus draws a small current from the screen. The controller then calculates the touch coordinates from the ratio of the four currents.

	Another form of capacitive touchscreen, digital- or zone-capacitive touchscreens, also depend on capacitive coupling between the user and the sensor coating. Digital-touchscreen coating is not continuous, however. The coating forms an array of isolated touch zones.
Figure 2
The controller scans through the touch-zone array, establishing an ac field at each zone and measuring the current. The user’s finger draws additional current from the touch zone by capacitive coupling. This current signals the controller that a touch has occurred within the zone.

Advantages	Disadvantages
High touch resolution Better image clarity Not affected by dirt, grease, moisture.	Must be touched by finger, will not work with any non-conductive input such as a pen or stylus

Acoustic Touchscreens Acoustic touchscreens rely on absorption of sound energy by the finger or stylus touching the screen. Such touchscreens operate by launching bursts of high-frequency (5-MHz) acoustic energy along two edges of the screen Figure 3. Reflector arrays along the edges divert the acoustic energy across the screen and redirect the energy to sensors. Because the speed of sound in the glass is constant, the energy’s arrival time identifies its path. A touch causes a dip in the received-energy waveform for both axes. A firmer touch causes a greater dip, providing acoustic systems with a third (z) measurement axis: pressure. The timing of the dips indicates the x and y touch-point coordinates.

Figure 3

You can use either surface-acoustic-wave (SAW) or guided-acoustic-wave (GAW) touchscreens. SAW screens confine most of the acoustic energy to the screen’s surface. GAW screens channel the acoustic energy into the full volume of the screen material.

Advantages	Disadvantages
High touch resolution Highest image clarity All glass panel, no coatings or layers that can wear out or damage	Must be touched by finger, gloved hand, or soft-tip stylus. Something hard like a pen won't work Not completely sealable, can be affected by large amounts of dirt, dust, and / or water in the environment.

Force-sensing touchscreens Force-sensing touchscreens come in two types: strain gauge or platform. The strain-gauge touchscreen measures at each corner the stresses that a touch to the screen produces. The ratio of the four readings indicates the touch-point coordinates. The platform touchscreen doesn’t use a screen. Instead, the monitor or display device rests on a platform with force-measurement sensors at the corners. A touch to the display device translates to forces at the platform’s corners. The platform’s controller performs the vector calculations that determine the touch point from the four force measurements through rigid-body mechanics. The controller tracks out static forces, such as gravity, and repetitive forces, such as vibration.

Advantages	Disadvantages
Useable  with any touch object High clarity                           Glass panel, no scratches	Poor touch resolution，and poor touch position accuracy