The structure of a capacitive touch screen mainly consists of a transparent conductive film layer coated on a glass screen, covered by a protective glass layer on top. This double-glass design thoroughly protects the conductive layer and sensors.
In addition, narrow electrodes are coated along the four edges of the additional touch screen, creating a low-voltage AC electric field within the conductive material. When a user touches the screen, a coupling capacitance is formed between the user's finger and the conductive layer due to the human body's electric field. The current generated from the electrodes flows toward the touch point, and its strength is proportional to the distance between the finger and each electrode. The controller behind the screen calculates the ratio and strength of the current to accurately determine the touch location. The double-glass design of the capacitive touch screen not only protects the conductor and sensors, but also effectively shields the screen from external environmental factors. Even if the screen is contaminated with dirt, dust, or grease, it can still accurately detect the touch location.
Capacitive touch screens offer better light transmittance and clarity compared to 4-wire resistive screens, though not as good as surface acoustic wave or 5-wire resistive screens. However, capacitive screens suffer from severe glare. The four-layer composite design used in capacitive technology results in uneven transmittance across different light wavelengths, causing color distortion. Reflections between layers also lead to blurred images and characters.
Fundamentally, capacitive screens treat the human body as one electrode of a capacitor. When a conductor comes close enough to generate sufficient capacitance with the ITO working surface, the resulting current may cause the screen to malfunction. While capacitance is inversely proportional to distance, it is directly proportional to the contact area and also depends on the dielectric constant of the medium. Therefore, large conductive surfaces like a palm or handheld metal object near the screen can cause false touches even without direct contact—especially in humid conditions. For example, simply resting your hand on the monitor, placing your palm within 7 cm, or your body within 15 cm of the screen may trigger false input.
Another drawback of capacitive screens is that they do not respond when touched with gloved hands or non-conductive objects due to the presence of more insulating material. The most significant issue with capacitive touch screens, however, is drift. Changes in environmental temperature, humidity, or electric fields can cause position drift and lead to inaccurate touches. For instance, drift can occur as the monitor heats up after being turned on, when the user’s body comes close to the screen, or even when large objects are moved nearby. If someone gathers around the screen while it’s being used, it can also lead to drift.
The root cause of this drift is an inherent technical flaw. Although environmental potential surfaces (including the user's body) may be farther from the screen than the finger, their larger area greatly affects touch position detection. Moreover, many theoretically linear relationships are actually nonlinear. For example, users with different body weights or finger moisture levels absorb varying amounts of current, and the relationship between total current change and individual electrode current changes is nonlinear. Capacitive screens use a custom four-corner coordinate system that lacks a fixed origin. When drift occurs, the controller cannot detect or correct it.
After the analog-to-digital conversion at the four corners, the calculation of the X and Y coordinates in a Cartesian system based on the four current values is complex. Without a fixed origin, capacitive screen drift is cumulative, and frequent recalibration is required on-site.
While the outer silica glass layer of the capacitive screen is highly scratch-resistant, it is vulnerable to impacts from fingernails or hard objects. A small chip can damage the ITO layer within. Whether the inner ITO layer is damaged during use, installation, or transport, the capacitive screen will no longer function properly.
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