A capacitive sensor consists of at least two conductive electrodes that are insulated from each other. The electrodes are usually arranged on a substrate and can have various shapes, such as surfaces, lines or grids.
The capacitance of such a sensor depends on the size of the electrodes, the distance between them and the dielectric properties of the medium between the electrodes.
If an object moves near the capacitive sensor or touches it, the capacitance of the sensor changes. This happens because the electric field lines between the electrodes are influenced by the dielectric medium and the object.
The change in capacitance is detected by the sensor and converted into an electrical signal. This signal can then be interpreted to provide information about the position, approach or contact of the object.
Capacitive sensors are often used in touch-sensitive screens - the capacitive touchscreen or "capacitive display". The best-known examples are smartphones and tablets. When a user touches the screen, the capacitance at the touch point changes and the sensor recognizes this as an input.
If the sensor is used as a capacitive pressure sensor, the operating surface is deformed or displaced by pressure, which changes the plate distance and thus the electrically measurable capacitance.
Capacitive touch sensors can be adapted to the specific requirements of an application by adjusting the sensitivity. In this way, the sensor can be optimized for different materials and distances.
Capacitive touch sensors are used as capacitive touch screens, i.e. in touch-sensitive screens of smartphones, tablets, laptops and other electronic devices to recognize user input via touch.
They are also used in industrial automation and for level measurement of liquids or solids in tanks or containers. They can also be found in medical technology, security systems, household appliances and in the field of aerospace technology.
The broad applicability of capacitive sensors makes them an important component in numerous industries and technological applications where the detection of touch, proximity or changes in the environment is required.
Capacitive sensors offer numerous advantages, especially in the non-contact detection of objects, but have their limits in certain applications. One major limitation is their sensitivity to environmental conditions such as humidity, dust or temperature fluctuations. Water and high humidity in particular can distort the measurement result as they influence the capacitance due to their high dielectric constant. Contamination or deposits on the sensor surface can also lead to incorrect measurements.
Another limiting factor is the short range of capacitive sensors. They are generally only designed for distances of a few millimetres to a few centimetres. For greater distances, other sensor technologies such as optical or inductive sensors are better suited. In addition, the function of capacitive sensors depends heavily on the dielectric properties of the material to be detected. This can be problematic if materials are unknown, inhomogeneous or changing, as this can affect measurement accuracy.
Capacitive sensors are also susceptible to electromagnetic interference. As they respond to very small changes in capacitance, electric fields in the environment can affect their operation, making additional shielding or careful installation necessary. Although they are in principle capable of detecting objects through non-conductive materials such as plastic or glass, accuracy decreases significantly with increasing material thickness or density.
Finally, capacitive sensors are less suitable for detecting metallic objects over longer distances. In such cases, inductive sensors usually offer a more robust and fail-safe alternative. Overall, capacitive sensors are therefore particularly suitable for applications with short distances, known material properties and controlled environmental conditions, while they reach their limits in harsh or highly varying areas of application.
Projected capacitive (PCAP) is a special type of capacitive sensor that is often installed in touch-sensitive screens. With PCAP sensors, a transparent layer with microscopically small conductive wires or electrodes is applied to the surface of a screen. These electrodes generate an electric field on the screen surface. When a conductive object (e.g. a finger) touches or approaches the surface, it disturbs the electric field and causes a change in capacitance, which is detected.
PCAP offers precise and fast touch detection and multi-touch functionality. When used behind glass, the sensors are protected against scratches and are durable.