Touch & Gesture
Microchip’s GestIC® technology is a patented 3D sensor technology that utilizes an electric field (E-field) for advanced proximity sensing. It allows the development of new user interface applications by supporting the detection, tracking and classification of a user’s hand or finger motion in free space.
An E-field is generated by electrical charges and spread three-dimensionally around the surface carrying the electrical charge. Applying direct voltages (DC) to an electrode results in a constant electric field.
Applying alternating voltages (AC) makes the charges and, thus, the field, vary over time. When the charge varies sinusoidal with frequency f, the resulting electro-magnetic wave is characterized by wavelength λ = c/f, where c is the wave propagation velocity in vacuum the speed of light.
How Does it Work?
Once a user intrudes the sensing area, the electrical field distribution becomes distorted. The field lines intercepted by the hand are shunted to ground through the conductivity of the human body itself. The simulation results in Figure 1 and Figure 2 show the influence of an earth-grounded body to the electric field.
As illustrated, the proximity of the body causes a compression of the equipotential lines and shifts the receiver (Rx) electrode signal levels to a lower potential which is detected by the respective GestIC technology product.
GestIC technology uses transmit (Tx) frequencies (f) in the range of 100 kHz, which reflects a wavelength of about three kilometers. With electrode geometries of typically less than 20 × 20 centimeters, this Tx wavelength is much larger in comparison.
Therefore, the magnetic component is practically zero and no wave propagation takes place. The result is a quasi-static electrical near field that can be used for sensing conductive objects such as the human body.