3.

Theory of Operation: Electrical Near-Field (E-Field) Sensing

Microchip’s GestIC technology is a 3D sensor technology that utilizes an electric field (E-field) for advanced proximity

sensing. It allows realization of new user interface applications by detection, tracking and classification of a user’s

hand gestures in free space.

E-fields are generated by electrical charges and propagate 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 vary over time and the field. When the charge varies sinusoidally with frequency ‘f’, the resulting

electromagnetic wave is characterized by wavelength λ = c/f, where ‘c’ is the wave propagation velocity — in

vacuum, the speed of light. In cases where the wavelength is much larger than the electrode geometry, the magnetic

component is practically zero and no wave propagation takes place. The result is quasi-static electrical near field that

can be used for sensing conductive objects such as the human body.

Microchip’s GestIC technology uses transmit (Tx) frequencies in the range of 100 kHz, which reflects a wavelength

of about three kilometers. With electrode geometries of typically less than fourteen by fourteen centimeters, this

wavelength is much larger in comparison. GestIC systems work without wave propagation.

In case a person’s hand or finger intrudes in the electrical field, the field becomes distorted. The field lines are drawn

to the hand due to the conductivity of the human body itself and shunted to ground. The three-dimensional electric

field decreases locally. Microchip’s GestIC technology uses a minimum number of four receiver (Rx) electrodes to

detect the E-field variations at different positions to measure the origin of the electric field distortion from the varying

signals received. The information is used to track movements and to classify movement patterns (gestures).

The two following figures show the influence of an earth-grounded body to the electric field. The proximity of the body

causes a compression of the equipotential lines and shifts the Rx electrode signal levels to a lower potential that is

measured.

Figure 3-1. Equipotential Lines of an Undistorted E-Field

MXG3141

Theory of Operation: Electrical Near-Field (E-Fiel...

Advance Information Datasheet

DS40001975C-page 8