User Manual

MGC3030/3130
DS40001667E-page 8 Advance Information  2012-2017 Microchip Technology Inc.
1.0 THEORY OF OPERATION:
ELECTRICAL NEAR-FIELD
(E-FIELD) SENSING
Microchip’s GestIC is a 3D sensor technology which
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 thus, the
field. When the charge varies sinusoidal 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 w/o wave
propagation.
In case a person’s hand or finger intrudes 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 calculate the
position, track movements (MGC3130) and to classify
movement patterns (gestures, MGC3X30).
Figure 1-1 and Figure 1-2 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 which is measured.
FIGURE 1-1: EQUIPOTENTIAL LINES
OF AN UNDISTORTED
E-FIELD
FIGURE 1-2: EQUIPOTENTIAL LINES
OF A DISTORTED E-FIELD