Datasheet
d
Conductive
Target
Eddy
Current
34
LDC1612
,
LDC1614
SNOSCY9A –DECEMBER 2014–REVISED MARCH 2018
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8 Application and Implementation
NOTE
Information in the following applications sections is not part of the TI component
specification, and TI does not warrant its accuracy or completeness. TI’s customers are
responsible for determining suitability of components for their purposes. Customers should
validate and test their design implementation to confirm system functionality.
8.1 Application Information
8.1.1 Conductive Objects in a Time-Varying EM Field
An AC current flowing through an inductor will generate an AC magnetic field. If a conductive material, such as a
metal object, is brought into the vicinity of the inductor, the magnetic field will induce a circulating current (eddy
current) on the surface of the conductor.
Figure 49. Conductor in AC Magnetic Field
The eddy current is a function of the distance, size, and composition of the conductor. The eddy current
generates its own magnetic field, which opposes the original field generated by the sensor inductor. This effect is
equivalent to a set of coupled inductors, where the sensor inductor is the primary winding and the eddy current in
the target object represents the secondary inductor. The coupling between the inductors is a function of the
sensor inductor, and the resistivity, distance, size, and shape of the conductive target. The resistance and
inductance of the secondary winding caused by the eddy current can be modeled as a distance dependent
resistive and inductive component on the primary side (coil). Figure 49 shows a simplified circuit model of the
sensor and the target as coupled coils.
8.1.2 L-C Resonators
An EM field can be generated using an L-C resonator, or L-C tank. One topology for an L-C tank is a parallel R-
L-C construction, as shown in Figure 50.