C

Oscillator

L(d)

Target Metal

Surface

Conductance

of Metal

Ls + L(d)

rs + R(d)

Distance d

Eddy

Currents

Metal

Target

d

LDC1000-Q1

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SLOS886B – SEPTEMBER 2014 – REVISED OCTOBER 2014

Feature Description (continued)

Figure 5. Inductor with a Metal Target

Eddy currents generated on the surface of the target can be modeled as a transformer as shown in Figure 6. The

coupling between the primary and secondary coils is a function of the distance and characteristics of the

the coil. The inductance L(d), which is a function of distance, d, is the coupled inductance of the metal target.

Likewise, R(d) is the parasitic resistance of the eddy currents.

Figure 6. Metal Target Modeled as L and R With Circulating Eddy Currents

Generating an alternating magnetic field with just an inductor consumes a large amount of power. This power

consumption can be reduced by adding a parallel capacitor, turning the right part of Figure 6 into a resonator as

only.

Figure 7. LC Tank Connected to Oscillator

The LDC1000-Q1 device does not directly measure the series resistance. Instead, the device measures the

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