Electromagnetic Field Penetration and Eddy Current Skin Depth Mechanics
Standard skin depth defines the exponential field decay boundary, dictating coil drive frequencies and target thickness minimums for displacement sensing.
Resonance Shift
Frequency Shift
Resonant circuit frequencies change when a sensor interacts with the electromagnetic fields of a nearby material. This alteration is a resonance shift, and it indicates the target’s properties or distance. By tracking the point of maximum amplitude on the frequency curve, the system can determine changes in the target’s position or conductivity.
This approach is highly sensitive and allows for the detection of very small displacements.
Sensor Coupling
Inductive or capacitive coupling between the sensor and the target determines the direction of the frequency change. In inductive systems, a closer target increases the mutual inductance, which causes a downward resonance shift. Capacitive systems exhibit the opposite behavior, where closer targets increase capacitance and also lower the resonant frequency.
The design of the sensor determines which coupling mechanism dominates the signal.
Circuit Tuning
Electronic feedback loops must be tuned to track the resonant frequency in real time. As the target moves, the circuit must adjust its drive frequency to maintain resonance and optimize the signal-to-noise ratio. If the tracking circuit is too slow, the sensor will lose lock and produce inaccurate measurements.
High-speed digital signal processors are used to ensure that the tuning is updated continuously during rapid target movements.
Thermal Influence
Ambient temperature changes can cause independent shifts in the circuit’s natural frequency. These thermal effects can be mistaken for a true resonance shift caused by target movement if they are not properly compensated. To prevent this, sensors use reference resonators that are shielded from the target but exposed to the same temperature.
Comparing the two signals allows the system to subtract the thermal drift and isolate the true target measurement, ensuring high stability in environments where temperature fluctuates rapidly.