Target Alloy Phase Selection for Inductive Sensing
Target alloy phase selection governs inductive sensor stability: unstable austenitic grades transform to ferromagnetic martensite under machining, inducing major drift.
Multi Frequency Sensing
Interrogation Technique
Electromagnetic interrogation techniques utilize several distinct excitation frequencies simultaneously or sequentially to evaluate a target material. This approach, known as multi frequency sensing, allows eddy current and inductive sensors to extract information from different depths within a conductor. Higher frequencies remain near the surface due to the skin effect, while lower frequencies penetrate deeper to assess subsurface properties.
By analyzing the complex impedance at multiple points, the system can distinguish between changes in lift-off and material conductivity. The simultaneous use of these frequencies increases the reliability of structural inspections in automated production environments.
Signal Processing
Demodulation algorithms extract the amplitude and phase information for each individual frequency from the returned signal. These components are analyzed using regression models or neural networks to separate different physical parameters of the target. This separation is necessary when multiple variables, such as temperature and distance, change simultaneously.
The combined data provides a more complete assessment than is possible with a single-frequency measurement.
Application Scope
Thickness measurements of non-magnetic coatings on metallic substrates rely on the distinct responses of high and low frequencies. The high-frequency channel measures the distance to the substrate surface, while the low-frequency channel assesses the bulk substrate. This method is utilized in manufacturing lines to monitor coating consistency in real time without stopping the process.
System Limitation
Increased complexity in the sensor electronics can introduce noise and drift if the channels are not properly isolated. Cross-talk between frequencies must be minimized through active filtering and careful shielding of the analog front end. Calibration is also more complex, requiring multiple reference standards to configure each channel.