Liftoff Tolerant Pancake Eddy-Current Sensor for the Thickness and Spacing Measurement of Nonmagnetic Plates

Huang

et al. 2021

Sensors

Self Cite

Electromagnetic eddy current sensors are commonly used to identify and quantify the surface notches of metals. However, the unintentional tilt of eddy current sensors affects results of size profiling, particularly for the depth profiling. In this paper, based on the eddy current thin-skin regime, a revised algorithm has been proposed for the analytical voltage or impedance of a tilted driver–pickup eddy current sensor scanning across a long ideal notch. Considering the resolution of the measurement, the bespoke driver–pickup, also termed as transmitter–receiver (T-R) sensor is designed with a small mean radius of 1 mm. In addition, the T-R sensor is connected to the electromagnetic instrument and controlled by a scanning stage with high spatial travel resolution, with a limit of 0.2 μm and selected as 0.25 mm. Experiments were conducted for imaging of an aluminium sheet with seven machined long notches of different depths using T-R sensor under different tilt angles. By fitting the measured voltage (both real and imaginary part) with proposed analytical algorithms, the depth profiling of notches is less affected by the tilt angle of sensors. From the results, the depth of notches can be retrieved within a deviation of 10% for tilt angles up to 60 degrees.

Section: Resultsmentioning

confidence: 99%

Analysis of Tilt Effect on Notch Depth Profiling Using Thin-Skin Regime of Driver-Pickup Eddy-Current Sensor

Huang

et al. 2021

Sensors

Self Cite

“…In recent years, the Dodd-Deeds formula [31] has been widely used for the inductance analysis of the air-core coil above the conductive plates [32]- [37]. For the designed eddy current sensor shown in Fig.…”

Section: Material-independent Algorithm and LII Feature A Original Analytical Formulationmentioning

confidence: 99%

“…where P t and P r are the integral of the Bessel series and α is related to the wavenumber of the incident transverse electric (TE) plane EM wave (in the free space) [31], [37]…”

Section: Material-independent Algorithm and LII Feature A Original Analytical Formulationmentioning

confidence: 99%

Inversion of Distance and Magnetic Permeability Based on Material-Independent and Liftoff Insensitive Algorithms Using Eddy Current Sensor

IEEE Trans. Instrum. Meas.

Huang

et al. 2021

Self Cite

Eddy current sensors can be used to test the characteristics and measure the parameters of the conductive samples. As the main obstacle of the multifrequency eddy current (MEC) sensor, the liftoff distance affects the effectiveness and accuracy of the measurement. In this article, a material-independent algorithm has been proposed for the restoration of the liftoff distance when using the MEC sensor, which is based on the approximation under the thin-skin effect. Experiment testing on the performance of the proposed method is presented. The results show that from the dual-frequency inductance, the liftoff distance could be restored with a maximum error of 0.24 mm for the distance up to 12 mm. Besides, the derived liftoff distance is used for the inversion of the magnetic permeability. Based on a liftoff insensitive inductance (LII) feature, the magnetic permeability of steels can be inversed in an iterative manner, with an error of less than 0.6 % for the liftoff distance up to 12 mm.

“…The maximum error between the analytical and experimental data is around 5.3 %. Since the test piece becomes more inductive under high working frequencies (referring to [38][39][40][41][42][43][44]), the magnitude for the imaginary part of voltage changes due to the crack is much larger than (around 20 times) that of the real part. Owing to the different sensitivity, a deeper crack results in a larger magnitude of voltage change.…”

Section: Scanned Voltage For T-r Sensor Across Notch Without Tilt Effectmentioning

confidence: 99%

Analysis of Tilt Effect on Notch Depth Profiling Using Thin-Skin Regime of Driver-Pickup Eddy-Current Sensor

Huang³

et al. 2021

Preprint

Self Cite

Electromagnetic eddy current sensors are commonly used to identify and quantify the surface notches of metals. However, the unintentional tilt of eddy current sensors affects results of size profiling, particularly for the depth profiling. In this paper, based on the eddy current thin-skin regime, a revised algorithm has been proposed for the analytical voltage or impedance of a tilted driver–pickup eddy current sensor scanning across a long ideal notch. Considering the resolution of the measurement, the bespoke driver–pickup, also termed as transmitter-receiver (T-R) sensor is designed with a small mean radius of 1 mm. Besides, the T-R sensor is connected to the electromagnetic instrument and controlled by a scanning stage with high spatial travel resolution , with a limit of 0.2 μm and selected as 0.25 mm. Experiments have been out on the voltage imaging of an aluminium sheet with 7 machined long notches of different depths using T-R sensor under different tilt angles. By fitting the measured voltage (both real and imaginary part) with proposed analytical algorithms, the depth profiling of notches is less affected by the tilt angle of sensors. From the results, the depth of notches can be retrieved within a deviation of 10 % for tilt angles up to 60 degrees.