Denis Ijike Ona

Project title

Investigation of Tx-Rx mutual inductance eddy current system for high lift-off inspection

Supervisors

Project description

We are designing a mutual inductance based Tx-Rx (Transmitter-Receiver) PEC (Pulse Eddy Current) system for high lift-off NDT&E (Non-destructive Testing and Evaluation) application. This would include applications such as thick insulated or buried structures and weld areas.

We are focusing on EC (eddy current) system configuration in solving the challenges caused by high lift-off inspection. The major parts of our study of the EC system are:

EC probe configuration
signal conditioning
excitation modes

We optimised the lift-off and coil gap of a Tx-Rx probe to mitigate the offset caused by the direct coupling of Tx-Rx coils to improve sensitivity. We have designed a signal conditioning circuit to remove the influence of self- impedance of the Rx coil. This will improve SNR at high lift-off.

We compared different excitation modes. This enabled us to select the best excitation mode for high lift-off inspection.

Result

Generally, the optimised Tx-Rx system extended the detection sensitivity of EC system to lift-off of about 30mm. This is much higher than the 5mm lift-off limit of a single-coil EC probe. The modified Maxwell’s inductance achieved more SNR (signal-to-noise ratio) and linearity range than conventional AC bridges.

Measurement errors caused by electromagnetic interference and stray capacitance effects were also reduced.

Our comparison of the excitation modes revealed that: