# An NDT Method for Measuring the Diameter and Embedment Depth of the Main Rebar in Cement Poles Based on Rotating Permanent Magnet Excitation

## TL;DR

A new non-destructive method using rotating magnets improves accuracy in measuring rebar in cement poles.

## Contribution

Proposes a magnetic rotation-based detection method with CNN-LSTM for rebar diameter and depth measurement.

## Key findings

- The method reduced RMSE by 46.71% for rebar diameter measurements.
- The method reduced RMSE by 35.57% for rebar embedment depth measurements.

## Abstract

Cement poles serve as supporting components for transmission lines and are widely used in medium- and low-voltage transmission networks. The main rebar is the primary load-bearing structure of the pole, and the accurate measurement of its diameter and embedment depth is crucial for quality control and safety assessment. However, existing non-destructive testing methods lack the accuracy of quantifying the internal main rebar of cement poles, and the measurement process is complex, cumbersome, and inefficient. To address this issue, this paper proposes a magnetic rotation-based detection method for measuring the diameter and embedment depth of the main rebar within cement poles. A specially designed H-type magnetic excitation structure is proposed, coupled with a detection technique utilizing rotating permanent magnets. The magnetic induction intensity data were acquired at seven distinct rotation angles using sensors, and the collected data were subsequently combined with a CNN-LSTM model to invert the diameter and embedment depth of the main rebar. The experimental results indicate that the method significantly improved the measurement accuracy compared with the condition of fixed magnetic excitation, with reductions in root mean square error (RMSE) of 46.71% and 35.57% for the diameter and embedment depth measurements, respectively. This method provides a robust, efficient, and accurate solution for quantifying the main rebar within cement poles, addressing the challenge associated with the quality assessment and health monitoring of these structures.