# A Quasi-Distributed Crack Sensor Based on Weakly Coupled Vertical U-Shaped Ring Array

## TL;DR

A new sensor design improves crack detection in metal structures by enabling large-area monitoring with high sensitivity.

## Contribution

A vertical U-shaped ring array sensor is proposed for large-area crack detection with consistent sensitivity.

## Key findings

- The sensor achieves a sensitivity of 0.95 GHz/mm² for crack depth detection.
- It also detects crack width with a sensitivity of 0.685 GHz/mm².
- The design allows large-area monitoring while maintaining high sensitivity.

## Abstract

Cracks are common defects in metallic components, the presence of which can significantly affect service life and operational stability. Sensors based on electromagnetic resonators have relatively high sensitivity; however, they are limited in size, which restricts their coverage and makes large-area monitoring unattainable. The uneven internal field distribution within the resonator is a critical factor contributing to sensitivity variation at different locations. In this study, a vertical U-shaped ring structure is excited using a microstrip line. This allows the sensor to achieve large-area monitoring while maintaining sensitivity. The shift in resonance frequency is investigated and extracted as a characteristic feature for crack identification. The sensitivity of the measurement is 0.95 GHz/mm2 for depth and 0.685 GHz/mm2 for width. The proposed sensor can be used to detect potential cracks in metal structures.