Monitoring fatigue crack growth and opening using antenna sensors

Abstract

Fatigue cracking is one of the most common failure modes of various load-bearing structures. Even though sensors of many different types have been developed for crack detection, very few can monitor crack growth with a high sensitivity. This paper presents an antenna sensor that is capable of monitoring the growth of fatigue cracks with a sub-millimeter resolution. According to microstrip patch antenna theory, the resonant frequencies of a dual-frequency patch antenna are inversely proportional to the electrical lengths of the corresponding antenna radiation modes. The presence of a crack in the ground plane or the elongation of the antenna patch due to crack opening increases the electric length, thereby causing a shift in its corresponding resonant frequency. As a result, crack propagation and opening can be monitored from the resonant frequency shifts of the patch antenna. The patch antenna's capability of monitoring crack growth was validated using fatigue testing of a compact tension specimen. The specimen preparation, sensor fabrication, and experimental procedure are presented. The experimental results demonstrated that the corresponding resonant frequency of the antenna sensor shifted linearly with crack growth. On average, 1 mm crack growth caused the antenna frequency to shift by 22.1 MHz. The orientation of the crack and the effect of crack closure on the resonant frequencies of the antenna sensor are also discussed.

Numerical simulation and experimental validation of a large-area capacitive strain sensor for fatigue crack monitoring

“…These sensors, often referred to as sensing skins, share one common feature of large size but operate under a wide variety of principles. Examples include carbon nanotube based sensors [10,11] , resistive sensor sheets [12] , printable conductive polymer [13] , patch antenna sensors [14,15] , and soft elastomeric capacitive (SEC) sensors [16,17,18] , etc. In particular, the SEC sensor is a highly scalable sensor due to its ease of fabrication and low cost materials.…”

Wireless Sensing in Complex Electromagnetic Media: Construction Materials and Structural Monitoring

“…It is observed that the concrete cover slightly decreases the resolution, from sub-μm to 1 μm level. Despite that, to the best of the authors' knowledge, this level of resolution in the complex medium is still better than those of the previously shown passive wireless sensors for SHM in literature, some of which were reported in free space [5], [18], [37]. The concrete plate experiments related with the drop of the resonance frequency and the resolution hold significance because the front cover is the only element whose effect on the sensor cannot be avoided.…”

Multimodal fatigue progress monitoring of construction steel elements

“…In this method the microwave patch sensors is used to monitoring the stress and crack growth in conductive material [8,9]. In case of stress monitoring microstrip sensor has its own ground plane (it is a part of the sensor).…”