Research and optimum selection of coupling agent materials in ultrasonic measurement

In the detection of metal defects by ultrasonic Lamb waves, the commonly used medical coupling agent is volatile, poor stability, and the coupling effect is easily affected. It is vital to find the coupler materials with better performance. This paper develops sodium alginate hydrogel and acrylamide hydrogel with higher curing degree, and compares them with deionized water and medical coupling agent. At the same time, epoxy glue and organic silicone, which commonly used as adhesives in the aerospace field are selected for performance research. Firstly, analyzing FTIR spectra of the three hydrogels. The results showed that the hydrogel composition are correct and subsequent experiments are reliable. Secondly, the performance characteristics of 6 couplings are studied from 5 aspects of acoustic impedance, ultrasonic energy transfer efficiency, stability, temperature characteristics and oxidation resistance. The results show that the acrylamide gel developed in this paper has higher viscosity and stability than the medical coupling agent, and has a wider application. Based on the five performance studies, it can be concluded that in the measurement environment of long-term fixed sensors in the industrial and aerospace fields, organic silicone can not only play the role of bonding sensors and insulation, but have the advantages of strong stability, high ultrasonic energy transfer efficiency, temperature tolerance, oxidation resistance, etc. It is the optimal coupling material in ultrasonic testing for complex environments. The research in this paper provides a reference for the selection of optimal coupling agent materials for more complex applications, which has important engineering significance.