Influence of backing layer on the non-metallic encapsulated acoustic emission sensor for concrete monitoring

Use acoustic emission sensors to monitor the acoustic emission phenomenon of concrete materials after being loaded has always been a hot spot in the field of civil engineering. Currently, the mixture of tungsten powder and epoxy resin was commonly used as the backing layer of acoustic emission sensors. Therefore, the influence of tungsten powder content on backing layer and acoustic emission sensor was studied. The backing layer of air has the largest acoustic reflection coefficient, and the mixture of epoxy resin and tungsten powder has the largest acoustic attenuation performance, which is benefit to improve the bandwidth of the acoustic emission sensor. As the content of tungsten powder increases, the acoustic reflection coefficient of the mixture of tungsten powder and epoxy resin gradually decreases, the acoustic impedance gradually increases, and the resolution of the acoustic emission sensor increases, both the resonant frequency and electrical impedance of the sensor gradually decrease. When the tungsten powder content in the backing layer reaches 50% of the total mass, the optimal backing layer of the sensor was prepared, and the fabricated sensor exhibits a higher peak-to-peak value of 7.5 V and a larger first wave amplitude of 3.4 V. It also possesses the widest -3 dB bandwidth of 7 kHz. The uniaxial compression experiment of concrete with equal strain rate was carried out. According to the variation law of acoustic emission characteristic parameters, the compression characteristics of concrete in uniaxial compression test were divided into three stages.