Fabrication Of Piezoelectric Ultrasonic Sensor And Its Application In Health Monitoring Of Concrete Structure

In recent decades, with the development of China’s economy, all kinds of civilengineering such as large-scale civil engineering, high-rise buildings, long-span bridges andwater conservancy facilities are constructing, the real time, and on-line structural healthmonitoring in civil engineering has gradually become a hot research topic of the academia andengineering, the application of smart materials in the field of engineering supplies useful waysto achieve the actual sense of the health monitoring of civil engineering.Piezoelectric materials have the characteristics of actuating and sensing; and many otheradvantages of fast response, good linearity, low energy consumption, low cost and easyprocessing. Therefore, piezoelectric material has been widely used in the field of concretestructure health monitoring. Piezoelectric ultrasonic sensor is smart device which withpiezoelectric material as sensing element, and it is an important part of concrete structurehealth monitoring system. Piezoelectric ultrasonic transducers are the devices that generateand receive ultrasound and convert the electric energy into ultrasonic energy, and vice verse.Its working mechanism is the positive and negative piezoelectric effect of piezoelectricmaterials. According to the working mechanism of piezoelectric ultrasonic sensors can bedivided into two kinds: emission type and reception type. In the background, Fabrication ofthe emission and reception piezoelectric ultrasonic sensors, and health monitoring forconcrete structures using sensors were researched in details in the paper and the main researchwork includes as follows.Firstly, piezoelectric ultrasonic sensors for emission type were researched and developed.The sensor was developed by using PZT-41piezoelectric ceramic. The influence of thematching layer and backing material on the performance of sensor was researched. The resultsindicate that when the thickness is2.5mm, the initial wave amplitude of sensors signal ismaximum, accord with quarter wave theory. When the mass ratio of tungsten powder andcement in the backing material is1.5:1, and the thickness of backing layer is6mm, the firstwave amplitude of sensor is bigger, and the signal attenuation is fast.Secondly, piezoelectric ultrasonic sensors for reception type were researched anddeveloped. The sensor was developed by using the1-3cement-based piezoelectric composite.The influence of the matching layer and backing material on the performance of sensor wasresearched. The experimental results showed that when ceramic column cross-sectional area is1×1mm2of1-3cement-based piezoelectric composite, sensor has the highest sensitivity,frequency bandwidth. The sensor with3mm thickness of the matching layer has the maximumfirst peak amplitude. At the same time, the result is agree with the theory of quarterwavelength. When the mass ratio of tungsten powder and cement in the backing material is2and the thickness of the backing is8mm, the bandwidth and receiving performance of thesensor is the best.Thirdly, concrete specimens were tested on the crack generation and propagationconditions using nonlinear ultrasonic technology. The received signals were analyzed usingtime domain and frequency spectrum of two signal processing methods. The concrete damagefeatures and degree are proposed in amplitude attenuation, waveform distortion, waveformand resonance. The experiment results showed that the amplitude of the response signal,resonance and nonlinear parameters can be good evidences to distinguish the crack damage inconcrete. The test results confirm that the use of embedded piezoelectric ultrasonic transducerfor concrete damage detection has good effectiveness.Fourthly, the compressive strength gain of concrete was monitored using the embeddedpiezoelectric ultrasonic sensors. By monitoring the acoustic signals and measuring thecompressive strength of concrete cubes in different ages, the correlations between concretestrength gain and ultrasonic acoustic parameters are founded. This method provides a newalternative for monitoring the compressive strength gain of concrete since the conventionalnondestructive detection techniques have many limitations. The test results show that methodof monitor the compressive strength gain of concrete based on embedded piezoelectricultrasonic sensors is feasibility.