Development of structural health monitoring system by using Piezoelectric sensors

Abstract

This research involves the application of piezoelectric sensors. It uses the property of converting pressure to the potential difference in the piezoelectric material. The piezoelectric sensor is patched on the specimen to measure the electrical signal, when the specimen is acted by external forces. This research will be divided into two parts. In the first part, we developed a structural health monitoring system by using piezoelectric sensors. The piezoelectric sensor was patched on specimens such as mortar, concrete, aluminum, wood, and acrylic plate to study the electrical signal. In addition, the piezoelectric sensor was embedded in mortar and concrete specimens to investigate the electrical signal when the specimen was acted by external force. In the second part, we investigated the obtained electrical signal from the piezoelectric sensor. It consists of three main parts. Firstly, it was the study of characteristics of the piezoelectric sensor, which considers the electrical signal produced by different piezoelectric sensor sizes. In this research, it was found that the size of the piezoelectric sensor was larger, the peak of the signal moved to a lower frequency. The temperature also affected in different response to the electric signal. As the temperature increased, the resonance frequency decreased. And when force was applied to the piezoelectric sensor, the signal peak was larger and tended to occur at lower frequencies. When the piezoelectric was immersed in an alkaline solution, the resonant frequency did not change. Secondly, we investigated the electric potential signal received when a mass as released onto a piezoelectric sensor. From the study, it showed that when a sensor was connected to an external resistance of 500 ohms, it produced the most electrical work, which was related to the resonant resistance of the sensor. It was also found that if the mass was dropped vertically at the center of the piezoelectric sensor, it provided the most electrical work. This was related to the force acting on the piezoelectric sensor. The greater the force acting, the more electrical work was obtained. In addition, we patched the three piezoelectric sensors on the surface of aluminum plate, acrylic plate, and wood plate. Three piezoelectric sensors were placed 15 cm apart and stimulated with a single pulse on the specimen plate. A sensor was installed in the center of the plate, and the other sensor was near the trigger point. The electrical signal received by the sensor was an underdamped oscillation and the envelope curve was entirely double exponential decay. Apart from piezoelectric sensors from acrylic plate and wood plate, the logarithm decrements of aluminum plate. acrylic plate, and wood plate were 2.1142, 3.6034, and 2.1271, respectively. The behaviors of oscillation for all plates are underdamped oscillation because the damping factors for aluminum, acrylic and wood plate were 0.3189, 0.4975 and 0.3207, respectively. The free vibrations of aluminum, acrylic, and wood plate were 22.11, 13.80, and 15.98 Hz, respectively. Third, the piezoelectric sensor was embedded in mortar and concrete specimens, after that, the mass was dropped on the specimen and we measured the electrical signal obtained from the piezoelectric sensor. It was found that when we connect the sensor with an external resistance of 500 ohms, it would get the most electrical work and also found that if we released a larger mass, higher release point, the position of embedded piezoelectric sensor in specimen was near surface of impact surface and side where the incident mass was perpendicular to the plane of the piezoelectric sensor, as a result the electrical work was greater due to the greater force exerted on the piezoelectric sensor. And when the mass was dropped onto the surface of the mortar sample, the electrical work tended to be the greatest at the center of the specimen and decreased as it falls further away. In the case of concrete, the point of incidence at the center of the specimen surface tended to produce lower electrical work compared to the edge of the concrete. It was also found that the age of the specimen affected the response to the electrical signal. The received signal dominated when the age of the specimen increased, and from 14 days of age, the signal became clearer. This was related to the compressive strength of the specimen. The compressive strength increased as the age of specimen increased. The results were obtained by the study of electrical impedance from the piezoelectric sensor by using the electrochemical impedance spectroscopy technique. The obtained impedance data was created graph in Nyquist plot. The shape of graph was semicircular. And it became larger as the age of specimen increased. When the electrical impedance was analyzed for the equivalent circuit by using the zview program, the R(Q(RW)) model was used for the analysis. The (Q(RW)) term was related to surface behavior, where Q was related to the constant phase element and it was replaced by a capacitor to compensate for the imperfect capacitor. This showed behavior of double layer capacitance. R was related to the charge transfer resistance at surface metal. It associated with the electrochemical reaction. W is the Warburg impedance, which was related to the diffusion of the charge through its surface. The studying found that the charge transfer resistance at the metal surface increased when aging of the cementitious specimen increased, and the Warburg impedance increased when aging of the cementitious specimen increased.