Properties Of 1-3 Polymer/cement Based Piezoelectric Composites

Cement based piezoelelctric composite has the characteristic of excellent compatibility with concrete and finer piezoelectric property, and the development of this composite also has widely application significance. 1-3 polymer/cement based piezoelectric composites are fabracated by cut-filling technique in order to improve the strength between cement matrix and piezoelectric ceramic and reinforce the flexibility and the whole property. The piezoelectric property, dielectric property, electromechanical coupling property, mechanical quality factor and acoustic impedance were studied, respectively.The influence of matrix on properties of the composites was researched. The results show that compared with polymer and cement based piezoelectric composites, polymer/cement based piezoelectric composites have high piezoelectric constant and low dielectric constant. Thickness electromechanical coupling factor Kt and frequency bandΔf are reinforced, while mechanical quality factor Qm is decreased at the same time. The acoustic impedance Z of composites is hardly influenced by the matrix. The influence of polymer/cement ratio on properties of the composites was researched. The results show that the piezoelectric strain constant d₃₃, piezoelectric voltage constant g33 and relative dielectric constantε_r all decrease obviously with the increase of cement mass percent in matrix. However, the dielectric loss tanδkeep to be constant with increasing the cement mass percent in matrix. Both planar electromechanical coupling factor Kp and thickness electromechanical coupling factor Kt decrease initially and then increase. Compared with P(LN)ZT, the thickness vibration mode of 1-3 type piezoelectric composites is strengthened obviously, but electromechanical quality factor Q-m is reduced. All of these are in favor of increasing the emission efficiency and receiver sensitivity. With the increase of cement mass percent, acoustic impedance Z of the composites increases gradually, which is close to that of the concrete.The influence of P(LN)ZT volume fraction on properties of the composites was researched. The results show that as the P(LN)ZT volume fraction increases, the piezoelectric strain constant d₃₃, relative dielectric constantε_r and acoustic impedance Z increase evidently, while the piezoelectric voltage constant g33 and the dielectric loss tanδdecrease. Compared with P(LN)ZT, the thickness vibration mode of 1-3 type piezoelectric composites is strengthened, however electromechanical quality factor Qm is reduced. When P(LN)ZT volume fraction is 30.86 %, the acoustic impedance value is 8.24 M rayl, which is close to that of the concrete (9.0 M rayl) and suitable for fabricating transducers for non destructive inspection.The influence of aspect ratio w/t on properties of the composites was researched. The results show that with the increase of aspect ratio w/t, piezoelectric strain constant d33 and dielectric constantε_r exhibit the trend of decrease evidently. Piezoelectric voltage constant g33 also decreases slowly. Planar electromechanical coupling Kp of the composites is hardly influenced by the aspect ratio w/t variation. With increasing of aspect ratio w/t, all of the series resonant frequency fs, parallel frequency fp, the frequency band△f and the capacity at 1 kHz exhibit the trend of increase. However, thickness electromechanical coupling factor Kt increase. When the aspect ratio w/t is 1.43, K_t could reach to 73.56%. With the increase of aspect ratio, acoustic impedance of the composites changes little, which fluctuates between 10-11 M rayl. At the same time, the influence of temperature on dielectric properties of the composites was studied. The results show that with increasing the temperature at the frequencies of 1 kHz and 150 kHz, the dielectric constant _εr exhibits the trend of increase. In the temperature range of -40℃-110℃, the dielectric loss tanδfirst increases slowly, then increases evidently when the temperature is larger than 80℃..