| Piezoelectric composites are a type of functional materials that are composed of a piezoelectric ceramic phase and an organic polymer phase according to a certain connection way.Piezoelectric composites have been widely studied because they integrate with the merits of each individual constituent phase,and have many important applications both in medical ultrasound probes and underwater acoustic transducers.The connection mode of 1-3 piezoelectric composites is one-dimensional connected inorganic piezoelectric ceramics embedded in a three-dimensional connected polymer matrix.Acoustic impedances of 1-3 piezoelectric composites are much lower less than acoustic impedances of PZT ceramics,so the transducer made of piezoelectric composite is easier to match with water and body tissue.Methods developed for processing 1-3 piezoelectric composites include dice-fill,lost mold etc.The dice-fill method is convenient and cost-effective,by which ceramic pillar width and spacing can be easily controlled as needed,so it is widely adopted for forming 1-3 piezoelectric composites.In this paper,we prepared the 1-3 PZT-Epoxy piezoelectric composites with different volume ratios of PZT ceramics and 1-3 BCZT-Epoxy piezoelectric composite with 31%volume ratio of BCZT ceramic by dice-fill,and studied their corresponding ultrasonic properties.The main results are as follows:(1)The influences of volume ratio of ceramic phase on the piezoelectric coefficient and acoustic impedance of 1-3 PZT43-Epoxy piezoelectric composites were investigated,and the relationship between electromechanical coupling coefficient kt and thickness of piezoelectric composites was discussed.Three piezoelectric composites were prepared with the ceramic volume ratios of 25%,31%and 40%,respectively.The result indicates that acoustic impedance Z and piezoelectric coefficientd33 increase as the volume ratio of ceramic phase is increased.A minimum value of acoustic impedance is 10.2 Mrayl,and a maximum value of d33 is 317 pC/N.Compared with PZT43 ceramics,the 1-3 PZT43-Epoxy piezoelectric composites have an improved electromechanical coupling coefficient kt,a reduced dielectric constant εr,an increased dielectric loss tanδ and a 2-order lower mechanical quality factor Qm.For all the 1-3 PZT43-Epoxy piezoelectric composites,kt shows the quite good temperature stability in the wide temperature range from-50℃ to 150℃,and increases first and then decreases with increasing the thickness.Maximum kt values are obtained at an aspect ratio of about 3.Typically,the 1-3 PZT43-Epoxy piezoelectric composite with a ceramic volume of 31%and a thickness of 1.4 mm shows the physical properties of d33=273 pC/N,Z =11 Mrayl,kt= 0.66,Qm= 4.1,εr= 410 and tanδ = 0.03.(2)The influences of volume ratio of ceramic phase on the physical properties of 1-3 PZT5H-Epoxy piezoelectric composite were investigated,and the relationship between electromechanical coupling coefficient kt and aspect ratio was discussed.Three piezoelectric composites were prepared with the ceramic volume ratios of 25%,31%and 40%,respectively.The result shows that electromechanical coupling coefficient kt decreases as the volume ratio of ceramic phase is increased.For the 1-3 PZT5H-Epoxy piezoelectric composite with ceramic volume ratio of 25%,the kt is increased by 40%compared with the PZT5H ceramic.Acoustic impedance Z and piezoelectric coefficient d33 increase as the volume ratio of ceramic phase is increased.A minimum value of acoustic impedance is 9.8 Mrayl,and a maximum value of d33 is 460 pC/N.For all the 1-3 PZT5H-Epoxy piezoelectric composites,kt increases first and then decreases with increasing the thickness,and kt of piezoelectric composites with the ceramic volume ratios of 25%,31%and 40%is optimal as the thickness is 1.2mm,1.4mm and1.6mm,respectively.Typically,the 1-3 PZT5H-Epoxy piezoelectric composite with a ceramic volume of 25%and a thickness of 1.2 mm shows the physical properties of d33 = 372 pC/N,Z = 9.8 Mrayl,kt = 0.7,Qm M 5.8,εr = 650 and tanδ =0.04.(3)The Influences of BaCO3 pretreatment on properties of BCZT piezoelectric ceramic were investigated.1-3 BCZT-Epoxy piezoelectric composite with the ceramic volume ratio of 31%was fabricated via a dice-fill method and the physical properties were discussed.BCZT ceramic with BaCO3 pretreatment shows the physical properties of kp=0.48,kt = 0.36 and Qm = 180,respectively.Electromechanical coupling coefficient kt and mechanical quality factor Qm of the 1-3 BCZT-Epoxy piezoelectric composite is 0.51 and 3.9,respectively.Compared with BCZT ceramics,the 1-3 piezoelectric composites have an improved electromechanical coupling coefficient kt and a 2-order lower mechanical quality factor Qm.The electromechanical coupling coefficient kt increases first and then decreases as increasing the thickness,a maximum value of ktis 0.51 when the thickness is 1.6mm. |
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