PZT Volume Fraction Research Articles

Piezoelectric properties of ferroelectric PZT-polymercomposites

The most widely used material for active transducer applications isthe ferroelectric ceramic PZT. Composites made of ferroelectric ceramicscombined with polymers have several advantages over pure ceramics. Diphasiccomposites of PZT (and La/Ca modified PZT) combined with various polymers suchas PVDF, PVC, PVA, epoxy resin and co-polymers have been widely studied andreported in the literature.In this paper we present the preparation and study of PZT-PVDF composites of0-3 connectivity. The composites are prepared by two methods, namely (i) thesolvent-cast method and (ii) the hot-press method. The piezoelectric straincoefficient (d33) is studied as a function of volume fraction of PZT inPVDF. The dielectric constant (k) is measured as a function of temperatureand the piezoelectric voltage coefficient (g33) of the composite isdetermined.The experimental values of the dielectric constant, d33 and g33 ofthe composites are compared with the earlier reported values and thetheoretical values proposed by Furukawa et al (Furukawa T, Ishida K andFukada E 1979 J. Appl. Sci. 50 4904) and Bhimasankaram et al (Bhimasankaram T, Suryanarayana S V and Prasad G P 1998 Curr. Sci. 4 967).The composite with 0.5 PZT volume fraction prepared by the hot-press method isfound to possess a reasonably high d33 value and exhibit good flexibilityand stability with time.

Resonance characteristics of lead zirconate titanate/epoxy 1–3 composite rings

Lead zirconate titanate (PZT)/epoxy 1–3 composite rings with PZT volume fractions ø ranging from 0.82 to 0.94 are fabricated, and their resonance characteristics are studied. These composite rings have sufficiently small epoxy width (∼ 77 μm) and can be treated as effective homogeneous media in which stopband resonances are not observed in the frequency band of interest (< 4 MHz). A mode coupling theory is applied to predict the longitudinal-thickness fH and lateral fL mode resonances of PZT elements inside the rings. By thinning the rings and by measuring the resonance peaks using an impedance analyzer, fH is observed to increase linearly with the decrease in element height while fL remains constant. When the height and width of the elements become comparable, mode coupling occurs. To avoid spurious modes being coupled to fH , the rings cannot be too thin in order to keep fH smaller than fL . In the lower frequency regime, they cannot be too thick to avoid coupling of fH with the wall-thickness fW and radial fR mode resonances. fW and fR are found to be independent of ring thickness but increase as Ø increases.

Nanocomposite ultrasonic hydrophones

Needle-type hydrophones for the calibration of medical ultrasonic transducers have been fabricated using lead zirconate titanate (PZT)/poly(vinylidene fluoride-trifluoroethylene) (PZT/P(VDF-TrFE)) 0–3 nanocomposite films. The 0–3 nanocomposite film has been prepared by incorporating nanosized PZT powder (derived from a sol–gel process) in a P(VDF-TrFE) matrix. Since the piezoelectric coefficients of PZT and P(VDF-TrFE) have opposite signs, the PZT and P(VDF-TrFE) phases in the nanocomposites have been poled in opposite directions in order to give enhanced piezoelectric activity. A nanocomposite hydrophone with 0.2 volume fraction of PZT has been characterized and found to be more sensitive than a P(VDF-TrFE) hydrophone of similar structure.

Application of piezoelectric composites and net-shape PZT ceramics as acoustic sensors and actuators

A ceramic injection molding process is used to custom manufacture piezoelectric composites for both sensors and actuators with operational frequencies from 100 Hz and 10 MHz. These piezoelectric composites can be specifically tailored to couple acoustic energy into and from a wide variety of mediums including air, water, biological tissue, polymers, composites, and metals. Both 1-3 and 2-2 piezoelectric composites have been made with different lead zirconate-titanate (PZT) formulations, element dimensions, PZT volume fractions, and polymeric matrices. Piezoelectric composite transducers are easily conformed to various substructures, shaded to adjust beam patterns, and sectioned into arrays for imaging. Examples include face-plated SonoPanels (and stiff matrix 1-3 piezoelectric composites for underwater actuation, sensing, and imaging. SmartPanels, capable of both sensing and actuating, have been recently introduced for active surface control. These devices integrate 1-3 piezoelectric composite actuators and pressure sensors and net-shape molded PZT velocity sensors in a large-area, low-profile panel. Multiple net-shape molded accelerometer elements have been designed, fabricated, and tested. Both single and double layer 100×100-mm SmartPanels have been characterized for sensor sensitivities, actuator authority, surface displacement uniformity, and sensor-actuator coupling. Also, recent developments of injection molded PZT bender arrays for low-frequency air acoustic transducers will be presented. [Work supported by ONR and DARPA.]

Thickness dependence of the poling and current–voltage characteristics of paint films made up of lead zirconate titanate ceramic powder and epoxy resin

A specially prepared paint made up of lead zirconate titanate (PZT) ceramic powder and epoxy resin was coated on an aluminum plate and was cured at room temperature, thus forming the paint film of 25–300 μm thickness with a PZT volume fraction of 53%. The paint film was then poled at room temperature, and the poling behavior was determined by measuring the piezoelectric activity as a function of poling field. The poling behavior shows that the piezoelectric activity obtained at a given poling field increases with an increase in the film thickness from 25 to 300 μm. The current–voltage characteristic of the paint film, on the other hand, shows that the increase in the film thickness leads not only to an increase in the magnitude of the current density at a given electric field but also to an increase in the critical electric field at which the transition from the ohmic to space-charge-limited conduction takes place. This fact indicates that the amount of the space charge of electrons injected into the paint film decreases as the film thickness increases. Furthermore, comparison of the current–voltage characteristic of the paint film with that of a pure epoxy film reveals that the space charge is accumulated largely at the interface between the PZT and epoxy phases in the paint film. On the basis of this finding, a model is developed for the poling behavior of the paint film by taking into account a possible effect of the space-charge accumulation and a broad distribution of the electric field in the PZT phase. This model is shown to give an excellent fit to the experimental data of the piezoelectric activity obtained here as a function of poling field and film thickness.

Preparation of Piezoelectric Paints and Application as Vibration Modal Sensors

Piezoelectric paints were prepared using lead zir conate titanate (PZT) ceramic powder as a pigment, and epoxy resin as a binder. The obtained paints were coated on aluminum beams and were dried at room temperature, thus forming films with thicknesses of 35 to 81 μm and PZT volume fractions of 30 to 53% . The films were then poled under electric fields of up to 350 kV/cm at room temperature, and the resulting piezoelectric activity was evaluated from vibration measurements on the aluminum beams. The piezoelectric activity obtained under a given poling field increases with increasing film thickness and with increasing volume fraction of PZT. The piezoelectric activity of the PZT/epoxy paint film has proved to be high enough to determine the natural frequencies and mode shapes of a structural material, thus demonstrating the potential of the paint film as a built-in vibration modal sensor.

Simple model for piezoelectric ceramic/polymer 1–3 composites used in ultrasonic transducer applications : IEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, Vol. 36, No. 4, pp. 434–441 (Jul. 1989)

A theoretical model is presented for combining parameters of 1-3 ultrasonic composite materials in order to predict ultrasonic characteristics such as velocity, acoustic impedance, electromechanical coupling factor, and piezoelectric coefficients. Hence, the model allows the estimation of resonance frequencies of 1-3 composite transducers. This model has been extended to cover more material parameters, and they are compared to experimental results up to PZT volume fraction nu of 0.8. The model covers calculation of piezoelectric charge constants d/sub 33/ and d/sub 31/. Values are found to be in good agreement with experimental results obtained for PZT 7A/Araldite D 1-3 composites. The acoustic velocity, acoustic impedance, and electromechanical coupling factor are predicted and found to be close to the values determined experimentally. >

Sandwich-layer transducer—a versatile design for ultrasonic transducers operating in air

Abstract This paper reports the results of our work concerning PZT/polymer 2-2 composites for airborne ultrasonic applications in industrial automation. The shape of rectangular piezoceramic plates is important for efficiency and radiation characteristics. Three distinct geometries are found interesting, having width-to-length ratios of less than 0.3, equal to 0.42 and between 1.0 and 1.2, respectively. The electroacoustic conversion efficiency increases with decreasing acoustic impedance of the sandwich. Contour extensional resonances can be controlled for a PZT-volume fraction as small as 2.5%, producing a gain in efficiency of +30 dB compared to the solid piezoelement. The efficiency is increased by additional polymer layers fixed on the radiating surface. Extreme broadband transducers have been developed for applications in the field of object recognition and acoustic holography by the use of rubber-like material for inactive layers.

Simple model for piezoelectric ceramic/polymer 1-3 composites used in ultrasonic transducer applications

A theoretical model is presented for combining parameters of 1-3 ultrasonic composite materials in order to predict ultrasonic characteristics such as velocity, acoustic impedance, electromechanical coupling factor, and piezoelectric coefficients. Hence, the model allows the estimation of resonance frequencies of 1-3 composite transducers. This model has been extended to cover more material parameters, and they are compared to experimental results up to PZT volume fraction nu of 0.8. The model covers calculation of piezoelectric charge constants d(33) and d(31). Values are found to be in good agreement with experimental results obtained for PZT 7A/Araldite D 1-3 composites. The acoustic velocity, acoustic impedance, and electromechanical coupling factor are predicted and found to be close to the values determined experimentally.

Dielectric and piezoelectric studies of La doped PZT polymer composites

Abstract Lanthanum doped Lead Zirconate Titanate (La:Zr:Ti = 4:51:49) has been shaped to porous three dimensional structures through BURPS (Burntout Plastic spheres) process. The materials are then framed to low-density, low-permittivity 3–3 composites with silicone rubber as the second phase. Poled composite ceramics have shown significant increase in piezo-electric voltage coefficients (g333) with a corresponding drop in dielectric permittivity. Volume fraction of PZT poled is estimated using a theoretical model where the PZT is assumed to be made up of small cubelets of 1 to 2 micrometers in size.

PZT/Polymer composites for medical ultrasonic probes

Abstract PZT/polymer composite sheets (PZT pillars embedded in polymer matrix) for high frequency use are fabricated using a dicing and filling technique. These piezo-composite sheets are intended for use as medical ultrasonic probes. It is found that dielectric and electromechanical properties depend not only on the PZT volume fraction v PZT but also on the PZT pillar shape w/t (width-to-thickness ratio). Thickness dilatational electromechanical coupling factor k t is as high as 0.75 when v PZT = 0.25 and w/t = 0.5 ∼ 0.6. The period of the embedded PZT pillar lattice, d, is also important in determining the electromechanical properties. When d is close to the wavelength of laterally propagating transverse waves, lateral mode resonances are observed.

Piezoelectricity of a high-content lead zirconate titanate/polymer composite

A binary system consisting of polyvinylidene fluoride (PVDF) and lead zirconate titanate (PZT) powder was investigated to determine its dielectric constant, piezoelectric constant, and Young’s modulus. An expression was obtained for the piezoelectric constant, and expressions for the dielectric constant and Young’s modulus were also mentioned. The calculated values had good agreement with the observed values for the composite with a large PZT volume fraction. The dielectric constant and the piezoelectric constant were 152 and 48.3×10−12 C/N, respectively, for the composite with the PZT volume fraction of 0.67. Changing the mixing ratio of PVDF and the fluorine elastomer, Young’s modulus was varied without changing the piezoelectric constant.

Composites of PZT and Epoxy for Hydrostatic Transducer Applications

Composites with 3–1 connectivity for transducer applications were made by embedding extruded PZT rods in an epoxy matrix. The effects of rod diameter, volume fraction of PZT, and composite thickness on the hydrostatic properties of the composites were determined. Due to decoupling of the d̄33 and d̄31 coefficients in a composite with 3–1 connectivity, the d̄n may be enhanced, even in composites of low volume fractions of PZT. Such composites alsojiave a low dielectric permittivity. The combination of high d̄n values and low ɛ33 value results in a greatly enhanced ḡn. Composites with 10 vol% PZT were made with values of d̄h and ḡh which are, respectively, two times (&gt;80×10 −12 C/N) and 25 times (&gt;70×10−3 (V·m/N) the solid PZT values.