Inorganic ceramic/polymer ferroelectric composite electrets

Ferroelectric composites are now an established alternative to conventional ferroelectric ceramic materials and to the more recently discovered ferroelectric polymers. These materials due to their unique blending of polymetric properties of mechanical flexibility, formability and low cost with high electro-active properties have been been suggested to be a viable alternative both in piezoelectric and pyroelectric transducer applications. This review is devoted to the piezoelectric and pyroelectric properties exhibited by these type of composites with a special reference to those made of ceramic particles embedded in a polymer matrix (i.e. 0-3 connectivity type composite). A review of models predicting the electro-active properties of 0-3 composites is presented together with a proposal for a new mixed connectivity cubes model to be applicable to the case of high ceramic loading and/or when the ceramic grain size incorporated in the polymer matrix is comparable to the thickness of the sample. A review of the experimental results of the piezo- and pyroelectric properties of various ferroelectric composite materials, reported by several workers, is also presented in this paper. Special reference is made to composites made from calcium modified lead titanate and poly(vinyldene fluoride-trifluorethylene) emphasizing their advantages in the poling process which is a critical phase in the process of obtaining successful electro-active 0-3 composite electrets     

Study of piezoelectric fibre/cement 1–3 composites

To improve the compatibility between the sensor material and civil engineering structural material, a new functional cement-based composite for smart structure applications has been studied. Piezoelectric lead zirconate titanate (PZT) fibres, fabricated using a slurry method, are embedded in a cement matrix to form PZT/cement 1–3 composites. By incorporating PZT fibres into the cement matrix, composites with low PZT volume fractions ranging from 0.05 to 0.22 have been fabricated. The 1–3 composites have good piezoelectric properties that agree quite well with theoretical modeling. The thickness electromechanical coupling coefficient of the composites could reach ～0.5 even for low volume fraction of PZT. These composites have potential to be used as sensors in civil structure health monitoring systems.     

Fabrication and properties of 1-3-2 multi-element piezoelectric composite

A design method is presented for 1-3-2 type multi-element piezoelectric composite so as to provide basis for the development and study of transducer and transducer array. The composite samples have been fabricated by a twice dice-filling process from lead zirconate titanate (PZT-4), epoxy resin and silicone, the properties of the composites have been measured and investigated physically. The results show that the piezoelectric, dielectric and electromechanical coupling properties of the composite exhibit a good consistency, while it has a high thickness electromechanical coupling factor K _t and a wide bandwidth of pulse-echo signal. The impedance plot of every element indicates good behavior that all elements show excellent frequency consistency, and on the other hand the chance of coupling of lateral resonance and thickness resonance is very small, and with a clear thickness resonance mode at around 100?kHz. Silicon has extremely decoupling properties which can efficiently block the transmission of the acoustic vibrations and eliminate coupling effect among elements. And the farther the distance between the incentive element and receiving element is, the smaller the response signal become, while the response signal decay rate exhibits the trend of increase, the largest up to 95%.     

Dielectric permittivity of PCLT/PVDF-TRFE nanocomposites

The use of ferroelectric polymer films as pyroelectric sensors and ultrasonic transducers has attracted considerable interest. Polymer-based 0-3 nanocomposites, consisting of nanocrystalline calcium and lanthanum modified lead titanate (PCLT) powder embedded in a vinylidene fluoride-trifluoroethylene (polyvinylidenefluoride (PVDF)-trifluoroethylene (TRFE)) copolymer matrix, also have shown good potential in pyroelectric and piezoelectric applications. The dielectric permittivity and loss in these composites are important parameters characterizing their performance. In this study, the relative permittivity and loss of PCLT/PVDF-TRFE nanocomposites with various volume fractions of ceramic have been measured as function of frequency and temperature. The copolymer and nanocomposites exhibit a dielectric relaxation at the ferroelectric-to-paraelectric phase transition and another relaxation near room temperature (at ~1 MHz). The influence of the room temperature relaxation on transducer performance is discussed     

FABRICATION AND ELECTRICAL PROPERTIES OF PZT-PVDF 0–3 TYPE COMPOSITE FILM

ABSTRACT

A film speaker was fabricated with 0–3 type piezoelectric composite. The 0–3 type composite was developed to incorporate the advantages of both ceramic and polymer. The pastes of PZT-PVDF composite were made with various mixing ratio. The paste was printed by conventional screen-printing method on ITO (Indium Tin Oxide) bottom electrode which was deposited on PET (polyethylene terephthalate) polymer film. The prepared composite film was about 80 μm in thickness. After printing the top-electrode of silver-paste, 4 kV/mm of DC field was applied at 120°C for an hour to align the electric dipole in the 0–3 composite film. The piezoelectric charge constant of d₃₃ was increased with increasing the PZT weight percent. The maximum value was 24 pC/N at 70 wt% of PZT. But the piezoelectric voltage constant of g₃₃ had the maximum value about 32 mV · m/N at 65 wt% of PZT. The SPL (Sound Pressure Level) of the speaker fabricated with the 65:35 composite film was tested at various driving voltages of 1 ～ 100V_rms. The SPL was saturated at the driving voltage of 70V_rms and the value was about 68 dB at 1 kHz.     

The effect of calcining temperature on the properties of 0-3 piezoelectric composites of PZT and a liquid crystalline thermosetting polymer

We report on the optimisation of a recently developed high performance 0-3 piezoelectric composite comprising of the piezoelectric Lead Zirconate Titanate (PZT) powder and a liquid crystalline thermosetting matrix polymer (LCT). The matrix polymer is a liquid crystalline polymer comprising of an HBA-HNA backbone with phenylethynyl end-groups. The use of a high performance polymer makes the composite a possible candidate to be used in sensor applications at elevated temperatures. The composite properties were optimised by calcining the PZT powder at different temperatures, prior to mixing the powders into the LCT matrix. The aim is to study the effect of the calcining temperature on the piezoelectric properties of the composite The PZT powders were characterised by X-ray diffraction and scanning electron microscopy. The dielectric constant and piezoelectric charge constant (d ₃₃ ) of the composite samples was measured. It was found that a relationship exists between the calcining temperature of the PZT powder and the piezoelectric properties of the composites. A maximum voltage constant of g ₃₃  = 63 mVm/N was obtained for a composite containing 40% (by volume) of PZT powder calcined at 1150°C.     

Ultrasonic transducer based on highly textured PMN-PT piezoelectric ceramic

A successful fabrication process of textured ceramics by homo-template grain growth (HTGG) is described. Two samples fabricated with this technique were characterised. Functional properties obtained are competitive with for example a thickness coupling factor over 50%. Different characteristics were compared with those obtained by a unit cell model previously developed for piezocomposites and extended to the case of two piezoelectric phases. Behaviours of several connectivities (0–3, 3–0 and 3–3) are calculated and results show that the spatial arrangement does not have a great influence on effective parameters. A transducer based on a textured ceramic sample has been fabricated and characterised. The measured performance shows the efficiency of these new piezoelectric materials. Finally, electroacoustic responses of identical single element transducer configurations have been simulated. They show that a sensitivity increase of 3dB can be obtained at equivalent relative bandwidth of 40% with textured ceramic sample in comparison with PMN-PT ceramic used as a matrix in the textured ceramic.     

Solid Freeform Encapsulation of 1-3-0 PZT Composites

Two types of encapsulated lead zirconate titanate (PZT) composite hydrophones have been built and tested: a straight walled 1-3-0 PZT composite design and a curved wall 1-3-0 PZT design. The solid freeform fabrication (SFF) technique was used to construct the polymer encapsulation for the two prototype designs.In the 1-3 composites soft PZT bars are embedded in a polymer matrix with a surrounding air gap. The polymer encapsulations were fabricated on a SFF stereolithography machine in order to enclose the gap and the PZT. Air gaps between the polymer and the PZT were shown to increase the hydrostatic piezoelectric response (d _h) by absorbing the lateral hydrostatic stress. Because of the small percentage of PZT, these composites had a low density (neutral buoyancy), low dielectric constant, and, therefore, a lower dielectric constant, and a corresponding higher hydrostatic voltage coefficient, g _h.The curved-wall composite design decoupled the PZT component more effectively from the lateral pressure, and thereby improved upon the direct piezoelectric effect. The large cap surface and the curved-wall further improved the amplification of the mechanical loading on the PZT element. The effective hydrostatic charge coefficient d _h, reached about 1100 pC/N which amplified the d ₃₃ coefficient, and greatly enhanced the d _h g _h figure of merit.     

浇铸法制备的PEO基偏铝酸锂复合固态电解质

通过浇铸法制备含快离子导体金属盐LiAlO2(LAO)的聚氧化乙烯(PEO)基复合固态电解质,对LAO不同质量分数的复合固态电解质进行电化学性能测试。复合固态电解质的电化学窗口拓宽,离子电导率提高到8.39×10^-5 S/cm。以复合物固态电解质组装Li/LiFePO4全固态电池,当LAO质量分数为4%,在60℃以0.1 C于2.5~4.0 V充放电,电池的首次放电比容量为153.61 mAh/g,循环50次的容量保持率仍在90%以上。     

A shoe-equipped piezoelectric transducer system based on PVDF film

Many piezoelectric transducers mounted in shoes have been conducted to harvest energy from walking. However, the energy harvested is influenced by some factors, such as the structure of piezoelectric transducer, piezoelectric material and so forth. Taking into account these factors, a wide-band energy harvester-shoe equipped piezoelectric transducer with cantilever beam structure based on polyvinylidene fluoride (PVDF) piezoelectric film is designed and examined in this paper. The piezoelectric transducer makes little difference in the sensation with the device mounted in the shoes when walking. The harvester can provide a maximum output power of 0.48 mW at the load resistance of 300 kΩ. This study demonstrates that it is feasible to scavenge energy from human motion by piezoelectric harvester to power wearable sensors, such as pedometer, respiration and pulse monitoring system and so on.     

Fabrication and characterization of flexible piezoelectric composites with natural rubber matrix

Abstract

This work aims to fabricate and characterize flexible piezoelectric composites with natural rubber (NR) matrix. Different amounts of Pb(Mg_1/3Nb_2/3)_0.65Ti_0.35O₃ (PMNT) powders were added in NR matrices. Porosity, tensile strength and percent elongation at break of composites tended to decrease with increasing PMNT content. The dielectric constant of the NR materials was found to be 3.5. It was raised up to 4.2, 5.0, 4.5, 4.8 and 5.1 when 60, 80, 100, 120 and 150 phr PMNT powders were added. However, dielectric loss of NR materials did not change with PMNT additions. Among this composite system, the NR/100PMNT composite showed the best piezoelectric properties, which its output voltage, piezoelectric coefficient (d₃₃) and piezoelectric voltage coefficient (g₃₃) values were equal to 1.61 V, 2.1?×?10^?4 pC/N and 5.4?×?10^?6 V?m/N, respectively. This composition composite is a promising material suitable for further improvement to be used as piezoelectric generators in energy harvesting applications.     

Piezoelectric materials for high frequency medical imaging applications: A review

The performance of transducers operating at high frequencies is greatly influenced by the properties of the piezoelectric materials used in their fabrication. Selection of an appropriate material for a transducer is based upon many factors, including material properties, transducer area, and frequency of operation. This review article outlines the major developments in the field of piezoelectrics with emphasis on materials suitable for the design of high frequency medical imaging ultrasonic transducers. Recent developments in the areas of fine grain and thin film ceramics, piezo-polymers, single crystal relaxor piezoelectrics, as well as lead-free and composite materials are discussed.     

Development and Electromechanical Properties of Multimaterial Piezoelectric and Electrostrictive PMN-PT Monomorph Actuators

Monolithic multimaterial monomorphs, comprised of varying ratios of piezoelectric 0.65Pb(Mg_1/3 Nb_2/3)O₃-0.35PbTiO₃ to electrostrictive 0.90Pb(Mg_1/3Nb_2/3)O₃-0.10PbTiO₃, have been co-fired at 1150^∘C. The relative permittivity, displacement, and polarization hysteresis were investigated for varying ratios of piezoelectric to electrostrictive material. The permittivity of the 1:1 multimaterial monomorphs followed the dielectric mixing laws, showing a dielectric constant of 5,500 at room temperature. The P-E hysteresis loop of the 1:1 sample exhibited a maximum and remnant polarization slightly less than the piezoelectric PMN-PT 65/35, but higher than the electrostrictive PMN-PT 90/10. Displacement was found to be higher for the 3:1 monolithic monomorph actuators, reaching 76 μ m at 6 kV/cm. The results indicate that by minimizing the electrostrictive layer thickness the tip displacement can be substantially increased while maintaining a lower hysteresis than that of the purely piezoelectric counterpart.     

Finite difference modeling of piezoelectric composite transducers with 0-3 connectivity

The mechanical and electrical properties of transducers are modelled by finite-difference representations of the relevant physical equations and the numerical problems are discussed. The theory is applied to a transducer consisting of a calcium-modified lead titanate (PTCa) ceramic mixed with the polymer P(VDF-TrFE), and comparison of /spl isin//sub 33/ with experimental values is found to be good. The introduction of ceramic into the mix has an immediate effect on the voltage, and s/sub 11/ and s/sub 12/. d/sub 31/ is not much affected by the presence of the ceramic until it reaches 70% of the mixture whereas d/sub 33/ changes sign rather quickly and then increases more slowly. A second transducer having the ceramic PZT5 mixed with P(VDF-TrFE) is also modelled and the characteristics of the 0-3 structure are compared with those of the 1-3 structure of the same components modelled in an earlier paper. The 1-3 construction brings the effect of the ceramic in much faster than the 0-3 construction. For example, at 50% ceramic, e/sub 33/, d/sub 3l/ and d/sub 33/ are roughly trebled compared to the 0-3 values.     

Piezoelectric Energy Harvesting under High Pre-Stressed Cyclic Vibrations

Cymbal transducers have been found as a promising structure for piezoelectric energy harvesting under high force (∼ 100 N) at cyclic conditions (∼ 100–200 Hz). The thicker steel cap enhances the endurance of the ceramic to sustain higher ac loads along with stress amplification. This study reports the performance of the cymbal transducer under ac force of 70 N with a pre-stress load of 67 N at 100 Hz frequency. At this frequency and force level, 52 mW power was generated from a cymbal measured across a 400 kΩ resistor. The ceramic diameter was fixed at 29 mm and various thicknesses were experimented to optimize the performance. The results showed that the PZT ceramic of 1 mm thickness provided the highest power output with 0.4 mm endcap. In order to accommodate such high dynamic pressure the transducer and cap materials were modified and it was found that the higher piezoelectric voltage constant ceramic provided the higher output power. Electrical output power as a function of applied ac stress magnitude was also computed using FEM analysis and the results were found to be functionally coherent with experiment. This study clearly demonstrated the feasibility of using piezoelectric transducers for harvesting energy from high magnitude vibration sources such as automobile.     

Anisotropic piezoelectric properties of 1–3 ceramic / polymer composites comprising rods with elliptic cross section

This paper is concerned with the study of effective piezoelectric properties of 1–3 ferroelectric ceramic / polymer composites. The aim of this paper is to show the role of a combination of the electromechanical properties of components and microgeometry of the 1–3 composite in determining its anisotropic piezoelectric response. The system of ceramic rods in the form of elliptic cylinders is an important microgeometric factor that influences the piezoelectric coefficients and their anisotropy. Examples of the piezoelectric response and anisotropy are analysed for the 1–3 composites based on either “soft” or “hard” ceramic and having either piezo-active or piezo-passive matrix. Combinations of the ceramic and polymer components are found that provide different volume-fraction dependences of the piezoelectric coefficients d_3j^* d_{3j}^{*} and g_3j^* g_{3j}^{*} : both monotonic, both non-monotonic, monotonic d_3j^* d_{3j}^{*} and non-monotonic g_3j^* g_{3j}^{*} , and vice versa. Examples of volume-fraction dependences of electromechanical coupling factors k_3j^* k_{3j}^{*} are also considered. A comparison of the effective piezoelectric coefficients calculated by the effective field method and the finite element method is carried out for different compositions in wide ranges of the ratio of semiaxes of the ellipse and of volume fractions of the components. Good agreement between data calculated by means of the aforementioned methods is obtained for the 1–3 structure comprising the elliptic cylinders.     

Thick piezoelectric coatings via modified sol-gel technique

Abstract

A hybrid sol-gel approach is reported for the deposition of high-quality composite PZT films of the thickness  1 μm. In this approach, the metallo-organic sol-gel precursor solution is mixed with fine piezoelectric powders and dip-coated onto Pt/Ti/SiO₂/Si substrates. Different organic viscous additives and deposition strategies were tried in order to deposit dense films with the properties approaching to those of bulk PZT. Using commercial PZT powder (TRS600FG) and ultrasonic mixing during deposition process, composite films having dielectric permittivity of ～2500 and saturation polarization ～35 μC/cm² were obtained. These values are intermediate between bulk ceramics and conventional sol-gel PZT films and therefore are indicative of good piezoelectric properties.     

Thickness mode high frequency MEMS piezoelectric micro ultrasound transducers

Thickness mode piezoelectric micro-electromechanical system (MEMS) ultrasound transducers, operating in the 50–75 MHz range, have been fabricated using a composite sol gel technique in combination with wet etching. The composite sol gel technique involves producing a PZT powder/sol composite slurry, which when spun down yields films a few micrometers thick. Repeated layering, and infiltration, has been used to produce PZT films between 20 and 40 μm thick. Due to the low firing temperature (<720°C) it has also been possible to integrate these PZT films with a micro-machined silicon support wafer. These PZT thick films have been structured using a wet etching technique to create free standing pillars that have been shown to resonate in thickness mode in the frequency range of 50–75 MHz. Examples of these structures and their resonant behaviour are presented.     

A poling study of PZT/P(VDF-TrFE) copolymer 0-3 composites

Abstract

0–3 composites of lead zirconate titanate (PZT) and P(VDF-TrFE) (piezoelectric copolymer of polyvinylidene fluoride and trifluoroethylene) with different volume fraction of piezoelectric ceramic were fabricated. The composites must be polarized by exposure to a high electric field to elicit piezoelectric response. One of the major consideration for poling a composite is the ratio of the resistivities of constituent phases since it governs the effective poling field across each phase. It is observed that the resistivity of the copolymer shows hysteresis upon heating and cooling, and abrupt changes are found at its Curie transition temperature upon heating (Tc↑) and on cooling (Tc↓). Previous reports stated that PZT/copolymer 0–3 composites of 50 volume percent ceramic do not exhibit piezoelectric response because the piezoelectric constants of the two materials are opposite in sign and cancellation occurs. In the present work, different poling conditions are used to pole the two phases oppositely so that the piezoelectric responses of the two phases reinforce each other. Details of poling and the resulting composite properties are reported.     

High performance thin film PZT ultrasonic transducer by CSD for distance measurements in water

Piezoelectric thin film ultrasonic transducers were realised and tested for short range distance measurements. Displacements in air and water as a function of frequency were modelled by Comsol Multiphysics finite element modelling (FEM) and transducer configurations with a two electrode layout were manufactured to enable larger displacements than with the conventional design. The transducer was fabricated on a silicon wafer by chemical solution deposition (CSD) with total PZT (Pb(Zr_0.53Ti_0.47)O₃) thickness of 2 µm. Subsequently, a cavity underneath the PZT was wet etched creating a bending membrane with a total thickness of ??13 µm. The displacements of the transducers as a function of frequency were modelled and measured by fiber-optic laser vibrometer. The effective piezoelectric d₃₃ coefficient of 300 nm/V and 144 nm/V in air and 48 nm/V and 18 nm/V in water was obtained for 260?×?260 µm² and 390?×?390 µm² membranes, respectively. The accuracy of the modelled resonance frequencies both in air and water was relatively good, of ??4-13% and ??5-20%, respectively.