Yoshinobu Ohara

PZT-polymer piezoelectric composites: A design for an acceleration sensor

Abstract PZT-polymer composites with 1–3 connectivity are fabricated using an ultrasonic cutter. The piezoelectric properties of the composite and the sensing properties of acceleration sensors using the composite are investigated. High output voltages, about twice that in a PZT monophase sensor, are observed in the composite acceleration sensor over a wide range of frequency, acceleration and added load. The 1–3 composite with a finely designed structure is found to be a promising transducer element with high efficiency and controllable properties.

PZT-polymer composites fabricated with YAG laser cutter

Piezoelectric composites have been constructed by YAG laser cutting of PZT ceramics and back-filling with silicone rubber. Composites containing 46–76 vol.% PZT have been prepared with several different rod sizes. The measured dielectric constant ranges from 310 to 598, d33 from 297 to 305 pC/N, and g33 from 87 × 10−3 to 62 × 10−3 V m/N. The influence of the new fabrication method on the piezoelectric properties of the composite is evaluated, and it is confirmed that an elastomer with low elastic modulus increases g33 and suppresses the radial mode vibration in resonance. For the PZT-silicone rubber composites made by YAG laser cutting, g33 can be enhanced in 1–3 composites to about three times the value for solid PZT. The piezoelectric properties are compared with those of 1–3 composites made by ultrasonic cutting. The g33 values of composites fabricated by ultrasonic cutting are larger than those fabricated by laser cutting. These results indicate that to get higher values of g33 it is necessary to perforate PZT with ditches of the same width.

Partially stabilized zirconia-polymer composites fabricated with an ultrasonic cutter

Piezoelectric transducers have been made of partially stabilized zirconia (PZT) ceramics with composition close to PbZr0.sTi0.50 3. Compared with other piezoelectrics, however, the piezoelectric voltage c o n s t a n t g33( = d33/g33 , where d33 and 633 are the piezoelectric charge constant and dielectric constant, respectively) of PZT is small. This problem can be solved by combining PZT and polymer in a composite with 1-3 connectivity [1,2]. This type of composite consists of PZT rods embedded in a polymer matrix, in which the rods are oriented perpendicular to the transducer electrodes. Several different techniques to make the composites have been reported in the literature [3]. A practical and simplified method for the fabrication (diamond saw dicing) of 1-3 composites was developed by Savakus et aI. [4] and Takeuchi et al. [5], but their process to cut the ceramics with a diamond saw is rather delicate and time-consuming. Safari et al. [6] fabricated composites by drilling holes in sintered PZT blocks using an ultrasonic cutter. Ceramics can be carved into various shapes and patterns using various kinds of tools by this method. This letter describes an alternative processing method, in which narrow grooves are carved in poled solid PZT discs with an ultrasonic cutter and are then back-filled with epoxy resin, urethane rubber or silicone rubber. The piezoelectric properties of the composites thus obtained are presented. Ceramic discs of poled PZT (Honda Electronics Co., Japan) were prepared by a conventional powder processing method and sintered to a density of 7.58gcm -3. The basic characteristics of the studied material are shown in Table I. The PZT disc was mounted on an ultrasonic cutter (UM5000-DA; Nihon Densi Kogyo Co., Japan). Ultrasonic cutting is a machining method which is designed to cut materials a little at a time using a combination of ultrasonic vibration generated from the tool with

Barium titanate fabricated from fur-fibres

Long-fibrous barium titanate (BaTiO3) particles were prepared by a hydrothermal reaction of potassium titanate hydrate (2K2O·11TiO2·3H2O) and barium hydroxide (Ba(OH)2). Effects of preparation conditions on crystal structure and powder morphology were examined. Fur-fibres of K2O·4TiO2, 1–10 mm long and 1–100 Μm in diameter, were obtained by heating a mixture of K2CO3 and TiO2 powders at 1000 ‡C for 100 h. Keeping the fur-fibres in ion-exchanged water for 4 days gave fur-fibres of 2K2O·11TiO2·3H2O). Long-fibrous BaTiO3, with fibres 100Μm–1mm long and 1–10 Μm in diameter, was obtained by a hydrothermal reaction of the hydrate and Ba(OH)2 (Ba/Ti ratio of 1) at 150 ‡C for 24 h. As-prepared long-fibrous BaTiO3 was composed of fine crystallites (average size about 270 nm) of cubic phase. The cubic phase and morphology of fur-fibres were maintained up to 1250 ‡C, but heat treatment at 1300 ‡C brought about a growth of crystallites to a few micrometers and a phase transformation to tetragonal phase. It was found that the hydrothermal reaction was effective in producing crystalline BaTiO3 powder at a low temperature of 150 ‡C.

Sintering of fibrous barium titanate powder compacts with preferred orientation

The sintering of fibrous BaTiO3 powder particles was investigated. Special emphasis was given to the role of particle orientation in the compact on densification and microstructure development. Compacts were made by dry-pressing. During the initial stage of sintering, the fibrous particles rearranged and bundles of particles were formed. The volume of pores between bundles of particles decreased on further heating. Grain growth started when the sintered density reached ca. 56% of the theoretical density. Higher temperatures of sintering increased the degree of the crystal axis orientation. Thus, highly orientated sintered bodies with high densities were prepared by heating at 1500 °C.