Atsushi Furuta

Destruction Mechanisms in Ceramic Multilayer Actuators

Destruction mechanisms were investigated in electrostrictor, piezoelectric and phase-change antiferroelectric ceramic multilayer actuators with an interdigital electrode configuration. Simultaneous observations were done by three different methods; visual observation with a charge coupled device (CCD) microscope, field-induced strain and acoustic emission (AE) measurements. During a cyclic electric field application, the crack was initiated from the edge of an internal electrode and propagated obliquely to another electrode in the piezoelectric sample, while in the antiferroelectric, the crack was initiated between a pair of electrodes and propagated parallel to the electrodes. The field-induced strain curve exhibited asymmetric and enhanced strains in all the samples during the crack propagation, probably due to the internal delaminations. The AE count also increased drastically before the destruction.

Destruction mechanism of multilayer ceramic actuators: Case of antiferroelectrics

In order to investigate destruction mechanism of crack propagation in multilayer ceramic actuators of antiferroelectric Pb0.99Nb0.02[(Zr0.7Sn0.3)0.955Ti0.045]0.98O3 with an interdigital electrode configuration has been observed dynamically under cyclic electric fields using CCD microscopy. The accompanying characteristics of the induced displacement and acoustic emission during crack propagation were measured simultaneously. Crack initiated slightly inside the edge of the internal electrode and propagated along the center area between electrode pairs, which differed markedly from the case of a piezoelectric actuator which displacement was proportional to the applied electric field. During the crack propagation process, the induced displacement of the multilayer actuator doubled in size, and the acoustic emission count increased remarkably. The effect of layer thickness on the destruction process has also been investigated. Reducing the layer thickness of the ceramic actuator, toughness of the actuator was...

Precise positioning stage driven by multilayer piezo actuator using strain gauge

A newly developed strain gauge with a Cr–N thin film was formed directly on a zirconia plate by sputtering without using any adhesive. Unevenness of sensitivity and drift caused by an adhesive layer could thus be suppressed. The gauge factor of the strain gauge was 6, three-fold that of a conventional strain gauge such as a Ni–Cu foil type. Four strain gauges were formed on one side of a zirconia plate. This zirconia plate was attached to sensor heads. When the sensor heads were moved, positive and negative strains were induced by a diaphram construction due to the use of a full-bridge circuit. A resistance of the strain gauge of 5 kΩ could be realized by thin and fine patterning in order to suppress joule heat. Therefore 10 V could be applied on a full-bridge circuit as bridge input voltage. The value was five-fold that of conventional bridge input voltage. By these improvements, higher sensitivity could be obtained and the S/N ratio could be improved. The precise positioning stage had a 5 nm resolution using this newly developed strain gauge as a displacement sensor.

Mechanical clamper using shape memory ceramics

The shape memory effect was observed in the composition of Pb/sub 0.99/Nb/sub 0.02/((Zr/sub 0.6/Sn/sub 0.4/)/sub 0.9365/Ti/sub 0.0635/)/sub 0.98/O/sub 3/. This effect was due to the phase transition from an antiferroelectric to a ferroelectric phase. To obtain the original antiferroelectric state, a small reverse bias electric field should be applied to the ceramic. A mechanical clamper was trial fabricated as an application of shape memory ceramics. A multilayer shape memory actuator was fabricated by stacking 10 rectangular plates and installed in a hinge level magnification mechanism. The magnification was about seven times.<<ETX>>

Field induced strains in antiferroelectrics

Lead zirconate-based materials with a slight content of titanium undergo an antiferroelectric-ferroelectric phase transition when an electric field is applied. The strains accompanying this field-induced transition are gigantic in comparison with the strain change in the antiferroelectric or ferroelectric state. In the case of components with a higher titanium content, the material will memorize the ferroelectric state, even under zero-field conditions, once the ferroelectric phase has been induced. The initial antiferroelectric phase is recovered with application of a small reverse bias or a thermal annealing. A mechanical clamp and a latching relay are typical applications of the shape memory ceramics.<<ETX>>

Development and application of shape memory ceramic actuators

Shape memory unimorph actuators have been trial manufactured using lead-zirconate-based antiferroelectric ceramics. The unimorph structure requires slightly larger Ti concentration than the simple disk, to obtain the shape memory effect. This is probably due to the compressive stress generated in the unimorph structure. The dynamic response has also been investigated in the shape memory unimorph. Only an electric field pulse with a short period of 5 ms is necessary to drive the unimorph, which gives advantages in control over conventional piezoelectric actuators. The shape memory unimorph has been applied to a latching relay. The size of the latching relay can be reduced considerably by using the shape memory unimorph, in comparison with the conventional electromagnetic latching relay.<<ETX>>