B. Jadidian

HIGH-DISPLACEMENT SPIRAL PIEZOELECTRIC ACTUATORS

A high-displacement piezoelectric actuator, employing spiral geometry of a curved piezoelectric strip is described. The monolithic actuators are fabricated using a layered manufacturing technique, fused deposition of ceramics, which is capable of prototyping electroceramic components with complex shapes. The spiral actuators (2–3 cm in diameter) consisted of 4–5 turns of a lead zirconate titanate ceramic strip with an effective length up to 28 cm. The width was varied from 0.9 to 1.75 mm with a height of 3 mm. When driven by the electric field applied across the width of the spiral wall, the tip of the actuator was found to displace in both radial and tangential directions. The tangential displacement of the tip was about 210 μm under the field of 5 kV/cm. Both the displacement and resonant frequency of the spirals could be tailored by changing the effective length and wall width. The blocking force of the actuator in tangential direction was about 1 N under the field of 5 kV/cm. These properties are adva...

Piezoelectric Properties of Novel Oriented Ceramic-Polymer Composites with 2-2 and 3-3 Connectivity

The processing of novel 2-2 and 3-3 PZT ceramic-polymer composites with various orientation of the ceramic phase with respect to the poling direction is presented. The volume fraction of the ceramic was chosen to be 30 percent for both types of composites. The orientation angle (θ) of the ceramic phase varied between 0° and 75° for both types of composites with 15° increments. The ceramic structures were fabricated using one of the Solid Freeform Fabrication (SFF) methods, particularly Fused Deposition of Ceramics (FDC). The sintered structures were embedded in hard epoxy and the effect of orientation angle on the electrical properties of the composites was evaluated. By increasing the orientation angle of the ceramic phase, the dielectric constant and the piezoelectric strain coefficient of both types of composites decreased. Although the piezoelectric voltage coefficient of the 2-2 composites showed a minor improvement with increasing θ at 45°, the g33 value of the 3-3 composites increased considerably with θ and reached 80 mV/N at θ = 45°. Further increase of the orientation angle reduced the g33 of such composites.

Fabrication and evaluation of a single-element Bi 0.5 Na 0.5 TiO 3 -based ultrasonic transducer

This paper discusses the fabrication and characterization of a single-element ultrasonic transducer with a lead-free piezoelectric active element. A piezoelectric ceramic with composition of 0.88Bi_0.5Na_0.5TiO₃–0.08Bi_0.5K_0.5TiO₃– 0.04Bi_0.5Li_0.5TiO₃ was chosen as the active element of the transducer. This composition exhibited a thickness coupling coefficient (kt) of 0.45, a dielectric constant of 440 (at 1 kHz), and a longitudinal piezoelectric coefficient (d₃₃) of 84 pC?N^–1. To make the transducer, the ceramic was sandwiched between an epoxy–tungsten backing layer and a silver epoxy matching layer. An epoxy lens was also incorporated into the transducer¿s design to focus the ultrasound beam. The focused transducer with a center frequency of about 23 MHz demonstrated a –6-dB bandwidth of 55% and an insertion loss of –32 dB; the –20-dB pulsed length was measured to be 150 ns. A phantom made of copper wires (30 μm in diameter) was utilized to investigate the imaging capability of the transducer. The results indicated that the fabricated transducer, with a lateral resolution of 260 μm and a relatively high depolarization temperature, could be considered as a candidate for replacement of lead-based ultrasonic transducers.

Processing of Piezoelectric Fiber/Polymer Composites with 3-3 Connectivity

The processing-property relationship of dielectric and piezoelectric properties of 3-3 fabric composites was studied. Fine PZT green fibers were woven into plane fabric, cut in 3 × 3 cm2 pieces, and stacked 8 plies high. The stacks were heat-treated with and without applied pressure and then embedded in soft and hard polymers. Increasing the applied pressure increased the density and electromechanical properties of composites due to the improvement of the ply-to-ply sintering. At an optimum uniaxial pressure of 588 Pa, the piezoelectric and dielectric properties of composites with ≈41 vol% PZT and soft matrix were K = 230, d33 = 220 pC/N, g33 = 108 mV/m, and d33g33 = 23778 × 10−15 m2/N. The porosity-permittivity relationship was used to determine the depolarizing factor of the composites, which represented the degree of ceramic continuity between electrodes. In general, composites with soft matrix had higher electromechanical properties than those with hard matrix. The effect of poling direction on the piezoelectric and dielectric properties was also investigated. The composites poled along the PZT fibers had higher electromechanical properties than those poled perpendicular to the PZT fibers.

Processing and properties of piezoelectric actuators developed by fused deposition technique

Fused Deposition of Ceramic (FDC) has been developed for rapid prototyping of electro-ceramic components via hot extrusion of ceramic-loaded polymer filaments. Several FDC filaments including PZT, PMN-PT ceramics, and electrode material (silver-palladium) have been developed and used successfully in the fabrication of a wide range of components. A new fused deposition facility capable of depositing up to four different materials in a single deposition step has also been designed and developed. Processing of single and multimaterial components and net-shape grain oriented parts is now under investigation. In this paper, processing and electromechanical properties of a few novel designs such as bellows, helical tubes, spiral and other multimaterial actuators are discussed.

Fabrication of bismuth titanate components with oriented microstructures via FDC and TGG

Fine Bismuth Titanate (Bi/sub 4/Ti/sub 3/O/sub 12/, BiT) powder and platelet seeds have been synthesized using sol-gel and molten slat techniques, respectively. BiT filaments of 48 vol.% solids loading (including 5 vol.% seeds) have been developed for fused deposition of net shape components. The survival of the seeds during filament fabrication (compounding and extrusion) has been monitored and necessary changes have been made to minimize seed damage during processing. The orientation of the seeds within the filament and the fabricated green components was studied to find the optimum deposition parameters and the conditions that yield maximum seeds alignment. The green FDC components were heated to remove the binder at 550/spl deg/C. During sintering and/or Templated Grain Growth (TGG) process at a temperature range of 1000 to 1100/spl deg/C, the seeds grew and induced an oriented microstructure by consumption of the fine grain matrix. X-ray technique and SEM were used to characterize the degree of orientation.

Development of fine scale piezoelectric ceramic/polymer composites via incorporation of fine PZT fibers

Lead zirconate titanate (PZT) fibers 50 to 70 /spl mu/m in diameter, formed by the Viscous Suspension Spinning Process (VSSP) were sized and incorporated into piezoelectric ceramic/polymer composites. Water soluble polymer solutions containing polyvinyl alcohol, polyethylene glycol, and ethylene glycol were used as sizing agents. The sized fibers formed a multifilament collimated bundle called a tow. The number of individual fibers in a tow varied between 10 and 500. The sized tows were dried at room temperature and cut to desired lengths, heat treated to remove the organic and fired to form straight rods. The rods were bundled and embedded in spurrs epoxy to fabricate 1-3 composites. Green tows were also woven into plain fabric and carpet structures. After firing, the diameter of the individual PZT fibers was 10 to 30 /spl mu/m. The effect of sizing solution chemistry and concentration on tow tightness and flexibility is reported. The microstructure and electromechanical properties of composites with a variety of architectures are also discussed.

Lead-free (Bi 0.5 Na 0.5 )TiO 3 -based thin films by the pulsed laser deposition process

We have studied the effect of deposition parameters on the microstructure, crystallinity, and ferroelectric properties of 0.88(Bi_0.5Na_0.5)TiO₃-0.08(Bi_0.5K_0.5)TiO₃-0.04BaTiO₃ thin films grown on SrRuO₃-coated SrTiO₃ substrates by pulsed laser deposition. The parameters studied were the repetition rates, substrate temperatures, oxygen pressures, and laser energies. It was realized that the films prepared at 800°C, 10 Hz, 400 mtorr, and 1.2 J·cm^-2 exhibited the highest ferroelectric properties. The measured remanent polarization, dielectric constant at 1 kHz, and coercive field for this film were about 30 μC·cm^-2, 645, and 85 kV·cm^-1, respectively. Increasing the oxygen pressure during deposition from 200 to 400 mtorr improved the crystallinity, microstructure, dielectric constant, and polarization of the films. The leakage current and dielectric loss were suppressed at 400 mtorr because of the lower concentration of oxygen vacancies and disappearing pinholes and surface undulations in the film deposited at this pressure.

Development of tube actuators with helical electrodes using fused deposition of ceramics

Fused Deposition of Ceramics (FDC), a Solid Freeform Fabrication technique, has been used to manufacture tube actuators with helical electrodes. It is expected that the special electroding along the length of the tubes results in higher axial displacements since d/sub 33/ coefficient is applicable as opposed to d/sub 31/ in radially poled tubes. A silver-palladium electrode filament with solids loading of 55 vol.% was developed. Two different methods of deposition were used to fabricate the tubes. with helical electrodes either within the tube wall or on the outer surface of the tubes. Electrodes with different thickness and width were deposited on the tubes. Modified heating procedures for binder burnout and sintering, as well as special electrode geometries were used to minimize the damage, occurring due to the oxidation and subsequent reduction of palladium at temperatures < 800/spl deg/C.

Electromechanical properties of piezoelectric spiral actuators

A new type of monolithic high-displacement piezoelectric ceramic actuator with spiral geometry is described. The actuators were fabricated using a Solid Freeform Fabrication (SFF) method, Fused Deposition of Ceramics (FDC), which is capable of prototyping electroceramic components with complex shapes. The spiral actuators (3, 0.06, and 28 cm in diameter, width, and length, respectively) produced displacements of up to 1,900 /spl mu/m under application of an electric field of 1.1, kV/mm. Both the displacement and resonant frequency of the spirals were tailored by changing the effective length and wall width. The blocking force of the actuators is on the order of 1 N. These properties are advantageous for high displacement-low force applications where bimorph or monomorph actuators are currently employed.