The electromechanical displacement properties of two recently developed piezoelectric actuators, referred to as RAINBOW and THUNDER, have been measured and compared. The actuators evaluated in this investigation are fabricated from 2.54 cm diameter PZT-5H and PZT-5A piezoelectric ceramic disks and are produced with the same total device thicknesses and ceramic-to-metal thickness ratios. For the compositions tested, the RAINBOW devices are found to exhibit 10–25% greater free-displacement properties than comparable THUNDER devices. This finding indicates that larger internal stresses are developed during the RAINBOW process, which lead to enhanced amplification of axial displacement.

Displacement properties of RAINBOW and THUNDER piezoelectric actuators

Excellent symmetric dielectric hysteresis is observed from lead zirconate titanate (PZT) thin films using transverse electric fields driven by interdigitated surface electrodes. The 1-μm-thick PZT films with a Zr/Ti ratio of 52/48 are prepared on ZrO2 buffered, 4-in.-diam silicon wafers with a thermally grown SiO2 layer. Both the ZrO2 buffer layer and PZT film are deposited by using a similar sol–gel processing. Remanent polarization of about 20 μC/cm2 with coercive field less than 40 kV/cm is obtained as measured using a triangle wave at 50 Hz. Thicker films are being developed and retention for the transversely polarized state is currently under study. One of the objectives of this study is to develop a large array of d33-driven unimorph sensing elements for a high-resolution acoustic imaging system.

Dielectric hysteresis from transverse electric fields in lead zirconate titanate thin films

Various external and internal leverage devices have been developed to amplify strain; however, these devices are commonly inefficient due to transmission losses and can be difficult to pack into constrained application volumes. A Recurve actuator architecture has been designed which amplifies direct material strains and allows for construction of highly compact, high-energy-density actuator arrays. The Recurve architecture enables arrays that can be tailored to produce specific force and displacement output and can be configured in a variety of ways to make efficient use of available design space. This paper describes a Recurve actuator architecture and presents a quasi-static model relating voltage, force, and deflection along with experimental results for fundamental Recurve actuator elements.

Recurve piezoelectric-strain-amplifying actuator architecture

THUNDER technology introduces a versatile new family of rugged, robust, reliable piezoelectric actuators and sensors. Because of their pre-stressed composite structure, these powerful yet lightweight devices exhibit unprecedented performance in a durable, solid state package. Both sensors and actuators can be manufactured in a variety of adaptable geometries - squares, rectangles and disks - from several millimeters to many centimeters in size. Wide bandwidth performance can be achieved and maintained even in harsh chemical and temperature environments. Based on an invention patented by NASA, THUNDER is an emerging, enabling technology that holds the promise of significant advancements in numerous 'smart' applications. Development of these applications for smart materials and structures requires extensive characterization of a variety of THUNDER devices in a range of configurations. This comprehensive characterization effort is especially challenging because of the extraordinary flexibility and range of motion demonstrated by THUNDER devices, even under significant load. This paper will discuss important new work in the ongoing program of THUNDER device characterization. The program includes not only development of the characterization process, but also design and manufacture of the test and measurement equipment necessary to conduct meaningful and reliable testing on these unique, high performance devices. Results will be presented on characterization of two configurations of THUNDER devices, including a circular and a rectangular model of different sizes constructed of varying materials. Data will be offered for a number of key performance characteristics, including displacement, block force, plus displacement vs. voltage and displacement vs. force.

Characterization of different types of high-performance THUNDER actuators

An assembly and method for micropositioning a disc drive head is described. An implementation of the assembly includes a gimbal, a piezoelectric element bonded to the gimbal and electrically connected to a voltage source, and a slider connected to the piezoelectric element. The assembly may also include at least a second piezoelectric element bonded to the gimbal and connected to the slider. The piezoelectric elements may be made of PZT material, and each may be in a monomorph or bimorph configuration.

Piezoelectric assembly for micropositioning a disc drive head

During the last several years novel piezoelectric bending actuators have been developed: RAINBOW, CERAMBOW, CRESCENT, d 3 3 bimorph and THUNDER A comparative experimental investigation of electromechanical characteristicsof these devices along with conventional d 3 1 bimorph and unimorph actuators was conducted in this work. All transducers were fabricated from soft piezoelectric ceramics. The experimental results show that d 3 3 bimorph and unimorph elements have superior quasistatic characteristics as compared to other type of bending-mode actuators. All these piezoelectric devices demonstrate a significant dependence of electromechanical performance on the magnitude of the driving electric field. It was found that the decrease in the mechanical quality factor and resonant frequency of bending vibrations in d 3 1 unimorph, RAINBOW, CRESCENT (CERAMBOW) and THUNDER with increasing electric field is much smaller than that in bimorph and d 3 3 unimorph actuators. The dependence of the behavior of these devices on the operating conditions governs the selection of a particular device for a specific application.

A comparative analysis of piezoelectric bending-mode actuators

A piezoelectric bimorph transducer utilizing piezoelectric d33 coefficient was developed. This bimorph consists of piezoelectric segments bonded by a polymeric agent and was fabricated by a dicing and layering technique. The transducer has superior piezoelectric characteristics compared to standard piezoelectric d31 bimorphs. Piezoelectric coefficients, electrical admittance, mechanical compliance, and losses of the actuator were found to increase with increasing driving electric field.

Caterpillar‐type piezoelectric d33 bimorph transducer

The PANEL (Piezoelectric Acoustic Noise ELiminator) transducer was developed for air acoustic noise cancellation in the frequency range of 200–1000 Hz. It has a thin panel structure, occupies less volume, and is lighter than an equivalent electromagnetic transducer. This device consists of a U‐shaped configuration of piezoelectric bimorph and unimorph actuators bridged by a triangular amplifying diaphragm, which acts as an effective source of the sound radiation into air. The role of the diaphragm is twofold: it amplifies by a factor of 5–20 the tip displacement of the piezoelectric actuators and it also increases the sound emitting area. Amplitude of the vibrations and usable frequency range of the transducer depend on the dimensions and material of the actuators and diaphragm. The overall dimensions of the device fabricated were 52×50×24 mm. Soft PZT ceramics were used. The diaphragm was made of a carbon fiber reinforced composite. The diaphragm vibrations reach 500 μm rms well below the fundamental res...

Sanjay Chandran

Papers

A comparative analysis of piezoelectric bending-mode actuators

Caterpillar‐type piezoelectric d33 bimorph transducer

PANEL: A novel piezoelectric air acoustic transducer