Safakcan Tuncdemir

Development of a High Power Piezoelectric Characterization System and Its Application for Resonance/Antiresonance Mode Characterization

We developed a new high power piezoelectric characterization system, and report its application for characterizing the resonance and antiresonance vibration performance in this paper. Although the traditional constant voltage measurement was improved by using a constant current measurement method, the conventional technique was still limited to the vicinity of the resonance. In order to identify a full set of high power electromechanical coupling parameters and the loss factors of a piezoelectric, both resonance and antiresonance vibration performance should be precisely measured simultaneously. However, the high power characterization across antiresonance has not been addressed previously in the literature. Our new high power characterization system reported here is capable of measuring the impedance/admittance curves by keeping the following various conditions: (1) constant voltage, (2) constant current, (3) constant vibration velocity of a piezoelectric sample, and (4) constant input power. In addition, the system is equipped with an infrared image sensor to monitor the heat generation distributed in the test sample. We demonstrated the usefulness of the new system in a rectangular piezoelectric plate in the whole frequency range including the resonance and antiresonance frequencies. The results clearly concluded that compared to the resonance mode, the antiresonance mode exhibits a higher mechanical quality factor QM and the same vibration amplitude/velocity under a smaller input electrical power and lower heat generation. This may suggest a superiority of the antiresonance mode usage to the resonance mode from the high power application viewpoint (i.e., ultrasonic motors, transformers).

Derivation of Piezoelectric Losses from Admittance Spectra

High power density piezoelectrics are required to miniaturize devices such as ultrasonic motors, transformers, and sound projectors. The power density is limited by the heat generation in piezoelectrics, therefore, clarification of the loss mechanisms is necessary. This paper provides a methodology to determine the electromechanical losses, i.e., dielectric, elastic and piezoelectric loss factors in piezoelectrics by means of a detailed analysis of the admittance/impedance spectra. This method was applied to determine the piezoelectric losses for lead zirconate titanate ceramics and lead magnesium niobate-lead titanate single crystals. The analytical solution provides a new method for obtaining the piezoelectric loss factor, which is usually neglected in practice by transducer designers. Finite element simulation demonstrated the importance of piezoelectric losses to yield a more accurate fitting to the experimental data. A phenomenological model based on two phase-shifts and the Devonshire theory of a polarizable–deformable insulator is developed to interpret the experimentally observed magnitudes of the mechanical quality factor at resonance and anti-resonance.

Design of Translation Rotary Ultrasonic Motor with Slanted Piezoelectric Ceramics

We designed and manufactured a multi-degree-of-freedom (MDoF) ultrasonic motor (USM) by using a single actuator. Although there have been numerous MDoF USMs reported in the literature, only a few of them cover the combined rotary and translational motions in a cylindrical-joint type configuration. Combining these two motions in one joint and controlling this combined motion through a novel USM is the main aim of this work. Here, we use smooth impact drive method (SIDM) with two distinct modes obtained at two distinct frequencies by the help of slanted ceramics and uneven square shaped excitation signals. The translational-rotary dual-mode motor can be driven by single source. The prototype of the motor (5 mm diameter, 25 mm total length) has 5 mm/s translational and 3 rad/s rotary speed under 4 mN blocking force, when the input signal is 20 Vp–p square wave.

Analysis on Loss Anisotropy of Piezoelectrics with ∞ mm Crystal Symmetry

The key factor for the miniaturization of piezoelectric devices is power density, which is limited by the heat generation or loss mechanisms. There are three loss components for piezoelectric vibrators, i.e., dielectric, elastic and piezoelectric losses. The mechanical quality factor, determined by these three factors, is the figure of merit in the sense of loss or heat generation. In this paper, quality factors of resonance and antiresonance for both k31 and k33 vibration modes are derived, and the method to determine loss factors in various directions is provided. For simplicity, we focus on materials with ∞ mm (equivalent to 6 mm) crystal symmetry for deriving the loss factors of polycrystalline ceramics, and ten different loss factors can be obtained from the measurements. Finite element simulations are made to prove the theory, and the analysis also demonstrates the significance of the piezoelectric loss factor which has usually been neglected by previous piezoelectric device designers.

Delta-Shaped Piezoelectric Ultrasonic Motor for Two-Dimensional Positioning

By fabricating on from lambda-shaped motors, bimorph delta-shaped motors have been developed and tested. A delta motor consists of two piezoelectric layers (bimorph structure) with four input electrodes and one common ground electrode – separated by an inactive bar that aids dimensional control in the sintering process. Two driving sources with a 90° phase difference were used for the x-, z-, and diagonal-axis direction driving. The design of the motor was modified and optimized by changing the relative dimensions and angle of the motor with the aid of ATILA finite element method (FEM) software. The optimum design with a small bandwidth between resonance modes, which provides the largest elliptical displacement, was fabricated using thick films. The fabricated motor size was below 10 mm2 with several hundreds of nano meter motion at the tip. The speed of revolution, torque and efficiency in the two-dimensional space were measured.

High Power Piezoelectric Transformers with Pb(Mg1/3Nb2/3)O3?PbTiO3 Single Crystals

Plate-shaped piezoelectric transformers were designed and manufactured with Pb(Mg1/3Nb2/3)O3–PbTiO3 single crystals (PMN-PT). Theoretical analysis was performed using Masons equivalent circuit model and finite element method (FEM) simulations. In the experiment, transformer performances, especially the power density, were compared among different materials, including lead zirconate titanate (PZT) ceramics, undoped PMN-PT, and manganese-doped PMN-PT (Mn-PMN-PT). High power density of 38 W/cm3 was obtained using single crystals, which was 5 times that of hard PZT ceramics. The power level of the single crystal transformer showed a significant dependence on doping, poling direction, and cutting orientation. Results also verified that the high power performance was mainly determined by the electromechanical coupling coefficient and mechanical quality factor of the material.

Comparison of Power Density Characteristics among Disk and Plate Shaped Piezoelectric Devices

High power density piezoelectric devices are required for smaller actuators and transformers. These devices are expected to perform similar to, or better than their larger scaled counterparts. Despite the superiority over their electromagnetic conjugates, piezoelectric devices are still limited in the amount of power they can handle. Commercial materials can carry vibration velocities up to 0.5 m/s (measured for a rectangular plate), which translates roughly into 25 W/cm3 power density. In this work, we examined the effect of shape and aspect ratio to the power density of two common actuator shapes, k31 type rectangular plates and kp type disks. Results demonstrate that the power density of disks can be an order of magnitude higher than plates. While the power density is 10 times higher, the equivalent resistance of a disk shaped resonator is 10 times lower, making it a better candidate to match low output impedances, needed for high power transformers. Disks also show higher mechanical quality factors when considering a fixed output power per volume as a criterion. The results of this study validate the use of disk shaped actuators for high power density applications including as transducers and step down transformers.

Meso-Scale Piezoelectric Gripper with High Dexterity

Design, fabrication and testing of a piezoelectrically actuated meso-scale dexterous gripper are reported. The gripper utilizes a piezoelectric ringmorph, which is excited by means of quarterly separated electrodes yielding 3 degree of freedom (3-dof) motion. Utilizing a specially designed arm, the 3-dof ringmorph actuation is transformed into a gripper motion bearing high dexterity. The combination of in- and out-of-plane motion unique to the gripper generates the herein explained sliding grip release, which improves the pick-and-place performance by avoiding sticking of the substrate. The 27×20×7 mm3 gripper can generate 300 mg gripping force while it has 110 µm out-of-plane and 30 µm in-plane no-load maximum stroke at ±100 V DC. The characterization of the device, including hysteresis and transient response are implemented as a function of loading condition and change in field intensity. The experimental results and sample pick-and-place tests have shown prominent force, stroke and frequency bandwidth of the gripper with a novel releasing method.

Analysis of longitudinal and torsional resonance vibrations of a piezoelectrically excited bar by introducing piezoelectric loss coefficients

In this study, a method to develop a resonance vibration model of a piezo-bar with slanted ceramics is presented by considering piezoelectric loss coefficients. The vibration model reported here predicts natural frequencies and mode shapes for longitudinal and torsional modes. Analytical results for the longitudinal and torsional vibration displacements were formulated as a function of material and geometric properties. Parametrical analysis of the resonance vibration modes and the explicit solution of the vibration displacement provide a tool for improving the design and developing control schemes for devices such as ultrasonic motors that utilize this structure. Model calculations were compared with ATILA™ finite element analysis simulations and good agreements were found. The model and the formulas to find the resonance frequencies and to calculate the vibration displacement were verified for different design parameters. Although the model was developed for a slanted ceramic stator of a multimode ultrasonic motor, the method to develop the model can be utilized for other single-degree-of-freedom piezoelectric ceramic applications.

Single Source Hybrid Drive for Multi-Functional Ultrasonic Motor

We previously reported a multi-functional single-stator piezoelectric motor, which can produce translational or rotary motions in a simple structure. In this paper, we will present the theoretical analysis and experimental verification of the hybrid driving technique for this motor. In order to benefit from the resonance operating conditions of ultrasonic motors and the structural superiority of inertial type piezoelectric motors, we blend these two drive methods as the new hybrid technique. Translational and rotary motions of mobile element are produced by inertial drive while the stator is excited with rectangular signals at longitudinal and torsional resonance frequencies, respectively.