PZT Ring Research Articles

Design and Prototyping of a Novel Type Piezoelectric Micro-pump

Using the extensional vibration mode of PZT ring, a piezopump is successfully made. The PZT ring is polarized with thickness direction. The traveling extensional wave along the circumference of the ring is obtained by dividing two standing waves which are temporally and spatially phase shifted by 90 degrees from each other. The proposed piezopump is consisted of coaxial cylindrical shells that are bonded piezoelectric ceramic ring. The pump takes an unobtrusive operation into the simple displacing mechanism using peristaltic traveling waves without the physical moving parts. The finite elements analysis on the proposed pump model is carried out to verify its operation principle and design by the commercial FEM software. Components of piezopump were made, assembled, and tested to validate the concepts of the proposed pump and confirm the simulation results. The performance of the proposed piezopump is about 580 <TEX>${\mu}l/min$</TEX> in flow rate with the highest pressure level of 0.85 kPa, when the driving voltage is 150 <TEX>$V_p$</TEX>, 57 kHz.

Dual‐frequency driving transducer for ultrasonic echography

We propose a novel ultrasonic imaging technique by transmitting ultrasonic pulse of dual‐frequency and receiving multifrequency echoes from the biological tissues. When the ultrasonic pulse of two frequencies is transmitted from a transducer, the secondary waves are generated during the nonlinear propagation through the biological media. A choice of f0 and 4f0 as the dual‐frequency results in the generation of 2f0, 3f0, and 5f0 components as the secondary waves. Multifrequency echoes are capable of improving the image quality by reducing the speckle noise. We have developed the following annular type transducer. The PZT disk of 7 mm in diameter is coaxially arranged in the PZT ring of 9 mm in inner diameter and 17 mm in outer diameter. The ring and circular transducers transmit the pulses of 2 and 8 MHz, respectively. It was confirmed that this transducer formed the ultrasonic beams of 4, 6, and 10 MHz as well as the beams of 2 and 8 MHz in degassed water. Then the experiments of imaging the agar‐gel phan...

Degradation of Lead Zirconate Titanate Piezoelectric Ceramics Induced by Water and AC Voltages

A comparison experiment was conducted in which some lead zirconate titanate (PZT) piezoelectric ceramic rings were simply immersed in a 0.01 M NaOH solution while other PZT rings were immersed in the solution with a 50 Hz AC voltage applied between the electrodes of the rings and a counter electrode in the solution. Though the simple immersion showed no noticeable influence on the PZT rings, those PZT rings treated with the application of the AC voltage were obviously degraded in their piezoelectric properties. It was proposed that the degradation resulted from the collaborated reactions of atomic hydrogen and oxygen generated in the AC voltage-induced electrolysis of water. Water may be an important origin for degradation of piezoelectric ceramic devices operating under AC voltages.

A Novel Micro-Actuator Made from PZT

Ceramic discs are prepared with PZT powder doped with Sr and Mn, which is prepared through a modified Pechini process. A micro-actuator consists of two concentric rings with thickness of 0.15 mm made of PZT doped with Sr and Mn, a copper disc, on which the PZT rings are firmly mounted with organic glue, and a ceramic rod of φ2.5x100 mm stuck at the center of the disc. The top of the ceramic rod serves as pointer of the actuator. The outer PZT ring is equally divided into four quadrants separated each other, of which two vicinal parts are poled with the same direction as that of the inner PZT ring. The other two quadrants in the outer ring are poled with the opposite direction. The inner ring and the four quadrants of the outer ring are excited by three DC powers, respectively. Bending deformation of the copper disc is caused by properly regulating the excitation voltages exerted on the PZT ceramics. The position of the top of the ceramic rod varies with the bending deformation of the copper disc.

A miniaturization of the multi-degree-of-freedom ultrasonic actuator using a small cylinder fixed on a substrate

Multi-degree-of-freedom ultrasonic actuator has been studied for robot arms and multidimensional precision table and so on because of its simple structure, silent operation, and holding force. In this study, we aim to miniaturize multi-degree-of-freedom ultrasonic actuator for fabrication on a substrate. This actuator consists of a stainless steel cylinder and a PZT ring. The cylinder is fixed on a substrate and the PZT ring is glued to the substrate near the cylinder. The 1st longitudinal vibration and the 2nd bending vibration are simultaneously excited in the cylinder to make elliptical motion at the top of the cylinder and a ball rotor placed on the cylinder rotates because of the friction force. Length of the cylinder was decided so as to tune the resonance frequency of the 1st longitudinal vibration to the 2nd bending one. Actuator performances are evaluated experimentally using a 14 mm height and 7 mm diameter stainless steel cylinder with a 0.5 mm thickness PZT ring. The rotation about the cylinder axis is tested using the two orthogonal bending vibrations with 90° phase difference. Also, the rotation about horizontal axes were investigated using the combination of the longitudinal vibration and one of two bending vibrations. We measured the rotation speed of a steel ball and obtained 15.8 rps using a 6 mm diameter ball rotor.

Current Oscillation of Piezoelectric–Ceramic Vibrators Driven by a Constant High Electric Field

Current oscillation will occur when a piezoelectric ceramic vibrator is driven by a high electric field. The mechanism of current oscillation is discussed, based on the results of the present experiment. Ring‐shaped lead zirconate titanate (PZT) piezoelectric vibrators are driven by a 5.65 V electric field with a fixed frequency of slightly less than resonance, to form an oscillating current. The sample current, temperature, and phase between the driven electric field and sample current are recorded. The resonance frequency of PZT rings shifts in the direction of low frequency under a high electric field due to the heat produced by dissipated power, and then shifts back due to the effects of aging, which results in current oscillation. The oscillation phenomenon is explained according to the production of strong internal stresses due to abrupt change in temperature, and then, aging process through the rearrangement of domains to relieve various stresses.

Configuration of a 30-mm-diameter 94 kHz Ultrasonic Longitudinal Vibration System for Plastic Welding

Vibration and welding characteristics of a 94 kHz ultrasonic plastic welding system are studied. The 94 kHz ultrasonic plastic welding systems consist of a 30-mm-diameter bolt-clamped Langevin-type PZT longitudinal transducers with four PZT rings, a stepped horn (vibration transform ratio N = 3.0) with a supporting flange at a nodal position and a catenoidal horn (N = 3.13) with an 8-mm-diameter welding tip. Maximum vibration velocity of the 94 kHz welding tip was 3.2 m/s (peak-to-zero value) at loaded condition. The welding characteristics of the 1.0-mm-thick polypropylene sheet specimens using the 94 kHz welding system were studied. Using the 94 kHz system, a weld strength of more than 370 N per one welded area was obtained at a vibration velocity of 2.7 m/sp-0 (peak-to-zero value), welding time of 0.8 s and static pressure of 600 kPa.

Finite element analysis on 1-3 piezocomposite rings for ultrasonic transducer applications

In this study, a commercial finite element code (FEM), ANSYS, is used to study the behaviors of 1-3 lead zirconate titante (PZT)/epoxy composite rings. The composite rings are fabricated by a dice-and-fill technique with an epoxy width of 80 μm. By using different number of cuts per direction (cpd), the composites with PZT volume fraction ( φ) from 0.88 to 0.93 could be obtained. It is found that the lateral characteristics (radial modes) of a PZT ring can be reduced significantly by using a 1-3 composite ring. Three-dimensional finite element models are built to understand and study the vibration characteristics of the composite rings. Good agreements are found between experimental results and FEM simulations. Results from this study can be used to optimize the number of cpd of the composite rings for practical transducer applications.

Experimental and numerical investigations of axisymmetric wave propagation in cylindrical pipe filled with fluid.

Acoustic wave propagation in fluid-filled cylindrical pipe with arbitrary thickness is investigated numerically and experimentally. The vibrational properties of the coupled fluid-pipe system are evaluated by a layerwise approach, which is similar to the finite-strip method. In this approach, the thick cylindrical wall is divided into a number of thin cylindrical layers in the thickness direction. The displacements in the thickness direction for each layer are approximated by linear-shape functions. The governing equation is obtained by using an energy minimization principle. The dispersion curves, distribution of vibrational energy between pipe wall and contained fluid, and displacement fields are examined. The dependence of the dispersion curves on wall thickness is discussed. Two PZT ring transducers adhered to the outer surface of pipe are used as source and receiver, respectively. The propagating waves generated by burst signals are measured. To localize transient signal both in time and frequency domains, the discrete wavelet transform is applied to decomposing the receiving signal into several components. Each component is limited to a narrower bandwidth. Therefore the frequency-dependent group velocity is estimated. The experimental and numerical results are compared.

Behavior of a PZT ring under non-uniform mechanical stress

Ring-shaped lead zirconate titanate (PZT) piezoelectric vibrators were subjected to non-uniform mechanical stress applied by bolt clamping. The effect of mechanical stress on the effective electromechanical coupling factor ( k eff) and mechanical quality factor ( Q m) of the thickness and wall thickness modes was studied by an equivalent electric circuit analysis. The initiation and propagation of cracks under mechanical stress were also discussed based on the resonance method and the indentation technique. k eff for both the thickness and wall thickness modes decreased with increase in mechanical stress due to de-poling of the PZT. Q m of the thickness mode dropped sharply with increase in mechanical stress while Q m of the wall thickness mode remained almost unchange. Existence of microcracks in a PZT vibrator can be detected by the occurrence of spurious vibrations at the wall thickness mode in the electrical impedance vs. frequency spectra.

Water-induced degradation in lead zirconate titanate piezoelectric ceramics

Water-induced degradation in lead zirconate titanate (PZT) piezoelectric ceramics was studied by a comparison experiment. In one treatment, PZT rings were immersed in a 0.01 M NaOH solution for long periods of time; in the other treatment, PZT rings were placed in a 0.01 M NaOH solution and hydrogen was evolved onto their silver electrodes by the electrolysis of water. No degradation occurred to samples immersed in the NaOH solution; but for the samples that were also treated by electrolysis of water, serious degradation occurred as their mechanical quality factor decreased dramatically and their dielectric loss increased considerably. I–V measurement showed that the resistance decreased greatly in the degraded samples, which could be explained by the formation of charge carriers due to the reduction reaction of atomic hydrogen from the electrolysis of water. It was proposed that the reduction reaction of atomic hydrogen at ambient temperature is an important origin for the degradation of piezoelectric ceramic devices.

Initiation and propagation of cracks in piezoelectric ring under non-uniform mechanical loading

Initiation and propagation of cracks in lead zirconate titanate (PZT) piezoelectric rings under a non-uniform mechanical loading were studied. The PZT ring was sandwiched between two pieces of metals and then compressed by a torque. Bolt clamping produced a non-uniform external stress on the PZT ring and caused various degree of depoling at different positions of the ring. A large torque also initiated cracking and breaking in the ring. Fracture features of the broken PZT ring were observed using scanning electron microscopy (SEM). Fracture toughness at the inner part of the ring changed significantly due to 90° domain rotation after a large torque had been applied. The ratio between the fracture toughness along the thickness direction and the fracture toughness along the radial direction varied from >1 to <1 due to loading. Cracks originated from the defects of the inner part of the ring and propagated mainly along the direction of low fracture toughness.

PIEZOELECTRIC RING-MORPH ACTUATORS FOR VALVE APPLICATION

This paper presents piezoelectric ring-morph actuators designed to produce a large flexural displacement for valve actuation application. The ring-shaped piezoelectric plate in the actuator produces a radial contraction or expansion and causes the center part of the metal disc to generate a large flexural displacement. The PZT ring creates a space under the metal disc which permits it to bend with a curvature larger than that of the conventional bimorph in the axis direction of the ring-morph when the PZT ring under the metal disc contracts. A prototype with diameter of 25.4 mm and thickness of 0.55 mm could produce a total stroke (static displacement) of over 130 μm under a driving voltage of ±300 V and a load of 2 N. The maximum generative force of ring-morph actuator was about 30 N.

Ring Type Uni/Bimorph Piezoelectric Actuators

This paper presents a ring type piezoelectric actuator that combines a ring-shaped piezoelectric component with a thin metal disc. In this actuator, the ring-shaped piezoelectric ceramic produces a radial contraction or expansion, and results in a large flexural displacement of the center of the metal disc. When the PZT ring under the metal disc contracts, the unbounded portion at the center of the disc is permitted to bend with a larger curve in positive (upper) direction. Both experimental results and FEM analysis support the new concept and confirm that the ring type uni/bimorph (ring-morph) configuration has a larger displacement output than that of conventional disc type uni/bimorph actuators with comparable dimensions.

Vibration characteristics of piezoceramic rings

Lead zirconate titanate (PZT) rings are used extensively in various kinds of transducer applications. However, there are not many reports on the study of the vibration characteristics of a PZT ring, especially when the ring has a thickness t comparable to its wall thickness w. In this study, the vibration characteristics of a PZT ring with 12.7 mm outer diameter are modeled by a finite element analysis (FEM) as functions of w and t. The resonant frequencies and effective electromechanical coupling coefficient keff of the rings are measured by an impedance analyzer. The vibration displacements at the various resonances are measured by a laser vibrometer. Good agreements are found between the experimental results and the FEM simulations. Results from this study can be used to optimize the dimensions of PZT rings in transducer designs.

Engineering resonance frequency charts of PZT rings of different sizes and at different clamping conditions

For developing ring type ultrasonic motors and piezoelectric transformers, the method by V. Stephenson for the computation of resonance frequency of piezoceramic rings was extended. Engineering charts of the resonance frequencies of PZT rings with different sizes and at different clamping conditions were constructed. The resonance frequencies obtained from the charts were in good agreement with the experiments. Some interesting features of the resonance frequency with respect to the ring dimensions (the outside and inside diameters. OD and ID) were found. The resonance frequency for rings with the same outside diameter decreased with decreasing OD/ID ratio. Clamping of the outer circumference of the ring reduced the resonance frequency. There was a minimum in the curve of the resonance frequency versus OD/ID, when the inside of the ring was clamped. These features provided methods to reduce the resonance frequency so as to miniaturize ultrasonic motors and other piezoelectric devices using PZT rings.

A novel high-displacement piezoelectric actuator for active vibration control

In this paper we discuss the design and testing of a novel hydraulic actuator which uses a PZT ring as the active component. The actuator is configured so that the PZT ring is part of the body of the actuator and it drives a piston hydraulically to achieve a high displacement capacity. Thus, the device is considerably more compact and simple than most actuators found in the literature using a similar principle. The performance of this actuator in terms of the force and displacement that it can produce is theoretically and experimentally studied and compared with the potential performance that can be obtained with other piezoelectric elements commercially available.

Axisymmetric wave propagation in fluid-loaded cylindrical shells. II: Theory versus experiment

The axisymmetric wave propagation along fluid-loaded cylindrical shells (excluding torsional modes) has been investigated both theoretically and experimentally. For a steel cylindrical shell with a fixed ratio of inner to outer radius, four different fluid configurations are considered: water inside and outside the steel shell, air inside and outside; water inside and air outside; and air inside and water outside. Calculations of the transient pressure response for the case of an axisymmetric ring source and a point receiver are made as a function of source–receiver separation. Experimentally, a PZT ring source and ring receiver are placed around a steel cylindrical shell with an outer radius of 9.53 mm and an inner radius of 7.94 mm. Waveforms are recorded for multiple source–receiver hydrophone spacings in the frequency band 50–240 kHz. Using a Prony’s method, the complex wave number for each of the modes in the system are derived from both the theoretical and experimental waveforms. These axisymmetric modes are grouped into three categories: steel modes, noncutoff fluid modes, and cutoff fluid modes. Excellent agreement is obtained between theory and experiment.

Axisymmetric wave propagation in fluid-loaded cylindrical shells: Theory versus experiment.

This paper discusses both theoretical and experimental aspects of axisymmetric wave propagation along fluid-loaded cylindrical shells (excluding torsional modes). For a steel cylindrical shell with a fixed ratio of inner to outer radius, four different fluid configurations are considered: water inside and outside the steel shell; air inside and outside; water inside and air outside; and air inside and water outside. Calculations of the transient pressure response for the case of an axisymmetric ring source and a point receiver are made as a function of source–receiver separation. Experimentally, a PZT ring source and ring receiver are placed around a steel cylindrical shell with an outer radius of 9.53 mm and an inner radius of 7.94 mm. Waveforms are recorded for multiple source–receiver hydrophone spacings in the frequency band 50–240 kHz. Using a Prony’s method, the complex wave number as a function of frequency for each of the modes in the system is derived from both the theoretical and experimental waveforms. These axisymmetric modes are grouped into three categories: steel modes, non-cutoff fluid modes, and cutoff fluid modes. Excellent agreement is obtained between theory and experiment.

Experimental and theoretical wave propagation in solid and hollow cylinders in fluid

A comparison between experiment and theory is made involving axi‐symmetric wave propagation along solid and hollow cylinders immersed in a fluid (i.e., water). The theoretical methods to generate waveforms include both integral representation and finite‐difference modeling. The dispersive modal characteristics are calculated from the waveforms. The experiments are made on solid and hollow steel cylinders of 0.75 in. and 0.625 in. The source and receiver transducers are made from PZT rings 1.0 in. and 0.5 in. high which freely slide along the cylinders. Data are collected as a function of source‐receiver spacing and over a frequency range of 40–240 kHz. A Prony's method is used to obtain the modal characteristics. Discussions will focus on the good agreement between theory and experiment, the differences between the mode structures in the two cases and the asymptotic behaviors at short and long wavelengths. Some interesting comparisons between monopole and dipole modes will also be made.