Metal Endcaps Research Articles

Vibration Characteristic of Cymbal Type Transducers

A cymbal transducer consists of a poled piezoelectric disk which is sandwiched between two metal endcaps, each containing a truncated cone-shaped cavity. Three different designs, an asymmetric cymbal, a symmetric cymbal and a thimble, were produced and their frequency responses were studied. The main vibration modes were identified and the frequency tunability by external mass addition was demonstrated.

Resonant Frequency Response of Cymbal Transducer

Piezoelectric and electroestrictive ceramics have been used in many actuator applications as displacement transducers, pressure sensor, shape controllers and precision micropositioners. To meet these needs a composite actuator, called "Cymbal", based on a flextensional transducer was developed. The device is composed by a PZT ceramic disc sandwiched between two truncated conical metal endcaps, having a shallow cavity between the metal and the ceramic. In this work the cymbal's mechanical vibration response as a function of the driving frequency is studied. The main vibration modes are identified.

A novel snap-through buckling behaviour of axisymmetric shallow shells with possible application in transducer design

In this study, the snap-through buckling behaviour of axisymmetric shells, subjected to axisymmetric horizontal peripheral load or displacement for various shell parameters and various boundary conditions, is investigated. Results obtained seem not to have been reported previously. An application of peripheral displacement type of loading is seen in metal-ceramic composite transducers developed by sandwiching a piezoelectric (PZT) ceramic between two metal end caps which serve as mechanical transformers for converting and amplifying the lateral displacement of the ceramic into an axial motion normal to the metal cap. In our numerical search, we have observed that snap-through and snap-back buckling is possible for shallow spherical caps for a very narrow range of the shell parameter used. When a hole is opened around the apex of the cap, buckling is possible for a larger range of the shell parameter. Obtaining the displacement amplification and the blocking or generative force for various material and geometric properties is necessary for the possible application of the findings in transducer design. The numerical results are presented in graphical forms.

Cymbal actuators fabricated using PMN-PT single crystal

Cymbal actuators with very high displacement have been fabricated and tested. A cymbal actuator consists of a piezoelectric disc sandwiched between two truncated conical metal endcaps. Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) single crystal is used as the piezoelectric driving element of the cymbal actuator. The influence of the piezoelectric coefficient of the driving element on the actuator performance has been studied. Due to its high piezoelectric d33 and d31 coefficients, a PMN-PT single crystal actuator gives a much higher displacement than a PZT actuator.

Concave cymbal transducers

A new type of cymbal transducer, called the concave cymbal, has been developed to increase the pressure tolerance and reliability of the transducer under high hydrostatic pressure. The main feature of the new design is a lead zirconate titanate ceramic ring sandwiched between two concave metal endcaps. It shows much improved pressure performance and can withstand a pressure of up to 6 MPa while maintaining high effective hydrostatic piezoelectric coefficients. When incorporated into a planar array with a radiating area of 5.5 cmx5.5 cm and weight of only 30 g, a transmitting voltage response of around 125 dB re 1 μPa/V @ 1m was obtained over a frequency range between 20 and 50 kHz.

An Ultrasonic Motor Using a Metal-Ceramic Composite Actuator Generating Torsional Displacement

An ultrasonic motor composed of three components; a stator, a rotor and a ball bearing is proposed. The stator is made of an active piezoelectric ring, poled in the thickness direction and bonded with two windmill-like slotted metal endcaps. The stator is excited through its two electrodes, generating ultrasonic vibration in the radial direction at a radial mode resonance frequency. The two identical metal endcaps on both sides of the ring, bonded after shifting 45° with each others, transfers the radial vibration into longitudinal and tangential vibrations. The combination of these vibrations (longitudinal and tangential) generates rotation due to frictional interaction between the center part of the top endcap and the periphery of the rotor. A prototype motor with 11.0 mm diameter was fabricated and its transient characteristics were measured. The maximum torque of 1.36 mNm was obtained at a speed of 480 rpm.

Tailoring the performance of ceramic-metal piezocomposite actuators, ‘cymbals’

A unique design of metal-ceramic actuators exhibits very high displacement and large generative forces. This new metal-ceramic composite actuator design, the ‘cymbal’, consists of a piezoelectric disk sandwiched between two truncated conical metal endcaps. The radial motion of the piezoelectric ceramic is converted into flextensional and rotational motions in the metal endcap. Based on previous studies of ceramic-metal composites, a simplified model has been developed to evaluate the properties of cymbals and to aid in materials selection. The influence of the stiffness of the metal, the piezoelectric coefficients of the ceramics and the characteristics of the epoxy bond on actuator performance have been evaluated. It is found that the higher the transverse piezoelectric coefficient, the higher the displacement of the actuator. The stiffness of the metal reduces the displacement but allows the composite to support higher loads. There is a thermally induced displacement of the piezocomposite with the temperature that is related to the thermal expansion mismatch between the metal endcaps and the ceramic. By selecting appropriate materials, it is possible to avoid this thermally induced displacement. Very low or negligible temperature dependence of the displacement is attained by using PZT ceramics with temperature-independent properties together with metal caps having higher Young's modulus and lower thermal expansion coefficients than the ceramics.

Scaling Analysis for the Axial Displacement and Pressure of Flextensional Transducers

We have examined the axial displacement, Δh, and maximum axial pressure, Pmax, of flextensional transducers such as the moonies and the rainbows with both scaling and mechanical analyses. For a constant electric field E across the transducer, Δh/t∝E/t2 where t is the thickness of the rainbow or the thickness of the metal end cap of the moonie and Δh/t, the relative axial displacement. Thus, for a constant voltage V across the transducer, Δh/t∝V/t3. As for the maximum pressure, Pmaxt2 for the rainbows and Pmax∝wt for the moonies where t is the thickness of the rainbow or the thickness of the metal end cap of the moonie and w the thickness of the piezoelectric disk of the moonie. These predictions agree well with the experimental results found in the rainbows and the moonies. Our analysis showed that although the rainbows and the moonies differ in design and processing, the underlying physics for the enhancement in the axial displacement are essentially the same: The nonuniform distribution of d31 through the thickness of the transducer causes the transducer to arch or flatten with an applied electrical field, which leads to the enhancement in the axial displacement. The only difference is that, for the transducer to arch, the applied field is in the opposite direction to the polarization in the rainbows but in the same direction as the polarization in the moonies.

Composite piezoelectric transducer with truncated conical endcaps "cymbal"

This paper presents original results obtained in the development of the moonie-type transducers for actuator applications. The moonie-type actuators fill the gap between multilayer and bimorph actuators, but its position-dependent displacement and low generative force are unacceptable for certain applications. The moonie transducers were modified systematically by using finite element analysis combined with experimental techniques. A new transducer design, named transducer, was developed with larger displacement, larger generative forces, and more cost-effective manufacturing. The cymbal transducers consist of a cylindrical ceramic element sandwiched between two truncated conical metal endcaps and can be used as both sensors and actuators. The cymbal actuator exhibits almost 40 times higher displacement than the same size of ceramic element. Effective piezoelectric charge coefficient, Eff. d/sub 33/, of cymbal is roughly 40 times higher than PZT itself.

Accelerometer Application of the Modified Moonie (Cymbal) Transducer

The modified Moonie (Cymbal) transducer has been investigated for an accelerometer application. High effective piezoelectric charge coefficients (d33) of the Cymbal transducer was observed around 15000 pC/N, which is much higher than that of the piezoelectric ceramic itself (∼550 pC/N). With this feature the Cymbal trasducer is a good candidate for high sensitive accelerometer applications. The sensitivity of the Cymbal accelerometer was measured as a function of driving frequency and compared with the single plate ceramic disk which was used as driving component in the transducer. Besides, the geometry of the transducer such as endcap thickness, the effect of different Lead Zirconate Titanate (PZT) compositions and metal endcaps on sensitivity was investigated. The sensitivity 50 times higher than the PZT disk was obtained.

Metal-Ceramic Composite Transducer, the "Moonie"

A new type of metal-ceramic composite transducer, the "moonie,' has been developed by sandwiching a poled lead zirconate titanate (PZT) ceramic between two specially designed metal end caps. Piezoelectric coefficients an order of magnitude larger than PZT itself are obtained. The metal-ceramic composites are being developed as fish finders, hydrophones, actuators, and transducers with integrated sensing and actuating capabilities. This paper describes the moonie principle, optimization of the moonie design using finite element analysis, and the performance of the device for several different applications.

Design optimization for metal-ceramic composite actuator, “moonie”

Abstract A piezoelectric ceramic-metal composite actuator has been developed to amplify the displacement of the piezoelectric ceramic. In this structure, the PZT ceramic is sandwiched between end caps with shallow cavities. This paper describes the design optimization of the flextensional transducer using finite element analysis (FEA). By using FEA, shape, material, and geometrical contributions to the displacement of the actuator were calculated. The effect of load on the displacement was also estimated. It was found that the displacement of the actuator increases with cavity diameter and depth, and that introducing a ring-shaped groove on the metal end caps of the actuator greatly enhances the displacement.

Metal–Ceramic Composite Actuators

A new type of actuator composed of metal (brass) end caps and piezoelectric ceramics has been developed as a displacement transducer. Shallow cavities positioned between the metal caps and the central ceramic disk convert and amplify the radial displacement of the piezoelectric ceramic into a large axial motion of the metal end caps. Large d33 coefficients exceeding 2500 pC/N are obtained with the composite actuators. The behavior of the electrically induced strain with geometric variables, such as the thickness of the metal end caps, and with pressing force and driving frequency has been evaluated. Sizeable strains are obtained with both PZT (piezoelectric lead zirconate titanate) and PMN (electrostrictive lead magnesium niobate) ceramics.

Conversion of the Electrohydraulic Electrode to an Electromechanical Stone Impactor: Basic Studies and a Case Report

A 3.3F electrohydraulic electrode (Wolf 2137.23) has been confined within a spring with a metal end cap, irrigated with water and covered with a 0.003-inch metal sheath (outside diameter 5F). The electrohydraulic lithotripsy discharge (Wolf Generator 2137.50) at El causes the metal cap to extend 3mm. at 1,500cm. per second and creates an impact pressure of 600 to 800 bar. Stone fragmentation efficiency of the electromechanical impactor was equivalent to unshielded electrohydraulic lithotripsy (gallstone 2.83mg. per pulse, struvite/apatite 1.41mg. per pulse, cystine 0.41mg. per pulse, uric acid 1.48mg. per pulse and 100% calcium oxalate monohydrate 0.10mg. per pulse).Studies of the discharge of the electromechanical impactor within the pig ureter showed that minimal ureteral submucosal edema and hemorrhage occurred at 300 shocks discharged at a single point, and disruption of the mucosa and partial injury to the muscle layer occurred after 600 shocks given at the site of a pinched pig ureter. Pushing the electromechanical impactor perpendicular to the wall of the pig bladder will create a mechanical perforation within 35 shocks (electrohydraulic lithotripsy within 2 shocks).One patient had excellent fragmentation of a lower ureteral mixed monohydrate and dihydrate stone under direct vision performed with the electromechanical impactor passed via a 9.5F uretero-scope. There was no evidence of mucosal injury with 500 shocks.The electromechanical impactor has been developed to provide a safe and inexpensive method of ureteral stone fragmentation or disimpaction. These studies were performed to establish limits of safety that may allow use of the electromechanical impactor for stone fragmentation in the ureter without the need for ureteroscopy.

Effects of Shielded or Unshielded Laser and Electrohydraulic Lithotripsy on Rabbit Bladder

The pulsed dye laser and electrohydraulic lithotriptor (EHL) are both effective devices for fragmenting urinary and biliary calculi. Both fragment stones by producing a plasma-mediated shockwave. Recently, a plasma shield consisting of a hollow spring and a metal end cap has been described for use with the laser and EHL devices in an attempt to minimize tissue damage without adversely affecting stone fragmentation rates. The tissue effects produced by a pulsed dye laser and an EHL device with and without plasma shields were examined and compared using rabbit urinary bladders. If blood was present, the unshielded laser perforated the bladder wall in two pulses. However, in the absence of blood, over 100 pulses were needed for the laser to perforate the bladder. A mean of six pulses were required to perforate the bladder wall with a shielded laser. The unshielded EHL perforated the bladder wall in two pulses, whereas, the shielded EHL required a mean of 35 pulses. Microscopically, areas of exposure revealed hemorrhage and tissue ablation. We conclude that all devices examined can produce significant tissue damage when discharged directly onto bladder epithelium. (J. Urol, 143: 857–860, 1990)

Shielded Electrohydraulic Lithotripsy of Urinary and Biliary Calculi: A New Possibility

A new transurethral lithotripsy concept, using an electrohydraulically generated shock wave to drive in a jackhammer manner a hollow spring with a metal end cap, was tested in vitro and shown to fragment urinary and biliary calculi effectively. The prototype device was fabricated from a hollow stainless steel expansion spring (1.6-mm outer diameter, 12-mm long). The primary electrohydraulic lithotripter used was the Wolf model 2137.50 (Richard Wolf Medical Instruments Corp.) with a 3.3F probe placed inside the prototype device and securely attached using a short piece of hypodermic tubing. The mechanism worked by confined electrohydraulic discharge, driving the spring and the cap to impact the stone. The results show that shielded electrohydraulic lithotripsy is effective in fragmenting both urinary and biliary calculi and is only 23% less efficient than an unshielded electrohydraulic discharge. However, the advantages to a shielded instrument may be substantial. When the shielded electrohydraulic device was discharged against the experimenter's finger, no pain was felt. Shielded electrohydraulic lithotripsy in the future may be used for ureterolithotripsy without the need for anesthesia or a ureteroscope.

Low frequency hydrophone

A pressure-balanced hydrophone having a low cut-off frequency which inclu a pair of piezo-ceramic tubes, wired in series, and having one end of each tube secured to a metal block in the center. The second end of one of the ceramic tubes is covered by means of a solid metal end cap and the second end of the other ceramic tube is covered by a porous sintered metal end cap. The unit is enclosed in an elastomeric cylindrical boot which is closed at the open end by a metallic disc. A pair of fill plugs are provided to fill the interior and the exterior of the piezo-ceramic tubes with a suitable oil. The unique feature of subject device is that a plurality of pores in the porous sintered metal end cap act as a plurality of capillaries for pressure balancing and thus make the hydrophone insensitive to hydrostatic pressure variations.

New underwater glass platform

The class V cymbal is a flextensional transducer commonly used in low-power ultrasonic applications. The resonance frequency of the transducer can be tailored by the choice of end-cap and driver materials, and the dimensions of the end-caps. The cymbal transducer has one significant limitation which restricts the operational vibration amplitude of the device. This is the limit imposed by the mechanical strength of the bonding agent between the metal end-cap and the piezoceramic driver. Therefore, when there is an increase in the input power or displacement, the stresses in the bonding layer can lead to debonding, thereby rendering the cymbal transducer ineffective for high-power ultrasonic applications. In this paper, several experimental analyses have been performed, complemented by the use of Abaqus/CAE finite element analysis, in order to develop a high-power ultrasonic cutting device for bone surgery using a new configuration of cymbal transducer, which is optimised for operation at high displacement and high input power. This new transducer uses a combination of a piezoceramic disc with a metal ring as the driver, thereby improving the mechanical coupling with the metal end-cap.