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CYMBAL机电换能器摘要：一种新型命名为cymbal的换能器已经出现了，它拥有更大的位移、更大的激振力以及更加经济有效的制造成本。cymbal换能器由夹在两片金属端帽之间的压电陶瓷片构成，即可用于传感器又可发生器。相同尺寸压电陶瓷片的cymbal发生器能产生大约40倍于普通的换能器的位移。1、简介本文描述一种新型复合换能器，cymbal,它有更大的位移和相当高的激振力。以下将描述直径为12.7mm、总高2mm的振子的设计和结构，以及位移、激振力和最快响应时间。cymbal振子是第二代月牙形复合换能器，通过有限元分析以及经验发展而来。在最初的月牙形构想中，位移由金属端帽的弯曲运动产生。但是，对cymbal换能器来说，位移则是弯曲和旋转的复合运动产生。而且，端帽通过冲压金属薄板就能容易得到。cymbal复合振子将在本文中与其他换能器的设计比较讨论。2、制造和布局方法 需要设计一套冲压模具，以便能以较低的成本、较高的效率制造圆锥形的“cymbal”端帽。通过切割工具钢可制造出所需的模具，它能冲直径为12.7mm并且带深0.2、直径为9.0mm的圆锥形空腔。在冲压成型过程中，也会产生变形。最终的产品需要表面处理来保证粘结质量。cymbal端帽可由0.25mm0.20mm厚的金属板制造，不同厚度金属板的特性见表1。cymbal换能器的基本结构如图1所示。A）cymbal振子的位移特性cymbal端帽被粘结到压电陶瓷片上，粘结剂为环氧树脂。环氧树脂层的厚度大约为20um.在0.1Hz、1kV/mm电场下，用LVDT测量的复合振子的位移大约为0.05um。同样使用LVDT系统，可以测得在静载荷条件下的激振力。响应特性包括用HP-4194A计算响应速度和评估粘结层。 图2表明与早期的cymbal振子（0.2mm厚端帽）相比，位移的位置独立性。位置独立的位移是早期月牙形的一个缺点。带有凹槽的月牙形端帽表明其有更少的位置依赖性。该cymbal设计传递一个在端帽中心一个宽的部分偏移量小于1微米均匀的位移。新端帽的大接触平面设计使得它比将单个振子堆在一起来达到大的位移更加实际。另外，新的堆积结构在轴对称载荷作用下更加稳定。175um的位移值相当于5个cymbal堆积在一起。图3表明金属端帽杨氏模量和陶瓷材料的类型对复合cymbal振子（0.25mm厚端帽）的影响。对于相同的金属端帽，有位移对陶瓷压电系数的独立性。PZT在径向以及空腔的收缩越大，金属端帽在轴向的位移也越大。金属端帽得位移会随着硬度的增大而变小，这与在端帽的 运动中高的机械损失有关。高硬度金属的位移大约是低硬度金属端帽可达到位移量的52-57%，且与陶瓷类型无关。压电、电致伸缩转换类型的电动陶瓷元件在cymbal设计中作为驱动元件。即使线性位移特性，压电陶瓷cymbal依然显示高的滞后现象。通过使用PMN-FT类型electrosuictive ceever 有电致伸缩驱动元件cymbal振子显示了非线性位移。这种材料的独特属性就是其在集中电场下的测定体积扩展。跟cymbal端帽设计一样，这种测定体积扩展被转变为负的轴向位移。图4显示有PNZST驱动元件的cymbal振子的位移滞后现象。B）最大激振力黄铜端帽cymbal振子的最大激振力大约是15N。对于cymbal振子来说，端帽材料的弹性是一个关键参数，因为端帽在集中力作用下容易像弹簧一样运动。cymbal振子的作用力范围与月牙形振子相比要大一些。由于使用了硬质金属端帽，力的范围可能明显地增加。钨端帽的cymbal振子表现出了一个大于100N的激振力。图5弹性模量对cymbal振子的位移和激振力性能的影响。C）cymbal振子最快响应时间对于振子来说，最快响应时间是一个重要的标准，它可以被定义为到达振子快和精确响应的时间。系统的机械谐振限制了实际的作用域。振子应该用于它们的谐振频谱的线性范围内。cymbal振子的最快响应时间由式t=（1/f）来评估，其中f是弹性响应频率。图6带有不同压电驱动元件的cymbal振子的FRT。在给定的尺度下，cymbal振子最快响应时间大约是50usec。D）cymbal有效压电系数压电电荷系数是一个材料参数。对于传感器来说正压电效应是重要的，而负压电效应对作动器很重要。由于月牙形和cymbal的复合设计，有效的压电系数用于区分材料常数。月牙形和cymbal换能器的压电系数可用 a modified Berlincourt meter来测量。例如，0.30mm厚的黄铜端帽，大约10,000 pC/N的压电系数在中心处被测量。月牙形振子端帽下方的空穴在月牙形的特性中扮演一个至关重要的角色。月牙形换能器的压电电荷系数也显示了与位移相似的位置依赖性。用cymbal端帽，压电系数增加大约60%。直径12.7mm和总厚1.7mm的cymbal，其有效压电系数大于在直径为3mm的cymbal换能器的中心部分的15000pC/N。我们推断，在月牙形金属端帽的边缘附近的厚金属区域是一个被动区域，它不仅不能协助压力的传递，相反还降低了总的效率。而cymbal端帽能更有效地传递压力，明显地改善能量传递。4.讨论A.Comparison of the Solid Stale Actuator Designs各种各样的固体作动器设计的几个特点被列出在表11中。由于几何学和特定应用中的不同操作环境的差异，比较不同振子是相当困难的。为了作一个公平的比较，每一个振子都被选择了相似的尺寸，且测量环境是在表11中指定的那些。有适度激振力和位移值得月牙形cymbal振子填补了多层和双压电晶片元件之间的鸿沟。每一个固体作动器的设计具有吸引人的特征，这些特征可以开发作为特定的应用。月牙形cymbal振子的优点是：通过改变空穴尺寸和端帽尺寸，能很容易的得到想要的振子的性能。它的另一优点就是制造方便。彩虹形振子也部分地填补了上述鸿沟。对于那种类型的振子，高温下陶瓷元件的处理期间一个变形阶段导致了一个半导体层和应力偏差。即使它表现出了一个弯曲运动，彩虹形可以被分为单晶体或者unimorph振子类。彩虹形的有效耦合因子在理论上依然比月牙形cymbal小。与cymbal相比，高集中场，位置独立位移和成本是彩虹形振子主要的缺点。在月牙形cymbal振子设计中，多层压电陶瓷晶片可能被用作驱动元件，这样就可以降低驱动电压。在这项研究中，为了研究端帽材料和驱动元件的影响，我们保持尺寸不变。并且，通过缩小结构尺寸达到更高的位移是可能的。以35mm的直径为例，可达到150um的位移值。cymbal换能器的有限元分析和比例缩放的研究将在其它的出版物中被发表。B）cymbal换能器的应用前景cymbal换能器在汽车工业中有很大的潜力。在汽车工业中，它们可以被用作传感器和振动抑制元件。cymbal振子也可在阀的设计中用作转换元件。在循环过程中，在月牙形cymbal换能器内部有一个体积的变化。该体积的改变可在微泵中得到应用。像CD-ROM和磁盘存储驱动器一样的高密度存储驱动器是另外一些可能的应用领域，因为cymbal振子有传递精确位置的能力。由于高的压电电荷系数，月牙形cymbal换能器可用作水听器，加速计和气-声换能器。在低的频率下，cymbal加速计比PZT陶瓷有更高的灵敏度。cymbal型水听器的优点就是有非常大的流体动力电荷和电压系数而且有轻一些的重量和便宜一些的制造成本。THE CYMBAL ELECTROMECHANICAL ACTUATOR Aydin Dogan, Jose F. Fernandez, Kenji Uchino, and Robert E. Newnham, ICAT-Materials Research Laboratory-The Pennsylvania State University University Park, PA 16802 Abstract- A new transducer design was developed named the Cymbal Transducer 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 actua- tor exhibits almost 40 times higher displacement than the same size of ceramic element. Effective piezoelectric charge coeficient, eff. d, of a cymbal is roughly 40 times higher than PZT itself. L INTRODUCIlON This paper describes a new composite transducer, the Cymbal, with a large displacement and relatively high generative (blocking) force. The design and construction of a 12.7 mm diameter actuator with 2 mm t o t a l thickness i s described. along with the displacement, generative force, and fastest response time. The cymbal actuator is a second generation moonie-type composite developed using FEA analysis in collaboration with experiment 1-51. Displace- ment is primarily a flexural motion of the endcap for the original moonie design, but for the cymbal, the displace- ment is created by the combination of flexural and rota- tional motions 5. Moreover, the endcaps are easily fabri- cated from sheet metal by punching, resulting in identical endcaps with minimal labor. The cymbal composite acwa- tor is compared with other actuator designs in the discus- sion part of this paper. 11. FABRICATION AND CHARACTERIZATION METHOD A punch die was designed to rapidly fabricate truncated conical shape cymbal endcaps at minimal cost. The die was manufactured from cutting tool steel for punching cymbal endcaps 12.7 mm in diameter with a 0.2 conical cavity depth and a 9.0 mm cavity diameter. Shaping and cutting operations are wried out simultaneously during processing. The final product requires only surface. ueat- ment for good bonding. The cymbal endcaps were fabri- cated from 0.25 and 0.20 mm thick sheets of various metals whose properties are listed in table I. The basic schematic of the cymbal transducer is shown in Fig. 1. The cymbal endcaps were bonded to the piezoelecuic, electrostrictive, or antifermelecmc-ferroelectric switching type of ceramic disk (12.7 mm in diameter and 1.0 mm thickness) around the circumference using Eccobond epoxy resin from Emerson & Cuming, taking special care not to fill the cavity. The thickness of the epoxy bonding layer was approximately 20 pm. The displacement of the composite actuator at 0.1 Hz under IkV/mm electric field was measured with a Linear Voltage Differential Transducer (LVDT) having a resolu- tion of approximately 0.05 pm. Generative (blocking) force measurements were done under static loading condi- tions, again using the LVDT system. Resonance character- istics were obtained with an Impedance/Gain Phase Ana- lyzer HP4194A to calculate the response speed and to evaluate the bonding layer. 1 C3D I t F i g . 1 Schematic o f the cymbal transduca. A) Displacement characteristics o f the cymbal actuator Fig. 2 shows the position dependence of the displace- ment cymbal actuators (0.2 mm thick endcaps) in compari- son w i t h earlier designs. Position-dependent displacement is a disadvantage of the original moonie. Moonies with grooved endcaps show significantly less position-dependent displacement. The cymbal design delivers a homogeneous displacement with deviations of . - . .I . .- . . i . j . ; . - 6 0 1 . I. I. I. I * I *I - I* 1 4.0 - 3 . 0 -2.0 -1.0 0.0 1 . 0 2-0 3 . 0 4.0 Applied Electric Field (kV/mm) Fig. 4 Displacement hysleresls of the cymbal wilh PNZST driwng element B) Maximum Generative (Blocking) Force The maximum generative force of the cymbal actuator with brass endcaps is around 15 N, (This corresponds to the in- tercept on the force axis at the point corresponding to the blocking force for which the displacement is equal to zero). The elasticity of the endcap material is a key parameter for the cymbal actuator since the endcaps tend to act like a spring under an applied force. The force range for the cymbal actuator is appreciably greater than that of the mmnie actuator. By using a stiff metal for the endcap, the force limit can be increased markedly. The cymbal actua- tor with tungsten endcaps exhibits a generative force of more than 100 N. Fig. 5 shows the effect of modules of elasticity on the displacement and generative force per- formance of the cymbal actuator. 214 C) Fastest response time of the cymbal actuator The fastest response time is an important criteria for the actuators and it can be defined as the time to achieve the quick and precise response of the actuator without over- shoot and ringing 6. The m e c h a n i c a l resonance of the system limits the practid actuation range. Actuators should be used in the linear range of their resonance spec- trum. The fastest response time (FRT) of the cymbal trans- ducer was evaluated from: t,=, = (l/fJ , where f, is the flextensional resonance frequency. Fig. 6 shows the FRT of the various cymbal actuators with different piezoelectric driving element as a function of sound velocity of metal endcaps. The fastest response time of the cymbal actuator is about 50 psec for the given dimensions. 85 30 80 75 0 P t f - 5 7O 0 65 60 25 P 0, n (. 20 z I 1s 10 50 100 150 200 2JO 300 350 40) 450 E s h p Y-WB Moddas (GP.) Fig. 5 Effect of modules of elasticity on the dirplaccmat and generative force performance o f the cymbal actuator i F a3 0 ; ; e d 42 40 38 36 34 32 30 28 3 3.5 4 4 .s 5 5.5 6 Sound Velodty In Endcap Metals (kmls) Fig. 6 FRT of the cymbal rcwuK as a furnon of sound velocity of the endcap rmferials D) Effective Piezoelectric Coeficient of the Cymbal The piezoelecmc charge coefficient is a material pa- rameter. The direct piezoelectric effect is important for sensors and the converse piezoelectric effect is important for actuators. Because of the composite design of moonie and cymbal, the effective piezoelectric coefficient is used to distinguish it from a material constant. The piezoelectric coefficient of the moonie and cymbal transducers were measured with a modified Berlincourt 4, meter. For sam- ples with 0.30 mm thick brass endcaps, a piezoelectric co- efficient of approximately 1 0 , O O O pCfN was measured at the center. The cavity beneath the endcap of the moonie actuator plays a crucial role on the characteristics of the moonie 3. The piezoelectric charge coefficient of moonie transducers also shows position dependent behavior similar to that of the displacement. With the cymbal endcaps the piezoelectric coefficients increased almost 60%. For a cymbal 12.7 mm in diameter and 1.7 mm in total thickness, an effective piezoelectric coefficient of more than 15,000 pC/N was measured over the 3 mm diameter center section of the cymbal transducer. We have concluded that the thick metal region near the edge of the moonie metal endcaps is a passive region which does not assist stress transfer, and acts to decrease the total efficiency. Cymbal endcaps transfer the stress more effi- ciently and improve the energy transfer markedly. IV. DISCUSSION A. Comparison of !he Solid Stale Actuator Designs Several features of the various solid state actuator de- signs are listed in Table 11. It is rather difficult to compare the different actuators because of differences in geometry and various operating conditions for specific applications. To make a fair comparison, similar dimensions for each actuator were selected, and the measurement conditions are those specified in Table 11. Flextensional moonie and cym- bal actuators with their moderate generative force and dis- placement values fill the gap between multilayer and bi- morph actuators. Each solid state actuator design has at- tractive features that can be exploited for certain applica- tions. Advantages of the moonie and cymbal actuators are the easy tailoring of the desired actuator properties by alter- ing the cavity size and endcap dimensions. Easy fabrica- tion is another advantage. The rainbow actuator also par- tially covers this gap 7. For that type of actuator a reduc- tion step during processing of the ceramic element at high temperature results in a semiconducting layer and stress- bias. Even though it shows flexural motion, the rainbow can be categorized as a monomorph or a unimorph type of actuator. The effective coupling factor of rainbow is theo- retically smaller than the moonie and cymbal. High ap- plied field, position-dependent displacement and cost are 215 t FEATURES MULTMYER J101 BIMORPH.lOI RuNBowm CYMBAL. Dimensions 5x5127 (Ixwxt) 12.7x1Ox0.6 $12.7 nun, t= 0.5 mm $ 12.7 mm. t= 1 . 7 mm OXWXll hiving Voitape 0 ) 100 100 450 100 Displacement (lull) 10 35 20 40 Contact surface (mm? 25 1 1 3 Generative Fora J ) 900 0 . 5 - 1 1-3 15 the main disadvantages of the rainbow actuator in compari- son with the cymbal. In the mwnie and cymbal design, a multilayer piezoelectric ceramic can be used as driving element to reduce the drive voltage. In this study, we kept the dimensions constant to investigate the effect of endcap materials and driving elements. Moreover, it is possible to reach higher displacement by scaling the structure. For the sample of 35 mm diameter, a displacement value of 1 5 - has been achieved. FEA and scaling studies of the cymbal transducer will be presented in some other publications. B) Potential Applications for The Cymbal Transducers The cymbal actuators have great potential in the auto- motive industry where they can be utilized as sensing and vibration suppression elements. The cymbal actuators can also be utilized as the switching element in valve designs. There is a volume change inside the moonie and cymbal transducers during cycling. This volume change can be utilized in minipump applications. The high density mem- ory storage driver sucb as CD-ROM driver and magneto- optic memory storage driver are other possible applications for cymbal actuators capable of delivering precise position- MOONIF, .31,41 0 1 2 . 7 mn t= 1 . 7 100 20 1 3 mm ACKNOWLEDGMENT ?be authors wish to thank D r . M. Meghe-rhi of PiezoKinetics Inc., and Mr. J.F. Tressla for their advice and assistance. The authors would like to express their gratitude f a the support to the following agencies and organi- zations: ONR Contract n o . N00014-92 J 1510. Turkish Science and Tech- nology Couocil (TUBITAK), Spanish Science Ministry (CICYT MAT94- 807 and DGICYT PR94-028. REFERENU3 l 2 R. E Newnbam, Q. C. Xu, and S. Yashikawa, Metal-Eiearoactive Ceramic Conposite Aauatas: U.S. patent 5.276657. Jan 4, 1994. A. Dogan. Q.C Xu. K . O n i m k a , S. Yoshikawa, K. Uchino, RE. Newnham High Displacement Ceramic-Metal Composite Actuata , F e d e c h x Vol. 156, pp. 1-6, 1994. A.Dogan, S . Yashikawa, K. Uchino, RE. Newnham The E f f e c t of Geometry on the Charaaeristia of the Moonie Transducer and Reli- abilit