Multilayer Piezoelectric Actuator

FIGURE 4.1.32 Walking piezomotor using an inchworm mechanism with four multilayer piezoelectric actuators by Philips. 

For further information on ceramic actuators, see Uchino (1993). It has been recognized that in modern multilayer piezoelectric actuators (MPAs), the combination of thermal, electrical and mechanical loads during service may affect the functional integrity of the devices. As the details of these effects and their synergistic coupling are still unknown, modeling of the nonlinear behavior of these temperature-sensitive functional properties and their implementation into finite element analysis (FEA) tools has been performed recently (Griinbichler et al., 2008). 

Chemical and physical processing techniques for ferroelectric thin films have undergone explosive advancement in the past few years (see Ref. 1, for example). The use of PZT (PbZri- cTi c03) family ferroelectrics in the nonvolatile and dynamic random access memory applications present potentially large markets [2]. Other thin-film devices based on a wide variety of ferroelectrics have also been explored. These include multilayer thin-film capacitors [3], piezoelectric or electroacoustic transducer and piezoelectric actuators [4-6], piezoelectric ultrasonic micromotors [7], high-frequency surface acoustic devices [8,9], pyroelectric intrared (IR) detectors [10-12], ferroelectric/photoconduc-tive displays [13], electrooptic waveguide devices or optical modulators [14], and ferroelectric gate and metal/insulator/semiconductor transistor (MIST) devices [15,16]. 

An example of a smart material is one developed by Toyota. The multilayer piezoelectric ceramic inside an automobile shock absorber has about five layers for sensing road vibrations. The multilayer stacks positioned near each wheel of the auto also have about 100 layers that act as the actuator, all part of the same ceramic. After analyzing the vibrational signals, a voltage is fed back to the actuator stack, and a response occurs by pushing on the hydraulic system of the auto to cancel the vibration. 

A dot-matrix printer is the first widely commercialized product using ceramic actuators. Each character formed by such a printer is composed of a 24 x 24 dot matrix. A printing ribbon is subsequently impacted by a multiwire array. A sketch of the printer head appears in Figure 4.1.28a [51]. The printing element is composed of a multilayer piezoelectric device, in which 100 thin ceramic sheets 100 xm in thickness are stacked, together with a sophisticated magnihca-tion mechanism (Fig. 4.1.28b). The magnihcation unit is based on a monolithic... 

Piezoelectric actuators are more and more often used for their accuracy and fast response. They are used in industrial applications together with a dedicated driver and a control loop. Optical applications were the first to use piezoelectric multilayer actuators. The past years have seen the development of adaptronic applications in machine tools and large scale application in automotive (gazole injectors) systems. 

Multilayer-type piezoelectric or electrostrictive actuators are used for several apphcations including the composite smart stmcture shown in Figure 9... 

Crytal chemitry. The effect of solid solution on the transition behavior of perovskite (ABX3) structures has been intensively scrutinized for more than 50 years. These materials have merited continuous attention because of their enormous technological versatility. As multilayer capacitors, piezoelectric transducers, and positive temperature coefficient (PTC) thermistors they generate a market of over 3 billion every year (Newnham 1989, 1997). In addition to ease of fabrication, these compounds exhibit a number of attributes required of ideal actuators (1) They display very large field-induced strains (2) They offer quick response times and (3) Their strain-field hysteresis can be chemically controlled to be very large or negligibly small, depending on the application. Details of their technical applications can be found in Jaffe et al. (1971) and Cross (1993). 

Beginning with the work by Ohno and Yonezawa on PFN-PFW systems in the late 1970s [8], many multicomponent dielectric systems have been evaluated and put into manufacture. Some of the patented compositions developed for multilayer capacitor (MLC) application were recently summarized by Shrout and Dougherty [9]. Other compositions were developed for piezoelectric sensors and electrostrictive actuator applications [10]. Most of the compositions used for capacitor dielectrics are based on PFN [8], PMN [11-14], or PZN [15]. 

The shape configuration of the mechanical actuator is important because it determines the ampUtude and the direction of the movement. Conventional shapes (like planar, tube or roll) are not able to induce linear contraction as can be found in muscles. One of the possibilities is to use a stack-like configuration inspired by piezoelectric technology. It consists of a multilayer stmcture of a planar actuator. When high voltage is applied, the entire device contraction is the sum of each layer thickness compression (Carpi et al., 2005). 

Ferroelectric and piezoelectric ceramics, in particular, play an ever-increasing role as materials for electrical and electronic applications that include multilayer capacitors (MLCs), bypass capacitors, dielectric resonators for frequency stabilization of microwave circuits, low-noise oscillators and low-insertion loss bandpass filters for microwave communication components, dielectric waveguide resonators, piezoelectric transducers and sensors, piezomechanical actuators and motors,... 

Bunn CW, Alcock TC (1945) The texture of polyethylene. Trans Faraday Soc 41 317-325 Cardoso VF, Minas G, Lanceros-Mendez S (2012) Multilayer spin-coating deposition of poly (vinylidene fluoride) films for controlling thickness and piezoelectric response. Sens Actuators A Phys 192 76-80... 

Kodama H et al. (2009) A study of time stability of piezoelectricity in porous polypropylene electrets. In Proceedings of IEEE international ultrasonics symposium, Roma, pp 1730-1733 Lekkala J, Paayanen M (1999) EMFi - new electret material for sensor and actuators. In Proceedings of the 10th international symposium on electrets, Athens, pp 743-746 Luo Z et al (2015) Multilayer ferroelectret-based energy harvesting insole. J Phys Conf Ser 660 012118... 

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