Applications actuators

Conventional actuator applications, and the potential advantages gained by replacing existing technologies with DEA, are given in Table 10.6. 

Although the polycrystalline relaxor-based compositions have useful piezoelectric characteristics, taking their properties overall into account they do not offer significant advantages over the well established PZT system. Their high electrostriction coefficients make them attractive for certain actuator applications (see Section 6.5.2), but the potentially important advance has been the production of single crystals. 

Through additions of PbTi03 to the prototype relaxor Pb(Mg1/3Nb2/3)03 the temperature at which the permittivity peaks can be adjusted and, close to the composition 0.9PMN-0.1 PT, it occurs at around room temperature. This is a composition suited to actuator applications. The dependence of electrostriction on grain size (Fig. 6.15) [14] is believed to be linked to the dependence of the size of the nanosized ordered regions on grain size (T. Mishima et al. [15]). 

Electrostrictive materials offer important advantages over piezoelectric ceramics in actuator applications. They do not contain domains (of the usual ferroelectric type), and so return to their original dimensions immediately a field is reduced to zero, and they do not age. Figure 6.24(a) shows the strain-electric field characteristic for a PLZT (7/62/38) piezoelectric and Fig. 6.24(b) the absence of significant hysteresis in a PMN (0.9Pb(Mg1/3Nb2/303-0.1 PbTi03) electrostrictive ceramic. 

The theory of Tanaka and Fillmore (Tanaka and Fillmore 1979) describes only the unloaded case. For actuator applications this case is almost impossible. 

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]. 

C.J. Tavares, S.M. Marques, L. Rebouta, S. L. Mendez, V. Sencadas, C.M. Costa, E. Alves, A.J. Fernandes, PVD-Grown photocatalytic Ti02 thin films on PVDF substrates for sensors and actuators applications . Thin Solid Films, 517, 1161-1166, (2008). 

Fig. 1.1 Schematic representation of the actuation mechanism for an IPMC actuator. Application of a bias voltage causes mobile ions to migrate to one of the electrodes. The concomitant migration of solvent causes the ion rich region to swell, generating a bending motion. Over time the actuator relaxes due to the built-up pressure gradient [2]. IEEE 2004, reprinted with permission...

Cameron CG, Underhill RS, Rawji M, Szabo IP (2004) Conductive filler elastomer composites for Maxwell stress actuator applications. Proc SPIE 5385 51... 

Opris, D.M., Molberg, M., Walder, C., Ko, Y.S., Fischer, B., N Fsch, FA, 2011. New silicone composites for dielectric elastomer actuator applications in competition with acrylic foil. Adv. Funct. Mater. 21, 3531-3539. 

Because temperature-sensitive hydrogels are stfll a relatively new material to the field of microfluidics, their full potential in actuation applications has not been reached. It is expected... 

Recently, the application of PS to chemical sensors has been considered [254-256]. The main advantages of this material for gas sensor and actuator applications are a unique combination of (i) a crystalline structure, (ii) a huge internal surface (200-500 m cm" ) [218, 257] that enables one to enhance the adsorbate effects, and (iii) a highly reactive surface, allowing efficient modification of the PS surface by various treatments such as contact with organic solvent, thermal annealing, or an illumination. 

Overall, within a proper operational range of 0.7 V the Ni-doped MFR IPMCs showed good paramagnetic characteristics and excellent electric responsive properties. This makes the developed MFR IPMCs attractive not only for actuator applications but also potentially for active damping applications. It is yet to be researched how the ionic liquids as potential electrolytes can improve the material to extend the operational voltage range. 

The magnitude of the induced strain x by an external electric field E is represented by tbis figure of merit (an important figure of merit for actuator applications) ... 

Relaxor-type electrostrictive materials, such as those from the lead magnesium niobate-lead titanate, Pb(Mgp 3Nb2/3)03-PbTi03 (or PMN-PT), solid solution are highly suitable for actuator applications. This relaxor ferroelectric also exhibits an induced piezoelectric effect. That is, the electromechanical coupling factor kt varies with the applied DC bias field. As the DC bias field increases, the coupling increases and saturates. Since this behavior is reproducible, these materials can be applied as ultrasonic transducers which are tunable by the bias field [12]. 

Actuator materials are classified into three categories piezoelectric, elec-trostrictive and phase-change materials. Modified lead zirconate titanate [PZT, Pb(Zr,Ti)03l ceramics are currently the leading materials for piezoelectric applications. The PLZT [(Pb,La)(Zr,Ti)03l 7/62/38 compound is one such composition [31], The strain curve is shown in Figure 4.1.19a (left). When the applied field is small, the induced strain x is nearly proportional to the field E (x = dE, where d is called the piezoelectric constant). As the field becomes larger (i.e. greater than about IkV/cm), however, the strain curve deviates from this linear trend and significant hysteresis is exhibited due to polarization reorientation. This sometimes limits the use of such materials for actuator applications that require non-hysteretic response. 

Electrostriction can generate mechanical deformation that is independent of the polarity of the electric field. It exists in almost all materials but is usually too weak for any practical use. However, it can be very large in electrostrictive materials, such as lead magnesium niobate (PMN) systems [11]. The nonlinearity often works to the advantage in such systems since it can produce tunable functional properties. As the effect is nonre-versible, electrostrictive materials are better for actuator applications. Unlike the piezoelectric effect, electrostriction can even exist in systems with center symmetry. Electrostrictive materials become piezoelectric under a dc bias field. 

Several new giant magnetostrictive materials have been developed in recent years for actuation applications. Bulk rare-earth-iron alloys Terfenol-D present typical static magnetostrains of 1000... 2000 ppm, which permit the building of low-frequency actuators and transducers. New composite materials offer an interesting possibility for high frequency ultrasonic applications. More recently, rare-earth-iron thin films have been also explored for actuation in microsystems. 

The shape memory effect was first discovered at the end of the 1940s in a gold-cadmium alloy. Since this extraordinary effect was recognized in the early 1950s as being caused by a martensitic transformation, new and improved shape memory alloys have been found. As prices for shape memory alloys are dropping, more and more commercial apphcations ranging from aviation to medicine - make use of the functional properties of those materials. In this contribution we will focus on the new and innovative field of actuator applications. 

If a SM actuator is employed only to switch between two different positions, a simple on/off-control of the heating current will be adequate. However, most SM actuator applications require fine positioning, which will be dealt with in this subsection. 

Activities in developer s premises and at site Merging of software in PE Addition of interfaces for sensors/actuators Application of safety-related E/E/PE to EUC... 

Additionally, it is important to realize that deformations at an N1 phase transition occur locally, on the level of a small volume of the material in the micrometer range. To observe the unique properties of LCEs on a macroscopic scale, the mesogens have to be aligned uniformly over the whole sample, yielding an LC monodomain or, at least, a sample with a well-defined overall director pattern (see Chap. 1). Thus, the use of LCEs as actuators always requires a step to orient the sample prior to final crosslinking [184]. Consequently, we will discuss first the influence of different preparation strategies on the orientation step, focusing on materials for actuator applications (Sect. 1.1). This sectimi will be followed by a discussion of properties needed for application. We will examine temperature-driven actuators (Sect. 2) and electrically driven systems (Sect. 3). 

Merryman, S. A. 1996. Chemical double-layer capacitor power sources for electrical actuation applications. 1st Intersociety Energy Conversion Engineering Conference. 

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