Electrostrictive Actuators Research Articles

Electromechanical Actuators for Haptic Feedback with Fingertip Contact

Haptic technology that provides tactile sensation feedback by utilizing actuators to achieve the purpose of human–computer interaction is obtaining increasing applications in electronic devices. This review covers four kinds of electromechanical actuators useful for achieving haptic feedback: electromagnetic, electrostatic, piezoelectric, and electrostrictive actuators. The driving principles, working conditions, applicable scopes, and characteristics of the different actuators are fully compared. The designs and values of piezoelectric actuators to achieve sophisticated and high-definition haptic effect sensations are particularly highlighted. The current status and directions for future development of the different types of haptic actuators are discussed.

Structure design and parameter optimization of GMA for ball screw pre-tightening

GMA (Giant Magnetostrictive Actuator) is used for ball screw pre-tightening in this paper. Compared with conventional electrostrictive actuator, GMA has greater output force, energy and strain, and it can achieve electric–magnetic-mechanical energy conversion. GM rod (Giant Magnetostrictive rod), which is a core component of GMA, is driven by the magnetic field of excitation coil to produce magnetostriction, thus a force (or displacement) is output to be used for ball screw pre-tightening. The designed GMA can output a force of about 1100 N and a displacement of about 100 μm. In order to make the excitation magnetic field intensity meet GMA’s work demand, this paper focuses on the structure design and parameter optimization of GMA, including GM rod, excitation coil, bias magnetic field and pre-compression device. GMA’s no-load displacement output experiment and the ball screw pre-tightening experiment were conducted, and the results show that the designed GMA can be used for ball screw pre-tightening through structure design and parameter optimization.

Accurate Electroadhesion Force Measurements of Electrostrictive Polymers: The Case of High Performance Plasticized Terpolymers.

Electroadhesion is a phenomenon ruled by many characteristic intrinsic parameters. To achieve a good adhesion, efficient and durable, a particular attention must be provided to the adhesion forces between the involved parts. In addition to the size and geometry of electrodes, parameters of materials such as dielectric constant, breakdown electric field, and Young’s modulus are key factors in the evaluation of electroadhesion efficiency for electrostrictive polymers and electroactive devices. By analyzing these material parameters, a method is proposed to justify the choice of polymer matrices that are fit to specific electroadhesion applications. Another purpose of this work aims to demonstrate a possibility of accurately measuring the electroadhesion force. This physical parameter has been usually estimated through equations instead, because of the complexity in setup implementation to achieve highly precise measure. Comparisons based on the parameters criterion reveal that besides the intrinsic properties of material, some other parameters relating to its physical phenomena (e.g., saturation of dipolar orientation under high electric field leads to decrease dielectric constant), or physical behavior of the system (i.e., surface roughness reduces the active electrode area) must be thoroughly considered. Experimental results pointed out that plasticized terpolymer leads boosted electroadhesion performance compared to the other counterparts, up to 100 times higher than conventional polymers. The developed materials show high potential in applications of active displacement control for electrostrictive actuation.

The effect of morphology on poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene)-based soft actuators: Films and electrospun aligned nanofiber mats

This paper analyzes soft actuators realized as unimorph cantilever beams, in which the active layer can have two different morphologies, i.e., either an extruded film or an aligned electrospun nanofiber mat of the poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene). Six different soft actuators are fabricated, with active layers of varying thicknesses and morphologies, to study the electrostrictive effect of the polymer and to evaluate the stiffening properties, the mechanical work, and the blocking forces of the actuators when stimulated by different direct current electric fields. The comparison between the different actuators is performed by introducing weight specific properties, i.e., specific stiffness and specific work, showing improved specific properties for the nanofibers-based actuators. Moreover, the blocking forces, the tip deflections, and the leakage currents of the actuators are evaluated when stimulated by alternating current electric fields. The experiments show faster viscoelastic relaxation and lower electrical power consumption for the nanofibers-based actuators. This study concludes that, thank to its electro-mechanical properties, the poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene) in the form of aligned electrospun nanofiber mat has high potential to be used as the active layer of electrostrictive unimorph beam soft actuators.

Ultrahigh electrostrictive effect in potassium sodium niobate-based lead-free ceramics

The longitudinal electrostrictive coefficient Q33 for perovskite-structured ferroelectric ceramics is usually between 0.01−0.04 m4/C2. However, an ultra-low Q33 of only 0.0047 m4/C2 was identified in the 0.9K0.5Na0.5NbO3-0.1SrTiO3 (KNN-ST) composition. Despite the fact that superior piezoelectricity has been observed in KNN-based ceramics, this value is obviously much smaller than the normal value, according to the general cognition and the thermodynamic relationship between piezoelectric coefficient d33 and Q33. Therefore, we synthesized (1−x)(K0.45Na0.49Li0.06)NbO3-xSrTiO3 (KNLN-ST) and studied phase structure, dielectric and ferroelectric properties systematically. Our findings show that the Q33 in the KNLN-ST system (0.012−0.027 m4/C2) is within the reasonable range for perovskite-structured ferroelectric ceramics. Furthermore, an ultra-high electrostrictive strain (>0.3%) with ultra-low hysteresis was achieved in the 0.8KNLN-0.2ST sample. This research not only clarifies the electrostrictive effect in KNN-based systems, but it also broadens the potential application field of KNN-based ceramics to electrostrictive actuators.

α-phase PVDF MEMS cantilever excited by electrostriction and evaluated up to 160 °C in air by laser-Doppler vibrometry

The electroactive polymer polyvinylidene fluoride (PVDF) has gained much interest in smart materials research with a wide application range for industry and consumer applications due to the low cost, flexibility, chemical resistance, non-toxicity, and light weight. In this work, we present an α-phase PVDF cantilever that exploits electrostriction as the main transducer mechanism for excitation. We realize thin PVDF films with a thickness of ∼190 nm and a low roughness (∼19 nm RMS). Electrostrictive cantilevers need high electric fields to achieve amplitudes comparable to piezoelectric counterparts. At thinner films, lower voltage levels are requested for comparable electric fields, thus making electrostrictive PVDF cantilevers a viable route and subsequently allowing broader use of PVDF in MEMS devices. We use an asymmetric electrode design that has the advantage of shifting the neutral axis out of the PVDF without enhancing cantilever thickness with a supporting device layer. In addition, these devices can be produced by CMOS compatible micromachining techniques. We measured the electrostrictive and piezoelectric actuation signal with laser-Doppler vibrometry and showed the frequency spectrum and curvature of such α-phase PVDF cantilevers. The cantilevers have a curvate of up to 120 m−1 at 1500 kV/cm. We demonstrate that the electrostrictive actuation has a low temperature dependency in the range from 25 up to 130 °C. A typical cantilever exhibits a geometry dependent low spring constant (k ∼ 0.3 N m−1) and a low quality factor (Q ∼ 75) in air.

Multifunctional BaTiO3-Based Relaxor Ferroelectrics toward Excellent Energy Storage Performance and Electrostrictive Strain Benefiting from Crossover Region.

Lead-free relaxor ferroelectrics (RFEs) exhibit a broader variety of phenomena in comparison with the "canonical" lead-containing compositions, rendering them attractive for newly multifunctional materials with low-cost and eco-friendly processing. Here, guided by the characteristics of relaxor ferroelectrics, lead-free (1 - x)BaTiO3-xKNbO3 systems are conceived and optimized to construct a special crossover region, which brings multiple benefits including tiny hysteresis loss while pursuing high maximum polarization, and large electrostrictive strain with low hysteresis, targeting multifunctional applications of energy storage capacitors, and electrostrictive actuators. We obtained fine-grained 0.96BaTiO3-0.04KNbO3 ceramic with a crossover region where nanodomains and nanosized polar regions with highly dynamic coexist, achieving a large recoverable energy density of 2.03 J/cm3 (300 kV/cm) simultaneously with sky-high charge-discharge efficiency of 94.5%, where low-cost production and environmental issues are warranted. By utilizing the crossover region, superior temperature-stable energy storage capacity (without a drop from 20 to 130 °C) guarantees the practical use. Meanwhile, this strategy favors large electrostrictive strain (0.146%) with ultralow hysteresis in 0.96BT-0.04KN at 80 kV/cm, which is suitable for electrostrictive actuators. It is expected that this strategy will stimulate future studies on lead-free multifunctional RFEs toward energy storage capacitors or electrostrictive actuators with low-cost and environmental compatibility.

Enhanced Electrostrictive Properties and Thermal Stability in Zn-Modified 0.9Pb(Mg1/3Nb2/3)O3-0.1PbTiO3 Ceramics

A 0.9Pb(Mg1/3Nb2/3)O3-0.1PbTiO3 (PMNT) relaxor ferroelectric ceramic is a good dielectric and electrostrictive actuator material. Nevertheless, important engineering problems of further enhancing its electrostrictive effect and increasing its thermal stability must be solved to promote its applications. In this work, the Zn-doped PMNT (PMNT/xZn2+) ceramics were prepared by the niobite precursor synthesis method. The transition of the PMNT/xZn2+ ceramics from relaxor ferroelectric to normal ferroelectric was realized, increasing the residual polarization (Pr), saturation polarization (Pm), the ferroelectric-paraelectric transition temperature at emax (Tm) and electric field induced strain (S) from x = 0.0 (Pr = 5.3294 μC/cm2, Pm = 26.6690 μC/cm2, Tm = 45°C, S = 1.08‰) to x = 8.0 (Pr = 19.9005 μC/cm2, Pm = 30.3718 μC/cm2, Tm = 70°C, S = 1.42‰). In addition, the upper temperature limit of the materials with a large electrostrictive effect (greater than 1‰) was extended from 40°C to 80°C. The main reason for these improved properties is that the magnesium ions were replaced by the highly reactive zinc ions at the B-site of the ferroelectric perovskite structure during the sintering and formed a certain amount of component segregation that increased the size of the polar nanoregions/domains and improved the polarizability of the materials.

Tunable Resonator as the Load of a Microstrip Line

A microstrip resonator is studied in which frequency tuning is carried out by micromechanical movements of the signal electrode above the substrate. The investigated resonator can be used as a component of a tunable antenna element, turned on as the load of the line. It is shown that the effective dielectric permittivity, which determines the resonant frequency, significantly decreases as a result of the movement of the signal electrode at a distance of several percents from the thickness of the substrate. Absolute values of the displacement usually stand tens or hundreds of micrometers depending on substrate thickness. Such displacements are available for modern piezoelectric or electrostrictive actuators. It opens an opportunity to implement the electrical type of tuning. For resonator performed on the substrate with dielectric permittivity about 10, resonant frequency tuning achieves more than 30 percent while the displacement of the signal electrode above the substrate does not exceed 10 percent. It is established that the variation range and sensitivity of the resonant frequency tuning can be increased by increasing the dielectric permittivity and decreasing the height of the microstrip line's substrate. Although the ratio between the width and the length of the resonator affects the tuning characteristics, the choice of these parameters is conditioned by the requirement for the formation of the required radiation pattern of the antenna element, the component of which is the viewed resonator. An equivalent circuit of a microstrip resonator as an element of a tunable antenna is proposed. The equivalent circuit model gives results that are satisfactorily consistent with those obtained based on a rigorous electromagnetic field model and a three-dimensional finite element method. At the same time, the schematic model simplifies the analysis of the influence of the geometric and electrophysical parameters of the resonant element on its characteristics and allows simplifying the design process of the antenna element and optimize its characteristics. The need to find the optimal parameters at the stage of designing the antenna element, in particular, arises during the matching of the feeder's and the radiator's characteristics and to provide the necessary range of the center frequency tuning.

Large electrostrictive effect in Mn-doped BCZT ferroelectric ceramics

The electric field in ferroelectric ceramics can induce notable deformations or strains based mainly on the electrostrictive effect if the driving field is sufficiently large (normally larger than the coercive field). Therefore, a large electrostrictive effect is highly desired to achieve a high strain output. In the present work, 0.5Ba(Zr0.2Ti0.8)O3-0.5(Ba0.7Ca0.3)TiO3 (BCZT50) ferroelectric ceramics doped with different numbers of Mn ions were synthesized and their dielectric and ferroelectric properties were studied to comprehensively evaluate the electrostrictive effect in this system. The doping levels were set as 0.0025, 0.005, 0.01, and 0.02. It was found that Mn ions could lower the temperature corresponding to the maximum permittivity, Tm, drastically and induce diffuse phase-transition behaviors simultaneously. Most importantly, a purely electrostrictive effect with a longitudinal electrostrictive coefficient, Q33, as large as 0.0466 m4/C2 was observed between 22 and 80 °C. The Q33 of Mn-doped BCZT50 ceramics is much higher than some representative lead-based and lead-free ferroelectric ceramics. In this paper, a potential lead-free ferroelectric system with a large electrostrictive effect, which has potential applications in electrostrictive actuators, is reported.

Effects of Ta2O5 addition on relaxation behavior and electric properties of PMS–PNN–PZT ceramics

Pb(Mn1/3Sb2/3)0.01(Ni1/3Nb2/3)0.495(Zr0.3Ti0.7)0.495O3+x wt% Ta2O5 (PMS–PNN–PZT, x = 0, 0.2, 0.4, 0.6, 0.8) lead piezoelectric ceramics were prepared by a traditional two-step solid-state reaction method. The effect of Ta2O5 content on the phase structure, microstructure, electrical properties and dielectric relaxation of PMS–PNN–PZT ceramics was investigated. The XRD patterns show that all ceramics have pure perovskite structure. Ta2O5 doping can promote the grain growth and improve electrical properties. And the ceramics have high relaxation behavior. When x = 0.4, it exhibits optimum electrical performance: d33 = 805 pC/N, kp = 66%, er = 6838, tanδ = 1.4%, Tc = 118.5 °C, γ = 1.9618, Ec = 3.652 kV/cm, Pr = 21.91 µC/cm2. This indicates that Ta2O5 can be used as an effective dopant in PMS–PNN–PZT ceramics and the ceramics can be used as the main material for multilayer ceramic capacitors and electro-strictive actuators.

Can Relaxor Ferroelectric Behavior Be Realized for Poly(vinylidene fluoride-co-chlorotrifluoroethylene) [P(VDF–CTFE)] Random Copolymers by Inclusion of CTFE Units in PVDF Crystals?

Relaxor ferroelectric (RFE) polymers are attractive for various electrical applications such as electrostrictive actuation, electromechanical sensors, electric energy storage, and electrocaloric co...

Complex Effective Dielectric Permittivity of Micromechanically Tunable Microstrip Lines

It is considered an influence of physical-topological parameters of controlled microstrip lines where characteristics modification is achieved by signal electrode movement over the substrate on effective dielectric permittivity and electromagnetic energy loss in the line expressed in form of complex permittivity. There are stated the ways of increase of sensitivity of effective dielectric permittivity modification to signal electrode shift and loss decrease. There are determined ultimate characteristics of tuning and loss. There are represented calculations of transfer factor effective permittivity corresponding to experimental results. These results can be used for development of controlled resonant elements and phase shifters with application of electrically tunable micromovement devices, such as piezo- and electrostrictive actuators or microelectromechanic systems. Due to application of invariant relations of physical-topological parameters represented calculations are suitable for estimation of tuning factors and loss of devices with micromechanical control in a wide range of operating frequency with application of wide range of materials.

Artificial Muscles: Mechanisms, Applications, and Challenges.

The area of artificial muscle is a highly interdisciplinary field of research that has evolved rapidly in the last 30 years. Recent advances in nanomaterial fabrication and characterization, specifically carbon nanotubes and nanowires, have had major contributions in the development of artificial muscles. However, what can artificial muscles really do for humans? This question is considered here by first examining nature's solutions to this design problem and then discussing the structure, actuation mechanism, applications, and limitations of recently developed artificial muscles, including highly oriented semicrystalline polymer fibers; nanocomposite actuators; twisted nanofiber yarns; thermally activated shape-memory alloys; ionic-polymer/metal composites; dielectric-elastomer actuators; conducting polymers; stimuli-responsive gels; piezoelectric, electrostrictive, magnetostrictive, and photostrictive actuators; photoexcited actuators; electrostatic actuators; and pneumatic actuators.

STUDY OF CONTROL INHOMOGENEITIES OF THE DIELECTRIC BETWEEN METAL PLANES OF MICROWAVE DEVICES IN PHASED ARRAY ANTENNAS

This article describes the phase shifters, based on micro-electromechanical elements connected to phased array antennas which operating in the frequency range 2–30 GHz. Estimations of controllability characteristics located between the metal dielectric planes, heterogeneity as an element of a micromechanical controlled microwave-devices. It is shown that when microdisplacements metal plane above the dielectric effective permittivity inhomogeneities it may vary from the values of the relative permittivity of the dielectric to one unit. Criteria required is small dielectric thickness or frequency at which the dielectric effect is not observed. The results can be used in the design of electromechanical devices managed using the MPN of piezoelectric and electrostrictive actuators or MEMS.

Spectral element formulation for an electrostrictive material embedded in a beam

In this paper, a spectrally formulated finite element in frequency domain for an electrostrictive material embedded in a composite beam is derived. The presence of quadratic non linearity of the electric field in the constitutive equation poses some challenge in the formulation of the model and we use convolution in the frequency domain. The formulation is carried out using Hamilton’s theorem and this is subsequently applied to a bimorph beam which has electrostrictive wafer mounted on the top as well as bottom surfaces of the beam. The bimorph beam is chosen so that we can control the beam by applying different and independent electric potentials for the top and bottom surfaces of the beam. The non linearity in the constitutive model results in the generation of additional nonlinear waves. The formulated spectral element elegantly captures these nonlinear waves. The efficiency of electrostrictive actuator for both single and multi modal open loop control is studied in detail. This aspect is demonstrated through a number of numerical examples. The studies also show that the control efficiency in electrostrictive actuator is limited by the amplitude of the electric field. When the electric field is beyond a certain level, it can be seen that although the amplitude of the primary wave decreases, non-linearity in the model causes sign reversal and splitting of incident and reflected waves. It can also be seen that the amplitude of nonlinear wave tend to increase with increase in applied electric field. The paper initially investigates the use of electrostrictive material as an actuator and this idea is gradually expanded to the use of electrostrictive material as a sensor. Various numerical experiments are carried out to demonstrate this aspect and its applications in the detection of the crack. It can be seen that the spectral element derived elegantly captures the location and size of the crack.

Study on the electromechanical properties of polyimide composites containing TiO 2 nanotubes and carbon nanotubes

New polyimide composite membranes were prepared by physical incorporation of different amounts of TiO2 nanotubes (TNTs) and carbon nanotubes (CNTs) into a poly(amic acid) solution, followed by film casting and thermal imidization. The poly(amic acid) was synthesized by polycondensation reaction of 4,4′-(1,3-phenylenedioxy)dianiline with 4,4′-oxydiphthalic anhydride, in N-methyl-2-pyrrolidone as solvent. TNTs having outer diameters of approximately 10–12 nm and length of several hundred of nanometers were obtained by hydrothermal method. Their surface was modified by treating with 3-aminopropyltriethoxysilane to enhance organic–inorganic compatibility and to avoid agglomeration. A study of microelectromechanical properties of these membranes was performed. The influence of filler content on nanometric displacements when an electric voltage is applied on the membrane surface was determined. Also, theoretical aspects on the combined effects thermal and electrostrictive actuation are presented. The longitudinal microactuation included only electrothermal effect. The microactuation including electrostrictive effect as well as electrothermal effect was remarkable to the small electric field intensity and to small temperature domain.

Enhanced ferroelectric order in Pb(Mg1/3Nb2/3)0.9Ti0.1O3 ceramics by ZnO modification

In this research, the effects of ZnO modification on ferroelectric order of Pb (Mg1/3Nb2/3)0.9Ti0.1O3 (PMNT) ceramics were studied through characterizations of dielectric and ferroelectric properties. The PMNT/xZnO (where x = 0, 0.4, 2.0, 4.0 and 11.0 mol.%) ceramics were prepared by solid state reaction and sintering process. The lattice parameter a and unit cell volume of pure PMNT ceramic were increased with ZnO modification. The temperature of maximum dielectric constant (Tmax), the freezing temperature (Tf), the depolarization temperature (Td) and the polar ordering temperature (TP) increased while the diffuseness parameter (δ) decreased with the increase in ZnO content, indicating an enhancement of ferroelectric ordering and a decrease in a degree of relaxor behavior of PMNT ceramics by ZnO modification. Polarization-electric field hysteresis loop and butterfly-like strain-electric field curve were displayed around room temperature in the 11.0 mol.% ZnO-modified PMNT sample, which indicated an establishment of polar macro domains. Electrostrictive coefficient (M) reached a highest value of 22.22 × 10−16 m2/V2 for the PMNT/4.0 mol.%ZnO ceramic, which made it a promising material for applications as electrostrictive actuators.

Microstructure And Dielectric Relaxation Of BT And ST Doped Ba(Fe0.5Nb0.5)O3 ceramics For Sensor Applications

Recently a new wave of interest has risen on complex perovskite structure due to their wide use in fabrication of multilayer ceramic capacitors, electrostrictive actuators, and electromechanical transducers. The polycrystalline ceramics of Ba(Fe0.5Nb0.5)O3 (BFN) and its solid solutions 0.89Ba(Fe0.5Nb0.5)O3-0.11BaTiO3 (BFN-BT11) and 0.89Ba(Fe0.5Nb0.5)O3-0.11SrTiO3 (BFN-ST11) were fabricated by a solid-state reaction Method. Processing parameters such as calcination temperature, sintering temperature and sintering durations were optimized to get best dielectric properties. It was found that the above ceramics sintered at 1250°C for 6 hours exhibited maximum density and uniform microstructure. X-ray diffraction studies of the compound showed the formation of single-phase monoclinic crystal structure at room temperature. Surface morphology of the compounds was studied by Scanning electron microscope (SEM). The effects of BaTiO3 and SrTiO3 substitution on the structure and on the electrical and ferroelectric properties of Ba(Fe0.5Nb0.5)O3 samples have been studied by performing x-ray diffraction and dielectric measurements. The electrical properties of the samples were investigated in a frequency range of 100 Hz - 1 MHz and temperature range of 30-350 °C using complex impedance spectroscopic technique. The frequency-dependent electrical data are also analyzed in the framework of conductivity and impedance formalisms.

Dielectric Relaxation Phenomena in some Lead and Non-Lead Based Ferroelectric Relaxor Materials: Recent Advances

Relaxors with general formula AA'BB'O3with different cationic distributions at A/B-sites have important device applications in capacitors, piezoelectric ultrasonic transducers, electrostrictive actuators, SAW substrates, etc. The doping or compositional changes in these ceramics can control the high electromechanical characteristics. Lead zirconate titanates (PZT) - based solid solutions exhibit excellent electrochemical properties and are widely used as actuators, transducers, ceramic filters, resonators, sensors and other electronic devices, due to their excellent piezoelectric properties. Although, there has been a concerted effort to develop leadfree piezoelectric ceramics, no effective alternative to PZT has yet been found; most other materials that possess high dielectric and piezoelectric coefficients still contain lead ions. Dielectric relaxation in these materials is of fundamental importance. Recently, new relaxor ferroelectric materials (Pb (B1/3Nb2/3)O3types) have been reported by our group in which the dielectric relaxation character is different from that observed in typical lead based relaxors. In the first part of the review, relaxor characteristics, strategies to synthesize phase pure lead based relaxors and dielectric relaxation phenomena are presented. Deviation of the frequency dependent susceptibility from Curie-Weiss law is analysed both in terms of Gaussian and Lorentzian formalisms. Lead based ferroelectric relaxor materials, due to environmental, health and social reasons are not preferred in devices and attempts are being made to eliminate the lead content from these materials. Sodium bismuth titanate (Na0.5Bi0.5TiO3, abbreviated as NBT), is considered to be one of the excellent candidates for lead-free piezoelectric material. However, pure NBT piezoelectric ceramics are difficult to pole due to its relatively large coercive field and high electrical conductivity. Therefore, many solid solutions of NBT with other ceramics are proposed to improve the relevant properties. In the second part of the review, relaxor behaviour of newly developed solid solutions of NBT is discussed. Finally, the future scope of research on these advance materials is presented.