Multilayer Actuators Research Articles

Low-temperature sintered (Na1/2Bi1/2)TiO3-based incipient piezoceramics for co-fired multilayer actuator application

Low-temperature sintered (Na1/2Bi1/2)0.935Ba0.065Ti0.975(Fe1/2Nb1/2)0.025O3 (NBT-BT-0.025FN) lead-free incipient piezoceramics were investigated using high-purity Li2CO3 as sintering aids. With the ≤0.5 wt% Li2CO3 addition, the introduced Li+ cations precede to enter the A-sites of the perovskite lattice to compensate for the A-site deficiencies. Once the addition exceeds 0.5 wt%, the excess Li+ cations will occupy B-sites and give rise to the generation of oxygen vacancies, which accelerate the mass transport and thus lower the sintering temperature effectively from 1100 °C down to 925 °C. It was also found that a small amount of Li+ addition has little effect on the phase structure and electromechanical properties of the system, but overweight seriously disturbs these characteristics because of the large lattice distortion. The sintered NBT-BT-0.025FN incipient piezoceramics with 1.25 wt% Li2CO3 addition at 925 °C provides a large strain of 0.33% and a corresponding large signal piezoelectric coefficient d*33 of 550 pm/V at 60 kV/cm, indicating this system is a very promising candidate for lead-free co-fired multilayer actuator application.

Tensile Piezoelectric Actuator: Fabrication, Characterization and Application

A multilayer piezoelectric actuator, with dimension of 10 mm×10 mm×60 mm, which can output a tensile displacement directly by exploring the d31 effect of piezoelectrics, was fabricated using soft Lead Zirconate Titanate (PZT) ceramics. The performance of the actuator was characterized by a special home-made experimental setup under electric fields varying from 200 to 1 000 V/mm with the preload varying from -150 to 100 N at room temperature. Results showed that it can output a maximum tensile displacement of 12 μm under unipolar electric field of 1 000 V/mm and preload was independent with generative displacement in the range of testing preload. Additionally, using the actuator, we built a micro loading apparatus, which can be used to test the fracture behavior of brittle materials.

Linear Piezoelectric Motor for Topography Detector of Diamond Wire

In topography detection procedures for diamond wire, precision motion control is one of the key preconditions; the motion control unit of detection needs both micron resolutions and centimeter strokes. In this paper, a linear motor with four sets of multilayer piezoelectric actuators was developed to achieve an actuator with high resolution and a large stroke. The stroke depended on the guideways of the system, which mar enlarged the stroke of a single multilayer piezoelectric actuator. The mechanism of differential actuation was analyzed by dividing an operation cycle into several states. A symmetrically arranged four-foot design was proposed, and a corresponding excitation method was devised. A prototype was fabricated to conduct a proof-of-concept operation test. Experimental results validated the feasibility of the prototype with a 10 mm stroke. The speed of the prototype increased when the amplitudes of driving voltage signals increased from 30 V to 100 V. Within the frequency range of 1 Hz to 120 Hz, the speed increased initially then decreased with driving frequency, the maximum of which was at 100 Hz. With an excitation voltage signal of 100 V and 100 Hz, the speed reached a maximum of 740 μm/s. With an excitation voltage signal of 30 V and 120 Hz, the resolution of the prototype reached 0.26 μm. The prototype satisfies precision motion control of topography detection for diamond wire. This work also provides an option for automatic systems that require high resolutions and large strokes.

An investigation of piezoelectric actuator high speed operation for self-sensing

Self-sensing (or “sensorless”) control of Multi-layer piezoelectric actuators (MPA) displacement has attracted much attention lately, especially for low speed operation (i.e. below 100 Hz). For high speed operations using resonance frequencies (i.e. Diminished Haptics for the transformation of surface texture and Resonant-type Smooth Impact Drive mechanism for nano-positioning), it is not clear whether the resistor based self-sensing approach developed for low speed operation can be used to monitor the operation is at resonance or not. Thus, the main objective of this study is to find out the answer. Firstly, mathematical investigation was carried out. Then, experiments were designed and conducted revealing how to use resistor for self-sensing of MPA at high speed operation.

Various cubic-based polymorphic phase boundary structures in (1-y)(Na0.5K0.5)(Nb1-xSbx)-yCaTiO3 ceramics and their piezoelectric properties

CuO-added (1-y)(Na0.5K0.5)(Nb1-xSbx)-yCaTiO3 ceramics with 0.0 ≤ x ≤ 0.1 and 0.04 ≤ y ≤ 0.055 were sintered at 970 °C. Various cubic-based polymorphic-phase-boundary (PPB) structures were formed: orthorhombic-tetragonal-cubic, and tetragonal-cubic PPB structures. The crystal structure of the specimens near Curie temperature is a mixture of Pm3m cubic and P4mm tetragonal structures and these ceramics showed ferroelectric properties. A schematic phase diagram of these ceramics has been suggested. The piezoelectric properties of these specimens were influenced by their crystal structure. All the specimens are expected to have good fatigue properties. In particular, the specimen with a tetragonal-cubic PPB structure (x = 0.04 and y = 0.045) has a large d33 of 338 pC/N and a high strain of 0.17% at 4.5 kV/mm. This specimen has good temperature stability; a d33 value of 300 pC/N and strain of approximately 0.12% were obtained at 175 °C, indicating that this specimen is a good candidate for use as a piezoelectric multilayer actuator.

BiFeO3-BaTiO3: A new generation of lead-free electroceramics

Lead-based electroceramics such as Pb(Zr.Ti)O3 (PZT) and its derivatives have excellent piezoelectric, pyroelectric and energy storage properties and can be used in a wide range of applications. Potential lead-free replacements for PZT such as potassium sodium niobate (KNN) and sodium bismuth titanate (NBT) have a much more limited range of useful properties and have been optimized primarily for piezoelectric applications. Here, we review the initial results on a new generation of lead-free electroceramics based on BiFeO3-BaTiO3 (BF-BT) highlighting the essential crystal chemistry that permits a wide range of functional properties. We demonstrate that with the appropriate dopants and heat treatment, BF-BT can be used to fabricate commercially viable ceramics for applications, ranging from sensors, multilayer actuators, capacitors and high-density energy storage devices. We also assess the potential of BF-BT-based ceramics for electrocaloric and pyroelectric applications.

Low-voltage planar PVC gel actuator with high performances

In this work, a novel planar actuator based on plasticized poly (vinyl chloride) gel and flexible silicone grease electrodes is proposed to realize a new soft actuator with high performance under low driving voltages. The proposed planar PVC gel actuator (PPGA) can demonstrate a strain of 21%, an output stress of over 0.6 MPa and a respond time of about 90 ms, only at a low driving voltage of 120 V. These performances are comparable to those of the biological muscle and are much better as compared to 10–12% strain and 0.09 MPa stress at 400 V for the traditional stainless electrodes-based multilayered PVC gel actuator (MPGA). In addition, compared to the typical planar dielectric elastomer actuator (DEA) (3 M VHB4905), the operating voltage and response time for the PPGA are reduced by one order of magnitude. A theoretical model is used to discuss the difference between the two types of actuators, finding a good agreement with the experimental results. Furthermore, the PPGA can be continuously actuated for more than 1 million times which shows a good durability. These results demonstrate the feasibility of PPGA as a soft actuator, so a wide application is expected.

A new integrated piezoelectric sensactor for eliminating the electric field interference

The piezoelectric sensactor with integrated structure normally consists of two parts: an actuating component and a sensor. The actuating component produces electric field interference, and might exert great influences on the accuracy of the sensor part, especially in high precision occasions. Therefore, in this paper, a novel approach is proposed to eliminate the effects of electric field interference. The idea of this approach is to use a compensation algorithm based on the Fast Fourier Transform (FFT) to reduce the influence of electric field interference. It can improve the sensing accuracy of piezoelectric sensactor. The designed piezoelectric sensactor does not need complex algorithms or circuit designs and is simpler, easier to be fabricated and more appropriate for the field in which multilayer piezoelectric actuator is needed. A prototype of piezoelectric sensactor with integrated structure was fabricated. Simulations and experiments were conducted to verify the feasibility of the compensation algorithm. The theoretical and experimental results show that the proposed scheme can reduce 90% of the sensor error and dramatically improve the sensing performance of the piezoelectric sensactor.

Implementation of Soft-Lithography Techniques for Fabrication of Bio-Inspired Multi-Layer Dielectric Elastomer Actuators with Interdigitated Mechanically Compliant Electrodes

Advancements in software engineering have enabled the robotics industry to transition from the use of giant industrial robots to more friendly humanoid robots. Soft robotics is one of the key elements needed to advance the transition process by providing a safer way for robots to interact with the environment. Electroactive polymers (EAPs) are one of the best candidate materials for the next generation of soft robotic actuators and artificial muscles. Lightweight dielectric elastomer actuators (DEAs) provide optimal properties such as high elasticity, rapid response rates, mechanical robustness and compliance. However, for DEAs to become widely used as artificial muscles or soft actuators, there are current limitations, such as high actuation voltage requirements, control of actuation direction, and scaling, that need to be addressed. The authors’ approach to overcome the drawbacks of conventional DEAs is inspired by the natural skeletal muscles. Instead of fabricating a large DEA device, smaller sub-units can be fabricated and bundled together to form larger actuators, similar to the way myofibrils form myocytes in skeletal muscles. The current study presents a novel fabrication approach, utilizing soft lithography and other microfabrication techniques, to allow fabrication of multilayer stacked DEA structures, composed of hundreds of micro-sized DEA units.

Multi-layer actuator array to render a vibration field on a point-excited panel speaker

Panel speakers often adopts the vibration actuator attached to a plate center to excite the whole panel. When a thin rectangular plate is excited by a point force, the generated bending wave is reflected quickly from the edges, so the plate is governed by the reverberant field. Because many vibrational modes participate even in the low frequencies, the radiated sound spectrum is involved with many peaks and troughs resulting a poor sound quality. To minimize the modal participation, the vibration is rendered to be confined and in-phase within a circular area enclosing the actuator point, and the vibration is being suppressed outside of it. An additional multi-layer actuator array surrounding the speaker zone is employed to control the vibration, thus fulfilling the rendered field. The study aim is now to obtain an appropriate gain of the actuators by solving the inverse problem consisting of the transfer matrix between field points and control actuators. The effect of the number of arrays is tested for the radius of 0.05–0.2 m. The control result reveals that the signal-to-noise ratio in the speaker and baffle zone is improved 8–11 dB by the three-layer array than by the single-layer array with the same size.Panel speakers often adopts the vibration actuator attached to a plate center to excite the whole panel. When a thin rectangular plate is excited by a point force, the generated bending wave is reflected quickly from the edges, so the plate is governed by the reverberant field. Because many vibrational modes participate even in the low frequencies, the radiated sound spectrum is involved with many peaks and troughs resulting a poor sound quality. To minimize the modal participation, the vibration is rendered to be confined and in-phase within a circular area enclosing the actuator point, and the vibration is being suppressed outside of it. An additional multi-layer actuator array surrounding the speaker zone is employed to control the vibration, thus fulfilling the rendered field. The study aim is now to obtain an appropriate gain of the actuators by solving the inverse problem consisting of the transfer matrix between field points and control actuators. The effect of the number of arrays is tested for th...

BNT-based multi-layer ceramic actuator with enhanced temperature stability

The large temperature dependence of electro-strain for Bi0.5Na0.5TiO3 (BNT)-based ceramics limits their practical applications. In this work, Li-doped BNT-based lead-free multi-layer piezoelectric ceramic actuators are prepared by solid-state reaction synthesis method. The multi-layer actuator structure is fabricated by gradient doping, in which each layer corresponds to different compositions, with enhanced temperature stability compared to the single-layer one. For specific composition, it could achieve maximum electro-strain value at a certain temperature. Therefore, the electro-strain of each layer in this BNT-based multi-layer actuator could compensate each other at different temperatures with improved temperature stability. Consequently, the electro-strain of the five-layer structure varies less than ∼12% when the temperature changes from 50 °C to 130 °C, and a large electro-strain of 600 pm/V could be obtained at 70 °C. This work provides an effective approach by gradient doping to broaden the use temperature range for BNT-based actuators with improved temperature stability.

Experimental investigation on the bending response of multilayered Ag-ionic polymer-metal composite actuator for robotic application

Experimental investigation on the bending response of multilayered Ag-ionic polymer-metal composite actuator for robotic application

Shifting the phase boundary: Potassium sodium niobate derivates

Abstract

Towards fully polymeric electroactive micro actuators with conductive polymer electrodes

The performance of micro devices actuated using electroactive polymers is often limited by the high stiffness of metallic electrodes, which prevents the polymeric components extension. In this work we report on an approach allowing to reduce the use of metals to a minimum by incorporating softer conductive polymer electrodes. A multilayered actuator incorporating polyimide (PI) substrate and a thin electroactive polymer (EAP) layer of P(VDF-TrFE-CFE) squeezed between polyaniline (PANI) electrodes was fabricated and characterized. The PANI layer was electrodeposited on the electroactive structures using cyclic voltammetry. Our results show that while the use of conjugate conductive polymer electrodes is feasible, the influence of the thin metallic seed layers required for electro-deposition is significant. The proposed electro-deposition based polymeric process is highlighted by its simplicity and relatively low cost, compared to common Physical Vapor Deposition processes, and can be extended to other polymers.

Large actuation strain over 0.3% in periodically orthogonal poled BaTiO3 ceramics and multilayer actuators via reversible domain switching

Lead titanate zirconate (PZT) ceramics based piezoelectric actuators always suffer from small output strains (typically 0.1%–0.15%) and have recently been criticized for the toxicity problem of the high-concentration lead. In our recent work (Li et al 2017 J. Appl. Phys. 122 074103), we realized large local actuation strain nearly 0.6% in a periodically orthogonal poled (POP) PZT ceramics via reversible domain switching. In this work, we applied the POP method to barium titanate (BT) ceramics and proposed a specially designed multilayer actuator which can output large uniform strain. The simple tetragonal structure of BT ceramics makes it easier to understand the mechanism of reversible domain switching in POP ceramics and its lead-free characteristic is more promising. Firstly, a POP BT ceramic piece was fabricated and the actuation testing results show that local large actuation strain of 0.36% can be obtained under a field of 2 kV mm−1 at 0.1 Hz. However, the actuation strain is non-uniform along the period direction, varying from 0.22% to 0.36%. Then, to output uniform large strain, a four-layer actuator based on the POP BT ceramics was designed and fabricated in which only the in-plane poled regions of the adjacent layers were bonded. Results show that the output strain turns to be uniform in this way, which is 0.34% under 2 kV mm−1, resulting in a very high large-signal (=Smax/Emax) of 1700 pm V−1. The large actuation strain is very stable and keeps unchanged after 20k cycles of operation. It drops quickly with the increasing frequency and is stabilized at 0.18% above 1.0 Hz. Finally, bipolar field testing was conducted on the POP BT based actuator. Results show that the actuator shows electrostriction-like symmetric bipolar actuation behavior with the repeatable actuation strain of 0.3% under 2 kV mm−1. This work may provide a feasible solution to low frequency, large-strain lead-free piezoelectric actuation.

A novel flying robot system driven by dielectric elastomer balloon actuators

Soft unmanned flying objects have been developed to improve communication in areas where natural disasters occur. This article investigates the design, modeling, and control of an unmanned flying robot, different from classic flying robots which are based on electric motors, robots driven by soft actuators that have advantages of low noise, deformable property, and fast response. Untethered system based on dielectric elastomer actuators can be controlled to move, theory and experiments are presented to show the movement accompanied by large voltage-triggered deformation. We connect a dielectric elastomer balloon-shaped shell to an inelastic chamber which has larger volume and apply voltage to trigger one-layer or two-layer VHB membrane without causing electrical breakdown. The results show that buoyancy force in the air for helium balloon system is inversely proportional to the altitude when the flight system goes up. Compared with single-layer balloon shell, we also generalize the concept of multi-layer soft actuators that offer larger deformation. The larger the original volume of the untethered system is, the more mass can be controlled at the actuated state. Voltage-triggered controllable motion is appreciating with our designed structure.

Examination of High-Torque Sandwich-Type Spherical Ultrasonic Motor Using with High-Power Multimode Annular Vibrating Stator

Spherical ultrasonic motors (SUSMs) that can operate with multiple degrees of freedom (MDOF) using only a single stator have high holding torque and high torque at low speed, which makes reduction gearing unnecessary. The simple structure of MDOF-SUSMs makes them useful as compact actuators, but their development is still insufficient for applications such as joints of humanoid robots and other systems that require MDOF and high torque. To increase the torque of a sandwich-type MDOF-SUSM, we have not only made the vibrating stator and spherical rotor larger but also improved the structure using three design concepts: (1) increasing the strength of all three vibration modes using multilayered piezoelectric actuators (MPAs) embedded in the stator, (2) enhancing the rigidity of the friction driving portion of the stator for transmitting more vibration force to the friction-driven rotor surface, and (3) making the support mechanism more stable. An MDOF-SUSM prototype was tested, and the maximum torques of rotation around the X(Y)-axis and Z-axis were measured as 1.48 N∙m and 2.05 N∙m, respectively. Moreover, the values for torque per unit weight of the stator were obtained as 0.87 N∙m/kg for the X(Y)-axis and 1.20 N∙m/kg for the Z-axis. These are larger than values reported for any other sandwich-type MDOF-SUSM of which we are aware. Hence, the new design concepts were shown to be effective for increasing torque. In addition, we measured the transient response and calculated the load characteristics of rotation around the rotor’s three orthogonal axes.

Effect of Gd on dielectric and piezoelectric properties of lead zirconate titanate ferroelectric ceramics

ABSTRACTIn view of the importance of rare – earth modified PZT, Gd-modified lead zirconate titanate (PGZT) ceramics with a general chemical formula Pb1-xGdx(Zr0.35Ti0.65)1-x/4O3 (x = 0, 0.07,0.10,0.12) near morphotropic phase boundary (MPB) have been prepared using high-temperature solid-state reaction route. The X-ray diffraction (XRD) study shows the formation of single phase rhombohedral structure for x 0.07 and tetragonal structure for x > 0.07 at room temperature. Dielectric properties (ϵr and tanδ) were studied as a function of temperature (25–500°C) at different frequencies (1–1000 kHz) exhibit a systematic change in dielectric constant, phase transition temperature and diffusivity. Results of detailed dielectric study indicate the diffuse phase transition at higher value of gadolinium concentration and non-relaxor behavior. The ac conductivity spectrum of PGZT/x/35/65 ceramics is found to obey Jonscher's Universal power law. The appearance of hysteresis loops below transition temperature supports the existence of ferroelectric properties in the studied compounds. The enhancement of remnant polarization (Pr) and piezoelectric constants (d33) was obtained with substitution of Gd for the PZT ceramics which can be used for multilayer capacitor, sensor and actuator applications.

Utilizing tension reduction in a dielectric elastomer actuator to produce compression for physiological application

A common prophylaxis against peripheral vascular diseases utilizes pneumatic active compression systems. Although effective, traditional active compression systems require the use of an air compressor and pump and are, therefore, ill-suited for ambulatory use. The current work introduces a novel approach to developing an ambulatory smart material–based active compression system. The actuation system is composed of a belt-like mechanism connected in conjunction with a multi-layered dielectric elastomer actuator. The belt mechanism allows compression to be applied directly with voltage application. By doing so, the proposed design limits the period during which the actuator should be charged and improves system power efficiency and lifetime. An analytical model which defines the pre-compression exerted by the actuation system before voltage application is presented and validated experimentally. Experimental results for the belt mechanism characterization, dielectric elastomer actuator characterization and actuation system testing are presented. Through experimental testing, it is shown that the initial pre-compression can be fine-tuned by varying the parameters of the system as defined in the analytical model, and that the pre-compression has little effect on the consequent actuation output amplitudes.

A low-working-field (2 kV/mm), large-strain (>0.5%) piezoelectric multilayer actuator based on periodically orthogonal poled PZT ceramics

In this work, we proposed a special designed multilayer actuator based on the periodically orthogonal poled (POP) PZT ceramics. Only the in-plane poled regions of the neighboring PZT layers were bonded together thus the large reversible switching strain in these regions can always be employed. A six-layer actuator was fabricated and testing results show that it can output actuation strains over 0.5% under a low field of 2 kV/mm at 0.1 Hz, about 3.5 times of that in conventional PZT actuators which is less than 0.15% under the same field. Furthermore, the output large strain is fairly uniform, which varies from 0.50% to 0.53% along the period direction, in comparison with that varying from 0.35% to 0.59% in a single-layer POP PZT. The large actuation strain drops quickly with the increasing frequency, and stabilized at about 0.2% under 2 kV/mm at or above 1 Hz. The low-frequency large strain is very stable and keeps unchanged after 20 k cycles of operation. To solve the charge accumulation problem during successive unipolar loading/unloading, an asymmetric bipolar field from −300 V/mm to 2 kV/mm is applied and meanwhile the actuation strain turns to be more uniform, only varying from 0.51% to 0.52% at 2 kV/mm. The low driving field, large strain of the proposed actuator makes it very promising in low-frequency, large strain/displacement actuation areas.