Piezoelectric Displacement Research Articles

Design, analysis and experimental investigations of a high precision flexure-based microgripper for micro/nano manipulation

In this paper, a flexure-based piezoelectric actuated microgripper is presented for high precision micro/nano manipulation tasks. A new design of microgripper based on a three-stage displacement amplification mechanism is utilized to magnify the piezoelectric actuator displacement. A bridge-type mechanism with a two-sided output port is serially connected with two consecutive lever mechanisms. The output motion on both sides is linearized by parallelogram mechanisms. The single-notch and double-notch circular flexural hinges were used in lever, bridge-type and parallelogram configuration. The displacement amplification and transmission mechanisms are arranged symmetrically to obtain stability of shape and compact layout of the entire microgripper. Analytical modeling was performed to establish an input and output displacement relationship. Finite Element Analysis (FEA) method was utilized to evaluate the performance of the microgripper. The design parameters of the microgripper were optimized through FEA method. The simulation results of the FEA method were validated through experimentation on the established design. The experimental results show that the total displacement amplification ratio of the microgripper is 12.76. The microgripper jaws have a high precision positioning accuracy. The microgripper also achieves a high-level working mode frequency of 1044 Hz, which is capable of accommodating rapid transient responses.

Improvement in piezoelectric properties of PLZT thin film with large cation doping at A-site

This paper reports improved piezoelectric properties of PLZT, designed by partially substituting larger trivalent cation (Bi3+) in place of La3+. For the present investigation, stoichiometric compositions of Pb0.92(La1-yBiy)0.08(Zr0.52Ti0.48)O3 (PLBZT) with y = 0.0, 0.3, 0.5 and 0.7 were prepared by chemical solution deposition method. The XRD results and Raman spectroscopy studies reveal the change in crystal structure with an increase in distortion of the tetragonal unit cell with Bi3+ concentrations. The FESEM study shows a distinct change in the microstructure of PLZT with increasing Bi3+ concentrations. The P-E hysteresis study on all the Bi3+ doped PLZT films give slimmer hysteresis loop, relatively low coercive field (20 kV/cm) and higher switching current (0.5 mA). The polarization fatigue property of PLZT film is improved with Bi3+ doping. The enhanced piezoelectric displacement in Bi3+ doped PLZT yielded almost 3 times higher d33 values than PLZT film at y = 0.5. The substantial enhancement in piezoelectric properties of PLBZT is correlated with the intrinsic contribution of the material that arises from crystal structure and extrinsic contribution that comes from the externally triggered domain wall movement.

Studies on composites based on HTV and RTV silicone rubber and carbon nanotubes for sensors and actuators

Nanofillers such as carbon nanotubes (CNT) are well known to significantly improve the properties of composites. In this work, CNTs were used as a reinforcing nanofiller in high-temperature vulcanized (HTV) silicone rubber, and room-temperature vulcanized (RTV) silicone rubber. At a low CNT content of 3 phr in HTV silicone rubber, the compressive and tensile moduli improved by 65% and 96%, respectively, and the resistance fell to 13 kΩ. Similarly, at 3 phr of CNT in RTV silicone rubber, the compressive and tensile moduli improved by 110% and 105%, respectively, and the resistance fell to 0.4 kΩ. The improved properties were used for applications in piezo-electric actuation and piezo-resistive strain sensors. With increase in voltage supply from 2 kV to 12 kV at 2 phr CNT, the piezoelectric actuation displacement increases to 920% (RTV silicone elastomer slab) and 1025% (HTV silicone elastomer slab). In addition, the rubber-based piezoresistive strain sensors showed a higher gauge factor with RTV silicone rubber than HTV silicone rubber. The piezoresistive strain sensors showed >100% stretchability. A series of experiments demonstrate that the use of CNTs improves the reinforcing, electrical properties, actuation, and strain sensors based on RTV and HTV silicone composites.

A Piezoelectric Bellows Round-Window Driver (PBRD) for Middle-Ear Implants

We describe a new implantable hearing-aid output device, a piezoelectric bellows round-window driver (PBRD), which is expected to be unaffected by external magnetic fields. The core elements of the PBRD are a piezoelectric element and a gold-coated copper bellows of low stiffness that transmits piezoelectric displacements, without significant attenuation, to the round window (RW). We analyzed structural and mechanical vibrations when confirming bellows transmission efficiency using a finite element model simulation. The PBRD was bench-tested under no-load conditions to determine its frequency response characteristics. We compared the outputs of the PBRD and a commercial floating-mass transducer in situ in human cadaveric temporal bones with responses measured using a laser Doppler vibrometer. PBRD outputs were excellent at both low (0.1–0.7 kHz) and high (2–16 kHz) frequencies; thus, the PBRD has the potential to compensate for conductive and/or sensorineural hearing loss. The frequency-response performance of the PBRD is better than that of conventional RW drivers (actuators or transducers).

Single spin resonance driven by electric modulation of the g -factor anisotropy

We address the problem of electronic and nuclear spin resonance of an individual atom on a surface driven by a scanning tunnelling microscope. Several mechanisms have been proposed so far, some of them based on the modulation of exchange and crystal field associated to a piezoelectric displacement of the adatom driven by the RF tip electric field. Here we consider a new mechanism, where the piezoelectric displacement modulates the g factor anisotropy, leading both to electronic and nuclear spin flip transitions. We discuss thoroughly the cases of Ti-H (S = 1/2) and Fe (S = 2) on MgO, relevant for recent experiments. We model the system using two approaches. First, an analytical model that includes crystal field, spin orbit coupling and hyperfine interactions. Second, we carry out density functional based calculations. We find that the modulation of the anisotropy of the g tensor due to the piezoelectric displacement of the atom is an additional mechanism for STM based single spin resonance, that would be effective in S = 1/2 adatoms with large spin orbit coupling. In the case of Ti-H on MgO, we predict a modulation spin resonance frequency driven by the DC electric field of the tip.

Piezoelectric displacement mapping of compliant surfaces by constant-excitation frequency-modulation piezoresponse force microscopy

A simple experimental method for piezoresponse force microscopy (PFM) measurements for reliable evaluation of piezoelectric surface displacements even on compliant surfaces is proposed based on atomic force microscopy (AFM) operated in frequency-modulation (FM) dynamic mode with constant excitation (CE), by using non-contact mode cantilevers. Surface displacement by piezoelectric effect after application of an electric potential to the conductive AFM probe translates into a likewise variation of the probe oscillation amplitude, while the related electrostatic forces mainly affect the oscillator resonant frequency, and cantilever bending is limited due to their high stiffness. Our non-contact CE-FM-PFM method is shown to reduce electrostatic force contributions as compared to contact-PFM modes. Converse piezoelectric effect mapping is demonstrated on poly(vinylidenefluoride) nanofibers obtained by electrospinning.

Implantability of endaurally insertable active vibratory middle-ear implants – an anatomical study

Background: Hearing loss is often treated with an acoustic hearing aid. However, distortion and insufficient gain may cause problems. Active non-acoustic vibratory middle-ear implants (AMEI) may contribute to solve this problem. We recently developed an AMEI which is to be implanted completely through the patient’s external auditory canal. The device uses a light-emitting diode (LED) in the external auditory canal that stimulates a photovoltaic sensor, placed in the middle ear, through the intact tympanic membrane. This results in activation of a vibratory miniaturized piezoelectric displacement transducer (MDT) (actuator) coupled to the auditory organ.Aims/objectives: The aim of this study was to evaluate the anatomical implantability of the novel AMEI using an exclusively endaural approach.Materials and methods: The internal components of our AMEI were implanted into 39 human temporal bones. The surgical procedure and the optimal size and anatomical fitting were systematically evaluated.Results: We can show here that implantation of all components of this novel AMEI into anatomical specimens proves to be a quick and easy procedure, performed using an endaural approach.Conclusions and significance: The anatomical data of this study establish the basis for further technical development of our AMEI and other future implantable hearing systems.

Core-shell structure-induced high displacement response in piezoelectric ceramics: A theoretical design

In this work, a series of piezoelectric composites with core-shell structure are proposed to pursue high displacement response under a low applied electric field. The shell and core consist of piezoelectric and non-piezoelectric material, respectively. A finite element method (FEM) is introduced to simulate the distribution of local electric field and the displacement response. The results show that the largest piezoelectric displacement response of these core-shell structural composites reaches twenty-five times larger than that of pure piezoelectric ceramic under the applied electric field of 2 kV/mm, which can be explained by the fact that the local electric field inside the shell is enhanced up to dozens of times as large as the applied electric field. It is also suggested that the displacement response of piezoelectric composites can be heightened by adopting smaller shell volume fraction, or increasing the permittivity or decreasing the Young's modulus of the core.

Enhanced ferro-photocatalytic performance for ANbO<sub>3</sub> (A = Na, K) nanoparticles

In this study, NaNbO₃ with average grain size of ~50 nm and KNbO₃ with average grain size of ~300 nm nanocrystals are prepared by the water-based citrate precursor sol-gel process. However, the KNbO₃ sample exhibits better photocatalytic performance than that of the NaNbO₃ sample by Rh B degradation experiment. By Rietveld refinements and piezoelectric displacement measurements, the KNbO₃ with the space group of Bmm2 is ferroelectric while the NaNbO₃ with the space group of Pbma is antiferroelectric. The polarization-modulated built-in electric fields in the ferroelectric KNbO₃ nanoparticles can efficiently enhance the separation of photo-generated charge carries and thus improve the photocatalytic activity. However, there is no internal electric field in the antiferroelectric grain because of the antiparallel spontaneous polarization in the adjacent unit cell. Therefore, KNbO₃ exhibits better oxidizing ability of organic dyes than NaNbO₃. The ferroelectric KNbO₃ nanoparticles exhibit an optimum photocatalytic performance for a complete degradation of Rh B in 100 min under UV-Vis light irradiation with auxiliary ultrasonic excitation. This study demonstrates that the perovskite-type ferroelectric nanocrystals are potentially to design high-performance catalysts for degradation of contaminant.

Enhanced ferro-photocatalytic performance for ANbO3 (A = Na, K) nanoparticles.

In this study, NaNbO3 with average grain size of ~50 nm and KNbO3 with average grain size of ~300 nm nanocrystals are prepared by the water-based citrate precursor sol-gel process. However, the KNbO3 sample exhibits better photocatalytic performance than that of the NaNbO3 sample by Rh B degradation experiment. By Rietveld refinements and piezoelectric displacement measurements, the KNbO3 with the space group of Bmm2 is ferroelectric while the NaNbO3 with the space group of Pbma is antiferroelectric. The polarization-modulated built-in electric fields in the ferroelectric KNbO3 nanoparticles can efficiently enhance the separation of photo-generated charge carries and thus improve the photocatalytic activity. However, there is no internal electric field in the antiferroelectric grain because of the antiparallel spontaneous polarization in the adjacent unit cell. Therefore, KNbO3 exhibits better oxidizing ability of organic dyes than NaNbO3. The ferroelectric KNbO3 nanoparticles exhibit an optimum photocatalytic performance for a complete degradation of Rh B in 100 min under UV-Vis light irradiation with auxiliary ultrasonic excitation. This study demonstrates that the perovskite-type ferroelectric nanocrystals are potentially to design high-performance catalysts for degradation of contaminant.

Isovalent Cation Ordering in the Polar Rhombohedral Perovskite Bi2FeAlO6

AbstractOrdering of cations in different structural types occurs when there is a significant difference in the oxidation states and ionic radii of the ions involved. Herein we report an unusual ordering of isovalent cations Fe3+ and Al3+ in the polar rhombohedral R3 double perovskite structure of Bi2FeAlO6 synthesized at high‐pressure (6 GPa) and high‐temperature (1000 °C). This ordered structure is derived from the 1:1 combination of the polar oxides BiFeO3 (R3c) and BiAlO3 (R3c), which results in reduction of symmetry to an R3 structure where the Fe3+ and Al3+ ions are ordered in a rock salt manner. However, these ions remain disordered in BiFe1−xAlxO3 (x=0.2, 0.3, 0.4) perovskites with R3c structure. The ordered compound undergoes antiferromagnetic ordering at TN≈280 K. The butterfly nature of piezoelectric displacement loop further confirms the polar nature of the cation‐ordered Bi2FeAlO6.

Isovalent Cation Ordering in the Polar Rhombohedral Perovskite Bi2 FeAlO6.

Ordering of cations in different structural types occurs when there is a significant difference in the oxidation states and ionic radii of the ions involved. Herein we report an unusual ordering of isovalent cations Fe3+ and Al3+ in the polar rhombohedral R3 double perovskite structure of Bi2 FeAlO6 synthesized at high-pressure (6 GPa) and high-temperature (1000 °C). This ordered structure is derived from the 1:1 combination of the polar oxides BiFeO3 (R3c) and BiAlO3 (R3c), which results in reduction of symmetry to an R3 structure where the Fe3+ and Al3+ ions are ordered in a rock salt manner. However, these ions remain disordered in BiFe1-x Alx O3 (x=0.2, 0.3, 0.4) perovskites with R3c structure. The ordered compound undergoes antiferromagnetic ordering at TN ≈280 K. The butterfly nature of piezoelectric displacement loop further confirms the polar nature of the cation-ordered Bi2 FeAlO6 .

Temperature behavior of graphene conductance induced by piezoelectric effect in a ferroelectric substrate

Graphene on a ferroelectric can be a promising candidate to create advanced field effect transistors, modulators, and electrical transducers. Recently, we have shown that alternating “up” and “down” piezoelectric displacement of the ferroelectric domain surfaces can lead to the increase in graphene channel conductance at room temperature because of the partial separation of the graphene channel from the ferroelectric substrate. The change in graphene conductance caused by the piezoelectric effect requires systematic studies of ambient conditions impact on its manifestations. This theoretical work studies the temperature behavior of the graphene conductance changes induced by piezoelectric effect in a ferroelectric substrate with the domain structure. We revealed the possibility of increasing up to 100 times the conductance of the graphene channel on the ferroelectric substrate by changing the ambient temperature for a given gate voltage and channel length. The obtained results can open the way towards advanced applications of graphene on ferroelectric in piezo-resistive memories operating in a wide temperature range.

A Comprehensive Analysis and Modeling of the Self-Powered Synchronous Switching Harvesting Circuit With Electronic Breakers

Self-powered realization for synchronous switching circuits is a hot spot for piezoelectric vibration energy harvesting. As a well-known approach, the electronic breaker is widely used for its simplicity and reliability. It plays an important role on the performance of the piezoelectric generator by affecting the available open-circuit voltage and the switching phase lag. In this paper, a comprehensive model is developed for improved performance analysis with missed factors included in comparison with previous investigations. The combined influence of the envelope resistor and the capacitor on both the phase lag and the open-circuit voltage is newly considered while the additional phase lag effect induced by charging the switch parasitic capacitance with the envelope capacitance is supplemented. Experiments and simulations validate the proposed model with better accuracy and the results show that these supplemented factors are important to the generator performance, especially for the micropower energy harvesting with small piezoelectric capacitance or displacement magnitude. Moreover, more detailed design guidelines are deduced from the proposed model.

Self-Sensing Method Considering the Dynamic Impedance of Piezoelectric Based Actuators for Ultralow Frequency

This letter presents a displacement self-sensing method for piezoelectric actuators that takes into account the effect of the deformation of these latter on their electrical impedance. A self-updating digital electrical impedance equivalent to that of the piezoelement is suggested in order to overcome the mismatch problem met when considering a static analog electrical impedance as classically used. Then, the design of an observer that performs a thorough separation of the electric current due to the direct piezoelectric effect from the measured electric current is proposed in order to estimate the piezoelectric actuator displacement. The experimental results validate the proposed approach and demonstrate the efficiency of the developed self-sensing circuit and its observer to estimate the displacement of the piezoceramics actuator for long duration measurement of constant step signal.

Design of piezoMEMS for high strain rate nanomechanical experiments

Nanomechanical experiments on 1-D and 2-D materials are typically conducted at quasi-static strain rates of 10−4/s, while their analysis using molecular dynamic (MD) simulations are conducted at ultra-high strain rates of 106/s and above. This large order of magnitude difference in the strain rates prevents a direct one-on-one comparison between experiments and simulations. In order to close this gap in strain rates, nanoscale actuation/sensing options were explored to increase the experimental strain rates. Using a combination of COMSOL multiphysics finite element simulations and experiments, it is shown that thermal actuation, which uses structural expansion due to Joule heating, is capable of executing uniaxial nanomechanical testing up to a strain rate of 100/s. The limitation arises from system inertia and thermal transients. In contrast, piezoelectric actuation can respond in the GHz frequency range. However, given that the piezoelectric displacement is limited in range, a sagittal displacement amplification scheme is examined in the actuator design, which imposes a lower frequency limit for operation. Through a combination of analytical calculations and COMSOL dynamic analysis, it is shown that a piezoelectric actuator along with a displacement amplifier is capable of achieving ultra-high strain rates of ∼106/s during nanomechanical testing.

Boundary Element Modeling of Dynamic Bending of a Circular Piezoelectric Plate

Accurate modelling of a coupled dynamic electro-mechanical response of circular piezoelectric plates under various loading conditions is of particular importance. Piezoelectric plates are not only basic structural elements, but with certain considerations can be conveniently fit for numerical simulation of piezoelectric sensors and transducers. In this work, a Laplace domain direct boundary element formulation is applied for dynamic analysis of three-dimensional linear piezoelectric moderately thick circular plates. Zero initial conditions, vanishing body forces and the absence of the free electrical charges are assumed. Weakly singular expressions of Laplace domain boundary integral equations for the generalized displacements are employed. Spatial discretization is based on the nodal collocation method. Mixed boundary elements are implemented. The geometry of the elements, generalized displacement and generalized tractions are represented with different shape functions: quadratic, linear and constant, accordingly. Integral expressions of the three-dimensional Laplace domain piezoelectric displacement fundamental solutions are used. After solving the problem on a set of Laplace transform parameter values, time-domain solutions are retrieved from the corresponding Laplace domain solutions by employing a numerical inversion routine. Numerical example is provided to show reliability and accuracy of the proposed boundary element formulation.

Graphene Exfoliation at a Ferroelectric Domain Wall Induced by the Piezoelectric Effect: Impact on the Conductance of the Graphene Channel

P-N junctions in graphene on ferroelectric have been actively studied, but the impact of piezoelectric effect in ferroelectric substrate with ferroelectric domain walls (FDWs) on graphene characteristics was not considered. Due to the piezo-effect ferroelectric domain stripes with opposite spontaneous polarizations elongate or contract depending on the polarity of voltage applied to the substrate. We show that the alternating piezoelectric displacement of the ferroelectric domain surfaces can lead to the alternate stretching and separation of graphene areas at the steps between elongated and contracted domains. Graphene separation at FDWs induced by piezo-effect can cause unusual effects. In particular, the conductance of graphene channel in a field effect transistor increases essentially, because electrons in the stretched section scatter on acoustic phonons. At the same time the graphene conductance is determined by ferroelectric spontaneous polarization and varies greatly in the presence of FDWs. The revealed piezo-mechanism of graphene conductance control is promising for next generations of graphene-based field effect transistors, modulators, electrical transducers and piezo-resistive elements. Also our results propose the method of suspended graphene fabrication based on piezo-effect in a ferroelectric substrate that does not require any additional technological procedures.

Application of a low-cost piezoelectric displacement estimation technique based on laser interferometry for hysteresis open-loop compensation in an AFM scanner

In this paper an open-loop actuation strategy based on a Prandtl-Ishlinskii hysteresis model is applied to a commercial atomic force microscope, equipped with an open-loop piezoelectric tube scanner. Estimates of the scanner vertical displacement, necessary to train the model, are obtained by exploiting the interference pattern generated by the laser beam used in the instrument to sense the cantilever deflection. Experimental results show that the undesired hysteresis effects are drastically reduced.

Comprehensive characterization of PVDF-TrFE thin films for microelectromechanical system applications

This paper presents a comprehensive characterization of a polyvinylidene fluoride-trifluoroethylene (PVDF-TrFE) thin film with 75/25 molar ratio for piezoelectric MEMS applications. PVDF-TrFE film was deposited on a silicon substrate using spin coating, and electrodes were formed using sputtering. Dielectric constant and dielectric loss factor were measured at different frequencies. Frequency and temperature dependence of the ferroelectric response was examined to investigate required poling conditions and maximum operating temperature. The lower limit for the coercive field was measured as 55 V/μm at room temperature. Coercive field decreased with temperature with a slope of −0.1 V/μm K, and ferroelectric to paraelectric transition occurred between 100 and 108 °C. Piezoelectric displacement measurements were performed using an atomic force microscope based method. Average value of the effective piezoelectric d33 coefficient was measured as −23.9 pm/V. No degradation was observed in this value after 2 × 105 unipolar excitation cycles. On the other hand, significant fatigue was observed in the piezoelectric response due to polarization switching; 1.8 × 105 cycles caused an average reduction of 33% in the effective d33. Presented data corroborates with the previous studies in the literature and can be used in the design of PVDF-TrFE based MEMS devices utilizing its dielectric, ferroelectric, and piezoelectric properties.