Piezo Stack Research Articles

Crack Growth Tests in Air Plasma-Sprayed Yttria Coatings for Alumina Ceramic Matrix Composites

Yttria coatings for all-oxide combustor walls were tested for their crack-growth behavior. These environmental and thermal barrier Y2O3-coatings were processed by atmospheric plasma spraying (APS). The stiffness and strength were measured for as-received and aged samples that were heat treated at 1000 °C, 1100 °C and 1200 °C for a 10 h dwell time. The results show a clear development with respect to the aging conditions. The changes of the modulus and the bending strength indicate that the microstructural changes are not completed, even after aging at 1200 °C for 10 h. The fracture toughness was tested for different orientations on samples aged at 1200 °C. Bending tests as well as indentation experiments were conducted. Furthermore, a bending device was designed to observe the crack-growth in situ. The device had to be rigid and is driven by a piezo stack. The crack growth resistance shows differences in the rise of the R-curves for different orientations of the crack propagation. This is in agreement with the microstructure that results from the plasma spray process.

Temperature prediction approach of piezo stacks used in jet valve

Overheating is an important factor which induces piezo stacks used in jet valve to damage. Temperature prediction by parameters can effectively prevent piezo stacks from overheating. The factors which affect heat amount generated by piezo stacks are studied through orthogonal experiment, and the finite element model of piezoelectric jet valve is established to analyze the thermal characteristics. Then, a BP (back propagation) neural network model is established to predict temperature of piezo stacks. The predicted results have a good agreement with the simulated and experimental results. The BP neural network model can be used in the valve controller to prevent piezo stacks from damage. It will also provide an analysis and predicting platform for development of piezoelectric jet valve.

Theoretical analysis and experimental investigation on a novel self-moving linear piezoelectric stepping actuator

Abstract A novel self-moving linear piezoelectric stepping actuator is proposed in this study, to address the performance differences between large strokes and high positioning precision in traditional linear piezoelectric actuators. The proposed actuator is comprised of an elastic cell and three driving units, including three piezo stacks. And it is able to achieve bidirectional movement with high resolution and large-strokes by applying defined sequence electric signals. Theoretical analysis is conducted to design the elastic cell, and the kinetic characteristic of the proposed actuator is analyzed to identify its two moving modes: stepping and sliding. A prototype is manufactured, assembled and experimented to investigate mechanical performances of the proposed actuator. Results indicate that the actuator prototype moves in the two modes according to the excitation voltage value of the input signals. A high positioning resolution of 7 nm is achieved when the actuator prototype worked in the sliding mode. Additionally, frequency sensitive measurements show that the maximum mean velocity of 1.5 mm/s for the actuator prototype is obtained when the driving frequency is 300 Hz. Finally, a maximum loading weight of 2000 g is reached as the excitation voltage is 50 V. The developed actuator presents promising applications in high precision positioning stages.

Micro-optical vibrometer/accelerometer using dielectric microspheres.

In this paper, an optical vibrometer/accelerometer is designed using micro-optical dielectric sensors based on whispering gallery modes (WGM) phenomena. The proposed design is created as a sphere made from polydimethylsiloxane (PDMS). The dielectric sensor would be laid between a piezo stack and a proof mass of 10-4 kg (implemented as body force to the sensor) in the vertical position. Once the piezo stack starts to impose a vibration in the vertical direction, the proof mass starts to vibrate, leading to a change in the morphology of the sensor. In turn, the WGM shifts would be seen on the transmission spectrum and would be related to the vibration/acceleration of the piezo stack. An analysis based on the force transmissibility from the piezo stack to the optical sensor and calibrations are carried out along with preliminary designs and experiments. Results showed that the proposed sensor could reach a very high resolution up to 8nano-g with sensitivity dλ/da≈2.33 pm/μg.

Experimental investigation on performance of disposable micropump with retrofit piezo stack actuator for biomedical application

Extensive researches are being conducted to develop miniaturized pumping systems to fulfill the need for accurate delivery of fluids at required rates, particularly in the biomedical field. This paper presents the design, fabrication, and testing of novel valveless micropump actuated through an amplified piezo actuator. The proposed model of the micropump pump has the unique feature of a disposable chamber and employs low-cost polymeric materials, conventional molding and machining operations for fabrication. The disposable part of the pump consists of a laser-cut pump chamber with nozzle/diffuser made of Polymethyl methacrylate (PMMA) and conventionally molded silicone rubber diaphragm. The retrofit part includes the amplified piezo actuator and support structures build from PMMA. Systematic characterization of the pump was carried with water and blood mimicking fluid to understand the effect of operating parameters such as driving frequency and actuation voltage on flow rate and back pressure of the micropump. Experimental results show that the proposed design was capable of pumping 3.3–3.4 ml/min of dye solution and 1.7–1.75 ml/min of blood mimicking fluid at a driving frequency of 5 Hz and actuation voltage of 150 V. The corresponding computed volume resolution/stroke of the pump was found to about 5.75 µl and 11.25 µl of blood mimicking fluid and dye solution, respectively. The proposed pump was found to work effectively against a maximum back pressure of 156 Pa with blood mimicking fluid and 250 Pa with the dye solution as the working fluid under the same operating condition of 5 Hz and 150 V.

Design, analysis, experiments and kinetic model of a high step efficiency piezoelectric actuator

This paper proposes a novel linear stick-slip piezoelectric actuator with compact structure and a dual-functional flexure hinge mechanism, which can realize motion of high step efficiency, high speed and precision. The flexure hinge mechanism is used in the actuator for realizing parasitic motion and amplifying the displacement of the piezo stacks to enhance the motion performance of the actuator. The structure and the operating principle is described in detail. The pseudo-rigid-body method and the finite element analysis method are adopted in the design process. A series of experiments are carried out based on a manufactured prototype to prove the validity of the proposed actuator, and motion parameters of the prototype are obtained. The resolution of the prototype is 0.594 µm, the largest velocity is 0.742 mm/s, the largest load capacity is 3.6 kg and the largest step efficiency is 0.934. And a valid kinetic model is established for further investigation and design guide.

Design and performance evaluation of a novel stick–slip piezoelectric linear actuator with a centrosymmetric-type flexure hinge mechanism

A stick–slip actuator with a centrosymmetric type flexure hinge mechanism was presented in this paper. The dimension of the actuator is approximately 83 mm × 82 mm × 19 mm. The positive and the negative motions could be achieved by two piezo stacks and one flexure hinge mechanism. To study the output characteristics, the actuator was fabricated and tested under various experimental conditions. The results showed that the maximum speeds of the positive and negative motions were 2.893 mm/s and 2.747 mm/s respectively, the maximum load was 3.8 N for both the positive and negative motions, the real displacement of a step of the positive and negative motions were 8.367 μm and 8.412 μm. Furthermore, the backward motion of the actuator had been greatly suppressed, which was beneficial to their wide applications in the fields of aerospace, precision-optics, nanomechanics, and so on.

Research and development of high temperature multilayer piezo stack based on Na0,5Bi4,5Ti4O15 lead-free ceramic system produced by tape-casting slurry technology

Multilayer piezo stack based on Na0,5Bi4,5Ti4O15 was produced by tape casting slurry technology. X-ray diffraction, dielectric permittivity, piezoelectric and pyroelectric studies have been performed on the specimens. It was established that specimens have a textured structure due to the orientation of basal planes (001) plate-like grains parallel to the direction of film casting. The Curie point (Tc = 645 °C) of the obtained stacks have been determined from the temperature-frequency dependences of the dielectric permittivity and loss tangent, it is established that they have a relatively high effective piezoelectric constant (d33*= 180 pC/N) for NBT based ceramic system. In concluding it has been analyzed the prospect of the specimens in high temperature applications.

Piezoelectric energy harvesting pedal integrated with a compliant load amplifier

Energy generation technologies that use piezoelectric materials as uninterrupted power supplies are one of the most practical solutions of low-power wireless sensor network. The piezoelectric generator collects mechanical energy from the environment and transforms it into electricity to supply to microelectronic devices. Thus, these alternative energy sources can reduce the consumption of batteries, thereby reducing environmental pollution. Piezoelectric materials can work in the bending, compression, and shear modes, which are named as d31, d33, and d15 modes, respectively. In this study, a piezo stack which worked in d31 mode has been designed and integrated into an energy harvesting pedal. A novel compliant amplifying mechanism has to be designed to amplify the input load so that the high-stiffness piezoelectric stack can achieve a large energy output at a lower input force. This compliant mechanism has been designed by the pseudo-rigid-body and topology optimization methods. The amplification ratios of different sized flexible amplification mechanisms are calculated through the finite element analysis and validated by experiments. Finally, a pedal generator has been made and the test results show that the collected electricity can effectively drive a low-power microcontroller, sensor, and other devices of these kinds.

Novel Linear Piezo Actuator

This publication presents a novel concept for an electromechanical piezoelectric actuator. This concept is intended to enable a piezoelectric actuator that exceeds the current state of the art in terms of achievable deflection at operating frequencies in the range of 0 Hz to 100 Hz. This will be realised by merging the strokes of individual piezo stacks. The concept enables linear or rotational movement. The linear version will be discussed here. An actuator of this type enables high-speed positioning of, for example, shafts, valves or lasers.

A Feasibility Study of Controllable Gas Foil Bearings With Piezoelectric Materials Via Rotordynamic Model Predictions

This study presents a new concept of controllable gas foil bearings (C-GFBs) with piezoelectric actuators. The C-GFB consists of a laminated top foil, bump foil, and piezo stacks and can simply change the bearing shape or film thickness locally and globally by varying the thickness of the piezo stacks with input voltages. The control schemes are (1) clearance control: the bearing clearance adjusted by changing overall piezo stack thickness, and (2) preload control: the mechanical preload modulated by the thickness expansion of several piezo stacks. Bearing lubrication performance is predicted for four cases of C-GFBs with different bearing clearances and preloads. The piezo stack control generates meaningful differences in the fluid-film thickness and pressure. Clearance control has a great effect on the dynamic force coefficients, but preload control slightly increases. Furthermore, the rotordynamic prediction of a rotor supported on two journal C-GFBs is conducted. As a result, both control modes for C-GFB are found to have a positive effect on rotordynamic amplitudes. Finally, using the orbit simulations, the C-GFB is controlled to have a small bearing clearance and large preload at critical speeds to make it possible to stably pass through the critical speeds. Consequently, it turns out that the C-GFB can improve bearing lubrication and rotordynamic performances by controlling only the input voltage of the piezo stacks. In addition, the C-GFB can be used to form various shapes to meet the operation conditions of an applied system.

Flight envelope expansion based on active mitigation of flutter via a V-stack piezoelectric actuator

The instability of the aircraft’s flexible control surfaces caused by uncontrolled vibrations represents a challenging issue of the aviation security. Flutter is a violent vibration whose amplitude grows strongly in a short time. Once the flutter is reached, the plane is destabilized and it can no longer be controlled. This paper proposes a specially designed demonstrator intended to extend the flight envelope by raising the speed limit at which the flutter occurs. The anti-flutter demonstrator is an intelligent airplane wing model made from a longeron covered by an aerodynamic layer. The wing has an aileron as a primary flight control surface, at one end, and a flange conceived to fix the wing in the aerodynamic tunnel, at the other end. The actuator consists in two V-shaped piezo stacks. The main advantage of the piezo actuator, the bandwidth (about 30 Hz), is exploited. The aero-elastic control is efficient if the deflection of the control surface is of a few degrees while the frequency is of at least 25-30 Hz. The control law is obtained through the receptance method of eigenvalues assignment using the on line input/output measured transfer function rather than the knowledge of system matrices.

Modeling a multilayer piezo-electric transducer by equivalent electro-mechanical admittance matrix

Piezoelectric transducers (sensors and actuators) are widely used to produce motion or to sense displacement. One of the most applicable types of the piezo-electric transducers is a transducer in which the piezo stacks are sandwiched between two vibrating masses by a connecting stud. These types of the piezo-electric transducers which are utilized for sensing applications are known as Tonpilz. A piezo-electric transducer is usually designed to work in the resonant frequency, and modeling and simulating its dynamics behavior to check the desired performance are very important. In this study, by considering the concept of the admittance expression, the dynamics model of a piezo-electric transducer is derived, and based on it, the characteristics of the longitudinal vibration of the piezo-electric transducer are calculated. The admittance expression is in the matrix notation which contains the equivalent admittance matrices correspond to the various composing parts of the transducer. The matrix notation provides a flexible and simple way for modeling the piezo-electric transducer, by combining the various containing parts of the piezo-electric transducers. To calculate the equivalent admittance matrix, at first, the equivalent admittance matrices of the metallic and piezo-electric parts of the transducer are derived, and then they are collected in one matrix diagonally. Then, by applying the boundary conditions via matrix operations, the equivalent admittance matrix of the transducer is obtained. One of the benefits of this modeling is obtaining the optimal design by considering different parameters. At last, the obtained analytic model is verified by experimental measurements of some fabricated transducers, which shows a good agreement.

Rate of injection measurements of a direct-acting piezoelectric injector for different operating temperatures

As the regulations for pollutant emissions in diesel engines are increasingly restrictive, the introduction of the piezoelectric direct-acting injectors seeks to improve the overall efficiency of the injection system, and consequently reduce combustion contaminants. In such systems, the needle lift is governed by the charge, or voltage, applied to the piezo stack, allowing for a more precise control over the fuel injection process. Although it is known that the performance of the piezoelectric crystals depends on its temperature of operation, the effect this has on the rate of injection is still unclear. In this research, a particular setup was used to measure the rate of injection of a direct-acting injector for different operating temperatures. It was mounted into an injection discharge rate curve indicator with a particular holder that has a cooling sleeve connected to a circuit running ethylene glycol, which is driven by a thermoregulator unit. A parametric sweep of different piezo stack control voltages for three rail pressures and operating temperatures was carried out. On the results, when needle lift does not influence internal flow development, the rate of injection was controlled by the injection pressure, with minimal impact from the working temperature, resembling results from conventional hydraulic injectors. At partial needle lift, two operating regions were observed, delimited by a particular voltage level. Above it, the needle throttling was able to control mass fuel flow accurately. But below it, the stabilized rate of injection values decreased drastically. The rate of this decline was dependent only on the injection pressure. The threshold level, named critical voltage, increased linearly with increasing injection pressure and working temperature. Also, to maintain a constant fuel mass flow for decreasing operating temperature, the voltage level of the control signal had to be reduced. These results highlight the importance of monitoring and controlling the operating conditions of the direct-acting injectors, as their performance and efficiency are both influenced by the working temperature of the piezo stack.

Mach-Effect thruster model

The Mach-Effect thruster is a propellantless propulsion concept that has been in development by J.F. Woodward for more than two decades. It consists of a piezo stack that produces mass fluctuations, which in turn can lead to net time-averaged thrusts. So far, thrust predictions had to use an efficiency factor to explain some two orders of magnitude discrepancy between model and observations. Here, a detailed 1D analytical model is presented that takes piezo material parameters and geometry dimensions into account leading to correct thrust predictions in line with experimental measurements. Scaling laws can now be derived to improve thrust range and efficiency. An important difference in this study is that only the mechanical power developed by the piezo stack is considered to be responsible for the mass fluctuations, whereas prior works focused on the electrical energy into the system. This may explain why some previous designs did not work as expected. The good match between this new mathematical formulation and experiments should boost confidence in the Mach effect thruster concept to stimulate further developments.

Traveling wave control of stringed musical instruments

Traveling wave control is a technique in which the energy propagating around a structure in the form of waves can be manipulated directly in order to change the overall dynamic behaviour of the structure. In this research, traveling wave control is applied to a musical instrument string with a view to affecting the timbre of the sounds produced by the string when vibrating. A highly linear custom optical sensor is built which is capable of detecting a wave traveling on a string in a single direction, and a piezo stack actuator is situated under the termination point of the string allowing the reflection of the wave to be manipulated directly. Various controllers are analyzed theoretically in terms of their performance, stability, and musical usefulness. They are then implemented and evaluated in terms of their relevance to the design of new musical instruments.

A Study on the Optimal Actuation Structure Design of a Direct Needle-Driven Piezo Injector for a CRDi Engine

Recently, the high-pressure fuel injection performance of common-rail direct injection (CRDi) engines has become more important, due to the need to improve the multi-injection strategy. A multiple injection strategy provides better emission and fuel economy characteristics than a normal single injection scheme. The CRDi engine performance changes with the type of high-pressure electro-mechanical injector that is used and its injection response in a multi-injection scheme. In this study, a direct needle-driven piezo injector (DPI) was investigated, to optimize its actuation components, including the plate length, number of springs, and the elasticity of the spring between the injector needle and the piezo stack. Three prototype DPIs were proposed by this research. They were classified as Type 1, 2, and 3, depending on whether the injector needle was hydraulic or mechanical. Then, the optimal prototype was determined by conducting four evaluation experiments analyzing the maximum injection pressure, injection rate, spray visualization, and real engine combustion application. As a result, it was found that the Type 3 DPI prototype, with several pan-springs and plates, had the highest injection pressure, a steady injection rate, and the fastest spray speed. It also demonstrated the most effective emission reduction for a two-stage rapid spray injection in a single-cylinder CRDi engine. The Type 3 DPI displays an increased elasticity from its hydraulic needle that provides a synergy effect for improving DPI actuation.

The effective frequency range of an active suspended handle based on the saturation effects of a piezo stack actuator

This paper presents a novel approach to the design of an active suspended handle by identifying the effective frequency range, based on the saturation effects of the piezo stack actuator, in terms of the force-displacement-voltage relationship as a function of the excitation frequency. The effective range allows for proper matching between the operating speed of the machine and the suspended handle. A model of the active suspended handle was developed, which took into account the non-linear saturation effect of the piezo stack actuator. A proportional-integral-derivative controller generated the counter voltage for the piezo stack actuator, using a proportional feedback gain (P) step up method, in order to attenuate the vibration transmitted to the handle. By including the saturation effect, the Pearson’s correlation coefficient (R2) of the model improved to 0.97, within the frequency range of 50 ∼ 500 Hz. Using this approach, we identified that the effective frequency range of isolation with transmissibility less than unity is between 250 ∼ 450 Hz. The active suspended handle was attached to a die grinder with a nominal operating speed of 25000 rpm and the vibration transmitted from the die grinder to the handle was reduced by 91%.

The Problem of Negative Vibration Isolation in Various Discrete Mechatronic Systems

In the work the problem of designing of mechatronic discrete systems have been studied for new possibilities of utilization of negative vibration isolation elements. Systems have cascade form and contains the piezo stack actuator and an external electric network connected to the mechanical discrete part. The main focus of the paper is given to the parameters related with negative damping, comparison of usage them based on dynamical flexibilities functions and study on constrains and limitations coming from potential practical application point of view. The new approach is related with placing the issue of negative value damping elements inside the synthesis process. Elements that can exhibits negative value, have been identified and found after distribution of dynamical characteristics, during creation of the mechanical displacement model.

Simultaneous cooling of coupled mechanical oscillators using whispering gallery mode resonances.

We demonstrate simultaneous center-of-mass cooling of two coupled oscillators, consisting of a microsphere-cantilever and a tapered optical fiber. Excitation of a whispering gallery mode (WGM) of the microsphere, via the evanescent field of the taper, provides a transduction signal that continuously monitors the relative motion between these two microgram objects with a sensitivity of 3 pm. The cavity enhanced optical dipole force is used to provide feedback damping on the motion of the micron-diameter taper, whereas a piezo stack is used to damp the motion of the much larger (up to 180 μm in diameter), heavier (up to 1.5 × 10(-7) kg) and stiffer microsphere-cantilever. In each feedback scheme multiple mechanical modes of each oscillator can be cooled, and mode temperatures below 10 K are reached for the dominant mode, consistent with limits determined by the measurement noise of our system. This represents stabilization on the picometer level and is the first demonstration of using WGM resonances to cool the mechanical modes of both the WGM resonator and its coupling waveguide.