Piezoelectric Foil Research Articles

Suppression of nonsynchronous vibration in a foil air bearing rotor system through piezoelectric actuation of the top foil—A theoretical investigation

It is well documented that the static and dynamic performance of foil air bearings (FABs) can be improved through the alteration of the radial clearance profile. One way of achieving such controllability is through piezoelectric actuation of the top foil. Such a piezoelectric foil air bearing (PFAB) avoids the dynamics complications introduced by alternative actuating mechanisms. So far, theoretical analysis of a PFAB pad in isolation has shown that top foil actuation can raise the static load capacity. This paper theoretically investigates the potential for improving the dynamic performance. A computational approach that uses Galerkin Reduction (GR) to model the air film and considers the detachment of the top foil from the bump foil is upgraded for multi-pad PFABs, thus facilitating parameter optimization. The investigation considers two conventional FAB rotor systems from the literature that exhibit strong sub-synchronous vibrations under high unbalance. It is found that the optimal voltage and placement of piezoelectric patches can result in total suppression of the strong sub-synchronous frequencies, as well as a rise in the onset of instability speed. The polarity of the voltage required for suppression of the sub-synchronous frequencies is found to be opposite to that required to raise the load capacity.

Surface acoustic wave spectroscopy for non‐destructive coating and bulk characterization at temperatures up to 600°C enabled by piezoelectric aluminum nitride coated sensor

Surface acoustic wave spectroscopy has been established as non‐destructive and fast method for characterization of mechanical properties of surfaces and bulk materials in both research and industry. The present work shows that by application of a novel and robust aluminum nitride (AlN) coated piezoelectric contact sensor the advantages of the method can be extended from room temperature to at least 600°C. An overview of sensor concepts and applications of the method is discussed first, followed by theoretical and practical considerations for design and coating of a novel temperature stable contact sensor. After fabrication of such a sensor using magnetron sputtering, it was tested in a modified surface acoustic wave spectroscopy setup with an incorporated heating table concerning signal amplitude and frequency range. The AlN coated sensor was found to perform well up to 600°C, with temperature limited by the specification of the heating table. At room temperature, performance was acceptable when compared with a conventional contact sensor using a PVDF piezoelectric foil. Application of the high temperature capabilities of the setup was demonstrated by measuring temperature stability of hydrogen‐free amorphous carbon coatings (a‐C and ta‐C) depending on their sp3 carbon ratio. In another example, high precision temperature dependent measurement of Young's modulus for ultrasonic fatigue test specimen was taken, achieving an accuracy better than 1%. Use of the developed sensor opens up new possibilities in material science for in situ study of temperature depending mechanical properties for coatings and surfaces.

Magnetic-repulsion-coupled piezoelectric-film-based stretchable and flexible acoustic emission sensor

This paper presents a stretchable and flexible acoustic emission (AE) sensor composed of patterned upper, lower piezoelectric film foils, magnets and stereolithographic structures. The proposed device possesses the following novelties. The piezoelectric sensing structures with magnetic repulsion is effective for AE signal coupling. The lower piezoelectric serpentine-shaped AE detection structure with stretchable and flexible characteristics allows sensing various curved surfaces. Additionally, the contact force between the sensing target and AE sensor can be evaluated by monitoring the structural characteristic change of the upper piezoelectric structure of the AE sensor. The magnetic-repulsion-enhanced AE sensor exhibits a better bandwidth compared to that with only a lower AE sensing structure. Also, the fabricated sensor subjected to a sensing target force ranging from 4.98 to 14.85 mN resulting in a frequency change of the piezoelectric sensing beam of the upper foil from 20.073 to 20.135 kHz is verified. The developed AE sensor can open a new field for various applications. For instance, AE waves can be monitored without contacting the target (e.g. interfacing with air). The detection mechanism of AE waves by an action at a distance is successfully demonstrated.

Crumpling for energy: modeling generated power from the crumpling of polymer piezoelectric foils for wearable electronics

We consider the possibility of embedding large sheets of polymer piezoelectrics in clothing for sensing and energy harvesting for wearable electronic applications. Power is generated by the crumpling of clothes due to human body movements. From the mechanics of a gently crumpled foil, we develop theoretical models and scaling laws for the open circuit voltage and short circuit current and verify these via experiments. It is concluded that stretching is the dominant charge generation mechanism with the open circuit voltage and short circuit current proportional to li and , respectively with and l the height of the crumple cone.

Bi-metal foil gas dynamic bearings with bimorph piezoelectric foils

The present paper considers application of bi-metal materials and coatings to provide necessary strength and wear resistance of the surfaces of rigid and elastic gas dynamic bearings. Authors suggest using multi-layer foils with bimorph piezoelectric elements that operate in the generator regime to determine the deformation of elastic elements, and in the actuator regime to form an optimal shape of the surface of the bearing.

A Self-Powered Insole for Human Motion Recognition.

Biomechanical energy harvesting is a feasible solution for powering wearable sensors by directly driving electronics or acting as wearable self-powered sensors. A wearable insole that not only can harvest energy from foot pressure during walking but also can serve as a self-powered human motion recognition sensor is reported. The insole is designed as a sandwich structure consisting of two wavy silica gel film separated by a flexible piezoelectric foil stave, which has higher performance compared with conventional piezoelectric harvesters with cantilever structure. The energy harvesting insole is capable of driving some common electronics by scavenging energy from human walking. Moreover, it can be used to recognize human motion as the waveforms it generates change when people are in different locomotion modes. It is demonstrated that different types of human motion such as walking and running are clearly classified by the insole without any external power source. This work not only expands the applications of piezoelectric energy harvesters for wearable power supplies and self-powered sensors, but also provides possible approaches for wearable self-powered human motion monitoring that is of great importance in many fields such as rehabilitation and sports science.

Conception of the system for traffic measurements based on piezoelectric foils

A concept of mechatronic system for traffic measurements based on the piezoelectric transducers used as sensors is presented. The aim of the work project is to theoretically and experimentally analyse the dynamic response of road infrastructure forced by vehicles motion. The subject of the project is therefore on the borderline of civil engineering and mechanical and covers a wide range of issues in both these areas. To measure the dynamic response of the tested pieces of road infrastructure application of piezoelectric, in particular piezoelectric transducers in the form of piezoelectric films (MFC - Macro Fiber Composite) is proposed. The purpose is to verify the possibility to use composite piezoelectric transducers as sensors used in traffic surveillance systems - innovative methods of controlling the road infrastructure and traffic. Presented paper reports works that were done in order to receive the basic information about analysed systems and their behaviour under excitation by passing vehicles. It is very important to verify if such kind of systems can be controlled by the analysis of the dynamic response of road infrastructure measured using piezoelectric transducers. Obtained results show that it could be possible.

An analysis of the possibility of Macro Fiber Composite transducers application in modernized freight wagon

Paper presents an analysis of the possibility of application of piezoelectric foils - Macro Fiber Composite (MFC) in modernized freight wagons. It was verified if they can be successfully applied as sensors in developed system for structural health monitoring and in energy harvesting system. It is a part of a research project that aim is to develop a technology of freight wagons modernization. The goal of the project is to elongate the period between periodic repairs (by better corrosion protection) and improve conditions of exploitation of modernized wagons (easier unloading during winter conditions - no freezes of the charge to the freight wagon body shell). The additional aim is to develop system for structural health monitoring of the modernized body of the freight wagon as well as the system supporting management of a fleet of wagons using GPS system with power supply based on the energy recovered by MFC's from the wagon's vibrations during its exploitation. Results of laboratory tests as well as results of measurements on the real freight wagon during observed driving of the wagon are presented. At the same time measurements of the electric voltage generated by the MFC transducers excited by low frequencies harmonic excitation were verified.

Durable sensors for measurement of foot plantar pressure with piezoelectric polyvinylidene fluoride foil

This paper presents application of polyvinylidene fluoride (PVDF) foil for sensors of foot plantar pressure for measurements in natural conditions (i.e. outside laboratory). The material has been evaluated for this application based on investigation of material resistivity, current and activation energy of electret depolarization process, and relationship between pressure and electrical signal. The investigation shows that PVDF foils can operate at temperatures up to 85°C, have high activation energy of 5.2eV and a linear dependence between pressure and piezoelectric signal, which makes them suitable candidates for foot plantar pressure transducers. Influence of foil stretching is eliminated via a design of the shoe insole, which prevents deformations. Design of an input amplifier which eliminates pyroelectric effect is also presented. For applications in measuring foot plantar pressure, sensor calibration can be eliminated by placing several pressure sensors in the shoe insole and expressing pressure as relative values between sensors. The paper also describes a wireless system for measurement of foot plantar pressure, and obtained measurements.

Powering In-pipe Wireless Sensors Using Flexible Piezoelectric Micro-generators

Abstract This paper presents a new piezoelectric energy harvester that generates sufficient energy to power wireless sensor nodes autonomously. Multiple PVDF-foils are layered alternately with electrode foils and wound to a spool. Due to induced turbulence inside standard flow pipes the piezoelectric foils are forced to oscillate converting kinetic energy into mechanical stress thus generating electrical charge. The new multilayer spool design tackles the common disadvantages of similar harvesters related to low piezoelectric coefficients of Polyvinylidene-fluoride or brittleness of Lead-zirconate-titanate. Wind channel experiments to prove the feasibility of the concept result in a harvested output power of 0.54 μW at a wind velocity of 7 m/s. With efficient duty cycling of the sensor node 324 μWs of energy are available for data transmission. The presented harvester is proposed as a universal power supply for sensors inside pipe systems. All of the systems components are included inside the pipe allowing for a maintenance-free deployment of sensors in remote locations.

Heat generation and distribution in the ultrasonic hot embossing process

Microstructures are fabricated from polymer foils in seconds by a new process called ultrasonic hot embossing. This process allows to realize new designs within a day and is suitable both for large- and small-scale production. The required investment costs are in the order of some 10,000 ź. In this paper, heat generation and distribution in ultrasonic hot embossing is investigated with piezo-electric and pyro-electric foils from the polymer polyvinylidene fluoride (PVDF) placed into a stack of polymer layers. This way, the influence of pre-structures on and powders between polymer layers is revealed.

Air Flow Conditions for Polymer Energy Harvesting

We present the results on the Karman vortex creations on the two circular cylinders. Changing the inlet velocity we examine static and dynamic pressure distributions. In such a configuration,a polymer piezoelectric foil, which could be placed inside turbulent boundary layers, can work as anenergy harvester. By matching the fluid flows predominant frequency with the natural frequency ofthe piezoelectric generator would maximize the piezoelectric power output.

English

English

Effect of Ni and FeCoV films on magnetoelectricity of piezoelectric Pb(Mg1/3Nb2/3)O3–PbTiO3 sandwich structures

To improve the magnetoelectric (ME) property of piezoelectric thin film systems, Ni and FeCoV magnetic films are respectively used to sandwich piezoelectric foil Pb(Mg1/3Nb2/3)O3–PbTiO3 (PMN–PT) in the middle. The ME voltages and coefficients have been characterized in the longitudinally magnetized and transversely polarized mode. The measurement was conducted under a static magnetic field superimposed with an alternating magnetic field. The influences of the static and the alternating field strength are discussed. The peak ME coefficient obtained in the FeCoV film-sandwiched structure reached 27.4×10−3mV/cm•A/m, which is about five times greater than the Ni film-sandwiched counterpart. A linear relationship is observed between the magnetoelectric voltage and the alternating field strength under a static field of 31.8kA/m for both structures. As FeCoV is also oxidation-resistant and low in cost, the FeCoV film-sandwiched structure (i.e., FeCoV/PMN–PT/FeCoV) makes a good candidate in miniature ME device applications.

Threshold value-based detection of relevant force inputs onto vehicle skin panels with piezoelectric signals

This article describes and compares autonomous threshold value-based processes for detecting force inputs onto vehicle skin panels. For this purpose, 13 piezoelectric foil sensors made from polyvinylidene fluoride are applied to the inside of the outer skin panels as sensors. Applied forces give rise to mechanical vibrations in the material, which, in the form of expansions in the sensor, result in a proportional output signal. On the basis of these signals, two static and two adaptive threshold value processes are presented and evaluated for differentiating between relevant events (including scratches, parking bumps) and irrelevant events (including wind, rain). At the same time, the central issue of optimum configuration of the threshold value is investigated, and solutions proposed.

Attenuation of ultrasound in severely plastically deformed nickel

Ultrasound attenuation was measured in nickel specimens of about 30mm diameter prepared using the high pressure torsion technique. The cold working process produced an equivalent shear strain increasing from zero at the center up to 1000% at the edge of the specimen. The fragmentation of the grains due to multiple dislocations led to an ultrafine microstructure with large angle grain boundaries. The mean value of the grain size distribution gradually decreased from ∼50μm at the center to 0.2μm at the edge. Laser pulses of 5ns were employed for the excitation of broadband ultrasound pulses covering the spectral range of 0.1–150MHz. The ultrasound pulses were measured from the opposite side of the specimen by means of an optical interferometer and a piezoelectric foil transducer in two experimental setups. The features of the detected signal forms are discussed. The absolute value of the attenuation decreases from the center to the edge of the specimen showing nearly linear frequency dependence. The variation of the phase velocity was measured in a 6mm-thick high pressure torsion nickel sample, revealing a velocity increase from the center to the edge.

Broadband optoacoustic measurements of ultrasound attenuation in severely plastically deformed nickel

Laser optoacoustics and immersion techniques allowed a broadband ultrasound spectroscopy which was used for measuring the attenuation of severely plastically deformed nickel. A disk shaped specimen of nickel of about 33 mm diameter and 2.5 mm thickness was prepared by the high pressure torsion method. The produced equivalent shear strain linearly increased from a minimum at the center up to 1000% at the edge, gradually refining the grain size distribution down to 200 nm. The metal water interface was illuminated by 5 ns laser pulses, generating longitudinal ultrasound pulses with a pronounced compression phase and a smooth spectrum covering the range from 0.1 up to 150 MHz. The laser beam spot diameter was 6 mm, yielding a maximum power density below 15 MW/cm2. The ultrasound passed through the sample thickness and a 2 mm layer of coupling water. The pulse was detected by a 25 μm thick piezoelectric foil transducer with a diameter of the sensitive area of 2 mm. The transient signals were locally measured at different radii of the specimen. The attenuation almost linearly increases with frequency while its absolute value decreases from the center to the edge of the specimen.

Determination of linear and nonlinear mechanical properties of diamond by laser-based surface acoustic waves

The laser-based excitation of surface acoustic wave (SAW) narrowband trains and broadband pulses is described. SAW detection with a piezoelectric foil transducer was used to determine the Young's modulus of rough nano- and microcrystalline diamond films with linear SAWs. For high quality films ~ 1000 GPa is approached, near the stiffness of ideal polycrystalline diamond of 1143 GPa, indicating that this property is predominantly controlled by the diamond crystallites and not the grain boundaries. With strongly nonlinear SAW pulses developing shocks, fracture experiments were performed for well-defined crystallographic geometries of single-crystal silicon. The critical stresses of several gigapascals and strains of about 0.01 realized in these measurements are sufficient to determine the strength of nano- and microcrystalline diamond films, as well as natural single-crystal diamond. Their strength is one to two orders of magnitude smaller than the ideal tensile (shear) strength of 95 GPa (93 GPa), and thus reaches only several gigapascals, accessible by the pulsed SAW method. The surprisingly low strength of diamond materials indicates that the quality of the grain boundaries and defects plays an essential role in the fracture process.

THE ANALYSIS OF CYMBAL TRANSDUCER'S EFFECTIVE PIEZOELECTRIC COEFFICIENTS BASED ON ANSYS

ABSTRACT The cymbal transducer is a type of metal-ceramic piezocomposite transducer which developed in recent years. The effective piezoelectric coefficient (d 33 e ) of cymbal transducer is much higher than that of conventional piezoelectric ceramic. In this work the cymbal transducer working mechanism was researched and the finite element analysis model on this transducer was established using ANSYS which is a kind of software about finite element analysis. Piezoelectric ceramic PZT-5A was used as piezoelectric phase and brass foil was used as end cap electrode of cymbal transducer. It was analyzed for the relationship between the longitudinal displacement of cymbal and the force applied on the brass foil. The effective piezoelectric coefficient, d 33 e , was calculated. The calculated results were compared with the experimental results.

Reliability of piezoceramic patch sensors under cyclic mechanical loading

Piezoceramic patch sensors have to withstand the primary stresses and strains of astructure during operation. In the leading project ‘Adaptronics’ a lifespan of106 cycles at 0.1% strain was required for sensors applied on components of steel and carbonfibre reinforced plastic (CFRP). In order to test the reliability of the patchesthemselves and of their adhesion on the substrate, special four-point bending tests werecarried out under quasistatic loading and under cyclic loading at different strainlevels. The specimens consisted in sheets of steel and CFRP as substrates onwhich the newly developed patches with embedded piezoelectric foils and fibreswere glued. In the quasistatic bending tests the performance of each sensor wascharacterized by measuring the sensor signal (charge) as a function of strain before andafter cycling. Damage of the specimens would result in a decreasing slope of thecharge–strain-curve after cycling. However, all the specimens tested survived107 cycles up to 0.12% strain without marked loss of performance.