Ware electronicpiezoelectric devices
Electronic devices using the piezoelectric effect contain piezoelectric materials: often crystals, but in many cases poled ferroelectric ceramics piezoceramics , polymers or composites. On the one hand, these materials exhibit nonnegligible losses, not only dielectric, but also mechanical and piezoelectric. In this work, we made simulations of the effect of the three types of losses in piezoelectric materials on the impedance spectrum at the resonance. We analyze independently each type of loss and show the differences among them.
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Piezoelectricity
Electronic devices using the piezoelectric effect contain piezoelectric materials: often crystals, but in many cases poled ferroelectric ceramics piezoceramics , polymers or composites. On the one hand, these materials exhibit nonnegligible losses, not only dielectric, but also mechanical and piezoelectric. In this work, we made simulations of the effect of the three types of losses in piezoelectric materials on the impedance spectrum at the resonance.
We analyze independently each type of loss and show the differences among them. On the other hand, electrical and electronic engineers include piezoelectric sensors in electrical circuits to build devices and need electrical models of the sensor element. Frequently, material scientists and engineers use different languages, and the characteristic material coefficients do not have a straightforward translation to those specific electrical circuit components.
To connect both fields of study, we propose the use of accurate methods of characterization from impedance measurements at electromechanical resonance that lead to determination of all types of losses, as an alternative to current standards.
We introduce a simplified equivalent circuit model with electrical parameters that account for piezoceramic losses needed for the modeling and design of industrial applications. New electronic devices need better components to get better performance and improved functionalities. In the case of devices using the piezoelectric effect, the heart of the device consists of a piezoelectric element: a crystal [ 1 ]; but in most cases, poled ferroelectric ceramics piezoceramics [ 2 ], polymers [ 3 ] or composite materials [ 4 ].
The crystal structure of piezoelectrics is noncentrosymmetric, but randomlyoriented polycrystals are centrosymmetric. An induced macroscopic noncentrosymmetry is needed for a polycrystal to be piezoelectric.
This induced symmetry can be provided by an external electric field poling or mechanical action stretching. Among the devices commonly using piezoelectric materials, we can find numerous sensors and actuators, which are classically used in telecommunications, medicine or industrial quality control, but new applications in energy storage or energy harvesting are also being developed nowadays. A piezoelectric material or device can be driven by an electric or mechanical stimulus and responds with both electrical and mechanical reactions.
System losses are defined as the rate of energy provided to the system that cannot be transformed into work. Usually, we call this loss of energy dissipation. This definition needs to be applied, and frequently rewritten, for every process involving energy conversion. Friction, dielectric dissipation, damping, etc. A piezoelectric material has losses originating from the dielectric response to an electrical field, the mechanical response to applied stress, or its piezoelectric motion, or its strain response to the electric field, or conversely, the charge or voltage generation as a response to the applied stress.
Losses in piezoelectric materials result in sample heating or noise production. These effects are detrimental in many applications, and this is why the understanding of loss mechanisms and knowledge of the actual value of the loss in the material becomes a key issue for the design of devices. Furthermore, the control of the loss mechanism is needed to optimize the efficiency of the electromechanical transduction and, consequently, the device performance.
For this reason, many authors have treated this topic in ferropiezoelectric ceramics and related materials [ 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 ]. To date, there is not a full agreement concerning the origin of the piezoelectric losses.
Here, to study losses in piezoelectric materials we will take a harmonic stimulus and response. The use of a single harmonic stimulus allows us to use complex numbers for the physical constants. In this case, we separate the inphase response as the real part of the constant and the inquadrature response as the imaginary part.
Then, for a material with mechanical losses, we obtain Equation 1 :. As can be seen, we write an explicit minus sign between the real and imaginary parts. This convention is the same used for dielectric losses. All of this implies:. For a wide range of piezoelectric applications, under adiabatic and linear response conditions, we can use the wellknown linear equations of the piezoelectricity:. All of these parameters must be described by complex numbers, z , and hence, we can define their corresponding loss tangent as:.
According to Holland [ 5 ], the imaginary parts of the elastic compliance and dielectric permittivity represent the mechanical and electrical losses. Both of them must be explained from the point of view of a delay in the response and may be used to calculate the energy lost as friction in the mechanical equation or as the Joule effect in the electrical one.
Then, the three characteristic constants must be written as:. For every crystalline class, due to crystal symmetries, we have different matrices of coefficients. In this work, we will use only those corresponding to electricallypoled piezoceramics 6mm group of symmetry [ 17 ], which can be used for other kind of materials such as composites or ferroelectric polymers.
In this case, Direction 3 is assumed as that corresponding to the polar axis, and Directions 1 and 2 are equivalents. Additionally, the whole matrix has only 10 independent elements five elastic, three piezoelectric and two dielectric coefficients :. We have no reason to assume that the piezoelectric coefficients in the matrix are not complex quantities if both elastic and dielectric coefficients are complex.
In fact, Holland [ 5 ] probes the necessity of using an imaginary part for the piezoelectric constants and found the limits imposed by thermodynamical considerations. The simplest explanation is that the imaginary part corresponds to losses during the energy conversion. From the point of view of the piezoelectric coefficient d :. We can read these losses as a delay between stimulus and response as we did above or as a result of crossed interactions between the two forms of energy frictional losses under electric fields and the increment of the electric resistance under mechanical stresses.
The ratio between energies gets us the efficiency of the mechanical conversion and is called the electromechanical coupling factor, defined as:. This factor is strongly dependent on the conditions of the transduction quasistatic, dynamic and, of course, the coefficients involved.
For dynamical conversion as those due to a harmonic stimulus , the coupling factor can be found by means of the relation:. We make use of complex quantities to include information about losses. It must be remarked that this works correctly only for single harmonic stimulus and response, as used with resonant methods of characterization, and only for the linear response range. In the rest of the cases, the representation of losses is more difficult, such that we must take into account nonlinear effects, intermodulation, coupling between modes, etc.
That means that for the relation between the three constants, in this case, the clamped compliance includes not only the mechanical response, but the interaction with the dielectric and piezoelectric one. We find the same behavior for the permittivity that includes the mechanical and piezoelectric responses.
Their respective losses will be, of course, related. Noticeably, the fact that piezoelectric coefficients of piezo materials have a complex form indicates the presence of extrinsic contributions to the piezoelectricity in these materials, regardless of the actual mechanisms involved [ 18 ].
Piezoelectric losses are the most controversial [ 13 , 19 ] and difficult to measure independently, because when the material deforms under the action of the piezoelectric effect, it also must endure mechanical loss. The hysteresis is also indicative of the loss.
Alternatively to the resonance method, a number of methods were proposed for the measurement of the phase angle between strain and field [ 14 , 18 ]. These alternative measurements [ 14 ] yield piezoelectric loss values in the linear range that are in good agreement with iterative methods at the resonance [ 20 , 21 ]. One of the most common ways to obtain an easy and accurate characterization is the resonant method. It consists of getting the complex impedance spectrum of a resonator, including at least one electromechanical resonance.
We consider the material sample as a resonant cavity a propagation media and its boundaries. Knowing the geometrical factors of the resonant cavity and a mathematical model for the impedance function that takes into account this resonance, we can obtain the elastic, piezoelectric and dielectric coefficients involved in this particular resonance. For reasons explained later, in some cases, the description in terms of admittance is easier than the impedance representation.
The most general function describing the impedance of a sample shape as a thin plate in the neighborhood of a resonance is:.
As we treat the sample as a resonant cavity, shape and dimension are the most important parameters to take into account for the study of the standing waves inside and getting information from them of the material.
The set of linear equations of the piezoelectricity is written under the assumption of the existence of an external force and an electric field by means of a voltage in electrodes.
Nevertheless, depending on the contour conditions, we can rewrite such linear equations as:. To get a complete characterization of a piezoceramic, we must get a set of 10 different parameters, the independent elements of the characteristic matrix.
Since these materials exhibit nonnegligible losses, it is needed to use alternative characterization methods to that proposed by the current standards [ 16 ], which do not account for all losses. Numerous authors have developed such alternative modes, and the interested reader can find reference to them in [ 22 ]. New methods keep on being published on this topic; among others, those based on the iterative modification of finite elements simulations to match measurements in the best possible way are noticeable [ 23 , 24 ].
Typically, the directly calculated parameters from a resonance mode are one elastic, one dielectric and one piezoelectric parameter except for the radial mode of disks, which provides two elastic constants.
The selection, based on the standards for measurements [ 16 ], of three resonator shapes and four modes of resonance, together with the smart combination of the parameters directly calculated from these analytical expressions with the remaining parameters, allow us to get the whole set of complex material parameters [ 28 ]. This method of analysis of the complex impedance curves has been also applied to the determination of the parameters from overtone resonances in the radial [ 29 ] and thickness [ 30 ] modes of thin disks to account for the frequency dependence of these parameters.
Besides, the principles for the application of this method to the determination of the properties of selfstanding films were developed and applied to lead zirconate titanate PZT cantilevers [ 31 ]. This procedure is not limited to piezoceramics, and we used it for the characterization of ferroelectric polymers Figure 2 and composites.
Example of the characterization of a piezoelectric polymer PVDF: polyvinylidene fluoride. The main limit of the resonance method consists of the coupling between modes.
This problem cannot be solved as suggested by the standard IEEE [ 16 ], because there is no a simple superposition of modes, but a coupling with energy exchange between them.
The impedance spectra of the shear plates used in standard characterization methods from resonance, inplane poled and excited in thickness, always show additional peaks, satellite resonances, around that of the main resonance. These correspond to natural modes of vibration of plates, such as contour modes, and are unavoidable, since they are excited simultaneously to the shear mode.
Accurate values of impedance around resonance and antiresonance frequencies are required to determine accurately the material parameters, including losses, which can only be obtained from uncoupled modes. For the optimum sample aspect ratios obtained in the first four periods, the dispersion in the someasured parameters are 0. An additional advantage of the use of the thickness poled shear plate for the full characterization of the piezoceramics is that, since it can be obtained from the disk after measuring it, in principle, this will allow the characterization from two resonators, a thin disk, thickness poled and a long rod or bar, length poled [ 34 ].
Finally, the higher consistency with the parameters is obtained from the thickness poled disk, since for both resonators, the spatial distribution of the polarization is identical.
Due to this enhanced consistency, a finite element modelling, based on the full matrix characterization using thickness poled shear plates, was successfully tested for both the impedance spectra and displacement patterns.
Good agreement with the experimental, electrical and laser interferometry measurements, respectively, was achieved in a range between kHz and 1. There are no standards for graphing the piezoelectric characterization in resonant mode. Most of the time, researchers represent asmeasured data from the impedance analyzer, i.
Using this plot, we can get a good idea about the electric antiresonance, which is clearly shown by the maximum electrical impedance. For some vibrational modes, as thickness extensional modes, where the direction of the electrical excitation and movement are parallel, due to the boundary conditions, the mechanical resonance corresponds to the maximum of the impedance, i.
However, for modes where the mechanical movement is perpendicular to the direction of the electrical excitation, e.
We use the frequency of the mechanical resonance to determine the complex mechanical compliance, s , or stiffness, c :. In Figure 3 , the three possible antiresonance frequencies are shown in admittance GB and impedance RX plots. The authors currently use a dual plot that includes the real parts of the impedance conductance, G and the admittance resistance, R that includes both peaks Figure 4.
The reproduction is carried out by introducing the calculated material parameters back into the analytical expression used for the iterative numerical solution of the impedance measurement:. As that is a monomodal resonance, there is a perfect agreement between the measured and the reproduced spectra.
W.A. Groen (Pim)
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Piezoelectric sensor
With the expansion of Internet of Things IoT and sensor network systems, transparent and flexible energy supply devices are becoming more vital for ultraconnected and highly convenient human interfaces. In particular, the mechanical energy harvesting technology using piezoelectric materials is very attractive due to the ability of direct energy conversion from wasted mechanical energy to useful electrical energy. In this work, we demonstrate a highly transparent and flexible piezoelectric energy harvester fPEH using a metallic nanowirepercolated piezoelectric copolymer on a flexible plastic substrate. The silver nanowire Ag NWs based conductor has been considered as a powerful future electrode material with high transparency and flexibility, while poly vinylidene fluoride co trifluoroethylene P VDFTrFE is a representative highperformance piezoelectric polymer material. Besides material and device characterizations, a multiphysics simulation was firmly investigated to clarify the properties of the transparent fPEH devices.
A piezoelectric transducer is a device that produces an acoustic wave from a radiofrequency RF input or, conversely, converts an acoustic wave to an RF output. Single crystals of lithium niobate are particularly suitable for these applications, because they exhibit large electromechanical coupling factors, have low…. For example, piezoelectric materials generate an electrical current when they are bent; conversely, when an electrical current is passed through these materials, they stiffen. This property can be used to suppress vibration: the electrical current generated during vibration could be detected, amplified, and sent back, causing the….
Piezoelectric device
Science Alert. Asian Journal of Scientific Research. Year: Volume: 6 Issue: 1 Page No.
Piezoelectrics is a method that can be used to drive active mixing in microfluidics. Objects become piezoelectric when a mechanical stress acts upon a solid object usually crystals and a charge is formed within the solid object. The term "piezoelectricity" has the actual meaning of electricity resulting from latent heat and pressure. In the world of microfluidics, piezoelectrics are used as ultrasonic mixers or actuators to combine two or more fluids within a device. Piezoelectrics are also used in microrobotics, noninvasive medical diagnostics, radio transmitters, microphones, and microscopes.
Active Mixing: Piezoelectrics  Ryan Thorpe
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A piezoelectric sensor is a device that uses the piezoelectric effect to measure changes in pressure , acceleration , temperature , strain , or force by converting them to an electrical charge. The prefix piezo is Greek for 'press' or 'squeeze'. Piezoelectric sensors are versatile tools for the measurement of various processes. They are used for quality assurance , process control , and for research and development in many industries.
Flexible electronic devices are regarded as one of the key technologies in wearable healthcare systems, wireless communications and smart personal electronics. For the realization of these applications, wearable energy and sensor devices are the two main technologies that need to be developed into lightweight, miniaturized, and flexible forms. The article was received on 26 Nov , accepted on 04 Jan and first published on 05 Jan If you are not the author of this article and you wish to reproduce material from it in a third party nonRSC publication you must formally request permission using Copyright Clearance Center.
The need to charge portable electronics like cell phones, radios, GPS, or entertainment devices has been met with backup battery and solar powered solutions. Many people around the world have access to cheap, portable electronics but lack a suitable means to charge them. Footpowered, peizo electric energy harvesting solutions are renewable and universal solutions to onthego charging needs. A charging system based on the present invention could be used in a variety of applications including being placed in insoles and embedded in shoes for charging mobile electronics.
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