Piezoelectric Losses Research Articles

Loss mechanisms in piezoelectrics: how to measure different losses separately.

Losses in piezoelectrics are considered in general to have three different mechanisms: dielectric, mechanical, and piezoelectric losses. This paper deals with the phenomenology of losses first, then how to measure these losses separately in experiments. We found that heat generation at off-resonance is caused mainly by dielectric loss tan delta' (i.e., P-E hysteresis loss), not by mechanical loss, and that a significant decrease in mechanical Qm with an increase of vibration level was observed in resonant piezoelectric ceramic devices, which is due to an increase in the extensive dielectric loss, not in the extensive mechanical loss. We propose the usage of the antiresonance mode rather than the conventional resonance mode, particularly for high power applications because the mechanical quality factor QB at an antiresonance frequency is larger than QA at a resonance frequency.

Comparison of minor to major loop properties in PMN-PT ceramics

The electromechanical properties of lead magnesium niobate-lead titanate (PMN-PT) ceramics are of great interest to transducer designers. Typically, the strain versus electric field and polarization versus electric field curves used to obtain those properties are measured over a major loop, i.e., one with a large dc bias and large ac signal. However, many devices are designed to operate at lower fields that fall entirely within the major loop, i.e., in a minor loop. Since the electromechanical properties of PMN-PT are strong functions of the bias and drive levels, it is crucial to understand how well properties derived from the major loop measurement correspond to the actual minor loop properties. In this study, electromechanical measurements on PMN-PT corresponding to minor loops at varying dc bias, ac drive, mechanical prestress, and temperature levels were made. The equivalent piezoelectric constant, dielectric constant, and dielectric loss factor for these minor loops will be compared to the corresponding major loop parameters. It will be shown that, in many cases, the parameters derived from the major loop agree quite well with the directly measured minor loops. An attempt to establish the lower limit for extracting minor loop properties from major loop data will be made.

Definition and measurement of the normalized electrical impedance of lossy piezoelectric resonators for ultrasonic transducers

Relevant equivalent circuit parameters and values of material constants of a piezoelectric resonator can be determined from measurements of its electrical input impedance as a function of frequency. The complex electrical impedance curves and the associated critical frequencies are the basis of this characterization by the piezoelectric resonance method. In this paper, the previously introduced concept of normalized electrical impedance of the lossy resonator, extended to include piezoelectric losses, is applied to the analysis of the effects of different types of intrinsic losses on peak values, bandwidths and characteristic frequencies. The resulting impedance patterns depend solely on the electromechanical coupling coefficient and the loss tangents, providing a useful tool for the analysis of low- Q resonators. The normalized impedance is experimentally evaluated from the basic data provided by an HP 4194A impedance analyser by means of specifically developed ASP programs.

Loss mechanisms in piezoelectrics and resonance/antiresonance

Losses in piezoelectrics are considered in general to have three different mechanisms: dielectric, mechanical and piezoelectric losses. This paper deals with the phenomenology of losses, first, then how to measure these losses experimentally. We will discuss two methods for measuring the electrical, mechanical, and piezoelectric coupling losses separately: (1) strain versus stress and field and displacement versus stress and field curves, and (2) a resonance/antiresonance technique. Also, one can measure heat generation at an off-resonance frequency to obtain a total loss. By combining the above methods, we can investigate the loss mechanisms in practical piezoelectric materials and their consequences in devices. It will be shown that heat generation is caused mainly by the dielectric loss, not by the mechanical loss. Furthermore, a drastic decrease in mechanical Q with an increase of vibration level is observed in resonant piezoelectric ceramic devices, a result not observable using conventional impedance analyzers at low power. Based on this loss knowledge, we will discuss the differing situations between piezoelectric resonance and antiresonance states. In particular, since the mechanical quality factor at an antiresonance frequency is larger than that at a resonance frequency the antiresonance mode seems to be superior for high-power applications.

Influence of the different loss parameters on piezoelectric material performances

Piezoelectric materials such as polymers (PVDF), copolymers (P(VDF-TrFE)), lead metaniobates or ceramic/polymer composites possess high losses. In this case, the characterisation method described in IEEE Standard on Piezoelectricity (1987) for low-loss materials is not applicable. Several methods have been proposed to determine the losses by introducing complex parameters in the piezoelectric constitutive equations. A number of these methods consider mechanical, dielectric and piezoelectric losses, but others only take into account mechanical and dielectric losses. In this paper, we investigate the influence of these types of losses on the electrical impedance of a thickness mode resonator. This study shows that piezoelectric losses have very little effect and that only dielectric and mechanical losses need to be taken into account for transducer design. Measurements were also performed on three different materials. The results using our method are compared to those of previously published studies.

Loss Mechanisms in Piezoelectrics

AbstractLosses in piezoelectrics are considered in general to have three different mechanisms; dielectric, mechanical and piezoelectric losses. This paper deals with the phenomenology of losses, first, then how to measure these losses separately in experiments.

Calculation of energy dissipation and temperature rise of piezoelectric metal-insulator-metal structures

Equations are given for calculating the temperature rise of thin-film piezoelectric transducers as a result of dielectric, mechanical, and piezoelectric losses and currents in the presence of electrostatic and harmonic excitation. The results of the article can be used in the design of optoelectronic and acoustic measuring devices.

The Measurement of High-Power Characteristics for a Piezoelectric Transducer Based on the Electrical Transient Response

In this paper, the theoretical and experimental considerations on the high-power characteristics of a piezoelectric transducer are presented. First, we propose a new measurement method for the large vibration amplitude region using an electrical transient response to eliminate the effect of temperature rise. Then, a new loss mechanism concerning the piezoelectric effect is explained by observing the relationship between the vibration velocity and the current and their harmonics. A `piezoelectric loss' is newly introduced in the equivalent circuit model to describe the real loss phenomena clearly.

Electromechanical Tuning of Self-Sensing Piezoelectric Transducers

The application of a self-sensing piezoelectric transducer included in a bridge readout network is here investigated taking into account the electromechanical interaction. The parametric uncertainties and the piezoelectric device losses as well as the tolerances of the electric components make the balancing of the bridge difficult to achieve in practice. A loss and uncertainties compensation, based on a real-time software implementation of the bridge reference arm is here presented and validated. The standard electrical and the proposed electromechanical balancing are both theoretically and experimentally compared in the case of a simple beam. The bridge output signal that is proportional to the strain rate is then fed back by means of a sharp phase second order low pass filter which is aimed at increasing the damping of the first bending mode of the beam.

Relationship between Mechanical Loss and Phases of Physical Constants in Lead-Zirconate-Titanate Ceramics

Mechanical loss in lead-zirconate-titanate (PZT) based piezoelectric ceramics was studied by introducing three complex physical constants: a complex elastic, a dielectric, and a piezoelectric constant. The elastic and dielectric losses had finite values, while the piezoelectric loss was negligibly small. More than 60% of the mechanical loss at resonance under a relatively low vibration-velocity was the elastic-origin component, and the rest was the dielectric-origin component. The dielectric-origin component rose sharply, however, as the vibration-velocity increased and became dominant at high vibration-velocity. The mechanical loss was reduced by doping Fe2O3 into the PZT, which was apparently caused by pinning of the ferroelectric domain wall.

An accurate equivalent circuit for the unloaded piezoelectric vibrator in the thickness mode

An equivalent circuit model for the unloaded piezoelectric vibrator in the thickness mode is presented. The model contains two branches, the motional branch and the static branch, like the lossless resonator model, but the circuit elements are generalized by making each a complex constant. The mechanical, dielectric and piezoelectric losses associated with the vibrator are accounted for by the imaginary components of the circuit elements. The model produced impedance curves that closely matched the impedance calculated by using equations derived from vibration theory and the data measured for lead zirconate titanate and PVDF - TRFE co-polymer samples. The calculation of the circuit parameters from the complex elastic, dielectric and piezoelectric material constants is straightforward and the model accurately fits both the baseline dielectric behaviour and the piezoelectric resonance around and below the fundamental resonance. Conversely, when the complex circuit parameters are known, the complex material constants can be derived by straightforward calculations without any loss of information.

High power piezoelectric characteristics and loss mechanisms of PMN-PT based ceramics

Application of ultrasonic transducers for high-power piezoelectric devices such as motors and actuators has been vigorously studied in recent years. Those devices are usually driven at a rather high vibration level. However, it was shown that a drastic change in the electromechanical properties, as well as a great amount of heat generation, occurred above certain vibration velocity due to the large electrical and mechanical loss. In this research, lead magnesium niobium oxide-lead titanium (PMN-PT) based material were prepared and studied. The PMN-based ceramics is intriguing due to their extremely high electro-mechanical coupling factors. Combined with lead titanium and modified by some dopants, the mechanical quality can be much improved. The properties under high level driving and loss mechanisms of PMN-PT with different dopants will be reported in this paper. [Work supported by ONR.]

Analysis of the loss and temperature behavior and the choice of the optimal excitation frequency of piezoelectric transducers

A method and the results of a calculation of the temperature of piezoelectric transducers under harmonic excitation are described. The energy dissipation in them depends on the dielectric, magnetic, and coupled electromechanical (piezoelectric) losses, which are determined experimentally. The frequency band in which a minimum of the heating temperature occurs for identical oscillation amplitudes is determined by numerical calculations.

Caterpillar-type piezoelectric d33 bimorph transducer

A piezoelectric bimorph transducer utilizing piezoelectric d33 coefficient was developed. This bimorph consists of piezoelectric segments bonded by a polymeric agent and was fabricated by a dicing and layering technique. The transducer has superior piezoelectric characteristics compared to standard piezoelectric d31 bimorphs. Piezoelectric coefficients, electrical admittance, mechanical compliance, and losses of the actuator were found to increase with increasing driving electric field.

The nonlinear, complex, induced-piezoelectric response of Pb(Mg1/3Nb2/3)O3–PbTiO3 relaxors

The amplitude-dependent complex piezoelectric response of Pb(Mg1/3Nb2/3)O3–PbTiO3 relaxors has been investigated using a single-beam interferometric technique as a function of ac electrical drive, superimposed dc electrical bias, and measurement frequency. Large-induced longitudinal piezoelectric coefficients (d33) were observed over a wide dc bias range below polarization saturation. On approaching polarization saturation, the value of d33 decreased, approaching values typical of poled piezoelectric ceramics. Investigations as a function of ac drive revealed the presence of strong nonlinearities, where the value of d33 increased with increasing drive. The nonlinear contribution was found to be on the order of 50% of the total response. In addition, large unexpected piezoelectric loss factors tan δ(piezo) were observed in materials which were otherwise characterized by anhysteresis in the polarization electric field behavior. The value of tan δ(piezo) was found to be in the range between 0.10 and 0.20, depending on various measurement conditions. With either increasing dc bias or ac drive, the value of tan δ(piezo) was found to decrease significantly.

Broadband active structural damping using positive real compensation and piezoelectric simultaneous sensing and actuation

The use of piezoelectric elements as a means for implementing broadband, low authority structural control with passive and active electrical impedance matching is investigated. Passive techniques are shown to be ineffective for truly broadband problems due to the relatively large inherent piezoelectric capacitance. Active techniques are developed using the simultaneous sensing and actuation (SSA) circuit. Detailed analysis of circuit tuning issues in conjunction with mechanical boundary conditions of the piezoelectric element is presented. The result is a set of guidelines for SSA component selection to enable the implementation of guaranteed stable positive real feedback for damping enhancement. Examples and experimental results on the SERC Interferometer Testbed are presented. Difficulties in implementation presented by the unmodeled piezoelectric losses and nonlinearities, which prove to be significant when using axially stacked elements, are discussed.

Investigations on evaluation of the three types of losses in piezoelectric materials

Abstract A new method for the determination of the piezoelectric, dielectric and elastic phase angles of a piezoelectric ceramic is proposed. This non-iterative method is based on the frequency dependence of the resistance around the series resonance frequency. In particular the piezoelectric loss angle may be properly obtained.

Piezoelectric properties of sol-gel-derived ferroelectric and antiferroelectric thin layers

The piezoelectric properties of ferroelectric and antiferroelectric thin layers were investigated by interferometry as a function of frequency and dc electric bias. Materials included: a ferroelectric lead zirconate titanate (PZT) with a Zr/Ti ratio of 53/47; a relaxor ferroelectric La-modified PZT with a Zr/Ti ratio of 70/30 and a La content of 7.8 at. %; and antiferroelectric lead zirconate. The hysteretic behavior of the piezoelectric coefficient due to polarization reversal was also studied. The layers were prepared by a sol-gel method, and were found to have properties similar to bulk ceramics. Significant strain levels could be achieved in the materials due to the relatively high electric strengths supported in thin-layer form. Polarization was found to be completely switchable between forward and reverse directions; however, the strain levels generated by switching were found to be inequivalent. In addition, pronounced piezoelectric relaxations and strong piezoelectric losses were observed.

Measurement of the real and imaginary piezoelectric, elastic, and dielectric constants for dispersive piezoelectric transducer materials

The recent past has seen the introduction of many new types of piezoelectric materials with relatively high dissipation and low mechanical Q (PVDF, ceramic–polymer composites). In order for designers to predict the performance of these materials in transducers, the imaginary components of the dielectric, elastic, and piezoelectric constants need to be known. This is typically done by analyzing the electrical impedance spectra and applying the methods described in the IEEE standard on piezoelectricity [IEEE Std. 176-1987] to calculate the relevant material constants. This paper describes new methods of analysis that expand on the IEEE standard and allow the experimenter to analyze materials with low mechanical Q and substantial piezoelectric loss factors. The paper also describes a technique to determine dispersion in the material constants from the experimental impedance or admittance spectra of the materials. [Work supported by DREA, DND-Canada.]

Improving Bonding to Piezoelectric Poly(vinylidene fluoride) for Sensor Applications

Abstract Argon, oxygen, nitrogen and ammonia plasmas and an acid etch pretreatment were performed on uniaxially stretched piezoelectric poly(vinylidene fluoride) film in order to improve wettability and bonding. Oxygen plasma was found to be too harsh, but nitrogen and argon plasmas improved wettability and resulted in a seven-fold increase in 180° peel strengths. However, this improvement in peel strength was accompanied by a 90% decrease in the piezoelectric properties of the polymer. The acid etch yielded contact angles similar to those of the plasma treated material, and improved peel strengths some twelve times over that of the untreated film. Significantly, no piezoelectric loss resulted from the acid etch.