Large Electromechanical Coupling Coefficient Research Articles

Electromechanical coupling correction for piezoelectric layered beams

This paper deals with the bending of layered piezoelectric beams (multimorphs) subjected to arbitrary electrical and mechanical loading. Weinberg (1999) obtained a closed-form solution to this problem using Euler-Bernoulli beam theory and integrated equilibrium equations. In his analysis, Weinberg assumes that the electric field is constant through the thickness of the piezoelectric layers. This approximation is valid for materials with small electromechanical coupling (EMC) coefficients. In this paper, we relax this constraint and obtain a solution which accounts for the effect of strain on the electric field in the layers. We find that Weinberg's solution can be extended to arbitrary EMC with a simple correction to the moment of inertia I of the piezoelectric layers. The EMC correction amounts to replacing I with (1+/spl xi/)I, where /spl xi/ is the square of the expedient coupling coefficient. The error in beam curvature introduced by neglecting the effect of EMC is shown to be proportional to /spl xi/. This effect can be quite significant for modern piezoelectric materials which tend to have large EMC coefficients. The formulation is applied to three example cases: a cantilever unimorph, an asymmetric bimorph and a three-layer multimorph with an elastic core. The theoretical predictions for the last two examples are compared to simulations using the finite-element method (FEM) and found to be in excellent agreement.

Ultra-high piezoelectric response in 〈110〉- oriented polydomain Pb(Mg1/3Nb2/3)O3- PbTiO3 single crystals

The piezoelectric constant and electromechanical coupling coefficients of 〈110〉-oriented polydomain0.71Pb(Mg1/3Nb2/3)O3-0.29PbTiO3 single crystals were determined experimentally by using resonance methods. It was confirmed that the single-crystal system has large electromechanical coupling coefficients k33 (∼91%), k′ 33 (∼83%), and k31 (∼81%), and piezoelectric constant d33 (∼1400 pC/N), which are comparable to those of 〈001〉-oriented crystals, and we also found that the values of k′ 33 and k31 are sensitive to the cuts of the crystals. X-ray-diffraction measurements on 〈110〉-oriented crystals have shown that the origin of the high piezoelectric response should be attributed to the orthorhombic distortion. Our results show that the 〈110〉-oriented crystals are also promising for a wide range of electromechanical transducer applications, since the 〈110〉-oriented crystals can be grown from 〈110〉-oriented seed crystals in the modified Bridgman technique.

Contribution to the electromechanical and nonlinear properties of GaPO4 crystals.

In the last decade, much attention has been given to piezoelectric crystals with large electromechanical coupling coefficient. The quartz homeotypes berlinite and gallium orthophosphate (GaPO4), along with the calcium gallo-germanates such as langasite are representative of these crystals. The coupling coefficient k26 associated with thickness-shear mode resonators is two times greater than that of quartz, increasing the spacing between the series and parallel resonance frequencies of resonators suitable for the frequency range from 1 to 100 MHz. This is important for some types of crystal oscillators and monolithic filters. The large electromechanical coupling coefficient also increases the difference between the temperature dependencies of the fundamental resonance frequency and its harmonics. In this paper, measured resonance frequency-temperature characteristics of the fundamental and third harmonics of selected rotated Y-cut GaPO4 resonators vibrating in the thickness-shear mode are presented. Further attention is given to the measurement of some nonlinear properties of rotated Y-cut GaPO4 resonators. Knowledge of such nonlinear interactions is important for the analysis of intermodulation phenomena in resonators, and for the application of GaPO4 resonators in crystal oscillators, filters and other electronic devices.

Low-Loss Wide-Band Floating Electrode Type Unidirectional Transducer Filters and Ladder-Type Resonator Filters Using High-Temperature-Stable High Electromechanical Coupling Surface Acoustic Wave Substrates

The important properties required for surface acoustic wave (SAW) substrates are large electromechanical coupling coefficients (k2), small temperature coefficient of frequency (TCF), low propagation loss, among other. LiNbO3 is a good SAW substrate because of its good properties and large size. We developed SiO2/rotated Y-cut, X-propagating LiNbO3 leaky SAW substrates with a large k2 (over 0.2) and zero TCF at a small thickness of SiO2 of H/λ=0.2 (H: SiO2 film thickness, λ: SAW wave-length) compared to those of other substrates and zero propagation attenuation in the case of metalized surface. In this paper, the theoretical and experimental results for SAW filters, resonators and resonator filters are described. The low-loss filters using floating electrode type unidirectional transducer (FEUDT) showed an insertion loss of below 1 dB at a center frequency of 400 MHz and bandwidth of 20 MHz. Also, the resonator showed the wide-band characteristics and resonator filters showed a bandwidth of 80 MHz at a center frequency of 500 MHz.

Analysis and optimization of trimorph ring transducers

The Kirchoff–Love plate theory and electroelasticity theory are combined to simulate the dynamic behaviors of the trimorph ring transducers under different boundary conditions. The transducer consists of an isotropic elastic ring laminated between two identical piezoelectric rings. Their electric current response, resonant frequencies, antiresonant frequencies and electromechanical coupling coefficients (EMCCs) are theoretically formulated and studied by numerical simulation. Also, the resonant frequencies and their corresponding mode shape are simulated by the finite element modelling to verify the theoretical results. Finally, to obtain the maximum energy conversion efficiency, the dynamic EMCC is optimized by varying the proportion of piezoelectric and elastic parts. It is shown that the dynamic EMCC depends on geometric thickness and radii ratios. Optimum settings for a particular transducer to reach the maximum dynamic EMCC are found for different boundary conditions. The trimorph ring transducer for the fixed inner and free outer surfaces boundary condition has slightly lower resonant and anti-resonant frequencies, and larger EMCCs than that for the free inner and fixed outer surfaces boundary condition does.

Characterization of piezoelectric materials with large piezoelectric and electromechanical coupling coefficients

The relaxor based ferroelectric (1− x)Pb(Zn 1/3Nb 2/3)O 3– xPbTiO 3 and (1− x)Pb(Mg 1/3Nb 2/3)O 3– xPbTiO 3 single crystals provided new challenges in property characterization because their extraordinarily large piezoelectric coefficients and electromechanical coupling coefficients. Large errors may occur in some of the derived material constants using conventional characterization techniques. This paper will analyze the inadequacy of the traditional characterization methods and provide some basic guidelines for properly characterizing piezoelectric materials with extremely high piezoelectric and electromechanical coupling coefficients.

Guided propagation of surface acoustic waves in AlN and GaN films grown on4H–SiC(0001)substrates

The propagation modes of surface acoustic waves ~SAW! in AlN and GaN layers are identified for the case of the acoustic wave being confined in the epitaxial layers by the fast-velocity SiC substrate. Higher-order Rayleigh modes emerge when the SAW wavelength is reduced to be below the layer thickness. We also report on the observation of an extremely-high-velocity SAW mode, which exists when the SAW wavelength is about an order of magnitude larger than the layer thickness. These guided modes enable us to utilize SAW velocities which can be even larger than the Rayleigh velocity in the substrate while maintaining the large electromechanical coupling coefficient of the overlayer.

High Temperature Stable Acoustic Surface Wave Substrates of SiO2/LiNbO3 Structure with Super High Coupling

In this study, in order to improve the temperature coefficient of frequency (TCF), the propagation characteristics of SiO2/Rotated Y-cut, X-propagating LiNbO3 leaky surface acoustic wave (SAW) substrates with a large electromechanical coupling coefficient (k2), zero attenuation and zero TCF are theoretically investigated. The results showed a large k2 of more than 0.2 (zero k2 of Rayleigh mode), zero TCF and zero propagation attenuation for leaky SAW in the case of a short boundary at a thin film thickness of H/λ\\fallingdotseq0.15–0.25 (H: SiO2 film thickness, λ: SAW wavelength). The experimental results agreed with the theoretical ones.

High Temperature Stable High Electromechanical Coupling Substrates and Application for Surface Acoustic Wave Devices

In this paper, in order to improve the TCF the propagation characteristics of SiO 2 /Rotated Y-cut, X-propagating LiNbO 3 leaky SAW substrates with a large electromechanical coupling coefficient (k 2 ) and zero temperature coefficient of frequency (TCF) are theoretically investigated. The results showed a large k 2 of leaky SAW over 0.2 (zero k 2 of Rayleigh mode), zero TCF and zero propagation attenuation in the case of metallized surface at thin film thickness of H/ u =0.15∼0.25(H: SiO 2 film thickness, u :SAW wave-length) were obtained. The experimental results agreeded to the theotetical ones.

Piezoelectric Aluminum Nitride Films Deposited by Triode Sputtering for Surface Acoustic Wave Devices

Aluminum nitride (A1N) thin films have been widely used in various applications due to their excellent properties such as chemical stability, electrical isolation, high acoustic wave velocity and large electromechanical coupling coefficient. For surface acoustic wave(SAW) applications, structures having A1N films on high acoustic velocity substrates such as diamond or sapphire offer much interest in forming high frequency SAW devices with phase velocities greater than 10000m/s. In this study, A1N films have been deposited on (001) sapphire and (100) silicon substrates by triode sputtering at low temperature in argon-nitrogen gas mixture. The crystal orientation, stoechiometry, optical acoustic and electrical properties were investigated. Dense AIN layers with very high electrical resistivity were obtained at high deposition rates. SAW filters were formed by development of interdigital transducers on the A1N/Silicon and A1N/Sapphire structures. The phase velocity was measured by a network analyzer as a function of A1N film thickness and substrate type.

Fabrication of GHz-range surface-acoustic-wavetransducers on LiNbO3 using imprint lithography

Because of its large electromechanical coupling coefficient, LiNbO3 is attractive as a substrate forsurface-acoustic-wave (SAW) devices. However, the fabricationof interdigital transducers with metal line widths of a fewhundred nanometres or less on LiNbO3 using electron-beamlithography is difficult as the material is not conductive. Wepropose an alternative method to produce high-frequency SAW transducers on the insulating substrate as well as on aconductive substrate. We demonstrate that SAW delay lines thatoperate in the GHz range can be fabricated using nanoimprintlithography.

Elastic, piezoelectric, and dielectric properties of multidomain 0.67Pb(Mg1/3Nb2/3)O3–0.33PbTiO3 single crystals

The elastic, piezoelectric, and dielectric constants of 0.67Pb(Mg1/3Nb2/3)O3–0.33PbTiO3 domain engineered single crystal were determined experimentally by using ultrasonic and resonance methods. It was confirmed that the single crystal system has large electromechanical coupling coefficient k33 (∼94%) and piezoelectric constant d33 (∼2800 pC/N) if the poling is done along the [001] of pseudocubic directions. A soft shear mode with a velocity of 880 m/s was observed in the [110] direction with displacement in [1̄10]. Using the measured data, the orientation dependence of phase velocities and electromechanical coupling coefficients were calculated. The origin of experimental errors and their influence on measured results are also examined.

Research of Super-High Electromechanical Coupling Surface Acoustic Wave Substrates

The properties of surface acoustic wave (SAW) devices mainly depend on the choice of piezoelectric substrate materials. The important properties required for SAW substrates are a large electromechanical coupling coefficient (k2), small temperature coefficient of delay (TCD), and low propagation loss, etc. Especially, super-high coupling substrates are very important for obtaining wide-band SAW filters, wide-band voltage controll oscilater (VCO) and delay lines with small insertion loss. KNbO3 single crystal has an extremely large electromechanical coupling coefficient (k2=53%) and zero TCD at approximately room temperature. Large-scale single-crystal growth technologies are now under investigation. In this study, the propagation characteristics of SAW in PZNT and KTP substrates are investigated experimentally in order to obtain higher coupling substrates than those of KNbO3. The experimental results show that the substrates have large k2. Also, theoretical SAW propagation characteristics with a k2 of about 100% are analyzed and their physical phenomena are discussed.

Theoretical Analysis of Surface Acoustic Wave Propagation Characteristics under Strained Media and Applications for High Temperature Stable High Coupling Surface Acoustic Wave Substrates

Among the important properties required for surface acoustic waves (SAW) substrates are a large electromechanical coupling coefficient (k2), small temperature coefficient of frequency (TCF) and low propagation loss. The LiNbO3 and LiTaO3 have good properties as the SAW substrates with a large size. Unfortunately, these possess the defect of having large values of TCF. In this paper, SAW-bonded composite substrates with a large k2, small TCF, low propagation loss and no dispersion using conventional bonders are investigated theoretically and experimentally. The propagation characteristics of SAWs under strained piezoelectric crystals using the higher-order elasticity theory have been analyzed. The theoretical results show zero TCF on LiNbO3/SiO2 substrates. The experimental results for LiNbO3/glass substrates revealed a TCF of [-19 ppm/°C]. The propagation properties were almost the same as those of the single crystal.

Temperature Self-Compensated Lithium Tantalate Piezoelectric Gyroscope for Higher Stability

We are studying the flexura H-type vibrational gyroscope using a LiTaO3 single crystal with large electromechanical coupling coefficients. The H-type LiTaO3 piezoelectric gyroscope sharply suppresses leakage output. As a result, temperature characteristics of drift and sensitivity can be calculated using an equivalent circuit deduced from the experiment. The resonant frequency and Q-value of the X mode are stable with the temperature. However, the resonant frequency and the Q-value of the Z mode show complicated fluctuations with temperature due to the effects of the support and other factors. As a countermeasure, the possibilities of applying an automatic temperature characteristic compensation method with the monitor transducer in the drive mode of operating in nonresonant drive and resonant detection were studied. By adding a new monitor that detects the vibrational mode of the drive, we can establish a stable reference signal for the synchronous detection of output. It is possible to greatly improve the temperature characteristics of sensitivity and drift.

High Frequency Thin Film Acoustic Ferroelectric Resonators

AbstractBoth ZnO and PZT Thin Film Bulk Acoustic Resonator filters were fabricated, tested and modeled in this study. The development of an accurate Mason model allows the effect of particular parasitic components on the microwave s-parameters in the region of the series and parallel resonances to be identified. The parasitic components that limit the performance of our ZnO and PbZr0.3Ti0.7O3 Thin Film Bulk Acoustic Resonator filters are analysed. From an analysis of PbZr0.3Ti0.7O3 Thin Film Bulk Acoustic Resonator measurements values for the longitudinal acoustic velocity and electromechanical coupling coefficient can be derived. Measured PbZr0.3Ti0.7O3 Thin Film Bulk Acoustic Resonator filter responses confirm that the larger electromechanical coupling coefficients in this material compared to ZnO give wider filter band-widths.

Source level and Urick

Source level (SL) is the first term in Bob Urick’s sonar equation, and it represents the root-mean-square pressure of sound radiated at the target, in decibels. The fundamental measure of source level is the signal-energy level (SEL) represented by the time integral of sound pressure squared, to which the detection index is proportional, in decibels. Despite using a form of sonar equation more natural for long-pulse transducers than for impulsive ones, he only described explosives in detail in his chapter on generation of underwater sound. When ‘‘Principles of Underwater Sound for Engineers’’ was published, there was a tendency to use impulsive sound sources to study sound interactions with the sea and to use narrow-band long-pulse transducers in sonar systems. The diminution of this tendency has been a very important development since Bob’s book was written, and it has occurred because of improvements in both kinds of transduction. Transducer bandwidth has been increased, both by materials with larger electromechanical coupling coefficients and by innovative designs. These include ‘‘hybrid’’ transducers that combine magnetostrictive and electrostrictive actuators and projector arrays designed to have no mechanical reactance. Improved impulsive sound sources such as air guns, sparkers, and explosive arrays now find sonar use.

A Surface Acoustic Wave Elastic Convolver using a KNbO3 Single Crystal Substrate

Elastic convolvers are very important in signal processing devices of spread spectrum communication (SSC) systems. Highly efficient convolvers are required in the application of the spread spectrum and next stage communication systems. A high value of the coupling coefficient is very important for wideband and high efficiency surface acoustic wave (SAW) devices, such as SAW convolvers. Potassium niobate (KNbO3) has large piezoelectric constants and a very large electromechanical coupling coefficient (K2) of 0.53 for surface acoustic waves, which is about 10 times higher than that of LiNbO3. Therefore, highly efficient elastic SAW convolvers using KNbO3 substrates are expected in the future. In this paper, the use of the rotated 60° Y-cut, X-propagating KNbO3 substrates in convolvers is demonstrated. The experimental results show that the efficiency of the convolver using 60° Y–X KNbO3 is 15 dB higher than that of the convolver using Y–Z LiNbO3.

Study on Surface Acoustic Wave Characteristics of SiO2/Interdigital-Transducer/ZnO/Diamond Structure and Fabrication of 2.5 GHz Narrow Band Filter

Surface acoustic wave (SAW) characteristics of the SiO2/interdigital-transducer(IDT)/ZnO/diamond structure were studied theoretically and experimentally. It was found that the 2nd mode in this structure can provide a zero temperature coefficient of frequency (TCF) as well as high velocity of 10,000 m/s and a large electromechanical coupling coefficient of 1.4%. Utilizing this wave, a 2.5 GHz narrow-band SAW filter was successfully fabricated with IDTs of 0.9 µm finger width, which resulted in superior characteristics for a retiming filter with a small insertion loss of 6.7 dB, Q value of 660 and small frequency deviation of 100 ppm in the temperature range from -40 to 85°C. The insertion loss is smaller than any other retiming filters which have ever been reported with quartz, a conventional SAW material, and also the frequency deviation with temperature is smaller than that in the case of ST-cut quartz.

Characteristics of a Conical Piezocomposite Transducer with an Apodized Vibration Area

A conical transducer with an apodized vibration area has been designed and fabricated using a piezocomposite material with 1–3 connectivity for creating limited-diffraction beams. The large electromechanical coupling coefficient k of the piezocomposite material increases the transducer sensitivity. It is shown that an almost uniform -6 dB beamwidth of 6–9 wavelengths is obtained in the axial range of z = 20 mm to 170 mm using a fabricated transducer 25 mm in diameter operating at 3.6 MHz. It is also demonstrated through preliminary experiments with B-mode imaging that high resolution is maintained over a large depth.