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A novel concept for the development of thin-film micro-acoustic resonators based on the coupling between different plate acoustic modes was demonstrated. The basic principles for the design and fabrication of intermode-coupled plate acoustic wave resonators on c-textured thin AlN films were presented and first experimental proof of coupling between laterally propagating waves and BAW was demonstrated. The experimental results demonstrate that the grating-assisted intermode coupling can be employed in high-frequency resonators inheriting the low dispersive nature of the S0 mode in combination with the energy localization in the plate bulk typical for the fundamental thickness shear resonance.

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Dispersion characteristics of surface acoustic waves (SAWs) propagating along the c-plane of single crystalline AlN under 2D tungsten (W) hexagonal gratings are studied using eigen-frequency and frequency response finite element analysis. Specifically, a 2D hexagonal grating with a 10 mu m distance between the W masses is considered and the frequency stopband SAW characteristics studied. For hexagonal W gratings with a thickness above a critical value (about 0.9 mu m in this case) SAW stopbands with a 0 rad and pi/6 rad angle of incidence penetrate in each other thus forming a forbidden SAW frequency band lying between the upper stopband edge of the 0 rad incident SAW and the lower stopband edge of the pi/6 rad incident SAW. In view of the above findings the existence of a complete frequency stopband is discussed.

Wurtzite AlN is a piezoelectric material with excellent electro-acoustic properties and is used for the fabrication of high frequency thin film micro-acoustic components, most notably filters, duplexers, resonators, etc. Its moderate electromechanical coupling coefficient (k(t)(2)) of 6%-7% is insufficient for applications requiring larger bandwidths. Recent theoretical and experimental studies indicate that AlN alloyed with Sc exhibits a substantially higher piezoelectric constant than pure AlN. This study aims at determining the main electro-acoustic parameters of Al(1-x)Sc-(x) N in view of large bandwidth applications. To this end, highly c-textured Al(1-x)Sc(x) N thin films have been synthesized with relative Sc concentrations of up to 0,15. Subsequently, FBAR resonators were fabricated and characterized as a function of the Sc content. It is seen that k(t)(2) increases linearly with the latter to a value of 12% for a Sc concentration of x=0,15, while the Q value decreases from 739 to about 348 in the same concentration range. Likewise, the TCF varies from -35,9ppm/degrees C to -39,8ppm/degrees C, while the dielectric constant increases from epsilon=10 to a value of 14,1 for x=0,15. Finally, the relative dielectric losses are seen to increase by approximately a factor of two.

Here we demonstrate experimentally a novel, small form factor, resonant architecture employing the intrinsic zero-group-velocity dispersion of the first order symmetric Lamb wave S1 propagating in piezoelectric AlN film membranes. Designs with different topologies were fabricated and compared. FEM analysis is used to verify the observed differences while providing a deeper insight to the resonator performance. Technique for improvement of the device performance are further proposed.

WISENET

Here we present three different thin-film Lamb waveresonant topologies employing reflection, zero-group velocity andintermode coupling respectively in view of energy confinement ofLamb waves propagating in c-textured thin aluminum nitridemembrane. The lowest order symmetric (S0) Lamb wavetopologies with both Bragg and edge reflection have beenextensively studied during the last decade. The other two types ofresonant topologies have been recently introduced for the firsttime and their potential is yet to be realized. The Zero-Group-Velocity Lamb wave resonator employs the native zero-groupvelocitycondition of the first order symmetric (S1) Lamb wave,eliminating thus the need of reflectors of any type. Theintermode-coupled Lamb wave resonator, on the other hand,employs refraction instead of reflection in order to couple thelaterally propagating S0 Lamb wave to the fundamentalthickness shear resonance of the plate (i.e the first orderasymmetric Lamb wave (A1) at cut-off)., Symposium organizwd by The 150th Committee on Acoustic Wave Device Technologyof the Japan Society for the Promotion of Science (JSPS), VR granted "Thin Film Guided Microacoustic Waves in Periodical Systems: Theory and Applications"

Two-port film plate acoustic resonators (FPAR) devices operating on the lowest order symmetric Lamb wave mode (S0) in C-oriented AlN membranes on Si were fabricated and tested for their power handling capabilities in a feedback-loop power oscillator circuit. The FPAR was operated at an incident power level of 24 dBm for several weeks without performance degradation. Its flicker noise constant was calculated from close-in phase noise data as αR=2.1×10^−36/Hz. The results indicate that IC-compatible S0 FPARs are well suited for integrated microwave oscillators with thermal noise floor (TNF) levels below −175 dBc/Hz., VR "Thin Film Guided Microacoustic Waves in Periodical Systems: Theory and Applications"

Piezoelectric c-textured Al(1-x)ScxN thin films, where the Sc relative concentration, x, varies in the range 0-0.15 have been studied in view of radio frequency (RF) electro-acoustic applications. Thin film bulk acoustic wave resonators (FBARs) employing these films were fabricated and characterized as a function of the Sc concentration for the first time. The measured electromechanical coupling is found to increase by as much as 100% in the above concentration range. The results from this work underline the potential of the c-textured Al(1-x)ScxN based FBARs for wide band RF applications., WISENET

The mass sensitivity of thin aluminum nitride (AlN) film S0 Lamb wave resonators is theoretically and experimentally studied. Theoretical predictions based on modal and finite elements method analysis are experimentally verified. Here, two-port 888 MHz synchronous FPARs are micromachined and subsequently coated with hexamethyl-disiloxane(HMDSO)-plasma-polymerized thin films of various thicknesses. Systematic data on frequency shift and insertion loss versus film thickness are presented. FPARs demonstrate high mass-loading sensitivity as well as good tolerance towards the HMDSO viscous losses. Initial measurements in gas phase environment are further presented., VR "Thin Film Guided Microacoustic Waves in Periodical Systems: Theory and Applications"

A concept for the development of thin film micro-acoustic resonators is demonstrated. The basicprinciples for the design and fabrication of zero-group-velocity Lamb acoustic wave resonators onc-textured thin aluminum nitride films are presented. The experimental results demonstrate that thezero-group-velocity waves can be employed in high frequency resonators with small form factors., VR, "Thin Film Guided Microacoustic Waves in Periodical Systems: Theory and Applications"

Thin film plate acoustic resonators devices operating in the lowest order symmetric Lamb wave mode (S0) in coriented aluminum nitride (AlN) membranes on Si were fabricated and tested for their sensitivities to pressure and mass as well as for their ability to work in liquid environment., VR "Thin Film Guided Microacoustic Waves in Periodical Systems: Theory and Applications"

In this work, pressure sensitivities of aluminium nitride (AlN) thin film plate acoustic resonators (FPAR) operating at the lowest-order symmetric (S0), the first-order asymmetric (A1) as well as the first-order symmetric (S1) Lamb modes are theoretically and experimentally studied in a comparative manner. The finite element method analysis has also been performed to get a further insight into the FPAR pressure sensitivity. The theoretical predictions are found to be in good agreement with the experiment. The S0 Lamb mode is identified as the most pressure-sensitive FPAR mode, while the A1 and S1 modes are found to be much less sensitive. Further, the S0 and the A1 modes exhibit almost equal temperature sensitivities, which can be exploited to eliminate the temperature drift by comparing the resonance frequencies of the latter two modes.

Mass sensitivity of thin aluminum nitride (AlN) film S0 plate wave resonators is theoretically and experimentally studied. Here, two-port 888MHz synchronous thin film plate acoustic resonators (FPAR) are micromachined and subsequently coated with plasma-polymerized hexamethyldisiloxane (pp-HMDSO) thin films of various thicknesses. Systematic data on frequency shift and insertion loss versus film thickness are presented in a comparative manner. Measurements in gas phase environment are further presented in a comparative manner., VR "Thin Film Guided Microacoustic Waves in Periodical Systems: Theory and Applications"

The characteristics of aluminum nitride (AlN) Lamb wave resonators utilizing the lowest symmetric (S0) mode with grounded, floating, and open bottom surface configurations are theoretically and experimentally investigated. The Lamb wave resonator without the bottom electrode exhibits a quality factor (Q) as high as 2,573 but a low effective coupling of 0.18% at 949.7 MHz. On the contrary, the Lamb wave resonator with a floating bottom electrode shows an effective coupling of 1.05% but a low Q of 850 at 850.3 MHz because the imperfect interface between the AlN plate and bottom electrode usually degrades the Q. Limited by the larger static capacitance, in contrast to the floating bottom electrode, the Lamb wave resonator with a grounded bottom electrode shows a smaller effective coupling of 0.78% and a low Q of 800 at 850.5 MHz. These results suggest that the resonator with a floating bottom surface is suitable for filter applications, whereas that with an open bottom surface is preferred for sensor and oscillator applications., VR "Thin Film Guided Microacoustic Waves in Periodical Systems: Theory and Applications"

Thin film plate acoustic resonators (FPAR) devices operating in the lowest order symmetric Lamb wave mode (S0),the first order asymmetric Lamb wave mode (A1) and the first order symmetric Lamb wave mode (S1), propagatingin c-oriented aluminum nitride (AlN) membranes on Si were fabricated and tested for their sensitivities to pressureand mass. Systematic data on frequency shifts versus rigid mass (layer) thickness and ambient pressure variations arepresented for the different Lamb wave resonances. Further the ability to work in liquid environment of the S0, A1 andS1 modes, respectively, has been tested in view of Bio-sensor applications., VR Granted

The paper is dedicated to improving the frequency response of FBAR filters by replacing some of the single FBARs with two resonators connected in parallel. The method is applied for the basic lattice filter architecture and its modification with twice fewer number of FBARs. The conditions that must satisfy the resonator parameters are derived by theoretical considerations and computer simulations.

This letter discusses the design of thickness shear mode thin-film bulk acoustic resonator (FBAR) sensor array for in liquid operation with respect to minimizing the observed Q-degradation and crosstalk., Electronically published since May 11, 2010, WISENET

Particle manipulation utilizing interface acoustic waves (IAWs) is proposed for the first time. An IAW-based manipulation system has been designed, micromachined and tested. This work addresses the issue of particle manipulation in microfluidic channels with particular emphasis on particles with submicron dimensions. The subject is of significant relevance for a range of bio-technological applications and in particular for lab-on-chip ones. Submicron particle manipulation in continuous flow has been demonstrated., VR Granted "Thin Film Guided Microacoustic Waves: Theory and Appliactions"

In this work the applicability of the coupling-ofmodes (COM) approach to the analysis of thin AlN film plate acoustic resonators (FPAR), utilizing the S0 Lamb wave, is discussed. Analysis based on the Floquet-Bloch theorem as well as COM parameter extraction from a micromachined FPAR test structure are simultaneously used to verify the applicability of the COM approach. Finite element model simulation is used to further study the contribution of the higher order mass loading effects over the Lamb wave propagation under a periodical grating. A possibility to achieve zero sensitivity of the FPAR resonance with respect to the grating strip thickness is identified and physically interpreted for the first time., VR granted "Thin Film Guided Microacoustic Waves in Periodical Systems: Theory and Applications"

VR "Thin Film Guided Microacoustic Waves in Periodical Systems: Theory and Applications "

The IC-compatible thin film bulk acoustic resonator (FBAR) technology has made it possible to move the thickness excited shear mode sensing of biological layers into a new sensing regime using substantially higher operation frequencies than the conventionally used Quartz Crystal Microbalance (QCM). The limitations of the linear range set by the film resonance using viscoelastic protein films are here for the first time addressed specifically for FBARs operating at 700MHz up to 1.5GHz. Two types of protein multilayer sensing were employed; one utilizing alternating layers of Streptavidin and Biotinated BSA and the other using stepwise cross-linking of fibrinogen with EDC/NHS activation of its carboxyl groups. In both cases the number of protein layers within the linear regime is well above the number of protein layers usually used in biosensor applications, further verifying the applicability of the FBAR as a biosensor. Theoretical calculations are also presented using well established physical models to illustrate the expected behavior of the FBAR sensor, in view of both the frequency and the dissipation shifts.

Micromachined thin film plate acoustic wave resonators (FPAR) utilizing the lowest order symmetric Lamb wave (S0) propagating in highly textured 2μm thick Aluminum Nitride (AlN) membranes have been successfully demonstrated [1]. The proposed devices have a SAW-based design and exhibit Q factors of up to 3000 at a frequency around 900MHz as well as design flexibility with respect to the required motional resistance. However, a notable drawback of the proposed devices is non-zero temperature coefficient of frequency (TCF) which lies in the range -20 ppm/K to –25 ppm/K. Thus, despite the promising features demonstrated, further device optimization is required. In this work temperature compensation of thin AlN film Lamb wave resonators is studied and experimentally demonstrated. Temperature compensation while retaining at the same time the device electromechanical coupling is experimentally demonstrated. The zero TCF Lamb wave resonators are fabricated onto composite AlN/SiO2 membranes. Q factors of around 1400 have been measured at a frequency of around 755 MHz. Finally, the impact of technological issues on the device performance is discussed in view of improving the device performance., WISENET

Theuse of thick NiSi electrodes in electroacoustic resonators allows front-endintegration with integrated circuit technology. Problems are identified in theformation of thick nickel silicide (NiSi) electrodes via a singledeposition of Ni onto blank Si wafers. An alternative fabricationprocess based on the deposition and silicidation of a multilayerfilm is presented. The films were found to have lowresistivity and smooth surfaces, with the layered structure preserved evenafter silicidation. Textured piezoelectric films of (002) wurtzite AlN demonstrateda diffraction-peak width that narrows to 3.5° when deposited ona thick 10 pair NiSi film., SSF ICTEA

Improved performance thin-film plate acousticwave resonators (FPAR) using the lowest order symmetricLamb wave (S0) propagating in highly textured AlN membraneshave been previously demonstrated for the first time.In this work, an experimental study of the resonators’ performancevs. a variety of design parameters is performed. Devicesoperating in the vicinity of the stopband center exhibiting aQ-value of up to 3000 at a frequency of around 875 MHz aredemonstrated. Further, low-loss high-Q micromachined 2-portlongitudinally coupled thin-film resonators using the S0 modeare demonstrated for the first time. For the analysis of theproposed structures, the coupling-of-modes (COM) approachis successfully employed. Initially, the COM model is used forthe extraction of physical parameters from one-port FPARmeasurements. Subsequently, using the COM model, a satisfactoryagreement with the proposed experimental frequencycharacteristics of S0 2-port FPARs has been achieved, andpossibilities for further improvements in the performance discussed.Finally, the frequency spectrum of the one-port deviceshas been studied and the excited plate modes at differentfrequencies identified and presented with their Q-factors andtemperature coefficients of frequency (TCF)., VR Funded "Thin Film Guided Microacoustic Waves in Periodical Structures: Theory and Applications"

WISENET

The work in question addresses the issue of continuous flow particle manipulation in liquid media with particularemphasis on particles with micron and sub-micron dimensions.The subject is of significant relevance for a range of biotechnological applications and in particular for lab-on-chip ones.Particle manipulation utilizing Interface Acoustic Waves (IAW)is proposed for the first time. Manipulation of submicron sized particles is successfully demonstrated in a streaming free regime., In Print, VR granted: "Thin Film Guided Microacoustic Waves in Periodical Systems: Theory and Applications"

In this study, two-port 880MHz FPAR devicesoperating on the lowest order fast symmetric Lamb wave mode(S0) in c-oriented AlN membranes on Si, were fabricated andsubsequently tested for their power handling capabilities in afeedback-loop power oscillator circuit. The S0 Lamb waves wereexcited and detected by a classical two-port resonator structure,as in Rayleigh SAW (RSAW) resonators. Incident power levels ofup to 24 dBm (250 mW) for the FPARs were provided by a high powersustaining amplifier in the loop. No measurable performance degradation was observed. The results from this study indicate that IC-compatible S0 FPAR devices can dissipate orders of magnitude higher RF-power levels than their RSAWcounterparts on quartz and are well suited for integrated microwave power oscillators with thermal noise floor (TNF) levelsbelow -175 dBc/Hz., In Print, VR granted: "Thin Film Guided Microacoustic Waves in Periodical Systems: Theory and Applications"

VR Granted: "Thin Film Guided Microacoustic Waves in Periodical Systems: Theory and Applications"

Micromachined Thin film plate acoustic wave resonators (FPAR) utilizing the lowest order symmetric Lamb wave (S0) propagating in highly textured 2μm thick Aluminum Nitride (AlN) membranes have been successfully demonstrated[1]. However, a notable drawback of the proposed devices is their non-zero temperature coefficient of frequency (TCF) which lies in the range -20 ppm/K to –25 ppm/K. In this work temperature compensation of thin AlN film Lamb wave resonators is studied and demonstrated. Temperature compensation, while retaining at the same time the device electromechanical coupling, isexperimentally demonstrated. The zero TCF Lamb wave resonators are fabricated onto composite AlN/SiO2 membranes. Q factors of around 1400 have been measured at a frequency of around 755 MHz., In print

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A systematic study of the mass sensitivity and its dependence on the material's properties and thicknesses in composite multilayer Thin Film Bulk Acoustic Resonators (FBAR) is presented. The Mason transmission line model has been employed in combination with the acoustic energy balance principle for the determination of the FBAR mass sensitivity. The results have been experimentally verified. Further, the mass sensitivity dependence on various parameters has been studied and correlated with wave reflection and interference within the composite structure in addition to the well-known dependence on resonator acoustic impedance and operation frequency. The mass sensitivity for both the fundamental and the second harmonic mode of operation has been studied in view of their practical relevance. In particular, sensitivity amplification induced by the presence of an on-top deposited low acoustic impedance layer has been identified for the first harmonic and its potential applicability discussed in terms of gas and in-liquid sensing. Optimized structures for both sensing applications are suggested by considering the overall sensor resolution defined by both the mass sensitivity and the FBAR performance., WISENET

For use in thin film electroacoustic (TEA) technology a few hundred nanometrethick nickel silicide (NiSi) electrode would need to be fabricated. A complete fabrication process for the formation of over 200 nm thick silicide films has been optimised for use as an electroacoustic electrode. Optimisation of silicidation temperature and identification of the mono phase of silicide is demonstrated. Thick electrodes are formed by depositing multilayers of silicon and nickel pairs onto silicon (Si) substrates before rapid thermal annealing. The numbers of multilayers and relative material thicknesses are optimized for both surface roughness and electrical resistivity. The growth of textured aluminium nitride (AlN) has been investigated on the optimised surfaces., SSF ICTEA, WISENET

A new design of a solidly mounted resonator (SMR) that utilizes an all-metal Bragg reflector eliminating thus the need for a bottom electrode is proposed. In this configuration, the role of the bottom electrode is taken by the Bragg reflector rendering the resonator “combined electrode-Bragg reflector SMR”. The main advantages of the proposed design are the substantially reduced electrode resistance (and hence higher Q), the utilization of the full piezoelectric coupling at high frequencies as well as expected improvement in power handling capabilities due to lower dissipation and improved heat conductivity. Resonators with the classical and the new design have been fabricated and evaluated. The measurements indicate that indeed the resonators with the new design demonstrate improved performance., WISENET, ICTEA (SSF)

SSF-ICTEA, WISENET

Surface acoustic waves (SAW) scattering into asemi-infinite solid have been studied since the early 60-ies. Inthe case of a substrate with finite plate-like dimensions thescattering into bulk waves (BAW) is transformed intoscattering to bulk plate modes. There have been some attemptsto model the phenomenon but the most interesting case ofinteraction of SAW with BAW resonator, i.e. scattering in aquasi-perpendicular direction was not considered. Theresonant interaction between Rayleigh SAW and near-onsetPlate Waves in isotropic solids, through the coupling effect ofan infinite periodical grating defined on the plate surface istheoretically described and its characteristics revealed. Theanalysis proposed is based on the Bloch theorem. The gratingboundary conditions are considered assuming a weak surfaceperturbation. Further, the eigenmodes along with amplituderatios inside such types of gratings are determined. Initialresults on Gulyaev-Bljustein wave (GBW) – thickness shearmode (TSM) interaction are also presented., In print, SSF MS2E Center of Excellence, Vinnova WISENET

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A shear mode thin film bulk acoustic resonator (FBAR) operating in liquid media together with a microfluidic transport system is presented. The resonator has been fabricated utilizing a recently developed reactive sputter-deposition process for AlN thin films with inclined c-axis relative to the surface normal with a mean tilt of around 30°. The resonator has a resonance frequency of around 1.2 GHz and a Q value in water of around 150. Sensor operation in water and glycerol solutions is characterized. Theoretical analysis of the sensor operation under viscous load as well as of the sensitivity and stability in general is presented. The theoretical predictions are compared with experimental measurements. The results demonstrate clearly the potential of FBAR biosensors for the fabrication of highly sensitive low cost biosensors, bioanalytical tools as well as for liquid sensing in general., WISENET

In this work we demonstrate a practically complete temperature compensation of the second harmonic shear mode in a composite Al/AlN/Al/SiO2 thin film bulk acoustic resonator (FBAR) in the temperature range 25 °C–95 °C. The main advantages of this mode are its higher Q value in liquids as well as its higher frequency and hence higher resolution for sensor applications. For comparative reasons the non-compensated fundamental shear mode is also included in these studies. Both modes have been characterized when operated both in air and in pure water. Properties such as Q value, electromechanical coupling, dissipation and sensitivity are studied. An almost complete temperature compensation of the second harmonic shear mode was observed for an oxide thickness of 1.22 µm for an FBAR consisting of 2 µm thick AlN and 200 nm thick Al electrodes. Thus, the measured temperature coefficient of frequency (TCF) in air for the non-compensated fundamental shear mode (1.25 GHz) varied between −31 and −36 ppm °C−1 over the above temperature range while that of the compensated second harmonic shear mode (1.32 GHz) varied between +2 ppm °C−1 and −2 ppm °C−1 over the same temperature interval. When operated in pure water the former type shows a Q value and coupling coefficient, k2t, around 180 and 2%, respectively, whereas for the second harmonic these are 230 and 1.4%, respectively., WISENET

Thin film plate acoustic wave resonators utilizing thelowest order symmetric Lamb wave (S0) propagating in highlytextured 2μm thick Aluminum Nitride (AlN) membranes weresuccessfully demonstrated for the first time [1]. Further theutilization of fast lateral modes in thin films has recently beingtargeted independently by other groups as well [2,3]. Theunperturbed S0 mode in thin film AlN has an acoustic wavevelocity in excess of 10 000 m/s with a weak dispersion andsufficient coupling. Q factors of around 1800 were demonstratedfor 890 MHz one-port synchronous resonators operating in thevicinity of the upper stopband edge [1]. In this work anexperimental study on the resonators’ performance vs variety ofdesign parameters is performed. Devices operating in thevicinity of the stopband center offering a Q of up to 3000 at afrequency of around 875 MHz are demonstrated. Further,micromachined 2-port longitudinally coupled thin filmresonators utilizing the S0 mode are demonstrated for the firsttime., SSF ICTEA, Vinnova WISENET

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WISENET

A fabrication process for thin film electroacoustic devices utilizing buriedelectrodes is presented. A one-step lithography process has been developedto bury electrodes resulting in a planarized surface. The proposedtechnology is expected to bring about a number of benefits concerning theperformance of a variety of thin film electroacoustic devices. With respectto thin film plate acoustic resonators (FPAR), burying the reflectorelectrodes results in improved reflectivity and potentially lowersusceptibility to acousto-migration effects. It is also shown that employingthe proposed technology for the fabrication of both thin film bulk acousticresonators (FBAR) and thin film solidity mounted bulk acoustic resonators(SBAR) eliminates certain macro-structural defects in the piezoelectric filmwhich is a prerequisite for substantially improved device performance andhigher power handling capability. The buried electrode electroacoustic (EA)technology is demonstrated for a thin aluminium nitride (AlN) piezoelectricfilm with electrodes of both molybdenum (Mo) and tungsten (W). The latterhave been primarily chosen because of their high electroacoustic materialquality. Thin film resonant structures produced by this technology arecharacterized and their features are discussed., SSF ICTEA

Highly c-oriented aluminum nitride (AlN) thin piezoelectric films have been grown by pulsed direct-current (DC) magnetron reactive sputter deposition. The films were deposited at room temperature and had a typical full width half maximum (FWHM) value of the (0 0 2) rocking curve of around 2°. Resonant devices in thin film plates having surface acoustic wave (SAW) based designs were fabricated by means of low resolution photolithography. The devices were designed to operate with the fast Rayleigh and Lamb modes respectively. Both types of devices exhibited propagation velocities in excess of 10 000 m/s and sufficient electromechanical couplings. The device measurements illustrate the big potential of these modes for the development of low cost IC compatible electroacoustic devices in the lower GHz range. The basic properties of the modes studied are discussed in a comparative manner. Potential commercial applications are also outlined.

TheGreen's function formalism has been applied to the analysis ofthe fundamental symmetric Lamb mode excited by means of longitudinalwave (LW) transducers. The Lamb wave Green's function has beenrelated to the properties of the effective permittivity defined asa function of the wave slowness and the relative platethickness. An electrostatic analysis that neglects the piezoelectric coupling isemployed to relate the charge density to the applied voltage.This analysis is subsequently used to calculate the radiation conductanceof a LW transducer. The results obtained are consistent withthe equivalent circuit approach and define the device coupling asa function of the plate thickness and the intrinsic Lambwave coupling.