P. Ventura

University of Nice-Sophia Antipolis, Nice, Provence-Alpes-Côte d'Azur, France

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Publications (11)7.68 Total impact

  • Pascal Ventura, William Steichen
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    ABSTRACT: Recent developments in wide bandwidth SAW filter design led to the use of complex electroacoustic cells, such as the Hanma-Hunsinger cell. For this kind of structure, it is not sufficient to use only a single electrode periodic FEM/BEM model to derive the P-matrix parameters. The present paper proposes a mixed FEM/BEM numerical model for the simulation of a periodic array of metallic electrodes, the elementary cell of which can be as complex as necessary: it can contain several electrodes, connected to active ports, or short-circuited, or floating.
    IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control 11/2007; 54(10):2052-9. · 1.82 Impact Factor
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    ABSTRACT: First Page of the Article
    Ultrasonics Symposium, 2005 IEEE; 10/2005
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    ABSTRACT: The demand for high frequency surface acoustic wave devices for modern telecommunication applications imposes the development of devices able to answer the manufacturer requirements. The use of high velocity substrates for which a piezoelectric layer is required to excite and detect surface waves has been widely investigated and requires the implementation of accurate theoretical tools to identify the best combinations of material. The present paper proposes a mixed formulation combining finite element analysis with a boundary integral method to accurately simulate the capability of massive periodic interdigital transducers to excite and detect guided acoustic waves in layered media. The proposed model is exploited for different typical configurations. © 2004 American Institute of Physics.
    Journal of Applied Physics 12/2004; 96(12):7731-7741. · 2.21 Impact Factor
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    ABSTRACT: The development of efficient computation tools based on mixed analytical and numerical calculation approaches allows precise descriptions and characterizations of surface acoustic waves (SAW) propagation, taking into account realistic electrical and mechanical boundary conditions. As an example, suppression of the leaky SAW, also called pseudo SAW (PSAW), attenuation has been predicted using such tools allowing to explain experimental occurrences for SAW devices on YX cut lithium niobate and lithium tantalate with thick aluminum strip gratings (6% < h//spl lambda/ < 10%). In this work, such a theoretical model is used to analyze the evolution of surface waves on standard YX lithium tantalate cuts versus aluminum strip height. It is shown that the surface skimming bulk wave (SSBW), which accompanies the pseudo SAW on such crystal orientations, may be trapped by the grating, exhibiting then a second pseudo SAW behavior when close to the Bragg condition. A device has been designed and fabricated to check these theoretical predictions. The experimental evidence of the existence of the phenomenon allows one to discuss its consequences on more classical devices built on (Y + 36/spl deg/, X) LiTaO/sub 3/ substrates.
    IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control 07/2002; · 1.82 Impact Factor
  • P. Ventura, J.M. Hode, J. Desbois, H. Solal
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    ABSTRACT: Because of more and more stringent requirements on SAW filter performances, it is important to compute, with very good accuracy, the SAW propagation characteristics, which include the calculation of reflection and scattering parameters. For that reason, the analysis of periodic structures on a semi-infinite piezoelectric substrate is one of the most important problems being investigated by SAW researchers. For infinite periodic grating modeling, we developed numerical mixed FEM/BEM (finite element method-boundary element method) models using an efficient interpolation basis function that takes into account the singularity at both edges of each electrode. In this paper, a review of the numerical program that has been developed during the past few years will be presented. For an infinite periodic grating, it is convenient to solve the propagation problem in the Fourier domain (wave number space and harmonic excitation), and important efforts have been spent to properly integrate the so-called periodic harmonic Green function. Using this numerical model together with the general P-matrix formalism, it is possible to compute all of the basic parameters with a very good accuracy. These consist of the single strip reflectivity, acoustic wave-phase velocity, and position offset between reflection and transduction centers. Simulations and comparisons with experiments are shown for each model.
    IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control 10/2001; · 1.82 Impact Factor
  • P. Dufilie, P. Ventura
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    ABSTRACT: The electroacoustic source strength for a periodic SAW transducer can be determined analytically. With the exception of sources close to the ends of the transducer, the source strength function does not depend on its position in the transducer. A Distributed Acoustic Reflection Transducer (DART) is not periodic and consists of two or more linewidths and strip periods. The source strength and effective source position of a strip is dependent on the widths and positions of the adjacent strips. Strips of a given width can exhibit source strength differences of 10% or more depending on their position in the DART. This paper presents two methods for predicting the source strength and effective position of a source in a DART. The first method uses an electrostatic Green's function analysis. The second more complete method uses a mixed FEM/BEM analysis to obtain a more accurate result. Results of these two methods are compared for various transducer configurations. Using the above results a 112 MHz filter was designed and built on a 112°YX LiTaO <sub>3</sub> substrate
    Ultrasonics Symposium, 1995. Proceedings., 1995 IEEE; 12/1995
  • P. Ventura
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    ABSTRACT: SAW devices are becoming more and more widely used in low-loss bandpass filtering (SPUDT filters, resonator filters, ...). For these SAW filters, the strip reflectivity is a key element of their design. Due to its very good temperature stability, quartz is the most commonly used substrate for narrow band applications. Due to small electroacoustic coupling, strip reflectivity on quartz is mostly due to the mechanical part of the electrode perturbation. Therefore, only experimental measurements or complex numerical models can be accurate enough to calculate this reflectivity. In this paper, we present a full experimental characterization of strip reflectivity on 38° Y rotated quartz: the metallization thickness ranges from 0.6% λ, to 315% λ, while the mark to period ratio varies from 0.25 to 0.8. A recently developed mixed FEM/BEM model has been used to compare these experimental data with simulations showing a very good agreement. Despite classical model predictions, maximum reflectivity mark to period ratio was found very thickness dependent. This property was used to greatly improve SPUDT designs
    Ultrasonics Symposium, 1994. Proceedings., 1994 IEEE; 12/1994
  • P. Ventura, J. Desbois, L. Boyer
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    ABSTRACT: Mechanical reflections of SAW or pseudo-SAW (PSAW) under metallic electrodes are the basic phenomena utilized for low loss bandpass filters. Their precise modelling is becoming a key element in the design of more and more compact filters. The mechanical perturbation depends on both the mass loading effect (density and elasticity) and the topographic effect (electrode profile). The first published modelizations of the electrode mechanical perturbation were only analytical and involved major simplifying assumptions on tile shape or on the height of metallizations leading to a poor determination of the topographic effect. Later, numerical models based on the Finite Element Method (FEM) were presented. They were able to take into account complex electrode profiles. Since most of them proposed to discretize both the electrode and tile substrate, important computational efforts were required. Recently, another method was presented mixing an electrode discretization and a periodic Green function formalism for the substrate. In the present paper, we propose a new method to compute the dispersion curve for SAW and PSAW propagation under electrode including the effect of mass loading. First the Floquet theorem is used to expand the acoustic fields into spatial harmonics. Then, the relationships between stresses and displacements are derived for the semi-infinite homogeneous anisotropic substrate. Finally, the FEM is applied only to the electrode in order to carry out the coupling between spatial harmonics of stress and displacement vectors at the electrode substrate interface. The calculation is not restricted to any particular crystalline symmetries and only involves the plane strain assumption, thus taking into account transverse components of the waves. The problem of the elementary reflection coefficient determination is also examined. Both theoretical explanations, validations and comparisons with experience will be shown
    Ultrasonics Symposium, 1993. Proceedings., IEEE 1993; 12/1993
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    ABSTRACT: Published design methods of single phase unidirectional (SPUDT) filters using internal reflections only allow for individual transducer optimization:electroacoustic transfer function (amplitude and phase), and, acoustic reflection of the loaded transducer. Consequently, multiple reflections between transducers are not taken into account for passband ripple optimization. We present a generalized method which optimizes directly the amplitude and group delay of the entire filter. The new method takes into account inter-transducer reflections, while controlling simultaneously each transducer. Furthermore, the reflection weighting functions of grating shields needed between transducers to obtain low feed through level are also taken into account in this new algorithm. Filtering characteristics as well as size reduction of various low loss bandpass filters have been dramatically improved using this new global optimization procedure : we present various SPUDT based filters designed using this algorithm. The size of a 71 MHz filter for mobile GSM was greatly reduced while keeping a two SPUDT structure: this filter fits in a SIP 5 package while the previous filter required a DIP 14 package
    Ultrasonics Symposium, 1993. Proceedings., IEEE 1993; 12/1993
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    ABSTRACT: The general design problem for the single-phase unidirectional transducer (SPUDT) is solved, resulting in a new nonlinear algorithm which computes quasi-optimum transduction and reflection functions for a given template. Load impedance effects are taken into account allowing the placing of constraints on the amplitude and phase of the transducer function as well as on the triple transit level. Several filters are presented showing how SPUDT can be used to design very linear and low triple transit levels or very compact filters for mobile radio applications
    Ultrasonics Symposium, 1992. Proceedings., IEEE 1992; 11/1992
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    ABSTRACT: The crosstalk between the elements of an acoustical array is a major cause of limitation of performance, when the pitch is around or below the wavelength. An accurate modelization of the mechanical part of the crosstalk can be obtained by finite element models. An original bidimensional mixed finite element/analytical analysis has been developed for infinite periodic arrays. The finite element method is used to analyze only one elementary transducer. Then, by expanding the electrical exitation of the array into harmonic exitations, the cross coupling is computed analytically for any combination of coupling layers including solid or fluid media. Both theoretical explanations and preliminary validations with previous analytical or numerical models are presented
    Ultrasonics Symposium, 1992. Proceedings., IEEE 1992; 11/1992