Are you B. Assouar?

Claim your profile

Publications (30)36.13 Total impact

  • Jiahong Ma, Zhilin Hou, Badreddine M. Assouar
    [Show abstract] [Hide abstract]
    ABSTRACT: In this paper, the mechanism for opening a locally resonant band gap in a thin elastic plate is investigated. Two previously suggested structures, which are constructed by periodically drilling holes on elastic plate and then filling them with the rubber-coated masses, or just by periodically stubbing the rubber rods with mass cap on the plate, are revisited. We find that, because of the partial band gaps for in-plane and out-of-plane plate modes cannot be appropriately overlapped, the full band gaps in both of the structures are generally narrow. The reason for this phenomenon is based on the selective coupling between the different resonant patterns of the resonant units and the in-plane and out-of-plane plate modes. Based on the understanding, a new structure with the three-layered spherical resonant units is proposed. Numerical results show that, making use of such kind of resonant units, a large sub-wavelength full band gap can be opened.
    Journal of Applied Physics 01/2014; 115(9):093508-093508-5. · 2.21 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: This paper explores the possibility of using AlN/sapphire piezoelectric bilayer structures for high-temperature SAW applications. To determine the temperature stability of AlN, homemade AlN/sapphire samples are annealed in air atmosphere for 2 to 20 h at temperatures from 700 to 1000°C. Ex situ X-ray diffraction measurements reveal that the microstructure of the thin film is not affected by temperatures below 1000°C. Ellipsometry and secondary ion mass spectroscopy investigations attest that AlN/sapphire is reliable up to 700°C. Beyond this temperature, both methods indicate ongoing surface oxidation of AlN. Additionally, Pt/Ta and Al interdigital transducers are patterned on the surface of the AlN film. The resulting SAW devices are characterized up to 500°C and 300°C, respectively, showing reliable frequency response and a large, quasi-constant temperature sensitivity, with a first-order temperature coefficient of frequency around -75 ppm/°C. Between room temperature and 300°C, both electromechanical coupling coefficient K(2) and propagation losses increase, so the evolution of delay lines' insertion losses with temperature strongly depends on the length of the propagation path.
    IEEE transactions on ultrasonics, ferroelectrics, and frequency control 05/2012; 59(5):999-1005. · 1.80 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Iridium is investigated as a potential metal for interdigital transducers (IDTs) in SAW devices operating at high temperatures. SAW delay lines based on such IDTs and langasite (LGS) substrate are fabricated and electrically characterized. The results show reliable frequency responses up to 1000°C. The strong increase of insertion losses beyond this temperature, leading to the vanishing of the signal between 1140 and 1200°C, is attributed to surface transformation of the LGS crystal, consisting of relevant gallium and oxygen losses, as evidenced by scanning electron microscopy, energy-dispersive X-ray spectroscopy, and secondary ion mass spectroscopy.
    IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control 02/2012; 59(2):194-7. · 1.82 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: In this paper, we report on the use of tantalum as adhesion layer for platinum electrodes used in high-temperature SAW devices based on langasite substrates (LGS). Tantalum exhibits a great adhesive strength and a very low mobility through the Pt film, ensuring a device lifetime at 900°C of about one hour in an air atmosphere and at least 20 h under vacuum. The latter is limited by morphological modifications of platinum, starting with the apparition of crystallites on the surface, followed by important terracing and breaking of the film continuity. Secondary neutral mass spectroscopy (SNMS), Auger electron spectroscopy (AES), X-ray diffraction (XRD) measurements, and comparison with iridium-based electrodes allowed us to show that this deterioration is likely intrinsic to platinum film, consisting of agglomeration phenomena. Finally, based on these results, we present a solution that could significantly enhance the lifetime of Pt-based IDTs placed in high-temperature conditions.
    IEEE transactions on ultrasonics, ferroelectrics, and frequency control 03/2011; 58(3):603-10. · 1.80 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: This paper describes the use of a general purpose modified simulator, first developed by K. Hashimoto to determine a priori the device responses of the specify Pt/LGS Y-X structure. The parameters for the analysis are determined as a function of the electrode type (physical constants, thickness) and substrate. The simulation responses are analyzed and compared to the experimental results and we should conclude how effectively the modified simulator is applicable to assessing Pt/LGS Y-X device performances as a function of temperature.
    01/2011;
  • [Show abstract] [Hide abstract]
    ABSTRACT: In this work, the performance of AlN/Sapphire structure in high frequencies is investigated. Several SAW devices were performed with various designs (gap, wavelength, metallization ratio, ...) to study simultaneously different parameters (acoustic velocity, electromechanical coupling (K2), acoustic propagation loss (α), TCF) versus frequency and temperature. Experimental results showed that as expected, a increases with temperature while K2 is enhanced at high temperatures. Due to the antagonistic evolution of these two parameters, insertion loss decreases or increases as function of the gap. We also evidenced that this structure allows fabrication of devices operating up to 1.5 GHz and that the frequency varies linearly with temperature.
    Sensors, 2011 IEEE; 01/2011
  • [Show abstract] [Hide abstract]
    ABSTRACT: This paper explores the potentiality to use AlN/sapphire structure as alternative piezoelectric material to langasite (LGS) for high-temperature SAW applications. In situ SAW measurements performed in vacuum up to 1050°C attest that AlN/Sapphire is more stable than LGS in such conditions. While in the case of LGS, the signal is completely lost after 8 hours at 1050°C, the device based on AlN/sapphire stays alive for 60 hours at this extreme temperature. Moreover, the degradation is attributed not to AlN but to the agglomeration phenomena undergone by the Iridium IDTs. The AlN/Sapphire structure shows also, between room temperature and at least 1050°C, a great sensitivity to temperature as well as a good linearity, which is very suitable for temperature sensor applications.
    Ultrasonics Symposium (IUS), 2011 IEEE International; 01/2011
  • Source
    Mourad Oudich, Yong Li, Badreddine M Assouar, Zhilin Hou
    [Show abstract] [Hide abstract]
    ABSTRACT: Using the finite element method, we have studied the acoustic properties of a novel phononic crystal (PC) structure constructed by periodically depositing single-layer or two-layer stubs on the surface of a thin homogeneous plate. Numerical results show that the extremely low frequency band gap (BG) of the Lamb waves can be opened by the local resonance (LR) mechanism. We found that the width of such a BG depends strongly on the height and the area of cross section of the stubs. The displacement field distribution of the oscillating modes is given to explain how the coupling of the modes induces the opening of the BG. The physics behind the opening of the LRBG in our phononic structures can be understood by using a simple 'spring-mass' model.
    New Journal of Physics 08/2010; 12(8):083049. · 4.06 Impact Factor
  • Source
    Li Yong, Hou Zhi-Lin, Fu Xiu-Jun, Badreddine M Assouar
    [Show abstract] [Hide abstract]
    ABSTRACT: It is well known that Lamb waves in a plate with a mirror plane can be separated into two uncoupled sets: symmetric and anti-symmetric modes. Based on this property, we present a revised plane wave expansion method (PWE) to calculate the band structure of a phononic crystal (PC) plate with a mirror plane. The developed PWE method can be used to calculate the band structure of symmetric and anti-symmetric modes separately, by which the depending relationship between the partial acoustic band gap (PABG), which belongs to the symmetric and anti-symmetric modes alternatively, and the position of the scatterers can be determined. As an example of its application, the band structure of the Lamb modes in a two-dimensional PC plate with two layers of void circular inclusions is investigated. The results show that the band structure for the symmetric and anti-symmetric modes can be changed by the position of the scatterers drastically, and larger PABGs will be opened when the scatterers are inserted into the area of the plate, where the elastic potential energy is concentrated.
    Chinese Physics Letters 07/2010; 27(7):074303. · 0.92 Impact Factor
  • Source
    Vincent Laude, Badreddine M Assouar, Zhilin Hou
    [Show abstract] [Hide abstract]
    ABSTRACT: We discuss the computation of the band structure of plate waves using the plane wave expansion (PWE) method. This method is generally used to formulate eigenvalue problems to compute dispersion diagrams for solid-solid phononic crystals. We show how the free surface boundary condition can be included implicitly in the form of the PWE solution, thus leading to an efficient eigenvalue problem. This generic method for wave dispersion is non-iterative and does not require an initial guess for the solution. Furthermore, surface acoustic wave velocities can be estimated from the slowest wave for large wave vectors. Examples for a single plate and a multilayer plate are given, and extension to piezoelectric materials is discussed.
    IEEE transactions on ultrasonics, ferroelectrics, and frequency control 07/2010; 57(7):1649-54. · 1.80 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: AlN/sapphire layered structure has been investigated as a potential substrate for surface acoustic wave (SAW) devices operating at high temperatures up to 950 °C under air atmosphere. Frequency characterizations of the SAW delay lines based on this structure indicate a slight increase of 2 dB in the insertion losses after annealing for 30 min at 900 °C. Scanning electron and atomic force microscopy as well as x-ray diffraction measurements suggest that theses losses are due to the deterioration of the Pt/Ta electrodes and to a slight oxidation of the AlN film.
    Applied Physics Letters 05/2010; 96(20):203503-203503-3. · 3.52 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: In this work, we have developed high frequency resonators for frequency source applications. These resonators were built using E-beam lithography on ZnO/NCD/Si substrate, exploiting the nucleation side of the NCD to allow for a reliable and reproducible lithography step. NCD films and substrates have also been used to minimize the acoustic losses due to large grain overlays favoring acoustic diffusion along the surface propagation. Single and double port resonators have been built in the 3-6 GHz frequency range. Double port resonators have revealed compatible with the oscillator application, yielding a first oscillator demonstration near 3 GHz. Considering the operation condition of this oscillator, one should improve the corresponding stability characteristics without too much efforts, simply developing an adapted packaging of the resonator and a robust low noise amplifier loop.
    Microelectronic Engineering 01/2010; · 1.22 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: This paper explores the possibility to use AlN/sapphire bilayer structure as substrate for surface acoustic wave (SAW) devices operating at high temperature in air atmosphere. Aluminium nitride (AlN) thin films deposited by magnetron sputtering on sapphire substrates were annealed for different periods (2 to 20 hours) and at different temperatures going from 700 to 1000°C. Investigated samples were characterized before and after annealing by X-ray diffraction (XRD), ellipsometry and secondary ion mass spectroscopy (SIMS). This experimental study attests that AlN/Sapphire is reliable up to 700°C in air. These results were also confirmed by in situ measurements of frequency responses coming from SAW devices based on Pt/AlN/Sapphire structure. Keywords-high-temperature; AlN; sapphire ; SAW
    01/2010;
  • Zhilin Hou, Badreddine M. Assouar
    [Show abstract] [Hide abstract]
    ABSTRACT: The mechanism of opening a band gap in the free phononic crystal (PC) thin plate with or without a mirror plane is investigated. It is found that, in a PC plate with a mirror plane, the permitted modes can be separated into symmetric and antisymmetric modes, and the band gap in such a system can be opened by the interaction between the modes of the same kind and/or the breaking of the degeneracy of the mode at the edge of the Brillouin zone. However, for a PC plate without a mirror plane, mode separation can no longer be performed, and interaction can occur between any two permitted modes. As a result, a new kind of band gap can be opened.
    12/2009: pages 325-331;
  • [Show abstract] [Hide abstract]
    ABSTRACT: We report on a novel method based on a plasma pretreatment for controlled nanostructuration and patterning of iron catalyst particles from a continuous film in view of carbon nanotube growth. The effects of the hydrogen plasma conditions on the diameter and the density of the catalyst nanoparticles was studied and discussed. We were then able to propose a comprehensive mechanism for the metallic nanostructuration. We showed that as the plasma power density increases, first a reduction of the iron nanoparticle size is observed followed by for the highest plasma powers a phenomenon of alteration in the deposited film. A better control of the nucleation process and the nanostructuration were observed for low hydrogen pressures. The correlation between the plasma parameters and the obtained iron nanoparticles was established. The growth of carbon nanotubes (CNTs) was carried out on the patterned catalyst nanoparticles under CH4/H2 microwave plasma. High quality double-walled and multiwalled CNTs of a diameter of about 5 nm have be obtained.
    Journal of Physical Chemistry C - J PHYS CHEM C. 05/2009; 113(20).
  • Zhilin Hou, Badreddine M Assouar
    [Show abstract] [Hide abstract]
    ABSTRACT: The propagation of wave modes in a two-layer free standing plate composed of a one-dimensional phononic crystal (PC) thin layer coated on a uniform substrate was investigated numerically by the modified plane wave expansion method. The band structures of the system with different thicknesses of the substrate were calculated. The numerical result showed that Bragg scattering by the periodic structure in a PC and wave scattering by the free surface could be coupled to each other with an added substrate layer. The properties of the confined modes in such a system, for example, the Love-wave-like mode, the confined PC mode (which is localized mainly in the PC layer) and the surface mode on the free surface of the substrate layer, were investigated.
    Journal of Physics D Applied Physics 03/2009; 42(8):085103. · 2.53 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: A lot of work has been dedicated to evaluate the interest of Diamond films for the development of high frequency surface acoustic wave (SAW) devices for various Radio- Frequency (RE) applications. The main interest of such a material consists in its very high acoustic phase velocities. In this work, different research groups are collaborating to identify the capability of diamond-based substrates to allow for the development of SAW resonators at 5 GHz and above, to stabilize RE oscillators in that frequency range. Nano-crystalline diamond (NCD) particularly is investigated in that matter, coupled with various piezoelectric layers. Design of single and double port SAW resonators operating near 5 GHz: are reported, as well as experimental results for SAW resonators built atop the considered material combinations These results allows for identifying the best configuration for the development of high frequency sources.
    01/2009;
  • [Show abstract] [Hide abstract]
    ABSTRACT: In this paper, we report on the use of tantalum and iridium as adhesion layers for platinum electrodes used in high temperature SAW devices based on langasite substrates (LGS). Unlike iridium, tantalum exhibits a great adhesive strength, and a very low mobility through the Pt film, ensuring a device lifetime of at least half an hour at 1000°C. The latter is limited by morphological modifications of platinum, starting by the apparition of crystallites on the surface, and followed by important terracing and breaking of the film continuity. SNMS and XRD measurements allowed us to show that these phenomena are likely intrinsic to platinum film, whatever be the nature of the adhesion layer. Finally, after having outlined a possible scenario leading to this deterioration, we consider some solutions that could replace platinum in order to increase the lifetime of LGS-based SAW devices in high temperatures conditions.
    01/2009;
  • [Show abstract] [Hide abstract]
    ABSTRACT: This work is oriented on the used of effective simulation tools to design high temperature SAW sensor. Physical constants of platinum and LGS and related temperature coefficients recently determined were implemented in FEM/SDA program. Plessky's parameters of the Pt/LGS structure were extracted for various temperatures and injected in COM software to calculate frequency response of SAW devices. A comparison between experimental and theoretical results showed good agreement up to 250degC and the requirement of a new LGS constants set.
    Ultrasonics Symposium, 2008. IUS 2008. IEEE; 12/2008
  • Zhilin Hou, Badreddine M Assouar
    [Show abstract] [Hide abstract]
    ABSTRACT: The mechanism of opening a band gap in the free phononic crystal (PC) thin plate with or without a mirror plane is investigated. It is found that, in a PC plate with a mirror plane, the permitted modes can be separated into symmetric and antisymmetric modes, and the band gap in such a system can be opened by the interaction between the modes of the same kind and/or the breaking of the degeneracy of the mode at the edge of the Brillouin zone. However, for a PC plate without a mirror plane, mode separation can no longer be performed, and interaction can occur between any two permitted modes. As a result, a new kind of band gap can be opened.
    Journal of Physics D Applied Physics 10/2008; 41(21):215102. · 2.53 Impact Factor