Acoustic Wave Filter Based on Periodically Poled Lithium Niobate

International audienceWe present results on the development of an acoustic bandpass filter based on periodically poled ferroelectric domains in lithium niobate. The fabrication of Periodically Poled Transducers (PPT) operating in the range 20 - 650 MHz has been achieved on a 3 '' 500 mu m thick wafer. This kind of transducer enables to excite elliptical as well as longitudinal modes, yielding phase velocity of about 3800 and 6500 m. s(-1) respectively. We propose then a new type of acoustic bandpass filter based on the use of PPTs instead of classical IDTs. The design and the fabrication of such a filter are presented as well as the experimental measurements. Finally we demonstrate the feasibility of such a PPTs-based filter

New acoustic resonator based on periodically poled transducer in lithium niobate or tantalate

International audienceIn this paper, we propose a new concept of acoustic resonator based on a waveguide structure. In the telecommunication market, composants used are indeed generally bases on Surface Acoustic Wave (SAW) or Bulk Acoustic Wave (BAW) devices. However, those systems present technological limits as short-circuits between the electrodes of the interdigital transducers (for SAW device) or the precise control of the piezoelectric material thick resonator (for BAW device). We suggest a new concept based on a periodically poled transducer (PPT) in a ferroelectric substrate (LiNbO(3) or LiTaO(3)), embedded between two guiding substrates in order to create an acoustic waveguide. Periodically poled transducers have been investigated recently as an alternative to classical inter-digital transducers for the excitation and detection of guided acoustic waves. A resonator operating at 131MHz has been successfully fabricated and used in order to stabilize an oscillator at this frequency. However, the developed resonator presents a significant thermal sensitivity. The following experiments have consisted in studying a Si/thinned PPT layer/Si structure in order to reduce the thermal sensitivity

Acoustic wave filter based on periodically poled lithium niobate

International audienceSolutions for the development of compact RF passive transducers as an alternative to standard surface or bulk acoustic wave devices are receiving increasing interest. This article presents results on the development of an acoustic band-pass filter based on periodically poled ferroelectric domains in lithium niobate. The fabrication of periodically poled transducers (PPTs) operating in the range of 20 to 650 MHz has been achieved on 3-in (76.2-mm) 500-μm-thick wafers. This kind of transducer is able to excite elliptical as well as longitudinal modes, yielding phase velocities of about 3800 and 6500 ms(-1), respectively. A new type of acoustic band-pass filter is proposed, based on the use of PPTs instead of the SAWs excited by classical interdigital transducers. The design and the fabrication of such a filter are presented, as well as experimental measurements of its electrical response and transfer function. The feasibility of such a PPT-based filter is thereby demonstrated and the limitations of this method are discussed

Acoustic resonator based on periodically poled transducers: Concept and analysis

International audienceThe demand for highly coupled high quality acoustic wave devices for radio-frequency (RF) signal processing based on passive devices has generated a strong innovative activity, yielding the investigation of new excitation principles and waveguide structures. Periodically poled transducers (PPTs) have been recently investigated [E. Courjon et al., J. Appl. Phys. 102, 114107 (2007)], as an alternative to classical interdigital transducers (IDTs) for the excitation and detection of guided acoustic waves. PPTs have two principal advantages compared to IDTs: the robustness of the excitation versus defects or surface contamination and the possibility to excite waves exhibiting a wavelength equal to the poling period. Here a new acoustic resonator concept is suggested, allowing high frequency operation with a simplified package. The idea consists of using a waveguide based on a PPT fabricated on a ferroelectric single-crystal substrate such as lithium niobate or tantalate inserted between two single-crystal substrates allowing the guidance of elastic waves without losses. The concept analysis points out optimum configurations of the structure allowing the excitation of elastic waves compatible with RF applications

A flux grown KTP crystal ridge optical waveguide for birefringence phase-matched second-harmonic generation

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Detector-electrode for alpha spectrometry in water sample, numerical and early feasibility investigation toward thermocompression bonding assembly process

International audienceThis study focuses on the feasibility of a detector-electrode for direct alpha measurement in aqueous samples. Such a device could be made by adding a boron doped diamond electrode on top of a standard silicon detector, with bonding and insulating layers. The impact of these different layers has been investigated by Monte-Carlo simulation (MCNP6), to find a compromise between alpha detection of the silicon, electrode and shielding properties of the diamond. The assembly process involving thermocompression between both substrates was successfully achieved under a clean room conditions

Fabrication and characterization of acoustic waveguides using Silicon/PPT/Silicon structures and analysis of diffraction effects for various modelings

International audienceIn this paper, we present new results on the development of a new acoustic waveguide concept using an. acoustic wave excited by a Periodically Poled Transducer (PPT) and guided by guiding layers. Periodically poled transducers have been investigated recently as an alternative to classical inter-digital transducers for the excitation and detection of guided acoustic waves. The fabrication of PPTs operating in the range 50 - 500 MHz has been achieved on 3 and 4 inches 500 mu m thick lithium niobate (LiNbO3) and tantalate (LiTaO3) Z-cut wafers. The compact structure proposed allows high frequency operation with a simplified package based on Si/LiNbO3/Si material combination. Dispersion properties have been studied for this structure in order to find operating points corresponding to a specific wthickness/period ratio. Two main devices have been fabricated, a Si/500 mu m thick PPT/Si structure in order to validate the concept and a Si/20 mu m thick PPT/Si structure to excite only one acoustic wave in the purpose of diffracting this wave. The experimental responses of the tested devices are compared to the predicted harmonic admittances, showing a good agreement between both results. The temperature sensitivity of the excited wave of both structures are also been measured and predicted. Finally, we expose different structures with impedance mismatches generating scattering effects

A flux grown KTP crystal ridge optical waveguide for birefringence phase-matched second-harmonic generation

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Cytomegalovirus, Chlamydia pneumoniae, and Helicobacter pylori IgG antibodies and restenosis after stent implantation: an angiographic and intravascular ultrasound study

OBJECTIVE—To determine the impact of previous infection with cytomegalovirus, Chlamydia pneumoniae, and Helicobacter pylori on neointimal proliferation after coronary angioplasty with stent implantation.
DESIGN—The study population was made up of 180 patients who had stent implantation in a native coronary artery with systematic angiographic and intravascular ultrasound (IVUS) follow up at six months. Quantitative coronary angiography was used to assess the late lumen loss. The mean area of neointimal tissue within the stent and the ratio of neointimal tissue to stent area were assessed from IVUS images. Previous cytomegalovirus, C pneumoniae, and H pylori infection was identified by IgG antibody determination.
RESULTS—Previous cytomegalovirus infection was detected in 50% of the population, previous C pneumoniae in 18%, and previous H pylori in 33%. Mean (SD) reference diameter was 2.94 (0.48) mm and mean minimum lumen diameter after stent implantation was 2.45 (0.42) mm. At six months, the mean late loss was 0.74 (0.50) mm, the mean neointimal tissue area was 3.8 (1.7) mm(2), and the average ratio of neointimal tissue area to stent area was 45 (18)%. None of these variables of restenosis was linked to any of the three infectious agents. By multivariate analysis, lesion length was the variable best correlated with mean neointimal tissue area, the ratio of neointimal tissue to stent area, and late loss, explaining respectively 31%, 39%, and 8% of their variability.
CONCLUSIONS—Previous infection with cytomegalovirus, C pneumoniae, or H pylori was not a contributing factor in the process of restenosis after stent implantation.


Keywords: restenosis; stent; ultrasonics; angiography; infectio