The Experts below are selected from a list of 96 Experts worldwide ranked by ideXlab platform

Masahiko Hirao - One of the best experts on this subject based on the ideXlab platform.

  • Picosecond ultrasound spectroscopy for studying elastic modulus of thin films: a review
    Nondestructive Testing and Evaluation, 2011
    Co-Authors: Hirotsugu Ogi, Nobutomo Nakamura, Masahiko Hirao
    Abstract:

    This article introduces an advanced acoustic method for measuring the out-of-plane longitudinal-wave modulus of thin films using picosecond ultrasound. The ultrafast light pulse is focused on the film surface to excite the coherent acoustic pulse, which propagates in the Thickness direction, and then, the time delayed probing light pulse irradiates the specimen for detecting the acoustic waves. For opaque thin films, the pulse echoes within the film or the Thickness Resonance Frequency of the film is measured to determine the modulus. For transparent films, Brillouin oscillations from the film are observed, and their frequencies yield the modulus. The film Thickness and refractive index are measured by X-ray reflectivity and ellipsometry, respectively. This method was applied to various thin films, providing important knowledge about the elasticity of thin films. Most thin films are softer than corresponding bulk materials, but some thin films are significantly stiffer.

  • Significant softening of copper nanowires during electromigration studied by picosecond ultrasound spectroscopy
    Physical Review B, 2010
    Co-Authors: Hirotsugu Ogi, A. Yamamoto, K. Kondou, K. Nakano, Ken-ichi Morita, Nobutomo Nakamura, Teruo Ono, Masahiko Hirao
    Abstract:

    High-Frequency vibrations related with copper nanowires on a silicon substrate are studied using picosecond ultrasound spectroscopy. The reflectivity change in the probe light pulse is monitored after irradiation of the specimen with the ultrafast light pulse, showing high $(\ensuremath{\sim}75\text{ }\text{GHz})$ and low $(l\ensuremath{\sim}15\text{ }\text{GHz})$ Frequency vibrations, which are identified to be Thickness Resonance of nanowires and collective-mode Resonances on the substrate, respectively. The nanowires are subjected to the current-loading test to induce electromigration. The Thickness Resonance Frequency significantly decreases as the progress of the electromigration while the other frequencies and the resistance remain nearly unchanged. The micromechanics analysis and the vacancy diffusion theory indicate the growth of thin defects at grain boundaries for softening the nanowires.

F. Montero De Espinosa - One of the best experts on this subject based on the ideXlab platform.

  • Nonlinear characterization with burst excitation of 1-3 piezocomposite transducers.
    Ultrasonics, 2003
    Co-Authors: J. A. Casals, A. Albareda, R. Pérez, José E. García, E. Minguella, F. Montero De Espinosa
    Abstract:

    Ultrasonic transducers made with 1–3 connectivity piezocomposites are frequently used in Medical applications and nondestructive testing. When the transducer is used for special applications as, for instance air-coupled transmission, it is necessary to compensate for the high difference of acoustic impedance between transducer and medium using high amplitude pulses to generate high acoustic signal. Thus, the nonlinear behavior of the transducer must be taken into account in similar application conditions. The newly developed method, which performs the nonlinear characterization with burst signal excitation near the Thickness Resonance Frequency, is based on the measure of the current as well as the vibration velocity of the piezocomposite transducer. The current of the stationary response is measured before the end of the burst signal excitation. Burst excitation enables us to measure the nonlinear characterization without producing overheating in the transducers. The amplitude level dependence of mechanical losses tanδm and the stiffness increases |Δc/c0| have been studied, as well as the velocity dependence of a point of the transducer, measured with a laser vibrometer. In this method, the power level applied to the transducers can be higher than other nonlinear measurement methods, providing measurements of high accuracy.

  • Nonlinear Measurements of High Power 1-3 Piezo-Air-Transducers with Burst Excitation
    Ferroelectrics, 2002
    Co-Authors: A. Albareda, J. A. Casals, R. Pérez, F. Montero De Espinosa
    Abstract:

    High power resonant transducers made with 1-3 piezocomposites are widely used in Non Destructive Testing (NDT) for industry and ultrasonic medical devices. A new nonlinear characterization method with burst excitation, in similar conditions to those in air-transducer applications, is proposed. It measures both the current flowing and the vibration velocity in the piezocomposite transducers, just before the end of the burst signal excitation, near the Thickness Resonance Frequency for different piezocomposites. Three amplitude level dependencies have been studied: a) mechanical loss tangent tan i m , b) the stiffness variations j c / c 0 and c) the ratio between velocity and current. This method allows us to characterize accurately the nonlinearity of piezocomposites as well as ceramics of low or high mechanical quality factor, avoiding the overheating of the transducer.

Hirotsugu Ogi - One of the best experts on this subject based on the ideXlab platform.

  • Picosecond ultrasound spectroscopy for studying elastic modulus of thin films: a review
    Nondestructive Testing and Evaluation, 2011
    Co-Authors: Hirotsugu Ogi, Nobutomo Nakamura, Masahiko Hirao
    Abstract:

    This article introduces an advanced acoustic method for measuring the out-of-plane longitudinal-wave modulus of thin films using picosecond ultrasound. The ultrafast light pulse is focused on the film surface to excite the coherent acoustic pulse, which propagates in the Thickness direction, and then, the time delayed probing light pulse irradiates the specimen for detecting the acoustic waves. For opaque thin films, the pulse echoes within the film or the Thickness Resonance Frequency of the film is measured to determine the modulus. For transparent films, Brillouin oscillations from the film are observed, and their frequencies yield the modulus. The film Thickness and refractive index are measured by X-ray reflectivity and ellipsometry, respectively. This method was applied to various thin films, providing important knowledge about the elasticity of thin films. Most thin films are softer than corresponding bulk materials, but some thin films are significantly stiffer.

  • Significant softening of copper nanowires during electromigration studied by picosecond ultrasound spectroscopy
    Physical Review B, 2010
    Co-Authors: Hirotsugu Ogi, A. Yamamoto, K. Kondou, K. Nakano, Ken-ichi Morita, Nobutomo Nakamura, Teruo Ono, Masahiko Hirao
    Abstract:

    High-Frequency vibrations related with copper nanowires on a silicon substrate are studied using picosecond ultrasound spectroscopy. The reflectivity change in the probe light pulse is monitored after irradiation of the specimen with the ultrafast light pulse, showing high $(\ensuremath{\sim}75\text{ }\text{GHz})$ and low $(l\ensuremath{\sim}15\text{ }\text{GHz})$ Frequency vibrations, which are identified to be Thickness Resonance of nanowires and collective-mode Resonances on the substrate, respectively. The nanowires are subjected to the current-loading test to induce electromigration. The Thickness Resonance Frequency significantly decreases as the progress of the electromigration while the other frequencies and the resistance remain nearly unchanged. The micromechanics analysis and the vacancy diffusion theory indicate the growth of thin defects at grain boundaries for softening the nanowires.

Xin Cheng - One of the best experts on this subject based on the ideXlab platform.

  • Identifying technology for structural damage based on the impedance analysis of piezoelectric sensor
    Construction and Building Materials, 2010
    Co-Authors: Xin Cheng, Shifeng Huang, Minhua Jiang
    Abstract:

    Abstract PZT piezoelectric ceramic was used as sensing element to fabricate piezoelectric sensor. The fabricated PZT piezoelectric sensor was embedded into and affixed to the structure to detect the structural damage, respectively. The structural crack damage was investigated using the impedance spectra of the sensor. The results show that the electric impedance of the PZT piezoelectric sensor with both different arrangements can reflect the variations of the structural crack damage in the testing Frequency ranges. In the Frequency range of 20–70 kHz, both the impedance value and the Resonance Frequency of the embedded PZT piezoelectric sensor can show the incipient crack damage and the increase of crack depth clearly. The impedance spectra of the affixed and embedded PZT piezoelectric sensors show the similar variation regularity with increasing the structural crack damage degree. Furthermore, the impedance spectra variation of the PZT piezoelectric sensor with different arrangements in the Thickness Resonance Frequency range is more obvious than that in the planar Resonance Frequency range. A scalar damage metric is presented based on the impedance spectra of the PZT piezoelectric sensor around the Resonance Frequency, and the cracks in different positions of the structure were also analyzed using the damage metric. The variation of structural crack damage can be observed effectively and obviously using this damage metric.

  • Fine scale 2-2 connectivity PZT/epoxy piezoelectric fiber composite for high Frequency ultrasonic application
    Sensors and Actuators A: Physical, 1
    Co-Authors: Hongyu Jia, Bo Lin, Liu Peng, Xin Cheng
    Abstract:

    Abstract High Frequency piezoelectric fiber composites have extensive application in fields of biomedical imaging, ultrasonic inspection, underwater acoustic imaging and so forth. In this paper, fine scale 2-2 connectivity PZT/epoxy piezoelectric fiber composites were tailored by using the dicing-filling-pressing method with poled ferroelectric ceramic (PZT) and epoxy resin, respectively. The effects of Thickness and volume fraction of PZT ceramic on piezoelectric, dielectric, and acoustic properties of the composites were discussed. The results showed that the piezoelectric strain constant, relative permittivity (e33T), Thickness electromechanical coupling coefficient (kt), mechanical quality factor (Qm) and acoustic impedance of the composites exhibit an increasing trend with the increase of the volume fraction of the PZT ceramics, while the piezoelectric voltage constant (g33) showed a decreasing trend. In the low Frequency range of 60-90 kHz, the planar Resonance peaks can be observed in the impedance-Frequency spectra, while in the high Frequency range of 2-6 MHz, there only exist clear Thickness Resonance peaks. With increasing the PZT volume fraction, the bandwidth of the Thickness vibration mode of the piezoelectric fiber composites under the same Thickness increases gradually. When the PZT volume fraction keep unchanged, the Thickness Resonance Frequency of the composites increases with decreasing the Thickness as well as the bandwidth of the Thickness vibration mode, which is conducive for improving the Frequency response range of the ultrasonic transducer made of the proposed piezoelectric fiber composites.

Nobutomo Nakamura - One of the best experts on this subject based on the ideXlab platform.

  • Picosecond ultrasound spectroscopy for studying elastic modulus of thin films: a review
    Nondestructive Testing and Evaluation, 2011
    Co-Authors: Hirotsugu Ogi, Nobutomo Nakamura, Masahiko Hirao
    Abstract:

    This article introduces an advanced acoustic method for measuring the out-of-plane longitudinal-wave modulus of thin films using picosecond ultrasound. The ultrafast light pulse is focused on the film surface to excite the coherent acoustic pulse, which propagates in the Thickness direction, and then, the time delayed probing light pulse irradiates the specimen for detecting the acoustic waves. For opaque thin films, the pulse echoes within the film or the Thickness Resonance Frequency of the film is measured to determine the modulus. For transparent films, Brillouin oscillations from the film are observed, and their frequencies yield the modulus. The film Thickness and refractive index are measured by X-ray reflectivity and ellipsometry, respectively. This method was applied to various thin films, providing important knowledge about the elasticity of thin films. Most thin films are softer than corresponding bulk materials, but some thin films are significantly stiffer.

  • Significant softening of copper nanowires during electromigration studied by picosecond ultrasound spectroscopy
    Physical Review B, 2010
    Co-Authors: Hirotsugu Ogi, A. Yamamoto, K. Kondou, K. Nakano, Ken-ichi Morita, Nobutomo Nakamura, Teruo Ono, Masahiko Hirao
    Abstract:

    High-Frequency vibrations related with copper nanowires on a silicon substrate are studied using picosecond ultrasound spectroscopy. The reflectivity change in the probe light pulse is monitored after irradiation of the specimen with the ultrafast light pulse, showing high $(\ensuremath{\sim}75\text{ }\text{GHz})$ and low $(l\ensuremath{\sim}15\text{ }\text{GHz})$ Frequency vibrations, which are identified to be Thickness Resonance of nanowires and collective-mode Resonances on the substrate, respectively. The nanowires are subjected to the current-loading test to induce electromigration. The Thickness Resonance Frequency significantly decreases as the progress of the electromigration while the other frequencies and the resistance remain nearly unchanged. The micromechanics analysis and the vacancy diffusion theory indicate the growth of thin defects at grain boundaries for softening the nanowires.