Based on the piezo-optic effect of medium, the refractive index of medium is the function of its density, and so it's also the function of acoustic pressure. Therefore, acoustic pressure in the optical path everyw...Based on the piezo-optic effect of medium, the refractive index of medium is the function of its density, and so it's also the function of acoustic pressure. Therefore, acoustic pressure in the optical path everywhere can be determined absolutely by laser-interferometric technique and relative distribution of pressure in the middle and far acoustic field, which can be obtained from theory or experiment respectively. Theory and experiment of measurement of pressure in acoustic field with laser-interferometer are introduced. Distribution of pressure radiated by a power ultrasonic transducer is determined by laser interferometric technique. The theoretical and experimental results are in good agreement. The receiving sensitivity of a PVDF (Polyvinylidene fluoride) transducer in free field is also calibrated absolutely due to above results and its sensitivity is -118.5 dB.展开更多
In order to understand the viscoelasticity of material, this research has been conducted to study the propagation characteristics of viscoelastic Rayleigh wave theoretically. A model is presented for the pulsed laser ...In order to understand the viscoelasticity of material, this research has been conducted to study the propagation characteristics of viscoelastic Rayleigh wave theoretically. A model is presented for the pulsed laser generation of ultrasound on viscoelastic medium surface. Referred to the Kelvin model, the frequency equation and the normal displacement of viscoelastic Rayleigh wave were derived, the influence of the viscoelastic modulus on dispersion and attenuation was discussed. From the theoretical calculation, it is shown that the effect of viscoelasticity on the attenuation of Rayleigh wave is more than that on its dispersion. In the case of a weak viscosity, the attenuation of viscoelastic Rayleigh wave is directly proportional to viscosity modulus; the effect of shear viscosity on the attenuation is much more than that of bulk viscosity. The transient response of viscoelastic Rayleigh wave was also simulated using Laplace and Hankel inversion transform, which are showed in good agreement with the theoretic predictions. The model provides a useful tool for the determination of viscoelastic parameters of medium.展开更多
The one-dimension thermal conduction equation and Navier-Stokes equa tion are used to get a pulse stress wave in a scmi-infinitc medium when a rectangular pulse laser of duration t_0 is incident on its surface. For bo...The one-dimension thermal conduction equation and Navier-Stokes equa tion are used to get a pulse stress wave in a scmi-infinitc medium when a rectangular pulse laser of duration t_0 is incident on its surface. For both tfansparent and opaque samples the ultrasonic stress waveforms arc discussed when the sample surface is con strained or free. The experimental results in these two different boundary conditions of an opaque sample are presented. It is shown, theoretically and experimentally,that the ultrasound pulse thermoelastically generated by a pulse laser is monopolar when the sample surface is constrained and it is bipolar when its surface is free.展开更多
The thermal conduction and Navier- Stokes equations are used to obtain the stress field generated by a chopped electron beam incident on a disk sample. The piezoelectric equation is then used to obtain the output sign...The thermal conduction and Navier- Stokes equations are used to obtain the stress field generated by a chopped electron beam incident on a disk sample. The piezoelectric equation is then used to obtain the output signal of the transducer coupled to the sample. The results lead to a consideration of the signal generation mechanism and spatial resolution in scanning electron acoustic microscopy ( SEAM). It is shown that a time- variant heat source generated both a thermal wave and an acoustic wave simultaneously, and thermal- to- acoustic wave mode conversion oc-cured on the boundary surfaces depends on the amplitudes and the gradients at boundary surfaces of both heat source and thermal waves. It is argued that the spatial resolution of a imaging system operated in the near field, such as SEAM and thermal wave microscope, is dependent on the distance between the heat source and scatterer and, at best, the lateral resolution in SEAM is of the order of the diameter of the focal spot of the electron beam.展开更多
基金National Natural Science Foundation of China!(No.59738150)
文摘Based on the piezo-optic effect of medium, the refractive index of medium is the function of its density, and so it's also the function of acoustic pressure. Therefore, acoustic pressure in the optical path everywhere can be determined absolutely by laser-interferometric technique and relative distribution of pressure in the middle and far acoustic field, which can be obtained from theory or experiment respectively. Theory and experiment of measurement of pressure in acoustic field with laser-interferometer are introduced. Distribution of pressure radiated by a power ultrasonic transducer is determined by laser interferometric technique. The theoretical and experimental results are in good agreement. The receiving sensitivity of a PVDF (Polyvinylidene fluoride) transducer in free field is also calibrated absolutely due to above results and its sensitivity is -118.5 dB.
基金the Natinal Natural Science Foundation of China (10234060,10134020)
文摘In order to understand the viscoelasticity of material, this research has been conducted to study the propagation characteristics of viscoelastic Rayleigh wave theoretically. A model is presented for the pulsed laser generation of ultrasound on viscoelastic medium surface. Referred to the Kelvin model, the frequency equation and the normal displacement of viscoelastic Rayleigh wave were derived, the influence of the viscoelastic modulus on dispersion and attenuation was discussed. From the theoretical calculation, it is shown that the effect of viscoelasticity on the attenuation of Rayleigh wave is more than that on its dispersion. In the case of a weak viscosity, the attenuation of viscoelastic Rayleigh wave is directly proportional to viscosity modulus; the effect of shear viscosity on the attenuation is much more than that of bulk viscosity. The transient response of viscoelastic Rayleigh wave was also simulated using Laplace and Hankel inversion transform, which are showed in good agreement with the theoretic predictions. The model provides a useful tool for the determination of viscoelastic parameters of medium.
文摘The one-dimension thermal conduction equation and Navier-Stokes equa tion are used to get a pulse stress wave in a scmi-infinitc medium when a rectangular pulse laser of duration t_0 is incident on its surface. For both tfansparent and opaque samples the ultrasonic stress waveforms arc discussed when the sample surface is con strained or free. The experimental results in these two different boundary conditions of an opaque sample are presented. It is shown, theoretically and experimentally,that the ultrasound pulse thermoelastically generated by a pulse laser is monopolar when the sample surface is constrained and it is bipolar when its surface is free.
文摘The thermal conduction and Navier- Stokes equations are used to obtain the stress field generated by a chopped electron beam incident on a disk sample. The piezoelectric equation is then used to obtain the output signal of the transducer coupled to the sample. The results lead to a consideration of the signal generation mechanism and spatial resolution in scanning electron acoustic microscopy ( SEAM). It is shown that a time- variant heat source generated both a thermal wave and an acoustic wave simultaneously, and thermal- to- acoustic wave mode conversion oc-cured on the boundary surfaces depends on the amplitudes and the gradients at boundary surfaces of both heat source and thermal waves. It is argued that the spatial resolution of a imaging system operated in the near field, such as SEAM and thermal wave microscope, is dependent on the distance between the heat source and scatterer and, at best, the lateral resolution in SEAM is of the order of the diameter of the focal spot of the electron beam.
