Impulsive Pulse Research Articles

1P1-O04 パリレンを用いた送受兼用可能なコンデンサ型MEMS超音波センサの開発(MEMSとナノテクノロジー)

The final goal of this research is to develop a condenser type micro ultrasonic sensor, which would be used as both receiver and transmitter. Polymer diaphragm is flexible and non-brittle, allowing good sensitivity and durability. Besides that, Parylene has good C-MOS compatibility, since it can be deposited at room temperature. Based on the FEM simulation results on the resonant frequency under tensile stress of Parylene, the diaphragm radius of 500〜1200 μm is employed to realize the bandwidth up to ultrasonic range of 40〜100 kHz. The influence of the number and the radius of acoustic holes on damping ratio is investigated by FEM simulation, in order to achieve a moderate damping of the diaphragm. Practical sensor devices are fabricated. They can receive an impulsive ultrasonic pulse transmitted by a spark discharge. The open-circuit sensitivity is 0.3 mV/Pa, in reference to B&K 4138 microphone. The ranging system using this sensor can detect the distance up to 1 m with the error less than 1 mm. The developed sensor can be approximated to be non-directional.

A nonperturbative calculation of nonlinear spectroscopic signals in liquid solution

Nonlinear spectroscopic signals in liquid solution were calculated without treating the field-matter interaction in a perturbative manner. The calculation is based on the assumption that the intermolecular degrees of freedom can be treated classically, while the time evolution of the electronic state is treated quantum mechanically. The calculated overall electronic polarization is then resolved into its directional components via the method of Seidner et al. [J. Chem. Phys. 103, 3998 (1995)]. It is shown that the time dependence of the directional components is independent of laser intensity in the impulsive pulse regime, which allows for flexibility in choosing the procedure for calculating optical response functions. The utility and robustness of the nonperturbative procedure is demonstrated in the case of a two-state chromophore solvated in a monoatomic liquid, by calculating nonlinear time-domain signals in the strong-field, weak-field, impulsive, and nonimpulsive regimes.

Shear viscoelasticity of ultrasonic couplers by broadband reflectivity measurements

The acoustic shear wave velocity and attenuation of ultrasonic couplers were investigated by broadband reflectivity measurements at around room temperature and 15–30 MHz. The feature of the present technique is to use impulsive pulse and normal incident waves against a reflective interface. Its characteristics are compared with the inclined incident wave technique used so far. It is found that the normal incident wave technique is nearly free from the effects of diffraction in contrast with the inclined incident wave technique. In the present work, the acoustic shear properties and their temperature dependence were investigated for nine commercial couplers at 15, 25, and 35 °C. The shear wave velocity dispersion was clearly observed in every measurement in the investigated frequency range; these data are useful for design in ultrasonic shear wave experiments. Furthermore, a linear relationship was found between the rigidity and Q value for hydroxyl carbons and naphten oils. The difference in the physical properties can be attributed to differences in the chemical properties of the samples. Therefore, the present technique is useful for investigating both the macroscopic and microscopic properties of viscoelastic materials.

Air Impact Drive for Positioning by Pulse and Continuous Air Pressure

In recent years, the application of impacts to precise positioning has been increased. Previously, the impulsive force or impact was generated by electromagnetic impulsive force or by the sudden deformation of a piezoelement. In this paper, a new actuator named as Air Impact Drive (AID) is introduced, in which the impact is generated by impulsive air pulse pressure. Free body diagrams and equations of this new actuator were drawn and determined. Experimental and theoretical results are in good agreement. The new actuator could displace a 0.2kg object at 0.1 of millimeter per pulse by pulse air pressure. By implementing suitable setup of parameters, the AID could move the object by continuous, constant air pressure with good linearity. This property is unique among other impact drives for positioning. By 0.3Mpa of source air pressure, the new actuator could move the mentioned object at the speed of approximately 13.4mm/s.

Excitation without demolition: Radiative excitation of ground-surface vibration by impulsive stimulated Raman scattering with damage control.

A pulse shaping strategy is developed for exciting the ground-surface vibrational motion while minimizing radiation damage. The scheme is based on a resonant impulsive stimulated Raman scattering process where the amount of population transferred to the excited surface is strictly controlled. The scenario begins with an impulsive pulse which creates an instantaneous dipole moment. It follows by a pulse 180\ifmmode^\circ\else\textdegree\fi{} out of phase with the instantaneous dipole which deposits vibrational energy into the ground electronic surface while blocking population transfer to the excited surface.

Theory of dynamic absorption spectroscopy of nonstationary states. 4. Application to 12-fs resonant impulsive Raman spectroscopy of bacteriorhodopsin

A time-dependent theory for femtosecond dynamic absorption spectroscopy is used to describe the creation and observation of molecular ground-state vibrational coherence through the resonance impulsive stimulated Raman mechanism. Model calculations show that the oscillatory absorption signal that arises from this ground-state coherence is maximized for a limited range of pulse lengths and that there is a complex relationship between the probe wavelength and the strength of the spectral oscillations. The generalized time-dependent linear susceptibility of the nonstationary system created by the impulsive pump pulse is defined and used to discuss the strong dependence of the measured signals on the properties of the probe pulse. Finally, calculations are presented to analyze the high-frequency oscillations ({approximately}20-fs period) recently observed in the transient absorption spectra of light-adapted bacteriorhodopsin (BR{sub 568}) following excitation with a 12-fs optical pulse. At the probe wavelengths used in this experiment, the contribution of stimulated emission is negligible at long times because of the extremely rapid excited-state isomerization; as a result, the spectral oscillations observed after this time are due to the impulsive excitation of coherent vibrations in the ground state. The transient response observed for BR{sub 568} is calculated using a 29-mode harmonic potential surface derived from amore » prior resonance Raman intensity analysis. Both the oscillatory signals and their dependence on the probe wavelength are satisfactorily reproduced. 68 refs., 11 figs.« less

Effect of Depth of a Point Source on the Motion of the Surface of an Elastic Solid Sphere

Summary An exact solution, obtained previously for the displacement of the surface of a uniform elastic solid sphere due to an impulsive compressional pulse from a point-source situated at depth d below the surface of a sphere of radius a is applied here to the problem of propagation from a source at d = a/32 and a/6400 and compared with results for d= a/8. Theoretical seismograms, radial and angular component, are given at distances 0 < θ < π from the source. Rayleigh waves are found due to all sources. In the high frequency limit they have the velocity of Rayleigh waves in a homogeneous half space. There is dispersion towards higher velocities. The Rayleigh waves from the shallow source have amplitudes more than ten times the amplitude of body waves. In the seismograms from the medium and deep sources their amplitude is smaller, they have less high-frequency components and show more dispersion. The amplitude of Rayleigh waves has a minimum at 90|Mo and 270|Mo. At 180|Mo and 360|Mo the radial component has a maximum of ten, seventeen and forty times the radial component at 90|Mo for the deep, medium and shallow sources respectively. The ratio of angular to radial amplitude is largest at 90|Mo and 270|Mo, decreasing to zero at 180|Mo and 360|Mo. The Rayleigh waves show phase shift, almost elliptical retrograde particle motion, change in form of ellipses with depth of source and deviations of the direction of the major axis from the vertical direction similar to results in observed seismograms. Higher modes of surface waves are found and their connection with groups of reflected pulses of mixed types given. As in several observed seismograms the second mode is especially predominant in the angular component. Whereas diffracted pulses connected with μ times reflected Pμ are encountered mainly in deep-focus events, diffraction phenomena connected with the transformed phases PμSv are found here at all depths and have in several cases amplitudes comparable to, or larger than, the reflected pulses.

Propagation of a P-pulse in a solid sphere

abstract An exact solution is obtained for the displacement of the surface of a uniform elastic solid sphere of radius a due to an impulsive compressional pulse from a point-source situated at a distance b from the center. The duration of the source is δa/c where c denotes the shear-wave velocity, and its time-variation is such that the surface-displacement stays finite when the time tends to infinity. The solution is applied to a source at a distance of one-eighth of the radius below the surface, approximating a deep-focus earthquake. Theoretical seismograms, radial and angular component, are given at distances 0 &amp;lt; ϑ &amp;lt; π for a source of duration 0.03a/c. Rayleigh waves are clearly seen at ϑ ≧ 45 °. Groups of reflected waves, especially predominant in the angular component, have the velocity of the lowest Airy phase in the group-velocity dispersion-curves. Diffracted waves, discussed in a previous paper, are found here again and in certain cases have an amplitude seven times larger than the amplitude of the direct pulse and also larger than any of the reflected pulses at the same distance. The transformed phases PSn, P2Sn have in general larger amplitude than the reflected Pn. Arrival times, initial amplitudes, reflection and convergence coefficients of pulses are obtained by steepest descents analysis and compared with the complete results.