Frequency spectra

Fokker Bond Tester. An ultrasonic inspection technique commonly used for aircraft structures is based on ultrasonic spectroscopy [2]. Commercially available instruments (bond testers) used for this test operate on the principle of mechanical resonance in a multi-layer structure. A piezoelectric probe shown in Figure 3b, excited by a variable frequency sine signal is placed on the surface of the inspected structure. A frequency spectrum in the range of some tens of kHz to several MHz is acquired by the instrument, see Figure 3a. 

UTDefect is basically working in the frequency domain so pulse problems are solved by superposing a number of frequencies. In principal any frequency spectrum can be used (an experimental one, for instance). As the standard spectrum the following simple one is used... 

For immersion probes we also get similar improvements using piezocomposite transducers as demonstrated by the third example. In Fig. 8 we compare pulse form and frequency spectrum for a 2 MHz probe Z2K with 10 mm transducer diameter. The echo of the composite probe has 11 dB more amplitude and is clearly shorter than for the old design, also indicated by the increase in bandwidth from 45 to 76 %. 

The Investigation of Frequency Spectrum while Ultrasonic Wave Propogation in Anisotropic Media. 

To determine the influence degree on both types of structure and volume of structural heterogeneity on the frequency spectrum characteristics of an ultrasonic pulse, research work using angle beam and straight beam probes was performed... 

First, as the element width is very narrow, and though they have a large elevation, the reflector is placed very close to the elements. That is in violation to the standards rules [1], but experience shows no effect on the frequency spectrum. 

In order to obtain a high signal-to-noise ratio sufficient acoustical power is necessary. For special applications a programmable pulser (transmitter) is required in order to optimize the frequency spectrum. 

Impact Echo -result showing waveform (top), single wave spectrum with peak echoes (middle) and average frequency spectrum for a series of tests at the same point. 

In this section we discuss the frequency spectrum of excitations on a liquid surface. Wliile we used linearized equations of hydrodynamics in tire last section to obtain the density fluctuation spectrum in the bulk of a homogeneous fluid, here we use linear fluctuating hydrodynamics to derive an equation of motion for the instantaneous position of the interface. We tlien use this equation to analyse the fluctuations in such an inliomogeneous system, around equilibrium and around a NESS characterized by a small temperature gradient. More details can be found in [9, 10]. 

The frequency spectrum measured for the drum head motion is therefore seen to... 

This model permits one to immediately relate the bath frequency spectrum to the rate-constant temperature dependence. For the classical bath (PhoOc < 1) the Franck-Condon factor is proportional to exp( —with the reorganization energy equal to... 

Finding the values of G allows the determination of the frequency-domain spectrum. The power-spectrum function, which may be closely approximated by a constant times the square of G f), is used to determine the amount of power in each frequency spectrum component. The function that results is a positive real quantity and has units of volts squared. From the power spectra, broadband noise may be attenuated so that primary spectral components may be identified. This attenuation is done by a digital process of ensemble averaging, which is a point-by-point average of a squared-spectra set. 

WASH-1400 did not analyze seismic events, but if they had, the risk they assessed would have been larger. Earthquake analysis was part of the FSAR for licensing a plant and had been practiced for some time before the RSS. This analysis included earthquake frequencies from historical records, ground-coupling models to estimate the intensity and frequency spectrum of the acceleration, and spring-mass models to estimate the forces on plant components under the... 

The disturbance caused by a noise depends on its intensity (equivalent pressure level L in dB(A)), its frequency spectrum (that is its energy distribution), and the acoustic characteristics of the medium in which the listener is kicated. 

In microprocessor systems, the FFT signature is formed by breaking down the total frequency spectrum into unique components, or peaks. Each line or peak represents a specific frequency component that, in turn. 

Apparently, the digital resolution (DR) depends on the amount of computer memory used in recording the spectrum. If the memory size is M, then there will be M/2 real and M/2 imaginary data points in the frequency spectrum, and the separation (in hertz) between these data points (DR) will be given by ... 

Frequency spectrum A plot of signal amplitude versus frequency, produced by the Fourier transformation of a time-domain signal. 

Another restriction we may often wish to place on the laser pulse is to limit the frequency range of the electric held in the pulse. One method that has been used to accomphsh this is simply to eliminate frequency components of the held that lie outside a specihed range [63]. Another possibility is to use a frequency hlter, such as the twentieth-order Butterworth bandpass hlter [64], which is a smoother way of imposing basically the same restrictions [41, 42]. In order to impose such restrictions on the frequency content of the pulse, the time-dependent electric held of the laser pulse must be Fourier transformed so as to obtain its frequency spectrum. After the frequency spectrum of the laser pulse has been passed through the hlter, it is back transformed to yield back a... 

In Section 40.3.5 we concluded that the resolution (Av) in the frequency spectrum is equal to the reciprocal of the measurement time. The longer the measurement time in the time domain, the better the resolution is in the frequency domain. The opposite is also true the longer the measurement time in the frequency domain (e.g. in FTIR or FT NMR), the better is the separation of the peaks in the spectrum after the back-transform to the wavelength or chemical shift domain. 

FIG. 9 Vibrational sum frequency spectrum in the OH mode region of the neat air-water interface at different temperature for the fundamental visible and infrared beams respectively s- and p-polar-ized and the SFG beam s-polarized. (From Ref. 120, copyright American Physical Society.)... 

FIG. 10 Vibrational sum frequency spectrum of saturated monolayers of dilauroyl- (DLPQ, dimyristoyl- (DMPC), dipalmitoyl- (DPPC), and distearoyl-phosphatidylcholine (DSPC) at the D2O-CCI4 interface at ambient temperature in the region of the methylene and methyl symmetrical stretches. (From Ref 139, copyright American Chemical Society.)... 

The model system is a periodic box of arbitrary unit side length. A linear cutoff N = 8 in the frequency spectrum of the Fourier decomposition corresponds to a minimal characteristic length A = 0.125 for the scalar fields investigated systems have goal curvatures Co chosen from the set 0.1,0.2,0.5,1,5,10. ... 

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