FREQUENCY-RESPONSE MEASUREMENTS

The frequency response measured between a pair of transducers having A<, = 32 ftm and Np = 50 finger pairs is shown in Figure 3.21 (page 79). The amplitude, shown on a log (decibel) scale, shows the characteristic sin(X)/X behavior. The delay line phase shift

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Figure 3.21 The frequency response measured between a pair of interdigital transducers. (Reprinted with pemission.

For the SCC of type II an example of a RTD modelled is shown in Figure 7, The model used is the dispersion model (sec Esq. 6). The values of the model parameters determined arc a Bodenstein number of 8.8 and a mean residence time of 0.6 s. It clearly shows that the model for the RTD explains the frequency response measurement up to a frequency of 2 Hz, At the frequency of 2 Hz the signal-to-noise ratio of 100 is reached. Any mixing processes which affect the transfer function above this frequency cannot be identified. 

The power spectra may be directly obtained using dynamic signal analyzers that measure signals as a function of time and perform the fast Fourier transform. The coherence function takes values betweaen 0 and 1 and characterizes statistical validity of the frequency response measurements ... 

Figure 15 shows the mathematically simulated amplitude ratio data. This data would be experimentally obtained directly along with phase angle 9 if direct frequency response measurements had been made. 

The evidence for several types of adsorption (four types plus an ultra-slow exponential due perhaps to internal oxygen diffusion) was sufficiently strong to justify study of the hydrogen-supported nickel system by actual frequency response measurement. 

The frequency response measurements of this particular system are limited by the calculated natural frequency. Volume fluctuations greater than 30 cycles/minute would not be transmitted due to interference by the inertia of the column. If a 10-ft-high column of mercury were used, only frequencies up to 17 cycles/minute could be used. Conversely a mercury column less than 76 cm (30 inches) would not remain stable during system evacuation the column would be uncontrollably upset by atmospheric air flooding the system. The maximum frequency theoretically available with no safety factor is then approximately 34 cycles/minute. 

Frequency Response Measurements of Diffusion in Microporous Materials... 

Richardson, M. andFormenti, D. L. Parameter estimation from frequency response measurements using rational fraction polynomials. In Proceedings of 1st International Modal Analysis Conference (Orlando, Horida, 1982), pp. 167-182. 

FREQUENCY-RESPONSE MEASUREMENTS OF DIFFUSION OF SORBATES IN ZEOLITES... 

Rees has talked about frequency response measurements in competitive adsorption studies. I have not seen too many better fits between theoretical models and experimental data than those shown in this work. The method finds application in pressure-swing gas separations. 

In this section, we will use electrical models for human skin as examples in a general discussion on the use of electrical models. An electrical model of the skin with only two components will obviously not be able to simulate the frequency response measured on skin—it is certainly too simple compared with the complex anatomy of human skin. 

Model 3 (descriptive) A third solution would be to consider the skin as a black box, make extensive measurements on it, and find the electric circuit that matches the admittance levels and frequency response measured. The anatomy of the skin is not considered in this model. 

Rees, L.V.C. and Shen, D., Frequency-response measurements of diffusion of xenon in silicalite-1. J. Chem. Soc., Faraday Trans., 86, 3687 3692, 1990. 

When the system responds in a linear range, however, the same information can be obtained from steady-state frequency response measurements . On the other hand, in the nonlinear response region this is no longer the case, and it is inappropriate to derive frequency response results from a Fourier or Laplace transform of transient response results. 

Finally, no discussion will be given of the powerful technique of ionic thermoconductivity, also known as thermally stimulated depolarisation ". This procedure is particularly useful in observing the relaxation of the polarisation of dipoles and/or the release of mobile charge from traps in the material. Neither of these processes is included in the present models, but thermally stimulated depolarisation measurements should certainly be made in parallel with ordinary transient and frequency response measurements whenever possible in order to characterize the system investigated more fully. 

The kinetic data resulting from the pulse and frequency response measurements on polycrystalline iron (r.d.e) in acidic sulfate solutions 0.3 < pH < 6, i (10 -5.10 ) mA cm (after prior anodic polarization by a current density of 70 mA cm" for 5 min in the measuring cell) were interpreted on the basis of the following branching reaction scheme ... 

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