Broad-band frequencies

G. Chattopadhyay, E. Schlecht, I. S. Ward, I. I. Gill, H. H. S. lavadi, F. Maiwald, and I. Mehdi, An all-solid-state broad-band frequency multiplier chain at 1500 GHz, IEEE Transactions on Microwave Theory and Techniques, vol. 52, pp. 1538, 2004. 

The ideal radar absorber would be thin, light, durable, easily applied, inexpensive, and have broad-band frequency coverage. Moreover, in the case of structural RAMs, we intend to have no size, weight, or cost penalty over standard structural materials. As might be expected, neither of these ideal RAM types has yet been formulated. To illustrate absorber design and performance, some typical widespread used RAM types are described and their properties are analysed, Although the emphasis is on broadband absorbers, we shall start primarily with simple, narrow-band, single-layer absorbers, which form the components for multi-layer broadband absorbers. 

Use of traveling wave tube (TWT) amplifiers at power levels of hundreds of watts has been proposed (54) for power appHcations, at least when the heating chamber is well shielded. The potential advantage is an improved uniformity of heating when a broad band of frequency is used, ie, excitation of many modes. Disadvantages are high cost and lower (<50%) efficiency of the TWT. 

Fluorometry and Phosphorimetry. Modem spectrofluorometers can record both fluorescence and excitation spectra. Excitation is furnished by a broad-band xenon arc lamp foUowed by a grating monochromator. The selected excitation frequency, is focused on the sample the emission is coUected at usuaUy 90° from the probe beam and passed through a second monochromator to a photomultiplier detector. Scan control of both monochromators yields either the fluorescence spectmm, ie, emission intensity as a function of wavelength X for a fixed X, or the excitation spectmm, ie, emission intensity at a fixed X as a function of X. Fluorescence and phosphorescence can be distinguished from the temporal decay of the emission. 

Systematic studies have been carried out for the purpose of studying how low-frequency tones, broad-band components, and/or time fluctuations in ventilation noise interfere w ith disturbance reactions, In one of these studies, the respondents were exposed to ventilation noise that is representative of the noise encountered in office premises. The respondents were asked to use a rotating potentiometer to set the most acceptable noise level and the least acceptable noise level for each noise, taking account of comfort, disturbance, and performance, w hile performing their work at the same time. The noise level was maintained at a constant level of 40 d.B(A). 

All the samples showed two kinds of OD bands a relatively sharp peak around 2760 cm l and one broad band at lower frequencies, whose limits were always within approximately 2700 and 2100 cm". The former is assigned to isolated OD species and the latter to OD species in interaction [15]. 

The presence of methylenic bands shifted at higher frequency in the very early stages of the polymerization reaction has also been reported by Nishimura and Thomas [114]. A few years later, Spoto et al. [30,77] reported an ethylene polymerization study on a Cr/silicalite, the aluminum-free ZSM-5 molecular sieve. This system is characterized by localized nests of hydroxyls [26,27,115], which can act as grafting centers for chromium ions, thus showing a definite propensity for the formation of mononuclear chromium species. In these samples two types of chromium are present those located in the internal nests and those located on the external surface. Besides the doublet at 2920-2850 cm two additional broad bands at 2931 and 2860 cm are observed. Even in this favorable case no evidence of CH3 groups was obtained [30,77]. The first doublet is assigned to the CH2 stretching mode of the chains formed on the external surface of the zeolite. The bands at 2931 and... 

Fig. 1.1 The regions for transient cavitation bubbles and stable cavitation bubbles when they are defined by the shape stability of bubbles in the parameter space of ambient bubble radius (R0) and the acoustic amplitude (p ). The ultrasonic frequency is 515 kHz. The thickest line is the border between the region for stable cavitation bubbles and that for transient ones. The type of bubble pulsation has been indicated by the frequency spectrum of acoustic cavitation noise such as nf0 (periodic pulsation with the acoustic period), nfo/2 (doubled acoustic period), nf0/4 (quadrupled acoustic period), and chaotic (non-periodic pulsation). Any transient cavitation bubbles result in the broad-band noise due to the temporal fluctuation in the number of bubbles. Reprinted from Ultrasonics Sonochemistry, vol. 17, K.Yasui, T.Tuziuti, J. Lee, T.Kozuka, A.Towata, and Y. Iida, Numerical simulations of acoustic cavitation noise with the temporal fluctuation in the number of bubbles, pp. 460-472, Copyright (2010), with permission from Elsevier...

Fig. 13.15 Frequency dependence of broad band SL spectra from argon-saturated KC1 solutions. The ultrasonic frequencies used are 28, 48, 115 kHz and 1.0 MHz (from bottom to top) [42] (Reprinted from the Institute of Electronics, Information and Communication Engineers. With permission)...

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