Spectrum analyzers applications

Filter-based instruments are often limited to applications where there is simple chemistry, and where the analytes can be differentiated clearly from other species or components that are present. Today, we may consider snch analyzers more as sensors or even meters, and the analytical instrument community does typically not view them as trne instraments. Since the late 1980s a new focns on instrumentation has emerged based on the use of advanced measnrement technologies, and as such is considered to be more of the con-seqnence of an evolution from laboratory instruments. Some of the first work on full-spectrum analyzers started with an initial interest in NIR instruments. The natnre of the spectral information obtained in the NIR spectral region is snch that an analyzer capable of measnring multiple wavelengths or preferably a fnll spectrnm is normally reqnired. 

Other demonstrated prototype devices include optical gyroscopes (144), broadband acoustic spectrum analyzers (145), 1x2 Y-fed directional couplers (146) and polarization-insensitive electrooptic modulators (147,148). For long-haul telecommimication applications, it is difficult to maintain polarization control thus, a need exists for polarization-insensitive modulators. Indeed, polarization insensitivity was one of the advantages claimed for gallium arsenide elec-troabsorptive modulators. By using different poling schemes, overall polarization insensitivity has been achieved for polymeric modulators (147,148). 

The appHcations of SAW devices are numerous, their implementation as deflectors, tunable filters, and frequency shifters, as described, are just a few of their possible uses. Other important device applications are time multiplexer, pulse compression of chirped signal, correlators, spectrum analyzer, and isolators. 

The primary application for a spectrum analyzer centers around measuring the occupied bandwidth of an input signal. Harmonics and spurious signals can be checked and potential causes investigated. Figure 20.63 shows a typical test setup for making transmitter measurements. 

Doemer, S., Schneider, T., Schroder,)., and Hauptmann, P. (2003) Universal impedance spectrum analyzer for sensor applications. Sensors, 2003. Proceedings of IEEE, Bd. 1, pp. 596-599. 

A confocal F.P,I, often called a spherical interferometer [4,33], consists of two spherical mirrors M, with equal curvatures (radius r) which oppose each other at a distance d = r (Fig,4,52a), These interferometers have gained great importance in laser-physics firstly, as high-resolution spectrum analyzers for detecting the mode structure and linewidth of lasers [4,34] and secondly, in the nearly confocal form, as laser resonators. We discuss the former application in this section, while laser resonators will be treated in a more general way in Sect,6,3,... 

Neural networks have been applied to IR spectrum interpreting systems in many variations and applications. Anand [108] introduced a neural network approach to analyze the presence of amino acids in protein molecules with a reliability of nearly 90%. Robb and Munk [109] used a linear neural network model for interpreting IR spectra for routine analysis purposes, with a similar performance. Ehrentreich et al. [110] used a counterpropagation network based on a strategy of Novic and Zupan [111] to model the correlation of structures and IR spectra. Penchev and co-workers [112] compared three types of spectral features derived from IR peak tables for their ability to be used in automatic classification of IR spectra. 

In many applications in mass spectrometry (MS), the sample to be analyzed is present as a solution in a solvent, such as methanol or acetonitrile, or an aqueous one, as with body fluids. The solution may be an effluent from a liquid chromatography (LC) column. In any case, a solution flows into the front end of a mass spectrometer, but before it can provide a mass spectrum, the bulk of the solvent must be removed without losing the sample (solute). If the solvent is not removed, then its vaporization as it enters the ion source would produce a large increase in pressure and stop the spectrometer from working. At the same time that the solvent is removed, the dissolved sample must be retained so that its mass spectrum can be measured. There are several means of effecting this differentiation between carrier solvent and the solute of interest, and thermospray is just one of them. Plasmaspray is a variant of thermospray in which the basic method of solvent removal is the same, but the number of ions obtained is enhanced (see below). 

ICP-OES is one of the most successful multielement analysis techniques for materials characterization. While precision and interference effects are generally best when solutions are analyzed, a number of techniques allow the direct analysis of solids. The strengths of ICP-OES include speed, relatively small interference effects, low detection limits, and applicability to a wide variety of materials. Improvements are expected in sample-introduction techniques, spectrometers that detect simultaneously the entire ultraviolet—visible spectrum with high resolution, and in the development of intelligent instruments to further improve analysis reliability. ICPMS vigorously competes with ICP-OES, particularly when low detection limits are required. 

In gas chromatography/mass spectrometry (GC/MS), the effluent from a gas chromatograph is passed into a mass spectrometer and a mass spectrum is taken every few milliseconds. Thus gas chromatography is used to separate a mixture, and mass spectrometry used to analyze it. GC/MS is a very powerful analytical technique. One of its more visible applications involves the testing of athletes for steroids, stimulants, and other performance-enhancing drugs. These drugs are converted in the body to derivatives called metabolites, which are then excreted in the... 

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