Radio frequency detector

Williams, H. P., Winefordner, J. D. Several high sensitivity radio frequency detectors for permanent gas analysis. J. Gas Chromatog. 6, 11 (1968). 

The radio frequency detector is generally designed with two halves, each mounted on the ends of a pole. Commonly called the two-box detector, this was the standard for many years for deep penetration. It also has the advantage of ignoring small trash items. This type will also respond... 

The essential elements of an NMR spectrometer are a powerful magnet, a radiofrequency generator, a radio-frequency detector, and a sample tube (Figure 13.4). 

Taking into account that it is necessary to make vary the flaw detector settings during the main part of the verifications, the total number of verifications is rather important. So, Technical Center for Mechanical Industries (CETIM) began the development of an electronic system enabling to benefit of the current possibilities of generation of synthesised radio frequency signals and help of personal computer for operator assistance and calculation. 

Optical parametric oscillator (OPO, see 20) is the real equivalent to the radio frequency shifter however OPO can be replaced by a simple addition of a local oscillator (e.g. laser) through a beam splitter. Multiplication takes place at the level of detectors. For sake of S5mimetry, detectors can be placed at both output of the beam splitter, the intermediate frequency is then the output of the differential amplifier. 

Theory. If two or more fluorophores with different emission lifetimes contribute to the same broad, unresolved emission spectrum, their separate emission spectra often can be resolved by the technique of phase-resolved fluorometry. In this method the excitation light is modulated sinusoidally, usually in the radio-frequency range, and the emission is analyzed with a phase sensitive detector. The emission appears as a sinusoidally modulated signal, shifted in phase from the excitation modulation and partially demodulated by an amount dependent on the lifetime of the fluorophore excited state (5, Chapter 4). The detector phase can be adjusted to be exactly out-of-phase with the emission from any one fluorophore, so that the contribution to the total spectrum from that fluorophore is suppressed. For a sample with two fluorophores, suppressing the emission from one fluorophore leaves a spectrum caused only by the other, which then can be directly recorded. With more than two flurophores the problem is more complicated but a number of techniques for deconvoluting the complex emission curve have been developed making use of several modulation frequencies and measurement phase angles (79). 

The basic instrumentation used for spectrometric measurements has already been described in Chapter 7 (p. 277). The natures of sources, monochromators, detectors, and sample cells required for molecular absorption techniques are summarized in Table 9.1. The principal difference between instrumentation for atomic emission and molecular absorption spectrometry is in the need for a separate source of radiation for the latter. In the infrared, visible and ultraviolet regions, white sources are used, i.e. the energy or frequency range of the source covers most or all of the relevant portion of the spectrum. In contrast, nuclear magnetic resonance spectrometers employ a narrow waveband radio-frequency transmitter, a tuned detector and no monochromator. 

Powerful and highly homogeneous electromagnet, radio-frequency signal generator and detector circuit, electronic integrator, glass sample tubes. 

A SAW device is configured as a delay line and fed by a radio frequency signal. Any change in the velocity Av is detected as a change AT in the phase delay of the wave, thanks to a phase detector that gives a voltage proportional to the difference of phase between signal input and output. 

Figure 2.4 Schematic diagram of an ICP torch. The sample is carried into the torch by the carrier argon gas, and is ignited by radio-frequency heating from the RF coils. The tangential argon flow lifts the flame from the burner, preventing melting. The position of the detector in axial or radial mode is shown. (From Pollard et al., 2007 Fig. 3-3, by permission of Cambridge University Press.)...

The detector system is used to note that energy is being transferred from the radiofrequency beam to the nucleus radio frequency. 

The quadrupole analyzer uses oscillating electrical fields to separate ions based on their stable trajectories. The analyzer consists of four parallel poles placed between the ion source and the detector in such a manner that the path of the ion beam travels through the middle. The rods have DC voltages applied to opposite rods to carry the same charge, yielding one set of positive rods and one set of negative rods. All four rods have an oscillating radio frequency (RP) applied to them (Honour, 2003). If the ion mass is too... 

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