Microwave klystron

Microwave Klystron backward wave oscillator Mica None Crystal diode... 

Waveguides are coimnonly used to transmit microwaves from the source to the resonator and subsequently to the receiver. For not-too-high-frequency radiation (<10 GHz) low-loss MW transmission can also be achieved usmg strip-lines and coaxial cables. At the output of a klystron an isolator is often used to prevent back-reflected microwaves to perturb the on-resonant klystron mode. An isolator is a microwave-ferrite device that pemiits the transmission of microwaves in one direction and strongly attenuates their propagation in the other direction. The prmciple of this device involves the Faraday effect, that is, the rotation of the polarization... 

In the microwave region tunable monochromatic radiation is produced by klystrons, each one being tunable over a relatively small frequency range, or a backward wave oscillator, tunable over a much larger range. Both are electronic devices. Absorption experiments are usually carried out in the gas phase, and mica windows, which transmit in this region, are placed on either end of the absorption cell, which may be several metres in length. Stark... 

Millimetre wave radiation may also be generated by a klystron or backward wave oscillator but, since klystrons produce only microwave radiation, the frequency must be... 

Two-photon absorption has been observed in the microwave region with an intense klystron source but in the infrared, visible and ultraviolet regions laser sources are necessary. 

Although many spectrometer designs have been produced over the years, the vast majority of laboratory instruments are based on the simplified block diagram shown in Figure 1.4. Plane-polarized microwaves are generated by the klystron tube and the power level adjusted with the Attenuator. The Circulator... 

Figure 1.7 Schematic drawing of a microwave-generating klystron tube.

We have previously defined the relative dB scale in Equation 2.11. The power in EPR is expressed in decibels (dB) attenuation (or alternatively in -dB amplification) of a maximum value. X-band microwave sources (either klystrons or Gunn diodes) have a constant output that is usually leveled off at 200 mW. This value then corresponds... 

The basic features of an epr spectrometer are shown in Figure 2.95. The microwave source is a Klystron tube that emits radiation of frequency determined by the voltage across the tube. Magnetic fields of 0.1 — 1 T can be routinely obtained without complicated equipment and are generated by an electromagnet. The field is usually modulated at a frequency of 100kHz and the corresponding in-phase component of the absorption monitored via a phase-sensitive lock-in detector. This minimises noise and enhances the sensitivity of the technique. It is responsible for the distinctive derivative nature of epr spectra. Thus, the spectrum is obtained as a plot of dA/dB vs. 

B, where A is the absorbance as shown in Figure 2.96. The microwaves emitted by the Klystron tube travel down a waveguide to the epr cavity, in which is positioned the electrochemical cell. The characteristics of the waveform set up in the cavity are a function of its geometry. For the flat, rectangular... 

High power microwaves are generated by vacuum tubes. The magnetron and klystron are the most commonly used tubes for the generation of continuous waves power for microwave processing. Power is normally launched from the microwave tube into a transmission line or waveguide, where it travels to a load or termination such an antenna or a microwave heating applicator. 

From Equation (29) one calculates the frequency v for resonance of unpaired electrons with gf = 2 to be of the order of 10 kMc./sec. for a magnetic field of several kilogauss. Thus for magnetic fields of the order of kilogauss which are readily available in the laboratory, the frequency required for resonance is in the microwave region. Two frequency bands are often used the X-band (8.20-12.40 kMc./sec.) and the K-band (18.00-26.50 kMc./sec.). Klystrons are used to generate microwave power (usually of the order of a hundred milliwatts), waveguides to transmit power from one point to another and a microwave cavity to contain the sample and provide the Hi field necessary for resonance. 

Resonant cavity accelerators consist of several resonant cavities in series energized by a single S-band klystron using a microwave power distribution system.51 Another type consists of a single VHF cavity energized by a triode tube that is less expensive than klystron. The resonant frequency of the latter is about 110 MHz, which is well... 

The setup for ESR spectroscopy is a cross between NMR and micro-wave techniques (Section 5.8). The source is a frequency-stabilized klystron, whose frequency is measured as in microwave spectroscopy. The microwave radiation is transmitted down a waveguide to a resonant cavity (a hollow metal enclosure), which contains the sample. The cavity is between the poles of an electromagnet, whose field is varied until resonance is achieved. Absorption of microwave power at resonance is observed using the same kind of crystal detector as in microwave spectroscopy. Sensitivity is enhanced, as in microwave spectroscopy, by the use of modulation The magnetic field applied to the sample is modulated at, say, 100 kHz, thus producing a 100-kHz signal at the crystal when an absorption is reached. The spectrum is recorded on chart paper. 

Microwave spectroscopy covers the frequency range from about 3 GHz to 300 GHz. The techniques used in the infrared, visible, and ultraviolet regions resemble one another closely, but the techniques of microwave spectroscopy differ considerably from those of optical spectroscopy. The source in microwave work is usually a klystron, which is an electronic tube... 

MICROWAVE SPECTROSCOPY. A type of adsorption spectroscopy used in instrumental chemical analysis that involves use of that portion of the electromagnetic spectrum hav ing wavelengths in the range between the far infrared and the radiofrequencies, i.e.. between 1 nun and. 111 cm. Substances to be analyzed are usually in the gaseous state. Klystron tubes are used as microwave source. 

Figure 29.9 shows a comparison between the components of a rudimentary EPR spectrometer and the corresponding elements of a more familiar apparatus for visible spectrometry. In EPR, the source of excitation radiation is a microwave device called a klystron. The microwaves would disperse in free space and must therefore be conducted to the sample by waveguide or coaxial cable. The sample, contained in the sample tube, is held in a microwave cavity between the poles of a magnet. The detector is usually a diode that produces a dc output propor-... 

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