Electromagnet transmittance

The attenuation of electromagnetic radiation as it passes through a sample is described quantitatively by two separate, but related terms transmittance and absorbance. Transmittance is defined as the ratio of the electromagnetic radiation s power exiting the sample, to that incident on the sample from the source, Pq, (Figure 10.20a). 

Multiplying the transmittance by 100 gives the percent transmittance (%T), which varies between 100% (no absorption) and 0% (complete absorption). All methods of detection, whether the human eye or a modern photoelectric transducer, measure the transmittance of electromagnetic radiation. 

Attenuation of radiation as it passes through the sample leads to a transmittance of less than 1. As described, equation 10.1 does not distinguish between the different ways in which the attenuation of radiation occurs. Besides absorption by the analyte, several additional phenomena contribute to the net attenuation of radiation, including reflection and absorption by the sample container, absorption by components of the sample matrix other than the analyte, and the scattering of radiation. To compensate for this loss of the electromagnetic radiation s power, we use a method blank (Figure 10.20b). The radiation s power exiting from the method blank is taken to be Pq. 

Foxboro s Model 823 transmitter uses a taut wire stretched between a measuring diaphragm and a restraining element. The differential process pressure across the measuring diaphragm increases the tension on the wire, thus changing the wire s natural frequency when it is excited by an electromagnet. This vibration (1800—3000 H2) is picked up inductively in an oscillator circuit which feeds a frequency-to-current converter to get a 4—20 m A d-c output. 

Electromagnetic interference (EMI) testing has become more prevalent for materials that either emit or are affected by EMI. Shielding efficiency (SE) of materials is deterrnined by measuring electric field strength between a transmitter and receiver with or without the presence of the material under test. Several researchers have suggested a correlation between volume resistivity and SE values (300,301). 

Electromagnetic (EM) Conductivity Measures the electrical conductivity of materials in microohms over a range of depths determined by the spacing and orientation of the transmitter and receiver coils, and the nature of the earth materials. Delineates areas of soil and groundwater contamination and the depth to bedrock or buried objects. Surveys to depths of SO to 100 ft are possible. Power lines, underground cables, transformers and other electrical sources severely distort the measurements. Low resistivities of surficial materials makes interpretation difficult. The top layers act as a shunt to the introduction of energy info lower layers. Capabilities for defining the variation of resistivity with depth are limited. In cases where the desired result is to map a contaminated plume in a sand layer beneath a surficial clayey soil in an area of cultural interference, or where chemicals have been spilled on the surface, or where clay soils are present it is probably not worth the effort to conduct the survey. 

The frequency of microwave radiation lies between that of IR radiation and high frequency radio waves and the boundaries between these regions are not fixed [221]. The microwaves are generated in a transmitter (magnetron) which possesses a stalk which penetrates Uke a radio antenna into a hollow energy guide (Fig. 48). This leads the electromagnetic waves into the reaction chamber (power about... 

These systems work by placing a sample between the pole pieces of a magnet (electromagnet or permanent), surrounded by a coil of wire. Radio frequency (r.f.) is fed into the wire at a swept set of frequencies. Alternatively, the magnet may have extra coils built onto the pole pieces which can be used to sweep the field with a fixed r.f. When the combination of field and frequency match the resonant frequency of each nucleus r.f. is emitted and captured by a receiver coil perpendicular to the transmitter... 

Classical pulse radar emits high power (Pr) short electromagnetic pulses using a directional transmitting antenna of gain Gt The power density at the target at distance R from the transmitter is equal to [44]... 

TD-NMR and HR-NMR spectrometer systems have a majority of components in common. All spectrometers consist of a magnet, magnet temperature sensors, magnet heater power supply, RF frequency synthesizer, pulse programmer, transmitter/amplifier, sample probe, duplexor, preamplifier, receiver, and ADC, all controlled by a computer. In addition to these items a HR-NMR has several other requirements which include an electromagnetic shim set, a shim power supply, and a second RF locking channel tuned to the resonance frequency of Li. The second RF channel is identical to that of the observed H channel. Figures 10.9 and 10.10 show the basic setup of TD-NMR and HR-NMR spectrometers, respectively. 

A dimensionless quantity, symbolized by t or T, equal to the transmitted radiant power, Ptr, divided by the radiant power incident on the sample, Po thus, t = Ptr/ Pq. It is a measure of the ability of a body, solution, entity, eta, to transmit electromagnetic radiation. It is synonymous with transmission factor. See also Internal Transmittance Transmission Density Total Transmittance Beer-Lambert Law Absorption Spectroscopy... 

Initiation by Radio Frequency (RF) Radiation. RF radiation, ie, radio wave radar transmitters can, under certain circumstances, initiate electroexplosive devices. This topic will be discussed under Radio Frequency Radiation, Effects on Explosives. Also see articles on Electromagnetic Compatibility Electromagnetic Field Hazard, Simulated in Vol 5, pp E70-71 and Electric Blasting Caps and RF Energy in Vol 5, p E25-L... 

The theory and instrumentation of Fourier transform mass spectrometry (FTMS) have been discussed extensively in this book and elsewhere [21-23]. All experiments were performed on a Nicolet prototype FTMS-1000 Fourier transform mass spectrometer previously described in detail [24] and equipped with a 5.2 cm cubic trapping cell situated between the poles of a Varian 15 in. electromagnet maintained at 0.85 T. The cell was constructed in our laboratory and utilizes two 80 transmittance stainless steel screens as the transmitter plates. This permits irradiation with a 2.5 kW Hg-Xe arc lamp, used in conjunction with a Schoeffel 0.25 m monochromator set for 10 nm resolution. Metal ions are generated by focusing the beam of a Quanta Ray Nd YAG laser (either the fundamental line at 1064 nm or the frequency doubled line at 532 nm) into the center-drilled hole (1 mm) of a high-purity rod of the appropriate metal supported on the transmitter screen nearest to the laser. The laser ionization technique for generating metal ions has been outlined elsewhere [25]-... 

Attention must now be paid to the exponential factor, exp( 2nir (n iij)/A), in Equation 6.5, where (n it) is known as the complex refractive index of a substance. It can be seen that the effect of this factor upon the electromagnetic wave increases with the distance Irl that the light travels in that medium. In the general case of an anisotropic medium, n and are referred to as a specific set of axes, usually chosen to coincide with the optical axes of the medium. For example, the axes of maximum and minimum transmittance are selected for anisotropic absorption. The extinction f for an anisotropic medium is related to the extinction coefficient through Equation 6.9. 

Radar level transmitters and gauges use electromagnetic waves, typically in the microwave bands to make a continuous liquid and some solid level measurements. The radar sensor is mounted on the top of the vessel and is aimed down, perpendicular to the liquid surface. Most tank-farm gauges are operated on the FMCW principle (Figure 3.121). Other gauges and transmitters, particularly the lowest-cost units, are operated on the pulse principle. Both principles are fundamentally based on the time of flight from the sensor to the level of the surface to be measured. In the FMCW method, this time of flight is tracked on a carrier wave in the pulse method, it is the echo return. 

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