Shielding sensitivity

An important application of ferrites is for shielding sensitive equipment (e.g. data-processing, telecommunications and audio-visual equipment) from electromagnetic interference (EMI). Both NiZn- and MZn-based ferrites components are capable of suppressing interference up to the GHz frequency range by virtue of the high impedance they present to high frequency currents. The ferrite parts are made in a variety of shapes to enclose the leads to be shielded, as shown in Fig. 9.17. 

A comparison of the MR4 -MF5 differences for Sb and As indicates the shielding sensitivity of Sb to be greater by a factor of 3.1 SbS at the deshielded end of the range is consistent with the highly deshielded environment created for %o by tetrahedral sulfurs and observed by Otto Lutz (10). 

On reaching Co, we see in Figure 5 that while the correlation is maintained, it has expanded in scale beyond anything encountered anywhere else in the Periodic Table. If within the Colli class we include Co(CN)5 and the phosphine complexes, both of which are atypical Co complexes and overlap the Co region, its range is an enormous 16,000 ppm centered on 6 7000. The Co compounds cover 1300 ppm around 6 1350 and Co compounds span 4100 ppm at 6 -2500. With three points available the linearity of the correlation is within 10% and the slope is 2600 ppm per oxidation state unit. To wonder at this extraordinary shielding sensitivity for a first transition series atom is not to explain it ... 

Cu and Zn + are closed shell d ° systems and exhibit relatively low intrinsic shielding sensitivities. This fact, together with the unfavourable size of the quad-rupole moment, the low receptivity in the case of Zn, and the ease of chemical exchange in the case of... 

The magnitude of the chemical shift varies considerably with the probe nucleus, and may be used as a measure of the shielding sensitivity. This may be estimated... 

Figure 1. Shielding ranges and shielding sensitivities for the early transition metals. Shielding increases from left to right. Shaded areas [M04]V[M(C0)j] , punctuated areas [MCltJVCMFj] . Broken lines encompass measurements on solids ( V, Nb) or extrapolated data ( Nb in [NbTeBr4] ).

Figure 2 illustrates a number of features of the chemical shifts of these nuclei. First there is the large range of the values, over 18,000 ppm for Co. Only for Pt can the shielding sensitivity be evaluated on the same basis as in Chapter 19. For [PtFs] " vs. [PtClg] , zf = 7 326ppm, over twice that for W, which has the largest sensitivity of the early transition metals. If the value for [Ru3(CO)i2] can be approximated to that of [M(CO)6] then Ru has a similar sensitivity to W on the basis of J5 M04—[M(CO)s]. However, from Figure2 it seems that Ru lies between Rh and Co in sensitivity and that Co has 1.5-2 times the sensitivity of Pt. These large shielding sensitivities mean that chemical shifts are responsive to the molecules environment (solvent, temperature, and pressure) and isotopic constitution.

The shielding of these metal nuclei has been discussed by Kidd. The observed range, relative to the free atom, is illustrated in Figure 1. The shielding sensitivity can-... 

A SQUID [2] provides two basic advantages for measuring small variations in the magnetic field caused by cracks [3-7]. First, its unsurpassed field sensitivity is independent of frequency and thus dc and ac fields can be measured with an resolution of better than IpT/VHz. Secondly, the operation of the SQUID in a flux locked loop can provide a more than sufficient dynamic range of up to 160 dB/VHz in a shielded environment, and about 140 dB/>/Hz in unshielded environment [8]. 

Strain-gauge load cells are sensitive to temperature gradients induced by, for example, radiant heat from the sun or resulting from high temperature wash down. Load cells should be shielded from such effects or given time to stabilize before use. 

A number of devices suggest the possibiUty of improvement in the basic limitations of resolution and sensitivity for single-photon instmmentation. One device (24) employs an array of pinholes in a hemispherical shield that Hes inside a hemispherical soHd-state detector array. Simulations and initial experience using early models have suggested that the device could achieve a resolution in the brain of less than 3 or 4 mm and possibly as low as 1 mm. 

Capital Costs A typical medium-scale RO seawater plant might produce 0.25 mVs (6 MGD). For a plant with an open sea intake, seawater salinity of 38 g/1, and conversion of 45 percent, the overall cost woiild be 26.5 miUiou (1996). A capital breakdown is given in Table 22-18. Capital charges are site specific, and are sensitive to the salinity of the feed. A plant of this size would likely contain six trains. For seawater RO, the Best estimate for the slopes of the family of lines in Fig. 22-55 is —0.6 for the equipment and 0.95 for the membranes. Capital charges, shown in TaBle 22-19, usually dominate the overall economics the numbers presented are only an example. Seawater economics are based on Shields and Moch, Am. Desalination Assn. Conf. Monterey CA (1996). 

An example is a LEIS study on a specific spinel, namely ZnAl204, for which cations (Zn) in tetrahedral sites are expected [3.145] to be less stable and therefore move to sites below the surface where they are better shielded, yielding a lower LEIS signal. This has been confirmed by Brongersma et al. [3.146] (Fig. 3.59). This figure shows that LEIS is very sensitive to Zn, as shown by LEIS from ZnO, but for the spinel no Zn is visible in the surface. 

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