Power penetration depth

It has been shown that the power dissipated In the dielectric medium Is controlled by the term e. Therefore  

Large variations of the Op can also occur in a material due to abrupt changes of the tan 5 with temperature. Hot pressed boron nitride is prone to such an effect as illustrated in Table 4 where the Dp reduces from 7.62 m to 45 cm as the temperature increases from 600°C to 950°C. 

The term applicator is a generic one and is used in microwave heating to refer to a device into which the material is inserted for processing. The domestic oven can be regarded as a form of applicator for cooking foodstuffs. 

Industrial microwave applicators for processing a variety of materials 

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Bows (1999) provided the following equation for calculating the microwave power penetration depth. 

It was also mentioned earlier, that quantitative information regarding the microwave-material interaction can be deduced by measuring the dielectric properties of the material, in particular of the real and imaginary part of the relative complex permittivity, f = — j , where the term ff includes conduction losses, as well as dielectric losses. The relative permeability is not a constant and strictly depends on frequency and temperature. A different and more practical way to express the degree of interaction between microwaves and materials is given by two parameters the power penetration depth (Dp) and the power density dissipated in the material (P), as defined earlier in a simplified version as follows ... 

It is Important to differentiate between power penetration depth and electric field or skin depth as shown in Figure 22. At the frequencies allocated for industrial use in the microwave regime, the penetration depths could be very small indeed and the size of the ceramic to be treated, particularly when it is fairly lossy, could be many times larger than Dp, resulting in unacceptable temperature non-uniformities. 

Conversely, effective loss f2K tors much larger than unity may present severe non uniformity of heating in that power penetration depths will be relatively small and so the dimensions of the ceramic to be treated become critical. It must be stressed, however, that irrespective of the value of the effective loss factor, careful consideration must be given In all potential applications to the type of applicator so that Its design Is tailored to the particular ceramic to be treated. 

As indicated above, the penetration depth is on the order of a micrometer. That means that in ATR, absorption of infrared radiation mostly occurs within a distance 8 of the surface and ATR is not as surface sensitive as some other surface analysis techniques. However, ATR, like all forms of infrared spectroscopy, is very sensitive to functional groups and is a powerful technique for characterizing the surface regions of polymers. 

According to definition, the penetration depth is the point where 37% (1/e) of the initially irradiated microwave power is still present [6]. The penetration depth is in-... 

The cylindrical reactor-applicator has steel wall with thickness dose to 30 mm. This thickness permits to reach internal pressures above 30 Mpa. These operating pressure conditions are above the critical point of water. The internal diameter of the reactor is 50 mm and its length is 500 mm. The system is powered simultaneously with two 6-kW generators placed at the both ends of the reactor. This simultaneous supply is necessary to overcome the penetration depth within water. 

The penetration depth of waves is defined as the distance from the surface of the material at which the power drops to 1 /e from its value at the surface. The penetration depth of microwaves is equal to 15 mm for water at 20 °C. The electromagnetic energy transfer is ensured by matched alumina windows. The propagated mode within the reactor is theoretically the TEn mode. The interest of this system is to make very specific chemical reaction such as oxidation in aqueous medium under critical conditions. 

More detailed analysis shows that the application of the low refractive index substrates not only increases the penetration depth into the cover media, but also since the mode profile is reversed places a larger portion of the electromagnetic power flowing in the waveguide structure into the cover media, thus increasing the sensor sensitivity for refractive index variations in the cover solution9 15. 

Calculate the power and penetration depth of metals heated by induction heating. 

The selection of EB equipment depends on the foam thickness and production rate. The foam manufacturers throughout the world are using equipment with electron accelerators with voltages ranging from 0.5 to 4 MV and power ratings from 10 to 50 kW. The penetration depth of a 1 MV unit is approximately 3 mm (0.12 in.). Irradiation on both sides doubles the thickness capability. ... 

The term, penetration depth, has three common, slightly different definitions. Their definitions and differences have been discussed (Buffler 1993). The internationally accepted definition is that distance in which the microwave power, once... 

Here, P(z)/PD represents the fraction of power remaining as a function of distance into the material. The units of distance, z, and penetration depth, dp are the same and are arbitrary as they occur as a ratio centimeters are most commonly used in the literature. 

The penetration depth (Dp) of the materials used to denote the depth at which the power density of microwave irradiation is reduced to 37% (i.e., 1/e) of its initial value at the surface of the material. It is proportional to the wavelength of the radiation and depends on the dielectric properties of the material. For lossy dielectrics (e"/e 1) the... 

The intrinsically low intensity of Raman scattering strongly influences both the sensitivity and penetration depth of SORS and its variants. Dominant noise components (photon shot noise or thermal/dark count [1]) can be minimised relative to signal by increasing absolute signal levels. In many Raman systems, collection optics, laser power and other relevant parameters are usually maximised for optimum performance of the system current detectors (CCD devices), for example, have detection efficiencies approaching 100%. Typically, acquisition time provides the only straightforward means available... 

The reason why Nm varies between nmax and tiy, is further elucidated in Fig. 5, which displays the penetration depths dpj = l/ kjz (j = S, C), into the substrate and the cover versus film thickness. Here, it is seen that when dp —> dCutoff> the penetration depth into that medium (substrate or cover) with highest RI goes to infinity, in which case practically all the mode power flows in this medium. This is why the mode s phase velocity vm -> c/nmax and him Umax- The penetration depth at cutoff into the lowest-RI medium has a finite value of dp,a = k l (n2m.AX - in) l/2. 

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