Effective loss factor

The effective loss factor e" is a fl equency-dependent parameter determined by the material properties that characterizes the ability of the material to absorb electromagnetic energy. It is defined as a product of the dielectric constant e and the loss tangent tan 8 (8 = phase angle between circuit currents)... 

The microwave energy dissipated in a material is used to melt the material during microwave welding. The amount of energy dissipated is a function of the electric field strength, frequency, and dielectric or effective loss factors (e eff)- + o/fiofi). The... 

Where is the permittivity of the air, s the dielectric constant, e the effective loss factor. 

The effective loss factor E " includes the effects of conductivity in addition to the losses due to polarization. It provides an adequate measme of total loss, since the mechanisms contributing to losses are usually difficult to isolate in most circumstances. 

Where Dp is the penetration depth Aq is the free space wavelength e is the dielectric constant and is the effective loss factor. 

The 9° = 7t/2 reorientation of n from a planar to a hruneotropic geometry under the electric field has been studied by dielectric spectroscopy by Kozak et al [109]. The mean directm patt deformation, , was determined from the effective loss factor transient bdiaviour, Xe( ) (20)) ... 

At the resonant frequency the noise spectral density has a maximum thus resonant frequencies should lie outside the bandwidth of the detector or be narrow enough to be filtered in the data analysis. Far from resonance, the spectral density of thermal noise is lower for low loss factors

test masses and the last stage of isolation systems are made of low loss materials. There is experimental evidence that for most materials the loss factor is almost independent of frequency thus below resonance x ( >) a T and above resonance x (isolation systems contribute with several modes, mainly the pendulum mode of the test mass and the violin modes of the suspension wires. Since test masses are suspended as pendulums, the effective loss factor is... 

Influence of an electrooagnetlc field Is the effective loss factor e. Both e and are frequency, temperature, density and electric field direction dependent and a considerable amount of data have been amassed on such variations. 

Table 2 shows the dielectric properties of a range of ceramic materials under various conditions and near the two frequencies for which Industrial equipment can be readily purchased. It is evident that the effective losses of various ceramics depend upon the material density and the temperature, frequency and field orientation, giving a range of effective loss factors from above 70 for silicon carbide to 3 x 10 for boron nitride. This latter cereimic can be considered as transparent to microwave energy and may be used as an insulating material in microwave Industrial equipment or as a microwave window in waveguides. In fact, any material with an effective loss factor... 

The data shown in Table 2 have been extracted from experimental results of e and as a function of the frequency with typical variations shown in Figures 8 and 9 for various ceramics. In Figure 8 pronounced dipolar relaxations occur for the titanate ceramics such as barium or barium/strontium titanate in the frequency range 10 MHz - 100 GHz. The effective loss factors of these two ceramics at 2.45 GHz are 0.2 and 0.3 respectively indicating that both these materials will readily absorb microwave radiation at this industrial allocated frequency. Lime alumina silicate, steatite and calcium titanate on the other hand have loss factors below 0.02 and as such are not obvious candidates for microwave heating. Figure 10 shows the material properties of a family of ferrites, some types can have extremely high loss factors. 

It is often required to express mathematically the effective loss factor or tan 5 in terms of the temperature. In specific temperature ranges such an expression can take the form of a straight line ... 

It is often required to estimate the amount of power that can be safely dissipated in a ceramic given that the effective loss factor is known. This can be obtained from considering the Poynting vector x H which leads to the... 

As the electromagnetic energy penetrates into the interior of the material it attenuates to an extent depending upon the effective loss factor The Inverse of the attenuation constant is defined as the skin depth, 5 ... 

The planar material to be processed 1s Inserted In a slot at the centre of the broad dimension along the waveguide length and absorbs an amount of energy from the travelling microwave field dependent upon the effective loss factor of the Insertion. Any remaining power Is absorbed by the matched water load, with very little energy reflected back towards the source. 

These applicators are widely used in the domestic sector and have also found many applications in industry. Multimode applicators are very versatile in that they can accept a wide range of material loads of different effective loss factors and sizes. 

How readily a ceramic absorbs the available microwave energy depends on the value of the effective loss factor. A simple rule of thumb suggests that in the range 0.05 < < 1 the ceramic material should heat up with little difficulty, provided there is no tendency of a thermal runaway situation... 

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. 

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