Microwave permeability

W.E. Courtney, Analysis and Evaluation of a Method of Measuring the Complex Permittivity and Permeability Microwave Insulators, IEEE Trans. MTT., 18, 476-485 (1970). 

Equation (3) shows that RL is dependent on permittivity, permeability, microwave frequency and sample thickness. For nonmagnetic dielectrics (or dielectric materials with very weak magnetism) such as ferric oxide, the value of /t, can be assumed to be 1 in the calculation of reflection loss. Thus, one may expect that the thickness dependence of RL of ferric oxide at commonly used microwave frequencies is mainly determined by permittivity. 

Chemical reagents are primarily concerned with dielectric liquids or solids. For metal oxides such as ferrites, however, magnetic losses occur in the microwave region. As for a dielectric material, a complex magnetic permeability is defined as given by Eq. (16) ... 

The real part is the magnetic permeability whereas the imaginary part is the magnetic loss. These losses are quite different from hysteresis or eddy current losses, because they are induced by domain wall and electron-spin resonance. These materials should be placed at position of magnetic field maxima for optimum absorption of microwave energy. For transition metal oxides such as iron, nickel, and cobalt magnetic losses are high. These powders can, therefore, be used as lossy impurities or additives to induce losses within solids for which dielectric loss is too small. 

To consider the application of microwave irradiation for organic synthesis, the first step is to analyze the reaction components together with their dielectric properties among which of the greatest importance is dielectric constant (cr) sometimes called electric permeability. Dielectric constant (er) is defined as the ratio of the electric permeability of the material to the electric permeability of free space (i.e., vacuum) and its value can derived from a simplified capacitor model (Fig. 1.4). 

It should also be noted that denaturing agents make cells permeable, facilitating antibody penetration. Moreover, these agents are used usually in combination with microwave heating. Therefore, the role of these agents in epitope retrieval needs to be explained in the context of their role in cell permeabilization as well as of the influence of elevated temperatures. 

Courtney, W.E. (1970) Analysis and evaluation of a method of measuring the complex permittivity and permeability of microwave insulators, IEEE Trans. 

To understand the principle of operation of important non-reciprocal (see below) microwave devices, consider what occurs when a plane-polarized microwave is propagated through a ferrite in the direction of a saturating field Ht. The wave can be resolved into two components of equal amplitude but circularly polarized in opposite senses, i.e. into a right-polarized and a left-polarized component. These two components interact very differently with the material, leading to different complex relative permeabilities H r+ = n r+ - j/r" i and /r - = /T- — j/r"-, as shown in Fig. 9.40. Because of the... 

Fig. 9.40 Dependence of the permeability on Ht for right and left circularly polarized components of a plane-polarized microwave of frequency to — yii0H0.

W. E. Courtney, Analysis and evaluation of a method of measuring the complex permittivity and permeability of microwave insulators, IEEE Trans. Microwave Theory Tech. 18 (1970) 476-485. B.W. Hakki and P.D. Coleman, A Dielectric Resonator Method of Measuring Inductive Capacities in the Millimeter range, IEEE Trans. Microwave Theory Tech. 8 (1960) 402-410. 

Figure 9-35. Permeability of the lestosil polymer membrane with respect to He, H2, CO2, and CH4 as function of microwave plasma treatment time o, Hne A, Hhj , Hcch +, ncH< microwave pulse power2 kW pulsing period 2 ms pulse duration 100 fis gas pressure in the microwave discharge chamber2 Torr nitrogen/oxygen ratio in the plasma gas N2 02 = 4 1 flow rate of the plasma gas 40 cm /s.

---