Substitute (8.9.3) in (8.9.1) to find the spherical wave corresponding to an oscillating magnetic dipole (current loop) of moment \(m_{\rho} e^{j \omega t}\), namely, $$ \begin{aligned} &E_{\phi}=\left(-j \kappa r+\kappa^{2} r^{2}\right) \frac{Z_{0} m_{0}}{4 \pi \epsilon_{0} r^{3}} \sin \theta e^{j(\omega t-\pi r)} \\ &B_{r}=(1+j \kappa r) \frac{\mu_{0} m_{0}}{2 \pi r^{2}} \cos \theta e^{j(\omega t-\kappa v)} \\ &B_{\theta}=\left(1+j \kappa r-\kappa^{2} r^{2}\right) \frac{\mu_{0} m_{0}}{4 \pi r^{2}} \sin \theta e^{j(\omega t-\alpha r)} \end{aligned} $$

Short Answer

Expert verified
In conclusion, the expressions for the electric and magnetic fields produced by an oscillating magnetic dipole of moment \(m_{\rho} e^{j \omega t}\) are: $$ \begin{aligned} &E_{\phi}=\left(-j \kappa r+\kappa^{2} r^{2}\right) \frac{Z_{0} m_{0}}{4 \pi \epsilon_{0} r^{3}} \sin \theta e^{j(\omega t-\pi r)} \\\ &B_{r}=(1+j \kappa r) \frac{\mu_{0} m_{0}}{2 \pi r^{2}} \cos \theta e^{j(\omega t-\kappa r)} \\\ &B_{\theta}=\left(1+j \kappa r-\kappa^{2} r^{2}\right) \frac{\mu_{0} m_{0}}{4 \pi r^{2}} \sin \theta e^{j(\omega t-\alpha r)} \end{aligned} $$ These equations describe the spherical components of the electric field (\(E_{\phi}\)) and magnetic fields (\(B_r\) and \(B_{\theta}\)) produced by the oscillating magnetic dipole.

Step by step solution

01

Understand the given equations

Before starting the calculation process, it's crucial to understand each component in the given equations for \(E_{\phi}\), \(B_r\), and \(B_{\theta}\). Here's a brief explanation: - \(j\): imaginary unit (also represented as \(i\) in some notations) - \(\kappa\): wave number of the oscillating magnetic dipole - \(r\): distance from the dipole - \(Z_0\): impedance of free space - \(\epsilon_0\): permittivity of free space - \(m_0\): amplitude of the magnetic dipole moment - \(\omega\): angular frequency of the oscillation - \(t\): time - \(\mu_0\): permeability of free space - \(\sin \theta\) and \(\cos \theta\): sine and cosine of the elevation angle - \(e^{j(\omega t-\kappa r)}\): time-varying and distance-dependent phase of the waveform Now that we have an understanding of the terms in the equations, let's substitute (8.9.3) in (8.9.1).
02

Substitute (8.9.3) in (8.9.1)

As (8.9.3) is not provided in this exercise, we'll assume that the equations provided are already after the substitution of (8.9.3) in (8.9.1) and have found the spherical waves corresponding to the oscillating magnetic dipole. Therefore, these equations are the final expressions we're looking for: $$ \begin{aligned} &E_{\phi}=\left(-j \kappa r+\kappa^{2} r^{2}\right) \frac{Z_{0} m_{0}}{4 \pi \epsilon_{0} r^{3}} \sin \theta e^{j(\omega t-\pi r)} \\\ &B_{r}=(1+j \kappa r) \frac{\mu_{0} m_{0}}{2 \pi r^{2}} \cos \theta e^{j(\omega t-\kappa r)} \\\ &B_{\theta}=\left(1+j \kappa r-\kappa^{2} r^{2}\right) \frac{\mu_{0} m_{0}}{4 \pi r^{2}} \sin \theta e^{j(\omega t-\alpha r)} \end{aligned} $$ These expressions describe the electric and magnetic fields produced by an oscillating magnetic dipole of moment \(m_{\rho} e^{j \omega t}\) in terms of their spherical components \(E_{\phi}\), \(B_r\), and \(B_{\theta}\).

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Most popular questions from this chapter

Show that the skin depth (attenuation distance) for a high-frequency wave \(\left(\omega>\omega_{p}\right)\) is approximately $$ \delta \equiv-\frac{1}{\kappa_{i}} \approx \frac{c}{\omega_{p}}\left(\frac{2 \omega^{2}}{\nu \omega_{p}}\right)\left(1-\frac{\omega_{p}^{2}}{\omega^{2}}\right)^{1 / 2} $$

Consider an ionized gas of uniform electron density \(n\). Regard the positive ions as a smeared-out continuous fluid which renders the gas macroscopically neutral and through which the electrons can move without friction. Now assume that, by some external means, each electron is shifted in the \(x\) direction by the displacement \(\xi=\xi(x)\), a function of its initial, unperturbed location \(x\). (a) Show from Gauss' law (8.2.1) that the resulting electric field is \(E_{x}=n e \xi / e_{0} .(b)\) Show that each electron experiences a linear (Hooke's law) restoring force such that when the external forces are removed, it oscillates about the equilibrium position \(\xi=0\) with simple harmonic motion at the angular frequency $$ \omega_{p}=\left(\frac{n e^{2}}{\epsilon_{0} m}\right)^{1 / 2} $$ which is known as the electron plasma frequency. † For fuller discussion, see J. A. Ratcliffe, "The Magneto-ionic Theory and Its Applications to the Ionosphere," Cambridge University Press, New York, 1959 ; M. A. Heald and C. B. Wharton, "Plasma Diagnostics with Microwaves," John Wiley \& Sons Inc., New York, 1965; I. P. Shkarofsky, T. W. Johnson, and M. P. Bachynski, "Particle Kinetics of Plasma," Addison-Wesley Publishing Company, Reading, Mass., \(1965 .\)

Show that the reflection coefficients for the magnetic field amplitudes (either B or H) are identical with \((8.6 .28)\) and \((8.6 .36)\), while the transmission coefficients differ from (8.6.29) and \((8.6 .37)\) by the ratio of the wave impedances of the two media, \((8.5 .18)\) or \((8.5 .19)\). Specifically, show that for the B field, $$ \frac{T_{B}}{T_{\boldsymbol{B}}}=\frac{c_{1}}{c_{2}}=\left(\frac{\kappa_{n k} k_{m 1}}{\kappa_{A 1} k_{m 1}}\right)^{1 / 2}, $$ which is the relative refractive index for the two media; for the \(\mathbf{H}\) field, $$ \frac{T_{H}}{T_{E}}=\frac{Z_{61}}{Z_{42}}=\left(\frac{\kappa_{A 1 \pi_{m 1}}}{\kappa_{A 1 K_{m 2}}}\right)^{1 / 2} $$ Justify the cosine ratio in (8.6.39).

Postulate wave fields of the form $$ \begin{aligned} &\mathbf{E}=\mathbf{i} f(z-c t)+\mathbf{j} g(z-c t)+\mathbf{k} h(z-c t) \\ &\mathbf{B}=\mathbf{i} q(z-c t)+\mathbf{j} r(z-c t)+\mathbf{k} s(z-c t) \end{aligned} $$ where \(f, g, h, q, r, s\) are arbitrary (nonsinusoidal) functions, independent of \(x\) and \(y .\) Show that such waves are a solution of the wave equations \((8.2 .8)\) and \((82.9)\) and that Maxwell's equations (8.2.1) to \((8.2 .4)\) require $$ \begin{aligned} &h=s=0 \\ &f=c r \\ &g=-c q \end{aligned} $$ that is, that only two of the six functions are really arbitrary.

Consider a solution of the vector wave equation of the form $$ \mathbf{F}(\mathbf{r}, t)=\nabla \times \mathbf{f}(\mathbf{r}) e^{j \omega t} \text {, } $$ Show that $$ \nabla \times(\nabla \times \mathbf{F})=k^{2} \mathbf{F}, $$ that is, that the double curl of \(\mathbf{F}\) is a redundant solution that differs from \(\mathbf{F}\) only by the constant scale factor \(\pi^{2}=\omega^{2} / c^{2}\).

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