Time Domain Characteristics of Huygens Dipole Antennas Excited with Zero-Area Pulses: Near-field, midrange, and far-field explorations.

Ultrathin metamaterial-inspired Huygens dipole antenna and rectenna arrays are presented for wireless power transfer (WPT) enabled IoT applications. The fundamental array element is the electrically small Huygens dipole antenna (HDA) that consists of two metamaterial-inspired structures: an Egyptian axe dipole (EAD) and a capacitively loaded loop (CLL). The EAD and CLL are designed on both sides of a single PCB substrate functioning as the in-phase and orthogonal electric and magnetic dipoles. A short-driven dipole close to the CLL excites the two radiators. Based on the single element HDA, an ultrathin, beam-steerable Huygens dipole antenna array (HDAA) with wide area coverage and small gain variation has been developed as a long distance WPT transmitter for battery-free applications. Experimental verifications of the simulated results are presented. Additionally, an HDA-based Huygens dipole rectenna array (HDRA) design is developed for the receiver side. Effective capture of the wireless energy to power IoT devices is illustrated. Both DC and RF combining schemes are discussed for different application scenarios.

Summary form only given. Although it is often assumed that all light-matter interactions at optical frequencies are mediated by electric dipole transitions, strong optical-frequency magnetic dipoles do exist. In fact, we see magnetic dipole emission every day from the many lanthanide ions (such as erbium, europium, and terbium) that help to illuminate everything from fluorescent lighting to telecom fiber amplifiers. Higher-order processes such as magnetic dipole and electric quadrupole transitions also play an important part in the light emission from transition metal ions and semiconductor quantum dots. Nevertheless, most applications have overlooked the device implications of these electric-dipole-forbidden transitions throughout the visible and near-infrared regime, and their contributions to many important emitters have not been fully characterized.In this presentation, we will experimentally characterize the "forbidden" transitions in a range of solid-state emitters and investigate their applications and implications for nanophotonics. We will examine the electric dipole approximation commonly used to describe light-matter interactions and discuss naturally occurring systems that exhibit higher-order magnetic dipole and electric quadrupole emission. We will illustrate how these nanoscale quantum transitions can provide both a new way to probe magnetic light-matter interactions and a new degree of design freedom for active electronic and photonic devices. Specifically, we will demonstrate how the different symmetries of multipolar transitions can be exploited to identify, quantify, and control light emission, even at sub-lifetime scales. Despite similar radiation patterns, magnetic and electric dipole emitters have different symmetries with respect to polarization and phase. Thus, in an inhomogeneous environment, we can tailor interference effects and the local density of optical states to selectively enhance either electric or magnetic dipole emission [1,2]. To examine the scope of such higher-order transitions, we will present quantum mechanical calculations that identify all the magnetic dipole and electric quadrupole emission lines in the trivalent lanthanide series in the visible to near-infrared spectrum [3]. Then, we will present an energyand momentum-resolved spectroscopy technique to directly quantify the electric and magnetic dipole contributions from any mixed transition. [4] Using energy-momentum spectroscopy, we will experimentally examine the higher order transitions in lanthanide ions [4,5], transition metal ions [6], and epitaxial quantum dots [7]. If time permits, we will then show how the symmetry differences between magnetic and electric dipoles can be used to address specific electronic states [6] and to dynamically tune emission spectra at sub-lifetime-scales [8].

All-dielectric nanoantennas are a promising alternative to plasmonic optical antennas for engineering light emission because of their low-loss nature in the optical spectrum. Nevertheless, it is still challenging to manipulate directional light emission with subwavelength all-dielectric nanoantennas. Here, we propose and numerically demonstrate that a hollow silicon nanodisk can serve as a versatile antenna for directing and enhancing the emission from either an electric or magnetic dipole emitter. When primarily coupled to both electric and magnetic dipole modes of a nanoantenna, broadband nearly-unidirectional emission can be realized by the interference of two modes, which can be spectrally tuned via the geometric parameters in an easy way. More importantly, the emission directions for the magnetic and electric dipole emitters are shown as opposite to each other through control of the phase difference between the induced magnetic and electric dipole modes of the antenna. Meanwhile, the Purcell factors can be enhanced by more than one order of magnitude and high quantum efficiencies can be maintained at the visible spectrum for both kinds of dipole emitters. We further show that these unidirectional emission phenomena can withstand small disorder effects of in-plane dipole orientation and location. Our study provides a simple yet versatile platform that can shape the emission of both magnetic and electric dipole emitters.

Traditional measurement-while drilling (MWD) logging tools use magnetic dipoles (coils) as transmitting and receiving antennas and operate at a fixed frequency. In this paper, a new MWD tool using electrical dipoles and using pulses as transmitting signals is investigated and its performance is compared to the coil-type MWD tool in the same formation using a numerical simulation technique. The performances of these two different tools are compared both in the time domain and in the frequency domain. A time-domain transmission-line-matrix (TLM) method is used to perform the analysis. It is shown that a pulsed electric-dipole type MWD tool is superior to a coil-type MWD tool in detection of formation boundaries in all the tested cases. It is further suggested that an MWD tool using electric dipole antennas may be more sensitive in practical applications.

Electromagnetic (EM) fields at a point in space generated by electric/magnetic dipole embedded in a general anisotropic stratified media can be analytically solved [1] by decomposing the fields into transverse electric (TE) and transverse magnetic(TM) modes. The electromagnetic field strengths are dependent on the nature (electric or magnetic) of dipoles, their placement in the stratified media, and relative location of dipoles. A three-layer stratified media has been employed in this paper to model the environment consisting of air, seawater, seabed. The mathematical formulations provided by Tang [1] are used for EM field calculation containing both magnitude and phase information of E and H fields for dipole antenna of 4 types namely: horizontal magnetic dipole along x- direction (HMDx), horizontal electric dipole along x- direction (HEDx), vertical magnetic dipole (VMD) and vertical electric dipole (VED). Parametric computational investigations are presented to delineate effects of i) the electric and magnetic properties of the media, ii) the nature and orientations of dipole sources, on EM fields at a specified observation point. It is observed that contributions from horizontal electric dipoles have comparable electric and magnetic field strengths at an observation point in the air.

Expressions for the total power radiated by magnetic and electric dipoles of arbitrary orientation located in a medium 1 at distance z0 from the interface to a homogeneous or planar stratified medium 2 are derived. A relation between the normalized powers radiated by magnetic and electric dipoles is established. For a homogeneous loss-free medium 2, curves of the normalized powers L(z0)/L∞ radiated by magnetic and electric dipoles versus the normalized distance z0/λ1 are presented for different values of the relative refractive index n = n2/n1 as the only parameter. The computer calculations are compared with analytical expressions derived for small and large distances. For n > 1, the contribution of the evanescent waves to the radiated power is calculated separately. We show that the classical results for the normalized radiated power yield the correct normalized spontaneous emission rates from an excited atomic state for electric and magnetic dipole transitions, respectively. We point out that the results for the electric dipole also give the change of the total power scattered by a small dielectric scattering particle when it is placed close to an interface.

Radiation from magnetic and electric dipole moments is a key subject in theory of electrodynamics. Although people treat the problem thoroughly in the context of frequency domain, the problem is still not well understood in the context of time domain, especially if dipole moments arbitrarily vary in time under action of external forces. Here, we scrutinize the instantaneous power radiated by magnetic and electric dipole moments, and report findings that are different from the conventional understanding of their instantaneous radiation found in textbooks. In contrast to the traditional far-field approach based on the Poynting vector, our analysis employs a near-field method based on the induced electromotive force, leading to corrective terms that are found to be consistent with time-domain numerical simulations, unlike previously reported expressions. Beyond its theoretical value, this work may also have significant impact in the field of time-varying metamaterials, especially in the study of radiation from subwavelength meta-atoms, scatterers and emitters that are temporally modulated.

Standards for electromagnetic protection taking into account human health have been established in a number of countries. Most of the present standards are expressed in terms of the intensities of electric and magnetic fields or the power density of the irradiating electromagnetic field. Usually, for conversion among these quantities, the relationship in the electromagnetic field at a distance far away (far field, plane wave) is used. However, near the electromagnetic source where the electromagnetic wave is the strongest, the relationship among the forementioned quantities varies depending on the location of the observation point or the type of the source. Therefore, there are recommendations to reconsider the standard values.The purpose of this paper is to provide fundamental references for modeling the electromagnetic sources in various electromagnetic equipment to reconsider the protection standard of the near field, and to develop the electromagnetic shielding theory in the near field. In this paper, the distance characteristics and the spatial distribution of the electromagnetic wave impedance characterizing the nature of the electromagnetic wave are studied near the elementary radiating elements such as the electric dipole, magnetic dipole, half‐wave dipole antenna, small current loop and small helical antenna.

A magnetic dipole array based time-domain (TD) modeling of electromagnetic near-field (NF) radiated by printed circuit boards (PCB) is introduced. The behavioral equivalent model of radiated emission using elementary magnetic dipoles compliments the previously described TD model using electric dipoles. The equivalent dipole model parameters are determined by the matrix inversion method from the time-dependent magnetic NF data. The proposed modeling approach was implemented in MATLAB. As a proof of concept, the TD magnetic NF radiated by a passive microstrip test PCB exited by a nanosecond-duration signal was considered. The modeled-magnetic NF maps were compared with the reference data in the observation planes situated at some centimeters above the tested PCB, showing good agreement. The comparison between magnetic and electric dipole models was performed, showing the advantage of the latter.

The problem of resonant energy transfer (RET) between an electric dipole donor, D, and an electric dipole acceptor, A, mediated by a passive, chiral third-body, T, is considered within the framework of molecular quantum electrodynamics theory. To account for the optical activity of the mediator, magnetic dipole and electric quadrupole coupling terms are included in addition to the leading electric dipole interaction term. Fourth-order diagrammatic time-dependent perturbation theory is used to obtain the matrix element. It is found that the Fermi golden rule rate depends on pure multipole moment polarizabilities and susceptibilities of T, as well as on various mixed electric and magnetic multipole moment response functions. The handedness of T manifests through mixed electric-magnetic dipole and mixed electric dipole-quadrupole polarizabilities, which affect the rate and, respectively, require the use of fourth-rank and sixth-rank Cartesian tensor averages over T, yielding non-vanishing isotropic rate formulae applicable to a chiral fluid medium. Terms of a similar order of magnitude proportional to the product of electric dipole polarizability and either magnetic dipole susceptibility or electric quadrupole polarizability of T are also computed for oriented and freely tumbling molecules. Migration rates dependent upon the product of the pure electric dipole or magnetic dipole polarizability with the mixed electric-magnetic or electric dipole-quadrupole analogs, which require fourth- and fifth-rank Cartesian tensor averaging, vanish for randomly oriented systems. Asymptotically limiting rate expressions are also evaluated. Insight is gained into RET occurring in complex media.

The classical theory of electrodynamics cannot explain the existence and structure of electric and magnetic dipoles, yet it incorporates such dipoles into its fundamental equations, simply by postulating their existence and properties, just as it postulates the existence and properties of electric charges and currents. Maxwell's macroscopic equations are mathematically exact and self-consistent differential equations that relate the electromagnetic (EM) field to its sources, namely, electric charge-density $\rho_{free}$, electric current-density $J_{free}$, polarization P, and magnetization M. At the level of Maxwell's macroscopic equations, there is no need for models of electric and magnetic dipoles. For example, whether a magnetic dipole is an Amperian current-loop or a Gilbertian pair of north and south magnetic monopoles has no effect on the solution of Maxwell's equations. Electromagnetic fields carry energy as well as linear and angular momenta, which they can exchange with material media - the seat of the sources of the EM field - thereby exerting force and torque on these media. In the Lorentz formulation of classical electrodynamics, the electric and magnetic fields, E and B, exert forces and torques on electric charge and current distributions. An electric dipole is then modeled as a pair of electric charges on a stick (or spring), and a magnetic dipole is modeled as an Amperian current loop, so that the Lorentz force law can be applied to the corresponding (bound) charges and (bound) currents of these dipoles. In contrast, the Einstein-Laub formulation circumvents the need for specific models of the dipoles by simply providing a recipe for calculating the force-density and torque-density exerted by the E and H fields on charge, current, polarization and magnetization.

Due to the recent interest in magnetic light-matter interactions, the magnetic dipole (MD) transitions in lanthanide ions have been studied for potential applications in nano-optics. Similar to lanthanide ions, transition-metal ions also exhibit strong MD emission at room temperature, but their prominent MD zero-phonon lines are often accompanied by significant electric dipole (ED) sideband emission. Here, we extend energy-momentum spectroscopy to time-resolved measurements, and use this technique to quantify the ED and MD contributions to light emission from trivalent chromium doped magnesium oxide (Cr(3+):MgO). This allows us to differentiate the MD (2)E → (4)A2 zero-phonon line from phonon-assisted (2)E → (4)A2 and (4)T2 → (4)A2 ED sidebands. We also demonstrate how the relative intensities of the sharp MD zero-phonon line and the broad ED sidebands can be used as a qualitative measure of the MD and ED local density of optical states.

The nonradiative electron transfer process between optically active ions in luminescent materials via electric dipole (ED)-magnetic dipole (MD) and magnetic dipole-magnetic dipole interaction has been investigated using a molecular quantum electrodynamics (QED) approach. The QED approach provides an intuitively simple but rigorous method of calculating the energy transfer probability through multipolar interactions such as the ED-MD and MD-MD interactions considered in this work. More details of this approach and its application to resonant energy transfer between molecules through the ED-ED interaction can be obtained from Craig and Thirunamachandran [1] and references therein. The energy transfer process between two ions in the present study is shown schematically in Figure 1. While the energy levels have been considered to be discrete within the QED formulation for calculating the transition probabilities, the broadening of the energy levels in solids has been processed using the spectral line shape functions without using the special normalization in the energy space used by Dexter [2]. The transition probabilities have been simplified further using experimentally observable spectroscopic parameters such radiative lifetime and absorption cross section. The final expressions for transition probability includes additional periodic functions that are meaningful only in the short wavelength regime of the electromagnetic radiation. In this presentation, we will consider two classes of Feynman diagrams to calculate the transition rates for the energy transfer process through ED-MD and MD-MD interactions. In all the cases, the interaction between two ions is mediated by photons. In one class of diagrams, the photon is emitted first by ion A, and then absorbed by ion B at a later time. In other class of diagram, the photon is absorbed by ion B first and then emitted by ion A. The second class pertains to emission and absorption of a virtual photon. The theoretical details of calculating the transition probabilities and their significance will be presented. It will also be shown how this approach could be used in other luminescence processes to determine their plausibility and the transition rates. [1] D. P. Craig and T. Thirunamachandran, Molecular Quantum Electrodynamics, Dover Publications, Mineola, New York (1998). [2] D. L. Dexter, J. Chem. Phys. 21, 836 (1953). Figure 1. A schematic diagram of energy transfer from ion A to ion B. The associated eigenstates and eigenenergies for each of these ions are indicated. The wavy line indicates transfer of energy from the ion A and B while the solid arrows indicate the electronic transitions each ion is going through simultaneously. Figure 1

We derive a novel expression for the relativistic energy of electric and magnetic dipoles in an external electromagnetic field and discuss its implications. In particular, we find the relativistic dependence of the energy of a dipole on its velocity, v, and show that in the most convenient presentation of the energy (when the proper electric (p0) and magnetic (m0) dipole moments are involved, whereas the electric (E) and magnetic (B) fields are defined in the laboratory frame), its value essentially depends on the orientation of the velocity, v, with respect to vectors p0, E, and m0, B. To better understand the relativistic behavior of the energy of electric and magnetic dipoles, we introduce the notion of “latent” momentum of an electric dipole, in addition to the known concept of “hidden” momentum of a magnetic dipole. We finally show that the contribution of energy terms related to “hidden” and “latent” momenta of an electric or magnetic dipole is important in the relativistic case.

The detectability of static electric and magnetic dipoles near the ocean bottom is examined. The search for these objects is assumed coherent and limited only by natural environmental noise. Short wavelength magnetic anomalies limit the range of the magnetic dipole source, while oceanic turbulence limits the range of the electric dipole. On a worldwide basis the maximum detectable range for a 10 watt torus is estimated to be 13-50 meters while the corresponding length for a 10 watt electric dipole is 90- 370 meters. Electrochemical effects at the receiving antenna will have to be minimized, however, to obtain the range advantage of the electric search.