Free-space Energy Research Articles

SIW‐backed multiplexing slot antenna for multiple wireless system integration

AbstractIn this letter, a planar cavity‐backed multiplexing antenna (SMA) is proposed and validated experimentally. A planar cavity is realized by using a novel transmission line known as substrate‐integrated waveguide (SIW) technology. The design comprises five SIW cavities and each one consisting of a slot for launching the energy in free space. Three different types of slots are employed for lower mutual coupling and compact circuit integration. The individual feeds are created in such a way, that antenna produces five distinct resonant frequencies in the dominant mode while maintaining sufficient mutual port isolation. Finally, the proposed concept is validated with experiments and results show acceptable agreement with the simulated counterparts. The design shows five operating frequency channels with center frequencies of 5.2, 5.5, 5.75, 6.2, and 6.8 GHz. The mutual isolation between any two radiating elements retains below −21 dB and the average gain of the antenna is better than 3.5 dBi at each resonant frequency. The proposed SMA element can be used to cover a wide range of wireless access points and seems suitable for multiple wireless system integration.

Conditions for Scalar and Electromagnetic Wave Pulses to Be “Strange” or Not

Vector-valued electromagnetic waves for which the integral of the electric field over time is zero at every location in space were characterized as “usual” by Bessonov several decades ago. Otherwise, they were called “strange”. Recently, Popov and Vinogradov studied conditions leading to usual waves using a spectral representation. Their main result is that pulses of finite energy in free space are usual and, consequently, bipolar. However, they do not exclude the possibility of the existence of finite-energy strange pulses, although quite exotic, in a vacuum. Our emphasis in this article is to examine what the relevant necessary and sufficient conditions are for usual and strange waves, particularly for scalar pulses. Illustrative examples are provided, including spherical symmetric collapsing pulses, propagation-invariant, and the so-called almost undistorted spatiotemporally localized waves. Finally, source-generated strange electromagnetic fields are reported.

Far-Field Wireless Power Harvesting: Nonlinear Modeling, Rectenna Design, and Emerging Applications

Continuous advances in ultralow-power electronics are a fundamental driving force of developing far-field wireless power harvesting techniques, which generally harnesses low/ambient energy in free space or dedicated wireless power from a power base station. This article reviews recent developments and technology trends in far-field (radiative) wireless power harvesting, including modeling of rectification process inside nonlinear devices, insights into rectenna system design, and demonstrations of emerging applications. The rectification process inside nonlinear devices will be explored, upon which a device selection guideline is provided to help quickly identify suitable devices. Then, the optimization of rectenna design is discussed to realize efficiency enhancement at a limited input power level. Since far-field wireless power harvesting has become a critical enabling technology for battery-free Internet of Things, a series of promising applications is demonstrated in this article to highlight the challenges and opportunities in the field.

Enhanced optical transmission of composite subwavelength rectangular-hole array based on metal silver thin-film

Metal nanostructures can effectively couple the optical radiation energy in free space to a highly confined surface mode due to the excitation of surface plasmons (SPs), resulting in a greatly enhanced local field in the nanoscale range of the metal surface, it’s great significance for the collection and excitation of broadband light. In order to achieve the broadband and high transmittance of metal nanostructures, a composite rectangular-hole array metal micro/nano structure was designed in this paper, and the transmission characteristics of the structure were studied by using the finite difference time domain (FDTD). The results showed that compared with the single hole array, the compound hole structure has many advantages, such as optical field enhancement, tenability and so on, and there are multiple transmission peaks in the transmission spectrum. In addition, we discussed the effects of the length and width of the rectangular holes on the light transmission characteristics of the structure array. For example, with the increase of the length b of the rectangular hole, the maximum transmittance of the structure increases from 79.7% to 88.3%, and corresponding to the central peak increases from 526 nm to 611 nm. Both the transmission bandwidth and transmittance are improved. While the change of the length a of the rectangular hole produces a peculiar multi-peak phenomenon, the analysis shows that when the length a of the rectangular hole is 250 nm, the maximum transmittance of the full symmetric composite rectangular hole array can reach up to 93% and the FWHM of the transmission peak is 354 nm, much larger than the 80 nm proposed in ref. [27] , so the frequency selectivity will be enhanced in the design of the filter. At the same time, the effect of the side length D of the center square hole on the transmission characteristics of the structure array is also discussed. The results of our research have certain guiding significance for the development of enhanced optical transmission theory and application value in the fields of novel optical sensors, t filter and optical transparent electrode.

Closed-form, localized wave solutions in optical fiber waveguides

A novel bidirectional decomposition of exact solutions to the scalar wave equation has been shown to form a natural basis for synthesizing localized-wave (LW) solutions that describe localized, slowly decaying transmission of energy in free space. We present a theoretical feasibility study that shows the existence of LW solutions in optical fiber waveguides. As with the free-space case, these optical waveguide LW solutions propagate over long distances, undergoing only local variations. Four different source modulation spectra that give rise to solutions similar to focus wave modes, splash pulses, the scalar equivalent of Hillion's spinor modes, and the modified power spectrum pulses are considered. A detailed study of the modified power spectrum pulse is performed, the practical issues regarding the source spectra are addressed, and the distances over which such LW solutions maintain their nondecaying nature are quantified.

LXXXIII.Suggested explanation of the contradiction between the Rayleigh-Jeans formula and experiment

Abstract Reasons are advanced, on classical grounds, to show that modes of resonance do not exist for radiant energy in free space bounded by a material surface. This leads to the conclusion that the Rayleigh-Jeans formula is not theoretically applicable to the partition of energy between space and a material body.