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Near and far field
About: Near and far field is a research topic. Over the lifetime, 15922 publications have been published within this topic receiving 220571 citations.
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94 citations
01 Nov 1961
TL;DR: In this paper, the amplitude and phase of each mode were calculated by a Fourier analysis of the measured near field, and the radiation pattern was obtained as a series of radially expanding modes containing these measured amplitudes and phases.
Abstract: A new method is described of predicting an aerial radiation pattern from near-field measurements. The essence of this method is the expansion of the radiated field in terms of a series of radially expanding modes. The amplitude and phase of each mode are calculated by a Fourier analysis of the measured near field, and the radiation pattern is obtained as a Fourier series containing these measured amplitudes and phases. The theory is described in detail for a cylindrical (2-dimensional) aerial, and experimental results are presented to confirm the validity of this theory. The way in which the method may be extended to 3-dimensional aerials is explained. The method has the advantage that it can be applied anywhere in the near field
94 citations
TL;DR: In this article, the authors used a graphene-based magnetic resonator to realize single, nanometer-scale acoustic graphene plasmon cavities, reaching mode volume confinement factors of 5 × 1010.
Abstract: Acoustic graphene plasmons are highly confined electromagnetic modes carrying large momentum and low loss in the mid-infrared and terahertz spectra. However, until now they have been restricted to micrometer-scale areas, reducing their confinement potential by several orders of magnitude. Using a graphene-based magnetic resonator, we realized single, nanometer-scale acoustic graphene plasmon cavities, reaching mode volume confinement factors of ~5 × 1010 Such a cavity acts as a mid-infrared nanoantenna, which is efficiently excited from the far field and is electrically tunable over an extremely large broadband spectrum. Our approach provides a platform for studying ultrastrong-coupling phenomena, such as chemical manipulation via vibrational strong coupling, as well as a path to efficient detectors and sensors operating in this long-wavelength spectral range.
94 citations
TL;DR: In this article, the main physical properties of the optical signals near a surface in the absence of any probe tip are discussed and the interpretation of the detection process is reviewed on the basis of a discussion about the possibility of establishing direct comparisons between experimental images and the solutions of Maxwell equations or the electromagnetic local density of states.
Abstract: This paper deals with the principles of detection of optical signals near a surface in a manner permitting the mapping of the distribution of the fields close to various kinds of illuminated samples. We begin with a discussion of the main physical properties of the optical fields near a surface in the absence of any probe tip. This mainly concerns phenomena involving evanescent waves for which the local decay lengths are governed not only by the sizes but also by the intrinsic properties of the surface structures. The interpretation of the detection process is reviewed on the basis of a discussion about the possibility of establishing direct comparisons between experimental images and the solutions of Maxwell equations or the electromagnetic local density of states.
94 citations
TL;DR: An ultraminiature 434 MHz antenna immune to impedance detuning caused by varying electromagnetic properties of the surrounding biological environment is proposed, contributing to the further development of a new generation of miniature in-body devices that involve complex and dense integration of sensors, logic, and power source.
Abstract: Progress in implantable and ingestible wireless biotelemetry requires versatile and efficient antennas to communicate reliably from a body. We propose an ultraminiature 434 MHz antenna immune to impedance detuning caused by varying electromagnetic properties of the surrounding biological environment. It is designed for a standard input impedance of 50 $\Omega $ . The antenna is synthesized and miniaturized using a hybrid analytical–numerical approach, and then optimized to conform to the inner surface of a 17 mm long biocompatible encapsulation (7 mm diameter). The substrate is 50 $\mu \text{m}$ thick. The capsule antenna is analyzed both in simplified and anatomically realistic heterogeneous phantoms. It remains matched at common implantation sites and through the whole gastrointestinal tract. Enhanced robustness allows using the antenna for a wide range of in-body applications. Computed reflection coefficients and radiation performance both show good agreement with measurements. The far field is characterized with the direct illumination technique using an analog fiber optic link. The realized gain (measured max. value −19.6 dBi) exceeds the counterparts by about 3 dBi. The proposed antenna contributes to the further development of a new generation of miniature in-body devices that involve complex and dense integration of sensors, logic, and power source.
94 citations