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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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08 Dec 2005
TL;DR: In this article, near field properties are used to determine a location by utilizing two magnetic antennas arranged so that the null axes are perpendicular and lie in a plane of interest, such as the horizontal plane.
Abstract: Near field properties are used to determine a location by utilizing two magnetic antennas arranged so that the null axes are perpendicular and lie in a plane of interest, such as the horizontal plane. The two antennas may be used as transmitting antennas or receiving antennas. The antennas may be driven so as to produce an equivalent of an omnidirectional pattern in the plane of interest by driving the antennas in an orthogonal manner. The orthogonal drive may be time orthogonal or phase orthogonal. A location is determined based on near field response which may include propagation properties, which may include amplitude, phase, relative amplitude, or phase, or other properties. In one embodiment, multiple transmitters are utilized to determine the location of a single receiver. In another embodiment, multiple receivers are utilized to determine the location of a single transmitter. A space efficient magnetic antenna is disclosed.
49 citations
TL;DR: An analytical model has been developed for the generation of surface acoustic (Rayleigh) waves in an isotropic solid by a thermoelastic laser line source and quantitative agreement has been found for experiments carried out with an interferometric optical probe on a duraluminum plate.
49 citations
TL;DR: Wilson et al. as mentioned in this paper proposed a single-chip optonanomechanical transducer based on a high-stress Si3N4 nanobeam monolithically integrated into the evanescent near field of SiO2 microdisk cavity.
Abstract: Placing a nanomechanical object in the evanescent near field of a high-Q optical microcavity gives access to strong gradient forces and quantum-limited displacement readout, offering an attractive platform for both precision sensing technology and basic quantum optics research. Robustly implementing this platform is challenging, however, as it requires integrating optically smooth surfaces separated by less than or similar to lambda/10. Here we describe an exceptionally high-cooperativity, single-chip optonanomechanical transducer based on a high-stress Si3N4 nanobeam monolithically integrated into the evanescent near field of SiO2 microdisk cavity. Employing a vertical integration technique based on planarized sacrificial layers, we realize beam-disk gaps as little as 25 nm while maintaining mechanical Qf > 10(12) Hz and intrinsic optical Q similar to 10(7). The combination of low loss, small gap, and parallel-plane geometry results in radio-frequency flexural modes with vacuum optomechanical coupling rates of 100 kHz, single-photon cooperativities in excess of unity, and large zero-point frequency (displacement) noise amplitudes of 10 kHz (fm) / root Hz. In conjunction with the high power-handling capacity of SiO2 and low extraneous substrate noise, the transducer performs particularly well as a sensor, with recent deployment in a 4-K cryostat realizing a displacement imprecision 40 dB below that at the standard quantum limit (SQL) and an imprecision-backaction product < 5h [Wilson et al., Nature (London) 524, 325 (2015)]. In this report, we provide a comprehensive description of device design, fabrication, and characterization, with an emphasis on extending Heisenberg-limited readout to room temperature. Towards this end, we describe a roomtemperature experiment in which a displacement imprecision 32 dB below that at the SQL and an imprecision-backaction product < 60h is achieved. Our results extend the outlook for measurement-based quantum control of nanomechanical oscillators and suggest an alternative platform for functionally integrated "hybrid" quantum optomechanics.
49 citations
01 Jan 1990
TL;DR: In this paper, an overview of the theory of the near-zone Doppler effect is presented. But, the authors do not consider the effect of near-zones on the spectrum of the reflector and Horn antennas.
Abstract: 1 Electromagnetic Waves in Chiral Media.- 2 Norms of Time-Domain Functions and Convolution Operators.- 3 An Overview of the Theory of the Near-Zone Doppler Effect.- 4 Analysis of Channeled-Substrate-Planar Double-Heterostructure Lasers Using the Effective Index Technique.- 5 Correlation Theory of Electromagnetic Radiation Using Multipole Expansions.- 6 On Fractal Electrodynamics.- 7 Fringing Field Effects in VLSI Structures.- 8 Some Methods of Reducing the Sidelobe Radiation of Existing Reflector and Horn Antennas.- 9 Group Symmetries of Antenna Arrays.- 10 Many-Body Problems in Electromagnetic Theory.- 11 Electromagnetic Shielding.- 12 Coherence Effects in Guided Wave Optical Systems.- 13 How Scattering Increases as an Edge Is Blunted: The Case of an Electric Field Parallel to the Edge.- 14 Electromagnetic Fields Determined from Two-Dimensional Infrared Thermal Patterns.- 15 Dielectric Waveguide Theory.- Author Index.
49 citations
TL;DR: In this paper, the authors studied the near-field enhancement and subwavelength imaging properties of a device comprising a coupled pair of two-dimensional arrays of resonant nanospheres.
Abstract: Near-field enhancement and subwavelength imaging properties of a device comprising a coupled pair of two-dimensional arrays of resonant nanospheres are studied. The concept of using two coupled material sheets possessing surface mode resonances for evanescent field enhancement is already well established in the microwave region. We show that the same principles can be applied also in the optical region, where the performance of the resonant sheets can be realized with the use of metallic nanoparticles. We present a design of such structures and study the electric field distributions in the image plane of such a device.
49 citations