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.

Canonical sources and duality in chiral media (antenna arrays)

Abstract: The authors examine the characteristics of antenna arrays embedded in unbounded chiral media using the Green's dyadic for electric sources and the Green's vector for magnetic sources. The purpose is to bring to light the new characteristics of sources, both point and extended, which interact with this medium and to examine general characteristics of sources located in a medium with handedness. Very simple quality relations are presented that are characteristic of chiral media when the results are written in terms of the circular eigenmodes. Appropriate measures of chirality such as the chirality admittance and impedance and a dimensionless chirality factor are introduced as needed. It is shown that, in the far field, both point and extended sources, whether electric or magnetic, radiate two electromagnetic eigenmodes which are of opposing handedness. Sources that access only one of the eigenmodes of the medium are demonstrated. Several applications of the results and array performance in chiral media are noted. >

Ultrasonic diagnostic imaging systems for varying depths of field

Abstract: An ultrasonic diagnostic imaging system is described in which a multi-element transducer array transmits a focused beam of energy from the transducer elements As the depths of focus'is varied between near and far field focusing under operator control, the nominal frequency of the transmitted ultrasound energy is varied correspondingly by the system, from relatively high frequency transmission in the near field to relatively low frequency transmission in the far field

Radiation forces on a Rayleigh dielectric sphere in a patterned optical near field

Abstract: We report on the study of the radiation forces exerted on a Rayleigh dielectric particle by a patterned optical near-field landscape at an interface decorated with resonant gold nanostructures. This configuration allows for the generation of a large array of surface subwavelength optical traps from an extended collimated beam, which may be of interest for parallel optical manipulation and sorting of submicrometer objects.

Amplitude- and Phase-Resolved Near-Field Mapping of Infrared Antenna Modes by Transmission-Mode Scattering-Type Near-Field Microscopy†

Abstract: We describe transmission-mode scattering-type near-field optical microscopy (s-SNOM) with interferometric detection. Using this technique, we map the near-field modes of infrared antennas in both amplitude and phase. The use of dielectric probing tips, higher-harmonic demodulation, and a complex-valued subtraction of residual background yields accurate near-field images of the antenna modes. We map metallic nanorods, disks, and triangles, designed for antenna resonance at mid-infrared frequencies, in good agreement with numerical calculations of the modal field distribution. Furthermore, we show that transmission-mode s-SNOM can map the z-component of the antenna near fields. Our results establish a basis for future near-field characterization of complex antenna structures for molecular sensing and spectroscopy.