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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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TL;DR: In this paper, the authors used the near field finite-difference time-domain method to calculate the current and specific absorption rate (SAR) distributions in an inhomogeneous model of a human head exposed to the electromagnetic waves irradiated from a cellular phone.
Abstract: The near field finite-difference time-domain method was used to calculate the current and specific absorption rate (SAR) distributions in an inhomogeneous model of a human head exposed to the electromagnetic waves irradiated from a cellular phone. The human head was simulated by a model of 57,263 block cells with inhomogeneous dielectric constant and conductivity. The cellular phone was modeled by an equivalent dipole antenna with an equivalent resistor of 120 ohms located at the center gap between the two arms of this dipole antenna. The transmitted power of the cellular phone was assumed to be 0.6 watts at a frequency of 835 MHz. For the head near the dipole antenna in the range of 1.0/spl sim/2.5 cm, the maximum currents and SAR's induced in the head were found in the ranges of 356/spl sim/551 mA and 1.23/spl sim/2.63 W/kg, respectively. It was also found that the maximum SAR induced in the head was below the IEEE's upper safety limit of 1.6 W/kg for the head to keep a distance from the dipole antenna by longer than 2.0 cm. >
72 citations
TL;DR: A study of these images shows that both the topography and the near electromagnetic field of the sample can be independently probed by this device, and clearly demonstrate a 20-nm (~lambda/35) resolution that has been achieved with smaller tips.
Abstract: Recently, a reflection-mode near-field optical microscope with an apertureless tungsten tip has been introduced and 100-nm resolution has been achieved [
R.
Bachelot
P.
Gleyzes
A. C.
Boccara
, Microsc. Microanal. Microstruc.5, 389–397 (1994)]. The optical signal is recorded in parallel with a tapping-mode atomic force microscope signal. By showing several images here, we confirm the capabilities of this device and clearly demonstrate a 20-nm (∼λ/35) resolution that has been achieved with smaller tips. A study of these images shows that both the topography and the near electromagnetic field of the sample can be independently probed by this device. Additionally, we discuss the principle of our approach, notably on the basis of interference phenomena between a Rayleigh scatterer and its image through the reflecting surface, and some of the setup’s experimental characteristics are presented.
71 citations
01 Oct 1975
TL;DR: In this article, general expressions for estimating the errors in the sum or difference far-field pattern of electrically large aperture antennas which measured by planar near-field scanning technique are derived.
Abstract: General expressions are derived for estimating the errors in the sum or difference far-field pattern of electrically large aperture antennas which measured by planar near-field scanning technique. Upper bounds are determined for the far-field errors produced by 1) the nonzero fields outside the finite scan area, 2) the inaccuracies in the positioning of the probe, 3) the distortion and non-linearities of the instrumentation which measures the amplitude and phase of the probe output, and 4) the multiple refractions. Computational errors, uncertainties in the receiving characteristics of the probe, and errors involved with measuring the input power to the test antenna are briefly discussed.
71 citations
TL;DR: In this article, a miniature magnetic-field probe for near-field measurements in 9-kHz-20-GHz bandwidth, which is applied to high-speed circuits, has been proposed and manufactured.
Abstract: A simple miniature magnetic-field probe for near-field measurements in 9-kHz–20-GHz bandwidth, which is applied to high-speed circuits, has been proposed and manufactured. The magnetic-field probe is built on a four-layer printed circuit board (PCB) using high-performance and low-loss Rogers material ( $\varepsilon _{r}= 3.48$ and tan $\delta = 0.0037$ ). Electric field coupling can be suppressed by PCB shielding structure of the magnetic-field probe. Coax-thru-hole via array technique is used to achieve impedance match. The resonance in working frequency band is suppressed through via fence, making $\vert S_{21}\vert $ rather smooth in the operation band. Experimental results show that the working frequency band is up to 9 kHz–20 GHz.
71 citations
TL;DR: In this paper, two fundamentally different approaches are used in deriving three sets of formulas that give the fields in the source-free half space z>z/sub 0/ in terms of their values on the scan plane z=z sub 0/.
Abstract: Time-domain planar near-field measurement techniques are formulated for acoustic and electromagnetic fields. Probe correction is ignored in that it is assumed that the probe measures the exact values of the field on the scan plane. Two fundamentally different approaches are used in deriving three sets of formulas that give the fields in the source-free half space z>z/sub 0/ in terms of their values on the scan plane z=z/sub 0/. In the first approach the time-domain formulas are obtained by inverse Fourier transforming the corresponding frequency-domain formulas. In the second approach the time-domain formulas are derived directly in the time domain by working with time-domain Green's functions. >
71 citations