In this paper, a novel design and implementation of a software‐defined high‐frequency ionospheric radar, the Penn State Ionospheric Radar Imager (PIRI), is described. Furthermore, preliminary results ...produced by the system (located at 40.71° N, 77.97° W) are presented. PIRI is designed to be a modest and low‐cost radar system, which is composed mostly of commercial‐off‐the‐shelf products and utilizing open‐source software to perform pulse generation, pulse coding, downconversion, data acquisition, and signal processing. It is designed to be mobile, as it can easily be deployed at temporary locations to study local ionospheric disturbances. For the results presented herein, the radar operating frequency was 5.125 MHz. However, as the system is software defined and short active receive antennas are used, only the transmit antenna needs to be changed to operate over the entire high‐frequency (HF) band. The two orthogonal receive antennas enable both linear and circular polarization measurements. Peak transmit power of the system is 500 W. PIRI is designed to be a modest and cost‐effective alternative to the current standard HF ionospheric sounding systems and can be readily replicated.
Key Points
Implementation of a low cost, software‐defined HF radar for ionospheric research is explained
Open‐source software and commercial‐off‐the‐shelf products are used
The system allows comprehensive analysis of events such as sporadic E and spread F
This study investigates a means through which commercially available computational electromagnetic modeling software can be used to predict radar cross sections (RCSs) of airborne organisms of ...interest as a preliminary step toward enabling detection and tracking of these organisms. This work aims to analyze this framework for the specialized case of the honey bee ( Apis mellifera ), given its critical role in food security as a major pollinator of agricultural crops. A Method-of-Moment (MoM) solver made available by Altair's FEKO is used to conduct the analysis over varying frequencies, illumination angles, and polarizations. A high degree of correlation between measured and modeled cross sections is noted. Maximum RCS root-mean-square errors (RMSEs) between the two are approximately 4 and 5 dB relative to 1 <inline-formula> <tex-math notation="LaTeX">\text{m}^{2} </tex-math></inline-formula> (dBsm) for Horizontal polarization (H-pol) and Vertical polarization (V-pol) X-band measurements, respectively. Findings of this study also highlight the sensitivity of both modeled and measured RCS estimates to the dielectric properties of honey bees and the corrupting effects that this may have if not accounted for accurately, where errors are shown to increase from 2 to 5 dBsm, but without significantly corrupting the overall RCS azimuth profile.
As vector wavefunctions are available to represent incident and scattered fields in an isotropic dielectric-magnetic medium endowed with magnetoelectric gyrotropy, a transition matrix can be ...conceptualized to relate the scattered field coefficients to the incident field coefficients for scattering by an arbitrary scatterer composed of a linear medium. The elements of the transition matrix must satisfy certain conditions for zero backscattering. For a scatterer composed of a uniaxial dielectric-magnetic medium endowed with magnetoelectric gyrotropy, the extended boundary condition method (EBCM) can be formulated to determine the transition matrix. The numerical results obtained thereby lead to the formulation of a sufficient set of three zero-backscattering conditions: (i) the scatterer is a body of revolution with the incident plane wave propagating along the axis of revolution; (ii) the impedances of both mediums are identical; and (iii) the magnetoelectric-gyrotropy vectors of both mediums are aligned along the axis of revolution, whether or not both magnetoelectric-gyrotropy vectors are co-parallel.
The energy extinction cross section of a concentrically layered sphere varies with velocity as the Doppler shift moves the spectral content of the incident signal in the sphere's co-moving inertial ...reference frame toward or away from resonances of the sphere. Computations for hollow gold nanospheres show that the energy extinction cross section is high when the Doppler shift moves the incident signal's spectral content in the co-moving frame near the wavelength of the sphere's localized surface plasmon resonance. The energy extinction cross section of a three-layer sphere consisting of an olivine-silicate core surrounded by a porous and a magnetite layer, which is used to explain extinction caused by interstellar dust, also depends strongly on velocity. For this sphere, computations show that the energy extinction cross section is high when the Doppler shift moves the spectral content of the incident signal near either of olivine-silicate's two localized surface phonon resonances at 9.7 μm and 18 μm.
•Energy extinction cross sections of layered spheres depend on velocity.•Doppler shift moves the incident signal toward or away from resonances.•A hollow gold nanosphere's cross section depends on thickness and velocity.
The extended boundary condition method can be used to study planewave scattering by an ellipsoid composed of an orthorhombic dielectric-magnetic material whose relative permittivity dyadic is a ...scalar multiple of its relative permeability dyadic. The scattered and internal field phasors can be expanded in terms of appropriate vector spherical wavefunctions with unknown expansion coefficients, whereas the incident field phasors can be similarly expanded but with known expansion coefficients. The scattered-field coefficients are related to the incident-field coefficients through a matrix. The scattering, absorption, and extinction efficiencies were calculated thereby in relation to the propagation direction and the polarization state of the incident plane wave, the constitutive-anisotropy parameters, and the nonsphericity parameters of the ellipsoid, when the eigenvectors of the real permittivity dyadic are aligned along the three semi-axes of the ellipsoid. As the electrical size of the ellipsoid increases, multiple lobes appear in the scattering pattern. The total scattering efficiency can be smaller than the absorption efficiency for some configurations of the incident plane wave but not necessarily for others. The nonsphericity of the object has a stronger influence on the total scattering efficiency than on the absorption efficiency. The forward-scattering efficiency increases monotonically with the electrical size for all configurations of the incident plane wave, and so does the backscattering efficiency for some configurations. For other configurations, the backscattering efficiency has an undulating behavior with increase in electrical size, and is highly affected by the shape and the constitutive anisotropy of the ellipsoid.
The simplest Lorentz-nonreciprocal medium has the constitutive relations (\({\bf D} =\epso {\bf E} -{\bf \Gamma}\times {\bf H}\) and \({\bf B} =\muo {\bf H} + {\bf \Gamma}\times{\bf E}\)). Scattering ...by a three-dimensional object composed of this medium was investigated using the extended boundary condition method. Scattering by this object in free space must be attributed to non-zero \(\Gamma=\vert\bf \Gamma\vert\). The differential scattering efficiency is immune to the transformation of the incident toroidal electric field phasor into a poloidal electric field phasor, or \textit{vice versa}, and a consequence of this source-invariance is the polarization-state invariance of the differential scattering efficiency when the irradiating field is a plane wave. Both the total scattering and forward-scattering efficiencies of an ellipsoid composed of the simplest Lorentz-nonreciprocal medium are maximum when the plane wave is incident in a direction {coparallel (but not antiparallel)} to \(\bf \Gamma\), and the backscattering efficiency is minimum when \(\bf \Gamma\) is {parallel} to the incidence direction. The total scattering and the forward-scattering efficiencies are maximum when the incidence direction is parallel to the largest semi-axis of the ellipsoid if the incidence direction is coparallel (but not antiparallel) to \(\bf \Gamma\). Lorentz nonreciprocity in an object is thus intimately connected to the shape of that object in affecting the scattered field.
Humans will launch spacecraft that travel at an appreciable fraction of the speed of light. Spacecraft traffic will be tracked by radar. Scattering of pulsed electromagnetic fields by an object in ...uniform translational motion at relativistic speed may be computed using the frame-hopping technique. Pulse scattering depends strongly on the velocity, shape, orientation, and composition of the object. The peak magnitude of the backscattered signal varies by many orders of magnitude depending on whether the object is advancing toward or receding away from the source of the interrogating signal. The peak magnitude of the backscattered signal goes to zero as the object recedes from the observer at a velocity very closely approaching light speed, rendering the object invisible to the observer. The energy scattered by an object in motion may increase or decrease relative to the energy scattered by the same object at rest. Both the magnitude and sign of the change depend on the velocity of the object, as well as on its shape, orientation, and composition. In some cases, the change in total scattered energy is greatest when the object is moving transversely to the propagation direction of the interrogating signal, even though the Doppler effect is strongest when the motion is parallel or antiparallel to the propagation direction.
The energy extinction cross section of a concentrically layered sphere varies with velocity as the Doppler shift moves the spectral content of the incident signal in the sphere's co-moving inertial ...reference frame toward or away from resonances of the sphere. Computations for hollow gold nanospheres show that the energy extinction cross section is high when the Doppler shift moves the incident signal's spectral content in the co-moving frame near the wavelength of the sphere's localized surface plasmon resonance. The energy extinction cross section of a three-layer sphere consisting of an olivine-silicate core surrounded by a porous and a magnetite layer, which is used to explain extinction caused by interstellar dust, also depends strongly on velocity. For this sphere, computations show that the energy extinction cross section is high when the Doppler shift moves the spectral content of the incident signal near either of olivine-silicate's two localized surface phonon resonances at 9.7 \(\mu\)m and 18 \(\mu\)m.
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