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A highly sensitive magnetic field sensor based on mode coupling effect in a microstructured optical fiber (MOF) was theoretically investigated by using the finite element method. Magnetic fluid with refractive index higher than silica was designed to be filled into one cladding air hole in MOF to form a defect core. The coupling wavelength between fiber core modes and defect core modes can be modulated by external magnetic field. Simulation results show that the measuring sensitivity of magnetic field and figure of merit reached 1620 pm/Oe, 0.081/Oe in x-polarized mode and 1790 pm/Oe, 0.045/Oe in y-polarized mode, respectively. Meanwhile, the intensity of magnetic field depicts a good linear relationship with the coupling wavelength for both orthogonal polarized directions in the range of 25–175.9 Oe. The performance of the designed magnetic field sensor can be improved by optimizing the structural parameters in MOF. [ABSTRACT FROM AUTHOR]

Whistler mode hiss acts as an important loss mechanism contributing to the radiation belt electron dynamics inside the plasmasphere and plasmaspheric plumes. Based on Van Allen Probes observations from September 2012 to December 2015, we conduct a detailed analysis of hiss properties in plasmaspheric plumes and illustrate that corresponding to the highest occurrence probability of plumes at L = 5.0–6.0 and MLT = 18–21, hiss emissions occur concurrently with a rate of >~80%. Plume hiss can efficiently scatter ~10‐ to 100‐keV electrons at rates up to ~10−4 s−1 near the loss cone, and the resultant electron loss timescales vary largely with energy, that is, from less than an hour for tens of kiloelectron volt electrons to several days for hundreds of kiloelectron volt electrons and to >100 days for >5‐MeV electrons. These newly obtained statistical properties of plume hiss and associated electron scattering effects are useful to future modeling efforts of radiation belt electron dynamics. Key Points: Plume hiss occurs concurrently with a rate of >~80%, corresponding to the highest occurrence rate of plumes at L = 5.0‐6.0 and MLT = 18‐21Plume hiss is efficient for pitch angle scattering ~10‐ to 100‐keV electrons near the loss conePlume hiss can drive more efficient scattering of >500‐keV electrons at higher L‐shells than normal frequency hiss at lower L‐shells [ABSTRACT FROM AUTHOR]

Abstract A magnetic field sensor based on magnetic fluids (MFs) selectively infilling photonic crystal fiber (PCF) is designed and analyzed by the finite-element method (FEM). The PCF consists of three-layer air holes in the cladding which are arranged in regular hexagonal lattice. The left and right sides of the fiber core are made up of two larger circular air holes while the upper and below sides are made up of four smaller circular air holes which are benefit to enhance the birefringent effect. MFs are injected into one air hole in the second cladding layer which generates a defect core with high confinement loss. Air holes around the defect core are asymmetrically distributed which can enhance the birefringence of the transmission mode in defect core. When the phase matching condition between core modes and defect core modes is satisfied, the light transmitting in the core couples to the defect core and a sharp decrease of light transmitting energy occurs. The refractive index of defect core modes is modulated by magnetic field strength. The peak wavelengths of confinement loss spectra depicts pretty well linear relationship with magnetic field strength in the detected range of 30–130 Oe. The magnetic field measuring sensitivity reaches to 584 pm/Oe for x-polarized mode and 700 pm/Oe for y-polarized mode, respectively. [ABSTRACT FROM AUTHOR]

Abstract: Plasmaspheric hiss is known to play an important role in radiation belt electron dynamics in high plasma density regions. We present observations of two crossings of a plasmaspheric plume by the Van Allen Probes on 26 December 2012, which occurred unusually at the post‐midnight‐to‐dawn sector between L ~ 4–6 during a geomagnetically quiet period. This plume exhibited pronounced electron densities higher than those of the average plume level. Moderate hiss emissions accompanied the two plume crossings with the peak power at about 100 Hz. Quantification of quasi‐linear bounce‐averaged electron scattering rates by hiss in the plume demonstrates that the waves are efficient to pitch angle scatter ~10–100 keV electrons at rates up to ~10−4 s−1 near the loss cone but become gradually insignificant to scatter the higher energy electron population. The resultant timescales of electron loss due to hiss in the nightside plume vary largely with electron kinetic energy over 3 orders of magnitude, that is, from several hours for tens of keV electrons to a few days for hundreds of keV electrons to well above 100 days for >1 MeV electrons. Changing slightly with L‐shell and the multiquartile profile of hiss spectral intensity, these electron loss timescales suggest that hiss emissions in the nightside plume act as a viable candidate for the fast loss of the ≲100 keV electrons and the slow decay of higher energy electrons. [ABSTRACT FROM AUTHOR]

A new scheme of antenna for wireless body area networks is proposed. A coupling-fed circular-patch antenna with TM01 mode is designed, simulated, and tested, which radiates omni-directional pattern along the body surface and has linear polarization normal to the surface. Both simulated and measured results show this antenna satisfies the expected 9% bandwidth (5.725–5.875 GHz) for return-loss ≤ -10 dB, and it is suitable for on-body communication application. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 2623–2627, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24712 [ABSTRACT FROM AUTHOR]

Scattering by plasmaspheric hiss is responsible for the newly reported reversed energy spectra with abundant high‐energy but fewer low‐energy electrons between hundreds of kiloelectronvolts and ~2 MeV in the inner magnetosphere. To deepen our understanding of the contributions of plasmaspheric hiss to the formation of reversed electron energy spectrum, we conduct a detailed theoretical parametric analysis through numerical simulations to explore the sensitivity of hiss‐induced reversed electron energy spectrum to ambient magnetic field, plasma density, and hiss wave distribution properties. Given L‐shell, variations of ambient plasma density and wave frequency spectrum contribute importantly to the formation of reversed electron energy spectrum, while variations of background magnetic field (which usually shows small changes in the plasmasphere) and wave normal angle distribution play a less effective role. Our study suggests that the reversed electron energy spectrum has important implications for unveiling the sophisticated energy‐dependent nature of wave‐particle interactions and energetic particle dynamics in geospace. Key Points: Variations of ambient plasma density and wave frequency spectrum contribute importantly to the formation of reversed electron energy spectraVariations of background magnetic field and wave normal angle distribution play a less effective roleReversed energy spectra are more likely to form and evolve more pronouncedly at lower pitch angles [ABSTRACT FROM AUTHOR]

Highlights • The proposed PCF filter can realize three kinds of filtering effects. • Two ultra-large air holes makes the process of plating gold film more convenient. • Ultra-high crosstalks and losses can be obtained at the communication windows. • The filtering bandwidth can reach 700 nm at the communication window of 1550 nm. Abstract In this study, we present a single-polarization photonic crystal fiber filter. The metallic gold is used as the surface plasmon resonance activity material, which is deposited on the inner wall of the two ultra-large holes. The properties of the photonic crystal fiber filter are investigated by the finite element method. By adjusting the structural parameters and gold film thickness, three kinds of filtering effects can be obtained at the communication windows. When the length of the optical fiber is 1 mm, one of the filtering effects can achieve loss of 588.900 dB/cm at the communication window of 1310 nm, and the corresponding filtering bandwidth equals to 270 nm; the other two kinds of filtering effects can be applied to the communication window of 1550 nm, and the losses are 569.682 and 971.330 dB/cm and the corresponding filtering bandwidths equal to 700 and 630 nm, respectively. The proposed photonic crystal fiber filter shows great advantages compared with some previous reports on filtering. [ABSTRACT FROM AUTHOR]

Both magnetosonic (MS) waves and plasmaspheric hiss can resonantly scatter outer radiation belt electrons, leading to various electron pitch angle distribution. Based on electron diffusion coefficients calculations and 2‐D Fokker‐Planck diffusion simulations, we perform a parametric study to quantitatively investigate the net electron scattering effect and the relative contributions of simultaneously occurring hiss and MS waves with groups of different wave amplitude combinations. It is found that the combined scattering effects are dominated by pitch angle scattering due to hiss emissions at L = 4, when their amplitude is comparable to or stronger than that of MS waves, thereby producing the butterfly, top‐hat, flat‐top, and pancake pitch angle distributions, while the butterfly distributions can evolve over a broader energy range when MS waves join the combined scattering effects. Our results demonstrate that the relative intensities of various plasma waves play an essential role in controlling the radiation belt electron dynamics. Plain Language Summary: The Earth's outer radiation belt electrons exhibit high dynamics in terms of both pitch angle and energy distributions. Because MS waves and hiss can frequently occur simultaneously inside the plasmasphere, it is important to understand their combined scattering effects on and relative contributions to the radiation belt electron dynamics. Although a number of case studies have been performed to analyze the consequences of combined scattering by these two concurrently occurring plasma waves, there lack parametric and comprehensive investigations to look into the combined scattering effects corresponding to groups of different intensities of the two wave modes. In this letter, by combining the calculations of wave‐induced electron diffusion coefficients and 2‐D Fokker‐Plank diffusion simulations, we quantitatively analyze electron pitch angle and energy distributions under the impacts of 255 different wave amplitude combinations of these two wave modes, which can lead to top‐hat, pancake, flat‐top, and butterfly PADs. Our results indicate that the relative wave amplitudes of these two waves play an essential role in controlling the dynamic variations of radiation belt electron distribution. Key Points: A parametric study is performed to investigate the combined electron scattering effect by hiss and MS waves with different wave amplitudesThe combined scattering effect of concurrent hiss and MS waves can lead to top‐hat, flat‐top, pancake, and butterfly PADsThe relative intensities of various plasma waves are important in controlling dynamic variations of radiation belt electron distribution [ABSTRACT FROM AUTHOR]

We develop a general 3-D relativistic test particle (TP) simulation code to examine the trajectories and pitch angle variations of test electrons. We investigate the conditions when the electrons transit broadband, parallel propagating H+ band electromagnetic ion cyclotron (EMIC) waves to find whether the classical quasilinear theory (QLT) can be applied to interactions between H+ band EMIC waves and radiation belt relativistic (and ultra-relativistic) electrons. We find that to reach good consistency between TP scattering coefficients and QLT calculations, the wave-particle resonant interaction time (which indicates the time of particles traveling in the wave fields and being resonant with the wave fields) must be carefully calculated to ensure the validity of the linear diffusion process. This wave-particle resonant interaction time depends largely on the wave amplitude, the bandwidth, and the initial parameters of electrons for TP simulations; once the time of electrons traveling in the wave fields becomes large enough when the pitch angles of electrons scattered by wave fields reach the maximal value limited by the resonance condition and cannot be diffused any longer, the linear diffusion process of particles defined by QLT will not be valid any longer. When the resonant electrons start to travel through the wave field, they undergo the linear diffusion process resulting from the pitch angle scattering by the H+ band EMIC wave field. As the time of traveling in the wave fields increases, the test electrons will suffer effective pitch angle scattering and the pitch angles of these electrons will reach the maximum value limited by the resonance condition, which is determined by the wave and electron parameters. These electrons are then reflected by the wave fields and the linear wave-particle interactions defined by QLT will not be valid anymore. This kind of wave-particle interaction subsequently introduces considerable deviation of TP diffusion coefficients from those predicted by QLT calculations. Our results demonstrate that the general validity of QLT in describing how broadband EMIC waves affect radiation belt relativistic electrons is highly related to the time of electron traveling in the wave fields, which tends to increase for smaller wave power and broader wave frequency spectra. [ABSTRACT FROM AUTHOR]

Abstract We propose and investigate a temperature sensor based on Sagnac interferometer with liquid crystal (LC) photonic crystal fiber (PCF) by finite element method (FEM). LC E7 which is anisotropic under electrical field is designed to be infiltrated into the cladding air holes of PCF. The birefringent PCF is then launched into a Sagnac interferometer. The interference spectrum of the Sagnac interferometer is influenced by the thermal effect of LC E7 and thus could be used to measure the temperature. The simulation results show that the temperature measuring sensitivity and resolution reach to 15 nm/K and 6.7E−4 K in the range of 290–320 K. The measuring range and sensitivity could be modified further by optimizing the PCF structure parameters. [ABSTRACT FROM AUTHOR]

Electromagnetic ion cyclotron waves have long been recognized to play a crucial role in the dynamic loss of ring current protons. While the field‐aligned propagation approximation of electromagnetic ion cyclotron waves was widely used to quantify the scattering loss of ring current protons, in this study, we find that the wave normal distribution strongly affects the pitch angle scattering efficiency of protons. Increase of peak normal angle or angular width can considerably reduce the scattering rates of ≤10 keV protons. For >10 keV protons, the field‐aligned propagation approximation results in a pronounced underestimate of the scattering of intermediate equatorial pitch angle protons and overestimates the scattering of high equatorial pitch angle protons by orders of magnitude. Our results suggest that the wave normal distribution of electromagnetic ion cyclotron waves plays an important role in the pitch angle evolution and scattering loss of ring current protons and should be incorporated in future global modeling of ring current dynamics. Plain Language Summary: Electromagnetic ion cyclotron (EMIC) wave is a class of electromagnetic wave that is frequently observed in the Earths' magnetosphere. EMIC waves can cause the loss of ring current protons by scattering them into the atmosphere. Previous attempts to quantify the loss of ring current protons by EMIC waves are mostly limited to the assumption that the waves are propagating exactly along the direction of geomagnetic field line. In this study, we show that this assumption will seriously break down once the waves are obliquely propagating. The obliquity of EMIC waves not only influences the pitch angle evolution of ring current protons but also affects their loss time scales. Our study confirms the importance of including the obliquity of EMIC waves in the modeling efforts of ring current dynamics. Key Points: The wave normal angle distribution strongly affects the EMIC wave‐driven scattering loss of ring current protonsQuantitative differences in the diffusion coefficients between field‐aligned and oblique waves are presentedPitch‐angle scattering of higher‐energy ring current protons is more sensitive to the variation of wave normal angle distribution [ABSTRACT FROM AUTHOR]

Bounce resonant interactions with magnetospheric waves have been proposed as an important contributing mechanism for scattering near-equatorially mirroring electrons by violating the second adiabatic invariant associated with the electron bounce motion along a geomagnetic field line. This study demonstrates that low-frequency plasmaspheric hiss with significant wave power below 100 Hz can bounce resonate efficiently with radiation belt electrons. By performing quantitative calculations of pitch angle scattering rates, we show that low-frequency hiss-induced bounce resonant scattering of electrons has a strong dependence on equatorial pitch angle αeq. For electrons with αeq close to 90°, the timescale associated with bounce resonance scattering can be comparable to or even less than 1 h. Cyclotron and Landau resonant interactions between low-frequency hiss and electrons are also investigated for comparisons. It is found that while the bounce and Landau resonances are responsible for the diffusive transport of near-equatorially mirroring electrons to lower αeq, pitch angle scattering by cyclotron resonance could take over to further diffuse electrons into the atmosphere. Bounce resonance provides a more efficient pitch angle scattering mechanism of relativistic ( ≥1 MeV) electrons than Landau resonance due to the stronger scattering rates and broader resonance coverage of αeq, thereby demonstrating that bounce resonance scattering by low-frequency hiss can contribute importantly to the evolution of the electron pitch angle distribution and the loss of radiation belt electrons. [ABSTRACT FROM AUTHOR]

A temperature sensor based on modes coupling effect in a liquid crystal-filled microstructured optical fiber was proposed and studied in this paper. The sensing characteristics were investigated by using a full-vectorial finite-element method (FEM) with perfectly matched layer and scattering boundary condition. For the purpose of temperature sensing, liquid crystal E7 was designed to be infiltrated into one cladding air hole in PCF to form a defect core. As the phase matching condition is satisfied, the core modes couple to several different ordered defect core modes, and finally experience a large increase in the confinement loss spectra. Furthermore, the loss spectra shift toward opposite directions in the two temperature segments (15–29 °C, 29–50 °C) for X-polarized (X-pol) direction, while it experiences a blue shift in the temperature range of 15–50 °C for Y-polarized (Y-pol) direction. Numerical simulation results show that the sensitivity reaches −5.26 nm/°C at 30 °C. The coupling effect between the core fundamental mode and high-order defect core modes utilized in this paper will be beneficial to the high-sensitivity detection. [ABSTRACT FROM AUTHOR]

A dual-polarized microstructure fiber sensor is based on surface plasmon resonance, which is arranged of pentagonal lattice to achieve refractive index sensing in the near-infrared spectrum. The gold nanowire-filled fiber sensor exhibits excellent sensing characteristics and improved transmission properties. Finite element method is used for computational analysis and structural optimization for the fiber sensor. When the refractive index of the analyte range from 1.32 to 1.38, dual-polarizd sensing can be implemented as a self-calibration with wavelengths increasing from 700 to 1200 nm. For the proposed sensor, the highest wavelength sensitivity of 10,286 nm/RIU is exhibited with a sensor resolution of 9.72×10−6 RIU, and the corresponding amplitude sensitivity and figure of merit are as high as 544.0 RIU−1 and 146.9. Moreover, the sensing length of at least 1.14 mm ensures accurate detection of optical signals for proposed sensor. Owing to the above advantages, the proposed sensor is suitable for high integration and high precision sensitivity detection. [ABSTRACT FROM AUTHOR]

We propose a Sagnac interferometer (SI) based on ethanol-filled photonic crystal fiber (PCF) with two ultra-large holes for temperature measurement. The phase birefringence of the fully-filled PCF varies significantly with the temperature which is realized by infiltrating ethanol into air-holes. Two ultra-large holes in y direction near the core result in a high birefringence of PCF. By selecting a fiber length of 2.5 cm, the average sensitivity of temperature can be up to -34 nm/°C with a resolution of 0.00029 °C in the wavelength range of 780 nm–2170 nm within temperature variation of 40 °C. The proposed PCF with the simple structure is easy to prepare in the experiment. Furthermore, due to the ultrahigh-sensitivity, the proposed sensor provides a new implementation for accurately temperature measurement. [ABSTRACT FROM AUTHOR]

Strong electrostatic electron cyclotron harmonic (ECH) waves on the dayside magnetosphere have been reported based on observations of the Magnetospheric Multiscale (MMS) spacecraft. In this study, we analyze high‐quality wave data from the four MMS satellites between 1 September 2015 and 30 August 2018 to investigate the statistical properties of dayside ECH emissions. The results show that dayside ECH waves are preferentially observed on the prenoon side in the outer magnetosphere (L = 8–12), with average wave amplitude Ew > 0.1 mV/m. In addition, besides the typical near‐equatorial (|MLAT| ≤ 15°) region, dayside ECH waves exhibit moderate occurrence rate and wave amplitude in higher latitudinal regions (i.e., 15 < |MLAT| ≤ 40°), possibly due to the off‐equatorial geomagnetic field minimum. Our reported double peaks of dayside ECH wave occurrence zone and considerable occurrence rates of prenoonside ECH waves suggest that dayside ECH waves can be a potentially important contributor to the formation of dayside diffuse aurora. Plain Language Summary: We use wave spectral data from the four Magnetospheric Multiscale (MMS) spacecraft to statistically analyze the distributions of wave amplitudes and occurrence rates as a function of L shell, MLT, geomagnetic activity (AE* and Kp indices), and MLAT for dayside first harmonic band electron cyclotron harmonic (ECH) waves. The conclusions are summarized as follows: (1) Dayside ECH waves preferentially occur on the prenoonside of the outer magnetosphere, with peak occurrence rates around 30%. (2) In higher latitudinal regions (|MLAT| = 15–25°,25–40°), contrary to previous conclusions regarding ECH wave occurrence patterns, dayside ECH waves occur with significant occurrence rates, comparable to that of dayside ECH waves in near‐equatorial areas. (3) Similar to the distribution of occurrence rates, dayside ECH waves have most intense electric field amplitudes over L = 8–12, MLT = 8–11, with an average wave strength >0.1 mV/m.Whistler mode chorus waves are considered as the primary mechanism to explain dayside diffuse aurora, but the role of ECH waves has not been systematically evaluated because of lack of dayside ECH observations. As shown by our results, moderate dayside ECH waves can be observed on the prenoonside of the outer magnetosphere. This observation could be of great importance in understanding the generation of dayside diffuse aurora. Key Points: Dayside ECH waves are preferentially observed with moderate average wave strength on the prenoonside to noonside in the outer magnetosphereIn higher latitudinal regions, dayside ECH waves have comparable occurrence rates and wave amplitude to that of the near‐equatorial regionsAlthough weak dayside ECH waves occur predominantly, the occurrence rates of moderate and strong dayside ECH waves are not negligible [ABSTRACT FROM AUTHOR]

By investigating the resonant energy and latitudinal resonance region of Landau resonance between H+ band electromagnetic ion cyclotron (EMIC) waves and radiation belt electrons and performing calculations of quasi‐linear diffusion coefficients, we find that Landau resonance with EMIC waves, characterized by a very broad range of resonant energies from below 1 eV to above 10 MeV and the strikingly small extent of the latitudinal resonance region well below 0.1°, can be a feasible candidate accounting for the pitch angle scattering of near‐equatorially mirroring electrons. Compared to the dominant pitch angle scattering caused by the cyclotron resonance for greater than ~2‐MeV electrons at equatorial pitch angles less than ~80° with the rates well above 10−4 s−1, Landau resonance with H+ band EMIC waves has the potential to drive more efficient pitch angle scattering of radiation belt electrons from ~10 MeV down to tens of kiloelectron volts at equatorial pitch angles greater than ~ 85°. Plain Language Summary: Electromagnetic ion cyclotron (EMIC) waves are thought to be very important for pitch angle scattering of radiation belt electrons, which may play a crucial role for the rapid dropout of relativistic electrons fluxes in the outer radiation belt during a geomagnetic storm, or for the intense relativistic electron precipitation. Although cyclotron resonance with EMIC waves acts as an important loss process during geomagnetic storms, this mechanism is believed to solely affect trapped electrons with small pitch angles well away from 90°. In the present work, we introduce the Landau resonance between H+ band EMIC waves and radiation belt electrons. The crucial role for pitch angle scattering near‐equatorially mirroring electrons by Landau resonance is investigated by Quasilinear diffusion theory (QLT) calculations in our work. Key Points: H+ band EMIC waves drive the Landau resonance with radiation belt electrons over a very broad energy range from >10 MeV to tenths of an eVLandau resonance between H+ band EMIC waves and electrons at > ~60 degrees occurs in a very limited rangeEMIC scattering electrons due to the cyclotron resonance and Landau resonance occur at two distinct ranges of equatorial pitch angle [ABSTRACT FROM AUTHOR]

We report a typical event that fast magnetosonic (MS) waves, exohiss, and two‐band chorus waves occurred simultaneously on the dayside observed by Van Allen Probes on 25 December 2013. By combining calculations of electron diffusion coefficients and 2‐D Fokker‐Planck diffusion simulations, we quantitatively analyze the combined scattering effect of multiple waves to demonstrate that the net impact of combined scattering does not simply depend on the wave intensity dominance of various plasma waves. Although the observed MS waves are most intense, the electron butterfly distribution is inhibited by exohiss and chorus, and electrons are considerably accelerated by combined scattering of MS and chorus waves. The simulated electron pitch angle distributions exhibit the variation trend consistent with the observations. Our results strongly suggest that competition and cooperation between resonant interactions with concurrently occurring magnetospheric waves need to be carefully treated in modeling and comprehending the radiation belt electron dynamics. Plain Language Summary: It has been acknowledged that wave‐particle interactions play an important role in energy exchange between plasma waves and radiation belt electrons. Most previous studies focused on the wave‐particle interaction effect of individual wave modes, while only rather limited investigations look into the competition and cooperation between various kinds of plasma waves upon their modulation of the radiation belt electron dynamics. In the present study, we report a typical event that magnetosonic waves, exohiss, and two‐band chorus waves occurred simultaneously on the dayside. By computations of the electron diffusion coefficients and 2‐D Fokker‐Planck diffusion simulations, we have found that the competition and cooperation between these three wave modes are delicate in that the net combined scattering impact does not simply depend on the dominance of wave intensity but requires careful analyses via diffusion simulations. Our results demonstrate the importance of incorporating the combined scattering effect by various simultaneously occurring magnetospheric waves during modeling and comprehending the complex radiation belt electron dynamics. Key Points: A typical event that MS waves, exohiss, and two‐band chorus waves occurred simultaneously in the dayside plasmatrough is reportedThe combined scattering effect makes a big difference to the radiation belt electron dynamics compared to contributions of individual wavesNumerical simulations can approximately explain the variation trend of observed electron pitch angle distributions [ABSTRACT FROM AUTHOR]