Attenuation Loss Research Articles

EM design and analysis of a substrate integrated waveguide based on a frequency-selective surface for millimeter wave radar application

Substrate integrated waveguide (SIW) technology makes it possible to realize an entire circuit including a transition, planar circuitry, waveguide components and devices in a single printed circuit board. In this paper, a new approach to design a substrate integrated waveguide using a single square loop and Jerusalem cross frequency-selective surface elements as the top wall in place of a metallic wall, for advanced millimeter wave radar systems is presented. The guided wave and modes operating at the high-frequency range in V-band, typically 40–75 GHz (57–64 GHz in the USA and 59–66 GHz in Japan), has been analyzed. The accurate analytical modeling is used to calculate the complex propagation constant and cut-off frequency of the SIW structure. The propagation constant of the analyzed structured is compared with a conventional SIW, and the wave propagation is presented in all topologies. The leakage and attenuation loss of an electromagnetic wave due to different factors such as dielectric, conductor and radiation are also studied. Finally, the numerical simulation has been performed based on finite element and finite difference time domain to prove the analytical formulation of the proposed structure. The obtained simulation results are encouraging for developing a new type of SIW structure for aerospace applications.

Optimisation of heliostat field layout for solar power tower systems using iterative artificial bee colony algorithm: a review and case study

ABSTRACT In this study, the Iterative Artificial Bee Colony Algorithm (IABCA) methodology was proposed to perform optimisation of a heliostat field for the Solar Power Tower (SPT) system. In this respect, a complete mathematical model of annual unweighted optical efficiency considering cosine losses, shadowing-blocking losses, atmospheric attenuation losses, interception losses and mirror reflectivity was developed firstly. A simple and efficient method is adopted to identify the heliostats with the highest possibility to shade or block another heliostat. The use of this method allows us to reduce the processing time of the shadowing and blocking efficiency and avoid unnecessary calculations. A case study of PS10 situated in Spain was used to validate the mathematical model and the proposed IABCA approach. The proposed IABCA maximize the annual unweighted optical efficiency. In order to evaluate the performance of the proposed approach, seasonal investigation on four different days 21 March, 21 June, 21 September, and 21 December at solar noon time was carried out. The results show that the proposed IABCA methodology boost significantly the performance of the heliostat field compared to the original PS10 layout. Percentage improvement for each studied day in terms of efficiency is 3.46%, 1.05%, 3.2%, 1.98%, respectively.

Dissipative Soliton Resonances in a Mode-Locked Holmium-Doped Fiber Laser

We demonstrate what is believed to be the first dissipative-soliton-resonance mode-locking of a holmium-doped fiber (HDF) laser. A telecommunication band fiber source was used to pump a piece of thulium-doped fiber, resulting in 1.9-μm band lasing, which was subsequently used to intra-cavity-pump another piece of HDF, resulting in lasing beyond 2 μm. A nonlinear optical-loop mirror incorporating two pieces of high nonlinear fiber (HNLF) was employed as an artificial saturable absorber, and, meanwhile, to enhance the cavity nonlinearity. By varying the pump power from ~2.1 to ~4 W, the produced pulse could be tuned from ~4.85 to ~20.8 ns in duration while maintaining a nearly constant peak power, i.e., peak power clamping (PPC) effect. By further incorporating different lengths of HNLF, it was found that the longer the HNLF, the larger the pulse duration and the lower the pulse peak power, due to the expected stronger PPC effect. Meanwhile, spectral blue-shifting effect has occurred due to the increased fiber attenuation loss. Based on our preliminary experiments using the HDF laser as a test bed, a higher pulse energy at a longer wavelength could be expected with further enhanced pumping and gain-tailoring designs.

Cobalt nanoparticles embedded nitrogen-doped porous graphitized carbon composites with enhanced microwave absorption performance

For high-efficiency microwave absorption, both of the self loss of materials (dielectric loss and magnetic dissipation) and structural attenuation (multiple scattering, interfacial polarization) play important roles. In addition, the magnetic/dielectric materials combination, and void volume introduction can also contribute to the optimization of impedance matching. Given that, 2D cobalt nanoparticles embedded nitrogen-doped porous graphitized carbon composites (Co@N-C) were fabricated via a simple sacrificial templates method, where the CoAl-layered double hydroxide (CoAl-LDH) nanosheets were prepared to hold ZIF-67 and then decomposed during the sintering process. In this work, strong dielectric attenuation, multiple microwave scattering and dielectric polarization, as well as shortened impedance matching all make for the nice microwave absorption performance. This work not only exhibits the importance in materials selection and structure design, but also demonstrates the close relation between matching thickness and response frequency at maximum reflection loss (RL) peak.

Fabrication, photoluminescence and terahertz absorption properties of Yb:YAG transparent ceramics with various Yb dopant concentrations

Highly transparent Yb:YAG laser ceramics with various Yb3+ doping level were successfully fabricated through vacuum sintering of co-precipitated powders in combination with the hot isostatic pressing process. The effects of various Yb3+ dopant concentrations (1–15 at.%) on the photoluminescence, terahertz absorption and optical characteristics of Yb:YAG transparent ceramics were investigated. Characterizations of the Near-IR photoluminescence emission and kinetics of the Yb:YAG ceramics revealed the corresponding 2F5/2 → 2F7/2 characteristic bands of Yb3+ and the lifetime enhanced with increasing Yb3+ dopant concentrations, confirming no concentration quenching effect in Yb:YAG. Measurements of terahertz absorption properties of Yb:YAG transparent ceramics by a time-domain spectroscopy evidenced that both the cutoff frequency and terahertz absorption coefficient of Yb:YAG samples depended upon the Yb3+ dopant concentrations. The underlying mechanisms by which such Yb3+ dopant concentrations affected the terahertz absorption and optical properties were also discussed. The optical attenuation loss values were measured at 1064 nm for all the samples, to be ∼0.030 cm−1, a value close to that observed for single crystal.

Small and Low but Potent: the Complex Regulatory Role of the Small RNA SolB in Solventogenesis in Clostridium acetobutylicum.

The recently revived Clostridium acetobutylicum-based acetone-butanol-ethanol (ABE) fermentation is widely celebrated and studied for its impact on industrial biotechnology. C. acetobutylicum has been studied and engineered extensively, yet critical areas of the molecular basis for how solvent formation is regulated remain unresolved. The core solventogenic genes (adhE1/aad, ctfA, ctfB, and adc) are carried on the sol locus of the pSOL1 megaplasmid, whose loss leads to asporogenous, "degenerate" cells. The sol locus includes a noncoding small RNA (sRNA), SolB, whose role is presumed to be critical for solventogenesis but has eluded resolution. In the present study, SolB overexpression downregulated the sol-locus genes at the transcript level, resulting in attenuated protein expression and a solvent-deficient phenotype, thus suggesting that SolB affects expression of all sol-locus transcripts and seemingly validating its hypothesized role as a repressor. However, deletion of solB resulted in a total loss of acetone production and severe attenuation of butanol formation, with complex effects on sol-locus genes and proteins: it had a small impact on adc mRNA or its corresponding protein (acetoacetate decarboxylase) expression level, somewhat reduced adhE1 and ctfA-ctfB mRNA levels, and abolished the ctfA-ctfB-encoded coenzyme A transferase (CoAT) activity. Computational predictions support a model whereby SolB expressed at low levels enables the stabilization and translation of sol-locus transcripts to facilitate tuning of the production of various solvents depending on the prevailing culture conditions. A key predicted SolB target is the ribosome binding site (RBS) of the ctfA transcript, and this was verified by expressing variants of the ctfA-ctfB genes to demonstrate the importance of SolB for acetone formation.IMPORTANCE Small noncoding RNAs regulate many important metabolic and developmental programs in prokaryotes, but their role in anaerobes has been explored minimally. Regulation of solvent formation in the important industrial organism C. acetobutylicum remains incompletely understood. While the genes for solvent formation and their promoters are known, the means by which this organism tunes the ratios of key solvents, notably the butanol/acetone ratio to balance its electron resources, remains unknown. Significantly, the roles of several coding and noncoding genes in the sol locus in tuning the solvent formation ratios have not been explored. Here we show that the small RNA SolB fine-tunes the expression of solvents, with acetone formation being a key target, by regulating the translation of the acetone formation rate-limiting enzyme, the coenzyme A transferase (CoAT). It is notable that SolB expressed at very low levels enables CoAT translation, while at high, nonphysiological expression levels, it leads to degradation of the corresponding transcript.

True amplitude recovery in reverse time extrapolation of plane and spherical waves

A challenging outstanding problem in reverse time extrapolation is recovering accurate amplitudes at reflectors from the receiver wavefield. Various migrations have been developed to produce accurate image locations rather than correct amplitude information because of inadequate compensation of attenuation, dispersion, and transmission losses. We have evaluated the requirements, and determined the theoretical feasibility, of true amplitude recovery of 2D acoustic and elastic seismic data by using the analytic Zoeppritz equations for plane-wave reflection and transmission coefficients. Then, we used synthetic acoustic and elastic wavefield data generated by elastodynamic finite differences to verify the recovery, in the reverse time propagation, of spherical waves and illustrated the salient differences between the incident wavefields reconstructed from reflection data only and from the combination of reflection and transmission data. These examples quantitatively verify that recovering an incident plane or a spherical wave requires the reverse time propagation of all reflections and transmissions in a model with the correct velocity and density. Accurate reconstruction of an incident wave is not possible by backward propagation of only reflections. As an application, we removed downgoing internal multiple reflections generated by upgoing waves incident at reflectors shallower than a horizontal well, in which geophones are deployed. The subtraction of the downgoing reflection involves wavefield reconstruction at depths shallower than the horizontal well and separation of upgoing and downgoing wavefields. This approach assumes that the correct acoustic (or elastic) velocity and density models are available in, and shallower than, the layer where the horizontal well is located. Incident-wave reconstruction works equally well for smooth models, as for models with sharp boundaries. Uncertainties in the model used for reconstruction, and incompleteness of the data aperture are propagated into the equivalent uncertainties, and incompleteness of the reconstruction.

Modal Analysis of Corrugated Plasmonic Rods for the Study of Field Localization, Conductor Attenuation, and Dielectric Losses

By virtue of the strong confinement of surface-wave fields that it provides, the transverse corrugated conducting rod is an important structure in the fields of plasmonics and metasurfaces, finding applications in focusing, sensing, imaging, spectroscopy, and subwavelength optics, among others. This paper presents an analytical modal method for treating such grated rods with generally dielectric-filled grooves, one which offers rapid yet accurate surface-wave modal solutions. Based on the asymptotic corrugation boundary conditions, the formulation is simple and elegant, providing not only the dispersion relationship between the frequency and wavenumber but also the explicit functional forms of the fields. Dispersion and modal field results obtained by the proposed method are validated with an independent full-wave solver. Because of its candidacy for microwave applications at high powers and high frequencies, as well as transmissions over long distances, studies of dielectric and conductor losses are also carried out, for both the grooved rod and its likewise corrugated circular waveguide counterpart. Parametric studies are conducted on three aspects, namely, the degree of field localization on the surface of the rod, as well as attenuation due to dielectric and metal losses. Measurements of dispersion and field decay properties conducted on a manufactured rod that concur with theory are also reported.

Acoustic Luneburg lens using orifice-type metamaterial unit cells

A two-dimensional acoustic Luneburg lens that can be easily expanded into a three-dimensional sphere is fabricated. The required spatial distribution of the refractive index for this Luneburg lens is realized using the characteristics of orifice-type metamaterial unit cells. Typical characteristics of the resulting acoustic Luneburg lens, such as its aberration-free performance and capability for antipodal focusing of the lens for the incident plane waves, are investigated through experiments and simulations with the attenuation loss at frequencies that satisfy the homogeneous medium condition of the metamaterial. With the designed metamaterial, we achieved the minimum spot that lies within the classical diffraction limit at the focal point.

Compensating Q effects in viscoelastic media by adjoint-based least-squares reverse time migration

Low values of P- and S-wave quality factors [Formula: see text] and [Formula: see text] result in strong intrinsic seismic attenuation in seismic modeling and imaging. We use a linearized waveform inversion approach, by generalizing least-squares reverse time migration (LSRTM) for viscoelastic media ([Formula: see text]-LSRTM), to compensate for the attenuation loss for P- and S-images. We use the first-order particle velocity, stress, and memory variable equations, with explicit [Formula: see text] in the formulations, based on the generalized standard linear solid, as the forward-modeling operator. The linearized two-way viscoelastic modeling operator is obtained with modulus perturbations introduced for the relaxed P- and S-moduli. The viscoelastic adjoint operator and the P- and S-imaging conditions for modulus perturbations are derived using the adjoint-state method and an augmented Lagrangian functional. [Formula: see text]-LSRTM solves the viscoelastic linearized modeling operator for generating synthetic data, and the adjoint operator is used for back propagating the data residual. With the correct background velocity model, and with the inclusion of [Formula: see text] in the modeling and imaging, [Formula: see text]-LSRTM is capable of iteratively updating the P- and S-modulus perturbations, and compensating the attenuation loss caused by [Formula: see text] and [Formula: see text], in the direction of minimizing the data residual between the observed and predicted data. Compared with elastic LSRTM results, the P- and S-modulus perturbation images from [Formula: see text]-LSRTM have stronger (closer to the true modulus perturbation), and more continuous, amplitudes for the structures in and beneath low-[Formula: see text] zones. The residuals in the image space obtained using the correctly parameterized [Formula: see text]-LSRTM are much smaller than those obtained using the incorrectly parameterized elastic LSRTM. However, the data residuals from [Formula: see text]-LSRTM and elastic LSRTM are similar because elastic Born modeling with a weak reflector in the image produces similar reflection amplitudes with viscoelastic Born modeling with a strong reflector.

Statistical characteristics and performance evaluation of FSO links with misalignment fading influenced by correlated sways

In this paper, we analyze the performance of a free space optical (FSO) link under the influence of attenuation loss, misalignment fading affected by correlation between the horizontal and vertical sways of an optical beam, and atmospheric turbulence-induced fading. In practice, the horizontal and vertical displacements of the signal that leads to misalignment may not necessarily be uncorrelated. Hence, we consider a generalized misalignment fading model for the analysis. Further, the atmospheric turbulence is characterised by the Gamma-Gamma fading. We investigate the statistical characteristics of the end-to-end instantaneous signal power to noise power ratio (SNR), and derive expression in closed form for the probability density function (pdf) and cumulative distribution function (cdf) of the SNR measured end-to-end, under given channel conditions. We develop mathematical analysis for the exact outage behaviour of the link and its asymptotic behaviour at high SNR regime. The exact and high SNR error performance of the system is also evaluated considering q-PSK and q-QAM modulated FSO link. We also discuss a special case of a binary phase shift keyed (BPSK) modulated FSO link and evaluate its bit error rate (BER) performance. Further, the exact average channel capacity is investigated for the FSO link and its asymptotic analysis at higher SNR is also presented. The obtained mathematical results are also illustrated and verified by the numerical plots.

S-Parameter Model of Three Parallel Interconnect Lines Generating Negative Group-Delay Effect

This paper develops a negative group-delay (NGD) microwave circuit theory regarding topology consists of three parallel interconnect lines (3-PILs). The NGD topology under study is built using completely distributed microstrip lines. The 3-PIL NGD theory is established from the S-parameters which are determined from the general admittance matrix of the 3-PILs. The analytical expressions of reflection coefficient (S11), transmission coefficient (S21) and group-delay ( $\tau$ ) which behave as periodical functions are presented. The frequency period proper to the 3-PIL topology is established. Then, S11, S21 and $\tau $ illustrating the possibility to generate bandpass NGD function are formulated in function of the PIL parameter physical lengths and attenuation loss. Then, the NGD characterization of the 3-PIL topology is presented. The relevance of the NGD theory is verified with simulations and experimentations around the NGD center frequency of about 2.3 GHz. To do this, a 3-PIL microstrip circuit is designed and fabricated as proof-of-concept. It is shown that the simulated and measured group-delays are well-correlated. As expected theoretically, the demonstrator with identical characteristic impedance enables to generate an NGD level of approximately −2 ns at 2.3 GHz. In the future, the NGD function can be potentially used for the microwave signal integrity improvement.

Reliability of Strip Line Method for Determination of Conductivity for Lossy Conductive Materials

Designing electro-textile antenna requires complex analysis as the material cannot be simply modeled as a conventional antenna with perfect metallic surface. Electro-textile has relatively lower conductivity compared with an ideal conductor. Due to its inhomogeneous and unique thread structure, exact conductivity, $\sigma _{c}$ , is difficult to be determined, which will result in inaccurate modeling during antenna designing. Significant deterioration in antenna efficiency can be observed when low conductivity element is used, and thus, accurate determination of bulk conductivity for customized electro-textile shall be performed. Previously, a strip-line method was proposed, and however, the reliability of the technique in correlation with material’s loss characteristics was not clarified. Furthermore, the practicality of the technique for higher frequency, such as ISM band, was not demonstrated. In this paper, the validity of the technique for lossless, low-loss, and high-loss materials for 2.45-GHz wearable application is clarified. A more practical and straightforward equation to calculate electro-textile’s bulk conductivity is derived, and the accuracy and reliability range of the equation is demonstrated through comprehensive electromagnetic simulation. Through analysis, the correlation between $\sigma _{c}$ , dielectric loss and attenuation loss is shown. For validation, two samples that consist of two conductors, namely copper and SHIELDIT, are fabricated on a low-loss RO5880 substrate. The $\sigma _{c}$ values of the conductors are calculated from transmission loss (S21) measurement. Good agreement of $\sigma _{c}$ is obtained for both cases, particularly when the actual $\sigma _{c}$ is within the threshold range of around 107 S/m.

Construction of SnO2/Co3Sn2@C and SnO2/Co3Sn2@Air@C hierarchical heterostructures for efficient electromagnetic wave absorption

Schematic of electromagnetic wave attenuation process and loss mechanism for SnO2/Co3Sn2@C and SnO2/Co3Sn2@Air@C absorbers and their absorption properties.

Active Control of Pressure Resonance in Long Pipeline of Bottom Founded Hydraulic Wind Turbines Based on Multi-Objective Genetic Algorithm

The long pipeline in bottom-founded hydraulic wind turbines will greatly reduce the system natural frequency, and pressure resonances can occur more easily at multiple frequencies under time-varying wind excitation, which will reduce the electrical power quality and endanger the safe operation of the system. First, the hydraulic system impedance model is established based on electric–hydraulic analogy, and the pressure transfer function of two ends of the long pipeline is obtained, based on which the pressure resonance condition equation is solved by theoretical derivation. Furthermore, the multiple parameters sensitivity analysis of resonant frequency is carried out by using Isight and MATLAB. A novel active control strategy of pressure resonance is proposed, where the variable motor is adopted as the control object for real-time control of the terminal impedance to make the resonance frequency avoid the excitation frequency, and its feasibility is verified. Finally, with the objectives of optimizing the pressure pulsation attenuation and wind energy loss, a multi-objective genetic algorithm is used to optimize the parameters of the control object. A reliable Pareto set is obtained through multiple iterations, and different degrees of resonance suppression can be achieved.

Research and development of continous wave 100 kW absorption harmonicfilter in X-band

A gradient leaky-wall waveguide loaded absorbing load filter structure is proposed, which is designed for harmonic suppression in super-high power transmitter of deep-space probe. The attenuation loss characteristics of the filter is analyzed according to the equivalent circuit method, and the massive structure is simulated by the electromagnetic field simulation software. The filter sample which includes one main waveguide, 288 deputy waveguides and 288 absorb loads is processed following the simulating and designing sizes. In order to prevent microwave from leaking and keep good air tightness under the condition of high power, all the components of the filter will be welded together by means of vacuum welding, and then the sample is cleaned ultrasonically. Finally, the filter sample is tested under small signal and large signal separately. According to our test results, the pass band max insertion loss of the filter is 0.3 dB, the min suppression of second harmonic is 75 dB, the min suppression of third harmonic is 50 dB, and the min suppression of fourth harmonic is 35 dB. The measured results show that they are almost the same as the simulation results, and consistent completely with the anticipated. We further conduct the high power experiment on the filter under a large signal of 100 kW, showing that the continuous wave power capacity of the filter can reach up to 100 kW through the power resistance test with the liquid-cooled system. All the test data show that the study and development are very successful. At present, the filer has been applied to a type of ground high power transmitter, and its performances and indicators behave well.

Optimizing alignment and growth of low-loss YAG single crystal fibers using laser heated pedestal growth technique.

The effect of misalignments of different optical components in the laser heated pedestal growth apparatus have been modeled using Zemax optical design software. By isolating the misalignments causing the non-uniformity in the melt zone, the alignment of the components was fine-tuned. Using this optimized alignment, low-loss YAG single crystal fibers of 120μm diameter were grown, with total attenuation loss as low as 0.5dB/m at 1064nm.

Suppression effects of cooling rate on crystallization in ZBLAN glass

ZBLAN glass is a heavy metal fluoride glass that shows great potential in the application of long-haul telecommunication cables. However, during processing in the fiber-drawing temperature region, the material tends to undergo heavy devitrification, resulting in a crystalline fiber that is not usable as an optical waveguide. In this study, ZBLAN glass was processed with different cooling rates to discern how the rate of cooling affects the process of crystallization. Rapidly cooled ZBLAN glass test samples were then analysed with a wide range of spectroscopy and imaging techniques including EDS, SEM, TEM and XRD. These techniques revealed there are two predominant crystal phases, one rich in zirconium and barium, the other in zirconium and sodium. Ultimately, a critical cooling rate was established to be somewhere between 900°C/min and 4000°C/min, with a theoretically predicted value of 1081°C/min for a test sample volume size of 9.4×10−8m3. Cooling above this critical cooling rate yielded fully amorphous ZBLAN test samples that were completely free of nano-crystalline inclusions. Using Kramers-Kronig relations, an attenuation loss for the fully amorphous ZBLAN test samples was estimated to be 0.09dB/Km at a wavelength of 1800nm.

Using dynamic flux chambers to estimate the natural attenuation rates in the subsurface at petroleum contaminated sites

In this work, we introduce a screening method for the evaluation of the natural attenuation rates in the subsurface at sites contaminated by petroleum hydrocarbons. The method is based on the combination of the data obtained from standard source characterization with dynamic flux chambers measurements. The natural attenuation rates are calculated as difference between the flux of contaminants estimated with a non-reactive diffusive model starting from the concentrations of the contaminants detected in the source (soil and/or groundwater) and the effective emission rate of the contaminants measured using dynamic flux chambers installed at ground level. The reliability of this approach was tested in a contaminated site characterized by the presence of BTEX in soil and groundwater. Namely, the BTEX emission rates from the subsurface were measured in 4 seasonal campaigns using dynamic flux chambers installed in 14 sampling points. The comparison of measured fluxes with those predicted using a non-reactive diffusive model, starting from the source concentrations, showed that, in line with other recent studies, the modelling approach can overestimate the expected outdoor concentration of petroleum hydrocarbons even up to 4 orders of magnitude. On the other hand, by coupling the measured data with the fluxes estimated with the diffusive non-reactive model, it was possible to perform a mass balance to evaluate the natural attenuation loss rates of petroleum hydrocarbons during the migration from the source to ground level. Based on this comparison, the estimated BTEX loss rates in the test site were up to almost 0.5kg/year/m2. These rates are in line with the values reported in the recent literature for natural source zone depletion. In short, the method presented in this work can represent an easy-to-use and cost-effective option that can provide a further line of evidence of natural attenuation rates expected at contaminated sites.

The roles of cation additives on the color center and optical properties of Yb:YAG transparent ceramic

The color center and optical characteristics of Yb:YAG transparent ceramic were investigated for various cation additives (Si4+, Mg2+ and Si4++Mg2+). The presence of a population of free electrons in the vacuum sintered Yb:YAG ceramics without additives, which imparted a green color and promoted the formation of Yb2+-F+ centers. The introduction of Si4+ additives were unable to remove the [Yb2+-F+] composite color centers. Theoretical analysis and experimental proofs revealed that the cation additives containing ions aliovalent to YAG introduces vacancies, which in turn induce the formation of Re2+-F+ (Re2+: Yb2+, Mg2+ or Ca2+) composite color centers. It was also demonstrated that the addition of a combination MgO+SiO2 sintering aid serves to inhibit abnormal grain growth and enhance densification, accompanied with the elimination of color centers. Furthermore, the underlying mechanisms by which these aliovalent cation additives influence color center formation and optical properties are discussed in detail. The lowest optical attenuation loss was measured at 1064nm in Yb:YAG ceramic with the MgO+SiO2 additives, to be 0.0031cm−1, a value close to that observed for single crystals.