Minimum Transmission Research Articles

Widely tunable frequency-doubling optoelectronic oscillator using a polarization modulator and a phase-shifted fiber Bragg grating

A frequency-doubling optoelectronic oscillator with wideband frequency tunability implemented using a polarization modulator (PolM) and a phase-shifted fiber Bragg grating (PS-FBG) is proposed and experimentally demonstrated. In the proposed structure, the output from the PolM is divided into two branches by an optical coupler. In the lower branch, an optoelectronic feedback loop is formed in which a tunable microwave photonic filter (MPF) is constructed by the joint operation of the PolM, the PS-FBG, a tunable laser source (TLS), a polarization controller (PC), and a polarizer, the MPF serves as an oscillation mode selector that its central frequency is a function of the frequency difference between the TLS and the notch of the PS-FBG. In the upper branch, an equivalent Mach–Zehnder modulator (MZM) is performed by the joint use of the PolM, a second PC, and a second polarizer, the second PC is adjusted to let the bias point of the MZM located at the minimum transmission point (MITP), which generates an optical signal with two sidebands at the ±first orders. By beating the two sidebands at a second photodetector (PD), a frequency-doubled microwave signal is generated. By simply adjusting the wavelength of the TLS, the central frequency of the MPF is shifted, and the fundamental oscillation and its frequency-doubled signals can be tuned. The detailed theoretical study is achieved, and a verified experiment is established. A fundamental oscillation signal with a frequency tuning range from 9.39 to 15.4 GHz is generated in the OEO loop, which is multiplied to generate a tunable frequency-doubled signal. Their overall performances are also investigated.

Synergic effect of additives on the structure and properties of nano strontium hexaferrite synthesized via the gel combustion method

Strontium hexaferrite (SrFe12O19) is a ferrimagnetic oxide that is widely used as a permanent magnetic material due to its excellent magnetic properties and low production cost. Modification of chemical composition and nanoscale structural refinement can improve its properties. In the present study, the synthesis process of strontium hexaferrite by the gel combustion method was investigated. SrFe12O19 was synthesized with the iron to strontium ratio of 10-12. The calcination temperature was also optimized by modifying this ratio. The effect of adding cobalt, manganese, zirconium, and zinc cations to the composition of SrFe12-2x(Mn Co Zn)x/3ZrxO19 (x = 0.0–1.0) was investigated. The samples were characterized by X-ray diffraction (XRD), thermal analysis (TGA/DTA), field emission scanning electron microscopy (FE-SEM), vibrating sample magnetometer (VSM), and vector network analyzer (VNA). The results showed that, in the free-additive samples, the pure strontium hexaferrite phase was formed only under the optimal conditions where the iron to strontium ratio and heat-treatment temperature were about 11 and 900 °C, respectively. In this case, clustered particles with the size of 64-145 nm were observed in the structure. In addition, partial substitution of different amounts of manganese, cobalt, zinc, and zirconium cations for Fe3+ in the hexaferrite structure affected its magnetic properties, such as saturation magnetization (Ms), remnant magnetization (Mr), coercivity (Hr), and Mr/Ms ratio. The dielectric constant, reflectance, transmittance, and absorption of electromagnetic waves were also changed. The sample with x = 0.8 showed the maximum reflectance (36.20%) and minimum transmittance (54.10%). The sample with x = 0.4 showed the desired reflectance loss of −9.24 dB at the frequency of 12.15 GHz.

Narrow-spectrum enhanced multiparameter gas sensor based on Fano resonance in an asymmetric MDM waveguide

In this study, a highly sensitive and narrow–spectrum enhanced multiparameter gas sensor is proposed based on Fano resonance in an asymmetric metal–dielectric–metal (MDM) waveguide. A side-coupled MDM structure comprising an upright rectangular cavity is initially investigated under different gaps. An assumed junction model is used to analyze the physical mechanism of a through coupled system (gap = 0) with an ultralow minimum transmission coefficient and higher refractive index sensitivity compared to other cases. Becausethe transmission spectrum of through-coupled structure is relatively broad, a ring resonator was added on the upper side of straight waveguide to generate an ultranarrow resonant mode as a discrete state that interferes with the previous broad mode serving as a quasicontinuum state to afford Fano resonance. Consequently, its full width at half maximum decreases by 420% from 496 to 11.56 nm. The response rate and detection difficulty of detection of y-asymmetric plasmonic nanostructures used in this study are exceed those of x-asymmetric plasmonic nanostructures. A multiparameter gas sensor can be developed by filling hydrogen- and methane-sensitive films in corresponding cavities of the plasmonic nanostructure. The sensitivities of methane and hydrogen can reach −2.863 and −0.265 nm/%, respectively, after optimizing relevant structural parameters. The proposed method provides an effective approach for designing narrow-spectrum enhanced and multichannel nanophotonic devices.

Symmetric Connectivity in Wireless Sensor Networks with π/3 Directional Antennas

Directional Wireless Sensor Networks (DWSNs) have been a very active research topic as they have a wide range of applications in both military and civilian areas. In this paper, we study the Antenna Orientation (AO) and Antenna Orientation and Power Assignment (AOPA) problems, two important issues in DWSNs. In the AO problem, given a set [Formula: see text] of sensors equipped with directional antennas with beam-width [Formula: see text], the objective is to determine an orientation of the antennas and a minimum transmission range [Formula: see text] such that the induced symmetric communication graph is connected. We prove that the AO problem is NP-hard. We then extend our proof technique and show that the AOPA problem for DWSNs equipped with [Formula: see text] directional antennas is also NP-hard where we have to determine an orientation of the antennas as well as a power assignment [Formula: see text] to the nodes such that the resulting symmetric communication graph is connected, and (2) [Formula: see text] is minimized ([Formula: see text] is the distance-power gradient, [Formula: see text]). We propose an [Formula: see text] heuristic algorithm and demonstrate by simulation that our method is better than the Ice-cream method.

Design of nanorod-embedded bandstop MIM waveguide filters with high filtering efficiency and sensitivity

A novel band-stop metal–insulator–metal plasmonic waveguide filter with high efficient filtering and high sensitivity is proposed and investigated theoretically. The relationship among the wavelength of the incident wave, the refractive index of the measured material and the transmittance of the incident wave is simulated by finite-difference time-domain (FDTD) and coupled mode theory (CMT) method. The filters which consist of a straight waveguide and two square resonators embedded with silver nanorods have minimum transmittance of 0.04%, 2.2%, 14.9% and 9.0% at the dips. The maximum sensitivity could reach 2860 nm/RIU. The sensitivity of the filter to detect plasma, hemoglobin, glucose and Sylgard184 reaches 2854 nm/RIU, 2852 nm/RIU, 2850 nm/RIU, 2851 nm/RIU, respectively. This waveguide filter may provide a new reference for highly integrated optical circuits and refractive index sensor.

A Collision-Free Scheduling Algorithm with Minimum Data Redundancy Transmission for TSCH

A Collision-Free Scheduling Algorithm with Minimum Data Redundancy Transmission for TSCH

A Modified Method for Beam-Forming Using Covariance Matrix in MIMO Radar System

A MIMO radar provides solution for beamforming, since transmit beampattern synthesis is well proven method for stimulating the antenna array to develop the beampattern. It is close to the desired one which can give minimum error between these two. A covariance matrix in beamforming contains the direction of invariable data and magnitude distribution in multidimensional space which decides the closeness with the desired beampattern. Here, selection of an optimal covariance matrix is constrained optimization problem with minimization of cost function. In high directivity radar systems, the antenna beam is needed to be steered to cover a large area for detection. In this proposed work, minimization of convex function and transmit beampattern synthesis is carried out with modifications of the covariance matrix ‘Rcov’ for minimum and maximum transmission power utilization constraints. The beampattern design problem is reformulated here, as semi-definite programming optimization problem and solved using convex optimization, with MATLAB simulation platform. The results show that the beampattern generated using this modified covariance matrix is optimally close to desired pattern.

Third-order optical nonlinearity measurements and optical limiting experiment in Tm: YAG crystal.

In this paper, we investigate the third-order nonlinearities and optical limiting effect of Tm: YAG crystal at a wavelength of 1064 nm. We experimentally measure different energy densities (6.4, 12.8, and 19.2J/cm2) and obtain the nonlinear absorption coefficient, nonlinear refractive index, and third-order nonlinear susceptibility of Tm: YAG crystal. Z-scan results show that Tm: YAG crystal exhibits a large nonlinear absorption coefficient (3.34×10-9m/W) at the wavelength of 1064 nm. We also measure the transmittance of Tm: YAG crystals of three different lengths (7, 15, and 20 mm) to evaluate its nonlinear optical limiting performance. For the 20 mm Tm: YAG crystal, the maximum transmittance without optical limiting effect and minimum transmittance with nonlinear optical limiting effect at a 1064 wavelength nm are 84.2% and 47.8%, respectively, which indicates that Tm: YAG crystal may be a solid material for nonlinear optical limiting at 1064 nm.

A highly transparent and photothermal composite coating for effective anti-/de-icing of glass surfaces.

Anti-/de-icing of glass surfaces is of great importance in present daily life. The long-standing challenge in this field is largely due to the lack of stable multifunctional coatings that can be conveniently and economically constructed on the glass surface, and more importantly, are capable of retaining the original transparency of glass ranging from the visible to the near infrared spectrum. Herein, a direct spraying sol method on the glass surface to prepare a highly transparent and photothermal composite coating is reported. Such multifunctional coating of Cu7S4 nanoparticles/organo-silicone sols has displayed a good photothermal conversion property and hydrophobic property and therefore yields excellent anti-icing and self-melting ice properties. The condensation time of water droplets can be extended to 86 s even at −10 °C, which is 3.42 times delayed relative to ordinary blank glass. And the adhesion strength of ice is largely reduced to 72 KPa, which is as low as ∼1/3 that of ordinary glass. Meanwhile, the subcooling of adhering droplets is reduced to −12 °C under one solar illumination condition and exhibits a rapid de-icing capability. More impressively, the prepared functional coating glass shows an outstanding transmittance of more than 75% in the visible region, while it is over the minimum glass transmittance limit allowed by Safety Standards for Glass (GB9656-2016, China). In addition, the multifunctional photothermal glass coating exhibits good physical/chemical stability, which facilitates the long-term application of the coating in different environments.

FAMILY OF CRANK-ROCKER MECHANISMS. A SUMMARY OF PRACTICAL EXERCISES ON THE PARAMETRIC ANALYSIS OF MECHANISMS

The material of a practical lesson on the parametric analysis of crank-rocker mechanisms is presented. A family of such mechanisms is considered, in which the maximum transmission angle is reached in the crank position at an angle of 75 degrees. The theoretical part provides brief information about the analyzed family of mechanisms. Formulas are obtained to determine the values of the relative lengths of the connecting rod and rocker arm, as well as the minimum transmission angle, as a function of the crank length. These formulas are used only to calculate mechanisms of the named family with equal connecting rod and rocker arm lengths. Formulas are obtained for establishing the values of the minimum transmission angles and swing angles of the rocker arm. These formulas are used in cases when the mechanism of the analyzed family corresponds in pairs to the mechanisms of known families. In the practical part of the article, the course of solving four types of problems is considered. These problems illustrate the application of the formulas proposed in the theoretical part.

Minimum Length Scheduling for Discrete-Rate Full-Duplex Wireless Powered Communication Networks

Wireless powered communication networks (WPCNs) will act as a major enabler of massive machine type communications (MTCs), which is a major service domain for 5G and beyond systems. The MTC networks will be deployed by using low-power transceivers with finite discrete configurations. This paper considers minimum length scheduling problem for full-duplex WPCNs, where users transmit information to a hybrid access point at a rate chosen from a finite set of discrete-rate levels. The optimization problem considers energy causality, data and maximum transmit power constraints, and is proven to be NP-hard. As a solution strategy, we define the minimum length scheduling (MLS) slot, which is slot of minimum transmission completion time while starting transmission at anytime after the decision time. We solve the problem optimally for a given transmission order based on the optimality analysis of MLS slot. For the general problem, we categorize the problem based on whether the MLS slots of users overlap over time. We propose optimal algorithm for non-overlapping scenario by allocating the MLS slots, and a polynomial-time heuristic algorithm for overlapping scenario by allocating the transmission slot to the user with earliest MLS slot. Through simulations, we demonstrate significant gains of scheduling and discrete rate allocation.

Applying switching and multiple access model for reducing packet loss and network overheads in watm

As an effectual simple wireless equivalent created in the telecommunications (telephone) industry, Wireless Asynchronous Transfer Mode (WATM) is utilized to stream unified traffics like video, data, and voice data. In the asynchronous data transfer mode, voice data transfer a packet with the same medium, and data share the networks and burst data. Effective WATM data transmission requires an extensive array of designs, techniques used for control, and simulation methodologies. The congestion of the network is among the key challenges that lower the entire WATM performance during this procedure, in addition to the delay in cell and the overload of traffic. The congestions cause cell loss, and it requires expensive switches compared to the LAN. Consequently, in this current study, the application of an effectual switching model together with a control mechanism that possesses multiple accesses is employed. The multiple access process and switching model are utilized to establish an effective data sharing process with minimum complexity. The switching model uses the synchronous inputs and output ports with buffering to ensure the data sharing process. The traffic in the network is decreased, and the loss of packets in the cells is efficiently kept to a minimum by the proposed technique. The system being discussed is employed through the utilization of software employed using OPNET 10.5 simulation, with the valuation of the WATM along with the investigational outcomes accordingly. The system's efficiency is assessed by throughput, latency, cell loss probability value (CLP), overhead network, and packet loss. Thus, the system ensures the minimum packet loss (0.1 %) and high data transmission rate (96.6 %)

Does blue-violet filtering in contact lenses improve contrast sensitivity?

PurposeThe work is aimed at (i) comparing photopic contrast sensitivity (CS) of healthy subjects in an indoor environment with either blue-violet filtering (BVF) or clear contact lenses (CLs) and (ii) investigating a possible dependence of the CS variation on the subjects' intrinsic CS, measured with clear CLs. MethodsOptical transmittance of BVF and clear CLs was measured by a spectrophotometer. Photopic CS was measured monocularly on forty-one subjects (nineteen in the age range 20–36 years and twenty-two in the age range 44–66 years) by a digital optotype system at spatial frequencies from 1.5 to 18 cpd, wearing either clear or BVF CLs. The results are indicated as CSclear and CSBVF, respectively. ResultsTransmittance curves in the visible range of the two CLs are very similar, despite an absorption band in the BVF CL spectrum with the minimum of transmittance at 428 ± 4 nm equal to about 79%. For both CSclear and CSBVF, no significant CS difference was found between younger and older adults. The difference [log(CSBVF) − log(CSclear)] showed a decreasing trend and changed sign from positive to negative as a function of log(CSclear) with correlation Spearman’s Rho coefficients ranging from 0.80 to 0.88 (p < 0.01 at all spatial frequencies). ConclusionIn the choice of a BVF CL, practitioners should take into consideration that it can influence photopic CS, improving it for subjects who have a relatively low CS with clear CLs, and worsening it for subjects who have a relatively high CS with clear CLs. BVF can affect positively the CS by reducing intraocular scattering. However, it can also cause a reduction in light intensity, which contributes to the formation of the retinal image. The positive or negative influence of BVF CLs compared to clear ones on CS is attributed to a balance among these effects.

Low-Frequency, Open, Sound-Insulation Barrier by Two Oppositely Oriented Helmholtz Resonators.

In this work, a low-frequency, open, sound-insulation barrier, composed of a single layer of periodic subwavelength units (with a thickness of λ/28), is demonstrated both numerically and experimentally. Each unit was constructed using two identical, oppositely oriented Helmholtz resonators, which were composed of a central square cavity surrounded by a coiled channel. In the design of the open barrier, the distance between two adjacent units was twice the width of the unit, showing high-performance ventilation, and low-frequency sound insulation. A minimum transmittance of 0.06 could be observed around 121.5 Hz, which arose from both sound reflections and absorptions, created by the coupling of symmetric and asymmetric eigenmodes of the unit, and the absorbed sound energy propagating into the central cavity was greatly reduced by the viscous loss in the channel. Additionally, by introducing a multilayer open barrier, a broadband sound insulation was obtained, and the fractional bandwidth could reach approximately 0.19 with four layers. Finally, the application of the multilayer open barrier in designing a ventilated room was further discussed, and the results presented an omnidirectional, broadband, sound-insulation effect. The proposed open, sound-insulation barrier with the advantages of ultrathin thickness; omnidirectional, low-frequency sound insulation; broad bandwidth; and high-performance ventilation has great potential in architectural acoustics and noise control.

Energy-Efficient Routing in Wireless Sensor Networks

Efficient data collection is the core concept of implementing Industry4.0 on IoT platforms. This requires energy aware communication protocols for Wireless Sensor Networks (WSNs) where different functions, like sensing and processing on the IoT nodes must be supported by local battery power. Thus, energy aware network protocols, such as routing, became one of fundamental challenges in IoT data collection schemes.In our research, we have developed novel routing algorithms which guarantee minimum energy consumption data transfer which is achieved subject to pre-defined reliability constraints. We assume that data is transmitted in the form of packets and the routing algorithm identifies the paths over which the packets can reach the Base Station (BS) with minimum transmission energy, while the probability of successful packet transmission still exceeds a pre-defined reliability parameter. In this way, the longevity and the information throughput of the network is maximized and the low energy transmissions will considerably extend the lifetime of the IoT nodes. In this paper we propose a solution that maximizes the lifetime of the nodes.

Beamforming Design for Multiuser uRLLC With Finite Blocklength Transmission

Driven by the explosive growth of Internet of Things (IoT) devices with stringent requirements on latency and reliability, ultra-reliability and low latency communication (uRLLC) has become one of the three key communication scenarios for the 5th generation (5G) and 6G communication systems. In this paper, we focus on the beamforming design problem for the downlink multiuser uRLLC system. Since the strict demand on the reliability and latency, in general, short packet transmission is a favorable way for uRLLC systems, which indicates the classical Shannon&#x2019;s capacity formula is no longer applicable. With the finite blocklength transmission, the achievable rate is greatly influenced by the reliability and finite blocklength. Using the developed achievable rate formula for finite blocklength transmission, we respectively formulate the problems of interest as the weighted sum rate maximization, energy efficiency maximization, and user fairness optimization by considering the maximum allowable transmission power and minimum rate requirement. These problems considered are non-convex and are hard to obtain the global optimal solution, even for the local optimal solution. To overcome these difficulties, some important insights have been discovered by analyzing the function of achievable rate. For example, an analytical solution of the minimum rate requirement is provided with respective to the signal-to-interference-plus-noise ratio. Based on the discovered results, we provide algorithms to optimize the beamforming vectors and power allocation, which are guaranteed to converge to a local optimum solution to the formulated problems with low computational complexity. Our simulation results reveal that our proposed beamforming algorithms outperform the zero-forcing beamforming algorithm with equal power or water filling allocation widely used in the existing literatures.

Correlation between the optical absorption and twisted angle of bilayer graphene observed by high-resolution reflectance confocal laser microscopy.

We report a systematic study of the optical absorption of twisted bilayer graphene (tBLG) across a large range of twist angles from 0° to 30° using a high-resolution reflectance confocal laser microscopy (RCLM) system. The high-quality single crystalline tBLG was synthesized via the efficient plasma enhanced chemical vapor deposition techniques without the need of active heating. The sensitivity of acquired images from the RCLM were better than conventional optical microscopes. Although the highest spatial resolution of RCLM is still lower than scanning electron microscopes, it possesses the advantages of beam-damage and vacuum free. Moreover, the high intensity-resolution (sensitivity) images firstly allowed us to distinguish the slight absorption differences and analyze the correlation between the optical absorption and twisted angle of tBLG after data processing procedures. A maximum absorption (minimum transmission) was observed at the stacking angle of tBLG from 10° to 20°, indicating the interplay between the laser and the electron/hole van-Hove singularities when tBLG oriented around the critical angle (θc∼13°). The twisted angle correlated optical absorption paves an alternative way not only to visibly identify the interlayer orientation of tBLG but also to reflect the characterization of the interlayer coupling via its band structure.

Comparison of angular-selective metasurfaces as tools for sub-THz single-frequency sensing

We demonstrate and numerically characterize a set of single-layer metasurfaces based on capacitively-coupled bent metal strips deposited on a thin polypropylene film operating as band-stop filters at 139.1 GHz. Due to a high inter-digital coupling capacitance between neighboring inclusions formed by the strips, the resonance of the metasurface becomes highly sensitive to the incidence angle of a plane wave. At the same time, a narrow-band resonance is achieved by reducing the conductor length along the vertical polarization direction of the incident wave. We propose to use both properties for designing a sensor, which analyses the thickness of a thin slab of a known substance deposited over the structure by tracking the angle at which the minimum of transmission can be measured at a single frequency. We compare three versions of the proposed geometry by numerical calculation of the transmission coefficient depending on both the incidence angle and analyte slab’s thickness. We select the most suitable structure for sensing.

Laser requirements for the designof fast laser-driven semiconductor switches for THz and mm-waves.

A reduced parameter model of fast laser-driven semiconductor switches of THz and mm-waves has been developed. The model predicts peak reflectivity and minimum transmissivity of switches, showing good agreement with experimental data, while requiring fewer inputs than published models. This simplification facilitated a systematic survey of laser parameters required for efficient switching. Laser energy density requirements are presented as a function of laser wavelength, laser pulse width, switched frequency, reflection angle, and semiconductor material (silicon or gallium arsenide). Analytical expressions have been derived to explain the dependence of laser requirements on switch parameters and to derive practical minima of required laser energy density. Diffusion is shown to quickly negate the shallow absorption advantage of laser wavelengths shorter than about 500nm in silicon or 800nm in gallium arsenide. Decreasing laser pulse width, to a derived limit, and switching S-polarized THz or mm-wave signals are shown to be means of lowering required laser energy. This is an especially useful result for devices operating at high power levels or THz frequencies, where extended switches are used in quasioptical systems.

Nonlinear Vibration Isolation via a NiTiNOL Wire Rope

Vibration isolators with both stiffness and damping nonlinearities show promise for exhibiting compound advantages for broadband vibration isolation. A nonlinear isolator with a NiTiNOL wire rope is proposed with cubic stiffness, hysteretic damping, and pinching effects induced by geometric constraints, inner frictions, and phase transitions, respectively. A combined method of a beam constraint model and a Bouc-Wen model is presented to characterize the restoring force of the NiTiNOL wire rope. The frequency responses of the nonlinear isolator were analyzed through a harmonic balance method with an alternating frequency/time domain technique. The generalized equivalent stiffness and the generalized equivalent damping ratio were defined for a comprehensive understanding of the nonlinear characteristics. The isolator exhibited a stiffness-softening-hardening characteristic. The pinching effect, the Bouc-Wen hysteresis, and the cubic stiffness mainly influenced the equivalent stiffness at the initial value, the small displacements, and the large displacements, respectively. The rate-independent damping ratio increased and then decreased with increasing displacement, and the parameters influenced the damping ratio change in different ways. Compared to an isolator with a steel wire rope, the isolator with a NiTiNOL wire rope exhibited less initial stiffness and a stronger damping effect, and thus, better vibration isolation performance. The relationships of the peak displacement transmissibility and the resonant frequency with the excitation amplitude were both non-monotonic due to the non-monotonic changes of the stiffness and the damping ratio. The minimum peak transmissibility, the lowest resonant frequency, and their corresponding excitation amplitudes depended on the isolator parameters. The isolator demonstrated stiffness–softening and stiffness–hardening types of jump phenomena with different parameters.