Half Wavelength Research Articles

Miniaturized triple band-notched quasi-self complementary fractal antenna with improved characteristics for UWB applications

This paper is a continuation and extension of a previous work [1]. In this paper, an enhanced UWB microstrip-fed quasi self-complementary fractal (QSCF) antenna with triple band notches is presented. These band notches are allocated at 3.5, 5.5 and 7.8 GHz. The proposed design supports coexistence with narrow band applications IEEE 802.16 WiMAX, IEEE 802.11 WLAN and X-band of satellite communications, respectively. Both slot and parasitic loading techniques are utilized to achieve this goal. A guided half wavelength U-shape slot is etched in the ground for creating band rejection at the WiMAX frequency band. To attain the WLAN band rejection, another half wavelength U-shape slot is inserted to the feed line. A split ring resonator (SRR) is embedded to the left and right of the feed line for avoiding interference with X-band. The prospective antenna is designed using low cost FR4 substrate of miniaturized size 32 × 16.5 × 1.5 mm3 which empowers it to be embedded in assorted portable devices. Nearly omnidirectional radiation patterns and stable gain are accomplished over the operating bandwidth from 2 to 11 GHz. For further clarification of the operating principle, an equivalent circuit model is considered showing good agreement with CSTMWS, HFSS and experimental results. Furthermore, a time domain analysis is investigated presenting satisfactory distortion performance between excited and received pulse validating it for diversified UWB applications.

Acoustic performance of noise barrier based on sonic crystals with resonant elements

Recent years have seen a growing interest in the potential for the use of sonic crystals as noise barriers. The frequencies of highest attenuation can be found by assuming that an integer number of half wavelengths fits the distance between the scatterers. However, this leads to a reduction in its usefulness as a viable noise barrier technology, due to the necessary increase in overall crystal size to increase frequency range of noise reduction. Additional attenuation bands may be achieved if the array is composed of resonant elements instead of solid cylinders. The paper presents resonant sonic crystal barrier that could be applied to stationary but movable noise sources eg. power generator. The results of simulation results were confronted with the results of previous work in this field. This work presents also sound insulation measurements conducted over sonic crystal noise barrier according to the European standard EN 1793-6. In most of the reference literature, sound insulation and reflection properties of sonic crystals are measured or a diffuse sound field or in a direct sound field including the top and side edge diffraction effects together with the transmitted (or reflected) components. The aim of this work is to perform free-field measurements over a real-sized sample in order to verify the points of strength and weakness of the application of standardised measurements to sonic crystals.

Precision measurement of relative permittivity of aluminum oxide for a high power resonant waveguide window with low return loss

An iterative method of estimating permittivity and window thickness with high precision is developed for half wavelength resonant waveguide windows for use in a lower hybrid launcher for DIII-D. The high Q factor of half-wavelength windows results in extreme sensitivity of return loss on small deviations in permittivity. Permittivity and loss tangent measurements of Morgan AL-995 99.5% aluminum oxide ceramic using a waveguide resonant cavity per ASTM D2520-13 determine variation of permittivity with frequency. Measurement of window resonant frequency in conjunction with the slope of permittivity from waveguide cavity measurements determine required thickness of a resonant window within 5 MHz of the desired resonant frequency. Methods to improve measurement accuracy of resonant peaks on a vector network analyzer are discussed. A sensitivity study to dimensional variations in window or sample rod geometry, and shift in resonant frequency due to RF heating of the window material is conducted.

3D acoustic metasurface carpet cloak based on groove structure units

A 3D acoustic metasurface carpet cloak (AMCC) based on groove structure units is proposed and investigated. The key idea behind this acoustic invisibility is the phase compensation via local phase modulation, and thus a cloak with a thickness of only of a half wavelength could be designed for objects with arbitrary geometric shapes and sizes. We first demonstrate the cloaking effect of hiding a conical object numerically, and find that the working bandwidth of the designed AMCC is from 6200–7500 Hz. Further experimental results are in good agreement with the numerical simulations, verifying that the AMCC works well for the normal incident wave and the small-angled incident waves. As another example, we also confirm that the proposed AMCC can hide a semispherical object. The present AMCC is thin, has a simple geometrical structure, and is easy to implement, which benefits future realistic applications.

DOA Estimation Exploiting Sparse Array Motions

This paper utilizes sparse array motion to increase the numbers of achievable both degrees of freedom (DOFs) and consecutive lags in direction-of-arrival (DOA) estimation problems. We use commonly employed environment-independent sparse array configurations. The design of these arrays is not dependent on the sources in the field of view, but rather aims at achieving desirable difference co-arrays. They include structured coprime and nested arrays, minimum redundancy array (MRA), minimum hole array (MHA), and sparse uniform linear array (SULA). Array motion can fill the holes in the spatial autocorrelation lags associated with a fixed platform and, therefore, increases the number of sources detectable by the same number of array sensors. Quasi-stationarity of the environment is assumed where the source locations and waveforms are considered invariant over array motion of half wavelength. Closed-form expressions of the number of DOFs and consecutive spatial correlation lags for coprime and nested arrays as well as SULA, due to array translation motion, are derived. The number of DOFs and consecutive lags for the specific cases of MRA an 5 avaluated. We show the respective DOA estimation performance based on sparse reconstruction techniques.

Slotted metal nanodisks supported by dielectric-coated metallic substrates for ultrahigh enhancement of coherent anti-Stokes and hyper-Raman scattering

Slotted metal nanodisks supported by dielectric-coated metallic substrates exhibit Fano resonances by the coherent coupling of slot and nanodisk modes. Local intensity enhancement in slot region reaches the values in the order of 104 in the spectral range of Fano resonance when excited with light polarized perpendicular to the axis of slot. With increasing the disk diameter, higher order resonance appears with a peak of field enhancement at around a half wavelength of pump, which is favorable for enhancing hyper-Raman scattering. Due to the ultrastrong field enhancement, these plasmonic nanostructures provide the enhancement factors 103 ~ 105 times higher than the thresholds for single molecule detection based on surface-enhanced coherent anti-Stokes Raman and hyper-Raman scattering. The proposed nanostructures hold great promises for the other nanophotonic applications such as highly efficient harmonic generation, benefiting from strong field enhancement.

A four‐way broadband filtering power divider with improved matching network for X‐band application

AbstractThis study presents a novel design methodology of one‐to‐four filtering power divider (FPD) with a broadband response. It comprises three one‐to‐two power dividers (PDs) and a broadband bandpass filtering circuit in series. The impedance transformer of the one‐to‐two PD is designed into a dual‐T‐type symmetrical structure for improving the matching network and broadening the bandwidth, which includes a tapered transmission line, two cascaded microstrip lines with the same characteristic impedance, as well as a stepped‐impedance open stub. The bandpass filtering circuit is formed by three coupled quarter‐wavelength microstrip lines in parallel, where the intermediate subresonator is grounded via a hole instead of half wavelength line for pursuing a wider bandpass characteristic. The proposed FPD is fabricated and measured. The good performance is achieved with the return loss of >13.8 dB for input/output ports as well as minimum insertion loss of <0.21 dB (over the −6 dB splitting ratio) from 7.3 to 13 GHz.

Design of Low Loss Filter for UWB Wireless Signal of Ship's Multi-user under Wind and Waves

ABSTRACT Zhu, Y.; Bi, Y., and Zhang, Y., 2018. Design of low loss filter for uwb wireless signal of ship's multi-user under wind and waves. In: Liu, Z.L. and Mi, C. (eds.), Advances in Sustainable Port and Ocean Engineering. Journal of Coastal Research, Special Issue No. 83, pp. 985–990. Coconut Creek (Florida), ISSN 0749-0208. The design of the low loss filter for the UWB wireless signal of ship's multiuser under the wind and waves is of great significance to the development of the ship communication in China. At present, the design of the filter in this aspect is completed according to the design principle of EML, and there is a problem of big difference between the test value and the actual value. The traditional UWB filter which has optimizes the structure of high pass short-ended stubs is as the design basis, in the half wavelength transmission line connecting short-ended stubs line, the resonator structure units of dual-mode and tri-mode stubs are loaded to achieve the performance of dual-trapping o...

DOA Estimation Exploiting Moving Dilated Nested Arrays

A novel dilated nested array is presented to obtain an enhanced fully filled difference coarray exploiting array motions. The proposed sparse array is suitable for the cases when the sensing environment can be assumed stationary over an array motion of half wavelength or shorter. Closed-form expressions of the number of degrees of freedom in the difference coarray of the combined array before and after the translation motion are presented for direction-of-arrival (DOA) estimation. It is shown that the maximum number of consecutive lags for this case is three times that of the corresponding conventional two-level nested array. Numerical results of DOA estimation using the proposed array are provided for performance comparison and to validate array analyses.

Highly directive 3D‐printed dual‐beam waveguide slotted antennas for millimeter‐wave applications

AbstractA highly directive 3D‐printed dual beam waveguide slotted antennas designed at 28 GHz are presented in this work. By having dual‐beam directional pattern, the coverage area can be doubled. The performance of dual‐beam waveguide slotted antennas is investigated with new metal 3D printing technique. The slots are basically designed at half wavelength dimension and distance with symmetrical and asymmetrical offset to form different phase radiations. The longitudinal slotted arrays are implemented on both side of the waveguide broad walls, thus enabling the dual beams on the antenna. The proposed antennas are simulated using computer simulation technology software and fully metal printed using EOS M280 machine. The simulated performance is validated experimentally using network analyzer measurement. The dimensional tolerance and surface roughness are profiled in this work. A good match better than 10 dB is achieved. The antennas are proposed for three‐dimensional beamforming in millimetre wave applications.

Influence of Underwater Bar Location on Cross-Shore Sediment Transport in the Coastal Zone

The effect of the underwater bar position on a sandy beach profile was studied on a timescale of one storm, using the XBeach numerical model. The largest shoreline regress occurred in the first hour of storm. For the chosen wave regime an underwater profile close to the theoretical Dean’s equilibrium profile is formed after 6 h. The position of the underwater bar affects the shoreline retreat rate. The lowest shore retreat occurs when the bar crest is located at a distance equal to 0.70–0.82 of the deep-water wavelength, corresponding to the period of the wave spectrum peak. The maximal shoreline retreat occurs when the bar is located at a distance that is close to a half wavelength. The shoreline recession depends on the heights of low-frequency waves. The smaller the mean wave period and the higher low-frequency waves’ height near the coast, the smaller the retreat of the shoreline. The distance of seaward sediment transfer is directly proportional to the significant wave height near shore.

Three-dimensional seismic analysis of Late Paleozoic coal-bearing series reflections in the Hangjinqi, North Ordos Basin, China

The study of sand bodies and coalbeds that formed during strong events is conducive to understand the relationship between source rocks and reservoirs. Two sets of Late Paleozoic coal-bearing sequences including the Late Carboniferous Taiyuan Formation and Early Permian Shanxi Formation, with an accumulated thickness of more than a half wavelength (90 m), were deposited in the Hangjinqi region on the northern margin of the Ordos Basin. These strata appear as two peaks and two troughs, three peaks and three troughs in the 3D seismic data. We analyzed this coal-bearing seismic response through a combination of well-data statistical analysis, the establishment of forward modeling, and the creation of crossplots. The coal-seam thicknesses of the Taiyuan and Shanxi Formations and the spacing between the two sets of coal indicate the major roles in the merging and bifurcation of events. The formation of three peaks and three troughs requires that the thicknesses of the two sets of coal are greater than 2 m. The spacing between the two sets of coal must also exceed 10 m with a detectable lateral extension, which would otherwise generate two peaks and two troughs. The two peaks and two troughs indicate a combined relationship between the thin sandstones at the bottom of the Shanxi Formation and the thick coalbeds in the Taiyuan and Shanxi Formations. The three peaks and three troughs suggest a combined relationship between the thick sandstones at the bottom of the Shanxi Formation and the thin coalbeds in the Taiyuan and Shanxi Formations. The drilling results clarified that the well situated at the two peaks and two troughs regions is accompanied by higher gas productivity, revealing that the coal-seam thickness has a significant influence on gas accumulation. The presence of two peaks and two troughs indicates favorability for natural gas exploration.

<inline-formula> <tex-math notation="LaTeX">$CSIsnoop$ </tex-math> </inline-formula>: Inferring Channel State Information in Multi-User MIMO WLANs

Channel state information (CSI) has been proposed to enhance physical layer security by functioning as a shared secret between a transmitter and a receiver, because it decorrelates over half wavelength distances and cannot be predicted based on locations of the transmitter and receiver in rich scattering environments. Consequently, CSI was employed to generate passwords, to authenticate the source of packets, and to inject artificial noise to thwart eavesdroppers. However, in this paper, we present CSIsnoop, and show that an attacker can infer CSI in a multi-user MIMO WLAN, even when both channel sounding sequences from the access point and CSI measurement feedback from the clients are encrypted during downlink (explicit) channel sounding, or when uplink (implicit) channel sounding is employed. The insights of CSIsnoop are that the CSI of clients can be computed based on transmit beamforming weights at the access point, and that the transmit beamforming weights can be estimated from downlink beamforming transmission. In other words, we reveal the fundamental conflict between using CSI to optimize PHY design by beamforming and ensuring the confidentiality of CSI. We implement CSIsnoop on a software defined radio and conduct experiments in various indoor environments. Our results show that on average CSIsnoop can infer CSI of the target client with an absolute normalized correlation of over 0.99, thereby urging reconsideration of the use of CSI as a tool to enhance physical layer security in multi-user MIMO WLANs.

A study of formation of high order wheel polygonalization

High frequency and high magnitude wheel-rail impact forces caused by high order wheel polygonalization have been associated with service failures of different structural components in high-speed rail vehicles. In this study, a long-term wear iterative scheme was developed to identify primary contributors of high order wheel polygonalization and its propagation over the service period. The wear model was formulated by integrating an Archard wear model to a coupled vehicle/track dynamic model of a high-speed railway car. The effects of different vehicle and track parameters such as the flexibilities of wheelset and rail, vehicle speed, wheelbase, and rail pad stiffness and damping on the wheel wear were further investigated. The bending vibration mode of the rail segment between two wheelsets, regarded as three half wavelength bending vibration mode near 650 Hz, was identified as the primary contributor to high magnitude wheel/rail contact force in the 500–800 Hz frequency range. This represented a nearly fixed-frequency loading condition. Variations in the vehicle speed and the track could help distribute wheel circumferential irregularities over a broader range of wavelength and thereby mitigate the growth rate of wheel polygonalization of a single order. It is further shown that the wheelset flexibility and higher rail pad stiffness accelerate the wheel wear and more likely contribute to the lower order wheel polygonalization. Increasing the rail pad damping could effectively reduce the rate of growth of high order wheel polygonalization.

Numerical and theoretical analysis of honeycomb structure filled with circular aluminum tubes subjected to axial compression

In this study, comprehensive investigations of an innovative composited cellular structure—Honeycomb cells filled with circular aluminum tubes (HFCT) are conducted by means of numerical simulation and theoretical analyses. A conventional honeycomb was modeled to calibrate the numerical model and a good agreement between numerical and experimental results was achieved. With the calibrated numerical model, extensive comparisons between mechanical performances considering the deformation modes, nominal stress and energy absorption property were carried out in terms of HFCT, conventional honeycomb, and multi-tubes. The interaction effects between internal filler and outside container of HFTC were discussed through the comparison considering representative volume elements (RVE) of three structures. In addition, obvious matching effects in terms of cell thickness were observed between the filler and container of HFCT. Afterward, a theoretical model based on the minimum energy principle which considering the basic fold element of HFCT was constructed to determine the key compression characteristics (half-wave length and nominal plateau stress). Agreement between them was found in plateau stress and geometrical description of post-deformation mode.

A compact wide-slot UWB antenna with reconfigurable and sharp dual-band notches for underlay cognitive radio applications

This paper presents a compact wide-slot ultrawide-band (UWB) antenna with reconfigurable and sharp dual-band notches compatible with the underlay cognitive radio systems. The antenna slot and tuning stub are reshaped in such a way that the proposed antenna operating bandwidth extends along the frequency band specified for UWB applications (3.1-10.6 GHz). In spite of their sharpness, the generated band notches perfectly cancel the interference with the entire 5 GHz wireless local area network (WLAN) frequency band (5.15-5.725 GHz) and that of the military X-band satellite communications downlink (7.25-7.745 GHz). The WLAN band notch is presented by attaching a pair of quarter wavelength parasitic elements to the antenna ground plane, while the other band notch is produced by engraving another pair of half wavelength parasitic elements within the antenna wide slot along the circumference of the antenna tuning stub. The reconfiguration of the band notches is achieved by inserting a pair of PIN diodes for each pair of parasitic elements. The simulated and measured results accentuate the UWB coverage of the proposed antenna, and also verify the reconfigurability and the sharpness of the antenna band notches. Moreover, the antenna has a noticeably stable radiation pattern over the entire band of operation with omnidirectional pattern convenient for portable UWB gadgets.

Compact Plasmonic Lens Based on Nanoslits in the Tree Age Chart Arrangement

A novel plasmonic planar slit lens, consisting of five slits in tree age chart arrangement with gradually decreasing widths and interspace distances, is proposed. The slits width and interspaces are related with each other by introducing a scaling constant k that was previously introduced in nanoparticle chains. At specific k values, the light propagates extraordinarily through the slits and causes focusing features beneath the metallic layer. The underlying physics behind the focusing is because of additional phase imposed on traveling light through the slits and their constructive interference. Numerical simulation is used to demonstrate the focusing behavior. Results show that the slit width should not be larger than half wavelength, and the scaling constant should be between 0.3 and 0.4. Salient features of the proposed structure are ultra-compactness, large transmission, and ease of fabrication.

Sparse DOA Estimation Algorithm Based on Fourth-Order Cumulants Vector Exploiting Restricted Non-Uniform Linear Array

Non-uniform linear array (NLA) has been widely used in the direction-of-arrival (DOA) estimation owing to its significant advantage of effectively expanding array aperture. In recent years, its related researches have been advanced due to the introduction of nested arrays and co-prime arrays. However, these NLAs require one or even many adjacent antennas whose spacing is the half wavelength of the incident source. In the practical application of the DOA estimation, if the frequency of the incident source is very high, the distances between adjacent antennas cannot reach half wavelength because of the existence of the actual antenna diameter. In this paper, a design method of the restricted NLA is proposed to solve this problem. First, a new NLA is designed by restricting the minimum spacing of adjacent elements, the set of fourth-order antenna spacing differences, and the maximum aperture of the array. Then, in order to solve the ambiguity problem in the DOA estimation caused by the spacing of adjacent antennas larger than half wavelength, we construct a single snapshot measurement sparse signal model by utilizing the fourth-order cumulants vector of the received signal after dimension reduction and by obtaining the estimation of DOA via a sparse reconstruction algorithm. Finally, compared with the minimum redundancy arrays, nested arrays, and co-prime arrays, the simulation experiments show that the proposed restricted NLAs have better performances of the DOA estimation.

Simulation and analysis of UHV half wavelength and DC hybrid transmission system

The scenarios of a half wavelength transmission line (HWTL) connected to the original DC asynchronous interconnection system are established based on the quasi-steady state model of HWTL, which include single or double loops of single channel and multi-channel scenarios with different starting and landing points. Firstly, the steady state power flow characters of multi-scenario transmission schemes are studied. The voltage distribution characters of HWTL are analyzed when its transmission power and power factor vary, and the influence of the DC power variation on voltage of HWTL is discussed. Then the transient characters of HWDHTS are explored. The DC commutation failure caused by the fault of HWTL is simulated and the power transfer capacity of HWTL while DC blocking is calculated in this paper.

Mutual coupling reduction with a novel fractal electromagnetic bandgap structure

This work shows the effect of a novel fractal-based electromagnetic bandgap (FEBG) structure between dual planar inverted-F antenna (PIFA) elements. The FEBG structure without any shorting pins builds on a well-known fractal structure called Sierpinski carpet, where two iterations have been applied as a uniplanar EBG between dual PIFAs elements to increase the isolation. The proposed antenna can operate at ~2.65GHz for wireless long-term evolution application with compact design dimensions. The simulations are carried out with Ansoft HFSS ver. 17.0. The second iterative order FEBG band-gap characteristic is verified using more computationally efficient analysis. An investigation on coupling reduction showed more than 27 and 40dB in E -plane and H -plane, respectively, between the dual antenna elements is achieved for an antenna spacing less than half wavelength. The proposed antennas with and without second iterative order FEBG are fabricated and measured. The measurement results are in good agreement with the simulated results. Moreover, the envelope correlation of antenna elements with the proposed FEBG is quite smaller than that of antenna elements without FEBG, which gives the proposed system an excellent diverse performance and suitable for the use in low-frequency narrow-band multiple-input, multiple-output applications.