In this study, a class of wideband bandstop filters is proposed based on wideband 180° phase shifters. Different from traditional signal–interference-based bandstop filters, they make use of a 180° ...phase shifting in a wide operating band in principle. After numerical analysis of the phase responses of the two coupling-line paths, the optimal solutions for the largest 180° phase-shifting bandwidth or minimum impedance ratio can be obtained. Then, the wideband bandstop filter based on these two unique coupling lines is intensively analysed to reveal that three transmission zeros are generated in the stopband as the two paths have a 180° phase difference, thus exhibiting its wideband property. Moreover, by enlarging the impedance of the two paths, good out-of-band characteristics of the bandstop filter can be attained, while in-band performances are almost unchanged. Next, two types of bandstop filters with extended bandwidth are proposed by cascading an extra delay line for both paths, and they hold similar filtering characteristics as the aforementioned one. Finally, the design process and demonstration are provided. The measured results of the three fabricated filters show that Type-I, Type-II, and Type-III filters can satisfactorily obtain a 3 dB bandwidth of 108, 122, and 130% with 25, 14.7, and 11.6 dB rejection level, respectively.
In this article, a simple kind of coplanar stripline (CPS) open-circuited series stub structure and its application in wideband bandpass filters (BPFs) are proposed and developed. Compared with its ...conventional dual-shunted CPS series stub counterparts, the proposed one is capable of achieving desired characteristics as the specified transmission-line (TL) prototypes behave. Based on such equivalent prototypes, three types of CPS open-circuited series stubs are then investigated to reveal the immunity against unexpected resonance caused by the underlying surface-wave-like mode. For demonstration, two examples, a second-order and a third-order wideband BPFs, are synthetically designed for equal-ripple Chebyshev response with prescribed fractional bandwidth (FBW) and return loss (<inline-formula> <tex-math notation="LaTeX">RL </tex-math></inline-formula>). Finally, these two proposed filters with a respective FBW of 49%/70%, an <inline-formula> <tex-math notation="LaTeX">RL </tex-math></inline-formula> of 16.426 dB, and a central frequency of 2 GHz are synthesized, simulated, fabricated, and measured. Measured and simulated results are reasonably in good agreement with each other, thus firmly validating the flexibility of the presented CPS series stub structure in the application of wideband BPFs.
Two novel bis‐cyclometalated iridium complexes are successfully applied in organic light‐emitting diodes (OLEDs). Because of their better carrier transport ability and shorter excited stated ...lifetimes, good electroluminescence performances of the complexes are observed.
•We propose a multi-impact imaging and localization method based on the scanning spatial-wavenumber filter.•The spatial-wavenumber filtering of multi-impact signal is realized without wavenumber ...measuring or modeling.•Identification of multiple impacts in the wavenumber-time image is achieved.•The angle-distance image can be generated to directly obtain the polar coordinates of the multiple impacts.•The multi-impact imaging and localization on a composite structure is realized.
Monitoring of impact and multi-impact in particular in aircraft composite structures has been an intensive research topic in the field of guided-wave-based structural health monitoring (SHM). Compared with the majority of existing methods such as those using signal features in the time-, frequency- or joint time-frequency domain, the approach based on spatial-wavenumber filter of guided wave shows superb advantage in effectively distinguishing particular wave modes and identifying their propagation direction relative to the sensor array. However, there exist two major issues when conducting online characterization of multi-impact event. Firstly, the spatial-wavenumber filter should be realized in the situation that the wavenumber of high spatial resolution of the complicated multi-impact signal cannot be measured or modeled. Secondly, it’s difficult to identify the multiple impacts and realize multi-impact localization due to the overlapping of wavenumbers. To address these issues, a scanning spatial-wavenumber filter based diagnostic imaging method for online characterization of multi-impact event is proposed to conduct multi-impact imaging and localization in this paper. The principle of the scanning filter for multi-impact is developed first to conduct spatial-wavenumber filtering and to achieve wavenumber-time imaging of the multiple impacts. Then, a feature identification method of multi-impact based on eigenvalue decomposition and wavenumber searching is presented to estimate the number of impacts and calculate the wavenumber of the multi-impact signal, and an image mapping method is proposed as well to convert the wavenumber-time image to an angle-distance image to distinguish and locate the multiple impacts. A series of multi-impact events are applied to a carbon fiber laminate plate to validate the proposed methods. The validation results show that the localization of the multiple impacts are well achieved.
In this paper, a dual-band filtering antenna with independent predetermined frequencies and low cross-polarization levels is proposed. In order to realize the independent control of frequencies of ...two radiation passbands, multiple additional structures such as rectangular slots, rectangular parasitic patches, and U-shaped slots are integrated on the traditional rectangular patch antenna to introduce new resonant modes and radiation nulls to the antenna, simultaneously. Since the generation structures of each frequency point are different, they do not affect each other. Besides, to obtain low cross-polarization levels, each additional structure is carefully adjusted such that the current vectors of each resonant frequency along the cross-polarized direction are quite weak. The proposed antenna operates in the 5G sub-6G (4050–4294 MHz) and the Wi-Fi 5.8 GHz band (5700–5920 MHz), and achieves cross-polarization levels of −37.8 and −36.8 dB in the lower and higher frequency bands, respectively. Compared to other multi-band filtering antennas, the proposed one has the advantages of independent predetermined frequencies and lower cross-polarization levels.
A balanced bandpass filter is proposed based on stub-loaded ring resonators (SLRRs) and loaded coupled feed-lines (CFLs) with high selectivity and common-mode (CM) rejection. By controlling the ...coupling coefficient of the CFLs, three transmission poles within the differential passband are achieved. The CFLs are loaded with open- and short-circuited stubs at the end of the traditional parallel-coupled feed-lines, which resulting in multiple transmission zeros (TZs) in differential mode (DM) and CM to improve the passband selectivity and CM suppression, simultaneously. Finally, the proposed filter is designed and fabricated, the simulated and measured results are in good agreement. The filter shows low insertion loss, multiple transmission zeros, high selectivity and enhanced CM rejection.
Heavy metal contamination has become a worldwide problem through disturbing the normal functions of rivers and lakes. Sediment, as the largest storage and resources of heavy metal, plays a rather ...important role in metal transformations. This paper provides a review on the geochemical forms, affecting factors and remediation technologies of heavy metal in sediment. The in situ remediation of sediment aims at increasing the stabilization of some metals such as the mobile and the exchangeable fractions; whereas, the ex situ remediation mainly aims at removing those potentially mobile metals, such as the Mn-oxides and the organic matter (OM) fraction. The pH and OM can directly change metals distribution in sediment; however oxidation–reduction potential (ORP), mainly through changing the pH values, indirectly alters metals distribution. Mainly ascribed to their simple operation mode, low costs and fast remediation effects, in situ remediation technologies, especially being fit for slight pollution sediment, are applied widely. However, for avoiding metal secondary pollution from sediment release, ex situ remediation should be the hot point in future research.
This study proposes a class of differential phase shifters based on the Schiffman type‐C and type‐F networks with wide phase shift range. After the phase and bandwidth properties of these two ...distinct networks are numerically analyzed, two unique advantages of wide phase shift range and wide phase shift bandwidth are revealed. Next, the optimal design parameters for different phase shift values up to 405° are presented to allow for a quick design process. To verify the proposed approach, a 180° differential phase shifter is designed, fabricated and measured. Good performance is achieved with an impedance ratio of 1.959 and 3.7° phase deviation over a phase shift bandwidth of 61%.
Modification with Au nanoparticles on the surface of semiconductor metal oxide (SMO) is a simple and effective mean to improve the sensing performance of pristine SMO sensor. ZnO nanorods are ...prepared via a simple precipitation reaction and subsequently modified by catalytic Au nanoparticles with effect on the surface through an ammonia deposition method. The gas response of sensor based on ZnO nanorods modified by Au nanoparticles is improved by 6.6 times to 100 ppm acetone at the optimal operating temperature of 172 °C, which is reduced from 219 °C for pristine ZnO sensor. Meanwhile, the response/recovery time is shortened to 1 s/20 s from 13 s/29 s. In addition, the sensing enhancement mechanism can be attributed to the electronic and chemical sensitization effects of Au nanoparticles.
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•The synthesis of ZnO nanorods is simple and the modification of Au NPs is easy.•The response of Au-ZnO sensor is improved by 6.6 times to 100 ppm acetone.•Au-ZnO sensor exhibits lower working temperature and shorter response/recovery time.
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