T-shaped Array Research Articles

A Novel Two-dimensional Low-redundancy Array Design for Solar Radio Imaging

The radioheliograph is an extensive array of antennas operating on the principle of aperture synthesis to produce images of the Sun. The image acquired by the telescope results from convoluting the Sun’s true brightness distribution with the antenna array’s directional pattern. The imaging quality of the radioheliograph is affected by a multitude of factors, with the performance of the “dirty beam” being simply one component. Other factors such as imaging methods, calibration techniques, clean algorithms, and more also play a significant influence on the resulting image quality. As the layout of the antenna array directly affects the performance of the dirty beam, the design of an appropriate antenna configuration is critical to improving the imaging quality of the radioheliograph. Based on the actual needs of observing the Sun, this work optimized the antenna array design and proposed a two-dimensional low-redundancy array. The proposed array was compared with common T-shaped arrays, Y-shaped arrays, uniformly spaced circular arrays, and three-arm spiral arrays. Through simulations and experiments, their performance in terms of sampling point numbers, UV coverage area, beam-half width, sidelobe level, and performance in the absence of antennas are compared and analyzed. It was found that each of these arrays has its advantages, but the two-dimensional low-redundancy array proposed in this paper performs best in overall evaluation. It has the shortest imaging calculation time among the array types and is highly robust when antennas are missing, making it the most suitable choice.

Hybrid T-Shaped Sensor Array Composed of Acoustic Vector Sensors and Scalar Sensors

Through the more available acoustic information or the polarization information provided, vector sensor arrays outperform the scalar sensor arrays in accuracy of localization. However, the cost of a vector sensor array is higher than that of a scalar sensor array. To reduce the cost of a two-dimensional (2-D) vector sensor array, a hybrid T-shaped sensor array consisting of two orthogonal uniform linear arrays (ULAs) is proposed, where one ULA is composed of acoustic vector sensors and the other is composed of scalar sensors. By utilizing the cross-correlation tensor between the received signals from the two ULAs, two virtual uniform rectangular arrays (URAs) of acoustic vector sensors are obtained, and they can be combined into a larger URA. It is shown that a larger acoustic vector sensor URA with M2+1 degrees of freedom (DOFs) can be obtained from the specially designed T-shaped array with M acoustic vector sensors and 2M scalar sensors. Furthermore, by means of the proposed tensor model for the larger URA, the inter-sensor spacing can be allowed to exceed greatly a half-wavelength. Accordingly, the proposed method can achieve both a high DOF and a large array aperture. Simulation results show that the proposed method has a better performance in 2-D direction-of-arrival estimation than some existing methods under the same array cost.

Sparse Billboard and T-Shaped Arrays for Two-Dimensional Direction of Arrival Estimation

In two-dimensional direction of arrival (2D-DOA) estimation, planar arrays can estimate the elevation and azimuth angles simultaneously. However, many planar array topologies such as billboard, L-shaped, T-shaped, and 2D nested arrays suffer from mutual coupling that results from the small separation between the physical sensors (antennas), which limits the estimation capability of the sensor array. In an attempt to reduce mutual coupling between sensors, this article proposes sparse billboard and T-shaped arrays in which the number of closely separated sensors is significantly reduced. In addition to extending the CRB for fourth order coarray, this article also derives closed-form expressions for the sensor locations and the number of consecutive lags or the uniform degrees of freedom (uDOF), in the fourth-order difference coarray (FODC). Simulation results demonstrate the robustness of the proposed sparse arrays against mutual coupling.

2D DOA estimation by a large-space T-shaped array

In this paper, a two-dimensional (2D) direction of arrival (DOA) estimation algorithm by a large-space T-shaped array is proposed. The used T-shaped array consists of a generalized unfolded co-prime array and a symmetrically unfolded co-prime array. The minimum element space (MES) of the proposed T-shaped array can exceed half-wavelength of received signals. The symmetry of the T-shaped array is used to construct an extended cross-covariance matrix, singular value decomposition (SVD) of which can obtain multiple signal subspaces. By combining the co-prime characteristic of element spacing with the rotational invariance of uniform linear array, three extended signal subspaces can be obtained without using virtual elements. Using the three extended signal subspaces, high-precision 2D DOA estimation can be got. The proposed T-shaped array has strong robustness to mutual coupling. The proposed method can eliminate angle ambiguity caused by large-space and has higher estimation precision than many similar 2D DOA estimation algorithms. Many simulation results can prove the performance of the proposed scheme.

Array model of shock pressure sensor for shooting point detection

The array model of double-T shock pressure sensor is established. Shock wave is produced by a supersonic object in the air. Pressure is produced in the process of shock wave transmission. Different shock pressure sensors have different time to receive the pressure signal. In this paper, the shooting point calculation model and the finite element model of the double T-shaped array method are established. The simulation experiment is carried out. The law of shock wave propagation is verified. The model can be used to calculate the coordinates of shooting point quickly. This method is suitable for small angle oblique fire location problem, and improves the detection accuracy of shooting point.

2d Doa Estimation by a Large-Space T-Shaped Array

2d Doa Estimation by a Large-Space T-Shaped Array

Application of Seismic Interferometry by Multidimensional Deconvolution to Earthquake Data Recorded in Malargüe, Argentina

Seismic interferometry (SI) refers to the principle of generating new seismic responses using crosscorrelations of existing wavefield recordings. In this study, we report on the use of a specific interferometric approach, called seismic interferometry by multidimensional deconvolution (SI by MDD), for the purpose of retrieving surface-wave responses. In theory, SI by MDD suffers less from irregularities in the distribution of (passive) sources than conventional SI. Here, we confirm this advantage for the application to surface waves originating from regional earthquakes close to Central Chile. For that purpose, we use the Malargüe seismic array in Argentina. This T-shaped array consists of two perpendicular lines of stations, which makes it rather suitable for the application of SI by MDD. Comparing the responses retrieved through SI by MDD to the responses retrieved using conventional SI, we find that the application of SI by MDD results in surface-wave responses that are both more accurate and more stable than surface-wave responses that are retrieved using conventional SI. That is, our results demonstrate that SI by MDD suffers less from non-uniformly distributed earthquakes and differences in the power spectra of earthquake responses. In addition, we show that SI by MDD mitigates the effect of site amplification on the retrieved surface waves.

Ultra-broadband THz absorber with doped silicon based on periodic T-shaped arrays

A polarization-independent ultra-broadband T-type absorber with doped silicon in the terahertz band is proposed, which consists of T-shaped Si/SiO2 arrays. The results show that the absorption is more than 95% at 1.0–5.3 THz. Such an absorber can have a center frequency and relative bandwidth ratio of 3.15 THz and 137%. In addition, the absorption of 90% can be achieved at 1.0–5.3 THz with the incident angle of 0–44°. The energy distribution of the electromagnetic field at the peak of the ultra-broadband absorber is clearly explained by finite element method. Furthermore, compared with the proposed reference planar absorber and the reported broadband absorber, the T-type absorber in this work has better absorption bandwidth, center frequency, and relative bandwidth ratio. The impedance of T-type terahertz absorber is demonstrated well by impedance matching theory. It is believed that the ultra-wideband terahertz absorber with silicon doped based on periodic T-shaped arrays has great potential in the wideband terahertz absorber field and can be applied in the biomedical field.

Reduction of polarization loss of five-splitting by T-shaped arrays

We present five-splitting equal-intensity laser output based on a T-shaped reflection grating under normal incidence, which is aimed to reduce polarization loss. Although five-splitting has been reported by a single-layer grating, a set of parameters can only be effective for either TE or TM polarization. Both TE and TM polarizations can be operated simultaneously by T-shaped arrays. For only one set of groove profiles, splitting efficiencies of 18.26%/19.32%/18.53% and 18.34%/18.25%/19.56% can be reached in ±2nd / ± 1st / 0th orders for TE and TM polarizations, respectively. Within the incident wavelength of 1544 to 1552 nm and the incident angle range of 0 deg to 0.19 deg, each reflective efficiency for a five-splitting laser output is >17 % . The diffraction mechanism inside the grating can be explained by the modal method. The polarization-independent T-shaped grating with five-splitting laser output presented here should be useful in various laser fields due to good manufacturing tolerance and incident performance.

Mixed near-field and far-field source localization revised: propagation loss included

This paper is concerned with source localization when path loss is taken into account. We modify multiple signal classification method to localize near-field sources whose received power is different in the sensors of the array due to path loss. Traditional methods fail to localize the sources, and they also fail to separate the bearing estimation and the range estimation of the sources, when path loss is considered. We suggest a T-shaped array avoiding multidimensional search to estimate source location parameters, separately. At the first step, the ranges of the signal sources are estimated, and then at the second step, the directions of arrival of the sources are estimated using the respective ranges determined at the first stage. The performance of the proposed method is assessed when mixed near-field and far-field sources coexist. Simulation results are presented to show the superior performance of the proposed algorithm compared to the existing techniques and the Cramer–Rao bound.

Capillary film and breakup mechanism in the squeezing to dripping transition regime at the mesoscale between micro and milli-fluidics.

We report a study of droplet generation in two phase flows of non-miscible fluids in a T-shaped array of circular channels, at the mesoscale between micro- and milli-fluidics. Our experiments show that the balance between the different types of forces (capillary forces, shear viscous forces, etc.) may differ significantly from that found by previous authors in smaller, microfluidics channels. The results may, therefore, be applied to practical systems in which droplets act as small chemical reactors or help enhance mixing. We suggest a possible interesting extension to the generation of drops inside porous media. We report experiments in which the length of the droplets and the residual thickness of the surrounding fluid film are systematically measured as a function of the respective flow rates of the two fluids: These results are carefully compared to theoretical models taking into account in different ways the capillary and viscous effects and to results obtained by other authors for smaller channels. Several dimensionless control variables are tested (capillary number, ratio of the flow rates of the two fluids, etc.). Capillary film thickness is shown to be a useful variable to identify the different regimes of formation. Testing of the theoretical models with the experimental data showed that the change from one formation regime to the other is accompanied by a change in the role of viscous effects. Two models of breakup mechanisms were tested: on the one hand, the pressure buildup mechanism and, on the other hand, a second mechanism corresponds to the balance of tangential shear stresses and interfacial tension. According to the formation regimes, both models have provided satisfactory predictions of the experimental results. However, at this mesoscale, the experimental data were better described by the models dependent on the capillary number, as previously reported in systems with a low degree of confinement.

A novel plasmonic elliptical nanocluster and investigating Fano response in π- and T-shaped arrays

ABSTRACTFano resonance has been considered especially in nanostructures for energy enhancement and creating hot spots in nanoparticles based on plasmonic properties. In this paper, a novel arrangement of elliptical nanoantenna has been noticed for improving the electric field and energy enhancement in hot spots for mid-infrared range. For this, elliptical cylinders and elliptical rings are developed for dark mode by the concentration of plasmonic charges in a limited area, and the interaction between bright and dark mode has been used for the Fano shape of the extinction cross section. The combination of dipole arrangement has been implemented based on elliptical hollow cylindrical particles with various inner radios for arousing the Fano resonance. Finally, π- and T-shaped models are studied for Fano resonance, and the electric fields are compared in all cases. Exactly, this study is important for two main reasons: (1) it shows how we can control the extinction cross section and (2) it shows that by distortion for linear array the Lorentzian shape is changed to Fano shape.

Tunable plasmon-induced transparency with graphene-based T-shaped array metasurfaces

The frequency tunable Plasmonic induced transparency (PIT) effect is researched with a periodically patterned T-shaped graphene array in mid-infrared region. We adjust the geometrical parameters to obtain the optimized combination for the realization of the PIT response and use the coupled Lorentz oscillator model to analysis the physical mechanism. Due to the properties of graphene, the PIT effect can be easily and markedly enhanced with the increase of chemical potential and carrier mobility. The frequency of PIT effect is also insensitive with the angle of incident light. In addition, we also propose the π shaped structure to realizing the double-peak PIT effect. The results offer a flexible approach for the development of tunable graphene-based photonic devices.

Analysis of the redundancy of Fourier telescopy transmitter array and its redundancy-strehl ratio-target texture distribution characteristic

The Fourier telescopy is a kind of active illumination imaging with high resolution by using multi-interfering fringes generated by the multi-beams from the large transmitter arrays. According to the imaging principle, the beams from one laser source are split and each beam is applied with a different tiny frequency shift so that the interfering fringes may moving across the target. The configuration of the beams changes so that they would generate fringes in different spatial frequencies and different directions. Recently, most of researches focused on the factors such as the baseline scale and data sampling efficiency that may affect the imaging quality. However, there are other two factors, i.e., the configuration of the transmitter and its redundancy, which need studying. In Fourier telescopy, if the direction and spatial frequency of the fringe patterns that are generated by the change of different baseline configurations match each other, the target surface information would be a crucial factor that affects the image quality.In the first part of this article, the practicability of zero redundancy of baseline is analyzed. The results show that the baseline cannot have zero redundancy due to the iteration algorithm. Then the minimum redundancy is analyzed and the minimum redundancy line is proposed. By using the Strehl ratio as the merit of the imaging quality, the concept of redundancy-strehl ratio-target texture distribution (RST) and calculation method are proposed. This method integrates the transmitter redundancy, target detail information and image quality together. The distribution of RST value on the frequency plane is compared with the minimum redundancy line. If the RST point is located on the horizontal side compared with the line, the target detail information on this baseline is mainly in the horizontal direction. On the other hand, if the RST point is located on the longitude side, the target information is mainly in the longitude direction. Therefore this new proposed method reveals the relationship between target spatial information and the baseline configuration. In this article T-shaped transmitter array is adopted, and the Fourier components are mainly distributed on the rectangle plane. According to this relationship and calculated RST value, the working transmitter may continuously rectify its scale and shifting patterns so that the spatial frequencies and directions of fringes may match the target Fourier components in time. In this article, three simulated images and two real images are tested by the proposed method, and the results show that the RST values and the distributions well reveale the relationship between the detailed information and the baseline configurations.Now the Fourier telescopy follows the procedure from laboratory setup to the real system research. Considering the convenience and cost of project realization, this method is helpful for analyzing the real system of the transmitter configuration and enhancing working efficiency.

Plasmonic Infrared Bandstop Reflective Filter

Various types of free-space plasmonic bandstop filters are reviewed. The plasmonic multilayer structure shows multiple localized surface plasmon (LSP) resonance modes with extraordinary high angle tolerance. Through modifying the plasmonic multilayer structure to a plasmonic T-shaped array, the multiple LSP modes can be suppressed. The filtering properties present a single resonance dip with a low sideband. Through modifying the plasmonic T-shaped array to be an asymmetric one, dual resonance modes can be easily designed. Finally, a nanoporous Au film is proposed to act as a bandstop filter. The fabrication processes are simple and the resonance dip can be manipulated by altering the annealing temperature.

Free-Space Plasmonic Filter with Dual-Resonance Wavelength Using Asymmetric T-Shaped Metallic Array

In this study, we propose a plasmonic free-space filter with dual resonance wavelength by using an asymmetric T-shaped array. The structure under the T-shaped structure forms two metal/insulator/metal cavities with different cavity length. Each cavity supports a specific resonance wavelength. A notch filter for second harmonic generation Nd:YAG laser is also proposed. The filter offers two resonance dips and low sideband. In addition, the filter properties are based on the localized surface plasmon. Therefore, the angle tolerance is extremely high. This makes the proposed structure easy to align. The proposed structure can be used in dual wavelength biosensing detection and dual wavelength thermal emission applications.

Discrete 3D T-Shaped Electrode Arrays for Moving Liquid by AC Electro-Osmosis

A novel 3D discrete T-shaped electrode array, fabricated by PolymMUMPs, is presented for pumping microscale liquid utilizing AC electro-osmosis (ACEO). Both the theoretical and experimental work has been carried out to evaluate the new design concept. A 3D finite element model of a unit cell incorporating a pair of electrodes is created to simulate pump performance. The new design is prototyped using the PolyMUMPs process and the experimental evaluation of its performance is conducted with saline solution at three different voltages. The maximum velocity obtained from the tracing particles at 30μm above the bottom of the channel was 90μm/s, 130μm/s and 200μm/s for a voltage of 6Vpp, 8Vpp and 10Vpp respectively.

Angle-independent plasmonic infrared band-stop reflective filter based on the Ag/SiO_2/Ag T-shaped array

A plasmonic infrared (IR) filter assisted by localized surface plasmon polaritons (LSPPs) in a Ag/SiO₂/Ag T-shaped array was theoretically and experimentally investigated. By using a Fourier transform infrared (FTIR) spectrometer, an angle-independent LSPP resonant mode caused by a Fabry-Pérot resonance in the structure was observed in agreement with the prediction from the rigorous coupled-wave analysis (RCWA) simulation. The resonant wavelength of the mode can also be controlled by modifying the geometry of the T-shaped structure. Such LSPP property can be used as an IR reflection-type band-stop filter with a single spectral bandwidth and an ultrahigh immunity to incident angles.

SETI-ITALIA 2008: On-going searches and future prospects

The Medicina Radioastronomical Station is located nearby Bologna, in Italy. It consists of two receiving antennas currently dedicated to the astronomical research at radio frequencies. The 32 m diameter parabolic dish performs observations from 1.4 to 22 GHz whereas the Northern Cross (a 30.000 m 2 wide T-shaped array transit antenna) works at 408 MHz. So far SETI observations have been performed using a SERENDIP IV high resolution spectrometer connected to the parabolic antenna. Data acquisition were performed meanwhile the antenna was employed in ordinary astronomical observations (piggy-back mode). An innovative method to search for possible extraterrestrial signals could be provided by using the UHF Northern Cross transit telescope. In this paper observational modalities and the required technological set-up are investigated.

Auditory perception versus automatic estimation of location and orientation of an acoustic source in a real environment

In this work, the perception of the position and orientation of a directional acoustic source in a real enclosed environment by blindfolded listeners is investigated and compared with a method that automatically estimates the position and orientation of the source using a T-shaped microphone array. In the subjective experiment using blindfolded listeners, a human speaker acted as an acoustic source and listeners judged the speaker's facing angle (one out of four possible orientations shifted by 90 � ) and position after listening to a spoken sentence. This procedure was performed twice, before and after a training phase. In the training, listeners were allowed to remove the blindfold and verify the speaker's position and orientation. After the training, the correct orientation ratio increased from 75.0 to 76.5% and the average position error decreased from 66.2 to 60.6 cm. In addition, a subjective experiment on orientation estimation with eight orientations shifted by 45 � in the same real environment showed that orientation estimation in a real environment was more difficult than that in an anechoic environment. Artificial neural networks (ANNs) were used in the automatic estimation method. A correct orientation ratio of 68.1% and an average position error of 48.0 cm were obtained by the T-shaped microphone array located nearest to the blindfolded listener among an array network consisting of eight T-shaped microphone arrays, enabling a rough comparison between human auditory perception and the automatic estimation method (a correct orientation ratio of 67% and a better average position error of 38.6 cm were the best results obtained by a T-shaped array in the network). It was clarified that the automatic estimation method cannot surpass the auditory system in terms of correct orientation ratio; however, it yielded better results in terms of the average position error.