Array Axis Research Articles

Wave Field Reconstruction Filtering in Cylindrical Harmonic Domain for With-Height Recording and Reproduction

For sound field reproduction that includes height (with-height reproduction), it is more efficient to record and reproduce the sound field with lower resolution in elevation than in azimuth due to the spatial abilities of human auditory perception. We propose a sound field reproduction method using horizontally arranged cylindrical arrays of microphones and loudspeakers, which is based on the wave field reconstruction (WFR) filter. With the use of cylindrical array configurations, it is possible to reproduce sound waves arriving from upper and lower directions with a smaller number of array elements at angular positions. The WFR filter is analytically derived in the cylindrical harmonic domain and allows direct transformation from the received signals of the microphones into the driving signals of the loudspeakers. A model in which microphones are mounted on a rigid cylindrical baffle is introduced to stabilize the WFR filter. Numerical simulation results indicated that the reproduction accuracy in the neighboring region along the central axis of the cylindrical array was better preserved when using the proposed method than when the method with planar arrays was used.

Molecular dynamics studies on the influences of a gradient electric field on the water chain in a peptide nanotube.

The structure and transportation characteristics of the water chain inside a 8×cyclo-(WL)4 peptide nanotube (PNT) were simulated under a gradient electric (GE) field. The gradient was defined by the ratio of a constant (Ea) and the z-directional length (Lz) of the simulation box. Ea varies from 0.0 to 0.9 V nm(-1). As the gradient increases, the probabilities of finding two water molecules in an α-plane zone and three in a midplane region increase. To accommodate more water molecules, the axial array of channel water molecules becomes more compact. Meanwhile, the H-bonded network between the channel water is greatly intensified when Ea increases from 0.3 to 0.9 V nm(-1). Nevertheless, the proportion of strong H-bonds does not increase significantly following the formation of a more compact axial array of water molecules. When Ea reaches 0.9 V nm(-1), the water molecule in an α-plane zone may be dragged by its neighboring water molecules into the midplane region, resulting in a significant deviation from the channel axis. With the augment of the gradient, the dipoles of channel water are gradually oriented along the tube axis in the sequence from gap 1 to 7, namely along the direction of the electric field. Nevertheless, even when E a reaches 0.9 V nm(-1), the dipole orientation of the channel water is not complete, and dipole flips still occur in gap 7. Under a GE field, the rightward and leftward hopping rates of channel water are no longer equal to each other, i.e., channel water performs an asymmetric transportation.

Interpenetration, deflection, and stagnation of cylindrically convergent magnetized supersonic tungsten plasma flows.

The interpenetration and interaction of supersonic, magnetized tungsten plasma flows has been directly observed via spatially and temporally resolved measurements of the Thomson scattering ion feature. A novel scattering geometry allows independent measurements of the axial and radial velocity components of the ions. The plasma flows are produced via the pulsed power driven ablation of fine tungsten wires in a cylindrical wire array z pinch. Fits of the data reveal the variations in radial velocity, axial velocity, and temperature of the ion streams as they interpenetrate and interact. A previously unobserved increase in axial velocity is measured near the array axis. This may be the result of v[over →]×B[over →] bending of the ion streams by a toroidal magnetic field, advected to and accumulated about the axis by the streams.

Influence of asynchronous actuation of the Angara-5-1 facility modules on the penetration of the magnetic field inside a wire array

The influence of asynchronous actuation of the Angara-5-1 facility modules on the implosion symmetry of the wire array plasma in the Z-pinch mode is studied. It is shown that an increase in the r.m.s. jitter in the start times of the modules leads to an appreciable azimuthal asymmetry of magnetic field penetration inside the wire array and, as a consequence, to an increase in the duration of the soft X-ray pulse, a decrease in its power, and a shift of the Z-pinch with respect to the array axis. Necessary conditions for axisymmetric pinch implosion are determined. Experimental data on the magnitude and azimuthal distribution of the current (magnetic field) inside the wire array were obtained from magnetic probe measurements. The position of the Z-pinch with respect to the wire array axis was determined from two-dimensional X-ray images and radial optical streak images.

Mode analysis of distant shipping noise in the SPICE experiment

A major source of ambient noise for frequencies below 100 Hz is due to distant shipping (Wenz, 1962). Shipping noise is trapped in the SOFAR channel and propagates long distances. Since this part of ambient noise excites the low normal modes, it decays with increasing depth. A modal analysis of shipping noise provides valuable insights about its depth dependence. SPICEX offered a unique opportunity to study the ambient noise in the Northeastern Pacific using two vertical line arrays an axial array and a deep array. A 40-hydrophone axial array spanned the SOFAR channel and recorded ambient noise at regular intervals over a year. The axial array data makes it possible to estimate the wavenumber-frequency spectra of ambient noise. We can estimate the mode powers associated with the angle-limited noise in the wavenumber-frequency spectra using a least squares fit. Given the estimated mode powers, depth-dependence of the shipping noise component is predictable. This talk compares the predicted noise levels as a function of depth with data measured by the deep SPICEX line array.

Polarized light-emitting backlight unit using a retardation film for improving light efficiency in a twisted nematic mode liquid crystal module

We propose and demonstrate a new polarized backlight unit (BLU) configuration to enhance light transmission in a twisted nematic (TN) mode liquid crystal (LC) panel. By adding an optimized phase retardation film (PRF) to the BLU, we efficiently controlled the polarization state of the light from the light guide plate (LGP), enabling it to be aligned along the transmission axis of the bottom polarizer of the LC panel. We designed and fabricated a 7 in. edge-lit BLU with a PRF. To obtain a uniform positional distribution in both light intensity and degree of polarization (DOP), the LGP was optimized with linear groove patterns. To maximize BLU light transmission through the bottom polarizer in a TN-mode LC panel, the slow axis of the PRF was aligned at 22.5° with respect to the LED array axis. We improved the transmittance from 45 to 72%.

Two-Dimensional Scanning Antenna Array Driven by Integrated Waveguide Phase Shifter

A Butler matrix-fed two-dimensional (2-D) scan linearly polarized 2 × 2 microstrip ring antenna array (MRAA) is proposed and validated in low-cost substrate integrated waveguide (SIW) technology for Ka-band applications. The highly efficient, compact, and passive beam forming network (BFN) consists of SIW cruciform couplers as coupling unit, and its special topology is well adapted for feeding planar arrays. The wideband and high radiation efficiency antenna elements are aperture-coupled through slots etched on the top of a high permittivity SIW feed substrate. Such four antenna elements are used to construct 2 × 2 MRAA and to form four fixed beams, one in each quadrant at an elevation angle of 20 ° from the broad side array axis. A triangular grid arrangement is chosen to avoid grating lobes in the visible space. A 50- Ω grounded coplanar waveguide (GCPW) to SIW transition is used to avoid spurious input feed radiation loss. The array is measured to exhibit 3-dB beam width of 30 ° in both of the orthogonal planes, radiation efficiency of 70% for each port, and stable radiation pattern bandwidth of 7.6% at 26.5 GHz. The physical size of the demonstrated 2 × 2 array is 2.86λo×2.86λo×0.22λo.

Rates of geodetic deformation across active faults in southern Italy

Abstract Active deformation in southern Italy is accommodated by a distributed number of faults with low–moderate slip rates. Outcropping extensional faults and mostly blind transcurrent faults are mapped within a western (or axial) and an eastern domain, respectively. We use a combination of continuous (2001.00–2011.84) and episodic (1995.68–2010.79) GNSS observations to firstly estimate the geodetic deformation rate on 32 faults. Geodetic results were successively compared with geological displacement estimates. In agreement with seismological and geological information, a net spatial segregation emerges between the extensional axial belt, and the eastern domain where strike–slip faults are geodetically active. Although uncertainties are at times large, average displacement rates show broadly consistent patterns within both domains. A longitudinal gradient in extension rate is observed for the axial fault array, with two sectors of higher magnitude (~ 0.8–1.7 mm/yr for individual faults). This result is consistent with geological observations and supports the notion that extension occurs in discrete patches. Faults of the eastern domain have lower (few 0.1 to ~ 1.2 mm/yr) strike–slip rates and an eastward-decreasing extensional component, but significant geodetic displacement is detected in areas lacking clear evidence of activity. Few faults with 1–2 mm/yr extension rate are locally found in the eastern domain, but, based on their limited length and on inconsistency with seismology and geology, they are considered as due to deep-seated gravitational spreading. For crustal faults, although geodetic slip and moment rates are larger than geological rates, the broad trend of long- to short-term rates is similar, indicating the feasibility of geodetic analysis to contribute estimating fault slip rate and testing tectonic models in the region. Whereas the western domain extension is thought to be controlled by potential energy related to the Tyrrhenian Moho uplift beneath the Apennines, strike–slip in the east is related to shear on inherited faults within the Adriatic crust.

Integrated ultrasound and magnetic resonance imaging for simultaneous temperature and cavitation monitoring during focused ultrasound therapies

Ultrasound can be used to noninvasively produce different bioeffects via viscous heating, acoustic cavitation, or their combination, and these effects can be exploited to develop a wide range of therapies for cancer and other disorders. In order to accurately localize and control these different effects, imaging methods are desired that can map both temperature changes and cavitation activity. To address these needs, the authors integrated an ultrasound imaging array into an MRI-guided focused ultrasound (MRgFUS) system to simultaneously visualize thermal and mechanical effects via passive acoustic mapping (PAM) and MR temperature imaging (MRTI), respectively. The system was tested with an MRgFUS system developed for transcranial sonication for brain tumor ablation in experiments with a tissue mimicking phantom and a phantom-filled ex vivo macaque skull. In experiments on cavitation-enhanced heating, 10 s continuous wave sonications were applied at increasing power levels (30-110 W) until broadband acoustic emissions (a signature for inertial cavitation) were evident. The presence or lack of signal in the PAM, as well as its magnitude and location, were compared to the focal heating in the MRTI. Additional experiments compared PAM with standard B-mode ultrasound imaging and tested the feasibility of the system to map cavitation activity produced during low-power (5 W) burst sonications in a channel filled with a microbubble ultrasound contrast agent. When inertial cavitation was evident, localized activity was present in PAM and a marked increase in heating was observed in MRTI. The location of the cavitation activity and heating agreed on average after registration of the two imaging modalities; the distance between the maximum cavitation activity and focal heating was -3.4 ± 2.1 mm and -0.1 ± 3.3 mm in the axial and transverse ultrasound array directions, respectively. Distortions and other MRI issues introduced small uncertainties in the PAM∕MRTI registration. Although there was substantial variation, a nonlinear relationship between the average intensity of the cavitation maps, which was relatively constant during sonication, and the peak temperature rise was evident. A fit to the data to an exponential had a correlation coefficient (R(2)) of 0.62. The system was also found to be capable of visualizing cavitation activity with B-mode imaging and of passively mapping cavitation activity transcranially during cavitation-enhanced heating and during low-power sonication with an ultrasound contrast agent. The authors have demonstrated the feasibility of integrating an ultrasound imaging array into an MRgFUS system to simultaneously map localized cavitation activity and temperature. The authors anticipate that this integrated approach can be utilized to develop controllers for cavitation-enhanced ablation and facilitate the optimization and development of this and other ultrasound therapies. The integrated system may also provide a useful tool to study the bioeffects of acoustic cavitation.

Fast-to-slow axis mode imaging for brightness enhancement of a broad-area laser diode array

Broad-area laser (BAL) diodes have found use in numerous applications requiring multi-watt powers, but remain limited by poor spatial beam quality. A novel laser cavity that enhances the brightness of a BAL array has been demonstrated. Wavelength beam combining (WBC) is used to spatially overlap output from the emitters. Improved beam quality is achieved by imaging the fast-axis mode onto the slow axis of the BAL array. The brightness is enhanced twofold over a typical Littman-Metcalf WBC cavity, reaching 47 MW·cm(-2)·sr(-1) at an output power of 1.16 W.

Synthesis and Magnetic Properties of Mn4Si7 and Si–Mn4Si7 Axial Heterostructure Nanowire Arrays

Manganese silicides nanostructures showed great potential applications in microelectronic and optoelectronic devices. In this study, Mn4Si7 and Si–Mn4Si7 axial heterostructure nanowire arrays were synthesized by the in-situ reaction between Si nanowire arrays and MnCl2. Depending on the reaction durations and processes, structures (Mn4Si7 nanowires or Si–Mn4Si7 axial heterostructure nanowires) and lengths of the Mn4Si7 nanowires could be readily tuned. Phase identification were performed by the XRD, TEM, HRTEM, and SAED means, which results indicated that the as-synthesized nanowire is Nowotny chimney ladder (NCL) structure Mn4Si7 with a tetragonal structure. The Mn4Si7 nanowire arrays exhibited enhanced ferromagnetism comparing with other bulk higher manganese silicides. The Curie temperature of the Mn4Si7 nanowire arrays is over 300 K, which is much higher than that of the previous reports. Because of the good compatibility with Si-based nanowire devices and many favorable properties, these Mn4Si7 nanowire arrays have wide potential applications in the Si-based self-assembly nanowire devices.

Wide range beam steering capability of a 1-D MEMS transducer imager array with directional beam pattern

A linear array of capacitive micromachined ultrasonic transducer (CMUT) has been designed as an alternative to conventional piezoelectric transducers. The proposed array is favorable for imaging applications where there is a need for high resolution detection in directions with an angle other than that perpendicular to the axis of the transducer array. The transducer array cells include a thin silicon nitride membrane that is suspended over a bottom electrode, fabricated on a silicon wafer. In immersion mode, the transducer cell shape and dimensions are optimized for an operating frequency of 10MHz. The proposed imager array is shown to be able to generate a pencil shape beam with a ∼1.5° half beam width for enhancing the detector resolution. A phased array technique is employed to excite multiple cells using time-delayed signals to steer the acoustic beam toward the object. Therefore, the need for mechanically moving the transducer array or the cell membrane is eliminated, which results in simplifying the transducer driving system. Moreover, unlike conventional transducers, the pencil beam can be effectively steered over a wide range of angles without producing grating lobes or degrading the power difference between the main lobe and side lobes. Consequently, in transmitting mode the power loss in any undesired directions is minimized and in receiving mode the noise level from other angles interfering with the data collection is suppressed, which improves the signal to noise ratio of the imager CMUT array.

ARRAY OF HIGH FREQUENCY LOUDSPEAKERS

The present invention is an array of high-frequency loudspeakers with three or more closely coupled bodies. Linear widths of said bodies of loudspeakers along a linear array axis are 5 centimeters or less and adjacent loudspeakers are separated by 5 centimeters or less.

Optimum design of shaped beam cylindrical array antenna with electronically scan radiation pattern

In this paper, the shaped beam cylindrical array is presented to obtain full angular scanning in the plane of the array. This array antenna is designed such that it produces sum and difference radiation patterns simultaneously. The array elements are wideband printed dipole antennas which operate in L- frequency band. To design of the array antenna at first step, certain numbers of the elements (16 elements) in a sector of the cylindrical array (active area) are used to synthesize by the Particle Swarm Optimization (PSO) method. In the second step to rotate the optimum radiation pattern extracted from the first step, appropriate feeding network is suggested to rotate the active area around the cylindrical array axis. Therefore the radiation patterns of the array antenna remain completely constant in all scan angles.

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Introduction: Millions of children and young adults are living with disabilities from traumatic brain injury (TBI) in childhood. Very little is known about age-dependent pathways of neuroplasticity on post-injury recovery. Hypothesis: We hypothesized that we could detect deficits in neuronal activity after TBI in the immature rat using electrophysiology recordings and functional magnetic resonance imaging (fMRI). Methods: Rats (P 16-18, n=10) underwent controlled cortical impact (CCI) to the left parietal cortex. Control rats (n=10) were age-matched, uninjured pups. Two weeks after CCI, the functional response of the uninjured (right) primary somatosensory cortex (S1) was measured with electrophysiology recording in response to left forepaw stimulation. Multi-unit activities (MUA) and local field potentials (LFP) were recorded with a 12-channel axial array electrode. The number of neuronal spiking events was calculated by post stimulus time histogram (PSTH) analysis of MUA. Rats also underwent blood oxygenation level dependent (BOLD) fMRI. Neuronal connections in the thalamo-cortical and cortical-cortical somatosensory pathways were evaluated by using manganese enhanced magnetic resonance imaging (MEMRI) and histology. Results: Electrophysiology recordings showed decreases in spiking rates across laminae II-V in the uninjured S1 of TBI rats (p<0.05). Stimulation on the left forepaw in TBI rats resulted in decreased LFP amplitude (laminae II-V) and increased LFP latency (laminae IV-V) in the uninjured S1 (p<0.05). Left forepaw stimulation also evoked decreases in the extent of fMRI responses in the uninjured S1 in TBI rats. MEMRI imaging did not show changes in the thalamo-cortical connections in the uninjured S1. However, luxo-blue staining showed decreases in the axon myelination volume along the corpus callosum connecting cortical-cortical somatosensory pathways (p<0.05, TBI vs controls). Conclusions: We conclude that TBI in immature rats adversely affects neuronal function of the contralateral (uninjured) S1 cortex, in part due to alterations in the cortical-cortical somatosensory pathways. These findings have implications for understanding recovery after pediatric TBI. Support: Johns Hopkins Brain Science Institute

Improving LMS/NLMS-Based Beamforming Using Shirvani-Akbari Array

ULA is the most common geometry exp lo ited in array signal processing. In the beamforming operation, em- ploying the ULA leads to obtaining narrower beamwidth with respect to other geometries in similar ele ment numbers. Re- cently, Shirvani and Akbari proposed a new array by adding two elements to the ULA in top and bottom of the array axis, named as SAA. Th is new array offers a considerable imp rovement in DOA estimation performance in detection and resolu- tion of signal sources placed at angles close to the array endfires. In this article, the performance of the proposed SAA is investigated especially in beamforming and co mpared with ULA. LMS and NLMS algorith ms that are popular adaptive beamforming methods are used for evaluation and co mparing the performance of SAA and ULA . Considering array factor, mean square erro r and bit error rate metrics, simu lation results show improved convergence speed and higher data trans- mission accuracy in different signal source locations, boresight angles as well as endfire ones, for SAA with respect to ULA .

Aerosol-based coherent random laser

We demonstrate coherent random lasing from an aerosol of dye-doped microdroplets in air. The aerosol is in the form of a linear array of polydisperse, arbitrarily shaped, and randomly spaced microdroplets with average dimensions of about 30 μm. Upon optical excitation, ultranarrow lasing modes were observed in the emission along the axis of the linear array, while the transverse emission exhibited intrascatterer resonance peaks. Direct spatiospectral imaging and lasing threshold studies confirmed the origin of the lasing peaks to be from spatial modes that extended over the array of the polydisperse microdroplets.

Rapidly Convergent Representations for Periodic Green's Functions of a Linear Array in Layered Media

Green's function representations are presented to rapidly compute the fields resulting from a linear (1D) periodic array of dipole current sources on or near a planarly layered medium in 2D and 3D space. The representation is formulated as spectral integral, which accounts for the reflected continuous spectrum of fields, and a series that accounts for the discrete spectrum of guided modes. It is exponentially convergent for observation points on and near the array axis and surface, and for complex phase shifts between periodic unit cells. It can be defined on alternate Riemann sheets with respect to any of the diffraction modes characterizing the array. A complete dyadic Green's function is derived to fully account for the reflected fields for all source current orientations. This Green's function representation can greatly accelerate the simulation of printed 1D periodic structures in optics and microwave engineering.

Experimental sduty of current distribution in wirearray Zpinch plasma

The current within imploding multiwire tungsten arrays is measured using micro magnetic probes in the Qiangguang-1 facility at a current of 1.3 MA and rise time of about 70 ns. Difference in current distribution in multiwire arrays between with and without foam cylinder on the array axis is studied. Stable and reliable results are obtained for tungsten wire array Z-pinch with a wire diameter of 4.2 μm and an annular diameter of 12 mm. The results shows that the output of magnetic probe at a radius of 3.2 mm lags about 20 ns behind the discharge current pulse. After that, the ratio of inside current to the total current increases 20% within 20 ns and keeps steady for 30-40 ns. It is found that the foam cylinder has no appreciable influence on the inside current value in the initial stage of implosioin.

Analysis of the near-field-far-field pattern of tilted planar antenna arrays

Based on the principle of planar near-field measurement and theory on the spatial pattern of planar antenna arrays, a comprehensive investigation on the spatial pattern of planar antenna arrays tilting away from the planar near-field scanning plane is performed. An efficient computational algorithm on the near-field-far-field pattern in the plane determined by the rotation axis and normal line of the tilted array is developed. The parametric equations on the intersecting curve locus between the plane and unit directional sphere of the planar near-field scanning are thus derived. Consequently, the spatial pattern of the tilted antenna array based on the near-field data is calculated by fast Fourier transform technique, and at the same time a two-dimensional interpolating scheme to evaluate the pattern in the plane is developed. The capability, efficiency, and feasibility of this new algorithm are demonstrated by the good consistency of the calculated results with the numerical simulations and experimental measurements.