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Orbital angular momentum of light has attracted great attention in recent years. Optical ferris wheel, composed of the superposition of different orbital-angular-momentum modes, further broadens the application of orbital angular momentum of light in many fields. Here, we experimentally demonstrate a simple way to produce optical ferris wheel with controllable orbital-angular-momentum modes using a mask of spiral arrays. We show that optical ferris wheel can be rotated by adjusting the spiral arrays, and the rotation angle is studied analytically and experimentally. Our technique shows the advantages of wide operation bandwidth and flexible manipulation and the simplicity of our method may find potential application in optical manipulation.

An ultrasound sparse array consists of a sparse distribution of elements over a 2-D aperture. Such an array is typically characterized by a limited number of elements, which in most cases is compatible with the channel number of the available scanners. Sparse arrays represent an attractive alternative to full 2-D arrays that may require the control of thousands of elements through expensive application-specific integrated circuits (ASICs). However, their massive use is hindered by two main drawbacks: the possible beam profile deterioration, which may worsen the image contrast, and the limited signal-to-noise ratio (SNR), which may result too low for some applications. This article reviews the work done for three decades on 2-D ultrasound sparse arrays for medical applications. First, random, optimized, and deterministic design methods are reviewed together with their main influencing factors. Then, experimental 2-D sparse array implementations based on piezoelectric and capacitive micromachined ultrasonic transducer (CMUT) technologies are presented. Sample applications to 3-D (Doppler) imaging, super-resolution imaging, photo-acoustic imaging, and therapy are reported. The final sections discuss the main shortcomings associated with the use of sparse arrays, the related countermeasures, and the next steps envisaged in the development of innovative arrays. [ABSTRACT FROM AUTHOR]

Ultra-wideband (UWB) phased array antennas are essential for radar, communication, and Electronic Warfare (EW) applications. Systems can operate over wide-band coverage. The high gain systems require wide-band, wide-angle scanning, good radiation pattern, and return loss over a multi-octave bandwidth. This review discusses the problems present in the UWB phased array system, which include mutual coupling, grating lobe rejection, active return loss, gain fluctuation with scanning, and multiple beam generation. In this, the aperture size of the array is limited by the overall gain requirement of the system. On the other hand, low gain systems require a wide-band with a good radiation pattern and axial ratio. Here the matching over wide-band is simpler as it depends on broadband balun configuration. This system has limited bandwidth over scan angles. These antennas are more preferred as wearable antennas in communication applications. This paper mainly discusses the existing UWB phased array antennas such as Vivaldi Arrays, All-metal Arrays, Spiral Arrays, Sinuous Arrays, and Coupled Arrays. This review paper presents a correct direction for selecting the type of antenna in terms of impedance bandwidth, gain, and materials influencing antenna performance, suited for different applications.

Orbital angular momentum of light has attracted great attention in recent years. Optical ferris wheel, composed of the superposition of different orbital-angular-momentum modes, further broadens the application of orbital angular momentum of light in many fields. Here, we experimentally demonstrate a simple way to produce optical ferris wheel with controllable orbital-angular-momentum modes using a mask of spiral arrays. We show that optical ferris wheel can be rotated by adjusting the spiral arrays, and the rotation angle is studied analytically and experimentally. Our technique shows the advantages of wide operation bandwidth and flexible manipulation and the simplicity of our method may find potential application in optical manipulation. [ABSTRACT FROM AUTHOR]

Ultrasound vector Doppler techniques for three-dimensional (3-D) blood velocity measurements are currently limited by low temporal resolution and high computational cost. In this paper, an efficient 3-D high-frame-rate vector Doppler method, which estimates the displacements in the frequency domain, is proposed. The novel method extends to 3-D an approach so far proposed for two-dimensional (2-D) velocity measurements by approximating the (x, y, z) displacement of a small volume through the displacements estimated for the 2-D regions parallel to the y and x directions, respectively. The new method was tested by simulation and experiments for a 3.7 MHz, 256-element, 2-D piezoelectric sparse spiral array. Simulations were also performed for an equivalent 7 MHz Capacitive Micromachined Ultrasonic Transducer spiral array. The results indicate performance (bias ± standard deviation: 6.5 ± 8.0) comparable to the performance obtained by using a linear array for 2-D velocity measurements. These results are particularly encouraging when considering that sparse arrays were used, which involve a lower signal-to-noise ratio and worse beam characteristics with respect to full 2-D arrays. [ABSTRACT FROM AUTHOR]

Ameliorating electronic/ionic transport and structural stability of electrode materials is important to the development of power‐intensive lithium ion batteries. Despite its great potential as a high‐power anode, titanium niobium oxide (Ti2Nb10O29, TNO) still underperforms due to its unsatisfactory electronic/ionic conductivity. In this work, a powerful synergistic strategy by combining ion doping and spiral array architecture to boost high‐rate performance of TNO is reported. Cr3+ doped TNO nanoparticles (Cr‐TNO) of 5–10 nm intimately grow on a conductive vertical graphene@TiC‐C (VGTC) skeleton, forming novel Cr‐TNO@VGTC spiral arrays. The unique spiral growth of TNO is achieved due to the confinement effect of VGTC skeleton. Meanwhile, a more open TNO crystal structure with faster ion transfer paths and enhanced structural stability is realized by Cr3+ doping, demonstrated via density functional theory calculation and in situ synchrotron X‐ray diffraction technique. Benefiting from the superior conductive network, enhanced intrinsic electronic/ionic conductivity of Cr‐TNO and reinforced structural stability, the Cr‐TNO@VTC arrays show prominent high‐power performance with a large capacity of 220 mAh g−1 at 40 C (power density of ≈11 kW kg−1) and superior durability (91% retention after 500 cycles). This work provides a new path for the construction of widespread high‐power electrodes for fast energy storage. [ABSTRACT FROM AUTHOR]

Major cardiovascular diseases (CVDs) are associated with (regional) dysfunction of the left ventricle. Despite the 3-D nature of the heart and its dynamics, the assessment of myocardial function is still largely based on 2-D ultrasound imaging, thereby making diagnosis heavily susceptible to the operator’s expertise. Unfortunately, to date, 3-D echocardiography cannot provide adequate spatiotemporal resolution in real-time. Hence, tri-plane imaging has been introduced as a compromise between 2-D and true volumetric ultrasound imaging. However, tri-plane imaging typically requires high-end ultrasound systems equipped with fully populated matrix array probes embedded with expensive and little flexible electronics for two-stage beamforming. This article presents an advanced ultrasound system for real-time, high frame rate (HFR), and tri-plane echocardiography based on low element count sparse arrays, i.e., the so-called spiral arrays. The system was simulated, experimentally validated, and implemented for real-time operation on the ULA-OP 256 system. Five different array configurations were tested together with four different scan sequences, including multi-line and planar diverging wave transmission. In particular, the former can be exploited to achieve, in tri-plane imaging, the same temporal resolution currently used in clinical 2-D echocardiography, at the expenses of contrast (−3.5 dB) and signal-to-noise ratio (SNR) (−8.7 dB). On the other hand, the transmission of planar diverging waves boosts the frame rate up to 250 Hz, but further compromises contrast (−10.5 dB), SNR (−9.7 dB), and lateral resolution (+46%). In conclusion, despite an unavoidable loss in image quality and sensitivity due to the limited number of elements, HFR tri-plane imaging with spiral arrays is shown to be feasible in real-time and may enable real-time functional analysis of all left ventricular segments of the heart. [ABSTRACT FROM AUTHOR]

Ultrasound vector Doppler techniques for three-dimensional (3-D) blood velocity measurements are currently limited by low temporal resolution and high computational cost. In this paper, an efficient 3-D high-frame-rate vector Doppler method, which estimates the displacements in the frequency domain, is proposed. The novel method extends to 3-D an approach so far proposed for two-dimensional (2-D) velocity measurements by approximating the (x, y, z) displacement of a small volume through the displacements estimated for the 2-D regions parallel to the y and x directions, respectively. The new method was tested by simulation and experiments for a 3.7 MHz, 256-element, 2-D piezoelectric sparse spiral array. Simulations were also performed for an equivalent 7 MHz Capacitive Micromachined Ultrasonic Transducer spiral array. The results indicate performance (bias ± standard deviation: 6.5 ± 8.0) comparable to the performance obtained by using a linear array for 2-D velocity measurements. These results are particularly encouraging when considering that sparse arrays were used, which involve a lower signal-to-noise ratio and worse beam characteristics with respect to full 2-D arrays.