Showing papers on "Angular aperture published in 2018"
TL;DR: In this paper, a gradient index (GRIN) metamaterial lens antenna with extremely high gain and high aperture efficiency is presented, which achieves a gain of 26.6 dBi, which corresponds to aperture efficiency greater than 90%.
Abstract: A gradient index (GRIN) metamaterial lens antenna with extremely high gain and high aperture efficiency is presented. The proposed antenna is much more advantageous in terms of gain and aperture efficiency without compromising in simplicity and stability. The gain and aperture efficiency are improved by using a new method to design the GRIN lens for a hybrid mode, which possesses both uniform amplitude and phase distributions on the aperture. At the center of frequency band (14.25 GHz), the proposed antenna achieves a gain of 26.6 dBi, which corresponds to aperture efficiency greater than 90%.
33 citations
TL;DR: Coherent compounding methods using the full or partial transmit aperture have been investigated as a possible means of increasing strain measurement accuracy in cardiac strain imaging; however, the optimal transmit parameters in either compounding approach have yet to be determined.
Abstract: Coherent compounding methods using the full or partial transmit aperture have been investigated as a possible means of increasing strain measurement accuracy in cardiac strain imaging; however, the optimal transmit parameters in either compounding approach have yet to be determined. The relationship between strain estimation accuracy and transmit parameters—specifically the subaperture, angular aperture, tilt angle, number of virtual sources, and frame rate—in partial aperture (subaperture compounding) and full aperture (steered compounding) fundamental mode cardiac imaging was thus investigated and compared. Field II simulation of a 3-D cylindrical annulus undergoing deformation and twist was developed to evaluate accuracy of 2-D strain estimation in cross-sectional views. The tradeoff between frame rate and number of virtual sources was then investigated via transthoracic imaging in the parasternal short-axis view of five healthy human subjects, using the strain filter to quantify estimation precision. Finally, the optimized subaperture compounding sequence (25-element subperture, 90° angular aperture, 10 virtual sources, 300-Hz frame rate) was compared to the optimized steered compounding sequence (60° angular aperture, 15° tilt, 10 virtual sources, 300-Hz frame rate) via transthoracic imaging of five healthy subjects. Both approaches were determined to estimate cumulative radial strain with statistically equivalent precision (subaperture compounding E(SNRe $\vert \varepsilon = 41$ %) = 3.56, and steered compounding E(SNRe $\vert \varepsilon = 41$ %) = 4.26).
15 citations
TL;DR: An angular aperture of an acousto-optical filter upon a linear frequency-modulated (chirp) control signal has been experimentally studied for the first time in this article.
Abstract: An angular aperture of an acousto-optical filter upon a linear frequency-modulated (chirp) control signal has been experimentally studied for the first time. The results of studying the spectral and angular dependences of the spectral transmission function of a filter upon a frequency modulation have shown the possibility of an efficient increase of the output optical signal. The value of the optical signal was increased by 2000 times using the selected design of the acousto-optical filter. This makes it possible to obtain a gain in the measurement time or in the value of the detected optical signal. Such an increase of the output signal upon a chirp control signal is provided by the increase of the angular aperture and broadening of the spectral transmission bandwidth together with the required proportional increase of the control signal power.
10 citations
TL;DR: The results suggest that a modest number of receivers arranged on a semi-cylindrical shell may be sufficient to enable passive acoustic imaging with single-cycle integration times (i.e. volumetric rates up to 0.75 MHz) for monitoring cavitation-based HIFU treatments of DVT.
Abstract: High intensity focused ultrasound (HIFU) can disintegrate blood clots through the generation and stimulation of bubble clouds within thrombi. This work examined the design of a device to image bubble clouds for monitoring cavitation-based HIFU treatments of deep vein thrombosis (DVT). Acoustic propagation simulations were carried out on multi-layered models of the human thigh using two patient data sets from the Visible Human Project. The design considerations included the number of receivers (32, 64, 128, 256, and 512), their spatial positioning, and the effective angular array aperture (100° and 180° about geometric focus). Imaging array performance was evaluated for source frequencies of 250, 750, and 1500 kHz. Receiver sizes were fixed relative to the wavelength (pistons, diameter = λ/2) and noise was added at levels that scaled with receiver area. With a 100° angular aperture the long axis size of the -3 dB main lobe was ~1.2λ-i.e. on the order of the vessel diameter at 250 kHz (~7 mm). Increasing the array aperture to span 180° about the geometric focus reduced the long axis by a factor of ~2. The smaller main lobe sizes achieved by imaging at higher frequencies came at the cost of increased levels of sensitivity to phase aberrations induced during acoustic propagation through the intervening soft tissue layers. With noise added to receiver signals, images could be reconstructed with peak sidelobe ratios < -3 dB using single-cycle integration times for source frequencies of 250 and 750 kHz (NRx ⩾ 128). At 1500 kHz, longer integration times and/or higher element counts were required to achieve similar peak sidelobe ratios. Our results suggest that a modest number of receivers(i.e. NRx = 128) arranged on a semi-cylindrical shell may be sufficient to enable passive acoustic imaging with single-cycle integration times (i.e. volumetric rates up to 0.75 MHz) for monitoring cavitation-based HIFU treatments of DVT.
7 citations
TL;DR: Theoretical and experimental analysis indicates that the AOTF can acquire a narrowband spectrum and big angular aperture with a proper incident angle and the correlation between the frequency tuning relation and the incident angle of light is demonstrated.
Abstract: Basing on the momentum mismatching together with the crystal rotatory property, we investigate the diffraction performance of an acousto-optic tunable filter (AOTF). The relationship between diffraction efficiency, momentum mismatching, incident optical wave vector, and ultrasound wave vector is analyzed. The correlation between the frequency tuning relation and the incident angle of light is demonstrated, which is usually ignored in the AOTF design. The diffracted wavelength can be decided by a particular acoustic frequency only when the incident angle of light is fixed. Theoretical and experimental analysis indicates that we can acquire a narrowband spectrum and big angular aperture with a proper incident angle.
4 citations
Patent•
01 Feb 2018TL;DR: In this article, the authors present a lighting module for a motor vehicle headlamp module including a light source able to emit light radiation, a processing device able to generate a light flux from said light radiation and an imaging optical system able to project an exit beam from the light flux.
Abstract: The present invention relates to a lighting module for a motor vehicle headlamp module including a light source able to emit light radiation, a processing device able to generate a light flux from said light radiation, and an imaging optical system able to project an exit beam from said light flux. The lighting module includes means for controlling an angular aperture of the exit beam, the angular aperture being chosen from a first aperture and a second aperture, the first aperture corresponding to a wider angle than the second aperture, so that, for a given intensity of the light radiation of the light source, the exit beam corresponding to the second aperture has a higher light intensity than the exit beam corresponding to the first aperture.
3 citations
TL;DR: It is shown that there exists a direct trade-off between the deviation power and the angular aperture/FOV for Risley prisms, that is, high refractive index and large opening angle yield a smaller angle aperture/ FOV.
Abstract: The constraints on directions of incoming and outgoing rays of Risley prisms, caused by total internal reflection and surface tilt, are investigated for the four typical configurations. After applying a nonparaxial ray-tracing method based on the vector form Snell’s law, the incident angles at prisms’ surfaces are calculated and compared with the critical angle. On this basis, the direction limitations of incoming and outgoing rays are investigated. The permissible incoming directions as well as the achievable outgoing directions depend on prisms’ orientation. Their ranges over which the rays can pass through the system at any prism orientation are defined as the angular aperture and angular field of view (FOV). The effects of the prisms’ refractive index, opening angle, and arrangement on angular aperture/FOV are discussed. It is shown that there exists a direct trade-off between the deviation power and the angular aperture/FOV for Risley prisms, that is, high refractive index and large opening angle yield a smaller angle aperture/FOV. Large angular aperture can be achieved by employing the 2121 configuration, while it is desirable to adopt a 1212 configuration to obtain large angular FOV. The research can afford guidance for prism material, geometry choices, and configuration setting in the design of a Risley prism system for wide-angle beam steering or imaging adjustment.
2 citations
TL;DR: In this paper, a theory on the diffraction of an elliptic Bethe-Bouwkamp aperture illuminated by a polarized plane-wave is established, and the magnetic densities of charges and currents are rigorously represented by rewriting Bouwkamp's partial differential equations into vectorial expressions, and hence the electromagnetic field is described in a compact form.
1 citations
01 Sep 2018
TL;DR: AO tunable filters as mentioned in this paper are fully software-controlled solid-state devices and do not require mechanical scanning, however, they suffer from a limited number of spectral channels or from a spatial noise caused by parasitic interferences.
Abstract: Spectrally tunable illumination is widely used for spectral imaging, spectroscopy, spectral-domain optical coherence tomography and other applications. Most of swept-wavelength light sources are based on mechanical change of narrow-band filters or on a supercontinuum laser coupled with a tunable filter. Such commercially available sources suffer either from a limited number of spectral channels or from a spatial noise caused by parasitic interferences. Here, we describe an alternative solution, which is free from the mentioned disadvantages and provides speckle-free uniform illumination. It is based on acousto-optic (AO) diffraction of a wide-band light. AO tunable filters (AOTFs) are fully software-controlled solid-state devices and do not require mechanical scanning. The selected wavelength of light is determined by the period of the volume phase grating induced in the crystal by an ultrasound wave, i.e. by the frequency of the electric signal applied to the piezo-transducer that excites ultrasound wave. Due to high spectral resolution, small entrance pupil diameter and small angular aperture of AOTFs, its utilisation together with wide-band light sources is problematic even with a specific optical coupling to optimize the light-energy and aberration parameters of the filtered light. In this paper, we show that efficiency of this approach may be radically improved by acoustic frequency modulation.
1 citations
Patent•
30 Oct 2018
TL;DR: In this paper, an optical system (2A) for receiving and collimating light includes collimating unit (200) comprising at least one parabolic concentrator (CPC) (220, 230) forming inlet (212) and outlet (214) and configured to reflect light entering inlet through the outlet and limiting the angular divergence of the light to the size of the input angular aperture (θ).
Abstract: FIELD: lighting.SUBSTANCE: invention relates to lighting systems. Optical system (2A) for receiving and collimating light includes collimating unit (200) comprising at least one parabolic concentrator (CPC) (220, 230) forming inlet (212) and outlet (214) and configured to reflect light entering inlet (212) through the outlet (214) and limiting the angular divergence of the light to the size of the input angular aperture (θ), and homogenizing unit (300) to impart spatial homogeneity to the light emerging from collimating assembly (200), comprising a lens array of dual lenses of a condenser-type lenses based on a microlens array, in which light from outlet (214) collected by the first lens illuminates a corresponding second lens to form a continuously emitting output aperture.EFFECT: increased brightness and uniformity of distribution of brightness over the area.76 cl, 9 dwg
Patent•
31 Jan 2018
TL;DR: In this paper, the authors present a lighting module for a motor vehicle headlamp module including a light source able to emit light radiation, a processing device able to generate a light flux from said light radiation and an imaging optical system able to project an exit beam from the light flux.
Abstract: The present invention relates to a lighting module for a motor vehicle headlamp module including a light source able to emit light radiation, a processing device able to generate a light flux from said light radiation, and an imaging optical system able to project an exit beam from said light flux. The lighting module includes means for controlling an angular aperture of the exit beam, the angular aperture being chosen from a first aperture and a second aperture, the first aperture corresponding to a wider angle than the second aperture, so that, for a given intensity of the light radiation of the light source, the exit beam corresponding to the second aperture has a higher light intensity than the exit beam corresponding to the first aperture.