Vertical Beamwidth Research Articles

Design of a metalens for beam collimation and angular amplification in optical phased array devices

We present an analytical design for increasing the beam sharpness (collimation) and field of view (FOV) of an optical phased array (OPA) device. In this work, a cylindrical metalens is used for collimation, while a set of metalens, with both concave and convex phase profiles, are incorporated to increase the FOV. Following the generalized vector law of reflection or refraction, the trajectories of the reflected or transmitted rays corresponding to the phase profile of phase gradient metasurfaces/metalens are obtained. Through the ray tracing method, the elliptical beam from the OPA device with a vertical beam (fast axis) width of 21 mm was collimated to a sharp spherical beam of width 1.5 mm by a metalens with a cylindrical phase profile. In addition, the incorporation of angular amplifier metalens with a 64-channel OPA device has shown an increased in FOV by almost threefold i.e., from 15 o to 41.96 o . Our results suggest that the use of metasurfaces/metalens can enhance the quality of output beam and provide significant advantages for compact on-chip integration with OPA devices in solid-state LiDAR applications.

Vertical and Horizontal Dipole Source Powered Broadband Wide Beamwidth Antenna

Vertical and Horizontal Dipole Source Powered Broadband Wide Beamwidth Antenna

High-frequency inlaid cylindrical piezoelectric transducer for high-sensitivity acoustics

This work develops a high-frequency high-sensitivity inlaid cylindrical hydroacoustic transducer by enhancing the electromechanical coupling coefficient, amplifying stress, and adopting circumferential inlaid techniques. Equivalent circuit and finite element simulation methods were used to determine the optimum parameters of the unit, then the transducer was fabricated. Tests show that the resonant frequency of every array unit was 220 kHz. The maximum emission voltage response and reception sensitivity were respectively about 172 dB and −177 dB, with emission and reception bandwidths both about 40 kHz at 3 dB loss. The horizontal and vertical beamwidths were 15° and 4° for each unit respectively.

Echolocating bats rapidly adjust their mouth gape to control spatial acquisition when scanning a target

BackgroundAs well known to any photographer, controlling the “field of view” offers an extremely powerful mechanism by which to adjust target acquisition. Only a few natural sensory systems can actively control their field of view (e.g., dolphins, whales, and bats). Bats are known for their active sensing abilities and modify their echolocation signals by actively controlling their spectral and temporal characteristics. Less is known about bats’ ability to actively modify their bio-sonar field of view.ResultsWe show that Pipistrellus kuhlii bats rapidly narrow their sensory field of view (i.e., their bio-sonar beam) when scanning a target. On-target vertical sonar beams were twofold narrower than off-target beams. Continuous measurements of the mouth gape of free-flying bats revealed that they control their bio-sonar beam by a ~3.6 mm widening of their mouth gape: namely, bats open their mouth to narrow the beam and vice versa.ConclusionsBats actively and rapidly control their echolocation vertical beam width by modifying their mouth gape. We hypothesize that narrowing their vertical beam narrows the zone of ensonification when estimating the elevation of a target. In other words, bats open their mouth to improve sensory localization.

Dispersive silicon–nitride optical phased array incorporating arrayed waveguide delay lines for passive line beam scanning

As optical phased arrays (OPAs), used as solid-state beam scanning elements, swiftly stride towards higher efficiency and faster scanning speed, the line beam scanner is emerging as a viable substitute for its counterpart relying on point-beam-incorporated raster scanning. However, line-beam scanners require active phase shifters for beam scanning; thus, they consume more power and have complex device designs. This study proposes and demonstrates a dispersive silicon–nitride OPA that allows for passive wavelength-tuned steering of a line beam with an elongated vertical beamwidth. To steer the line beam passively covering the two-dimensional field of view, we deployed an array of delay lines with progressive delay lengths across adjacent channels. Furthermore, adiabatic tapers that allow precise effective array aperture adjustment are used as emitter elements to flexibly realize different vertical beamwidths. Combinations of different delay-length differences and taper tip-widths resulted in beam coverage (lateral × vertical) ranging from 6.3° × 19° to 23.8° × 40° by tuning the wavelength from 1530 to 1600 nm. The main lobe emission throughput was as small as − 2.8 dB. To the best of our knowledge, the embodied OPA is the first demonstration of a passive line beam scanner facilitating an adjustable beam coverage with quick operation and enhanced efficiency.

A high gain wideband array antenna based on metasurface for ETC application

Free flow electronic toll collection (FFETC) has played an important role in building convenient and safe transportation systems in many countries. The most challenging problem when researching and developing this system is shortening the payment cycle so that vehicles passing through the stations do not need to stop or keep going at a speed greater than 60 Km/h. Designing roadside unit (RSU) reader antennas with high gain and suitable radiation pattern is the most feasible and economical solution. This paper proposes a left-handed circularly polarized (LHCP) 2×4 array antenna using sequential phase rotation power dividers at 5.8 GHz band. The element antenna is a square patch antenna with a slit in the middle for better impedance matching, six trapezoidal parasitic patches added to either side of the main patch to create resonance at high frequencies, and a metasurface placed on top of the main patch. The proposed metasurface is a 4×4 array of dual circular unit cells to improve gain and extend axial ratio (AR) bandwidth. The proposed antenna array has a high gain of 17 dBi, -3 dB vertical and horizontal beamwidths of 33.20 and 17.10, which cover over one lane, are expected for any ETC system to avoid interference with other lanes. Impedance bandwidth and AR bandwidth are 2.19 GHz (37.75%) and 2.06 GHz (35.52%), respectively. The overall dimensions of the proposed array antenna are approximately 152×76×6.4 mm3. With the above merits, this antenna is a suitable candidate for the RSU reader antenna in the FFETC

Vertical sonar beam width and scanning behavior of wild belugas (Delphinapterus leucas) in West Greenland.

Echolocation signals of wild beluga whales (Delphinapterus leucas) were recorded in 2013 using a vertical, linear 16-hydrophone array at two locations in the pack ice of Baffin Bay, West Greenland. Individual whales were localized for 4:42 minutes of 1:04 hours of recordings. Clicks centered on the recording equipment (i.e. on-axis clicks) were isolated to calculate sonar parameters. We report the first sonar beam estimate of in situ recordings of wild belugas with an average -3 dB asymmetrical vertical beam width of 5.4°, showing a wider ventral beam. This narrow beam width is consistent with estimates from captive belugas; however, our results indicate that beluga sonar beams may not be symmetrical and may differ in wild and captive contexts. The mean apparent source level for on-axis clicks was 212 dB pp re 1 μPa and whales were shown to vertically scan the array from 120 meters distance. Our findings support the hypothesis that highly directional sonar beams and high source levels are an evolutionary adaptation for Arctic odontocetes to reduce unwanted surface echoes from sea ice (i.e., acoustic clutter) and effectively navigate through leads in the pack ice (e.g., find breathing holes). These results provide the first baseline beluga sonar metrics from free-ranging animals using a hydrophone array and are important for acoustic programs throughout the Arctic, particularly for acoustic classification between belugas and narwhals (Monodon monoceros).

Utilizing the Shift-or-Shrink Algorithm to Optimize the Direct Coupling from Laser Diodes to Diffused Channel Waveguides

Several formulae for computing the direct coupling efficiencies from laser diodes to diffused channel waveguides, based on mathematic models for approximating the corresponding laser beams and the waveguiding modes, have been derived in this paper. Then, the authors utilize a simple shift-or-shrink (SOS) algorithm to seek their optimal coupling conditions, including the incident positions of the laser beams and the corresponding horizontal and vertical beam widths. The simulation results are presented and compared.

Spherical-Omnidirectional Piezoelectric Composite Transducer for High- Frequency Underwater Acoustics.

Spherical-omnidirectional acoustic source has become a powerful tool to provide a near-ideal omnidirectional beam pattern for acoustic tests and communications. Current spherical-omnidirectional acoustic sources do not combine an omnidirectional beam pattern with a high transmitting voltage response (TVR) in the frequency range of above 200 kHz. This work presents the design, fabrication, and measurements of a high-frequency spherical-omnidirectional transducer that can provide a near-ideal omnidirectional beam pattern and a high TVR. The active element of the transducer consists of six identical square coupons with spherical curvature 1-3 piezoelectric composites operating in thickness mode. Electroacoustic responses of the fabricated transducer in water were measured. The measured resonance frequency of the transducer was 280 kHz. The maximum TVR was 161.3 dB re 1 μ Pa/V@1 m. The horizontal and vertical beamwidths of the transducer were 360° and 346°, respectively. Measurements show that the spherical piezoelectric composite transducer has a favorable spherical-omnidirectional behavior and a high TVR at high frequency. These results demonstrate that the spherical piezoelectric composite transducer is potentially a strong candidate for a high-frequency underwater acoustic source that requires an omnidirectional response.

Vertical sonar beam width of wild belugas (Delphinapterus leucas) in West Greenland

Echolocation signals of wild beluga whales (Delphinapterus leucas) were recorded in 2013 using a vertical, linear 16-hydrophone array at two locations in the pack ice of Baffin Bay, West Greenland. Individual whales were localized for 12 min of 1:04 h of recordings where on-axis clicks were isolated to calculate sonar parameters. We report the first sonar beam estimate of in situ recordings of belugas with an average 3-dB asymmetrical vertical beam width of 5.7 deg, showing a wider ventral axis. This is narrower than the commonly used estimates in the literature obtained from captive whales, suggesting beluga sonar beam width may be different in captive and wild contexts and is not necessarily symmetrical. Apparent source levels ranged from 210 to 220 dB pp re 1 μPa and whales were shown to vertically scan the array from 120 m distance. Our findings support the hypothesis that highly directional sonar beams and high source levels are an evolutionary adaptation for Arctic odontocetes to reduce noise and surface echoes from ice. These results provide the first baseline beluga sonar metrics from free-ranging animals using a hydrophone array and are important for acoustic programs throughout the Arctic, particularly for acoustic classification between belugas and narwhals (Monodon monoceros).

Online Antenna Tuning in Heterogeneous Cellular Networks With Deep Reinforcement Learning

We aim to jointly optimize antenna tilt angle, and vertical and horizontal half-power beamwidths of the macrocells in a heterogeneous cellular network (HetNet). The interactions between the cells, most notably due to their coupled interference render this optimization prohibitively complex. Utilizing a single agent reinforcement learning (RL) algorithm for this optimization becomes quite suboptimum despite its scalability, whereas multi-agent RL algorithms yield better solutions at the expense of scalability. Hence, we propose a two-step compromise algorithm. Specifically, a multi-agent mean field RL algorithm is first utilized in the offline phase so as to transfer information as features for the second (online) phase single agent RL algorithm, which employs a deep neural network to learn users locations. This two-step approach is a practical solution for real deployments, which should automatically adapt to environmental changes in the network. Our results illustrate that the proposed algorithm approaches the performance of the multi-agent RL, which requires millions of trials, with hundreds of online trials, assuming relatively low environmental dynamics, and performs much better than a single agent RL. Furthermore, the proposed algorithm is compact and implementable, and empirically appears to provide a performance guarantee regardless of the amount of environmental dynamics.

Transmission beam pattern and dynamics of a spinner dolphin (Stenella longirostris).

Toothed whales possess a sophisticated biosonar system by which ultrasonic clicks are projected in a highly directional transmission beam. Beam directivity is an important biosonar characteristic that reduces acoustic clutter and increases the acoustic detection range. This study measured click characteristics and the transmission beam pattern from a small odontocete, the spinner dolphin (Stenella longirostis). A formerly stranded individual was rehabilitated and trained to station underwater in front of a 16-element hydrophone array. On-axis clicks showed a mean duration of 20.1 μs, with mean peak and centroid frequencies of 58 and 64 kHz [standard deviation (s.d.) ±30 and ±12 kHz], respectively. Clicks were projected in an oval, vertically compressed beam, with mean vertical and horizontal beamwidths of 14.5° (s.d. ± 3.9) and 16.3° (s.d. ± 4.6), respectively. Directivity indices ranged from 14.9 to 27.4 dB, with a mean of 21.7 dB, although this likely represents a broader beam than what is normally produced by wild individuals. A click subset with characteristics more similar to those described for wild individuals exhibited a mean directivity index of 23.3 dB. Although one of the broadest transmission beams described for a dolphin, it is similar to other small bodied odontocetes.

Rotation Estimation of Acoustic Camera Based on Illuminated Area in Acoustic Image

In this paper, the concept of illuminated area, an important characteristic in acoustic images, is formalized, which can be applied to tasks such as the 3D mapping of underwater environment. Unmanned exploration using underwater robots is gaining attention among the scientific community. A way to sense the underwater environment is to employ the acoustic camera, a next generation forward looking sonar with high resolution even in turbid water. It is more flexible than common underwater sonars; however, studies on acoustic cameras are still at the early stage. Acoustic cameras have a fixed vertical beam width able to generate a limited bright area on acoustic images which is named illuminated area. In this paper, we propose the concept of illuminated area and the method to detect the illuminated area under a flatness assumption of the ground. Then, it is shown how the knowledge of the illuminated area can be fused with depth information to estimate the roll and pitch angles of the acoustic camera. The estimated quantities can be employed to carry out a 3D mapping process. Experiment shows the validity and effectiveness of the proposed method.

Non-Orthogonal Multiple Access for mmWave Drone Networks With Limited Feedback

Unmanned aerial vehicle (UAV) base stations (BSs) can be a promising solution to provide connectivity and quality-of-service guarantees during temporary events and after disasters. In this paper, we consider a scenario where UAV-BSs are serving a large number of mobile users in a hot spot area (e.g., in a stadium). We introduce non-orthogonal multiple-access (NOMA) transmission at UAV-BSs to serve more users simultaneously considering user distances as the available feedback for a user ordering during NOMA formulation. With millimeter-wave transmission and multi-antenna techniques, we assume that UAV-BS generates directional beams and multiple users are served simultaneously within the same beam. However, due to the limitations of physical vertical beamwidth of the UAV-BS beam, it may not be possible to cover the entire user region at UAV altitudes of practical relevance. During such situations, a beam scanning approach is proposed to maximize the achievable sum rates. We develop a comprehensive framework over which outage probabilities and respective sum rates are derived rigorously and we investigate the optimal operational altitude of UAV-BS to maximize the sum rates using our analytical framework. Our analysis shows that NOMA with distance feedback can provide better outage sum rates than orthogonal multiple access.

A Doubly-Curved Piezoelectric Composite with 1–3 Connectivity for Underwater Transducer Applications

Aim to increase the horizontal and vertical beam width of the high frequency transducer simultaneously, we present a doubly-curved 1-3 piezoelectric composite element. It consists of 54% piezoelectric ceramic volume fraction and two phases polymer matrix. The finite element analysis (FEA) is used to evaluate the dynamic response of composite. Electroacoustic response in water was measured for the doubly-curved composite being considered as underwater transducer. An underwater transducer was fabricated using the doubly-curved 1-3 piezoelectric composite element. The -3 dB full angle beam width of transducer is approximately 106° and 36° in the horizontal and vertical plane respectively. Both the FEA simulations and experimental results show the potential of a broad covered area of the composite transducer in underwater environment.

Receiving antenna mode of troposcatter passive ranging based on the signal group delay

The beyond-line-of-sight (BLOS) ranging of radiation sources can be realised through the troposcatter propagation of electromagnetic signals. Present troposcatter ranging systems are based on multi-station cross localisation theory wherein synchronisation and data fusion of all stations are not tractable. The troposcatter signal group delay properties provide a new ranging mechanism that can be realised through a single station conveniently and inexpensively. However, for radiation sources with multibeams, e.g. frequency-scanned radar, which forms several sub-beams with different elevation angles in the vertical direction, the scattering signal of sub-beams with high elevation angles has overall hysteresis compared to lower ones. This effect is called group delay between sub-beams. In this study, a one-to-one correspondence between group delay and target distance is derived to a closed-form expression with target and receiver antenna parameters. Furthermore, a group-delay-based passive ranging mechanism is proposed for exploiting this correspondence to increase the range of the BLOS target. Then two indicators for evaluation, ranging resolution and delay-measure requirement, are proposed for investigating ranging performance under the receiving antenna mode with different elevation angles, vertical beamwidths and erection heights. Results show the ranging resolution is ∼0.1–0.3 μs/300 km and delay-measure requirement is ∼0.002–0.033 μs for the given parameters.

Asymptotic Analysis on Directivity and Beamwidth of Uniform Circular Array

In this letter, the directivity and beamwidth of uniform circular array (UCA) are asymptotically analyzed with respect to the number of antenna elements and the size of UCA. In our analysis, we assume that beamforming is done on the azimuth plane by using UCA. Then, we show that the maximum directivity on the target direction increases with $\Theta (N^{3/2})$ , where $N$ is the number of antenna elements in UCA. In addition, vertical and horizontal beamwidths decrease with $\Theta (1/\sqrt{N})$ and $\Theta (1/N)$ , respectively.

Transmission beam characteristics of a spinner dolphin (Stenella longirostris)

Transmission beam characteristics have been described in a small number of odontocete species, providing insight into the biological and ecological factors that have influenced the design of the outgoing echolocation beam. The current study measured the on-axis spectral characteristics and transmission beam pattern of echolocation clicks from a small oceanic delphinid, the spinner dolphin (Stenella longirostis). A formerly stranded individual was rehabilitated in captivity and trained to station underwater in front of a 16 element hydrophone array. Preliminary analysis of a subset of recorded clicks showed on-axis spectral characteristics with a mean center frequency of 68 kHz and a mean peak frequency of 52 kHz. The dolphin exhibited both a circular beam shape and also varying degrees of a dorso-ventrally compressed transmission beam. The mean angular beamwidth for all clicks was 16.6 and 14.3 degrees in the horizontal and vertical planes, respectively, though some clicks exhibited horizontal beamwidths that were almost twice as wide as the vertical beamwidth. The overall beam was generally broader than the beams of previously described species, with a mean directivity index for all clicks of 21.5 dB. These results are the first reports of transmission beam characteristics from a spinner dolphin.

Optimizing Radio Network Parameters for Vertical Sectorization via Taguchi's Method

In vertical sectorization, multiple antenna elements form two beams to better serve users based on their locations in the cell. However, it is not known how to choose the radio network parameters to ensure good network performance and the amount of capacity gain achievable with vertical sectorization. In this paper, we propose an optimization approach based on Taguchi's method for vertical sectorization deployment to improve the 50th and the 5th percentile user throughput. Unlike conventional works, our proposal is a scientifically disciplined approach optimizing jointly the downtilt angles, vertical beamwidths, and transmit powers of the two beams and taking into account the interaction amongst these network parameters. With the proposed method, the resulting 50th and 5th percentile user throughput and the total network throughput outperform those of the conventional networks without vertical sectorization.

Three-dimensional sonar beam control of FM echolocating bats during natural foraging revealed by large scale microphone array system

In this study, 3-D flight paths and directivity pattern of the sounds emitted by Pipistrellus abramus during natural foraging were measured by a large scale microphone array system. The results show that the bats approached prey with covering the direction of them within their sonar beam. The means of horizontal and vertical beam widths were 49 deg and 46 deg, respectively. Just before capturing prey, the bats decreased the terminal frequency (TF) of the pulse. Simultaneously, the beam widths were expanded to 64 deg (horizontal) and 57 deg (vertical). We assumed a circular piston model to estimate how much the beam width was changed by decreasing the frequency of emitted pulse. It was found that the observed expansion of the beam width was smaller than those of theoretical estimations. This suggests that the bats decrease the TF of pulse for compensating their beam width narrowed by taking a large bite for the prey. We also measured echolocation calls and flight behavior of Myotis macrodactylus during natural foraging. M. macrodactylus uses FM echolocation pulse which is similar to P. abramus, but they forage for prey above the water surface. We compare echolocation strategies between two FM bats with different foraging habitat.