Ka-band metasurface antennas, with their low-cost, low-profile design and superior beam-steering capabilities, show significant potential in the field of satellite communications. However, the constraints of limited satellite resources and significant atmospheric losses at Ka-band frequencies require these antennas to achieve wide-angle beam scanning capabilities and high antenna gain, adding considerable complexity to their design.

In order to achieve the design of a multifunctional and highly efficient meta-antenna, the design optimization will involve numerous parameters, greatly increasing the use of computational resources and optimization time. Addressing the critical issue of balancing multiple optimization objectives, such as gain and scanning angle, while improving optimization speed, remains a key challenge in the design process.

To address these challenges of meta-antenna design, researchers from the University of Electronic Science and Technology of China, Tongji University, and City University of Hong Kong have joined forces in an extensive collaboration.

Leveraging their long-term expertise in the field of meta-optics, they proposed a Ka-band meta-antenna design method based on a Physics-Assisted Particle Swarm Optimization (PA-PSO) algorithm. Using this method, they designed and fabricated a Ka-band meta-antenna. The study is published in the journal Opto-Electronic Science.

The antenna proposed in the paper is designed using the PA-PSO algorithm. Compared to the traditional PSO algorithm, the optimization direction of particles in the PA-PSO algorithm is guided by extremum conditions derived from the variational method. This not only reduces computation time but also decreases the likelihood of finding suboptimal designs.

The final optimized results indicate that the relative strength achieved by the PA-PSO algorithm is 94.62806, which is comparable to the relative strength of 94.62786 achieved by the traditional PSO algorithm. However, the computational cost of the PA-PSO algorithm is significantly lower; it reaches the optimal state after only 650 iterations, whereas the traditional PSO algorithm requires 4100 iterations.

This means the computation time of the PA-PSO algorithm is less than one-sixth of that for the PSO algorithm. Therefore, the PA-PSO method can guide particle swarms more efficiently, reducing computation time, making it an important tool for addressing complex multivariate and multi-objective optimization challenges.

Based on the phase distribution optimized by the PA-PSO algorithm, the team designed and fabricated a hexagonal meta-antenna sample with a focal length of 22 mm, diagonal length of 110 mm, and a thickness of only 1.524 mm.

The antenna has an f-number of only 0.2, a beam scanning angle of ±55°, a maximum gain of 21.7 dBi, and a gain flatness of within 4 dB. This innovative hexagonal meta-antenna, with its wide scanning angle, compact design, and high transmission gain, exhibits enormous potential for applications in satellite communication, radar systems, 5G networks, and the Internet of Things, among many other fields.

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Mountain chickadees in Boulder have evolved a different tune to avoid getting mixed up with their cousins, according to a new CU Boulder-led study published Oct. 9 in the Journal of Evolutionary Biology.

The results provide real-time evidence for one of Charles Darwin’s famous theories and shed light on how pressure from human activity can impact wildlife’s evolution.

Mountain chickadees, common in the high-elevation conifer forests on North America’s west coast and in the Rocky Mountains, are vocal animals. They constantly whistle a chirpy “bee-bee-bee-bee” song to attract mates or defend their territories.

Black-capped chickadees are their close relatives. The two birds look very similar, except that mountain chickadees have a pair of white eyebrow-like stripes above their eyes. Black-capped chickadees tend to live at lower elevations, and in certain regions, such as Colorado’s Boulder County, the two birds’ habitats overlap.

Scott Taylor, one of the paper’s senior authors and associate professor in the Department of Ecology and Evolutionary Biology, wondered whether this unique living arrangement would push the chickadees to evolve different traits. His team’s hypothesis is based on Darwin’s “character displacement” theory, which suggests that closely related species with overlapping habitats tend to diverge in traits—such as appearance and call—to reduce competition or costly hybridization between different species.

Galápagos finches are a classic example. These closely related birds on the Galápagos Islands evolved different beak shapes and sizes from one another to specialize in eating different types of seeds, reducing competition.

In Boulder, where two species of chickadee coexist, researchers wondered if the birds had started humming a different tune.

“In birds, song is an important characteristic for individuals to recognize each other,” said Olivia Taylor, the paper’s first author and a recent graduate of the Department of Ecology and Evolutionary Biology.

To explore this, the team collaborated with researchers at the University of Western Ontario and Cornell University, who recorded more than 2,000 chickadee songs. They sampled black-capped and mountain chickadees in Boulder, where the two species coexist. They also followed populations of mountain chickadees in California and black-capped chickadees in New York, where each species lives by themselves.

They found that Boulder’s mountain chickadees sing differently compared to those in California. Instead of the common four-note “bee-bee-bee-bee” song, Boulder’s mountain chickadees whistle with more notes. For instance, many of their songs have five to six notes, which is significantly longer than the two-note songs of black-capped chickadees living in the same area.

Boulder’s mountain chickadees are also more likely to include one or two introductory notes—short chirps at the beginning of a song—compared with the Californian mountain chickadees and their black-capped cousins.

“Our ears couldn’t really pick up these longer introductory notes, and we only noticed that after we recorded and analyzed the songs. But the birds’ hearing is so much better than ours, so they can certainly tell them apart,” said Scott Taylor, who has led the Boulder Chickadee Study at CU Boulder’s Mountain Research Station for six years.

Previous research shows black-capped chickadees are dominant over mountain chickadees when they coexist. Black-capped chickadees often chase mountain chickadees away if they get too close, and mountain chickadees usually wait for black-capped chickadees to finish eating and leave before they approach feeders.

While the two species can breed with each other, female hybrid offspring produced from a black-capped chickadee and a mountain chickadee are likely sterile.

Singing a different song can help mountain chickadees distinguish between friends or foes and avoid interbreeding, the authors said.

“There’s a reproductive cost in hybridizing with each other. From an evolutionary perspective, sterile females are a dead-end in reproduction. And maybe the hybrid males also suffer some physiological costs we don’t yet know about. Given the two species are adapted to different elevations, some hybrids may struggle to survive cold winters in the high mountains,” Scott Taylor said.

A few hundred years ago, mountain chickadees inhabited Boulder’s conifer forests alongside likely far fewer black-capped chickadees than today. As settlers moved in and planted ash and maple trees, they also created excellent habitats for black-capped chickadees. As a result, the black-capped population is likely much larger now, and the birds are interacting more frequently with local mountain chickadees.

“It’s very interesting to see how these species are responding to what is ultimately a human-introduced pressure,” said Olivia Taylor. “For that, I think it’s important to document and understand our impacts on wildlife and how they adapt to co-exist.”

A team of wildlife managers at the U.S. Geological Survey in San Diego, California, working with a colleague from the San Diego Natural History Museum, have uncovered the areas in San Diego County that need the most scrutiny if bat populations in the area are to be saved.

In their study published in PLOS ONE, the group used existing data on the bat population in the San Diego County area to find out which bats need the most attention to avoid extinction.

As the research team points out, San Diego County hosts 22 of 41 known bat species in the United States. Sixteen of those species are at risk of extinction. Preserving bat populations is important in the San Diego area and around the world as bats are a major natural source of insect control. A single bat can eat up to 1,000 insects in just one hour. In this new effort, the researchers sought out which parts of San Diego County should be prioritized for bat conservation efforts.

The researchers analyzed bat population data from San Diego County. Most notably, they focused on two data points—species richness and threats. The species richness data revealed information regarding bat diversity, including population size and health and current conservation efforts surrounding each. Threats included anything in the environment that could jeopardize individual bats or their communities.

The research team mapped the places where different species of bats lived and hunted for food. They found that the bats faced three major threats: artificial lights, urbanization and non-conserved land (land not in its natural state). They noted that urbanization and artificial lighting make life particularly hard for bats because they impinge on their natural behaviors.

Urbanization means fewer resources and artificial lighting can confuse the bats because they are nocturnal and use light to tell them when to feed and when to head back to their shelter. The data also helped plan conservation efforts involving the installation of bat boxes and the planting of native vegetation.

The team’s efforts helped establish a plan of action centered on helping the bats in San Diego survive as humans continue to change the landscape in which they live.

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