Search Results (13)

Current optical tweezering techniques are actively employed in the manipulation of nanoparticles, e.g., biomedical cells. However, there is still huge room for improving the efficiency of manipulating multiple nanoparticles of the same composition but different shapes. In this study, we designed an array of high-index all-dielectric disk antennas, each with an asymmetric open slot for such applications. Compared with the plasmonic counterparts, this all-dielectric metasurface has no dissipation loss and, thus, circumvents the Joule heating problem of plasmonic antennas. Furthermore, the asymmetry-induced excitation of quasi-bound states in continuum (QBIC) mode with a low-power intensity (1 mW/µm²) incidence imposes an optical gradient force of −0.31 pN on 8 nm radius nanospheres, which is four orders of magnitude stronger than that provided by the Fano resonance in plasmonic antenna arrays, and three orders of magnitude stronger than that by the Mie resonance in the same metasurface without any slot, respectively. This asymmetry also leads to the generation of large optical moments. At the QBIC resonance wavelength, a value of 88.3 pN-nm will act on the nanorods to generate a rotational force along the direction within the disk surface but perpendicular to the slot. This will allow only nanospheres but prevent the nanorods from accurately entering into the slots, realizing effective sieving between the nanoparticles of the two shapes. Full article

This paper proposes a circularly polarized ultra-wideband (UWB) antenna for a Uni-Traveling-Carrier Photodiode (UTC-PD) to meet the growing demand for bandwidth and polarization diversity in terahertz (THz) communication. In the design of the UTC-PD integrated antenna, the planar electrodes of the chip are directly integrated with the antenna to simplify the integration process. However, this integration introduces new problems, such as asymmetry inside the spiral antenna, which leads to a deterioration in the corresponding high-frequency performance. To address this issue, the antenna’s structure is optimized, and a lens is integrated to enhance directivity and eliminate surface waves. As a result, the proposed antenna achieves a 100–1500 GHz (175%) impedance bandwidth and a 150–720 GHz (131%) axial ratio bandwidth for the UTC-PD. The maximum gain of the antenna is 21.05 dBi at 1 THz. Full article

The task of directional hearing faces most animals that possess ears. They approach this task in different ways, but a common trait is the use of binaural cues to find the direction to the source of sound. In insects, the task is further complicated by their small size and, hence, minute temporal and level differences between two ears. A single symmetric flagellar particle velocity receiver, such as the antenna of a mosquito, should not be able to discriminate between the two opposite directions along the vector of the sound wave. Paired antennae of mosquitoes presume the usage of binaural hearing, but its mechanisms are expected to be significantly different from the ones typical for the pressure receivers. However, the directionality of flagellar auditory organs has received little attention. Here, we measured the in-flight orientation of antennae in female Culex pipiens pipiens mosquitoes and obtained a detailed physiological mapping of the Johnston’s organ directionality at the level of individual sensory units. By combining these data, we created a three-dimensional model of the mosquito’s auditory space. The orientation of the antennae was found to be coordinated with the neuronal asymmetry of the Johnston’s organs to maintain a uniformly shaped auditory space, symmetric relative to a flying mosquito. The overlap of the directional characteristics of the left and right sensory units was found to be optimal for binaural hearing focused primarily in front of, above and below a flying mosquito. Full article

To overcome the limitations of traditional frequency selective surfaces in flexible state switching at the same frequency, this paper proposes a novel active frequency selective surface (AFSS) that simultaneously exhibits conversion between absorption and transmission modes at the same frequency band. By welding PIN diodes on the bottom structure of the AFSS, the conversion between band-pass (transmission) and band-stop (absorption) filters can be controlled electronically. In the common-frequency switch between absorption and transmission modes, the impedance matching of the AFSS is attained by altering the capacitance value of the varactors embedded on the top structure of the AFSS. The functionalities of the proposed AFSS design are investigated by full-wave simulations (in HFSS software) at 11.4 GHz. Furthermore, the operating principle is analyzed using an equivalent circuit model (in AWR software). To verify the concept, a prototype is manufactured, and the responses of mode switching are measured by adjusting the bias voltage. The measurement result is consistent with the simulation analysis. Owing to the tunability of the varactors, the structural asymmetry is compensated to achieve 80% absorptivity and transmissivity within a field of view of ±35°. The developed AFSS structure is highly valuable to be used in scenarios such as antenna domes, etc. Full article

Terahertz (THz) technology has great potential for applications in various fields, such as security imaging detection, optical communication, environmental quality monitoring, and life sciences. Most of these applications require THz detectors with high sensitivity, fast response, and a miniaturized size that can operate at room temperature. In this study, we present a graphene THz detector integrated with an asymmetric bowtie antenna. The asymmetric antenna confines the incident THz waves into the graphene active layer, leading to photocurrent generation and its directional flow. The maximum responsivity of this device can reach 19.6 V/W at 2.52 THz, with a noise–equivalent power (NEP) of 0.59 nW /Hz^0.5. Additionally, the response time is less than 21 μs, with an active area of less than 1500 μm². Such a small device enables THz imaging with a spatial resolution as small as 200 μm. These results provide a feasible way to design miniaturized and integrable two–dimensional material–based THz detectors. Full article

Broadcasting, radar, sonar and space telecommunication systems use phased arrays to produce directed signals to be transmitted at the desired angle. This system requires a large number of antenna elements. The presence of faulty element(s) in an array causes asymmetry, which results in a deformed radiation pattern with higher sidelobe levels. Higher sidelobe levels indicate waste of energy by transmitting and receiving signals in unwanted directions. Hence, it is important to develop a method that detects faulty elements and corrects the radiation pattern. To correct the failed radiation pattern, failed elements in an array must be identified first. There have been various studies conducted on linear array failed radiation pattern correction and the finding of faulty elements, but investigation on the planar array is limited. Further, the optimization suggested for linear arrays does not necessarily work for the planar array. In this study, planar array faulty antenna detection was developed with pattern search (PS), simulated annealing (SA), and particle swarm optimization (PSO) methods by reducing the Signal to Noise Ratio (SNR) as the objective function. The analysis was varied for 8 × 8 and 6 × 6 planar arrays with different types of failures. The results were compared to find the best method to identify the faulty element’s location in a planar array. The pattern search method produced outstanding results in finding the faulty element’s locations by providing 100% accuracy for all types of failure, while other methods failed to do the same. Full article

A simple model is presented to describe how the radio frequency electromagnetic field modifies the plasma density the antenna faces in tokamaks. Aside from “off-the-shelf” equations standardly used to describe wave-plasma interaction relying on the quasilinear approach, it invokes the ponderomotive force in presence of the confining static magnetic field. The focus is on dynamics perpendicular to the $B_o$ magnetic field. Stronger fields result in density being pushed further away from the launcher and in stronger density asymmetry along the antenna. Full article

Based on helioseismological measurements (1996–2017), the entire Sun shrinks during solar maximum and regrows during the next solar minimum by about a few km (~10⁻⁵ effect). Here, we observe, for the first time, that the solar radius variation resembles a 225-day relationship that coincides with Venus’ orbital period. We show that a remote link between planet Venus and Sun’s size must be at work. However, within known realms of physics, this is unexpected. Therefore, we can only speculate about its cause. Notably, the driving idea behind this investigation was some generic as-yet-invisible matter from the dark Universe. In fact, the 11-year solar cycle shows planetary relationships for a number of other observables as well. It has been proposed that the cause must be due to some generic streaming invisible massive matter (IMM). As when a low-speed stream is aligned toward the Sun with an intervening planet, the IMM influx increases temporally due to planetary gravitational focusing, assisted eventually with the free fall of incident slow IMM. A case-specific simulation for Venus’ impact supports the tentative scenario based on this investigation’s driving idea. Importantly, Saturn, combined with the innermost planets Mercury or Venus, unambiguously confirms an underlying planetary correlation with the Sun’s size. The impact of the suspected IMM accumulates with time, slowly triggering the underlying process(es); the associated energy change is massive even though it extends from months to several years. This study shows that the Sun’s size response is as short as half the orbital period of Mercury (44 days) or Venus (112 days). Then, the solar system is the target and the antenna of still unidentified external impact, assuming tentatively from the dark sector. If the generic IMM also has some preferential incidence direction, future long-lasting observations of the Sun’s shape might provide an asymmetry that could be utilized to identify the not isotropic influx of the assumed IMM. Full article

Phased arrays are widely used in different fields, such as broadcasting, radar, optics, and space communications. The principle of phased arrays is to generate a directed signal from a large number of antennas to be steered at any desired angle. This, however, increases the probability of defective elements in an array. Faulty elements in an array cause asymmetry and result in increased sidelobe levels which rigorously distort the radiation pattern. Increased sidelobe radiation wastes energy and can cause interference by radiating and receiving signals in unintended directions. Therefore, it is necessary to find a method that can provide accuracy in the radiation pattern transmitted or received in the presence of failed element(s) in an array. This paper compares the few available optimization methods, namely, simulated annealing (SA), Genetic Algorithm (GA), Particle Swarm Optimization (PSO), and Pattern Search (PS) methods. For each method, various types of failures were examined, and the most suitable techniques to recover the far-field radiation are recommended. The optimization is then carried out by selecting the optimal weights of the remaining working elements in the planar array. The optimized radiation pattern’s efficiency was evaluated by comparing the Signal to Noise Ratio (SNR) value of the optimized radiation with reference and failed radiation patterns. The PSO method showed a better performance compared to all the other methods in reducing the failed radiation pattern’s SNR value. In various types of failure tests, this method reduced the failed radiation pattern’s SNR from 1 to 10 dB. This method also successfully produced a radiation pattern that closely matches the reference pattern before any failed element(s) are presented in the array. The life cycle of a planar array system with faulty elements can be increased by optimizing the remaining active elements in the array with the PSO method. It also reduces the cost of restoring and replacing the failed elements in an array regularly. This approach also prevents near-field measurement that requires complicated processes using costly equipment. Full article

Environmental stress can affect trait size and cause an increase in the fluctuating asymmetry (FA) of bilateral morphological traits in many animals. For insect parasitoids, feeding of hosts on transgenic maize, expressing a Bacillus thuringiensis toxin gene is a potential environmental stressor. We compared the size of antennae, forewings, and tibia, as well as their FA values, in two parasitoids developed on two East African host species feeding on non-transgenic vs. transgenic maize. The two lepidopteran stem-borer hosts were the native Sesamia calamistis Hampson (Lepidoptera: Noctuidae) and a recent invader, Chilo partellus Swinhoe (Lepidoptera: Crambidae). The two braconid parasitoids were the native, gregarious larval endoparasitoid Cotesia sesamiae and the recently introduced Cotesia flavipes. Both parasitoids attacked both hosts, creating evolutionarily old vs. novel interactions. Transient feeding of hosts on transgenic maize had various effects on FA, depending on trait as well as the host and parasitoid species. These effects were usually stronger in evolutionarily novel host–parasitoid associations than in the older, native ones. These parameters have capacity to more sensitively indicate the effects of potential stressors and merit further consideration. Full article

Several species of social bees exhibit population-level lateralization in learning odors and recalling olfactory memories. Honeybees Apis mellifera and Australian social stingless bees Trigona carbonaria and Austroplebeia australis are better able to recall short- and long-term memory through the right and left antenna respectively, whereas non-social mason bees Osmia rufa are not lateralized in this way. In honeybees, this asymmetry may be partially explained by a morphological asymmetry at the peripheral level—the right antenna has 5% more olfactory sensilla than the left antenna. Here we looked at the possible correlation between the number of the antennal sensilla and the behavioral asymmetry in the recall of olfactory memories in A. australis and O. rufa. We found no population-level asymmetry in the antennal sensilla distribution in either species examined. This suggests that the behavioral asymmetry present in the stingless bees A. australis may not depend on lateral differences in antennal receptor numbers. Full article

Asymmetry of brain function is known to be widespread amongst vertebrates, and it seems to have appeared very early in their evolution. In fact, recent evidence of functional asymmetry in invertebrates suggests that even small brains benefit from the allocation of different functions to the left and right sides. This paper discusses the differing functions of the left and right sides of the brain, including the roles of the left and right antennae of bees (several species) in both short- and long-term recall of olfactory memories and in social behaviour. It considers the likely advantages of functional asymmetry in small and large brains and whether functional asymmetry in vertebrates and invertebrates is analogous or homologous. Neural or cognitive capacity can be enhanced both by the evolution of a larger brain and by lateralization of brain function: a possible reason why both processes occur side-by-side is offered. Full article

The honeybee Apis mellifera, with a brain of only 960,000 neurons and the ability to perform sophisticated cognitive tasks, has become an excellent model in life sciences and in particular in cognitive neurosciences. It has been used in our laboratories to investigate brain and behavioural asymmetries, i.e., the different functional specializations of the right and the left sides of the brain. It is well known that bees can learn to associate an odour stimulus with a sugar reward, as demonstrated by extension of the proboscis when presented with the trained odour in the so-called Proboscis Extension Reflex (PER) paradigm. Bees recall this association better when trained using their right antenna than they do when using their left antenna. They also retrieve short-term memory of this task better when using the right antenna. On the other hand, when tested for long-term memory recall, bees respond better when using their left antenna. Here we review a series of behavioural studies investigating bees’ lateralization, integrated with electrophysiological measurements to study asymmetries of olfactory sensitivity, and discuss the possible evolutionary origins of these asymmetries. We also present morphological data obtained by scanning electron microscopy and two-photon microscopy. Finally, a behavioural study conducted in a social context is summarised, showing that honeybees control context-appropriate social interactions using their right antenna, rather than the left, thus suggesting that lateral biases in behaviour might be associated with requirements of social life. Full article