Spherical Reflector Research Articles

Improved modeling for dark photon detection with dish antennas

A vector dark matter candidate, also known as dark photon, would induce an oscillating electric field through kinetic mixing. One detection strategy uses a spherical reflector to focus the induced emission at its center of curvature. First, we investigate the effects of diffraction in this type of experiment from an analytical standpoint, making use of the Kirchhoff integral theorem in the low-curvature dish limit. Next, we estimate the impact of mode matching, in the case of detection by a pyramidal horn antenna. We show that the expected signal intensity can be significantly reduced compared to usual estimates. Our method is applied to the reinterpretation of the SHUKET experiment data, the results of which are shown to be degraded by a factor of ∼50 due to both diffraction and mode matching. The analytical method allows optimizing some experimental parameters to gain sensitivity in future runs. Our results can be applied to any dish antenna experiment using a low-curvature reflector. Published by the American Physical Society 2024

Laser wireless power transmission based on spherical reflector intra-cavity beam splitting

The powersphere is an energy reception device in a laser wireless power transmission system, converting light into electricity, and also has a certain effect of light uniformity. However, in the actual application process, limitations due to laser power, photovoltaic cell absorption rate, and direct irradiation area restrict light uniformity, thus reducing photoelectric conversion efficiency. A spherical reflector at the center of the powersphere to enhance internal reflection and improve light uniformity was proposed. Utilizing LightTools software, we established a simulation model to simulate the energy distribution of light on the powersphere after reflection by the sphere, analyzing light uniformity and constructing an experimental platform for validation. Results show the reflector significantly boosts uniformity, doubling the powersphere’s output power and reducing voltage and current disparities, thereby enhancing system conversion efficiency.

An electromechanically driven dielectric elastomer based tunable reflector

Deformable optics offer numerous advantages over conventional optical assemblies, including compactness, cost-effectiveness, efficiency, and flexibility. This study focuses on a reflector based on dielectric elastomer actuators (DEAs) with an internal fluid (air) coupling. DEAs are a class of electroactive materials adept at accommodating substantial actuation strains and rapid responses. Fluid distributed between the active and passive parts remains entirely enclosed by the device and transmits actuation pneumatically. Dynamic maneuvers conducted through a series of controlled electrical signals demonstrate proper control over optical characteristics. However, DEs exhibit inherent flaws in dynamic actuation, referred to as instabilities, which are mitigated by applying an initial pre-stretch. The study identifies optimal parameters that confer stability to the reflector: minimum to no creep, zero residual vibrations, and low viscous losses. An analytical framework is developed to assess device performance, focusing on the spherical curvature assumption that closely resembles the behavior of tunable spherical reflectors. Additionally, an optical bench setup is employed to demonstrate the relationship between focal length and applied pressure. Notably, this paper underscores the potential of a DE-based variable focal length reflector to function effectively within a dynamic environment.

Conception, realization and testing of a solar cooker built with a spherical reflector in Burkina Faso

A system was conceived, realized and tested for solar cooking purpose. It has a spherical shape reflector as concentrator, mounted on two frames for a better orientation towards the sun. The engineering of the system makes it able to reach theoretical geometrical mean concentration of 720 and a theoretical efficiency of 0.42. Thus, the system is easy to manipulate since only the azimuth angle is tracked. An optional rocking of the reflector also allows the system to be used in equatorial and tropical zones when the sun goes closer to the zenith. Series of tests were conducted around November 20th, in Ouagadougou, Burkina Faso with a latitude angle of 12.21°. Experiments on oil in a pot allowed it to reach successively a maximum temperature of 184°C at 1:00pm the first day and 221°C at 1:30pm the second day. Boiled sweet potatoes, fried sweet potatoes, spaghetti and fish dishes were cooked in a reasonable amount of time and ready for lunch. Water tests were also conducted around March 14th following the protocol, and allowing comparison with other systems. In conclusion, experiments were taken without rocking the system and by only tracking the azimuth angle. The water result gives convincing outcomes in comparison with other concentrating cooking systems. Most of all, sub-Saharan users will not have to change their habits: the system, by always concentrating, is less constricting for tracking the sun and less time consuming to manipulate. Finding the focal point and eye safety issues shall be addressed, but overall indicators, including financial one, give more credit for the system to be implemented in sub-Saharan region.

Development of Space-Borne Antenna Reflector via 3D Printing

The growing necessity of large aperture-based structures for many aerospace applications emphasizes the need to deploy large antenna structures in space. The space antennas should be light in weight and have low stowage volume, with efficient membrane packaging. The concept of additive manufacturing has been introduced to reduce weight as well as cost. In this paper, a comparative study has been done to analyze the advancement made in reducing weight with adequate strength. Based on the study, the main objectives are to develop a 3D-printed spherical reflector model with high specific strength and to assess the consistency of the model's shape. For determining the specific strength, tensile testing is performed on four different infill densities (20%, 40%, 60%, and 80%) with a grid infill pattern. It was observed that the specimen with 80% infill density has the highest tensile strength, 36.56 MPa, which is 23.51% more than 20% infill. However, the specimen with 20% infill density has the highest specific strength of 19.323 GPa/kg among the four specimens, which is approximately 64.64% higher than the 100% infill density. As a result of the testing, the spherical reflector model is 3D printed with 20% infill density, and it was found that the model achieves its shape stability and shape consistency with adequate specific strength.

Cholesteric Spherical Reflectors with Tunable Color from Single-Domain Cellulose Nanocrystal Microshells.

The wavelength- and polarization-selective Bragg reflection of visible light exhibited by films produced by drying cholesteric liquid crystal (CLC) suspensions of cellulose nanocrystals (CNCs) render these biosourced nanoparticles highly potent for many optical applications. While the conventionally produced films are flat, the CLC-derived helical CNC arrangement would acquire new powerful features if given spherical curvature. Drying CNC suspension droplets does not work, because the onset of kinetic arrest in droplets of anisotropic colloids leads to severe buckling and loss of spherical shape. Here, these problems are avoided by confining the CNC suspension in a spherical microshell surrounding an incompressible oil droplet. This prevents buckling, ensures strong helix pitch compression, and produces single-domain cholesteric spherical reflector particles with distinct visible color. Interestingly, the constrained shrinkage leads to spontaneous puncturing, leaving every particle with a single hole through which the inner oil phase can be extracted for recycling. By mixing two different CNC types at varying fractions, the retroreflection color is tuned throughout the visible spectrum. The new approach adds a versatile tool in the quest to utilize bioderived CLCs, enabling spherically curved particles with the same excellent optical quality and smooth surface as previously obtained only in flat films.

Development of a spherical solar collector with a cylindrical receiver

Solar energy can be used for substitution of the depleting fossil fuels in thermal applications and electricity generation through thermal route. For medium and high temperature applications, a system for collecting solar energy at high temperatures was developed and built in this research work. The system, built at the center of development of renewable energy of the Algiers, consists of a 2=60°C included angle, R0=0.90 m diameter spherical reflector with a cylindrical receiver filled with water, tracking reflector which moves into the focus following the sun's movement. The system is capable of heating water or other fluids to temperatures above 350 °C, thus making it possible to obtain process heat for domestic use and to store solar energy in a compact and economical way. An analysis of the system's optical characteristics was performed to aid in the design of the spherical reflector and cylindrical receiver. The thermal performance of the system was analyzed. The effects of mirror reflection, concentration ratio, heat transfer to the fluid (water), incidence angle, size and form of the cylindrical receiver, environmental conditions (wind, ambient temperature), have been studied by means of thermal model. The performance of the spherical reflector was tested by the temperature of the water. Total efficiencies (solar to thermal) of = 60% - 70% were obtained for a wide range of temperatures up to 350 °C. The results of the present study show that it is possible to use the spherical reflector for systems requiring process heat and make possible substantial utilization of solar energy and considerable savings relative to fossil energy in the sunny countries of the world.

Adaptive Petal Reflector: In-Lab Software Configurable Optical Testing System Metrology and Modal Wavefront Reconstruction.

This paper addresses two aspects of the metrology of spherical, petal polymer reflectors which are part of an effort by the European Space Agency (ESA) to develop actively controlled foldable reflectors, enabling larger apertures on CubeSats and small satellites. The first problem is that of measuring the surface figure error of the spherical reflector alone during the development phase, and to assess the quality before assembling the telescope (large stroke, low accuracy). The SCOTS (Software Configurable Optical Testing System) appears to provide a fast and satisfactory solution to this problem. The second problem is the wavefront error reconstruction when the petal reflector is mounted on the telescope, because parts of the petals are obscured by the secondary mirror, in such a way that the petals appear completely disconnected, making the gradient-based metrology impossible. Using the fact that the petals have common mechanical boundary conditions at the central support ring, the problem is solved by using a set of orthogonal modes satisfying the same boundary conditions. The vibration modes are used for this purpose; the modal amplitudes are reconstructed from slope data outside the obstruction, allowing for wavefront error reconstruction over the entire surface.

Optical system design of double-sided telecentric microscope with high numerical aperture and long working distance.

The working distance of the high numerical aperture visible video microscope is extremely short, which greatly limits its application scenarios. To solve this problem, this paper proposes an unobstructed design method of double-sided telecentric microscope with high numerical aperture and long working distance. First, aiming at the obstruction problem of the image-side telecentric catadioptric microscope objective, the structure of the catadioptric optical system is improved. Then, the aspheric design method based on the best aberration compensation is analyzed theoretically to better correct the primary aberration of the high-numerical aperture microscope objective. Finally, a double-sided telecentric microscope optical system with a numerical aperture (NA) of 0.8 and a working distance of 10.0 mm was designed, which is composed of a spherical reflector, a beam splitter plate, a collimating lens group, and an image-side telecentric eyepiece optical system. The design results show that the imaging resolution of this high numerical aperture video microscope is as high as 0.42 µm, and the microscope has a magnification of about 220× for the image with 1080P (1920 × 1080 pixels) resolution. This double-sided telecentric microscope has the advantages of a large field of view, compact structure, good stray light suppression ability, and manufacturability, and has high practical value in the field of high-precision measurement and detection.

Determination of permanent corrections of ball reflectors

Today, there are many manufacturers of triple-prism, spherical reflectors with different mechanical characteristics. That is why there is a problem of matching the signal reflection center with the geometric one. The purpose of this work is to evaluate the methods of determining permanent corrections of electronic tacheometers, ball reflectors and to develop recommendations for their use. Method. To determine the instrument correction, a displacement interferometer is used. It contains a two-frequency He-Ne laser with a wavelength of l = 0.63 μm (red range). The study compared the results of length measurements by an interferometer and an electronic total station with a ball reflector. This allowed determining the instrument correction. The research defined the constant correction of reflectors and total stations on the phase section of the field base using the method of created linear observations. Results. Experimental studies of ball reflectors of various manufacturers and Leica electronic tacheometers were conducted. The determination of constant instrument corrections of the total station and reflector using the displacement interferometer can be performed with an accuracy of 0.1 mm. This significantly depends on the accuracy of measuring lines with the total station. The use of ball reflectors with a built-in triple prism allows significant increase of distance measurement accuracy by reducing centering errors, considering the constant instrument correction (up to 0.4 mm for Leica 1201 total stations). Scientific novelty. The methods of determining permanent corrections of ball reflectors and total stations were investigated. The proposed method determines the measurement interval length with the exception of systematic constant correction of the electronic total station and reflector. Practical relevance. The use of ball reflectors is recommended for quick and unambiguous installation at points, convenience of their use for monitoring observations, as well as for increasing the accuracy of linear measurements due to the reduction of centering errors. In order to achieve high-precision measurements of short lines, it is recommended, according to the performed studies, to carefully determine the constant correction of the total station and ball prisms. This makes it possible to increase the accuracy of line measurements at least three times compared to the declared accuracy of the total station manufacturer.

A novel two-dimensional reflective coherent gradient sensor and its applications in residual deformation measurement of laser repaired metal components

Directed Energy Deposition (DED), known as an important branch of additive manufacturing, are becoming increasingly crucial in different industrial fields. However, this extreme manufacturing process may bring about quality issues for the DED product, and in-situ monitoring for characterizing mechanical parameters of thick DED products still needs to be improved. In this manuscript, for the convenient in-situ bidirectional residual deformation measurement of thick DED metal components, a novel two-dimensional coherent gradient sensor (2D-CGS) is established based on crossed Ronchi gratings. Firstly, the diffraction characteristic of the crossed Ronchi grating used in 2D-CGS is analyzed, and then the principles of 2D-CGS are analyzed in detail for bidirectional out-of-plane displacement gradient measurement. Furthermore, two temporal phase-shifting techniques: plane-parallel plate rotating (PPR) method and prism translation (PT) method, are extended from one dimension to 2D for improving the accuracy of 2D-CGS post-processing, named as 2D-PPR method and 2D-PT method. Verification experiment shows that the 2D-CGS system can synchronously measure the bidirectional curvature fields of the standard spherical reflector with the maximum relative error of 3.80%, which is equivalent to the accuracy of typical CGS. Finally, in the application of zig-zag deposited DED process, the bidirectional residual deformation fields of repaired components are in-situ monitored by portable 2D-CGS system, and the relationship of dwell time between adjacent tracks and the residual deformation is analyzed based on bidirectional centerline curvature on the bottom surface of substrate. A new parameter named as the orthotropic symmetry coefficient is defined based on curvature to analyze the full-field in-plane orthogonal anisotropy. Results show that both the degree of in-plane orthogonal anisotropy and value of residual deformation decreases with the increase of dwell time from 0 to 5 s, while varying a little with the dwell time exceeding 5 s, which also indicates the proposed parameter could well evaluate the degree of full-field orthotropic anisotropy. Meanwhile, the position of maximum curvature also gradually moves from the end toward the beginning in deposition direction. In summary, the proposed 2D-CGS method can measure the full-field bidirectional deformation in high efficiency, which may be promising in future in-situ monitoring applications.

Active Damping, Vibration Isolation, and Shape Control of Space Structures: A Tutorial

This tutorial reviews the author’s contributions to the active control of precision space structures over the past 35 years. It is based on the Santini lecture presented at the IAC-2022 Astronautical Congress in Paris in September 2022. The first part is devoted to the active damping of space trusses with an emphasis on robustness. Guaranteed stability is achieved by using decentralized collocated actuator–sensor pairs. The so-called integral force feedback (IFF) is simple, robust, and effective, and the performances can be predicted easily with simple formulae based on modal analyses. These predictions have been confirmed by numerous experiments. The damping strategy for trusses has been extended to cable structures, and also confirmed experimentally. The second part addresses the problem of vibration isolation: isolating a sensitive payload from the vibration induced by the spacecraft (i.e., the unbalanced mass of attitude control reaction wheels and gyros). A six-axis isolator based on a Gough–Stewart platform is discussed; once again, the approach emphasizes robustness. Two different solutions are presented: The first one (active isolation) uses a decentralized controller with collocated pairs of the actuator and force sensor, with IFF control. It is demonstrated that this special implementation of the skyhook, unlike the classical one, has guaranteed stability, even if the two substructures it connects are flexible (typical of large space structures). A second approach (passive) discusses an electromagnetic implementation of the relaxation isolator where the classical dash-pot of the linear damper is substituted by a Maxwell unit, leading to an asymptotic decay rate of −40 dB/decade, similar to the skyhook (although much simpler in terms of electronics). The third part of the lecture summarizes more recent work done on the control of flexible mirrors: (i) flat mirrors for adaptive optics (AO) controlled by an array of piezoelectric ceramic (PZT) actuators and (ii) spherical thin shell polymer reflectors controlled by an array of piezoelectric polymer actuators (PVDF-TrFE) aimed at being deployed in space.

Pixelating Structural Color with Cholesteric Spherical Reflectors

While structural color is a powerful means of obtaining saturated and durable pigments that minimize absorption, scattering, and negative environmental impact, appearing naturally in animals and plants as well as in carefully designed artificial composites, it is fundamentally limited to spectral colors, leaving white and other mixed colors elusive. It also normally suffers from a strong viewing angle dependence, making color definition difficult. Herein, it is demonstrated that these challenges can be overcome by using cholesteric spherical reflectors (CSRs), spheres of polymerized cholesteric liquid crystal with radial alignment of the self‐assembled helical structure. Exhibiting omnidirectional selective retroreflectivity of well‐defined color, CSRs are discrete “packages” of structural color. This allows them to be used as pixels for generating nonspectral colors, following the principle of digital displays. A method of creating densely packed monolayers of CSRs with red (R), green (G), and blue (B) retroreflection is developed. Mixing them in equal proportions gives a white surface. By embedding the CSRs in an index matching transparent medium, nonselective specular reflections and scattering are avoided. The approach can be used to create arbitrary colors, including nonspectral ones, without any absorption or nonselective scattering, opening doors to decorating surfaces as desired while minimizing light loss.

Joint calculation of mechanical and radar characteristics of calibration folding spherical reflectors

Combined modeling of the shape of the surface of the grid canvas belt stretched on the wireframe and statistical radar characteristics of the calibration reflector has been performed. To solve the problem, a complex computer model is proposed and implemented. The model provides analysis of the stress state of the grid canvas belt forming the surface of the folding spherical reflector, numerical electrodynamic calculation of the spatial backscattering diagram and estimation of statistical radar characteristics corresponding to the arbitrary location direction in the process of observation. Using the complex computer model, the equilibrium shape of the reflecting surface has been calculated for the selected design version of the folding spherical reflector, the facet 3D electrodynamic model has been developed, spatial backscattering diagrams have been calculated and statistical RCS characteristics for various wave sizes of the object have been evaluated. The presented complex computer model may be used in studies related to analysis of radar characteristics of calibration folding spherical radar reflectors with various versions of power wireframe design.

ГЕОДЕЗІЯ, КАРТОГРАФІЯ І АЕРОФОТОЗНІМАННЯ

The developments of the scientific and pedagogical staff of the Department of Engineering Geodesy of the Lviv Polytechnic National University in the direction of increasing the accuracy of geodetic measurements in the construction, operation and repair of unique buildings, structures or separate technological equipment, which is particularly important for their safe operation, are considered. Auxiliary equipment (improved light-reflecting mark, device for linear-angular measurements, spherical reflector with a stand, two-prism transducer-vector) has been developed to increase the accuracy of measurements of parameters of engineering structures by electronic total stations. On the basis of theoretical calculations, an optimal image of the geodetic mark for viewing at different distances is proposed, and a three-dimensional holder is developed to compensate for the non-perpendicular error. A technique was developed and implemented in a device for linear-angular measurements, which made it possible to determine the length of segments from 1 to 30 meters with an accuracy of 0.1-0.3 mm. In order to transfer the coordinates of the geodetic base from the reference network to the measurement points of building structures, a spherical reflector and a stand were developed, in the process of using which errors in centering, reduction and height measurement are compensated. The application of the developed spherical reflector was tested during the restoration of the design position of the large-sized equipment of the power complex facility with an accuracy of 0.5 mm. To determine the dimensions of irregularly shaped structures in order to minimize the angles of the prism (to directly determine the coordinates of the prism tip), a two-prism encoder vector was theoretically justified and developed. The accuracy of determining the spatial coordinates by the vector encoder was investigated using the final measure as a reference value. According to the results of research, the deviation of the distances determined with the help of the vector transducer from the reference value is 0.3 mm.

Adaptive Deployable Thin Spherical Shell Reflectors

This paper begins with a quick survey of potential space applications and a brief review of previous experiments on the shape control of a spherical shell reflector with a thin film of PVDF-TrFE. Next, the problem of thermal sensitivity is addressed numerically; it is found that, because of the large thermal expansion of the active material, the surface figure error generated by a linear thermal gradient on a unimorph reflector is considerable and its correction requires large control voltages. The surface figure accuracy can be greatly improved by a balanced design (i.e., adding a passive layer symmetrical to the PVDF-TrFE layer) and using a low CTE substrate. Finally, the paper considers a petal reflector; the unimorph design is even more sensitive than the full reflector to the thermal gradient, but the balanced design turns out to be better than the full reflector, both from the point of view of the surface figure error and the control voltages.

ГЕОДЕЗІЯ, КАРТОГРАФІЯ І АЕРОФОТОЗНІМАННЯ

Today in Ukraine there are dozens of turbogenerators (TG) in operation, a significant part of which have been in operation for over 35 ÷ 50 years, which exceeds their service life in accordance with regulatory documents. The actual technical condition of the TG is determined by many geometrical parameters, among which the crucial ones are those that characterize it as a mechanical system (axis of the aggregate and the axis of the stator). Today, the control of the position of the axes must be performed with an accuracy of 0.5 mm, and is carried out in three ways (using a string, using an optical autoreflex system (PPS-11), using a test shaft). The purpose of these studies is to develop a method for monitoring the geometric parameters of the TG stator when replacing it with geodetic methods using high-precision electronic total stations and its testing on site. Based on previous research, we propose to solve the following problems by the spatial method of electronic total station using a high-precision total station Leica TCRP1201R300. We performed a priori estimation of accuracy and a number of experiments (research to determine refocusing error, determination of distance measurement error at short lengths using a spherical reflector, study of the effect of non-perpendicularity of the measuring laser to the reflector) to develop methods for improving measurement accuracy using electronic total station. This technique has been tested on site during the repair (replacement) of the generator stator. As a result of the work carried out, the spatial position of the axes of the aggregate and the stator was determined with an accuracy of 0.3 mm, which were fixed in the conditional coordinate system by four marks. The method provides for the selection of optimal conditions for electronic tacheometer measurements, which compensate for errors in the initial data, instrumental, external conditions, sighting, centering and fixing. Also, the method provides for the control of each stage of work on a standard deviation of up to 0.2 mm. The number of measurement methods is determined by achieving the accuracy of each stage of 0.2 mm.

Twisted Rainbow Light and Nature‐Inspired Generation of Vector Vortex Beams

AbstractTwisted vector light beams (optical vortices) arise from a spiral modulation of the geometric (Pancharatnam–Berry) phase converting the light spin to the orbital angular momentum. The preferred geometric‐phase elements using liquid crystals and plasmonic metasurfaces realize this conversion by structuring their building blocks, i.e., precisely orienting individual crystal molecules or plasmonic nanoantennas. Here, an analogous mechanism is discovered in the spiral phase modulation of light reflected by dielectric spheres and first demonstrated in natural phenomena, namely in the rainbow formation. The spiral geometric phase is documented by holographic imaging of full circle primary and secondary rainbows created in the laboratory. The measurement uses a wide‐angle holographic camera (field of view ≈120°) taking time‐resolved self‐correlation holograms (300 ms). The holograms allow a quantitative restoration of the spiral geometric phase of light reflected from thousands of randomly falling water drops. The capability of individual drops to generate vector vortex beams under circularly polarized illumination is proven theoretically and demonstrated in experiments using glass microspheres. The spherical reflectors are discovered as simple generators of vector vortex beams and vortex arrays, inspiring novel geometric‐phase elements.

THE RESONANT SYSTEM OF A SUB-TERAHERTZ LOCAL OSCILLATOR

Purpose. The excitation efficiency is investigated of the first higher-order axially asymmetric oscillation mode (TEM10q) excited in a hemispherical open resonator (OR) at the frequencies of the fundamental and second-order harmonics of the Gunn diode in the 4-mm and 2-mm wavelength ranges. The hemispherical resonator is coupled to its input waveguide via aperture-type coupling elements. The diameter 2a of the OR mirror apertures is 38 mm, while the curvature radius of the spherical reflector is R = 39 mm and the normalized distance between the mirrors is L/R = 0.593. Two aperture coupling elements of dimensions a× b = 6.9 × 9.6 mm are used to excite the OR. They permit controlling separately the functions of field-to-field matching (modes in the resonator and in the waveguide) and volume- to-volume coupling of the structural elements (the resonator and the waveguide). They are located at the center of the planar mirror. The field matching is determined by the geometric dimensions of the coupling elements, whereas the coupling matching is determined by the period of the one-dimensional E-polarized grating in their apertures. The Gunn diodes are used as generators, operating at the frequencies of the fundamental (75 GHz) andthe second-order (150 GHz) harmonics. The excitation efficiency of the TEM1011 oscillation in the OR of the geometry specified here, using aperture-type coupling elements as described, is 81.5%. Design/methodology/approach. The excitation efficiency of higher-order oscillation modes ТЕМ10q in the OR being driven by an incident ТЕ10 mode that arrives via two rectangular guides, is evalua-ted using the antenna surface utilization factor. The reflection coefficient from the OR and the loaded Q-factor are estimated in the familiar technique of partial reflection coefficients summation. Findings. As has been shown, in an OR of parameters 2а= 38 mm, R= 78 mm, and L/R= 0.287 TEM1022 oscillations are excited at the frequency of the Gunn diode’s second-order harmonic (i.e., 150 GHz) with an efficiency of 84%. In that same resonator, the excitation efficiency of the TEM1011 mode at the fundamental Gunn diode’s harmonic (frequency of 75 GHz) equals 54%. By placing one-dimensional (E-polarized) wire gratings in the aperture of the coupling elements it proves possible to match the resonator with the waveguide. It has been found that in the case of a l = 0.2 mm spatial period of the wire grating and matched excitation of the resonator at f = 150 GHz (i.e. Г150 = 0), the reflection coefficient Г75 from the OR at f = 75 GHz equals 0.637. Upon excitation in the OR of oscillations in the TEM1022 mode, the total loss at f = 150 GHz is –1.23 dB. With TEM1011 oscillations excited in the same resonator at a frequency of 75 GHz, the total losses increase up to –5.4 dB. Conclusions. The analysis has shown that an OR implementing the proposed method of excitation of higher-order axially asymmetric for constructing a subterahertz range local oscillator. Moreover, such a resonant system may be considered both as a power combiner and a diplexer (filter).

On the scattering of a disk source by a rigid sphere for directivity broadening.

The purpose of this study is to model a circular planar loudspeaker placed near a spherical reflector to broaden its directivity pattern, which would otherwise become increasingly narrow at high frequencies. Through ray tracing, it seems intuitively feasible to thus create a virtual point source at very high frequencies, but we provide a more rigorous analysis to determine what will happen at intermediate frequencies where the wavelength is of a similar magnitude to the diameter of the disk or sphere. We show that a smoother off-axis response is obtained with a dipole pressure source, which does not obstruct the scattered sound, rather than a monopole velocity source. Hence, an electrostatic loudspeaker, for example, would be more suitable than a dynamic one. The sphere may also serve as a spherical approximation of a human head, in which case the loudspeaker would become an open headphone that is not sealed to the ear.