Conical Array Research Articles

The dependence of light extraction improvement on optimized surface microstructure for AlGaN-based UVC-LEDs considering TM-polarized emission

In order to improve the light extraction of AlGaN-based short wavelength ultraviolet light emitting diodes (DUC-LEDs), a type of microstructure with high aspect ratio is introduced and optimized on the AlN substrate surface. And, particle swarm optimization (PSO) algorithm is used to inverse design of the surface microstructure to maximize the light extraction efficiency (LEE). Considering that the propagation characteristics of TM-polarized light are different from that of TE-polarized light, the optical field distribution and LEE is analyzed for the UVC-LEDs with different TE-polarized component when the optimized surface microstructure is applied. Furthermore, the preparation process tolerance of the high aspect ratio structure is discussed by calculating the LED's LEE when the structural deviation occurs or morphology changes. Simulation results show that, by using the optimized surface microstructure based on parabola cone array, the LEDs' LEE is increased from 4.4% to 8.7% and from 0.4% to 3.7% for TE-polarized and TM-polarized emission, respectively. In addition, it is demonstrated that the light extraction improvement by the surface microstructure has a good tolerance to the structural deviation and morphology. The results are significant for improving light extraction and realizing high efficient short wavelength AlGaN-based UVC-LEDs by designing surface microstructures.

1-D and 2-D Direction of Arrival Estimation in a Conical Conformal Array: Design and Implementation.

Direction of arrival (DOA) estimation for conformal arrays is challenging due to non-omnidirectional element patterns and shadow effects. Conical conformal array (CCA) can avoid the shadow effect at small elevation angles. So CCA is suitable for DOA estimation on both azimuth and elevation angles at small elevation angles. However, the element pattern in CCA cannot be obtained by conventional directional element coordinate transformation. Its local element pattern also has connection with the cone angle. The paper establishes the CCA radiation pattern in local coordinate system using 2-D coordinate transformation. In addition, in the case of large elevation angle, only half elements of the CCA can receive signal due to the shadow effect. The array degrees of freedom (DOF) are reduced by halves. We introduce the difference coarray method, which increases the DOF. Moreover, we propose a more accurate propagator method for 2-D cases. This method constructs a new propagation matrix and reduces the estimation error. In addition, this method reduces computational complexity by using linear computations instead of eigenvalue decomposition (EVD) and avoids spectral search. Simulation and experiment verify the estimation performance of the CCA. Both demonstrate the CCA model established in this paper is corresponding to the designed CCA antenna, and the proposed algorithms meet the needs of CCA angle detection. When the number of array elements is 12, the estimation accuracy is about 5 degrees.

Graphene-Based Flexible Sensors for Respiratory and Airflow Monitoring

Flexible devices have been rapidly developed and applied in various applications. However, there have been few reports on printable graphene-based sensors with customized structures and properties capable of respiratory and airflow monitoring. In this study, a graphene-based flexible sensor with a conical microdot array (GSCA) made by the direct-ink writing 3D printing method for real-time personal signals and air-coupled detection is reported. GSCA 3D structures with microdot features on the sensing layer can deliver a fast response of below 60 ms and improve the sensitivity by 32.4% (26–78 kPa), 800% (78–102 kPa), and 600% (102–160 kPa) by adjusting the printing parameters. The sensor exhibits a low detection limit of 11.4 Pa and a large detection range with a linear sensitivity of 1.4–509 kPa. The spider leg-like micro-/nanofibers between two adjacent microdots contribute to electron transport and airflow sensing. The results show the feasibility of the graphene-based sensor with dots to recognize air strength and direction for respiration and airflow. Further validation of the GSCA in real-time personal monitoring demonstrates the potential for multitasking wearable sensors.

Research on Calibration Sources for a 35–40 GHz Millimeter-Wave Solar Radio Observation System

The microwave spectra in the optically thin regime provides unique information about the solar corona magnetic field; thus, a millimetre-wave solar radio observation system (35-40 GHz) in the Chashan Observatory is newly established to obtain relevant data. Herein, we design and develop a blackbody calibration source employing a metal cone array and absorbing patch to calibrate the system and obtain accurate solar observation data for analysis and decision-making. The reflectivity of the calibration source is simulated and measured to characterize its emissivity. The reflectivity is obtained by the finite-integration (FIT) method under various fitting conditions, i.e., the thickness of the absorbent patches and aspect ratios of the cone. The temperature gradient of cones is determined by the finite-element method (FEM). A 5×5 array microwave blackbody was developed based on a cone with a low scattering coefficient and excellent temperature uniformity. To reduce the influence of spurious signals, the time-domain gate technique is used to test the reflectivity of the target. The results demonstrate that the emissivity of the blackbody is higher than 0.9995 in the 35-40 GHz band. The temperature difference between the cone top and the cone bottom is 0.20 °C.

Highly Durable Janus Fabrics Based on Transfer Prints for Personal Moisture Management.

Janus fabrics with moisture management ability have great potential for improving both physiological and psychological comfort of human body. However, current methods for creating Janus fabrics are typically complex, environmentally unfriendly, and costly. More importantly, the prepared Janus fabrics have demonstrated insufficient mechanical properties and poor fastness, rendering them unsuitable for practical applications. Here, this work proposes a method for constructing Janus fabrics through thermal transfer printing of hydrophobic transfer prints onto a superhydrophilic cotton fabric, followed by creation of a conical micropore array on the fabric surface. The as-prepared Janus fabrics exhibit excellent unidirectional liquid transport capacity, capable of transporting 50µL water completely in 11.6 s in the positive direction. Attributed to the durable property of the transfer prints, the Janus fabrics are capable of withstanding over 900 friction cycles and 250 home laundry cycles, which is a great advance in this research field. Additionally, the fabrication process has no detrimental effect on the fabric's breathability, elasticity, and flexibility. Furthermore, the Janus fabric can maintain human body temperature 3.6 °C cooler than that worn with cotton fabric. The fabrication method can provide useful insights for the design and creation of durable Janus fabrics to maximize personal comfort.

A comprehensive SERS, SEM and EDX study of individual atmospheric PM2.5 particles in Chengdu, China

Characterization of atmospheric fine particulate matter (PM2.5) in large cities has important implications for the study of their sources and formation mechanisms, as well as in developing effective measures to control air pollution. Herein, we report a holistic physical and chemical characterization of PM2.5 by combining surface-enhanced Raman scattering (SERS) with scanning electron microscopy (SEM) and electron-induced X-ray spectroscopy (EDX). PM2.5 particles were collected in a suburban area of Chengdu, a large city in China with a population over 21 million. A special SERS chip composed of inverted hollow Au cone (IHAC) arrays was designed and fabricated to allow direct loading of PM2.5 particles. SERS and EDX were used to reveal the chemical composition, and particle morphologies were analyzed from SEM images. SERS data of atmospheric PM2.5 indicated qualitatively the presence of carbonaceous particulate matter, sulfate, nitrate, metal oxides and bioparticles. The EDX showed the presence of the elements C, N, O, Fe, Na, Mg, Al, Si, S, K, and Ca in the collected PM2.5. Morphology analysis showed that the particulates were mainly in the form of flocculent clusters, spherical, regular crystal shaped or irregularly shaped particles. Our chemical and physical analyses also revealed that the main sources of PM2.5 are automobile exhaust, secondary pollution caused by photochemical reactions in the air, dust, emission from nearby industrial exhaust, biological particles, other aggregated particles, and hygroscopic particles. SERS and SEM data collected during three different seasons showed that carbon-containing particles are the principal sources of PM2.5. Our study demonstrates that the SERS based technique, when combined with standard physicochemical characterization methods, is a powerful analytical tool to determine the sources of ambient PM2.5 pollution. Results obtained in this work may be valuable to the prevention and control of PM2.5 pollution in air.

Wearable Plasmonic Sweat Biosensor for Acetaminophen Drug Monitoring.

Monitoring the acetaminophen dosage is important to prevent the occurrence of adverse reactions such as liver failure and kidney damage. Traditional approaches to monitoring acetaminophen dosage mainly rely on invasive blood collection. Herein, we developed a noninvasive microfluidic-based wearable plasmonic sensor to achieve simultaneous sweat sampling and acetaminophen drug monitoring for vital signs. The fabricated sensor employs an Au nanosphere cone array as the key sensing component, which poses a substrate with surface-enhanced Raman scattering (SERS) activity to noninvasively and sensitively detect the fingerprint of acetaminophen molecules based on its unique SERS spectrum. The developed sensor enabled the sensitive detection and quantification of acetaminophen at concentrations as low as 0.13 μM. We further evaluated the sweat sensor integrated with a Raman spectrometer for monitoring acetaminophen in drug-administered subjects. These results indicated that the sweat sensor could measure acetaminophen levels and reflect drug metabolism. The sweat sensors have revolutionized wearable sensing technology by adopting label-free and sensitive molecular tracking methods for noninvasive and point-of-care drug monitoring and management.

Omnidirectional color shift suppression of full-color micro-LED displays with enhanced light extraction efficiency.

The three-primary-color chip array is the most straightforward to realize full-color micro-LED displays. However, the luminous intensity distribution shows high inconsistency between the AlInP-based red micro-LED and GaN-based blue / green micro-LEDs, resulting in the issue of angular color shift with different viewing angles. This Letter analyzes the angular dependence of color difference of conventional three-primary-color micro-LEDs, and proves that the inclined sidewall with homogeneous Ag coating has a limited angular regulation effect for micro-LEDs. Based on this, a patterned conical microstructure array is designed on the micro-LED's bottom layer to effectively eliminate the color shift. This design cannot only regulate the emission of full-color micro-LEDs to perfectly meet Lambert's cosine law without any external beam shaping elements, but also improve the light extraction efficiency of top emission by 16%, 161%, and 228% for red, green, and blue micro-LEDs, respectively. The color shift Δ u ' v ' of the full-color micro-LED display is also kept below 0.02 with the viewing angle ranging from 10° to 90°.

Fabrication of nanoindentation array-based SERS substrate using Conical and Berkovich indenters

This paper reports a study of the effect of indenter geometry on the morphologies of the indentation arrays using a home-made nanoindentation system. Two typical indenters, that is, Conical and Berkovich indenters are chosen to conduct all the indentation process on a pure aluminum block surface. Single-row and multiple-row indentation arrays are machined, and the effect of the spacing value between the adjacent indentations with different indenters are studied in detail. Results show that the overlapping of the indentations and the material filling by the following penetration are the two main factors of the surface topography quality of the obtained structures. The smaller the spacing value is, the larger the indentation deformation is, and the worse the quality of the periodic structure is. In addition, the surface enhanced Raman scattering (SERS) substrates are prepared by the machined indentation arrays, and the SERS spectra is measured using Rhodamine 6G (R6G). The results show that a higher Raman enhancement factor is obtained on the Conical indentation arrays, which is attributed to the higher depth-to-width ratio of the indentation array. Therefore, this work can provide a guidance for the preparation of SERS substrate with suitable indenter geometries and the indentation interval values.

A model volcanic fissure with adjustable geometry and wall temperature

Fissure eruptions initiate with magma ascending and spreading through cracks in the ground that can extend for kilometres at the surface. Eruptions eventually localise to form one or a few persistent conduits and ultimately an array of discrete cones or craters. We built a new experimental apparatus to investigate the influences of fissure shape and wall-rock temperature on localisation within a volcanic fissure, and the thermal feedbacks associated with variability of these parameters. Our artificial fissure, or “Artfish,” has a slot geometry with adjustable shape and wall temperature. We can simulate both starting variability in fissure geometry and wall temperature, as well as changes in these parameters during an experiment to replicate, for example, blockage by wall-rock collapse, widening by wall-rock erosion, and warming by adjacent intrusions. We use polyethylene glycol (PEG 600) for our analogue fluid. A variable-speed pump allows for a range of fluid injection and ascent rates. Initial tests showcase the capabilities of the model and the types of data that may be acquired. Additional key features achieved include a stable and planar injection system, fluid recycling, and the use of particle tracers for monitoring flow patterns and velocities. The thermal evolution of the fluid-wall interface is quantitatively measured with thermal sensors, and the change in state of the PEG provides a clear visual indication of flow behaviour and solidification progress recorded on video. The potential experiments that can be conducted with this highly versatile model are numerous and will be used to gain a better understanding of the thermal controls on flow localisation and conduit development. This will assist hazard modellers to assess controls on eruption evolution and potentially to forecast sites where an initial fissure eruption may focus.

Supersonic water jets as point-like sources of extremely high pressure

Two interacting supersonic water jets and collisions of a water jet with an aluminum target are studied experimentally and by hydrodynamic simulations. Supersonic water jets form, when shocks generated by underwater electrical explosions of conical wire arrays converge. The arrays are supplied by a ∼250 kA, ∼1 μs rise time current pulse. Underwater explosion of two conical arrays placed face to face produces jets propagating in air with velocities of ∼2.5×103 m/s leading to hot plasma formation at a temperature of ∼2200–3000 K, pressure ∼1.7×1010 Pa, and density >1029 m−3. When a single array explodes underwater in front of an aluminum target, the collision of the jet with the target produces a local pressure of ∼3×1010 Pa on the surface of the target.

Self-cleaning and anti-fogging hierarchical structure arrays inspired by termite wing

Wings of the Formosan subterranean termite (Coptotermes formosanus Shiraki) covered with micrometer-scale hairs and nanometer-scale wax patches, allow them to greatly reduce adhesions to water droplets of various sizes. Inspired by the anti-wetting structures, we develop a colloidal lithography-based strategy integrated with a scalable self-assembly approach to engineer hierarchical conical structure arrays. The resulting structure arrays provided a water contact angle as high as 175.3° and a low contact angle hysteresis of 2.7° after surface modification. Importantly, the resulting superhydrophobic structures even feature distinguished self-cleaning and anti-fogging capabilities. The dependence of structure configuration on the anti-wetting functionalities is also investigated in this research.

Tabletop 360-Degree Three-Dimensional Light-Field Display Based on Viewpoint-Fitting Encoding Algorithm for Reducing Facet Braiding.

Since the effect of the facet braiding phenomenon, the display quality of reconstructed image degrades with increasing depth of field in tabletop three-dimensional light-field display. Here, to analysis the facet braiding, the imaging process of the tabletop 360-degree three-dimensional light-field display based on conical lens array is mathematically modeled. A viewpoint-fitting encoding algorithm is proposed to reduce the effect of the facet-braiding phenomenon and improve the range of depth of field, which is optimized to form the best synthetic encoded image by fitting the reconstructed image seen by the simulated human eye to the parallax image captured at the corresponding location. The effectiveness of the proposed optimization algorithm is verified by simulation analysis and optical experiments, respectively. In the experiment, the clear depth of field range of the display system is increased from 13 cm to 15 cm, and the visualization effect of the reconstructed three-dimensional image is enhanced.

A robust and 3D-printed solar evaporator based on naturally occurring molecules

The interfacial solar desalination has been considered a promising method to address the worldwide water crisis without sophisticated infrastructures and additional energy consumption. Although various advanced solar evaporators have been developed, their practical applications are still restricted by the unsustainable materials and the difficulty of precise customization for structure to escort high solar-thermal efficiency. To address these issues, we employed two kinds of naturally occurring molecules, tannic acid and iron (III), to construct a low-cost, highly efficient and durable interfacial solar evaporator by three-dimensional (3D) printing. Based on a rational structural design, a robust and 3D-printed evaporator with conical array surface structure was developed, which could promote the light harvesting capacity significantly via the multiple reflections and anti-reflection effects on the surface. By optimizing the height of the conical arrays, the 3D-printed evaporator with tall-cone structure could achieve a high evaporation rate of 1.96 kg m–2 h−1 under one sun illumination, with a photothermal conversion efficiency of 94.4%. Moreover, this evaporator was also proved to possess excellent desalination performance, recycle stability, anti-salt property, underwater oil resistance, as well as adsorption capacity of organic dye contaminants for multipurpose water purification applications. It was believed that this study could provide a new strategy to fabricate low-cost, structural regulated solar evaporators for alleviating the dilemma of global water scarcity using abundant naturally occurring building blocks.

Array Decomposition Method for Arbitrary-Element Regular Arrays Using Higher Order Basis Functions

The full-wave array decomposition method for regular antenna arrays with arbitrary elements using higher order hierarchical basis functions is investigated. We show that the use of higher order basis functions results in significantly reduced memory consumption and computation time for a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathbf {10\!\times\!10}$</tex-math></inline-formula> element conical horn array with an aperture size of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$22\!\times\!22\lambda$</tex-math></inline-formula> , without the need for analytical nor numerical approximations. In addition, we demonstrate that by employing higher order basis functions, the far-field error is considerably lower than by using common first-order basis functions for the same total number of unknowns.

Directional transport behaviour of droplets on the surfaces with asymmetric slanted cone arrays

Directional transport behaviour of droplets on the surfaces with asymmetric slanted cone arrays

Directional transport behaviour of droplets on the surfaces with asymmetric slanted cone arrays

Directional transport behaviour of droplets on the surfaces with asymmetric slanted cone arrays

Design and Implementation of a Ku-Band High-Precision Blackbody Calibration Target.

Microwave radiometers can be used in human tissue temperature measurement scenarios due to the advantages of non-destructive and non-contact temperature measurement. However, their accuracy often cannot meet the needs of practical applications. In this paper, a Ku-Band high-precision blackbody calibration target is designed to provide calibration for microwave radiometers and meet the requirements of a high temperature-measurement accuracy and high temperature-measurement resolution. From a practical application point of view, the blackbody calibration target needs to have the characteristics of high emissivity and high temperature uniformity. However, previous studies on blackbody calibration targets often focused on the scattering characteristics or temperature uniformity of the calibration target separately, and thus lack a comprehensive consideration of the two characteristics. In this paper, the electromagnetic scattering model and the temperature-distribution model of the calibration target are established through the multi-physical simulation combined with the Finite Element Method. Then, according to the simulation results of the two characteristic models, the structural parameters and composition of the coated cone array are continuously optimized. In addition, to achieve high-precision temperature control of the blackbody calibration target, this paper studies three PID controller parameter self-tuning algorithms, namely, BP-PID, PSO-PID and Fuzzy-PID for the optimal parameter tuning problem of traditional PID algorithms and determines the optimal temperature-control algorithm by comparing the performance of heating and cooling processes. Then, the blackbody calibration target is processed and manufactured. The arch test system is used to validate the reflectance of the calibration target, the emissivity is calculated indirectly, and the temperature-distribution uniformity of the temperature-control panel of the calibration target is tested by a multi-point distribution method. Finally, the uncertainty of the brightness temperature of the blackbody calibration target is analyzed.

Enhanced light extraction by optimizing surface microstructure for AlGaN-based deep ultraviolet light emitting diodes with 265 and 280 nm emission

In order to improve the light extraction for the deep ultraviolet light emitting diodes (DUV-LEDs), the surface microstructure based on a parabola cone array is used and optimized in work. In the optimization of the surface structure, inverse design based on a particle swarm optimization intelligent algorithm is applied to maximize the light extraction. The optimization results show that compared with the traditional planar structure, the optimized surface structure improves the light extraction efficiency by more than 200%. In addition, the influence of the designed surface microstructure on the light propagation is also explored by comparing the light field distribution and the light extraction process with the planar structure DUV-LEDs. It is revealed that the high aspect ratio of an array microstructure can change the light propagation and greatly expand the angle of a light escape cone. This effect can be maximized by the inverse design based on the intelligent algorithm, which has great potential in improving the light extraction of AlGaN-based DUV-LEDs.

Conical Conformal Tightly Coupled Dipole Arrays Co-Designed With Low-Scattering Characteristics

Conformal designs and scattering reduction have long been significant challenges to ultrawideband phased arrays. In this work, a conical conformal tightly coupled dipole array (TCDA) with low-scattering characteristics is developed. The design procedure from a planar antenna element to a two-dimensional (2-D) conformal finite array is presented in detail. In this design, a novel structure of conformal resistive strips is used as a cover layer for the radiating dipoles to control scattering, and its ability to control scattering is insensitive to variations in the dimensions of the designed conformal array. To achieve a wide scanning range and reduce scattering in a wide band, a metasurface composed of full-split rings is employed as the superstrate. The final designed array achieves a 3:1 impedance bandwidth for scanning up to ±60° in two principal planes. Moreover, scattering is reduced by more than 10 dB throughout the entire operating band. Finally, an array prototype is fabricated and measured. Measured results are in good agreement with the simulated results, thus demonstrating the effectiveness of the proposed array.