Focal Point Location Research Articles

Graphical Interface in MATLAB for design and analysis of reflectors for lighting systems or solar collectors on parabolic surfaces

This project introduces the successful development of a MATLAB graphical interface for the design and analysis of reflectors and solar concentrators on parabolic surfaces. The integration of spline techniques for precise modeling of these surfaces has been implemented, along with the capability to generate STL files for 3D printing. The interface not only enables detailed and adaptable design of reflectors but also includes an advanced simulator for projecting incident rays and analyzing their reflection on the parabolic surface, focusing specifically on the focal point location. This has led to a significant increase in the efficiency of solar concentrators and lighting systems by enabling the precise placement of absorbers to maximize energy transfer. The obtained results confirm the initial hypothesis, demonstrating that the interface enhances the precision and efficiency in the design of these systems, thereby offering a valuable tool in both educational and professional realms in the fields of solar energy and lighting.

Sunvoyager: Interstellar Precursor Probe Mission Concept Driven by Inertial Confinement Fusion Propulsion

The Sunvoyager is a concept mission for a space probe that can be sent outside of the solar heliosphere to a distance of 1000 AU in a trip time of only 3.4 years traveling at speeds of 1500 km/s or 325 AU/year. It is an advanced Voyager flyby probe, but the concept design is unique in that it would utilize an inertial confinement fusion propulsion engine driving a gram-scale capsule mass at 10 Hz pulse frequency using 5 MJ laser driver energy reaching the capsule. Such a design may be possible in the latter part of the 21st century. The probe would carry a 100-ton scientific payload for the purpose of observations from the location of gravitational focal point, a dwarf planet flypast, and imaging of interstellar asteroids. Secondary science objectives would include measurements of the interstellar medium, measurements of astrometry, and the search for extraterrestrial power and propulsion emission signatures. The propulsion engine is characterized by 23 kN thrust, 54 GW jet power, and 147 kW/kg specific power. This paper outlines the science goals in addition to calculations that scope out the design space using a recently constructed propulsion performance and mission analysis numerical tool called HeliosX.

S.M.A.R.T. F.U.S: Surrogate Model of Attenuation and Refraction in Transcranial Focused Ultrasound

Low-intensity focused ultrasound (LIFU) is an increasingly applied method for achieving non-invasive brain stimulation. However, transmission of ultrasound through the human skull can substantially affect focal point characteristics of LIFU, including dramatic attenuation in intensity and refraction of focal point location. These effects depend on a high-dimensional parameter space, making these effects difficult to estimate from previous work. Instead, focal point properties of LIFU experiments are often estimated using numerical simulation of LIFU sonication through skull. However, this procedure presents many entry barriers to even computationally savvy investigators and often requires expensive computational hardware, impeding LIFU research. We present a novel MATLAB toolbox (data: doi:10.5068/D1QD60; Matlab Scripts: https://doi.org/10.5281/zenodo.5811122) for rapidly estimating beam properties of LIFU transmitted through bone. Users provide specific values for frequency of LIFU, bone thickness, angle at which LIFU is applied, depth of the LIFU focal point, and diameter of the transducer used and receive an estimation of the degree of refraction/attenuation expected for the given parameters.

The Effect of Fresnel Lens Focal Point Location on Heat Transfer in Phase Change Material (PCM) Enhanced Dynamic Solar Facade

Abstract In recent years, the demand for energy-efficient technological solutions in the building sector has risen significantly worldwide. The exploitation of phase change material as a medium for thermal energy storage in building envelopes has increased due to its superior properties. There is still a knowledge gap to cover in the way to the effective solar thermal energy storage in the building envelope – to enhance the heat transfer, to reduce the heat loss, etc. This paper deals with the optimisation of heat transfer using a solar concentrator (Fresnel lens). This study examines the effect of Fresnel lens focal point location on heat transfer in a dynamic solar facade prototype that stores thermal energy in phase change material. Nine different setups (solar façade compositions) were tested in the laboratory – two parameters with three alternatives each. Testing conditions simulate the relevant Northern Europe climate. By changing the air gap configuration and location of the Fresnel lens focal point, the heat transfer to phase change material was observed by measuring temperatures in the phase change material container using five thermocouples. The results show the improved thermal performance in test modules with larger cone diameter by 7.2 % and Fresnel lens focal point positioning closer to the back of the phase change material container by 5.4 %.

Multi-objective optimization and analysis for laser beam cutting of stainless steel (SS304) using hybrid statistical tools GA-RSM

A laser beam machine is a non-traditional manufacturing technique that uses thermal energy to cut nearly all types of materials. The quality of laser cutting is significantly affected by process parameters. The purpose of this study is to use a genetic algorithm (GA) in conjunction with response surface approaches to improve surface roughness in laser beam cutting CO2 with a continuous wave of SS 304 stainless steel. The effects of the machining parameters, such as cutting speed, nitrogen gas pressure, and focal point location, were investigated quantitatively and optimized. The tests were carried out using the Taguchi L9 orthogonal mesh approach. Analysis of variance, main effect plots, and 3D surface plots were used to evaluate the impact of cutting settings on surface roughness. A multi-objective genetic algorithm in MATLAB was used to achieve a minimum surface roughness of 0.93746 μm, with the input parameters being 2028.712 mm/m cutting speed, 11.389 bar nitrogen pressure, and a focal point position of - 2.499 mm. The optimum results of each method were compared, as the results the response surface approach is less promising than the genetic algorithm method.

Optimizing Ballistic Motion of Partially Coherent Multiple Airy Beams by Quadratic and Linear Phases

AbstractBy applying quadratic and linear phase modulations (QPM and LPM), the propagation properties of the partially coherent dual and quad Airy beams which maintain acceleration in free space are studied. They are generated by superimposing two and four partially coherent Airy beams whose phase is modulated in the source field. It is demonstrated that the trajectories of the partially coherent light beams and the location and number of focal points, along with maximum altitude and range of the trajectories can be easily dominated by adjusting the appropriate values of QPM p and LPM l. Furthermore, for the quad case, the transverse spectral density distribution of lacking side lobes exhibits the structure of the optical frame which may be flipped under certain conditions. Both the peak intensity of the beams and the divergence speed of the optical frame can be managed by choosing the different characteristic transverse width of the beams. These results show an energizing new idea in the manipulation of partially coherent multiple fields of accelerating beams.

Field validation of an actuated convergent-beam acoustic Doppler profiler for high resolution flow mapping

Energetic river and tidal flow environments feature complex hydrodynamic conditions. Conventional acoustic Doppler profiling instrumentation typically requires assumptions of flow homogeneity over the spatial scales of the divergent beam separation. This removes the ability to measure spatio-temporal variability within the flow. However, velocity variability within these spatial scales is often important in the design of structures and devices exposed to such flow, informing dynamic and peak hydrodynamic load predictions. The research presented outlines the development and testing of a flow measurement instrument consisting of multiple spatially-separated single beam acoustic Doppler profilers converging on a remote focal point, the location of which can be programmatically adjusted through actuation. This increases the spatial resolution at which remote field measurements can be made in energetic flow environments. Field testing of the instrument was conducted in a tidal channel at Sequim Bay Inlet, WA, USA. Results are compared with independent reference measurements made by a co-located, motion-corrected acoustic Doppler velocimeter. This comparison, across tidal velocities of 0.4–0.7 m s−1, showed a mean velocity error of 0.5%–13.2% across nine sample locations within a 3.00 m × 2.25 m plane. To the authors’ knowledge, this is the first publication of flow velocity results from non-intrusive acoustic measurements at an off-axis, focal point location that features 3D positional control.

The Use of Intelligent Sensing Algorithm for Internet of Things and Hash Spatial Information Location Technology

This exploration is aimed at quickly obtaining the spatial position information of microseismic focal points and increasing the accuracy of microseismic rapid positioning, to take timely corresponding measures. A microseismic focal point location system completely different from the traditional microseismic location method is proposed. The search engine technology is introduced into the system, which can locate the microseismic focal point quickly and accurately. First, the propagation characteristics of microseismic signals in coal and rock layers are analyzed, and the focal position information is obtained. However, the collected microseismic signal of the coal mine contains noise, so it is denoised at first. Then, a waveform database is established for the denoised waveform data and focal point position. The structure and mathematical model of the location‐sensitive hash (LSH) based on P stable distribution are introduced and improved, and the optimized algorithm multiprobe LSH is obtained. The microseismic location model is established according to the characteristics of microseismic data. The values of three parameters, hash table number, hash function family dimension, and interval size, are determined. The experimental data of the parameters of the search engine algorithm are analyzed. The results show that when the number of hash tables is 6, the dimension k of the hash function family is 14, and the interval size W is 8000, the retrieval time reaches a relatively small value, the recall rate reaches a large value, and the proportion of retrieved candidates is large; the parameters of the search engine algorithm of the measured coal mine microseismic data are analyzed. It is obtained that when the number of hash tables is 4, the dimension k of the hash function family is 6, and the interval size W is 500, the retrieval time reaches a relatively small value, the recall rate obtains a large value, and the proportion of retrieved candidates is large. The contents studied are of great significance to the evaluation of destructive mine earthquakes and impact risk.

Source Image Squeezing and Field Tunneling for Propagating Light Beyond-Limit Focusing to Reach the Intermediate Zone

The physics for beyond-limit focusing has great academic importance, particularly for light propagation with control over focal point location and spot size. Asymmetric boundary confinement for a beyond-limit focusing lens in a metallic subwavelength structure redirects the surface current at the inner edges of the interface between an upstream double slit with width much smaller than the wavelength and a downstream slit with width close to one wavelength. This induces intense localized fields and tightly squeezes spatial distributions for the wave sources and corresponding images that are critical for focusing beyond the diffraction limit, as opposed to separated sources in super-oscillatory lenses and metalenses for optically large areas. This squeezing simultaneously increases the distance between source and image peaks and reduces their distribution widths one order less than the wavelength. The corresponding spatial spectrum alters to excite an inward-propagation wave mode with strong lateral wave momentum for focusing. The radiated inward propagation wave mode can be manipulated to help the focused field tunnel through the downstream slit, such that the focal point can reach the intermediate zone. Source and image radiation confirmed that focused field propagation had good agreement with simulation results. The proposed analytical Green’s method opens new physics applications for this fundamental focusing process, offering new opportunities to further reduce spot size and tailoring the focal length for important potential plasmonic applications.

Exploitation of Velocity Gradients by Sympatric Stream Salmonids: Basic Insights and Implications for Instream Flow Management

AbstractHydraulic heterogeneity can strongly influence habitat selection by stream fishes. Velocity gradients created by channel roughness and flow obstructions may be particularly important for species that feed on drifting invertebrates, where maintaining focal points in low‐velocity microhabitats adjacent to faster water allows fish to scan a larger water volume for prey while minimizing swimming costs. However, these velocity gradients are rarely integrated into habitat suitability criteria used for defining instream flow requirements, which are generally based on mean column velocity measurements at the focal point location. It is also unclear how velocity gradient exploitation differs among sympatric drift‐feeding species. We measured the use of velocity gradients by two sympatric juvenile salmonids, Coho Salmon Oncorhynchus kisutch and steelhead O. mykiss, in a midorder cobble–boulder‐dominated river. We compared focal point velocities of fish to adjacent velocities within their foraging area and compared the magnitude of velocity and kinetic energy gradients between species. We then explored how lateral velocity gradients may bias instream flow assessments by deriving two sets of velocity habitat suitability curves (HSCs): conventional HSCs using average water column velocities measured at focal point locations and spatially averaged HSCs incorporating adjacent velocities (four body lengths from focal points). These contrasting HSCs were then used as input into the physical habitat simulation model to predict the influence of flow on habitat availability. Both species often used focal velocities that were lower than adjacent points, but the magnitude of these velocity gradients was higher for steelhead, consistent with known differences in foraging behavior, habitat selection, and physiology. Incorporating adjacent velocities into HSCs resulted in a ~40% (steelhead) and ~10% (Coho Salmon) increase in flows predicted to optimize habitat availability. Thus, small‐scale heterogeneity in velocity used by drift‐feeding fish can lead to large biases in flow assessments.

Periphery excitation of laser-induced CN fluorescence in plasma using laser-induced breakdown spectroscopy for carbon detection

Carbon is hard to be sensitively detected in laser-induced breakdown spectroscopy (LIBS). The optical emission can be significantly enhanced by resonantly exciting CN radicals in the plasma center using LIBS assisted with laser-induced fluorescence (LIBS-LIF). However, the nitrogen source for CN formation is provided by ambient gas. Therefore, we propose a new approach of periphery excitation in plasma to improve CN fluorescence. The optical and spatial characteristics of CN radicals in plasma were discussed. A fluorescence map was established by combining focal point location and fluorescent intensity, demonstrating that plasma periphery had 4.2 times stronger fluorescence than the center.

Heterogeneous Angular Spectrum Method for Trans-Skull Imaging and Focusing

Ultrasound, alone or in concert with circulating microbubble contrast agents, has emerged as a promising modality for therapy and imaging of brain diseases. While this has become possible due to advancements in aberration correction methods, a range of applications, including adaptive focusing and tracking of the microbubble dynamics through the human skull, may benefit from even more computationally efficient methods to account for skull aberrations. Here, we derive a general method for the angular spectrum approach (ASA) in a heterogeneous medium, based on a numerical marching scheme to approximate the full implicit solution. We then demonstrate its functionality with simulations for (human) skull-related aberration correction and trans-skull passive acoustic mapping. Our simulations show that the general solution provides accurate trans-skull focusing as compared to the uncorrected case (error in focal point location of 1.0 ± 0.4 mm vs 2.2 ± 0.7 mm) for clinically relevant frequencies (0.25-1.5MHz), apertures (50-100 mm), and targets, with peak focal pressures approximately 30 ± 17% of the free field case, with the effects of skull attenuation and amplitude shading included. In the case of source localization, our method leads to an average of 75% error reduction (from 2.9 ± 1.8 mm to 0.7 ± 0.5 mm) and 40-60% increase in peak intensity, evaluated over the range of frequencies (0.4-1.2 MHz), apertures (50-100 mm), and point source locations (40 mm by 50 mm grid) as compared to the homogeneous medium ASA. Overall, total computation times for both focusing and point source localization of the order milliseconds (166 ± 37 ms, compared with 44 ± 4 ms for the homogeneous ASA formulation) can be attained with this approach. Collectively our findings indicate that the proposed phase correction method based on the ASA could provide a computationally efficient and accurate method for trans-skull transmit focusing and imaging of point scatterers, potentially opening new possibilities for treatment and diagnosis of brain diseases.

Beamforming Microwave-Induced Thermoacoustic Imaging for Screening Applications

This paper presents a beamforming microwave-induced thermoacoustic (TA) imaging system for screening applications. Near-field/quasi-near-field beamforming with multiple applicators focuses the radio-frequency (RF) energy to the target location in depth and enhances the TA signal generation, thereby lowering the peak-power requirements of the solid-state RF power amplifier (PA). More importantly, the proposed beamforming method reduces surface heating at the skin interface by distributing the excitation power over multiple sites and, hence, reducing the per-element peak at a similar acoustic signal-to-noise ratio (SNR). A 3-D printed setup in a conformal configuration is designed and used to demonstrate signal enhancement with RF focusing. By tuning the phase of each channel, the system can focus RF energy to specific locations and steer the focal point location across the region of interest. With a four-element array, measurements confirm a 15.8-dB acoustic intensity SNR improvement compared with a single power-limited excitation and 3.8-dB improvement compared to a PA with the same total peak power (i.e., $4\times P_{\text {out}}$ ). The results herein suggest the potential benefits of the proposed beamforming system and imply further enhancements once scaled to a larger array.

A chirp excitation for focussing flexural waves

In this paper, the dispersive nature of flexural waves is exploited to generate a shock response at an arbitrary location on a waveguide. The input waveform is an up-chirp whose instantaneous frequency is chosen to ensure synchronous arrival at an arbitrary focal point. An analytical expression is derived for the required chirp waveform as a function of bandwidth and focal point location given prior knowledge of the dispersion relation.The principle is illustrated for an analytical model of a uniform beam. Simulated results show that it is possible, in theory, to achieve peak responses that are at least an order of magnitude larger than steady state response due to harmonic excitation. Further, the peak response increases with approximately the square root of distance from the point of excitation when damping is negligible. Velocity, acceleration, normal strain and shear stress exhibit qualitatively similar results which differ quantitatively owing to their different frequency responses with respect to the input.A single degree-of-freedom model of an electrodynamic shaker is coupled to the analytical beam model in order to predict peak mechanical responses per peak input voltage of the chirp waveform. The coupled electromechanical model is then validated experimentally through both frequency response and transient measurements. The technique is potentially applicable to situations where a large and reasonably localised transient response is required on a beam or plate-like structure using minimal instrumentation.

Spatiotemporal evolution of the plasma from dual-pulsed laser-induced breakdown in an atmospheric air

The spatiotemporal evolution of dual-pulsed laser-induced breakdown (DPLIB) was experimentally investigated in a quiescent atmospheric air. DPLIB with time intervals between pulses of 30–100 ns and pulse energies of 10–30 mJ were compared to a single laser-induced breakdown of the same total energy. An intensified CCD camera was used to capture direct images from the onset of the breakdown until 300 ns after the breakdown. The spatial and temporal temperature and electron number density were obtained from the N II spectrum at 500 nm. With increasing laser pulse energy, the breakdown perimeter, temperature and electron number density all increase. For DPLIB, the second breakdown occurs on the outside axial edges of the first breakdown increasing the breakdown perimeter. The uneven distribution of energy to the plasma creates an uneven temperature distribution. The electron number density is increased at the edges of the DPLIB for times less than 150 ns after the first breakdown. Depending on the electron number density of the first breakdown and the focal point location of the second breakdown, the second breakdown could occur on either the near side (closest to the focusing lens) or the far side (furthest from the focusing lens) of the focal point in the axial direction of the laser beam.

Computational study of acoustic streaming and heating during acoustic hemostasis

High intensity focused ultrasound (HIFU) has many applications ranging from thermal ablation of cancer to hemostasis. Although focused ultrasound can seal a bleeding site, physical mechanism of acoustic hemostasis is not fully understood yet. To understand better the interaction between different physical mechanisms involved in hemostasis a mathematical model for acoustic hemostasis is developed. This model comprises the nonlinear Westervelt equation and the bioheat equations in tissue and blood vessel. In a three dimensional domain, the nonlinear hemodynamic equations are coupled with the acoustic and thermal equations. Convective cooling and acoustic streaming effects are incorporated in the modeling study. Effect of acoustic streaming on the blood flow out of the wound has been studied for two wound shapes and different sonication angles. It was theoretically shown that if focused ultrasound beam is applied directly to the bleeding site, the flow out of the wound can be reduced due to the acoustic streaming effect. Bleeding can be completely stopped even for a big wound, if the focal point location, ultrasound power and sonication angle are appropriately chosen. The sonication angles should be chosen in the range between 45° and 90°. The temperature around 70°C can be achieved within a second on the blood vessel wall, thus showing the theoretical possibility of sealing the bleeding site by focused ultrasound.

Development of an Omnidirectional-Capable Electromagnetic Shock Wave Generator for Lipolysis.

Traditional methods for adipose tissue removal have progressed from invasive methods such as liposuction to more modern methods of noninvasive lipolysis. This research entails the development and evaluation of an omnidirectional-capable flat-coil electromagnetic shock wave generator (EMSWG) for lipolysis. The developed EMSWG has the advantage of omnidirectional-capable operation. This capability increases the eventual clinical usability by adding three designed supports to the aluminum disk of the EMSWG to allow omnidirectional operation. The focal pressures of the developed EMSWG for different operating voltages were measured, and its corresponding energy intensities were calculated. The developed EMSWG was mounted in a downward orientation for lipolysis and evaluated as proof of concept. In vitro tests on porcine fatty tissues have been carried out. It is found that at a 6 kV operating voltage with 1500 shock wave exposures, a 2 cm thick subcutaneous hypodermis of porcine fatty tissue can be ruptured, resulting in a damaged area of 1.39 mm2. At a 6.5 kV operating voltage with 2000 shock wave exposures, the damaged area is increased to about 5.20 mm2, which can be enlarged by changing the focal point location, resulting in significant lipolysis for use in clinical applications.

The effect of receiver geometry on the optical performance of a small-scale solar cavity receiver for parabolic dish applications

Concentrated Solar Power (CSP) can be used as an efficient low cost energy conversion system to produce different types of energy, such as electricity, through the use of concentrated parabolic dish systems. In the study of CSP, most of the researchers focus on the heat losses and their relationships to the receivers' geometries. The present study concentrates on the optical efficiency as well as the flux distribution of the three different geometries: cylindrical, conical and spherical, of a cavity receiver, with the objective of analysing their behaviour using an advanced ray tracing method.The results of this study have shown that there is a connection between the flux distribution on the internal surfaces of the cavities and their optical efficiency. Moreover, the conical shape receiver received, as well as absorbed, a higher amount of reflected flux energy than the other shapes. The optical efficiency reached 75.3%, 70.1% and 71.5% for the conical, spherical and cylindrical shapes respectively at surface absorptivity of 85%. Also, the focal point location depends on the shape of the cavity receiver and its absorptivity. Thereby, there is an optimum distance for each design depending on these two factors. The results of the simulated work are validated using the experimental work found in the literature.

The optical efficiency of three different geometries of a small scale cavity receiver for concentrated solar applications

The demand for energy is continually increasing day after day; but at the same time, investigations around the world into sustainable sources of power are growing in number. Concentrated Solar Power (CSP) can act as an efficient low cost energy conversion system to produce electricity which could lead to reducing the continuous demand on conventional fossil fuels. Most of the literature concerning CSP concentrates on the heat losses and their relationship to the receivers’ geometries; where these receivers are evaluated according to their thermal efficiency. The majority of the literature has often neglected heat gain enhancement by the receivers’ geometries, which helps to increase the heat transfer to the working fluid. This work concentrates on the optical efficiency as well as the heat flux distribution of three different geometries. The cylindrical, conical and spherical geometries of a cavity receiver are considered with the objective of analysing their optical and thermal behaviour optically and thermally, using the ray tracing method and a Computational Fluid Dynamic (CFD) model. The results showed that the conical shape of the receiver gathered, as well as absorbed, a higher amount of reflected flux energy than the other shapes, with about 91% and 82% for 75% and 85% absorption ratios respectively. The cavity receiver shapes and their absorption ratio are key parameters which affect the focal point location; thereby there is an optimum distance for each design depending on these two parameters. The results of the simulated work are validated using the experimental work found in the literature. Overall, in order to evaluate the heat balance, 3-D thermal analysis was employed using Fluent 15 and the amount of heat losses for the three shapes was determined. It was observed that the conical shape receiver experienced a lower heat loss. To ensure more confidence in the results, the thermal outcomes were validated against experimental works in the literature and they demonstrated good agreement.

Simple Broadband Quasi-Optical Spatial Multiplexer in Substrate Integrated Technology

We present a new type of broadband spectral-spatial quasi-optical decomposer for microwave analog signal processing fully implemented in substrate integrated waveguide (SIW) technology. An input SIW is modulated to couple energy to a near-field focused surface wave inside the hosting substrate. Due to its inherent spatially dispersive response, the focal point location varies with frequency. Thus, by placing output SIW ports at the appropriate positions, the focused signal can be extracted for each frequency providing instantaneous spectral decomposition. A design with six output channels from 11 to 16 GHz with 4-dB insertion losses and 1-ns group-delay swing is illustrated. Experiments on a prototype are reported to prove the feasibility of the proposed approach.