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The waveguide acoustic black hole (WAB) effect is a promising approach for controlling wave propagation in various applications, especially for attenuating sound waves. While the wave-focusing effect of structural acoustic black holes has found widespread applications, the classical ribbed design of waveguide acoustic black holes (WABs) acts more as a resonance absorber than a true wave-focusing device. In this study, we employ a computational design optimization approach to achieve a conceptual design of a WAB with enhanced wave-focusing properties. We investigate the influence of viscothermal boundary losses on the optimization process by formulating two distinct cases: one neglecting viscothermal losses and the other incorporating these losses using a recently developed material distribution topology optimization technique. We compare the performance of optimized designs in these two cases with that of the classical ribbed design. Simulations using linearized compressible Navier-Stokes equations are conducted to evaluate the wave-focusing performance of these different designs. The results reveal that considering viscothermal losses in the design optimization process leads to superior wave-focusing capabilities, highlighting the significance of incorporating these losses in the design approach. This study contributes to the advancement of WAB design and opens up new possibilities for its applications in various fields.

The geodesic Luneburg lens has been revisited as a suitable solution for applications requiring directive beams in the millimeter waveband. Among its advantages, its rotational symmetry and high efficiency stand out. However, one of its drawbacks is the need for a certain height to produce the desired focusing properties of the lens. Here, we propose a low-profile solution based on rotationally symmetric ridges that mimic, similar to geodesic lenses, the effective refractive index of a Luneburg lens. Moreover, we show that both rectangular and trapezoidal ridges perform similarly, opening the possibility for other manufacturing techniques. We demonstrate this concept with a prototype that is fully metallic and provides a scanning range of +/- 62 degrees over a broadband of operation, from 24 to 34 GHz. In this prototype, the height of the lens is 18 times more compact than the original Rinehart-Luneburg lens, allowing the lens to be vertically stacked, which is beneficial, for example, for producing linear arrays. This technique could be used to produce other type of lenses., QC 20240715

Unequal “directivity orders” between two figure8 directional microphones/hydrophones are proposed and analyzed in this paper for beamforming. Specifically, two figure 8 sensors here, possibly of different “directivity orders”, are (i) orthogonally oriented to facilitate spatial filtering in both the azimuth and the elevation, and (ii) spatially colocated with an isotropic sensor (thereby decoupling the incident source's azimuth-elevation-radial dimensions from the impinging signal's time-frequency dimensions). This versatility (in the sensors’ diverse “directivity orders”) contrasts with all prior open literature on beamforming using a colocated triad of possibly directional sensors. Instead, this paper analytically explores how unequal directivity orders between two perpendicularly colocated figure-8 acoustic sensors would affect the triad array's “spatial matched filter” beam steering. The resulting “actionable” insights show which directivity-order combinations allow the beam of full maneuverability toward any azimuthal direction, and which directivity-order combinations only partial maneuverability.

In this article we propose a conceptual framework to study ensembles of conformal predictors (CP), that we call Ensemble Predictors (EP). Our approach is inspired by the application of imprecise probabilities in information fusion. Based on the proposed framework, we study, for the first time in the literature, the theoretical properties of CP ensembles in a general setting, by focusing on simple and commonly used possibilistic combination rules. We also illustrate the applicability of the proposed methods in the setting of multivariate time-series classification, showing that these methods provide better performance (in terms of both robustness, conservativeness, accuracy and running time) than both standard classification algorithms and other combination rules proposed in the literature, on a large set of benchmarks from the UCR time series archive.

Imaging is a field of mathematics and physics that aims to retrieve information about the internal structure of an object that can only be accessed on its boundary. Many imaging methods are based on the following principle: a source outside of the object emits a wave. The wave propagates through the object. Wherever the physical structure of the object changes, scattered waves are induced. These scattered waves are measured by receivers outside of the object, and these scattered data are used to invert for the interior composition of the medium under investigation. The Marchenko integral was originally introduced for one-dimensional inverse scattering problems in the context of quantum mechanics. It can be related to Green's functions and so-called focusing functions - fields that produce a focus when injected into a medium from a single side. About ten years ago, the Marchenko integral was extended to two and three dimensions. This paved the way for, e.g., the elimination of imaging artefacts due to multiple scattering and Green's function retrieval for virtual source locations. However, many questions about the full potential as well as the accuracy of the Marchenko equation in two and three dimensions remain unanswered. In this thesis we present a new derivation for the multidimensional Marchenko integral. Our derivation is based on a generalised framework for wavefield focusing and circumvents the limiting assumptions of the previous extension. As we use partial differential equations rather than integral equations to define focusing functions, it allows for new physical insights. For instance, our approach indicates that it is possible to model Marchenko-type focusing functions with a conventional wave equation. Ultimately, this enables us to study Marchenko-type focusing in different 2D and 3D media and learn about the accuracy of the concept. We present a straightforward modelling approach for 1D as well as a least-squares modelling approach for 2D and 3D. Th

This paper proposes an accurate geometric registration method by estimating blur effects from a degraded image with image markers for augmented reality. A small and inexpensive camera used in augmented reality systems sometimes captures degraded images because its focus and/or iris are fixed. This degradation of a captured image affects the accuracy of the detected positions of feature points in the image. The proposed method improves the accuracy of the estimated camera position and posture by estimating blur effects from the captured image, and by correcting the detected positions of feature points through the results. The effectiveness of the method is confirmed through experiments of corner estimation from simulated images and extrinsic camera parameter estimation from real images., ISMAR 2007 : 6th IEEE and ACM International Symposium on Mixed and Augmented Reality , Nov 13-16, 2007 , Nara, Japan

There are many roles to play in the bug fixing process in open source software development. A developer called ``Committer'', who has a permission to submit a patch into software repository, plays a major role in this process and hold a key to the successfulness of the project. In this work, we have observed each committer activities from the Eclipse-Platform bug tracking system and version archives. Despite the importance of committer's activities, we suspected that sometimes committers can make mistakes, which have negative consequences to the bug fixing process. Our research focus on studying the consequences of each committer's activities to this process. We collected each committer's historical data and evaluated each of them by comparing the more cautiousness to less cautiousness committers. Then we looked deeper into each committer's characteristics to see the reasons why some committers tend to make mistakes more than the others. From our results, we would like to make a humbly suggestion to the OSS's committers to be aware of their importance to the projects and be cautious before doing their jobs., 2011 Joint Conference of the 21st International Workshop on Software Measurement and the 6th International Conference on Software Process and Product Measurement, 3-4 Nov. 2011, Nara, Japan

To enhance the quality of software, many software development support tools and software development methodologies have been proposed. However, not all proposed tools and methodologies are widely used in software development. We assume that the evaluation of tools and methodologies by developers is different from the evaluation by researchers, and that this is one of the reasons why the tools and methodologies are not widely used. We analyzed the decision criteria of software developers as applied to the tools and methodologies, to clarify whether the difference exists or not. In behavioral economics, there are theories which assume people have biases, and they do not always act reasonably. In the experiment, we made a questionnaire based on behavioral economics, and collected answers from open source software developers. The results suggest that developers do not always act to maximize expected profit because of the certainty effect and ambiguity aversion. Therefore, we should reconsider the evaluation criteria of tools such as the f-measure or AUC, which mainly focus on the expected profit., SANER 2016 : 2016 IEEE 23rd International Conference on Software Analysis, Evolution, and Reengineering, 14-18 March 2016, Suita, Japan

Continuous microfluidic focusing of particles, both synthetic and biological, is significant for a wide range of applications in industry, biology and biomedicine. In this study, we demonstrate the focusing of particles in a microchannel embedded with glass grooves engraved by femtosecond pulse (fs) laser. Results showed that the laser-engraved microstructures were capable of directing polystyrene particles and mouse myoblast cells (C2C12) towards the center of the microchannel at low Reynolds numbers (Re < 1). Numerical simulation revealed that localized side-to-center secondary flows induced by grooves at the channel bottom play an essential role in particle lateral displacement. Additionally, the focusing performance proved to be dependent on the angle of grooves and the middle open space between the grooves based on both experiments and simulation. Particle sedimentation rate was found to critically influence the focusing of particles of different sizes. Taking advantage of the size-dependent particle lateral displacement, selective focusing of micrometer particles was demonstrated. This study systematically investigated continuous particle focusing in a groove-embedded microchannel. We expect that this device will be used for further applications, such as cell sensing and nanoparticle separation in biological and biomedical areas.

This study presents a promising method for microwave imaging using the mathematical characteristics of the Veselago lens. The Veselago lens is a perfect lens that exhibits unique focusing phenomena. The research aims to achieve several key objectives: 1) to investigate the impact of the Veselago lens in regularizing the ill-posedness of the inverse scattering problem; 2) to formulate a simpler solution to the inverse problem by deriving a regularizing Green's operator that improves matrix conditionality, facilitating inversion; 3) to develop a new mathematical foundation for faster, non-expensive, and non-iterative algorithms; and 4) to enhance the accuracy and spatial resolution of reconstructed images, surpassing the diffraction limit and allowing for sub-wavelength resolution. To accomplish these objectives, a comprehensive study was conducted to understand the implications of incorporating the Veselago lens in the inverse scattering problem associated with microwave imaging. A new Helmholtz equation was derived, and explicit analytic expressions for the corresponding Green's function were obtained. The lens was applied in an imaging scenario with an actual lens, and a novel data equation employing the Veselago lens Green's function was used to solve the inverse problem. Numerical analysis of synthetic data confirmed the efficacy of the new operator, demonstrating superior quality reconstructed images even for small features. The study also introduced novel filtering techniques to address noise in reconstructed images caused by the Veselago lens inverse operator. These techniques utilized truncated Singular Value Decomposition of the operators. Although the physical implementation of a Veselago lens may pose challenges, the research explored the possibility of using a virtual Veselago lens in microwave imaging. A mathematical formulation demonstrated the feasibility of virtualizing the lens utilization, allowing for high-quality imaging without the physical prese

This article is based on the concept of exposing the world through the lens of cinema by a cinematographer. Without a cinematographer, movies are not as visually and emotionally impactful on audiences. Cinema is trying to penetrate beyond things and create an utterly phenomenological experience. Cinematographers are responsible for creating the audience's emotions through various cinematic techniques. It is perhaps one of their most significant roles is to promote the cinematic frame as a mediator. This research claims that the cinema’s camera illuminates the world through focusing and framing components. It provides the cinematic image with a cinematic presence and makes it feasible in a phenomenological sense (return to things themselves). And eventually, this leads to viewer buoyancy and immersiveness.

This paper presents a treatment of aspectual formation in Russian based on the eventive characteristics of verbal forms. Unlike other proposals of this kind, my hypothesis assumes that aspect-changing processes in this language transform the event structure of the verb in two different ways: the perfectivizing prefixation selects for certain parts of the simple event as well as adds some extra bits of idiosyncratic meaning related to the manner of action (intensity, attenuation, adversity, etc.); the imperfectivizing suffixation, in turn, is in charge of multiplying events or visualizing their preparatory phase. Thus, it is also confirmed that the mentioned processes are applied at different levels: the former is basically lexical and the letter syntactic. Concrete examples of the event structure transformations throughout the aspectual derivation are given.

Marchenko-type integrals typically relate so-called focusing functions and Green's functions via the reflection response measured on the open surface of a volume of interest. Originating from one dimensional inverse scattering theory, the extension to two and three dimensions set in motion various new developments regarding imaging in complex materials. This extension, however, is based on wavefield decomposition inside the volume and a truncated medium state, i.e. a version of the medium that is reflection-free underneath the focusing location, suggesting that evanescent, refracted and diving waves cannot be included in the representation. We elaborate on a new derivation for Marchenko-like integrals that (i) extends the concept of wavefield focusing by using a generalised homogeneous Green's function, (ii) is based on partial differential equations and thereby allows for additional insights and a new physical intuition for Marchenko equations, (iii) unifies wavefield focusing for open and closed boundary systems, (iv) does not require wavefield decomposition or a truncated medium state, thus including the full wavefield Green's function, (v) enables using forward modelling to obtain, e.g., Marchenko-type, time-compact focusing functions. We place a particular focus on the latter point, illustrating and investigating how to solve the underlying partial differential equations for various types of focusing functions. This paves the way for a deeper understanding of focusing functions as well as advanced full wavefield Marchenko schemes. While the derivations are generally presented for the 3D case, we show numerical examples in 1D., Applied Geophysics and Petrophysics

In this article, a systematic approach is suggested to identify unexplored opportunities and recommend a business model for sustainability for startups. Considering a particular sector, following the proposed approach, an entrepreneur should first determine the importance of the different areas which could be improved in that sector. Then the current performance of these areas is also evaluated. Subsequently, by an importance-performance analysis, an entrepreneur can obtain information on areas that can be improved but that are currently underperforming. These are the areas that can be considered as opportunities with high success rate by the entrepreneurs for being survival. The proposed approach is applied to the case of dairy farming in The Netherlands. Data is collected from a sample of top experts in this field and analyzed using best-worst method and importance-performance analysis. We found that, of the technological, social, and organizational areas in Dutch dairy farming, the social area is the one area where the performance does not reflect its importance. Following the business model for sustainability, the entrepreneurs are advised to adopt archetypes that are suitable for the social area.

Ellipsoidal and plane-elliptical surfaces are widely used as reflective, point-to-point focusing elements in many optical systems, including X-ray optics. Here the classical optical path function approach of Fermat is applied to derive a closed-form expression for these surfaces that are uniquely described by the object and image distances and the angle of incidence at a point on a mirror surface. A compact description facilitates design, modeling, fabrication, and testing to arbitrary accuracy. Congruent surfaces in two useful coordinate systems - a system centered on the ellipsoid's axes of symmetry and a mirror-centered or `vertex' system with the surface tangent to the xy plane at the mirror's center - are presented. Expressions for the local slope and radii of curvature are derived from the result, and the first several terms of the Maclauren series expansion are provided about the mirror center.

On X-ray beamlines and telescopes, glancing-incidence mirrors with parabolic profiles are used to collimate, focus, and collect light. Here, analytic descriptions for paraboloidal, plane-parabolic, and parabolic cylindrical mirrors in several congruent geometries that are commonly used in fabrication, metrology, and modeling are provided. The exact expressions are derived directly from Fermat's principle, without coordinate transformations, in several mirror-centered coordinate systems, including one with the surface tangent to the central point of intersection. Coefficients for a sixth-order polynomial series approximation are calculated for that coordinate system.

Over the past few years, sub-surface imaging techniques at the nano-scale have become increasingly important in the semiconductor industry, whereby voids, cracks and other heterogenous features can be detected using disturbances in penetrating waves inside the substrate. A certain modality called photo-acoustic subsurface Atomic Force Microscopy (passAFM) is currently in development at the DMN group in TU Delft. PassAFM uses two fs pulsed lasers to generate and detect acoustic waves inside an AFM cantilever. This technique promises a lateral resolution of subsurface imaging in the order of the AFM tip size. It is required to focus the acoustic waves inside the tip and obtain sufficient acoustic power to detect a signal back from the tip. Therefore, acoustic lensing devices are designed and the improvement in detected signal is studied in this research., Mechanical Engineering | High-Tech Engineering

Monostatic pursuit refers to the operating mode formed by two monostatic synthetic aperture radar (SAR) systems that follow an identical orbit with a separation in a time of several seconds. The detected changes between SAR scenes with several seconds of time difference are most likely the changes caused by ground moving targets. Hence, this operating mode opens an opportunity to detect ground moving targets by SAR change detection methods. This article investigates this possibility to detect ground moving targets using change detection and to combine change detection and ground moving target indication (GMTI) for GMTI. In this combination, a GMTI method will help to classify the detected changes obtained with a change detection method. Some GMTI results are provided in the article based on the measurements in the monostatic pursuit mode with deployed targets, conducted by TerraSAR-X and TanDEM-X in Sweden in early 2015., open access

Within Artificial Intelligence, Deep Learning (DL) represents a paradigm that has been showing unprecedented performance in image and audio processing by supporting or even replacing humans in defect and anomaly detection. The railway sector is expected to benefit from DL applications, especially in predictive maintenance applications, where smart audio and video sensors can be leveraged yet kept distinct from safety-critical functions. Such separation is crucial, as it allows for improving system dependability with no impact on its safety certification. This is further supported by the development of DL in other transportation domains, such as automotive and avionics, opening for knowledge transfer opportunities and highlighting the potential of such a paradigm in railways. In order to summarize the recent state-of-the-art while inquiring about future opportunities, this paper reviews DL approaches for the analysis of data generated by acoustic and visual sensors in railway maintenance applications that have been published until August 31st, 2021. In this paper, the current state of the research is investigated and evaluated using a structured and systematic method, in order to highlight promising approaches and successful applications, as well as to identify available datasets, current limitations, open issues, challenges, and recommendations about future research directions.

Attending to the challenges of describing first-person experience, this article illustrates different uses of the Focusing method in interaction design and HCI, offering a systematic way of accessing the subtle qualities of lived experiences for design use. In this approach, the implicit bodily knowledge -or felt sense- becomes the material capture of aesthetic experiences used to inform data collection, ideation and prototyping. We offer a high-level, yet systematic coverage of Focusing applied to two case studies, informing both a set of instructions to use the method and a series of design considerations to adopt this understudied tool of introspection in interaction design research and practice., QC 20220914

This work reviews and compares different airgap reluctance calculation approaches with experimental results, focusing on the Schwarz-Christoffel transformation. The modelling of the airgap reluctance in two dimensions is tested against FEM simulations for typical airgap geometries. Then, an approach to obtain the three-dimensional reluctance is shown, and the limited experimental data shown in previous works is expanded to validate the different airgap calculation methods in EE cores. For the case of pot cores, a geometrical transformation is proposed and validated, allowing the application of the Schwarz-Christoffel methodology to other common core geometries.

Nanocellulose is regarded as a green and renewable nanomaterial that has attracted increased attention. In this study, we demonstrate that nanocellulose materials can exhibit high thermal conductivity when their nanofibrils are highly aligned and bonded in the form of filaments. The thermal conductivity of individual filaments, consisting of highly aligned cellulose nanofibrils, fabricated by the flow-focusing method is measured in dried condition using a T-type measurement technique. The maximum thermal conductivity of the nanocellulose filaments obtained is 14.5 W/m-K, which is approximately five times higher than those of cellulose nanopaper and cellulose nanocrystals. Structural investigations suggest that the crystallinity of the filament remarkably influence their thermal conductivity. Smaller diameter filaments with higher crystallinity, that is, more internanofibril hydrogen bonds and less intrananofibril disorder, tend to have higher thermal conductivity. Temperature-dependence measurements also reveal that the filaments exhibit phonon transport at effective dimension between 2D and 3D., QC 20230613

Die Hauptziele der Studie waren (1) Effekte von intern versus extern fokussiertem Training (IF, EF) auf die Bewegungsqualitätsbeurteilung von GerätturnenKampfrichterInnen bezüglich Gleichgewichtsaufgaben auf einem Schwebebalken zu untersuchen; (2) den Zusammenhang zwischen der Bewegungsqualitätsbeurteilung und der Bewegungskomplexität abzuklären. Zusätzlich wurde überwacht, ob sich die IF- versus EFGruppe hinsichtlich der Neigung zur bewussten Beteiligung an der Bewegungssteuerung (trait reinvestment) unterschied. Es wurde hypothetisiert (H1), dass EF überlegen gegenüber IF sein würde in Bezug auf die Beurteilung der Bewegungsqualität nach einem Schwebebalkentraining mit entweder extern oder intern fokussierten Anweisungen, und (H2), dass die Beurteilung der Bewegungsqualität durch KampfrichterInnen mit der objektiv gemessener Bewegungskomplexität korrelieren würde. Dreiundzwanzig Probanden wurden nach dem Zufallsprinzip zugeteilt in eine IF- oder EF-Gruppe und absolvierten einen Vor- und Nachtest, mit jeweils drei Aufgaben die in einer Einzel- und Doppelaufgabenbedingung durchgeführt wurden: Neutral- und Zehenspitzen Gehaufgabe (walking neutral, WN; walking tiptoes, WT) und Tandem-zu-Zehenspitzen Aufgabe (tandem to tiptoes, TTT). Die Bewertungen der Bewegungsqualität wurden von (inter)nationalen KampfrichterInnen im Gerätturnen ermittelt. An den kinematischen Ganzkörperdaten wurden Hauptkomponentenanalysen (principal component analyses) durchgeführt, um Hauptbewegungen (principal movements, PMs) zu extrahieren. Die Bewegungskomplexität wurde bestimmt, indem die kumulativen relativen Varianzen der aufgabenspezifisch dominantesten PMs berechnet wurden. Es wurden signifikante Haupteffekte des Trainings in allen drei Doppelaufgaben sowie in der WT Einzelaufgabe gefunden, wobei sowohl IF- als auch EF-Training die Bewegungsqualitätsbeurteilung verbesserte. Die TTT Einzelaufgabe zeigte einen signifikanten Interaktionseffekt, welcher darauf hindeutete, dass das EF- effekti, The main objectives were (1) to investigate internal versus external focus training effects (IF, EF) on the movement quality judgement of gymnastics related balance tasks on a balance beam, and (2) to link the movement quality judgement to the movement’s complexity. It was additionally monitored whether the IF versus EF group differed in terms of the propensity to being consciously involved in the action control (trait reinvestment). It was hypothesized (H1) that EF would be superior to IF in terms of movement quality judgement, after a balance beam training with either externally or internally focussed instructions, and (H2) that movement quality judgement would be correlated to the movement complexity, revealing an objective measure of movement quality. Twenty-three subjects were randomly assigned to an IF or EF group and completed a pre- and post-test, containing three tasks performed in a single and dual task condition: neutral and tiptoes walking tasks (WN, WT) and tandem-to-tiptoes task (TTT). Movement quality judgement scores were obtained by (inter)national judges in artistic gymnastics. Principal component analyses were performed on the whole-body kinematic data, to extract principal movements (PMs). Movement complexity was determined by calculating the cumulative relative variances of the task specific most dominant PMs. Significant training effects based on the IF as well as EF instructions could be established to enhance movement quality judgement in most tasks (all except WN and TTT single task). The TTT single task showed a significant interaction effect, revealing EF to be superior to IF (supporting H1). H2 was supported in a substantial fraction of the performed correlations. The IF versus EF group did not differ significantly in terms of conscious motor control (trait reinvestment). These results suggest that form-based sports like gymnastics can benefit from both IF and EF. It is suggested that EF instructions could be more effective than IF instru, Simone Beekhuizen, Zusammenfassung in deutscher Sprache, Masterarbeit University Innsbruck 2022

Phased arrays in near-field communication allow the transmitter to focus wireless signals in a small region around the receiver. Proper focusing is achieved by carefully tuning the phase shifts and the polarization of the signals transmitted from the phased array. In this paper, we study the impact of polarization on near-field focusing and investigate the use of dynamic polar-ization control (DPC) phased arrays in this context. Our studies indicate that the optimal polarization configuration for near-field focusing varies spatially across the antenna array. Such a spatial variation motivates the need for DPC phased arrays which allow independent polarization control across different antennas. We show using simulations that DPC phased arrays in the near-field achieve a higher received signal-to-noise ratio than conventional switched- or dual-polarization phased arrays., Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public., Team Nitin Myers, Microwave Sensing, Signals & Systems, Signal Processing Systems

Unmanned aerial vehicle (UAV) has been more and more widely used in military and civilian, with its unique advantages of flexibility, convenience, and wide coverage. As flying stations, UAVs can quickly set up relay communication links for different missions, to enhance the receiving signal power, increase the system capacity, and expand the communication coverage. In this paper, we investigate a two-way multi-hop UAV relaying network, where there are two ground users as sources and multiple UAVs as relays to help the two ground sources exchange information. For purpose of enhancing the efficiency of the investigated UAV-assisted relaying, we come up with a productive two-way multi-hop UAV relaying pattern, which can achieve a data rate of 1 2 data packets per time slot with decode-andforward protocol. Then, we further formulate a joint transmit power and trajectory optimization problem for the UAVs in this two-way multi-hop relaying scenario. The formulated problem is non-convex which makes it difficult to solve directly, hence we propose an iterative algorithm to obtain an approximate optimal solution based on block coordinate descent and successive convex optimization techniques. Numerical results demonstrate that our proposed two-way multi-hop UAV relaying network achieves significant throughput gains compared with other benchmark schemes. IEEE

A Green's function in an acoustic medium can be retrieved from reflection data by solving a multidimensional Marchenko equation. This procedure requires a priori knowledge of the initial focusing function, which can be interpreted as the inverse of a transmitted wavefield as it would propagate through the medium, excluding (multiply) reflected waveforms. In practice, the initial focusing function is often replaced by a time-reversed direct wave, which is computed with help of a macro velocity model. Green's functions that are retrieved under this (direct-wave) approximation typically lack forward-scattered waveforms and their associated multiple reflections. We examine whether this problem can be mitigated by incorporating transmission data. Based on these transmission data, we derive an auxiliary equation for the forward-scattered components of the initial focusing function. We demonstrate that this equation can be solved in an acoustic medium with mass density contrast and constant propagation velocity. By solving the auxiliary and Marchenko equation successively, we can include forward-scattered waveforms in our Green's function estimates, as we demonstrate with a numerical example., Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public., Applied Geophysics and Petrophysics

This communication proposes a broadband and efficient integrated focal plane array solution based on a near-field focused connected array of slots. The focused aperture provides: 1) broadband and highly efficient illumination of the quasi-optical system and 2) scanning capabilities within a focusing system. The connected array antenna in turn allows for a fully integrated solution that can synthesize a focused aperture while providing broadband impedance matching. Focused connected array antennas enable the coupling to a reflector system over bandwidths in excess of one octave and with aperture efficiencies in excess of 60%. To demonstrate the concept, we present two printed circuit board (PCB) prototypes operating in the band 3-6 GHz and yielding more than 60% reflector aperture efficiency under broadside illumination and allowing to scan one beamwidth at the lowest frequency with a frequency-averaged scan loss of 0.2 dB. The feasibility of scaling this concept to THz frequencies and with dynamic beam-steering capabilities is discussed in the context of a superconducting device., Tera-Hertz Sensing

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Reconstructing the details of subsurface structures deep beneath complex overburden structures, such as subsalt, remains a challenge for seismic imaging. Over the past few years, the Marchenko redatuming approach has proven to reliably retrieve full-wavefield information in the presence of complex overburden effects. When used for redatuming, current practical Marchenko schemes cannot make use of a priori subsurface models with sharp contrasts because of their requirements regarding initial focusing functions, which for sufficiently complex media can result in redatumed fields with significant waveform inaccuracies. Using a scattering framework, we evaluate an alternative form of the Marchenko representation that aims at retrieving only the unknown perturbations to focusing functions and redatumed fields. From this framework, we have developed a two-step practical focusing-based redatuming scheme that first solves an inverse problem for the background focusing functions, which are then used to estimate the perturbations to focusing functions and redatumed fields. In our scheme, initial focusing functions are significantly different from previous approaches because they contain complex waveforms encoding the full transmission response of the a priori model. Our goal is the handling of not only highly complex media but also realistic data ? band-limited, unevenly sampled, free-surface-multiple contaminated data. To that end, we combine the versatility of Rayleigh-Marchenko redatuming with our scattering-based scheme allowing an extended version of the method able to handle single-sided band-limited multicomponent data. This scattering-Rayleigh-Marchenko strategy accurately retrieves wavefields while requiring minimum preprocessing of the data. In support of the new methods, we evaluate a comprehensive set of numerical tests using a complex 2D subsalt model. Our numerical results indicate that the scattering approaches retrieve accurate redatumed fields that appropriat

A novel super-resolution volumetric photoacoustic microscopy, based on the theory of structured-illumination, is proposed in this paper. The structured-illumination will be introduced in order to surpass the diffraction limit in a photoacoustic microscopy (PAM) structure. Through optical excitation of the targeted object with a sinusoidal spatial fringe pattern, the object’s frequency spectrum is forced to shift in the spatial frequency domain. The shifting in the desired direction leads to the passage of the high-frequency contents of the object through the passband of the acoustic diffraction frequency response. Finally, combining the low-frequency image with the high-frequency parts in four regular orientations in the spatial frequency domain is equivalent to imaging the targeted object with an imaging system of two-fold bandwidth and thus half lateral resolution. In order to obtain the image of out-of-focus regions and improve the lateral resolution outside the focal region of a PAM imaging system, Fourier-domain reconstruction algorithm based on the synthetic aperture focusing technique (SAFT) using the virtual detector concept is utilized for reduction in the required computational load and time. The performance of the proposed imaging system is validated with in vivo and ex vivo targets. The experimental results obtained from several tungsten filaments in the depth range of 1.2 mm, show an improvement of -6 dB lateral resolution from 55-287 μm to 25-29 μm and also an improvement of signal-to-noise ratio (SNR) from 16-22 dB to 27-33 dB in the proposed system. IEEE

Дипломний проєкт присвячений розробці пристрою для лікування хвороби Паркінсона з використанням сфокусованого ультразвуку. Об’єм дипломного проекту становить: розрахунково-пояснювальна записка – 40 сторінок та графічна частина, яка складається із 3 креслеників. Завданням даного проєкту є розробка та розрахунок первинного перетворювача (а саме, рефрактора) для фокусування ультразвуку у визначеній області мозку пацієнта, розробка електричної принципової схеми приладу та опис методики застосування розробленого пристрою в медичних цілях. У проєкті приведені розрахунки коефіцієнту акустичного тракту, дані рекомендації по вибору напруги випромінювання. Також обґрунтовано вибір схеми, підібрані необхідні сучасні електронні компоненти для її реалізації. В графічній частині курсового проекту розроблена схема електрична принципова на форматі А1, специфікація на схему електричну принципову на форматі А4(3), складальний кресленик на форматі А4(4) та функціональна схема на форматі А3 (1)., The diploma project is devoted to the development of a device for the treatment of Parkinson's disease using focused ultrasound. The volume of the diploma project is: a calculation and explanatory note - 40 pages and a graphic part, which consists of 3 drawings. The task of this project is to develop and calculate a primary transducer (namely, a refractor) for focusing ultrasound in a specific area of the patient's brain, to develop an electrical schematic diagram of the device and a description of the method of using the developed device for medical purposes. The project provides calculations of the coefficient of the acoustic path, gives recommendations for the choice of radiation voltage. The choice of the scheme is also substantiated, the necessary modern electronic components for its realization are selected. In the graphic part of the course project the electric basic scheme on the A1 format, the specification for the electric basic scheme on the A4 format, the assembly drawing on the A4 format and the functional scheme on the A3 format are developed.

Due to the discouragement to express emotion excessively in Chinese culture, Chinese people may be more inclined to show unexpressed emotions through alternative ways, such as physical symptoms, which may lead to some psychosomatic issues. Expressive arts therapy has its advantage in facilitating non-verbal expressions. But can this western approach work for Chinese population that holds different views on the relationship between physical and psychological aspects? This study explored the use of expressive art therapy to help clients with psychosomatic issues from Chinese backgrounds. The method included development of a method inspired by Focusing-oriented art therapy for a client with ulcerative colitis. After three sessions of color and word associations, body scan meditations, coloring a body outline pages and reflections, the participant gained a better body awareness, developed a closer connection with her body, and improved her bowel symptoms. Results suggested that expressive arts therapy has the potential to deal with psychosomatic issues in Chinese origin population, especially when combined with meditation. However, more research needs to be done with a larger sample, control group, and more quantitative data for further investigation.

In emerging economies, infrastructure projects are in full swing. There is a wealth of replicable experience for exploitation. Simultaneously, more technologies and methodologies require further exploration. This makes fostering ambidextrous innovation strategies (i.e., the tradeoff between exploitative and exploratory innovation strategies) a common and vital practical issue. Large infrastructure projects are unique one-off endeavors but have somewhat repetitive and persistent characteristics. It is a particular “intermediate” form between temporary projects and permanent organizations. Previous research on fostering ambidextrous innovation strategies cannot simply be replicated in large infrastructure projects. To address this issue, this article investigates the relationship between team heterogeneity and ambidextrous innovation strategies and also the role of team learning and identification in large infrastructure projects. Data were collected from 269 responses from 31 large infrastructure project delivery teams in China. The findings show that team heterogeneity has a positive linear effect on exploratory and ambidextrous innovation strategies and an inverted U-shaped effect on exploitative innovation strategies; team heterogeneity can better foster ambidextrous innovation strategies through improving team learning; the moderating role of team identification in the overall mechanism differs from the usual assumptions in permanent organizations. Overall, this article extends the existing ambidexterity research in the “intermediate” form between temporary projects and permanent organizations. It provides insights and guidance on fostering ambidextrous innovation strategies in large infrastructure projects., Integral Design and Management

We report a unique tuneable analogue trend in particle focusing in the laminar and weak viscoelastic regime of elasto-inertial flows. We observe experimentally that particles in circular cross-section microchannels can be tuned to any focusing bandwidths that lie between the “Segre-Silberberg annulus” and the centre of a circular microcapillary. We use direct numerical simulations to investigate this phenomenon and to understand how minute amounts of elasticity affect the focussing of particles at increasing flow rates. An Immersed Boundary Method is used to account for the presence of the particles and a FENE-P model is used to simulate the presence of polymers in a Non-Newtonian fluid. The numerical simulations study the dynamics and stability of finite size particles and are further used to analyse the particle behaviour at Reynolds numbers higher than what is allowed by the experimental setup. In particular, we are able to report the entire migration trajectories of the particles as they reach their final focussing positions and extend our predictions to other geometries such as the square cross section. We believe complex effects originate due to a combination of inertia and elasticity in the weakly viscoelastic regime, where neither inertia nor elasticity are able to mask each other’s effect completely, leading to a number of intermediate focusing positions. The present study provides a fundamental new understanding of particle focusing in weakly elastic and strongly inertial flows, whose findings can be exploited for potentially multiple microfluidics-based biological sorting applications., Funding details: European Research Council, ERC, ERC- 2013-CoG-616186; Funding details: Vetenskapsrådet, VR, VR 2014-5001; Funding text 1: LB was supported by the European Research Council Grant No. ERC- 2013-CoG-616186, TRITOS, and by the Swedish Research Council (Grant No. VR 2014-5001). The authors acknowledge computer time provided by SNIC (Swedish National Infrastructure for Computing). QC 20220207

There is a growing interest amongst the HCI community to access and articulate the core of experiences for design use. The premise is that, by accessing detailed accounts of everyday experiences, we can obtain refined material for the design of interactive systems more connected with our bodies and emotions. This TEI studio aims to introduce participants to the basis of phenomenologically grounded techniques in combination with the use of tangible materials as a way to articulate experience from the inner self, applied to the evaluation of existing technologies. This studio offers an alternative to assessment tools that rely on a predefined repertoire of feelings, to instead focus on emergent, complex and unclear aspects of our emotions. These strange collections of emotions -or felt senses will be further explored through self-reporting tools and group exercises., QC 20210517

© The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Whitehead, J. A. Fluid flow with three upstream configurations in freezing tubes. Journal of Geophysical Research: Earth Surface, 126(6), (2021): e2020JF005969, https://doi.org/10.1029/2020JF005969., The accumulation of frozen liquid around a central passageway of melt as it flows through a freezing region can make calculations very challenging. To both illustrate and to quantify some of these challenges from freezing, a model equation is developed. It simplifies the solution of Holmes (2007, https://gfd.whoi.edu/wp-content/uploads/sites/18/2018/03/MHolmesGFDReport_30151.pdf) for low Reynolds number single component liquid flow through a long tube that has a wall kept at subfreezing temperature. This model equation is used in conjunction with three different upstream configurations, each with parameters expressing their behavior. Analytical and numerical results give the parameters that have criteria for: the freezing of a compressible upstream reservoir that includes oscillatory behavior; the freezing of flow fed through a constriction with a large upstream pressure, just like a dripping water faucet during winter; the evolution of flow in multiple tubes connected by an upstream manifold, where some tubes end up with full flow and others freeze shut. Numerical runs with 1,000 tubes give a formula for the spacing between actively flowing (non-frozen) tubes over wide ranges of the two upstream parameters (flow rate and manifold resistance). Results have implications in various areas in earth science. Some are: oscillatory and freezing shut criteria for flow of magma from a compressible region, a criterion for wintertime ice accumulation at natural springs, and the spacing between volcanos., Emeritus funds are provided by Woods Hole Oceanographic Institution.

Continuous microfluidic focusing of particles, both synthetic and biological, is significant for a wide range of applications in industry, biology and biomedicine. In this study, we demonstrate the focusing of particles in a microchannel embedded with glass grooves engraved by femtosecond pulse (fs) laser. Results showed that the laser-engraved microstructures were capable of directing polystyrene particles and mouse myoblast cells (C2C12) towards the center of the microchannel at low Reynolds numbers (Re < 1). Numerical simulation revealed that localized side-to-center secondary flows induced by grooves at the channel bottom play an essential role in particle lateral displacement. Additionally, the focusing performance proved to be dependent on the angle of grooves and the middle open space between the grooves based on both experiments and simulation. Particle sedimentation rate was found to critically influence the focusing of particles of different sizes. Taking advantage of the size-dependent particle lateral displacement, selective focusing of micrometer particles was demonstrated. This study systematically investigated continuous particle focusing in a groove-embedded microchannel. We expect that this device will be used for further applications, such as cell sensing and nanoparticle separation in biological and biomedical areas., identifier:2079-6374

La banda de frecuencias de ondas milimétricas (MMW), caracterizada por una elevada atenuación atmosférica y un gran ancho de banda disponible, se ha convertido de gran interés para aplicaciones de imágenes de radar de alta precisión. El desarrollo continuo de la tecnología de circuitos de microondas monolíticos integrados (MMIC) da lugar a la aparición de diferentes transceptores de radar comerciales (COTS) en esta banda de frecuencia, donde las antenas están totalmente integradas en el chip para evitar pérdidas en el sustrato. Las lentes se utilizan para corregir el frente de fase de estos chips mejorando la directividad y, por tanto, el rango de funcionamiento. Las lentes geodésicas, que pueden ser construidas utilizando sólo metales, ofrecen las propiedades atractivas de las lentes dieléctricas comunes sin sus pérdidas en el metarial. En este trabajo de fin de máster se ha diseñado una antena del tipo lente geodésica específica con propiedades de enfoque para mejorar las capacidades de imagen de radar del transceptor TRA-120-002 que trabaja en la banda ISM de 120 GHz. Se ha hecho un estudio de diferentes transiciones para los puntos singulares de la antena, minimizando reflexiones sin aumentar las aberraciones en la lente. En el trabajo se muestra un diseño optimizado de la apertura de la antena donde se utilizan corrugacions para mejorar el diagrama de radiación. Se ha diseñado también una pequeña antena de apertura con una metasuperfície de pines periódicos para maximizar la transmisión de energía entre el transceptor COTS y la lente. Finalmente, se ha añadido una metasuperfície basada en agujeros con simetría deslizada para evitar fugas entre las placas de la antena debido a posibles limitaciones en su fabricación. Los resultados muestran que se puede conseguir una antena de tipo lente de 5l de radio totalmente metálica con directividad superior a 19,5 dB y niveles de lóbulos secundários (SLL) entre -10,5 dB y -9,2 dB dentro de la banda de 119 GHz - 125,5 GHz, La banda de freqüències d'ones mil·limètriques (mmW), caracteritzada per una elevada atenuació atmosfèrica i un gran ample de banda disponible, ha esdevingut de gran interès per a aplicacions d'imatges de radar d'alta precisió. El desenvolupament continu de la tecnologia de circuits de microones monolítics integrats (MMIC) dona lloc a l'aparició de diferents transceptors de radar comercials (COTS) en aquesta banda de freqüència, on les antenes estan totalment integrades al xip per evitar pèrdues en el substrat. Les lents s'utilitzen per corregir el front de fase d'aquests xips millorant la directivitat i, per tant, el rang de funcionament. Les lents geodèsiques, que poden ser construïdes utilitzant només metalls, ofereixen les propietats atractives de les lents dielèctriques comuns sense les seves pèrdues en el material. En aquest treball de fi de màster s'ha dissenyat una antena del tipus lent geodèsica específica amb propietats d'enfocament per millorar les capacitats d'imatge de radar del transceptor TRA-120-002 que treballa a la banda ISM de 120 GHz. S'ha fet un estudi de diferents transicions per als punts singulars de l'antena, minimitzant reflexions sense augmentar les aberracions a la lent. En el treball es mostra un disseny optimitzat de l'obertura de la antena on s'utilitzen corrugacions per millorar el diagrama de radiació. S'ha dissenyat també una petita antena d'obertura amb una metasuperfície de pins periòdics per maximitzar la transmissió d'energia entre el transceptor COTS i la lent. Finalment, s'ha afegit una metasuperfície basada en forats amb simetria lliscada per evitar pèrdues entre les plaques de l'antena a causa de possibles limitacions en la seva fabricació. Els resultats mostren que es pot aconseguir una antena de tipus lent de 5l de radi totalment metàl·lica amb directivitat superior a 19,5 dB i nivells de lòbuls secundaris (SLL) entre -10,5 dB i -9,2 dB dins de la banda de 119 GHz - 125,5 GHz mentre que l'antena focalitza a 30 cm., The Millimiter Wave (mmW) frequency band, characterized by a high atmospheric attenuation and wide available bandwidth has become of big interest for high accuracy radar imaging applications. The continuous development of the Monolithic Microwave Integrated Circuit (MMIC) technology yields to the appearance of different commercial-off-the-shelf (COTS) radar transceivers at that frequency band, where the antennas are fully integrated into the chip. Lenses are being used to correct the phase front of those MMIC improving the directivity and therefore the operating range. Fully metallic geodesic lenses offer the attractive properties of common dielectric lenses without their material losses. In this master thesis, a specific water-drop geodesic lens antenna with focusing properties has been designed to enhance the radar imaging capabilities of the theTRA-120-002 transceiver working at the 120 GHz Industrial, Scientific and Medical (ISM) band. Different transitions for the antenna singular points have been studied to minimize reflections without increasing aberrations in the lens. An optimized design of a radiating flare is shown where corrugations are used to improve the antenna radiation pattern. A small feeding horn antenna with a bed-of-nails Electromagnetic Band-Gap (EBG) metasurface has been designed to maximize the energy transmission between the COTS transceiver and the lens. Finally, a glide-symmetric holey metasurface has been added to prevent leakage between the antenna plates due to manufacturing limitations. The results show that a fully metallic folded lens antenna with 5l radius can achieve directivities higher than 19.5 dB and side-lobe levels (SLL) between -10.5 dB and -9.2dB within the 119 GHz - 125.5 GHz band while having an image point located at 30cm from the antenna.

We present the optical investigation of crescent-shaped dielectric pillars that comprise a periodic structure named as crescent photonic crystals (CPC). The circular symmetry of individual cells of periodic dielectric structures is broken by replacing them with crescent shapes. The degree of freedom to manipulate the light propagation occurs due to the rotational sensitivity of CPC. The anisotropic equi-frequency contours allow sending light beams along any certain direction which is independent of the lattice periodicity of regular photonic crystals., IEEE Photon Soc, TUBITAK, Aselsan, KOC Univ

We present the optical investigation of crescent-shaped dielectric pillars that comprise a periodic structure named as crescent photonic crystals (CPC). The circular symmetry of individual cells of periodic dielectric structures is broken by replacing them with crescent shapes. The degree of freedom to manipulate the light propagation occurs due to the rotational sensitivity of CPC. The anisotropic equi-frequency contours allow sending light beams along any certain direction which is independent of the lattice periodicity of regular photonic crystals., IEEE Photon Soc, TUBITAK, Aselsan, KOC Univ

In this manuscript, we propose the design of an inhomogeneous artificially modeled graded photonic crystal (PC) medium to control and enrich the polarization insensitive focusing ability of light by using annular type all-dielectric materials. To obtain the graded annular PC structure, the lattice spacing along the transverse direction is modulated according to a parabolic function. The inner and outer radii of the annular PCs are optimized to attain frequency response of the graded structure. Even though the frequency responses of the transmission spectrum for different radial parameters exhibit different oscillation patterns for both TE and TM polarizations, optimum radii are determined where overlapping high transmission region is observed. Light focusing characteristics at those overlapping frequency regions are systematically and quantitatively investigated. Polarization insensitive focusing is achieved for bandwidth corresponding to similar to 6%. The designed structure can be used in integrated nanophotonics as a compact optical element with flat surfaces operating at both polarizations with high power transmission efficiency., IEEE Photon Soc

We investigated the sensitivity of fully focused SAR (FF-SAR) processing of Cryosat-2 altimeter data to Earth rotation. Earth’s rotation causes scatterers at varying cross-track locations to have a different relative velocity with respect to the satellite. This second-order effect of Earth rotation on the phase is currently not corrected for in FF-SAR processing of altimetry data. The difference is largest near the poles, where the satellite flies parallel to the equator. Not correcting for the second-order effect yields a parabolic shape in the counter-rotated phase, which increases with the cross-track distance. Its effect is, however, limited by the time-in-view of the scatterer, which is shorter at the edge of the altimeter footprint, and therefore destructive interference will not occur when using Cryosat-2 data. For Cryosat-2, the only expected effect is a reduction in power and along-track resolution in the waveform tail and in the grating lobes. If the FF-SAR processor focuses on one point, and there is a bright scatterer at another, then there is a residual parabolic phase, whose sign and shape depend on the cross-track distance and whether the signal is left or right of the chosen focal point. In theory, if the viewed scene only has few bright coherent scatterers, then it might be possible to determine the cross-track position of each. In practice, however, natural targets are rarely coherent over the integration time., Mathematical Geodesy and Positioning, Astrodynamics & Space Missions, Physical and Space Geodesy, Atmospheric Remote Sensing

Manipulation of particles and cells in viscoelastic fluids has received substantial interest because this phenomenon provides high-quality focusing. Here we present an enhanced particle focusing and separation in spiral channels, at a ten-fold increase of Reynolds number as compared to current state of the art elasto-inertial microfluidics and report stable particle focusing in spiral low aspect ratio channels at flow rates two magnitudes higher than that previously reported at a high throughput of 2 mL/min is demonstrated with an separation efficiency of 99% for the 15-micron and 91% for the 10-micron particles is demonstrated., Not duplicate with DiVA 1082892QC 20210915

This thesis conceptualizes the design of a planar electrode for employment in microfluidic devices to achieve dielectrophoretic focusing and separation of micro-scale entities. The planar electrode has corrugations with two such electrodes placed parallelly to form a pair and the electric field is generated between them; the presence of corrugations enhances the non-uniformity of the electric field. For purposes of 3D focusing, two pairs of electrodes are used with each pair on both sides of the microchannel. When the applied electric voltages are equal, the micro-scale entity is focused at the center of the microchannel and when the applied electric voltages are unequal, the micro-scale entity is focused at locations other than the center of the microchannel. For purposes of achieving size-based separation, four electrode pairs are used with each pair placed on one side the microchannel; the first two pairs of electrodes 3D focus the micro-scale entities next to one of the side walls while the other two pairs of electrodes subject the big micro-scale entity to negative dielectrophoresis while the small micro-scale entity experiences negligible dielectrophoresis and this pushes the big micro-scale entity inside the microchannel hence achieving separation of particles. The conceptualized microfluidic device is mathematically modelled with the model consisting of multiple governing equations; equations of motion, continuity equation, Navier-Stoke equations, and electric voltage and electric field equations make up the mathematical model. The model experiences phenomena’s such as inertia, drag, dielectrophoresis, gravity, buoyancy, and virtual mass. All equations of the model are solved numerically using Finite Difference Method. The model is validated using experimental results from literature. The model is subsequently used for evaluating the effect of operating and geometric parameters on the performance metrics of the focusing and separation device; the performa

In this study, we propose the metaheuristic design of a polarization-insensitive diffractive lens. The designed lens structure consists of concentric dielectric rings with optimally modulated widths and heights. Here, the evolutionary optimization approach is conducted to find the optimum values of concentric rings' widths and heights to obtain polarization-insensitive subwavelength focusing effect of the incident light. Three-dimensional finite-difference time-domain (3D FDTD) method is incorporated with the optimization algorithm to evaluate the focusing ability of instantly designed lens structures throughout the optimization process. The presented lens structure is designed at operating frequency of 10 GHz, and has a diameter of 18.45 cm with thickness of 2.4 cm. The detailed analysis of the polarization-insensitive focusing effect of designed diffractive flat lens is numerically investigated at microwave frequency regime considering the scenario of experimental verification to be conducted at the same spectral region. Possible experimental verifications are discussed along with the 3D-printing of the designed lens structure. As a further step, the presented design concept may be applied to design metasurfaces operating at visible wavelengths. © 2019 IEEE.

Acoustic metamaterials have become a novel and effective way to control sound waves and design acoustic devices. In this study, we design a 3D acoustic metamaterial lens (AML) to achieve point-to-point acoustic communication in air: any acoustic source (a speaker) in air enclosed by such an AML can produce an acoustic image where the acoustic wave is focused (the field intensity is at a maximum, and the listener can receive the information), while the acoustic field at other spatial positions is low enough that listeners can hear almost nothing. Unlike a conventional elliptical reflective mirror, the acoustic source can be moved around inside our proposed AML. Numerical simulations are given to verify the performance of the proposed AML., QC 20190716

[ES] En este trabajo se ha realizado un estudio teórico de la eficiencia de transmisión de lentes de Fresnel. Los resultados muestran que la distribución de las regiones transparentes y opacas de la lente no influye cuando se considera onda plana u onda esférica. No obstante, si se considera el uso de transductores directivos, como suele ser típico en el campo de la acústica o las microondas, la posición de las regiones transparentes desempeña un papel importante en la eficiencia de transmisión de la lente y su perfil de focalización. Además, se han realizado medidas experimentales que permiten validar el modelo teórico presentado, demostrando una mejora en la eficiencia de transmisión e intensidad focal cuando las regiones opacas ocupan las posiciones pares a lo largo de la lente., [EN] In this work, a theoretical analysis of the transmission efficiency of acoustic Fresnel lenses has been developed. Results show that the distribution of transparent and opaque regions along the lens does not have any impact when plane or ideal spherical wave incidences are considered. However, when a directional transducer is employed, which is the usual case in most acoustic and microwave applications, the position of the transparent regions along the lens plays an important role in the transmission efficiency and focusing profile of the lens. In addition, experimental measurements have been carried out, which are in good agreement with the theoretical model and demonstrate an imporvement in both transmission efficiency and focal intensity when opaque regions are distributed along even positions of the lens.