Surface waves in solar granulation observed with {\sc Sunrise}

Solar oscillations are expected to be excited by turbulent flows in the intergranular lanes near the solar surface. Time series recorded by the IMaX instrument aboard the {\sc Sunrise} observatory reveal solar oscillations at high resolution, which allow studying the properties of oscillations with short wavelengths. We analyze two times series with synchronous recordings of Doppler velocity and continuum intensity images with durations of 32\thinspace min and 23\thinspace min, resp., recorded close to the disk center of the Sun to study the propagation and excitation of solar acoustic oscillations. In the Doppler velocity data, both the standing acoustic waves and the short-lived, high-degree running waves are visible. The standing waves are visible as temporary enhancements of the amplitudes of the large-scale velocity field due to the stochastic superposition of the acoustic waves. We focus on the high-degree small-scale waves by suitable filtering in the Fourier domain. Investigating the propagation and excitation of $f$- and $p_1$-modes with wave numbers $k > 1.4$\thinspace 1/Mm we find that also exploding granules contribute to the excitation of solar $p$-modes in addition to the contribution of intergranular lanes.Comment: 12 pages, 4 figures, to appear in a special volume on Sunrise in Astrophysical Journal Letter

Coherent strong-coupling of terahertz magnons and phonons in a Van der Waals antiferromagnetic insulator

Emergent cooperative motions of individual degrees of freedom, i.e. collective excitations, govern the low-energy response of system ground states under external stimulations and play essential roles for understanding many-body phenomena in low-dimensional materials. The hybridization of distinct collective modes provides a route towards coherent manipulation of coupled degrees of freedom and quantum phases. In magnets, strong coupling between collective spin and lattice excitations, i.e., magnons and phonons, can lead to coherent quasi-particle magnon polarons. Here, we report the direct observation of a series of terahertz magnon polarons in a layered zigzag antiferromagnet FePS3 via far-infrared (FIR) transmission measurements. The characteristic avoided-crossing behavior is clearly seen as the magnon-phonon detuning is continuously changed via Zeeman shift of the magnon mode. The coupling strength g is giant, achieving 120 GHz (0.5 meV), the largest value reported so far. Such a strong coupling leads to a large ratio of g to the resonance frequency (g/{\omega}) of 4.5%, and a value of 29 in cooperativity (g^2/{\gamma}_{ph}{\gamma}_{mag}). Experimental results are well reproduced by first-principle calculations, where the strong coupling is identified to arise from phonon-modulated anisotropic magnetic interactions due to spin-orbit coupling. These findings establish FePS3 as an ideal testbed for exploring hybridization-induced topological magnonics in two dimensions and the coherent control of spin and lattice degrees of freedom in the terahertz regime

Various modulated hybrid pulse compression for advanced ultrasound technology and its non-destructive testing application

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University LondonUltrasound is a sound wave with a frequency greater than 20 kHz. It obeys the propagation laws of reflection, refraction, diffraction, and scattering. Because of its excellent physical properties, ultrasound has been used in a variety of fields, including industry and medicine. There are many techniques that use ultrasound as detection methods in the field of non-destructive testing (NDT) and medical treatment. In a typical ultrasound system, a sine wave or pulse signal with a fit window is considered as the transmitted signal. This results in low accuracy in some special situations, such as testing high attenuation material. The signal-to-noise ratio (SNR) is an important parameter for evaluating the performance of an echo signal or imaging. However, under high attenuation materials or noisy conditions, SNR will significantly decrease. Under these conditions, valid information in the received signal will be obscured by noise. This situation can cause errors in the detection system. In an ultrasound system, increasing the SNR of the echo signal can reduce detection errors and improve accuracy. First, in ultrasound systems, a noise reduction method based on pulse compression has been investigated and applied. Convolution and modulation were used in the proposed method to generate new hybrid emission signals. The hybrid codes can only be distinguished by a special matched filter that is related to the emission signals. The echo signals processed by a special matched filter have a high main lobe and a very low side lobe, implying that the side lobe level and SNR will increase. When compared to traditional denoising methods, the proposed method can significantly improve SNR while only requiring a change in the transmission code without requiring any hardware changes. Second, in a low voltage ultrasonic testing (UT) system, a hybrid phase modulated code excitation method based on the Barker and Golay code pairs was proposed and implemented. In a UT system, the lower the pulsing voltage, the lower the SNR of the signal. Attempting to reduce the pulsing voltage will result in noisy and unusable results. The proposed hybrid method can increase main lobe power in low average power transmitted and received signals. The proposed method has been theoretically examined and then tested in simulation studies. The experimental results showed that the main lobe level of the code produced by convolution of Barker code and Golay code pairs is around 30 dB higher than the simple pulse, and the main lobe of the combined code is around 15 dB higher than the traditional Barker code, with the sidelobe being the same as the Baker code that constitutes this combined code. As a result, the combined code’s peak sidelobe level (PSL) is approximately 5 dB lower than the traditional Barker code. Because of this, UT devices can be used in real-world applications, even in low-voltage situations. Third, the torsional wave mode T(0,1) hybrid phase modulated code excitation method has been proposed and applied in a long range guided wave testing (GWT) system. The proposed hybrid method combines the Barker and Golay code pair and is modulated by a fitted sine wave. This method combines the benefits of these two coding methods and increases code length flexibility. The SNR and PSL of the processed signal are used to assess the method’s performance. The proposed method has been tested in GWT using both finite element method (FEM) simulation and real-world testing. The results of pipeline laboratory testing revealed that the best increasing SNR of BCG is around 33.5 dB when compared to a simple pulse at 40 kHz, and the peak sidelobe level is around -24 dB. The proposed method, as well as other traditional methods, were used for pipeline defect detection testing. The results of the tests showed that the hybrid coded excitation method can detect notches that are difficult to detect with other methods and effectively improve the SNR. The applied method’s increasing SNR is around 6 dB, which agrees with the simulation and laboratory testing results. In UGW testing, the proposed coded excitation method was highly regarded. Finally, the non-linear frequency modulated (NLFM) hybrid pulse compression method has been proposed and implemented in an ultrasound imaging (UI) system. The proposed code combines the Barker and Golay codes and is modulated using a non-linear frequency method based on the Zak transform. Theoretical research on signal generation and decoding has been presented, as well as cyst phantom simulation. The simulation analysis shows that the novel code method can improve the contrast ratio by 15.96 dB and the SNR by 36.64 dB when compared to a simple pulse signal. Overall, this study demonstrated that the proposed novel method can be effectively used in ultrasound detection methods to improve performance

Magnetomotive ultrasound for nanomedicine : a mechanistic approach to detection, evaluation and safety assessment

Cancer is one of the leading causes of death worldwide, but reliable diagnosis and staging can contribute to optimal treatment planning, and is a crucial factor in reducing mortality and maintaining quality of life. Soft tissue mechanical properties are promising indicators of cancer that can be assessed non-invasively using functional imaging. Additionally, lymphatic involvement is considered a key aspect in staging of many types, including colorectal and breast cancer. Magnetomotive ultrasound, MMUS, is an imaging technique proposed for cancer staging and treatment. It relies on magnetically induced motion, transferred from a contrast agent to the tissue of interest. The tissue response to this perturbation is related to its mechanical properties, and thereby to cancer progression. Typically, the contrast agent consists of magnetic nanoparticles; These can be incorporated into microbubbles, that could allow for drug transport and site-specific delivery. Exploring these properties and possibilities of MMUS clarifies its clinical potential. The aim of this work was therefore to examine (a) the relation between tissue mechanical properties and magnetomotion, (b) the feasibility of magnetic microbubbles as a contrast agent and (c) the cellular response to magnetic nanoparticles and forces. Points (a) and (b) were addressed by comparing MMUS images conducted on real and phantom tissue to finite element analysis outputs; Transmission electron microscopy and quantitative cell based assays were used in exploring point (c). Magnetomotion was found to depend on tissue compressibility and elasticity, both potential cancer indicators. Tissue elasticity was also found to affect the tissue deformations induced by magnetic microbubbles. Furthermore, lymphatic drainage of magnetic microbubbles was demonstrated, validating their potential as a contrast agent in cancer imaging. Finally, cells were confirmed to take up nanoparticles, and no adverse effects of magnetic excitation was detected. In summary, there is merit to further development of MMUS for cancer diagnostics and treatment

Ultrafast Spin Dynamics of Next-Generation Nanomagnetic Technologies

Over the past 50 years, our society has experienced a technological revolution that has fundamentally changed the way our world operates. At the heart of this revolution are the computational building blocks that work together to perform mathematical operations and save the results. For many years, the size of the computing elements (e.g. transistors) has been consistently shrunk so that more devices could fit on a chip in order to increase computational power. To provide adequate data storage for the ever-increasing number of computations, the hard-disk drive (HDD) was developed in the 1980s and would forever revolutionize the landscape of memory storage. Today, HDDs still account for a vast majority of the data stored worldwide. These devices store information using the magnetization of nanoscopic domains in a granular magnetic film, however, in recent years it has become increasingly challenging to reduce the size of the domains further without fundamentally changing the HDD. Indeed, the latest iteration of this technology has incorporated lasers into the devices to leverage multiple degrees of freedom in order to achieve higher bit densities. This example highlights a common trend for all next-generation computational technologies – the strong coupling between distinct physical systems must be utilized to sustain the improvements our society has become accustomed to. In order to realize this lofty goal, the physics of nanoscale systems must be well understood to predict their behavior. As our collective understanding of this field continues to flourish, novel effects are found that open doors to previously unimaginable technologies that may usher in a revolution of their own. Indeed, there are both technological and fundamental interests to study nanostructured devices.In this thesis, the time-resolved magneto-optic Kerr effect (TR-MOKE) will be utilized to probe the ultrafast spin dynamics of magnetic films, multilayer heterostructures, and nanostructures. Our experimental observations of these systems are evaluated by combining various field of science and technology, including (but not limited to) condensed matter theory, signal processing, and optics. In doing so, we seek to fully explain the data and to enrich the understanding of these underexplored systems to inform the rational design of next-generation technologies. Specifically, a great deal of attention will be paid to emergent nanotechnologies that leverage the coupling between the magnetic system and either the electronic or mechanical properties of the device to tailor the performance. In this work, a novel method to restore the intrinsic magnetization dynamics and simultaneously improve the magneto-optical response of dense nanomagnet arrays will be presented. Then, our work on the spin dynamics of isolated nanomagnets resonantly excited by microwave-frequency acoustic waves will be reviewed, wherein we show for the first time that the coupling efficiency is ultimately limited by the damping of the magnetic system. In addition, the role of the nanomagnet geometry and the acoustic wavelength will be fully explored to determine critical parameters that govern the dynamic magneto-elastic resonance. Lastly, the development of an optical system to study the interplay between ultrafast all-optical switching and surface acoustic waves will be reviewed

Characterization of Magnetization Dynamics in Structured Magnetic Films

The focus of this thesis is investigating of the magnetization dynamics in patterned magnetic films by time-resolved Kerr microscopy (TR-MOKE). Therefore, various magnetic films and structures are studied using the developed TR-MOKE and inductive microwave magnetometry setup. The results of this thesis reveal new aspects of complicated magnetization dynamics in such magnetic systems. Also, it provides the knowledge of tailoring dynamic magnetic properties of modern magnetic structures. Initially, the magneto-dynamic response of Landau-like magnetic domain configurations are examined and a method to separate the in- and out-of-plane Kerr signals is proposed. This method indicates a more elaborated model for fast magnetization processes in soft magnetic elements. In addition, the direct observation of spin-wave generation and propagation from oscillating pinned magnetic structures is reported, and the fundamental properties of them are analyzed. Using this knowledge, an alternative way to generate and propagate spin waves that do not require any artificial structure (e.g., antenna or wave-guide) is proposed. Moreover, the results of experimental TR-MOKE imaging together with complementary micromagnetic simulations were used to design an experiment, where the spin waves are emitting from magnetic elements corners and edges. The frequencies of such spin waves shown to be tunable by the excitation frequency. Finally, the dynamic magnetic response of weak antiferromagnetically coupled and structured magnetic films are presented. The multilayer film dynamic properties are compared to the single-layer film, and the impact of patterning on magnetization dynamics is shown

Vortex Motions in the Solar Atmosphere: Definitions, Theory, Observations, and Modelling

Vortex flows, related to solar convective turbulent dynamics at granular scales and their interplay with magnetic fields within intergranular lanes, occur abundantly on the solar surface and in the atmosphere above. Their presence is revealed in high-resolution and high-cadence solar observations from the ground and from space and with state-of-the-art magnetoconvection simulations. Vortical flows exhibit complex characteristics and dynamics, excite a wide range of different waves, and couple different layers of the solar atmosphere, which facilitates the channeling and transfer of mass, momentum and energy from the solar surface up to the low corona. Here we provide a comprehensive review of documented research and new developments in theory, observations, and modelling of vortices over the past couple of decades after their observational discovery, including recent observations in Hα, innovative detection techniques, diverse hydrostatic modelling of waves and forefront magnetohydrodynamic simulations incorporating effects of a non-ideal plasma. It is the first systematic overview of solar vortex flows at granular scales, a field with a plethora of names for phenomena that exhibit similarities and differences and often interconnect and rely on the same physics. With the advent of the 4-m Daniel K. Inouye Solar Telescope and the forthcoming European Solar Telescope, the ongoing Solar Orbiter mission, and the development of cutting-edge simulations, this review timely addresses the state-of-the-art on vortex flows and outlines both theoretical and observational future research directions

Magnetomotive Ultrasound Imaging to Estimate Tissue Elastic Properties - Experiments and Simulations

Magnetomotoriskt ultraljud är en ny bildgivande teknik som kombinerar vanligt ultraljud med ett pålagt tidsvarierande magnetfält för att åstadkomma en detekterbar rörelse i vävnad. Genom att injicera magnetiska nanopartiklar i området man vill undersöka kan på så sätt viktig information tillgodogöras. Superparamagnetiska järnoxidpartiklar har i drygt ett årtionde varit ett godkänt kontrastmedel för andra bildgivande system och har visat sig kunna utnyttjas även för magnetomotoriskt ultraljud. I denna rapport undersöktes möjligheterna för denna nya bildgivande teknik att, i samband med superparamagnetiska järnoxidpartiklar, användas för både förundersökningar och under operationer för att identifiera den s.k. portvaktskörteln. Magnetomotoriska ultraljudsundersökningar genomfördes i denna rapport på egentillverkade vävnadsfantomer. Fantomerna preparerades för att få liknande egenskaper som de i litteratur funna elasticitetsvärden för frisk respektive tumörvävnad. Ett mjukvaruprogram användes för att numeriskt modellera och analysera utgången av experimenten och jämföra dessa med de uppmätta värdena. Resultaten i rapporten visar att man med magnetomotoriskt ultraljud, i kombination med nanopartiklar som kontrastmedel, kan detektera en vävnadsrespons som beror på elasticitetsparametrar hos vävnaden. För två olika uppställningar med elasticitetsvärden på 2.5 kPa respektive 2.8 kPa kunde en relativ rörelseskillnad på 30 % detekteras. För att denna metoden ska vara av värde i kliniska sammanhang behöver den evalueras ytterligare.Magnetomotive ultrasound imaging is an imaging technique that utilizes regular ultrasound in combination with an applied time varying magnetic field to induce motion of magnetic nanoparticles injected in the region. This motion can be detected and give valuable information about the particle laden region. Superparamagnetic iron oxide nanoparticles have been approved for over a decade for use with other imaging techniques and are now utilized for magnetomotive ultrasound imaging research as well. In this report, the possibilities for the use of magnetomotve ultrasound imaging as a pre- and intraoperative method for detecting metastases in the sentinel lymph node was investigated. In this report magnetomotive ultrasound measurements were performed on tissue mimicking phantoms with elastic properties simulating healthy and cancerous tissue. A model of the setup was created in a multi physics software tool and used to confirm and explain the observed behavior. The results in this report indicate that a difference in tissue response exists and can be detected. For two different setups with elastic properties of 2.5 kPa and 2.8 kPa we see a relative change in detected displacement of about 30 %. However, for this approach to be utilized clinically, more studies are needed.Detektion av cancermetastaser med en ny ultraljudsbaserad metod Bröstcancer och hudcancer är två av de vanligaste cancerformerna i Sverige. Båda kan spridas via lymfsystemet och skulle därför dra nytta av en metod som undersöker just metastaser i detta system. Dagens metoder för att göra detta är omständliga och dyra, men på senare tid har man fått upp ögonen för fördelarna med att utnyttja ultraljud istället. Genom att kombinera traditionellt ultraljud, en bildgivande metod med många fördelar, med ett magnetiskt fält och magnetiska nanopartiklar öppnas en värld av möjligheter för att undersöka sjukdomsförlopp på molekylär nivå. Frisk vävnad skiljer sig från tumörvävnad på så vis att de uppvisar olika elastiska egenskaper. För att undersöka om cancer har spridit sig i kroppen är det av intresse att detektera dessa elasticitetsskillnader. Både bröst- och hudcancer sprids metodiskt och främst via lymfsystemet. Den s.k. portvaktskörteln är den lymfkörtel där det är mest troligt att finna metastaser om cancern har spridit sig, då lymfvätska filtreras i lymfkörtlarna och portvaktskörteln är den första som lymfvätska från tumörområdet kommer till. Genom att därför undersöka just denna körtel kan man direkt avgöra risken för spridning. Helst bör detta göras på ett vis som undviker onödiga operationer för patienterna. En alternativ metod med potential för mycket hög upplösning är traditionellt ultraljud i kombination med en magnet och ett kontrastmedel. Detta kontrastmedel är magnetiska nanopartiklar som injiceras i lymfsystemet och söker sig till portvaktskörteln. Magneten sätter dessa nanopartiklar i rörelse och efter databehandling av ultraljudsbilderna kan man tillgodogöra sig information som berättar något om elasticitetsvärdena i den undersökta regionen. För att undersöka detta fenomen tillverkades små bitar av en vävnadsliknande substans, PVA. PVA, eller polyvinylalkohol, är en lösning som har samma elastiska egenskaper som vävnad. De magnetiska nanopartiklarna injicerades i PVA-bitarna och sedan undersöktes dessa med ultraljud. Detta fenomen simulerades även i ett datorprogram, där modellen byggdes upp för att efterlikna den experimentella situationen. Simuleringen möjliggjorde fler och snabbare undersökningar jämfört med de verkliga experimenten. Resultaten från de experimentella och de simulerade processerna visade på att man faktiskt kan se en rörelseskillnad på vävnad med olika elasticitet. Man kunde se ett mönster där symboliserad mjukare vävnad har en större rörelseförändring jämfört med symboliserad hårdare vävnad

Novel Approaches for Nondestructive Testing and Evaluation

Nondestructive testing and evaluation (NDT&E) is one of the most important techniques for determining the quality and safety of materials, components, devices, and structures. NDT&E technologies include ultrasonic testing (UT), magnetic particle testing (MT), magnetic flux leakage testing (MFLT), eddy current testing (ECT), radiation testing (RT), penetrant testing (PT), and visual testing (VT), and these are widely used throughout the modern industry. However, some NDT processes, such as those for cleaning specimens and removing paint, cause environmental pollution and must only be considered in limited environments (time, space, and sensor selection). Thus, NDT&E is classified as a typical 3D (dirty, dangerous, and difficult) job. In addition, NDT operators judge the presence of damage based on experience and subjective judgment, so in some cases, a flaw may not be detected during the test. Therefore, to obtain clearer test results, a means for the operator to determine flaws more easily should be provided. In addition, the test results should be organized systemically in order to identify the cause of the abnormality in the test specimen and to identify the progress of the damage quantitatively