The estimation of geoacoustic properties from broadband acoustic data, focusing on instantaneous frequency techniques

The compressional wave velocity and attenuation of marine sediments are fundamental to marine science. In order to obtain reliable estimates of these parameters it is necessary to examine in situ acoustic data, which is generally broadband. A variety of techniques for estimating the compressional wave velocity and attenuation from broadband acoustic data are reviewed. The application of Instantaneous Frequency (IF) techniques to data collected from a normal-incidence chirp profiler is examined. For the datasets examined the best estimates of IF are obtained by dividing the chirp profile into a series of sections, estimating the IF of each trace in the section using the first moments of the Wigner Ville distribution, and stacking the resulting IF to obtain a composite IF for the section. As the datasets examined cover both gassy and saturated sediments, this is likely to be the optimum technique for chirp datasets collected from all sediment environments

RRS Discovery Cruise DY017, 20 Oct - 05 Nov 2014. Outer Hebrides process cruise

The continental shelf region immediately west of the UK and North of Ireland is thought to be a key region for the exchange of nutrients, carbon and water between the NW European continental shelf and the open North Atlantic Ocean yet it remains comparatively under sampled. Within the context of the NERC/DEFRA co-funded Shelf Sea Biogeochemistry programme, which aims to improve our understanding of the role of shelf seas in the global carbon cycle, this cruise undertook a regional scale survey to determine the distribution and concentrations of dissolved inorganic carbon, inorganic nutrients, trace metals, and other ancillary data on the Malin and Hebridean Shelves. Of the seven planned transects, six were completed with the seventh abandoned due to poor weather but a rich dataset of key biogeochemical parameters has been collected which will enable work on the stoichiometry of dissolved nutrients and exchange with the open ocean to be undertaken

U.S. Law of the Sea Cruise to Map the Southern Flank of the Kingman Reef-Palmyra Atoll section of the Line Islands, Equatorial Pacific Ocean

U.S. Law of the Sea Cruise to Map the Southern Flank of the Kingman Reef-Palmyra Atoll section of the Line Islands, Equatorial Pacific Ocean CRUISE KM1009 May 17, to June 16, 2010 Pago Pago, American Samoa to Honolulu, H

Dielectric-based Components and Methods for Terahertz Sensing

[ES] En el presente trabajo, se investigan algunos aspectos de la interacción de los materiales dieléctricos con ondas de THz. La banda de THz, que incluye las frecuencias de 100 GHz a 30 THz, ha despertado un gran interés sobre todo por su baja energía y su buena capacidad de penetración en materiales de uso diario como tejidos y plásticos. Las características peculiares de estas ondas permiten su aplicación en diversos campos tecnológicos, especialmente como herramientas científicas y para la inspección de control de calidad. Para avanzar en la aplicación práctica de la radiación THz, la presente tesis doctoral investigó varios caminos. En primer lugar, se trataron métodos alternativos de bajo coste para la fabricación de componentes pasivos de THz, centrándose en los polarizadores. El interés en el control de la polarización nace de la demanda de un mayor control sobre las características físicas de los haces de THz. Asimismo, se han investigado los polarizadores wire grid flexible basados en el efecto de absorción dicroica. Se han fabricado polarizadores con grafito y GaIn24,5 depositados en materiales ordinarios utilizados como sustratos (papel y polímeros como PVA y PVC). Mediante la colaboración con el grupo de investigación chino dirigido por el profesor Liu de la Universidad de Tsinghua, se investigaron procesos de fabricación alternativos. Todos los componentes se simularon mediante un simulador comercial basado en la técnica de integrales finitas FIT (CST Microwave Studio). En segundo lugar, se investigó el potencial de la técnica de fixed delay para la detección rápida de elementos homogéneos y transparentes con posible aplicación en la inspección de calidad industrial. En este esquema, la variación de corriente del haz de THz en un punto específico está relacionada con la variación de sus parámetros ópticos, por lo que se demostró la capacidad de detectar defectos, así como de estimar sus volúmenes bajo ciertas condiciones. Por último, un enfoque diferente para el beam profile basado en un slit dieléctrico fue evaluada como alternativa a los métodos convencionales utilizados en la región de THz y la óptica. Todas las mediciones, tanto la espectroscopia como el control de la polarización, se hicieron por medio de un sistema basado en fibra TDS-THz, con antenas fotoconductoras (PCA), tanto para la generación como para la detección de THz.[EN] In the present work, some aspects of the role of dielectric materials when interacting with THz waves were investigated. The THz bandgap, which covers the frequencies from 100 GHz to 30 THz, has aroused great interest mainly due to its low energy and its good penetration capacity in some materials of daily use such as fabrics and plastics. The peculiar features of terahertz waves enable their application in various technological fields, especially as scientific tools and for quality control inspection. To advance in the practical application of THz radiation, the present doctoral thesis researched several paths. Firstly, alternative low-cost methods for manufacturing THz passive components, in particular, THz polarizers was treated. The interest in polarization control is derived from the demand for greater control over the physical characteristics of THz beams. Flexible wire grid polarizers based on the dichroic absorption effect have been investigated. The polarizers have been manufactured using graphite and GaIn24.5 deployed on ordinary materials used as substrates (paper and polymers such as PVA and PVC). Through a collaboration undertaken with the Chinese research group led by Professor Liu at Tsinghua University, alternative manufacturing processes were researched. All components were simulated through a commercial simulator based on the FIT finite integrals technique (CST Microwave Studio). Secondly, the potential of the fixed delay technique was investigated for rapid sensing of homogeneous and transparent items with possible application to industrial quality inspection. In this scheme, the current variation of the THz beam at a specific point is related to the variation of its optical parameters, thus it was demonstrated the ability of the method in detecting voids as well as in roughly estimating their volumes under certain conditions. Finally, a different approach for beam profiling based on a dielectric slit aperture was evaluated, as an alternative to the conventional methods used in the THz region and optics All measurements, both spectroscopy and polarization control, were made by means of a TDS-THz fibre-based system, with photoconductive antennas (PCA), both for the generation and detection of THz.[CA] En el present treball, s'investiguen alguns aspectes del paper dels materials dielèctrics quan interactuen amb ones de THz. El bandgap de THz, que cobreix les freqüències de 100 GHz a 30 THz, ha despertat un gran interés principalment a causa de la seua baixa energia i la seua bona capacitat de penetració en alguns materials d'ús diari com els teixits i els plàstics. Les característiques peculiars de les ones de terahertz permeten la seua aplicació en diversos camps tecnològics, especialment com a eines científiques i per a la inspecció de control de qualitat. Per a avançar en l'aplicació pràctica de la radiació THz, la present tesi doctoral investiga diversos camins. En primer lloc, es s'han tractat mètodes alternatius de baix cost per a la fabricació de components passius de THz, centrant-se principalment en polaritzadors de THz. L'interés en el control de la polarització es deriva de la demanda d'un major control sobre les característiques físiques dels feixos de THz. Així mateix, s'han investigat els polaritzadors amb reixes de filferro flexible basats en l'efecte d'absorció dicroica. Els polaritzadors s'han fabricat utilitzant grafit i GaIn24,5 desplegats en materials ordinaris utilitzats com a substrats (paper i polímers com el PVA i el PVC). Mitjançant una col·laboració empresa amb el grup d'investigació xinés dirigit pel professor Liu de la Universitat de Tsinghua, es van investigar processos de fabricació alternatius. Tots els components es van simular mitjançant un simulador comercial basat en la tècnica d'integrals finites FIT (CST Microwave Studio). En segon lloc, s'ha investigat el potencial de la tècnica de retard fix per a la detecció ràpida d'elements homogenis i transparents amb possible aplicació a la inspecció de qualitat industrial. En aquest esquema, la variació actual del feix de THz en un punt específic està relacionada amb la variació dels seus paràmetres òptics, per la qual cosa es va demostrar la capacitat del mètode per a detectar els buits així com en l'estimació aproximada dels seus volums sota certes condicions. Finalment, un enfocament diferent per al perfil de feix basat en una obertura d'escletxa dielèctrica ha sigut avaluada, com a alternativa als mètodes convencionals utilitzats a la regió de THz i l'òptica.Tots els mesuraments, tant l'espectroscòpia com el control de la polarització, es van fer per mitjà d'un sistema basat en fibra TDS-THz, amb antenes fotoconductores (PCA), tant per a la generació com per a la detecció de THz.Colleoni, MPM. (2020). Dielectric-based Components and Methods for Terahertz Sensing [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/149569TESI

Direct monitoring of active geohazards: emerging geophysical tools for deep-water assessments

Seafloor networks of cables, pipelines, and other infrastructure underpin our daily lives, providing communication links, information, and energy supplies. Despite their global importance, these networks are vulnerable to damage by a number of natural seafloor hazards, including landslides, turbidity currents, fluid flow, and scour. Conventional geophysical techniques, such as high-resolution reflection seismic and side-scan sonar, are commonly employed in geohazard assessments. These conventional tools provide essential information for route planning and design; however, such surveys provide only indirect evidence of past processes and do not observe or measure the geohazard itself. As such, many numerical-based impact models lack field-scale calibration, and much uncertainty exists about the triggers, nature, and frequency of deep-water geohazards. Recent advances in technology now enable a step change in their understanding through direct monitoring. We outline some emerging monitoring tools and how they can quantify key parameters for deepwater geohazard assessment. Repeat seafloor surveys in dynamic areas show that solely relying on evidence from past deposits can lead to an under-representation of the geohazard events. Acoustic Doppler current profiling provides new insights into the structure of turbidity currents, whereas instrumented mobile sensors record the nature of movement at the base of those flows for the first time. Existing and bespoke cabled networks enable high bandwidth, low power, and distributed measurements of parameters such as strain across large areas of seafloor. These techniques provide valuable new measurements that will improve geohazard assessments and should be deployed in a complementary manner alongside conventional geophysical tools

산소 플라즈마 애싱 공정을 이용한 응력 구배 MEMS 외팔보가 있는 Ka밴드 대역 가변형 메타물질 흡수체

학위논문(박사) -- 서울대학교대학원 : 공과대학 전기·정보공학부, 2022. 8. 김용권.This dissertation proposes and realizes the first Ka-band frequency tunable metamaterial absorber with stress-induced MEMS cantilever with oxygen plasma ashing process. To employ a MEMS-driven actuator for LC resonance frequency tuning method in the GHz regime, the split-ring resonator (SRR) structure of the metamaterial unit cell is designed to have a sub-mm scale cantilever as a capacitor element of the unit cell. To enlarge capacitance change, the MEMS cantilever is released with a large out-of-plane deflection by the plasma ashing process. This MEMS cantilever with stress gradient is arranged at four parts of a symmetrical SRR unit cell, and the two cells compose the absorber sample as an array structure. The overall cantilevers of the absorber actuate from the initial bent upward state to pulled down state when the electrostatic voltage is applied. The decrease of deflection reduces the gap between cantilevers and bottom electrodes to increase capacitance for frequency tuning to lower frequency. To verify and improve the uniformity of the mechanical behavior of the absorber, this research proposes and demonstrates 3 different design types of releasing on stress-induced cantilevers. First, the array design of 12 cantilevers with 400 μm in length and 50 μm widths is modified from a cantilever with 400 μm in length and 800 μm widths. To overcome the limitation on the mechanical behavior of cantilever arrays due to their nonuniformity, further modification on etching hole rearrangement is reflected in the 2nd type of rectangular cantilever. The space length of etch hole varies depending on the position from the open end of cantilevers. This incremental space length between 8 μm etch holes from the open end enables sequential releasing of cantilevers during photoresist oxygen plasma ashing. The cyclic process was performed in the ashing process to lower the distribution of fabrication results. Finally, the last design to have a semicircle shape with incremental space length between etching holes to improve the uniformity of the cantilever to prevent such drawbacks of a wrinkled profile which the previous design shows. Also, our last design is driven by a digital drive creating 5 different reconfiguration states. With full-wave simulations, the performance of the proposed absorber demonstrates experimentally in each of 5 different reconfiguration states. The initially measured deflection of the cantilever beam is 51.8 μm on average. At the initial state, the resonant frequency and the absorptivity are 32.95 GHz and 80.95%. When all the cantilevers are pulled down, the frequency shifts a total of 4.08 GHz from the initial state showing a tuning ratio of 12.29 %. The error between the measured value and the simulation value came within 0.39 GHz in all five states. This dissertation demonstrated the potential of MEMS as a tuning method for Ka-band absorbers.이 논문은 산소 플라즈마 애싱 공정을 사용하여 응력구배 MEMS 외팔보를 사용한 최초의 Ka 대역 주파수 가변 메타물질 흡수체를 제안하고 검증하였다. GHz 영역에서 LC 공진 주파수 가변 방식에 MEMS 액추에이터를 구동하기 위해 메타물질 단위 셀인 분할링공진기 구조는 mm 스케의 외팔보를 정전용량의 요소를 갖도록 설계하였다. 정전용량 변화를 최대화하기 위해 MEMS 외팔보는 플라즈마 애싱 공정에 의해 수직 방향으로 큰 편향차를 갖도록 설계하였다. 응력구배 MEMS 외팔보는 대칭의 분할링 공진기 구조의 단위 셀 4곳에 배열되고 두 셀은 배열구조로 설계되었다. 이 때, 풀인 전압 이상의 높은 전압을 인가 시 외팔보는 바닥전극에 붙게 되어 정전용량을 키우고 LC 공진 주파수를 낮춘다. 흡수체의 기계적 거동에 대한 균일성을 개선하기 위해 총 3가지 다른 모양의 외팔보를 설계하였다. 먼저 길이 400μm, 너비 50μm인 외팔보를 12개의 배열상태로 설계하여 컴퓨터 시뮬레이션과 측정값을 확인하였다. 첫 번째 흡수체의 플라즈마 애싱 공정을 통한 외팔보 구현 공정의 결과, 96개의 외팔보의 평균 값은 41.5 μm이고 표준 편차는 15.4 μm였다. 첫 번째 흡수체의 경우 제작 외팔보의 산포가 상당히 큼에도 불구하고, 15 V까지 아날로그 튜닝을 하여, 초기 상태의 28 GHz의 공진주파수에서 25.5 GHz의 공진주파수 변화하여 총 2.5 GHz의 주파수 가변범위를 도달하였다. 반사계수는 초기 -5.68 dB에서 -33.60 dB까지 변화하였고, 투과 계수의 경우 -40에서 -60 dB를 유지하였다. 흡수율 계산 결과, 각 공진 주파수에서의 흡수율은 0 V일 때 72.9%에서 계속 증가하며 15 V일때 99.9%의 흡수율을 도달하였다. 그럼에도 불구하고, 외팔보 어레이 갖는 넓은 편향값 산포가 컴퓨터 시뮬레이션과의 괴리가 있어 개선된 설계를 다시 시도하였다. 앞선 설계의 단점을 극복하기 위해 점진적으로 증가하는 패턴의 식각 구멍을 외팔보에 적용하였다. 이 두 번째 구조 또한 제작, 컴퓨터 계산 및 실험 검증하였다. 이러한 식각 구멍 패턴은 외팔보를 산소 플라즈마 애싱 공정으로 구현 시, 제작 균일성을 크게 증가시킨다. 나아가 플라즈마 애싱 공정 또한 시간을 분할하여 제작함으로써 균일도를 크게 증가시킨다. 또한 두번째 설계부터는 응력 구배로 인한 큰 편향을 갖는 외팔보가 갖는 비평형 구동 방식의 해석 어려움에 따라 전압을 개별적으로 인가하며 on/off 형태의 디지털 구동방식으로만 구동하게끔 시스템 구동방식을 변경하였다. 2개의 메타물질 단위 구조에 4개의 전극을 분리하여 총 5개의 구조적으로 다른 상태를 구현하였다. 모든 외팔보가 위로 휘어진 상태에서 전극에 전압을 순차적으로 인가하여 2개씩 바닥에 붙게 하여 최종적으로 모든 외팔보가 바닥에 붙게 하였다. 두 번째 흡수체의 경우, 외팔보 구현이 크게 개선됨에도 불구하고 초기 32.24 GHz의 공진 주파수 값에서 2.14 GHz만 변화하여 최종 30.10 GHz의 공진주파수 측정 결과를 보였다. 흡수율의 경우에도 초기 83.59%에서 최종 90.75%의 결과를 보였지만 컴퓨터 계산과 많은 차이를 보였다. 최종적으로 앞선 2개의 설계를 보완한, 최종 진화한 형태인, 반원형 응력 구배 외팔보를 갖는 흡수체를 설계, 제작, 및 실험 검증하였다. 특히, 외팔보가 갖는 불안정한 기계적 거동을 단순화하여 디지털 구동을 하게끔 흡수체를 설계하였다. 식각 패턴의 거리를 2 μm씩 늘리며 반원 형태의 외곽으로부터 설계한 결과 재현성과 균일성이 매우 크게 개선되었다. 특히 반원 형태의 외팔보의 경우 최고점 편향 높이가 항상 반원 중간에서 구현되기 때문에 반원형 외팔보 간의 모양이 균일하게 유지된다. 제작된 18개 흡수체 샘플에서 144개의 외팔보를 측정한 결과 평균 편향 높이의 평균 값이 51.8 μm였으며 표준 편차는 3.1μm였다. 4개의 전극에서 기반한 5개 상태의 서로 다른 구조에 따른 반사 계수와 투과 계수를 도파관 측정으로 실험 값을 얻었다. 상용 유한요소법 컴퓨터 계산과 비교 검증하였다. 초기 상태에서 공진 주파수는 32.95 GHz였고, 모든 외팔보가 풀인 전압 인가로 인해 바닥 전극에 붙으면 하면 주파수 28.87 GHz가 되어 총 4.08GHz 이동하여 12.29%의 주파수 가변율을 갖는다. 측정값과 유한요소 시뮬레이션 값의 오차는 5개 상태 모두에서 0.39GHz 이내였다. 흡수율의 경우 각 상태에서 80.95 %, 88.17 %, 86.29 %, 99.21 %, and 86.51% 값을 보였다. 이 논문은 Ka-대역 흡수체의 튜닝 방법으로서 MEMS의 가능성을 보여주었다.CHAPTER 1. Introduction 1 1.1 Background 1 1.1.1 Advent of metamaterial 1 1.1.2 Application of metamaterial 2 1.1.3 Physics of metamaterial 3 1.1.4 Meta-atom 10 1.1.5 Electromagnetic absorber to metamaterial absorber 14 1.1.6 Reconfigurable metamaterial 17 1.1.7 MEMS reconfigurable metamaterial 21 1.1.8 Tunable metamaterial absorber 24 1.1.9 MEMS reconfigurable metamaterial absorber 27 1.1.10 Tunable metamaterial absorber for Ka-band 29 1.2 Originality and contribution 32 1.3 Document structure 33 CHAPTER 2. Stress-induced sub-mm scale cantilever 34 2.1 Initial design 34 2.2 Cantilever arrays with stress gradient 37 2.2.1 Preliminary experiment 37 2.2.2 Design 38 2.2.2 Fabrication results 39 2.3 Rectangular shape sub-mm scale cantilever with incremental etch hole spacing 40 2.3.1 Preliminary experiment 40 2.3.2 Design 42 2.4 Semicircular sub-mm scale cantilever with incremental etch hole 49 2.4.1 Design of semicircular sub-mm scale cantilever with incremental etch hole 49 2.4.2 Fabrication 52 CHAPTER 3. The 1st design of MEMS tunable metamaterial absorber with cantilever arrays for continuous tuning 57 3.1 General overview 57 3.2 Design 59 3.2.1 Split ring resonator and simulation 61 3.2.2 Capacitance of cantilever with stress gradient 64 3.2.3 Electrostatic driving of cantilever 67 3.2.4 Stress analysis & PR ashing 69 3.3 Fabrication 71 3.3.1 Fabrication process 71 3.3.2 Fabrication results 74 3.4 Simulation 77 3.5 Experiment 81 3.5.1 Experiment setup 81 3.5.2 Experiment results 84 3.6 Summary 86 CHAPTER 4. The 2nd design of MEMS tunable metamaterial absorber with rectangular shape sub-mm scale stress-induced cantilever with an incremental etch hole spacing for digital driving 87 4.1 General overview 87 4.2 Design 90 4.3 Fabrication 93 4.4 Simulation 98 4.5 Experiment 100 4.6 Summary 102 CHAPTER 5. The 3rd design of MEMS tunable metamaterial absorber with semicircular sub-mm scale stress-induced cantilever with an incremental etch hole spacing for digital driving 103 5.1 General overview 103 5.2 Design 107 5.2.1 Electromagnetic properties 107 5.2.2 Design parameter 109 5.3 Fabrication 112 5.4 Simulation 119 5.4.1 Simulation setup 119 5.4.2 Simulation results 122 5.5 Experiment 126 5.5.1 Experiment setup 126 5.5.2 Preliminary experiment 130 5.5.2 Experiment results 133 5.6 Further Analysis 137 5.6.1 The waveguide simulation 137 5.6.2 The periodic metamaterial unit cell simulation 141 5.6.3 Analysis on the surface current 148 5.7 Summary 152 5.7.1 Summary of the 1st, 2nd, and 3rd design 152 5.7.2 Comparison with MEMS tunable metamaterial absorber 155 5.7.3 Comparison with Ka-band tunable metamaterial absorber 157 CHAPTER 6. Conclusion 159 Bibliography 161 초록 (국문) 180박

Electromagnetic Imaging of the marine subsurface : a novel approach to assess sediment patterns and dynamics on clastic shelf systems

Electromagnetic (EM) imaging is a new approach to investigate marine near-surface sediments. The EM data provide information about electric conductivity and magnetic susceptibility of the sediments. Both are important physical parameters in exploration geophysics. Electric conductivity of marine sediments is a function of porosity, tortuosity and chemistry of the pore fluid. Magnetic susceptibility indicates the magnetic particle concentration and is hence related to the mineral composition of the sediment. In this thesis data processing, inversion and machine learning methods for a novel marine EM profiling system are developed, with the goal to explore the internal structure and spatial variability of sediment patterns in coastal and shelf regions. The investigated EM data were acquired on the NW Iberian shelf during the Meteor cruise M84/4b with the bottom towed electromagnetic profiler MARUM NERIDIS III. This non-conductive, non-magnetic fiberglass sled accommodates a controlled source electromagnetic system based on a frequency-domain concentric-loop EM induction sensor. In order to estimate quantitative seafloor sediment properties from the NERIDIS III EM data, the approach developed in this thesis follows three main steps: The first step is to calibrate the EM data such that instrument related bias is removed and the EM response is solely controlled by the frequency of the source signal, the system geometry, the electric conductivity and magnetic susceptibility of the seawater and the sediment. Calibration is necessary to make data from different measurements and surveys comparable and to enable solving of the ill-posed inverse problem for electric conductivity and magnetic susceptibility. This thesis shows that calibrating the primary EM field alone, by means of independently measured water conductivity and constant water susceptibility, is not sufficient. Therefore, a calibration methodology is developed which firstly calibrates the recorded EM data to compensate for bias in the primary EM field followed by a secondary EM field calibration by means of ground-truth data. The second step involves the inversion of the EM data, which can be subdivided into a half-space and 1-D inversion. The half-space inversion aims for the reconstruction of bulk sediment conductivity and susceptibility of the uppermost approximately 0.5 to 1 m. It is demonstrated that recovered half-space conductivity and susceptibility well reflect the main sediment patterns on the NW Iberian shelf and allow the reconstruction of sediment pathways. The 1-D inversion can be used to reconstruct the vertical conductivity structure of the subsurface. An algorithm is developed which employs the half-space susceptibility as a priori information and hence allows the utilisation of the in-phase component of the complex earth response increasing the depth of investigation. It is shown that vertical conductivity variations down to approximately 3 m below the seafloor can be reconstructed revealing the internal structure of the Galician Mud Belt. The third step covers the predictive modelling of grain-size from the electric conductivity and magnetic susceptibility of the sediment. Correlation analyses are carried out which reveal a strong relation between the electromagnetic and textural sediment properties. A radial basis function network is developed which predicts the entire grain-size distribution for each EM measurement location along shelf wide survey lines. The predicted grain-size distributions are used to identify the well-known sediment facies on the NW Iberian shelf and give new insights into their distribution and transitions

Workshop report ; the Asian Seas International Acoustics Experiment (ASIAEX) ; final planning meeting, Kailua Kona, Hawaii, June 21-23, 2000

http://archive.org/details/workshopreportas00rampN