Contactless measurement of electric current using magnetic sensors

We review recent advances in magnetic sensors for DC/AC current transducers, especially novel AMR sensors and integrated fluxgates, and we make critical comparison of their properties. Most contactless electric current transducers use magnetic cores to concentrate the flux generated by the measured current and to shield the sensor against external magnetic fields. In order to achieve this, the magnetic core should be massive. We present coreless current transducers which are lightweight, linear and free of hysteresis and remanence. We also show how to suppress their weak point: crosstalk from external currents and magnetic fields

Design of the new electromagnetic measurement system for RFX-mod upgrade

A major modification of the RFX-mod toroidal load assembly has been decided in order to improve passive MHD control and to minimize the braking torque on the plasma, thus extending the operational space in both RFP and Tokamak configurations. With the removal of the vacuum vessel, the support structure will be modified in order to obtain a new vacuum-tight chamber and the first wall tiles will be directly in front of the passive stabilizing shell inside of it, so increasing both the poloidal cross section and the plasma-shell proximity. This implies the design of a new vacuum fit electromagnetic measurement system. The new local probes will be installed in vacuum onto the copper shell, behind the graphite tiles, and shall operate up to a maximum temperature of 180\ub0C to allow for baking cycles for first wall conditioning. Because of the reduced room available, tri-axial pickup probes have been designed, with the additional advantage of allowing the minimization of alignment errors. The paper describes the detailed design of the new probe set, in particular highlighting advantages and effectiveness of different probe solutions. Preliminary tests carried out on local probe prototypes to characterize their electromagnetic behaviour are also reported

A High-resolution Scintillating Fiber Tracker With Silicon Photomultiplier Array Readout

We present prototype modules for a tracking detector consisting of multiple layers of 0.25 mm diameter scintillating fibers that are read out by linear arrays of silicon photomultipliers. The module production process is described and measurements of the key properties for both the fibers and the readout devices are shown. Five modules have been subjected to a 12 GeV/c proton/pion testbeam at CERN. A spatial resolution of 0.05 mm and light yields exceeding 20 detected photons per minimum ionizing particle have been achieved, at a tracking efficiency of more than 98.5%. Possible techniques for further improvement of the spatial resolution are discussed.Comment: 31 pages, 27 figures, pre-print version of an article published in Nuclear Instruments and Methods in Physics Research Section A, Vol. 62

고해상도 CMOS 이미지 센서를 위한 나노광학소자

학위논문(박사) -- 서울대학교대학원 : 공과대학 전기·정보공학부, 2021.8. 이병호.Image sensor is a device that converts electromagnetic waves scattered by the objects or environment into electric signals. Recently, in the mobile device and autonomous vehicle industries, multiple image sensors having different purposes are required for a single device. In particular, image sensors with more than 100 million pixels are being developed in response to the development of a display to a high resolution of 8K or more. However, due to the limited space of the mobile device, the size of pixels constituting the sensor must be reduced for a high-resolution image sensor, which causes factors that reduce image quality, such as a decrease in light efficiency, a decrease in quantum efficiency, and color interference. Metasurface is a device that modulates electromagnetic waves through an array of antennas smaller than wavelength. It has been proposed as a device that replaces the color filter, lens, and photodiode constituting the optical system of the image sensor. However, the performance of the metasurface corresponding to the miniaturized pixel size was limited by the operating principle that requires several array of nano-antennas. In this dissertation, I present a metasurface optical device that can improve the image quality of an existing image sensor composed of micropixels. First, an absorption type color filter that suppresses reflection is discussed. The reflection that inevitably occurs in the conventional metasurface color filter elements causes a flare phenomenon in the captured image. In this dissertation, I design a color filter that transmits only a specific band and absorbs the rest of the absorption resonant band of a hyperbolic metamaterial antenna using a particle swarm optimization method. In particular, I present a Bayer pattern color filter with a pixel size of 255 nm. Second, I introduce a color distribution meta-surface to increase the light efficiency of the image sensor. Since the photodiode converts light having energy above the band gap into an electric signal, an absorption type color filter is used for color classification in image sensor. This means that the total light efficiency of the image sensor is limited to 33% by the blue, green, and red filters constituting one pixel. Accordingly, a freeform metasurface device is designed that exceeds the conventional optical efficiency limit by distributing light incident on the sub-pixel in different directions according to color. Finally, an optical confinement device capable of increasing signal-to-noise ratio (SNR) in low-illuminance at near-infrared is presented. Through the funnel-shaped plasmonic aperture, the light is focused on a volume much smaller than the wavelength. The focused electric and magnetic fields interact with the spatially distributed semiconductors, which achieve a Purcell effect enhanced by the presence of the metasurface. This dissertation is expected to overcome the conventional nanophotonic devices for image sensors and become a cornerstone of the development of micropixel or nanopixel image sensors. Furthermore, it is expected to contribute to building a new image sensor platform that will replace the optical system constituting the image sensor with metasurface.이미지 센서는 환경에 의해 산란되는 전자기파를 전기신호로 바꾸는 소자로, 최근 모바일 기기와 자율 주행 자동차 산업에서 단일 디바이스에 다른 목적을 가진 이미지 센서들이 요구되고 있다. 특히, 디스플레이가 8K 이상의 고해상도로 발전함에 대응하여 1억화소 이상의 이미지 센서가 개발되고 있다. 그러나, 모바일 기기의 제한된 공간에 의해 고해상도 이미지 센서를 위해서는 센서를 구성하는 픽셀의 크기를 줄여야 하며, 이는 광 효율 감소, 양자 효율 감소, 색 간섭 등의 화질을 감소시키는 요소들을 야기한다. 메타표면은 파장보다 작은 안테나들의 배열을 통해 전자기파를 변조해주는 소자로, 이미지 센서의 광학 시스템을 구성하는 색 필터, 렌즈, 포토 다이오드를 대체하는 소자로 제안되었다. 하지만, 소형화 된 픽셀 크기에 대응하는 메타표면은 나노 안테나의 동작원리와 배열의 한계에 의해 성능이 제한되었다. 본 논문에서는 초소형 픽셀로 구성된 기존 이미지 센서에 대한 화질을 높일 수 있는 메타표면 광학소자를 제시한다. 첫째로, 반사를 억제하는 흡수형 색 필터에 대해서 논의한다. 기존 메타표면 색 필터 소자에서 필연적으로 발생하는 내부 반사는 찍은 이미지에서 플레어 현상을 유발한다. 본 논문에서는 쌍곡 메타물질 안테나의 흡수 공진 대역을 입자 무리 최적화 방식을 이용해 특정 대역 만을 투과하고 나머지는 흡수하는 색 필터를 설계한다. 특히, 255 nm 크기 픽셀의 베이어 패턴 색 필터를 제시한다. 둘째로, 이미지 센서의 광 효율을 높이기 위한 색 분배 메타표면을 제시한다. 이미지 센서의 포토 다이오드는 밴드 갭 이상의 에너지를 가지는 빛에 대해 전기신호로 변환하므로, 색 구분을 위해 흡수형 색 필터를 사용한다. 이는 하나의 픽셀을 구성하는 청, 녹, 적색 필터에 의해 이미지 센서의 전체 광 효율이 33 %로 제한되는 것을 의미한다. 따라서, 서브 픽셀에 입사하는 빛을 색에 따라 다른 방향으로 빛을 분배하여 기존의 광 효율 한계를 넘어서는 자유형 메타표면 소자를 설계한다. 마지막으로, 저조도의 근적외선에서 신호 대 잡음비를 높일 수 있는 광 집속 소자를 제시한다. 깔대기 모양의 플라즈모닉 개구를 통해 빛을 파장보다 매우 작은 크기의 영역에 집중시킨다. 집속된 전기장과 자기장은 공간적으로 분포된 반도체와 상호작용함으로써, 메타표면의 존재에 따라 강화된 Purcell 효과를 얻는다. 본 박사학위 논문은 이미지 센서를 위한 기존의 제한된 메타표면 소자를 극복하고, 초소형 픽셀의 이미지 센서 개발의 초석이 될 것으로 기대된다. 나아가, 이미지 센서를 구성하는 광학 시스템을 메타표면으로 대체할 새로운 플랫폼을 구축하는 것에 기여할 것으로 기대된다.Chapter 1 Introduction 1 1.1 Overview of CMOS image sensors 1 1.2 Toward high-resolution miniaturized pixel 2 1.3 Nanophotonic elements for high-resolution camera 3 1.4 Dissertation overview 5 Chapter 2 Light interaction with subwavelength antennas 7 2.1 Overview of plasmonic antenna 7 2.2 Overview of dielectric metasurface 9 2.3 Overview of hyperbolic metamaterials 11 Chapter 3. Absorptive metasurface color filter based on hyperbolic metamaterial for noise reduction 14 3.1 Introduction 14 3.2 Principle of hyperbolic metamaterial absorbers 17 3.3 Absorptive color filter design based on particle swarm optimization method 19 3.4 Numerical analysis on optimized metasurface color filters 23 3.4.1 Single color filter optimization 23 3.4.2 Angle tolerance for optimized metasurface color filters 26 3.5 Sub-micron metasurface color filter array 29 3.6 Conclusion 35 Chapter 4 High-efficient full-color pixel array based on freeform nanostructures for high-resolution image sensor 37 4.1 Introduction 37 4.2 Optimization of metasurface full-color splitter 40 4.3 Implementation of color splitters 46 4.4 Image quality evaluation 52 4.5 Discussion about off-axis color splitters 55 4.6 Conclusion 59 Chapter 5 Plasmonic metasurface cavity for simultaneous enhancement of optical electric and magnetic fields 60 5.1 Introduction 60 5.2 Working principle and numerical results 63 5.2.1 Principle of funnel-shaped metasurface cavity 63 5.2.2 Discussion 67 5.3 Experimental results 69 5.4 Purcell effect 72 5.5 Conclusion 74 Chapter 6 Conclusion 75 Appendix 78 A.1 Colorimetry 78 A.2 Color difference CIEDE2000 79 B. Related work 80 Bibliography 81박

Study of current measurement method based on circular magnetic field sensing array

© 2018 by the authors. Licensee MDPI, Basel, Switzerland. Classic core-based instrument transformers are more prone to magnetic saturation. This affects the measurement accuracy of such transformers and limits their applications in measuring large direct current (DC). Moreover, protection and control systems may exhibit malfunctions due to such measurement errors. This paper presents a more accurate method for current measurement based on a circular magnetic field sensing array. The proposed measurement approach utilizes multiple hall sensors that are evenly distributed on a circle. The average value of all hall sensors is regarded as the final measurement. The calculation model is established in the case of magnetic field interference of the parallel wire, and the simulation results show that the error decreases significantly when the number of hall sensors n is greater than 8. The measurement error is less than 0.06% when the wire spacing is greater than 2.5 times the radius of the sensor array. A simulation study on the off-center primary conductor is conducted, and a kind of hall sensor compensation method is adopted to improve the accuracy. The simulation and test results indicate that the measurement error of the system is less than 0.1%