2,284 research outputs found
Optical Yagi-Uda nanoantennas
Conventional antennas, which are widely employed to transmit radio and TV
signals, can be used at optical frequencies as long as they are shrunk to
nanometer-size dimensions. Optical nanoantennas made of metallic or
high-permittivity dielectric nanoparticles allow for enhancing and manipulating
light on the scale much smaller than wavelength of light. Based on this
ability, optical nanoantennas offer unique opportunities regarding key
applications such as optical communications, photovoltaics, non-classical light
emission, and sensing. From a multitude of suggested nanoantenna concepts the
Yagi-Uda nanoantenna, an optical analogue of the well-established
radio-frequency Yagi-Uda antenna, stands out by its efficient unidirectional
light emission and enhancement. Following a brief introduction to the emerging
field of optical nanoantennas, here we review recent theoretical and
experimental activities on optical Yagi-Uda nanoantennas, including their
design, fabrication, and applications. We also discuss several extensions of
the conventional Yagi-Uda antenna design for broadband and tunable operation,
for applications in nanophotonic circuits and photovoltaic devices
Angular and Polarization Response of Multimode Sensors with Resistive-Grid Absorbers
High sensitivity receiver systems with near ideal polarization sensitivity
are highly desirable for development of millimeter and sub-millimeter radio
astronomy. Multimoded bolometers provide a unique solution to achieve such
sensitivity, for which hundreds of single-mode sensors would otherwise be
required. The primary concern in employing such multimoded sensors for
polarimetery is the control of the polarization systematics. In this paper, we
examine the angular- and polarization- dependent absorption pattern of a thin
resistive grid or membrane, which models an absorber used for a multimoded
bolometer. The result shows that a freestanding thin resistive absorber with a
surface resistivity of \eta/2, where \eta\ is the impedance of free space,
attains a beam pattern with equal E- and H-plane responses, leading to zero
cross polarization. For a resistive-grid absorber, the condition is met when a
pair of grids is positioned orthogonal to each other and both have a
resistivity of \eta/2. When a reflective backshort termination is employed to
improve absorption efficiency, the cross-polar level can be suppressed below
-30 dB if acceptance angle of the sensor is limited to <60degrees. The small
cross-polar systematics have even-parity patterns and do not contaminate the
measurements of odd-parity polarization patterns, for which many of recent
instruments for cosmic microwave background are designed. Underlying symmetry
that suppresses these cross-polar systematics is discussed in detail. The
estimates and formalism provided in this paper offer key tools in the design
consideration of the instruments using the multimoded polarimeters.Comment: 22 pages, 15 figure
Antennas and Propagation
This Special Issue gathers topics of utmost interest in the field of antennas and propagation, such as: new directions and challenges in antenna design and propagation; innovative antenna technologies for space applications; metamaterial, metasurface and other periodic structures; antennas for 5G; electromagnetic field measurements and remote sensing applications
Non-Invasive Electromagnetic Biological Microwave Testing
Blood glucose monitoring is a primary tool for the care of diabetic patients. At present, there is no noninvasive monitoring technique of blood glucose concentration that is widely accepted in the medical industry. New noninvasive measurement techniques are being investigated. This work focuses on the possibility of a monitor that noninvasively measures blood glucose levels using electromagnetic waves. The technique is based on relating a monitoring antennaβs resonant frequency to the permittivity, and conductivity of skin, which in turn, is related to the glucose levels. This becomes a hot researched field in recent years. Different types of antennas (wideband and narrowband) have been designed, constructed, and tested in free space. An analytical model for the antenna has been developed, which has been validated with simulations. Microstrip antenna is one of the most common planar antenna structures used. Extensive research development aimed at exploiting its advantages such as lightweight, low cost, conformal configurations, and compatibility with integrated circuits have been carried out. Rectangular and circular patches are the basic shapes that are the most commonly used in microstrip antennas. Ideally, the dielectric constant Ξ΅r, however, and other performance requirements may dictate the use of substrate whose dielectric constant can be greater. As in our prototype blood sensor, the miniaturized size is one of the main challenges
κ³ ν΄μλ CMOS μ΄λ―Έμ§ μΌμλ₯Ό μν λλ Έκ΄νμμ
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Όλ¬Έ(λ°μ¬) -- μμΈλνκ΅λνμ : 곡과λν μ κΈ°Β·μ 보곡νλΆ, 2021.8. μ΄λ³νΈ.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.μ΄λ―Έμ§ μΌμλ νκ²½μ μν΄ μ°λλλ μ μκΈ°νλ₯Ό μ κΈ°μ νΈλ‘ λ°κΎΈλ μμλ‘, μ΅κ·Ό λͺ¨λ°μΌ κΈ°κΈ°μ μμ¨ μ£Όν μλμ°¨ μ°μ
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λ§μ§λ§μΌλ‘, μ μ‘°λμ κ·Όμ μΈμ μμ μ νΈ λ μ‘μλΉλ₯Ό λμΌ μ μλ κ΄ μ§μ μμλ₯Ό μ μνλ€. κΉλκΈ° λͺ¨μμ νλΌμ¦λͺ¨λ κ°κ΅¬λ₯Ό ν΅ν΄ λΉμ νμ₯λ³΄λ€ λ§€μ° μμ ν¬κΈ°μ μμμ μ§μ€μν¨λ€. μ§μλ μ κΈ°μ₯κ³Ό μκΈ°μ₯μ 곡κ°μ μΌλ‘ λΆν¬λ λ°λ체μ μνΈμμ©ν¨μΌλ‘μ¨, λ©ννλ©΄μ μ‘΄μ¬μ λ°λΌ κ°νλ Purcell ν¨κ³Όλ₯Ό μ»λλ€.
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Όλ¬Έμ μ΄λ―Έμ§ μΌμλ₯Ό μν κΈ°μ‘΄μ μ νλ λ©ννλ©΄ μμλ₯Ό 극볡νκ³ , μ΄μν ν½μ
μ μ΄λ―Έμ§ μΌμ κ°λ°μ μ΄μμ΄ λ κ²μΌλ‘ κΈ°λλλ€. λμκ°, μ΄λ―Έμ§ μΌμλ₯Ό ꡬμ±νλ κ΄ν μμ€ν
μ λ©ννλ©΄μΌλ‘ λ체ν μλ‘μ΄ νλ«νΌμ ꡬμΆνλ κ²μ κΈ°μ¬ν κ²μΌλ‘ κΈ°λλλ€.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 81λ°
A Review of 2D and 3D Plasmonic Nanostructure Array Patterns: Fabrication, Light Management and Sensing Applications
Abstract: This review article discusses progress in surface plasmon resonance (SPR) of two-dimensional (2D) and three-dimensional (3D) chip-based nanostructure array patterns. Recent advancements in fabrication techniques for nano-arrays have endowed researchers with tools to explore a materialβs plasmonic optical properties. In this review, fabrication techniques including electron-beam lithography, focused-ion lithography, dip-pen lithography, laser interference lithography, nanosphere lithography, nanoimprint lithography, and anodic aluminum oxide (AAO) template-based lithography are introduced and discussed. Nano-arrays have gained increased attention because of their optical property dependency (lightmatter interactions) on size, shape, and periodicity. In particular, nano-array architectures can be tailored to produce and tune plasmonic modes such as localized surface plasmon resonance (LSPR), surface plasmon polariton (SPP), extraordinary transmission, surface lattice resonance (SLR), Fano resonance, plasmonic whisperinggallery modes (WGMs), and plasmonic gap mode. Thus, light management (absorption, scattering, transmission, and guided wave propagation), as well as electromagnetic (EM) field enhancement, can be controlled by rational design and fabrication of plasmonic nano-arrays. Because of their optical properties, these plasmonic modes can be utilized for designing plasmonic sensors and surfaceenhanced Raman scattering (SERS) sensors
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