Optical tunable multifunctional slow light device based on double monolayer graphene grating-like metamaterial

A very simple optical tunable device, which can realize multiple functions of frequency selection, reflection and slow light, is presented at the investigation. The proposed device is constructed by a periodic grating-like structure. There are two dielectrics (graphene and silicon) in a period of the equivalent grating. The incident light will strongly resonate with the graphene of electrostatic doping, forming an evanescent wave propagating along the surface of graphene, and this phenomenon is the surface plasmon. Under constructive interference of the polaritons, a unique plasmonic induced transparency phenomenon will be achieved. The induced transparency produced by this device can be well theoretically fitted by the bright and dark mode of optical equivalent cavity which can be called coupled mode theory (CMT). This theory can well analyze the influence of various modes and various losses between the function of this device. The device can use gate voltages for electrostatic doping in order to change the graphene carrier concentration and tune the optical performance of the device. Moreover, the length of the device in y-direction is will be much larger than the length of single cycle, providing some basis for realizing the fast tunable function and laying a foundation for the integration. Through a simulation and calculation, we can find that the group index and group delay of this device are as high as 515 and 0.257 picoseconds (ps) respectively, so it can provide a good construction idea for the slow light device. The proposed grating-like metamaterial structure can provide certain simulation and theoretical help for the optical tunable reflectors, absorbers, and slow light devices.

Tunable Spacing Dual-Wavelength Q-Switched Fiber Laser Based on Tunable FBG Device

A tunable spacing dual-wavelength Q-switched fiber laser is experimentally demonstrated based on a fiber Bragg grating tunable device incorporated in an erbium-doped fiber laser (EDFL). The system utilizes two identical fiber Bragg gratings (FBGs) at 1547.1 nm origin to enable two laser lines operation. The wavelength separations between two laser lines are controlled by fixing one of the FBGs while applying mechanical stretch and compression to the other one, using a fiber Bragg grating tunable device. The seven steps of wavelength spacing could be tuned from 0.3344 to 0.0469 nm spacing. Pulse characteristics for both close and wide spacing of dual-wavelength Q-switched fiber laser are successfully being recorded. The findings demonstrate the latest idea of dual-wavelength fiber laser based on FBG tunable device, which offers a wide range of future applications.

A THz Coupler based on Graphene Patterns with SU-8 Photoresist Dielectric Layer

Leveraging both method and concept, a novel multi-layer structure based on Graphene patterns and SU-8 photoresist dielectric is proposed at THz frequency range. By considering reflection and transmission channels as outputs, a simple THz coupler is provided. The structure is described exploiting equivalent circuit model while results are verified by full wave simulations. According to simulation results, the proposed device is able to reflect and transmit THz waves with high sensitivity versus gate biasing. The operation involves five bands in entire THz spectrum while the structure behavior can be adjusted by external gate biasing. Such a tunable device is in great demand to realize optical sensors and systems in several fields from indoor communications, security and medical imaging.

Tunable Zeroth-Order Resonator Based on Ferroelectric Materials

Tunable microwave devices have the benefits of added functionality, smaller form factor, lower cost, and lightweight, and are in great demand for future communications and radar applications as they can extend the operation over a wide dynamic range. Current tunable technologies include several schemes such as ferrites, semiconductors, microelectromechanical systems (MEMS), and ferroelectric thin films. While each technology has its own pros and cons, ferroelectric thin film-based technology has proved itself as the potential candidate for tunable devices due to its simple processes, low power consumption, high power handling, small size, and fast tuning. A tunable Composite Right Left-Handed Zeroth Order Resonator (CRLH ZOR) is introduced in this chapter and it relies mainly on the latest advancement in the ferroelectric materials. It is common that for achieving optimum performance for the resonant structure, this involves the incorporation of an additional tuning by either mechanical means (i.e. with tuning screws) or other coupling mechanisms. The integration between electronic tuning and High-Temperature Superconducting (HTS) components yields a high system performance without degradation of efficiency. This leads not only low-loss microwave components that could be fine-tuned for maximum efficiency but will provide a tunable device over a broadband frequency spectrum as well. The dielectric properties of the ferroelectric thin film, and the thickness of the ferroelectric film, play a fundamental role in the frequency or phase tunability and the overall insertion loss of the circuit. The key advantages of using ferroelectric are the potential for significant size-reduction of the microwave components and systems and the cabibility for integration with microelectronic circuits due to the utilization of thin and thick ferroelectric film technology. In this chapter, ZOR is discussed and the conceptual operation is introduced. The ZOR is designed and simulated by the full-wave analysis software. The response is studied using electromagnetic characteristics with the applied electric field, ferroelectric thickness, and the operating temperature.

Design and development of a catheter-based tunable device for percutaneous mitral repair through coronary sinus

According to the American Heart Association, the cardiac disease accounts for over 800,000 deaths every year (1 of every 3 deaths) in the US alone. Mitral regurgitation, which occurs in 2% of the population, has become the dominant valvular disease contributing to the high death rate caused by cardiac disease. The existing percutaneous treatments of mitral regurgitation suffer from compression of left circumflex artery, limiting their performance and causing serious iatrogenic consequences. Moreover, they are not tunable resulting in limited functionality. In this thesis, a catheter-based tunable device is designed to be implanted inside the coronary sinus for improving mitral regurgitation grade while minimizing the applied force on the left circumflex artery. A comprehensive computed tomography scan image analysis and experiments are performed to extract the required information for the design of the device and its evaluation with FEM simulations. A new effective engagement mechanism for integrating the device with the steerable catheter is designed and tested through large-scale experiments. Additionally, a temperature insensitive force/torque sensor is designed for guiding and introducing the device. This sensor can also be used in other catheter-based devices such as cardiac ablation catheters. The sensing structure of the sensor and its sensing method are evaluated by FEM simulations and large-scale prototyping. The actual-scale prototype of the sensor is fabricated, and the experiments are performed for analyzing the static and dynamic response of the sensor and its temperature cross-sensitivity.

Design and development of a catheter-based tunable device for percutaneous mitral repair through coronary sinus

According to the American Heart Association, the cardiac disease accounts for over 800,000 deaths every year (1 of every 3 deaths) in the US alone. Mitral regurgitation, which occurs in 2% of the population, has become the dominant valvular disease contributing to the high death rate caused by cardiac disease. The existing percutaneous treatments of mitral regurgitation suffer from compression of left circumflex artery, limiting their performance and causing serious iatrogenic consequences. Moreover, they are not tunable resulting in limited functionality. In this thesis, a catheter-based tunable device is designed to be implanted inside the coronary sinus for improving mitral regurgitation grade while minimizing the applied force on the left circumflex artery. A comprehensive computed tomography scan image analysis and experiments are performed to extract the required information for the design of the device and its evaluation with FEM simulations. A new effective engagement mechanism for integrating the device with the steerable catheter is designed and tested through large-scale experiments. Additionally, a temperature insensitive force/torque sensor is designed for guiding and introducing the device. This sensor can also be used in other catheter-based devices such as cardiac ablation catheters. The sensing structure of the sensor and its sensing method are evaluated by FEM simulations and large-scale prototyping. The actual-scale prototype of the sensor is fabricated, and the experiments are performed for analyzing the static and dynamic response of the sensor and its temperature cross-sensitivity.

Study on the fluctuating wind responses of constructing bridge towers with magnetorheological elastomer variable stiffness tuned mass damper

Constructing bridge towers are high-rise and flexible structures subjected to significant wind induced vibrations. Tuned Mass Dampers (TMDs) have been widely used to reduce dynamic responses of high-rise structures under fluctuating wind loadings. By resonance with main structure, TMD can effectively suppress structural vibrations. However, the natural frequencies of bridge tower usually decrease continuously during its construction progress. The frequency shift characteristic will cause the detune of TMD, leading to a great control efficiency loss. As a novel stiffness tunable device made of magnetorheological elastomer (MRE), MRE-TMD can adjust its natural frequency in real-time to track the main structure, avoid detuning and achieve better control performance. To study the wind induced vibration control performance of MRE-TMD, this paper explores the fluctuating wind responses of constructing bridge towers in along wind and cross wind directions. The fluctuating wind loads are generated by harmonic superposition method with the along wind fluctuating wind speed spectrum and the empirical power spectrum of fluctuating lift force. By comparing among the uncontrolled, TMD controlled and MRE-TMD controlled constructing bridge towers, the simulation results show that the MRE-TMD system can effectively maintain the tuning state, and significantly reduce the wind induced vibrations during whole construction process.

Frequency-tunable device based on a multilayer strip-slot transition and its application for measuring the dielectric properties of materials

The paper presents the results of theoretical and experimental researches of a frequency-tunable device based on the multilayer strip-slot transition with the U-shaped slot resonator of the variable length. The application of the presented device makes it possible to implement a resonant method for measuring the dielectric properties of materials in the microwave frequency range. The numerical simulation in the rigorous formulation of the electrodynamics problem is performed for the theoretical research. The aim of the theoretical research is to determine the electrical characteristics of the multilayer strip-slot transition with the U-shaped slot resonator of the variable length. The results of numerical simulation prove the possibility of applying the multilayer stripslot transition with the U-shaped slot resonator of the variable length to implement the resonant method for measuring the dielectric properties of materials in the microwave frequency range. The experimental research is performed on the sample of the multilayer strip-slot transition with the U-shaped slot resonator of the variable length in the frequency range (850–1250) MHz. Measurements of S-parameters of the multilayer strip-slot transition with the U-shaped slot resonator of the variable length are accomplished using the vector network analyzer. The material under research is BaFe10Ti2O19. The results of theoretical and experimental researches are in good qualitative and quantitative agreement.