Detecting activity states of Licensed Users (LUs) has great significance for the utilization of l... more Detecting activity states of Licensed Users (LUs) has great significance for the utilization of limited radio spectrum, especially when activity states of licensed users can be more accurately detected. However, the spectrum detection will always have the wrong detection of a LU state, and it will result in increased communication overhead, extra network energy consumption, and node premature death. To deal with these issues, an energy-efficient cooperative spectrum sensing scheme is proposed which can select a representative sensor node set in Cognitive Radio Sensor Network (CRSN), under given constraints. The representative nodes set which consists of the nodes can provide gains for detecting the LU states is a subset of the nodes deployed in the network. Based on the spectrum detection information provided by the selected representative nodes, the D-S theory of evidence is employed to derive the activity states of LU while keeping the same spectrum sensing accuracy if not better....
A strong and dynamically controlled circular dichroism (CD) effect has aroused great attention du... more A strong and dynamically controlled circular dichroism (CD) effect has aroused great attention due to its desirable applications in modern chemistry and life sciences. In this Letter, we propose a graphene-metal hybrid chiral metamaterial to generate mid-infrared CD with an intensity of more than 10%, which can be actively controlled over a wide wavelength range. In addition to the strong tunability, the CD signal intensity of our nanostructure is drastically larger than that of the purely graphene-based chiroptical nanostructures. Our design offers a new strategy for developing tunable chiral metadevices, which could be used in various applications, such as biochemical detection and information processing.
Origami is the art of folding two-dimensional (2D) materials, such as a flat sheet of paper, into... more Origami is the art of folding two-dimensional (2D) materials, such as a flat sheet of paper, into complex and elaborate three-dimensional (3D) objects. This study reports origami-based metamaterials whose electromagnetic responses are dynamically controllable via switching the folding state of Miura-ori split-ring resonators. The deformation of the Miura-ori unit along the third dimension induces net electric and magnetic dipoles of split-ring resonators parallel or anti-parallel to each other, leading to the strong chiral responses. Circular dichroism as high as 0.6 is experimentally observed while the chirality switching is realized by controlling the deformation direction and kinematics. In addition, the relative density of the origami metamaterials can be dramatically reduced to only 2% of that of the unfolded structure. These results open a new avenue toward lightweight, reconfigurable, and deployable metadevices with simultaneously customized electromagnetic and mechanical pro...
Confining light into a sub-wavelength area has been challenging due to the natural phenomenon of ... more Confining light into a sub-wavelength area has been challenging due to the natural phenomenon of diffraction. In this paper, we report deep sub-wavelength focusing via dispersion engineering based on hyperbolic metamaterials. Hyperbolic metamaterials, which can be realized by alternating layers of metal and dielectric, are materials showing opposite signs of effective permittivity along the radial and the tangential direction. They can be designed to exhibit a nearly-flat open isofrequency curve originated from the large-negative permittivity in the radial direction and small-positive one in the tangential direction. Thanks to the ultraflat dispersion relation and curved geometry of the multilayer stack, hyperlens can magnify or demagnify an incident beam without diffraction depending on the incident direction. We numerically show that hyperlens-based nanofocusing device can compress a Gaussian beam down to tens-of-nanometers of spot size in the ultraviolet (UV) and visible frequenc...
Data warehousing is the foundation of DSS (decision support system), of which the goal is to enab... more Data warehousing is the foundation of DSS (decision support system), of which the goal is to enable decision makers to make better business decisions based on analysis of historic data related to the business operation. Data warehousing has become a major business trend, both for product and service sectors and for application to daily business in all industries. In this thesis, we compare and discuss the two data models and two methods of OLAP (MOLAP and ROLAP). The two data models and two OLAPs are not mutually exclusive in any project. An example of the hybrid design is presented in a case study. In this project, we are able to apply two data models at different stages of the data warehouse. By combining ER model, Star Schema and aggregate table in one architecture, we are able to maximize on both storage capacity and query performance. In addition to the selection of data models, the choice between MOLAP and ROLAP is discussed. When the objectives of the client are clearly defined, the functional requirements of the data warehouse are determined, and the amount of data is relatively small, MOLAP would likely be a better choice because of its superior performance and intuitive querying mechanism. ROLAP becomes a more suitable candidate for OLAP when the amount of data is exceedingly large, and the client does not want to leave out anything. Again, it is possible, even desirable, for both OLAP methods to be applied in one project to compliment each other.
Far-field imaging beyond the diffraction limit is a long sought-after goal in various imaging app... more Far-field imaging beyond the diffraction limit is a long sought-after goal in various imaging applications, which requires usually mechanical scanning or an array of antennas. Here, we propose to solve this challenging problem using a single sensor in combination with a spatio-temporal resonant aperture antenna. We theoretically and numerically demonstrate that such resonant aperture antenna is capable of converting part evanescent waves into propagating waves and delivering them to far fields. The proposed imaging concept provides the unique ability to achieve super resolution for real-time data when illuminated by broadband electromagnetic waves, without the harsh requirements such as near- field scanning, mechanical scanning, or antenna arrays. We expect the imaging methodology to make breakthroughs in super-resolution imaging in microwave, terahertz, optical, and ultrasound regimes.
We demonstrate a semiconductor based broadband near-field superlens in the mid-infrared regime. H... more We demonstrate a semiconductor based broadband near-field superlens in the mid-infrared regime. Here, the Drude response of a highly doped n-GaAs layer induces a resonant enhancement of evanescent waves accompanied by a significantly improved spatial resolution at radiation wavelengths around λ = 20 μm, adjustable by changing the doping concentration. In our experiments, gold stripes below the GaAs superlens are imaged with a λ/6 subwavelength resolution by an apertureless near-field optical microscope utilizing infrared radiation from a free-electron laser. The resonant behavior of the observed superlensing effect is in excellent agreement with simulations based on the Drude-Lorentz model. Our results demonstrate a rather simple superlens implementation for infrared nanospectroscopy.
General expressions of transformed medium parameters are derived for cylindrical cloaks with poly... more General expressions of transformed medium parameters are derived for cylindrical cloaks with polygon cross sections. An irregular polygon cloak is designed to show the flexibility of the method. Its invisibility to external incident waves is verified by full-wave simulations. Since a polygon can be tailored to resemble any objects to be concealed, the method in this paper provides a powerful tool to design 2D cloaks with arbitrary geometries.
ABSTRACT We propose that 2D rectangular lattice photonic crystals composed of dielectric rods can... more ABSTRACT We propose that 2D rectangular lattice photonic crystals composed of dielectric rods can be utilized for wide-range and tunable diffraction management. The control of diffraction for a normally incident beam is achieved by either properly choosing the operating frequency or changing the refractive index of the dielectric rods. The convergent, collimated, and divergent beam behaviors corresponding to a wide range of diffraction are clearly illustrated using FDTD simulations. The tunability of diffraction around the frequency of super-collimation is also analyzed and demonstrated.
... The results verify the invisibility properties of the designed cloaks and the effectiveness o... more ... The results verify the invisibility properties of the designed cloaks and the effectiveness of the proposed method. ... The blue solid line is for the three layers background without any object embedded (corresponding to figure 2(a)). The black line marked by crosses is for the three ...
Detecting activity states of Licensed Users (LUs) has great significance for the utilization of l... more Detecting activity states of Licensed Users (LUs) has great significance for the utilization of limited radio spectrum, especially when activity states of licensed users can be more accurately detected. However, the spectrum detection will always have the wrong detection of a LU state, and it will result in increased communication overhead, extra network energy consumption, and node premature death. To deal with these issues, an energy-efficient cooperative spectrum sensing scheme is proposed which can select a representative sensor node set in Cognitive Radio Sensor Network (CRSN), under given constraints. The representative nodes set which consists of the nodes can provide gains for detecting the LU states is a subset of the nodes deployed in the network. Based on the spectrum detection information provided by the selected representative nodes, the D-S theory of evidence is employed to derive the activity states of LU while keeping the same spectrum sensing accuracy if not better....
A strong and dynamically controlled circular dichroism (CD) effect has aroused great attention du... more A strong and dynamically controlled circular dichroism (CD) effect has aroused great attention due to its desirable applications in modern chemistry and life sciences. In this Letter, we propose a graphene-metal hybrid chiral metamaterial to generate mid-infrared CD with an intensity of more than 10%, which can be actively controlled over a wide wavelength range. In addition to the strong tunability, the CD signal intensity of our nanostructure is drastically larger than that of the purely graphene-based chiroptical nanostructures. Our design offers a new strategy for developing tunable chiral metadevices, which could be used in various applications, such as biochemical detection and information processing.
Origami is the art of folding two-dimensional (2D) materials, such as a flat sheet of paper, into... more Origami is the art of folding two-dimensional (2D) materials, such as a flat sheet of paper, into complex and elaborate three-dimensional (3D) objects. This study reports origami-based metamaterials whose electromagnetic responses are dynamically controllable via switching the folding state of Miura-ori split-ring resonators. The deformation of the Miura-ori unit along the third dimension induces net electric and magnetic dipoles of split-ring resonators parallel or anti-parallel to each other, leading to the strong chiral responses. Circular dichroism as high as 0.6 is experimentally observed while the chirality switching is realized by controlling the deformation direction and kinematics. In addition, the relative density of the origami metamaterials can be dramatically reduced to only 2% of that of the unfolded structure. These results open a new avenue toward lightweight, reconfigurable, and deployable metadevices with simultaneously customized electromagnetic and mechanical pro...
Confining light into a sub-wavelength area has been challenging due to the natural phenomenon of ... more Confining light into a sub-wavelength area has been challenging due to the natural phenomenon of diffraction. In this paper, we report deep sub-wavelength focusing via dispersion engineering based on hyperbolic metamaterials. Hyperbolic metamaterials, which can be realized by alternating layers of metal and dielectric, are materials showing opposite signs of effective permittivity along the radial and the tangential direction. They can be designed to exhibit a nearly-flat open isofrequency curve originated from the large-negative permittivity in the radial direction and small-positive one in the tangential direction. Thanks to the ultraflat dispersion relation and curved geometry of the multilayer stack, hyperlens can magnify or demagnify an incident beam without diffraction depending on the incident direction. We numerically show that hyperlens-based nanofocusing device can compress a Gaussian beam down to tens-of-nanometers of spot size in the ultraviolet (UV) and visible frequenc...
Data warehousing is the foundation of DSS (decision support system), of which the goal is to enab... more Data warehousing is the foundation of DSS (decision support system), of which the goal is to enable decision makers to make better business decisions based on analysis of historic data related to the business operation. Data warehousing has become a major business trend, both for product and service sectors and for application to daily business in all industries. In this thesis, we compare and discuss the two data models and two methods of OLAP (MOLAP and ROLAP). The two data models and two OLAPs are not mutually exclusive in any project. An example of the hybrid design is presented in a case study. In this project, we are able to apply two data models at different stages of the data warehouse. By combining ER model, Star Schema and aggregate table in one architecture, we are able to maximize on both storage capacity and query performance. In addition to the selection of data models, the choice between MOLAP and ROLAP is discussed. When the objectives of the client are clearly defined, the functional requirements of the data warehouse are determined, and the amount of data is relatively small, MOLAP would likely be a better choice because of its superior performance and intuitive querying mechanism. ROLAP becomes a more suitable candidate for OLAP when the amount of data is exceedingly large, and the client does not want to leave out anything. Again, it is possible, even desirable, for both OLAP methods to be applied in one project to compliment each other.
Far-field imaging beyond the diffraction limit is a long sought-after goal in various imaging app... more Far-field imaging beyond the diffraction limit is a long sought-after goal in various imaging applications, which requires usually mechanical scanning or an array of antennas. Here, we propose to solve this challenging problem using a single sensor in combination with a spatio-temporal resonant aperture antenna. We theoretically and numerically demonstrate that such resonant aperture antenna is capable of converting part evanescent waves into propagating waves and delivering them to far fields. The proposed imaging concept provides the unique ability to achieve super resolution for real-time data when illuminated by broadband electromagnetic waves, without the harsh requirements such as near- field scanning, mechanical scanning, or antenna arrays. We expect the imaging methodology to make breakthroughs in super-resolution imaging in microwave, terahertz, optical, and ultrasound regimes.
We demonstrate a semiconductor based broadband near-field superlens in the mid-infrared regime. H... more We demonstrate a semiconductor based broadband near-field superlens in the mid-infrared regime. Here, the Drude response of a highly doped n-GaAs layer induces a resonant enhancement of evanescent waves accompanied by a significantly improved spatial resolution at radiation wavelengths around λ = 20 μm, adjustable by changing the doping concentration. In our experiments, gold stripes below the GaAs superlens are imaged with a λ/6 subwavelength resolution by an apertureless near-field optical microscope utilizing infrared radiation from a free-electron laser. The resonant behavior of the observed superlensing effect is in excellent agreement with simulations based on the Drude-Lorentz model. Our results demonstrate a rather simple superlens implementation for infrared nanospectroscopy.
General expressions of transformed medium parameters are derived for cylindrical cloaks with poly... more General expressions of transformed medium parameters are derived for cylindrical cloaks with polygon cross sections. An irregular polygon cloak is designed to show the flexibility of the method. Its invisibility to external incident waves is verified by full-wave simulations. Since a polygon can be tailored to resemble any objects to be concealed, the method in this paper provides a powerful tool to design 2D cloaks with arbitrary geometries.
ABSTRACT We propose that 2D rectangular lattice photonic crystals composed of dielectric rods can... more ABSTRACT We propose that 2D rectangular lattice photonic crystals composed of dielectric rods can be utilized for wide-range and tunable diffraction management. The control of diffraction for a normally incident beam is achieved by either properly choosing the operating frequency or changing the refractive index of the dielectric rods. The convergent, collimated, and divergent beam behaviors corresponding to a wide range of diffraction are clearly illustrated using FDTD simulations. The tunability of diffraction around the frequency of super-collimation is also analyzed and demonstrated.
... The results verify the invisibility properties of the designed cloaks and the effectiveness o... more ... The results verify the invisibility properties of the designed cloaks and the effectiveness of the proposed method. ... The blue solid line is for the three layers background without any object embedded (corresponding to figure 2(a)). The black line marked by crosses is for the three ...
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Papers by Kan Yao