Intrinsic localized modes in parametrically driven arrays of nonlinear resonators

We study intrinsic localized modes (ILMs), or solitons, in arrays of parametrically driven nonlinear resonators with application to microelectromechanical and nanoelectromechanical systems (MEMS and NEMS). The analysis is performed using an amplitude equation in the form of a nonlinear Schrödinger equation with a term corresponding to nonlinear damping (also known as a forced complex Ginzburg-Landau equation), which is derived directly from the underlying equations of motion of the coupled resonators, using the method of multiple scales. We investigate the creation, stability, and interaction of ILMs, show that they can form bound states, and that under certain conditions one ILM can split into two. Our findings are confirmed by simulations of the underlying equations of motion of the resonators, suggesting possible experimental tests of the theory

Reconfigurable Reflectarrays and Array Lenses for Dynamic Antenna Beam Control: A Review

Advances in reflectarrays and array lenses with electronic beam-forming capabilities are enabling a host of new possibilities for these high-performance, low-cost antenna architectures. This paper reviews enabling technologies and topologies of reconfigurable reflectarray and array lens designs, and surveys a range of experimental implementations and achievements that have been made in this area in recent years. The paper describes the fundamental design approaches employed in realizing reconfigurable designs, and explores advanced capabilities of these nascent architectures, such as multi-band operation, polarization manipulation, frequency agility, and amplification. Finally, the paper concludes by discussing future challenges and possibilities for these antennas.Comment: 16 pages, 12 figure

Optomechanical zipper cavity lasers: theoretical analysis of tuning range and stability

The design of highly wavelength tunable semiconductor laser structures is presented. The system is based on a one dimensional photonic crystal cavity consisting of two patterned, doubly-clamped nanobeams, otherwise known as a "zipper" cavity. Zipper cavities are highly dispersive with respect to the gap between nanobeams in which extremely strong radiation pressure forces exist. Schemes for controlling the zipper cavity wavelength both optically and electrically are presented. Tuning ranges as high as 75nm are achieved for a nominal design wavelength of 1.3micron. Sensitivity of the mechanically compliant laser structure to thermal noise is considered, and it is found that dynamic back-action of radiation pressure in the form of an optical or electrical spring can be used to stabilize the laser frequency. Fabrication of zipper cavity laser structures in GaAs material with embedded self-assembled InAs quantum dots is presented, along with measurements of photoluminescence spectroscopy of the zipper cavity modes.Comment: 20 pages, 8 figure

On collective behaviour of coupled micro/nano electromechanical sensors

With advances in nanotechnology, resonant sensors based on micro/nano electromechanical systems (M/NEMS) have been manufactured utilising a process similar to that of microelectronics. By providing a frequency shift proportional to the mass/stiffness change, these small resonators enable rapid detection of extremely minute changes in mass and force. For example, they can be used to trace the concentration of pathogens. M/NEMS resonators also demonstrate excellent compatibility with electronic circuits, hence offering multi-function and single-chip solutions for next-generation sensing applications. Resonators are coupled to provide extra degrees of freedom for multi-sensing, while reducing a majority of connections required. The collective behaviour of coupled systems gives rise to new sensing methods such as eigenvalue and eigenvector sensing, which exhibit enhanced sensitivity and linearity as opposed to the traditional frequency-shift approach. However, the mechanisms of coupling have not yet been fully exploited. Coupled micro/nano systems are exposed to several challenges. First, process variability is known to degrade sensor performance. Moreover, the readout and signal processing issues in large arrays have not been addressed. Hence, actuating and testing coupled sensors are expensive and time-consuming. These hurdles can be circumvented using a novel inverse eigenvalue analysis (IEA) method proposed in this thesis, which is capable of characterising coupled systems based on inverse and forward analysis. The method extracts the system matrix, which carries deterministic information about process and sensitivity, by attaching a peripheral electrical resonator to the MEMS array, therefore providing the advantages of simplified actuation, accurate calibration and sensitivity trimming. To explore the ultimate limit of scaling, prototype sensors consisting of different numbers of coupled resonators have been designed, fabricated and tested for sensing. By investigating the unique behaviour of eigenvalues, various approaches have been proposed to enhance the accuracy of inverse eigenvalue sensing in large coupled systems

Enhancement of Antenna Array Performance Using Reconfigurable Slot-Ring Antennas and Integrated Filter/Antennas

As modern communication system technology develops, the demand for devices with smaller size, higher efficiency, and more functionality has increased dramatically. In addition, highly integrated RF-front-end modules with a reduced footprint and less transition loss between cascaded devices are desirable in most advanced wireless communication systems. Antenna arrays are widely used in wireless communication systems due to their high directivity and beam steering capability. Moreover, antenna arrays are preferred in mobile communication systems for diversity reception to reduce signal fading effects. In order to meet the various requirements of rapidly developing wireless communication systems, low cost, compact, multifunctional integrated antenna arrays are in high demand. Reconfigurable antennas that can flexibly adapt to different applications by dynamically changing their frequency and radiation properties have attracted a lot of attention. Frequency, radiation pattern, polarization, or a combination of two or more of these parameters in the reconfiguration of antennas was studied and presented in recent years. A single reconfigurable antenna is able to replace multiple traditional antennas and accomplish different tasks. Thus, the complexity of wireless communication systems can be greatly reduced with a smaller device size. On the other hand, the integration of antennas with other devices in wireless communication systems that can improve the efficiency and shrink the device size is a growing trend in antenna technology. Compact and highly efficient integrated filters and antennas were studied previously; the studies show that by seamlessly co-designing filters with patch antennas, the fractional bandwidth (FBW) of the antennas can be enhanced as compared to stand-alone antennas. However, the advantages of both the reconfigurable antenna and integrated filter/antenna technology have not been fully applied to antenna array applications. Therefore, this dissertation explores how to maximize the antenna array performance using reconfigurable antennas and integrated filter/antennas. A continuously frequency reconfigurable slot-ring antenna/array with switches and varactors is presented first. By changing the state of the loaded switches, the reconfigurable slot-ring antenna/array is able to operate as an L-band slot-ring antenna or a 2x2 S-band slot-ring antenna array. In each frequency band, the operation frequency of the antenna/array can be continuously tuned with the loaded varactors. To further enhance the functionality of the reconfigurable slot-ring antenna array, a dual-polarized fractal-shaped reconfigurable slot-ring antenna/array is developed with a reduced number of switches and an increased FBW. Additionally, ground plane solutions are explored to achieve single-sided radiation. The benefits of filter/antenna integration are also investigated in both linearly polarized patch phased arrays and circularly polarized patch antenna arrays. Finally, a preliminary study of a tunable integrated evanescent mode filter/antenna is conducted to validate the concept of combining reconfigurable antennas and integrated filter/antennas

Performances of conformal and planar arrays

Static and dynamic deformations can have a severe impact on the performance of conformal antennas on aircrafts and other vehicles. Therefore it is essential to study the different deformation and vibration mechanisms and their influence on the antenna's radiation pattern. This presentation gives an overview of different approaches concerning electromagnetic modelling of array antennas and investigations on antenna deformations presented in the scope of TG20