Microwave apparatus for gravitational waves observation

In this report the theoretical and experimental activities for the development of superconducting microwave cavities for the detection of gravitational waves are presented.Comment: 42 pages, 28 figure

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

Kytketyt MEMS-resonaattoriverkot

Micromechanical resonance frequencies are in a standard manner a few tens of MHz and can even cover the requency range up to a few GHz. When using high quality material such as quartz of silicon, also internal losses are very low. By physical coupling of resonators into a network, one can realize various mechanical signal processing, filtering or for example neural network type behavior. Since coupling between resonators are realized by some kind of bridge, which can be either rather linear or alternatively intentionally very nonlinear, the overall behavior of the whole network is very complex. Of general interest are effects that originate from multiple inputs and outputs and which could lead to a rather unexpected spectral or transient behavior of the signals, which can be found by computer modelling.Mikromekaaniset resonanssitaajuudet ovat tyypillisesti muutamia kymmeniä megahertsejä mutta voivat kattaa taajuuskaistan aina muutamiin gigahertseihin asti. Käytettäessä korkealaatuisia materiaaleja kuten kvartsia tai piitä myös signaalin häviöt ovat erittäin pieniä. Kytkemällä resonaattoreita fyysiseksi verkoksi voidaan mekaanisilla rakenteilla suorittaa signaalinkäsittelyä, realisoida suodattimia ja jopa neuroverkkoja. Koska yksittäisten resonaattorien välinen kytkentä on jonkinlainen silta, joka voi olla joko melko lineaarinen tai vaihtoehtoisesti tarkoituksellisesti erittäin epälineaarinen, on koko verkon käyttäytyminen erittäin monimutkaista. Yleisesti kiinnostavia ovat useista sisäänmenoista ja ulostuloista johtuvat ilmiöt, jotka voivat johtaa signaalien spektrin tai transienttivasteen melko odottamattomaan tai epäintuitiiviseen käyttäytymiseen, jonka voi löytää ja tulkita tietokonesimulaatioilla

Symmetry-Related Electromagnetic Properties of Resonator-Loaded Transmission Lines and Applications

This paper reviews the recent progress in the analysis and applications of the symmetry-related electromagnetic properties of transmission lines loaded with symmetric configurations of resonant elements. It will be shown that the transmission characteristics of these reactively loaded lines can be controlled by the relative orientation between the line and the resonant elements. Two main types of loaded lines are considered: (i) resonance-based structures; and (ii) frequency-splitting structures. In resonance-based transmission lines, a line is loaded with a single resonant (and symmetric) element. For a perfectly symmetric structure, the line is transparent if the line and resonator exhibit symmetry planes of different electromagnetic nature (electric or magnetic wall), whereas the line exhibits a notch (resonance) in the transmission coefficient if the symmetry planes behave as either electric or magnetic walls (symmetric configuration), or if symmetry is broken. In frequency-splitting lines, paired resonators are typically loaded to the transmission line; the structure exhibits a single notch for the symmetric configuration, whereas generally two split notches appear when symmetry is disrupted. Applications of these structures include microwave sensors (e.g., contactless sensors of spatial variables), selective mode suppressors (of application in common-mode suppressed differential lines, for instance) and spectral signature barcodes, among others

Piezoelectric MEMS Disk Resonator and Filter Based on Epitaxial Al0.3Ga0.7As Films

In this work, a new class of disk, contour-mode, piezoelectric, micromechanical resonators based on single-crystal Al0.3Ga0.7As films has been developed. The shape of the disk resonator is based on the velocity propagation profile of the elastic wave in the plane of the piezoelectric film, with lateral dimensions scaled to the half wave length of the desired resonance frequency. The resonators are designed with supports to emulate free-free boundary conditions. Finite element analysis (FEA) model for this resonator is created in Ansys software, the simulation results validate the design concept. The performance parameters extracted from the FEA models show that this novel disk resonator outperforms the beam type counterpart. A unique 7-mask MEMS fabrication process based on the epitaxial, heterostructure Al0.3Ga0.7As films has been developed and successfully implemented to produce the prototypes of the new disk resonators. Fully experimental characterizations on the prototypes were conducted and the measured results from the prototypes are: a Q factor of 7031 at 30.2 MHz with 1.11 kΩ intrinsic motional resistance; a Q factor of 6515 at 40.8 MHz with 1.26 kΩ intrinsic motional resistance; a Q factor of 3300 at 62.3 MHz with 2.43 kΩ intrinsic motional resistance. The measured power handling level is about 1.6 mW, which is the highest power handling capability to date. These measured performance aspects are better than that of the previously developed beam type resonators. Based on this new disk resonator, two novel, two-port resonators (i.e., filters) designs have been introduced. The FEA models of both designs were created and the simulation results verify these design concepts. Equivalent circuit models for these filters were established with the parameters obtained from the FEA models. Furthermore, the optimal electrode configuration to provide minimum insertion loss is obtained through the analytical transadmittance function of the equivalent circuit. The prototypes of the filters were successfully fabricated. Measured results on these prototypes are summarized here: for the circular patter design, the best insertion loss is -45.7 dB at 37.8 MHz with quality factor 4372; for the half plane electrode design, the best insertion loss is -42.8 dB at 38.1 MHz with quality factor 3632

A Recent Approach towards Fluidic Microstrip Devices and Gas Sensors: A Review

This paper aims to review some of the available tunable devices with emphasis on the techniques employed, fabrications, merits, and demerits of each technique. In the era of fluidic microstrip communication devices, versatility and stability have become key features of microfluidic devices. These fluidic devices allow advanced fabrication techniques such as 3D printing, spraying, or injecting the conductive fluid on the flexible/rigid substrate. Fluidic techniques are used either in the form of loading components, switching, or as the radiating/conducting path of a microwave component such as liquid metals. The major benefits and drawbacks of each technology are also emphasized. In this review, there is a brief discussion of the most widely used microfluidic materials, their novel fabrication/patterning methods

Design of Distributed Spiral Resonators for the Decoupling of MRI Double-Tuned RF Coils

© 1964-2012 IEEE. Objective: A systematic analytical approach to design Spiral Resonators (SRs), acting as distributed magnetic traps (DMTs), for the decoupling of concentric Double-Tuned (DT) RF coils suitable for Ultra-High Field (7 T) MRI is presented. Methods: The design is based on small planar SRs placed in between the two RF loops (used for signal detection of the two nuclei of interest). We developed a general framework based on a fully analytical approach to estimate the mutual coupling between the RF coils and to provide design guidelines for the geometry and number of SRs to be employed. Starting from the full-analytical estimations of the SRs geometry, electromagnetic simulations for improving and validating the performance can be carried out. Results and Conclusion: We applied the method to a test case of a DT RF coil consisting of two concentric and coplanar loops used for 7 T MRI, tuned at the Larmor frequencies of the proton (1H, 298 MHz) and sodium (23Na, 79 MHz) nuclei, respectively. We performed numerical simulations and experimental measurements on fabricated prototypes, which both demonstrated the effectiveness of the proposed design procedure. Significance: The decoupling is achieved by printing the SRs on the same dielectric substrate of the RF coils thus allowing a drastic simplification of the fabrication procedure. It is worth noting that there are no physical connections between the decoupling SRs and the 1H/23Na RF coils, thus providing a mechanically robust experimental set-up, and improving the transceiver design with respect to other traditional decoupling techniques