Electrically tuned microwave devices using liquid crystal technology

An overview of liquid crystal technology for microwave and millimeter-wave frequencies is presented. The potential of liquid crystals as reconfigurable materials arises from their ability for continuous tuning with low power consumption, transparency, and possible integration with printed and flexible circuit technologies. This paper describes physical theory and fundamental electrical properties arising from the anisotropy of liquid crystals and overviews selected realized liquid crystal devices, throughout four main categories: resonators and filters, phase shifters and delay lines, antennas, and, finally, frequency-selective surfaces and metamaterials.Pouria Yaghmaee, Onur Hamza Karabey, Bevan Bates, Christophe Fumeaux and Rolf Jakob

Predicting complexity perception of real world images

The aim of this work is to predict the complexity perception of real world images.We propose a new complexity measure where different image features, based on spatial, frequency and color properties are linearly combined. In order to find the optimal set of weighting coefficients we have applied a Particle Swarm Optimization. The optimal linear combination is the one that best fits the subjective data obtained in an experiment where observers evaluate the complexity of real world scenes on a web-based interface. To test the proposed complexity measure we have performed a second experiment on a different database of real world scenes, where the linear combination previously obtained is correlated with the new subjective data. Our complexity measure outperforms not only each single visual feature but also two visual clutter measures frequently used in the literature to predict image complexity. To analyze the usefulness of our proposal, we have also considered two different sets of stimuli composed of real texture images. Tuning the parameters of our measure for this kind of stimuli, we have obtained a linear combination that still outperforms the single measures. In conclusion our measure, properly tuned, can predict complexity perception of different kind of images

A new enhanced differential CMOS Colpitts oscillator

This paper represents a new enhanced Colpitts oscillator, which is designed based on gm-boosting of a conventional Colpitts oscillator. The proposed topology increases the negative resistant and enhances the start-up difficulty of the conventional Colpitts oscillator. This enables the Colpitts oscillator to operate in low-power consumption. Moreover, the differential and balanced structure helps limit even-order harmonics and degrades the common mode noise effects in output. The proposed circuit is designed using 0.18 μm technology and is simulated under 1.8 V supply voltage in advanced design system (ADS). Simulations show the output phase noise of -140 dBc/Hz at 1 MHz offset frequency when the operating frequency is 1 GHz

A new enhanced differential cmos Colpitts oscillator

This paper represents a new enhanced Colpitts oscillator, which is designed based on gm-boosting of a conventional Colpitts oscillator. The proposed topology increases the negative resistant and enhances the start-up difficulty of the conventional Colpitts oscillator. This enables the Colpitts oscillator to operate in low-power consumption. Moreover, the differential and balanced structure helps limit even-order harmonics and degrades the common mode noise effects in output. The proposed circuit is designed using 0.18 μm technology and is simulated under 1.8 V supply voltage in advanced design system (ADS). Simulations show the output phase noise of -140 dBc/Hz at 1 MHz offset frequency when the operating frequency is 1 GHz.Amir Ebrahimi and Pouria Yaghmae

Effect of polyimide layers on the permittivity tuning range of liquid crystals

Liquid crystals have potential applications in the design of tunable microwave devices. Polyimide films are commonly incorporated in designs to achieve reproducible molecule alignment in the unbiased state. In this investigation two separate resonator elements are designed and investigated: One is fabricated with polyimide layers and one without. Experimental results obtained with a patch resonator illustrate that about half of the maximum tuning range is achieved without polyimide layers. Since substrates able to sustain a temperature range of 180-300 °C are required for the polyimide film curing process, avoiding polyimide enables using even lower heat resistant substrates for various tunable microwave applications and can lead to faster fabrication processes.Pouria Yaghmaee, Thomas Kaufmann, Bevan Bates and Christophe Fumeau

A Comparative Clinical Trial of Topical Triamcinolone (Adcortyle) and a Herbal Solution for the Treatment of Minor Aphthous Stomatitis

Introduction & Objective: Aphthous stomamtitis is characterized by single or multiple painful recurrent lesions in oral mucosa. Lesions can relapse in some patients for several years. Therefore treatment of such cases seems necessary. The aim of this study was to compare the therapeutic effect of topical Myrtus communis (myrtle) solution with topical triamcinolone (Adcortyle) in the treatment of minor apotheosis. Materials & Methods: This clinical-trial study was conducted at Kurdistan University of Medical Sciences in 2009. 100 patients were randomly assigned into 2 groups. The 1st group received topical myrtle solution. The 2nd group received topical trimcinolone (Adcortyle). After one week, patients' declaration about time of the recovery of the pain and deterioration of oral lesion was recorded. The gathered data was then analyzed using the SPSS statistical software using t-test and chi-square. Results: After treatment, both groups showed response to topical medications with no significant difference between them (p>0.05). Conclusion: results of this study showed that topical myrtle solution is effective in the treatment of minor aphthous stomatitis and its therapeutic effect is comparable with topical triamcinolone (Adcortyle)

Intelligent modeling of a piezoelectric tube actuator

Various model-based control methods are currently used in control of piezoelectric tubes, others such as internal model control and model predictive control are anticipated to be employed soon. All these control systems are designed based on black box models. However, systematic black box modeling of piezoelectric tubes has been overlooked in the literature to a large extent or has been presented in a too brief and faulty way. In this article, a novel structure of artificial neural networks is used to model and to assess the nonlinearity of piezoelectric actuators. Apart from nonlinearity, other features of the achieved models like delay time, sampling time, orders as well as system identification process are clearly stated, and more importantly, it is clarified that different definitions of accuracy are needed for different purposes of black box modeling, with change in model features, the accuracy may decrease for one purpose (e.g. predictive control) and increase for another one (e.g. simulation). This highly critical point has never been raised and addressed in modeling of piezoelectric tubes, and a definition of accuracy which suits static systems/models has been widely used in the past to assess models of piezoelectric tubes which are obviously dynamic. Experimental results support the proposed modeling ideas.Morteza Mohammadzaheri, Steven Grainger, Mohsen Bazghaleh, Pouria Yaghmae

A multi-layered tunable stepped-impedance resonator for liquid crystal characterization

The characterization of a tunable band-pass filter based on stepped-impedance resonator (SIR) is presented in this work. The designed filter uses a half-wavelength resonator patch above a multi-layer substrate, with liquid crystal as its central layer, making it continuously tunable at frequencies around S-band. Two liquid crystal samples are considered for three different approaches: lumped-element circuit simulation, full-wave electromagnetic simulations and prototype measurements. The results demonstrate the possibility of using a simple lumped-element circuit simulation for rapid calculation of the performances of liquid crystal devices at microwave frequencies.Pouria Yaghmaee, Ali K. Horestani, Bevan Bates and Christophe Fumeau