Vesna Crnojevic-Bengin

Fractal Geometries of Complementary Split-Ring Resonators

Complementary split-ring resonators (CSRRs) are typically used as negative-permittivity particles in microstrip left-handed structures. In this paper, novel CSRRs that use a square Sierpinski fractal curve are proposed and studied in detail. It is shown that the application of fractal geometries results in significant miniaturization of the metamaterial unit cell in comparison with conventional and equivalent meander structures. Multiple fractal CSRRs are also analyzed. The influence of different geometrical parameters and the order of the fractal curve on the performances are investigated, as well as the efficiency of excitation of the particles. When used in the design of left-handed transmission lines, fractal complementary split rings improve frequency selectivity in the upper transition band when compared to other nonfractal topologies.

Compact Tri-Band Bandpass and Bandstop Filters Based on Hilbert-Fork Resonators

In this work, a multi-mode Hilbert-fork resonator consisting of two dual-mode resonators is presented. The behavior of the proposed configuration is analyzed in detail. To demonstrate the potential of the proposed resonator, tri-band bandpass and bandstop filters operating at 2.4/3.5/5.2 GHz have been designed, fabricated and measured. Both filters are characterized by good performances and very compact size of only 0.21λ<i>g</i> × 0.11λ<i>g</i> and 0.22λ<i>g</i> × 0.1λ<i>g</i> , respectively.

Complementary Split Ring Resonators Using Square Sierpinski Fractal Curves

Split ring resonators and complementary split ring resonators are used in a left-handed media to obtain negative values of permeability and permittivity, respectively. In this paper, novel split ring geometry using square Sierpinski fractal curves is proposed, that reduces resonant frequency of the structure and achieves improved frequency selectivity in the upper transition band. In order to validate the results, left-handed microstrip line that uses square Sierpinski complementary split ring resonators is designed, fabricated and measured

Flexible Sierpinski Carpet Fractal Antenna on a Hilbert Slot Patterned Ground

This paper presents a novel design of fractal antenna on a flexible substrate that operates in UMTS band (universal mobile telecommunication system, 1.92–2.17 GHz). The antenna consists of a Sierpinski carpet fractal radiator, which reduces the overall size of the antenna, and it is realized on top of a Hilbert slot in the ground layer, to achieve required impedance matching. The antenna is compact with the overall dimensions equal to 70 mm × 31 mm × 0.075 mm. Influence that folding has on the initial planar topology is investigated in detail. The obtained results show that the proposed antenna is more tolerant to folding than the conventional patch and that it exhibits relatively stable radiation patterns even when folded in complex manners.

Comparison of Commercially Available Full-Wave EM Simulation Tools for Microwave Passive Devices

A great number of software packages specialized for CAD and EM simulation of microwave components is commercially available today. However, choosing optimal package for an application is not trivial. This paper presents comparison of two widely used full-wave EM simulation tools: Ansofts High Frequency Structure Simulator and EMSight - EM simulator in Microwave Office from Applied Wave Research (AWR)

Fabrication and Characterization of Flexible and Miniaturized Humidity Sensors Using Screen-Printed TiO2 Nanoparticles as Sensitive Layer

This paper describes the fabrication and the characterization of an original example of a miniaturized resistive-type humidity sensor, printed on flexible substrate in a large-scale manner. The fabrication process involves laser ablation for the design of interdigitated electrodes on PET (Poly-Ethylene Terephthalate) substrate and a screen-printing process for the deposition of the sensitive material, which is based on TiO2 nanoparticles. The laser ablation process was carefully optimized to obtain micro-scale and well-resolved electrodes on PET substrate. A functional paste based on cellulose was prepared in order to allow the precise screen-printing of the TiO2 nanoparticles as sensing material on the top of the electrodes. The current against voltage (I–V) characteristic of the sensor showed good linearity and potential for low-power operation. The results of a humidity-sensing investigation and mechanical testing showed that the fabricated miniaturized sensors have excellent mechanical stability, sensing characteristics, good repeatability, and relatively fast response/recovery times operating at room temperature.

A Sensor for the Measurement of the Moisture of Undisturbed Soil Samples

This paper presents a very accurate sensor for the measurement of the moisture of undisturbed soil samples. The sensor relies on accurate estimation of the permittivity which is performed independently of the soil type, and a subsequent calibration. The sensor is designed as an upgrade of the conventional soil sampling equipment used in agriculture—the Kopecky cylinder. The detailed description of the device is given, and the method for determining soil moisture is explained in detail. Soil moisture of unknown test samples was measured with an absolute error below 0.0057 g/g, which is only 2.24% of the full scale output, illustrating the high accuracy of the sensor.

Novel Reconfigurable Left-handed Unit Cell for Filter Applications

In this paper a novel, super compact, left-handed unit cell, called ForeS is proposed. ForeS consists of Four Spirals, which are both mutually coupled and end-coupled with microstrip line. Single unit cell is studied together with its modifications that could be realized with simple diode arrangements. By changing bias voltage, different resonant frequencies, insertion losses and spurious responses can be obtained. Simulated characteristics of ForeS exhibit a smaller attenuation, better stop-band characteristic and considerable size reduction in comparison to zeroth-order resonator (ZOR). DOI: 10.2529/PIERS061016120829

Novel Hilbert soil-moisture sensor based on the phase shift method

In this paper, novel soil-moisture sensor based on the Hilbert fractal curve is proposed. The developed sensor is intended to be integrated into wireless sensor network whose goal is the monitoring of the agricultural soils. The operating principle of this sensor is based on the phase shift method which in essence represents the measurement of the soil permittivity. Analytical expressions for the calculation of optimal operating frequency and the absolute moisture content derived from effective permittivity are presented. The influence of the order and the number of fractal curves used to the sensor characteristics are analyzed. The proposed sensor operates at 1.2 GHz and provides phase shift in the range of 70.76° for the extreme cases of the soil moisture content (2 % and 20 %).

On the Orientation of Split-Ring Resonators in Metamaterial Media

Split-ring resonators (SRR) are used both in microstrip and waveguide metamaterial structures to obtain negative values of permeability, whereas complementary split- ring resonators (CSRR) result in negative permittivity when placed below the microstrip. While the orientation of SRR positioned next to the microstrip transmission line significantly influences its performances, it is generally accepted that such dependence does not exist in the case of CSRR-loaded microstrip or SRR-loaded waveguide. In this paper, we show that SRR and CSRR can not be arbitrarily orientated, neither in microstrip nor in waveguide structures. The influence of the orientation is especially visible in the case of multiple CSRR geometries. To validate simulation results, microstrip lines loaded with multiple CSRRs were designed, fabricated and measured.