Ali K. Horestani

Displacement Sensor Based on Diamond-Shaped Tapered Split Ring Resonator

Split-ring resonators (SRRs) are ideal structures for the realization of compact high-sensitivity and high-resolution sensors due to their high-quality factor resonance, compact size, and high sensitivity to changes in the constituent materials and physical dimensions. This paper presents a displacement sensor based on a diamond-shaped tapered SRR coupled to a coplanar waveguide. Two significant improvements over previous designs are reported. Firstly, the proposed sensor has higher dynamic range and linearity for displacement sensing. Secondly, compared with previous designs, where the displacement changes both the resonant frequency and depth of the transmission notch, the proposed sensor has a fixed resonant frequency. This is an important improvement since the sensor can be operated at a single fixed frequency and bypass the need for a frequency-sweeping microwave source and measurement system such as an expensive network analyzer. It is shown that, while preserving the compact size, the proposed sensor also benefits from a lower operating frequency. The design principle and simulation results are validated through measurement.

Rotation Sensor Based on Horn-Shaped Split Ring Resonator

This paper presents a rotation sensor based on a modified split ring resonator (SRR) coupled to a coplanar waveguide. It is shown that compared with previous SRR-based rotation sensors, the proposed sensor benefits from a higher dynamic range and superior linearity. It is shown that the geometry of the SRR can be optimized to compensate for the non-uniformity of the magnetic flux through the SRR, in order to suppress the unwanted frequency shift in the resonance. This is a significant improvement because the sensor can be operated as an inexpensive single frequency system. The concept and simulation results are validated by experimental measurements.

Metamaterial-Inspired Bandpass Filters for Terahertz Surface Waves on Goubau Lines

This paper is focused on the application of split ring resonators (SRRs) to the design of compact bandpass filters for terahertz surface waves on single-wire waveguides, the so-called planar Goubau lines (PGLs). Through equivalent circuit models, electromagnetic simulations, and experiments, it is shown that, while a pair of SRRs coupled to a PGL inhibits the propagation of surface waves along the line, introducing a capacitive gap to the PGL switches the bandstop behavior to a bandpass behavior. In order to highlight the potential application of the proposed structure to the design of practical higher order terahertz bandpass filters, two types of compact bandpass filters are designed and fabricated: 1) third-order periodic bandpass filters based on SRR/gap-loaded PGL and 2) coupled-resonator bandpass filters. It is shown that, while the frequency response of the both filter types can be controlled by altering the physical dimensions of the structure, a wider bandwidth can be achieved from the coupled-resonator filters. The design concept and simulation results are validated through experiments.

S-Shaped Complementary Split Ring Resonators and Their Application to Compact Differential Bandpass Filters With Common-Mode Suppression

This letter presents an S-shaped complementary split ring resonator (S-CSRR) for application in compact differential filters. The working principle of the proposed S-CSRR is explained and a circuit model is developed and validated through electromagnetic simulations. It is shown that an S-CSRR-loaded differential microstrip line with series gaps can be used in the design of compact differential bandpass filters (BPFs) with common-mode suppression. The filter design procedure is explained and the theoretical concept is validated through fabrication and measurement of a compact (0.09λg ×0.25 λg) third-order differential BPF with common-mode suppression.

Reconfigurable and Tunable S-Shaped Split-Ring Resonators and Application in Band-Notched UWB Antennas

This paper proposes a compact reconfigurable (bandstop/bandpass) and frequency-tunable structure based on S-shaped split-ring resonators (S-SRRs). It is known that an S-SRR coupled to a coplanar waveguide (CPW) provides a stopband in the transmission characteristic of the line. It is shown here that this behavior of the S-SRR can be switched between fundamental resonance and second harmonic response by introduction of a p-i-n diode in the center segment of the S-SRR. Alternatively, if the S-SRR is loaded with a varactor diode instead of a switch, the frequency of the stopband can be continuously tuned from the S-SRRs fundamental resonance frequency to its second harmonic. Furthermore, it is shown that if a pair of shunt p-i-n diodes are introduced across the slots of the host CPW, the structure can be reconfigured from a bandstop to a bandpass structure. Thus, the proposed resonator structure can be used as the building block of reconfigurable (bandstop/bandpass) filters with tunable operating frequency. Finally, to demonstrate a practical application of the proposed structure, an ultrawideband antenna with a tunable band notch is designed and experimentally validated.

Split Ring Resonators With Tapered Strip Width for Wider Bandwidth and Enhanced Resonance

This article presents a modified edge-coupled split ring resonator (SRR). The proposed SRR is composed of two concentric metallic rings with a nonuniform strip width, which is tapered based on the current and voltage profile in the SRR structure. In contrast to other SRR miniaturization methods, which are based on increasing the equivalent capacitance of the SRR, the proposed SRR benefits from both increased capacitance and inductance to preserve the strength and bandwidth of the resonance. It is also shown that compared to a uniform SRR, a tapered SRR with the same electrical size provides a stronger resonance with 84% wider bandwidth, as desired in wideband filter design. The theory and simulation results are validated through measurement.

Coplanar Waveguides Loaded with S-Shaped Split-Ring Resonators: Modeling and Application to Compact Microwave Filters

This letter studies the transmission characteristics of coplanar waveguides (CPWs) loaded with single-layer S-shaped split-ring resonators (S-SRRs) for the first time. Two structures are analyzed: 1) a CPW simply loaded with an S-SRR, and 2) a CPW loaded with an S-SRR and a series gap. The former exhibits a stopband functionality related to the resonance of the S-SRR excited by the contra-directional magnetic fluxes through the two connected resonator loops; the latter is useful for the implementation of compact bandpass filters. In both cases, a lumped-element equivalent circuit model is proposed with an unequivocal physical interpretation of the circuit elements. These circuits are then validated by comparing the circuit response with extracted parameters to full-wave electromagnetic simulations. The last part of the letter illustrates application of the S-SRR/gap-loaded CPW unit cell to the design of a bandpass filter. The resulting filter is very compact and exhibits competitive performance.

Tunable electric-LC resonators using liquid crystal

A concept of tunable electric-LC (ELC) resonators is presented in this work. The voltage-controlled tunability is achieved by using liquid crystal in a micro-fluidic channel running through the central capacitive gaps. To attain the largest tunability, the structure is optimized through a parametric analysis using full-wave electromagnetic simulations. The simulation results predict a 6% continuous frequency tuning for this ELC resonator around the frequency of 4.5 GHz. The achieved results demonstrate the possibility of using these ELC resonators in an array to form a tunable frequency selective surfaces (FSS). The principle can be scaled for operation at higher microwave frequencies, where the dissipation of liquid crystal is low.

Compact wideband filter element-based on complementary split-ring resonators

A double resonance defected ground structure is proposed as a filter element. The structure involves a transmission line loaded with complementary split ring resonators embedded in a dumbbell shape defected ground structure. By using a parametric study, it is demonstrated that the two resonance frequencies can be independently tuned. Therefore the structure can be used for different applications such as dual bandstop filters and wide bandstop filters.

Designing of high-Q slow-wave coplanar strips for CMOS MMICs

In contrast to conventional coplanar transmission lines, slow-wave coplanar transmission lines offer higher quality factor and smaller on-chip area. Among coplanar transmission lines, coplanar strips have the advantage of higher level of integration and a balanced structure that has favourable features for integrated voltage controlled oscillators (VCO) and low noise and power amplifiers. In this article, the affect of geometrical dimensions of slow-wave coplanar strips on the quality factor, characteristic impedance, and on-chip wavelength are investigated. Based on the presented guidelines mm-wave slow-wave coplanar strips operating at 60 GHz in a standard CMOS process were optimised for a 50 Ω characteristic impedance with a 250% improvement in quality factor of 31.