Jordi Naqui

Common-Mode Suppression in Microstrip Differential Lines by Means of Complementary Split Ring Resonators: Theory and Applications

This paper is focused on the application of complementary split-ring resonators (CSRRs) to the suppression of the common (even) mode in microstrip differential transmission lines. By periodically and symmetrically etching CSRRs in the ground plane of microstrip differential lines, the common mode can be efficiently suppressed over a wide band whereas the differential signals are not affected. Throughout the paper, we present and discuss the principle for the selective common-mode suppression, the circuit model of the structure (including the models under even- and odd-mode excitation), the strategies for bandwidth enhancement of the rejected common mode, and a methodology for common-mode filter design. On the basis of the dispersion relation for the common mode, it is shown that the maximum achievable rejection bandwidth can be estimated. Finally, theory is validated by designing and measuring a differential line and a balanced bandpass filter with common-mode suppression, where double-slit CSRRs (DS-CSRRs) are used in order to enhance the common-mode rejection bandwidth. Due to the presence of DS-CSRRs, the balanced filter exhibits more than 40 dB of common-mode rejection within a 34% bandwidth around the filter pass band.

Novel Sensors Based on the Symmetry Properties of Split Ring Resonators (SRRs)

The symmetry properties of split ring resonators (SRRs) are exploited for the implementation of novel sensing devices. The proposed structure consists of a coplanar waveguide (CPW) loaded with movable SRRs on the back substrate side. It is shown that if the SRRs are placed with the slits aligned with the symmetry plane of the CPW, the structure is transparent to signal propagation. However, if the symmetry is broken, a net axial magnetic field can be induced in the inner region of the SRRs, and signal propagation is inhibited at resonance. The proposed structures can be useful as alignment sensors, position sensors and angle sensors. This novel sensing principle is validated through experiment.

Transmission Lines Loaded With Bisymmetric Resonators and Their Application to Angular Displacement and Velocity Sensors

This paper is focused on the analysis of coplanar waveguides (CPWs) loaded with circularly shaped electric-LC (ELC) resonators, the latter consisting of two coplanar loops connected in parallel through a common gap. Specifically, the resonator axis is aligned with the CPW axis, and a dynamic loading with ELC rotation is considered. Since the ELC resonator is bisymmetric, i.e., it exhibits two orthogonal symmetry planes, the angular orientation range is limited to 90°. It is shown that the transmission and reflection coefficients of the structure depend on the angular orientation of the ELC. In particular, the loaded CPW behaves as a transmission line-type (i.e., all-pass) structure for a certain ELC orientation (0°) since the resonator is not excited. However, by rotating the ELC, magnetic coupling to the line arises, and a notch in the transmission coefficient (with orientation dependent depth and bandwidth) appears. This feature is exploited to implement angular displacement sensors by measuring the notch depth in the transmission coefficient. To gain more insight on sensor design, the lumped element equivalent-circuit model for ELC-loaded CPWs with arbitrary ELC orientation is proposed and validated. Based on this approach, a prototype displacement sensor is designed and characterized. It is shown that by introducing additional elements (a circulator and an envelope detector), novel and high precision angular velocity sensors can also be implemented. An angular velocity sensor is thus proposed, characterized, and satisfactorily validated. The proposed solution for angular sensing is robust against environmental variations since it is based on the geometrical alignment/misalignment between the symmetry planes of the coupled elements.

Alignment and Position Sensors Based on Split Ring Resonators

In this paper compact alignment and position sensors based on coplanar waveguide (CPW) transmission lines loaded with split ring resonators (SRRs) are proposed. The structure consists of a folded CPW loaded with two SRRs tuned at different frequencies to detect both the lack of alignment and the two-dimensional linear displacement magnitude. Two additional resonators (also tuned at different frequencies) are used to detect the displacement direction. The working principle for this type of sensor is explained in detail, and a prototype device to illustrate the potential of the approach has been designed and fabricated.

Modeling Split-Ring Resonator (SRR) and Complementary Split-Ring Resonator (CSRR) Loaded Transmission Lines Exhibiting Cross-Polarization Effects

The purpose of this letter is to understand and model the electromagnetic properties of transmission lines loaded with split-ring resonators (SRRs) and complementary split-ring resonators (CSRRs) arbitrarily oriented. It is shown that if the slits of these resonators are aligned in a nonorthogonal direction to the line axis, cross-polarization effects arise. Namely, the particles (SRRs or CSRRs) are excited through both magnetic and electric coupling. It is pointed out that the previously reported lumped element equivalent circuit models of SRR- and CSRR-loaded lines (where cross polarization is not considered) are valid as long as the slits are orthogonally oriented to the line axis, and new models that include cross polarization are presented and discussed. The validity and accuracy of the models is demonstrated through parameter extraction and comparison to full-wave electromagnetic simulations and measurements.

Differential Bandpass Filter With Common-Mode Suppression Based on Open Split Ring Resonators and Open Complementary Split Ring Resonators

Differential (balanced) microstrip bandpass filters (BPFs) implemented by combining open split ring resonators (OSRRs) and open complementary split ring resonators (OCSRRs) are proposed. The OSRRs are series connected in both strips of the differential line, whereas the OCSRRs are paired face-to-face and connected between both line strips in a symmetric configuration. For the differential mode, the OCSRRs are virtually connected to ground and the structure can be modeled, to a first-order approximation, by a cascade of series resonators (OSRRs) alternating with shunt resonators (OCSRRs), i.e., the canonical circuit model of a BPF. These filters have the ability to suppress the common mode by properly adjusting the metallic area surrounding the OCSRRs. An order-3 balanced Chebyshev BPF is designed and fabricated to illustrate the possibilities of the approach. The filter does not require vias (contrary to previous single-ended microstrip BPFs based on OSRRs and OCSRRs), filter dimensions are small, and the common mode is efficiently suppressed with more than 20 dB rejection within the differential filter pass band.

Angular Displacement and Velocity Sensors Based on Electric-LC (ELC) Loaded Microstrip Lines

Planar microwave angular displacement and angular velocity sensors implemented in microstrip technology are proposed. The transducer element is a circularly shaped divider/combiner, whereas the sensing element is an electric-LC resonator, attached to the rotating object and magnetically coupled to the circular (active) region of the transducer. The angular variables are measured by inspection of the transmission characteristics, which are modulated by the magnetic coupling between the resonator and the divider/combiner. The degree of coupling is hence sensitive to the angular position of the resonator. As compared with coplanar waveguide angular displacement and velocity sensors, the proposed microstrip sensors do not require air bridges, and the ground plane provides backside isolation.

Angular Displacement and Velocity Sensors Based on Coplanar Waveguides (CPWs) Loaded with S-Shaped Split Ring Resonators (S-SRR)

In this paper, angular displacement and angular velocity sensors based on coplanar waveguide (CPW) transmission lines and S-shaped split ring resonators (S-SRRs) are presented. The sensor consists of two parts, namely a CPW and an S-SRR, both lying on parallel planes. By this means, line-to-resonator magnetic coupling arises, the coupling level being dependent on the line-to-resonator relative angular orientation. The line-to-resonator coupling level is the key parameter responsible for modulating the amplitude of the frequency response seen between the CPW ports in the vicinity of the S-SRR fundamental resonance frequency. Specifically, an amplitude notch that can be visualized in the transmission coefficient is changed by the coupling strength, and it is characterized as the sensing variable. Thus, the relative angular orientation between the two parts is measured, when the S-SRR is attached to a rotating object. It follows that the rotation angle and speed can be inferred either by measuring the frequency response of the S-SRR-loaded line, or the response amplitude at a fixed frequency in the vicinity of resonance. It is in addition shown that the angular velocity can be accurately determined from the time-domain response of a carrier time-harmonic signal tuned at the S-SRR resonance frequency. The main advantage of the proposed device is its small size directly related to the small electrical size of the S-SRR, which allows for the design of compact angular displacement and velocity sensors at low frequencies. Despite the small size of the fabricated proof-of-concept prototype (electrically small structures do not usually reject signals efficiently), it exhibits good linearity (on a logarithmic scale), sensitivity and dynamic range.

Dual-Band Differential Filter Using Broadband Common-Mode Rejection Artificial Transmission Line

A new balanced dual-band bandpass fllter with strong common-mode rejection is presented in this paper. Common-mode rejection is provided by a section of a periodic microstrip difierential line that behaves as a low-pass fllter under common-mode operation. In contrast, the difierential line exhibits very good all-pass behavior under difierential mode operation. This structure is combined with a difierential dual-band bandpass fllter based on embedded resonators. Simulations and experiments conflrm that the combined structure has good common-mode rejection within the passbands of the dual-band difierential fllter.

On the symmetry properties of coplanar waveguides loaded with symmetric resonators: Analysis and potential applications

This paper is focused on the analysis of coplanar waveguides (CPW) loaded with symmetric resonators (such as split ring resonators and stepped impedance resonators) whose symmetry plane behaves as an electric wall at the fundamental resonance frequency. If these resonators are symmetrically etched in the back substrate side of the CPW, the resonators are not excited, and signal propagation along the CPW is allowed. Conversely, if the symmetry is truncated, the magnetic wall of the CPW (fundamental mode) is not aligned with the electric wall of the resonator, and signal propagation is inhibited in the vicinity of the first resonance frequency. These structures can be of interest for the design of novel sensors or radiofrequency (RF) bar codes, based on the deviation from symmetry. The principle of operation of such structures is illustrated and experimentally validated by proof-of-concept devices.