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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 behaviour of the S-SRR can be switched between fundamental resonance and second harmonic response by introduction of a PIN 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 PIN 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, in order to demonstrate a practical application of the proposed structure, an ultrawideband antenna with a tunable band-notch is designed and experimentally validated.Index Terms-Reconfigurable antennas, S-shaped split ring resonator (S-SRR), ultrawideband antenna.

This paper proposes a two-dimensional alignment and displacement sensor based on movable broadside-coupled split ring resonators (BC-SRRs). As a basis for this sensor, a one-dimensional displacement sensor based on a microstrip line loaded with BC-SRRs is presented firstly. It is shown that compared to previously published displacement sensors, based on SRR-loaded coplanar waveguides, the proposed one-dimensional sensor benefits from a much wider dynamic range. Secondly, it is shown that with modifications in the geometry of the BC-SRRs, the proposed one-dimensional sensor can be modified and extended by adding a second element to create a high-dynamic range two-dimensional displacement sensor. Since the proposed sensors operate based on a split in the resonance frequency, rather than the resonance depth, they benefit from a high immunity to environmental noise. Furthermore, since the sensors' principle of operation is based on the deviation from symmetry, they are more robust to ambient conditions such as changes in the temperature, and thus they can be used as alignment sensors as well. A prototype of the proposed two-dimensional sensor is fabricated and the concept and simulation results are validated through experiment.Keywords: metamaterials, alignment sensor, displacement sensor, two-dimensional, high dynamic range Preprint submitted to Sensors and Actuators A: Physical January 17, 2014 Pre-print of: Horestani, Ali K., et al. "Two-dimensional alignment and displacement sensor based on movable broadside-coupled split ring resonators" in Sensors and actuators (Ed. Elsevier), vol. 210

This letter proposes a two-dimensional displacement and alignment sensor based on two open-ended transmission lines, each loaded with a split ring resonator (SRR). In this arrangement, the depth of resonanceinduced notches in the reflection coefficients can be used to sense a displacement of the loading SRRs in two orthogonal directions. Since the operation principle of the sensor is based on the symmetry properties of SRR-loaded transmission lines, the proposed sensor benefits from immunity to variations in ambient conditions. More importantly, it is shown that in contrast to previously published metamaterial-inspired twodimensional displacement and alignment sensors, the proposed sensor can be operated at a single fixed frequency. The concept and simulation results are validated through measurement.Introduction: In recent years, the application of metamaterial-inspired resonators such as split ring resonators (SRRs) to sensors has attracted an increasing interest [1,2,3,4]. This has arisen because of the subwavelength dimensions, high quality factor resonance and sensitivity of the resonance characteristics of these elements to their physical dimensions and constituent materials. Various types of displacement and rotation sensors based on variation of resonance frequency, quality factor and notch depth in the transmission spectrum of SRR-loaded transmission lines (TLs) have been proposed in the literature [1,5,6,7,8]. The concept was also extended for the design of two-dimensional displacement sensors [9,10].This letter proposes a two-dimensional displacement and alignment sensor based on the variation in the depth of resonant notch in the reflection coefficients of two SRR-loaded microstrip lines. Since both SRRs and microstrip lines are inherently compact structures, the proposed sensor benefits form a small size. Furthermore, since the operation principle of the sensor is based on the symmetry properties of the SRRs, the sensor is robust to ambient conditions such as changes in temperature. It is also shown that because the excitation from microstrip lines imposes an almost constant loading effect on the SRRs, displacement is only manifested in the depth of notch, leaving the resonance frequency intact. This is an important feature because it enables the sensor to work at a fixed frequency. This sensing mode allows to operate based on two reflection coefficients rather than using the transmission coefficient of the structure, where at least two fixed frequencies are required for the operation of two-dimensional displacement sensors [9,10].