Reconfigurable split ring resonators using pneumatics
Creators: name: Tang, Xutao
Publisher: name: RMIT University
Year: 2024
Subjects: classificationCode: 400899
subject: Electrical engineering not elsewhere classified

description: During the past decades, the rapid development of communication systems has extended to every aspect of modern technology. To better satisfy the need of people to interact with the world, investigations into the critical communication components mostly within the Radio-Frequency (RF) range have faced a diverse range of operational requirements and environment. The development of reconfigurable devices conforms to these demands with broader applicability. The resonant circuit, consisting of an inductance and capacitance, is fundamental to the design of passive resonant devices. The adjustment of their inherent inductance or capacitance provides a pathway for frequency reconfiguration.<br><br>The split ring resonator (SRR) is first introduced to generate negative permeability in artificial materials. The physical geometry of a SRR features a gap in a broken conductive ring, and is characterised as a compact sized resonant circuit due to the effective capacitance and inductance occurring on the gap and ring respectively. The integration of SRRs to RF devices has been widely explored, not just to enhance the performance but also enable reconfiguration in some resonant devices. The concept of tuning the intrinsic capacitance or inductance of the SRR has been realised by the addition of active devices such as diodes and MEMS switches. However, interference to the electromagnetic properties due to the additional components and their bias line networks, and tolerance control on the placement of the controlling element is a serious concern. If tuning is required in array structures such as metamaterials, component count, and bias issues are significantly elevated.<br><br>The aim of this research is to investigate and conceive pneumatic levitation systems as a mean of changing the structural arrangement of SRRs to reconfigure their resonant frequency or other parameters. Rotation, elevation and lateral movement of the SRRs are realised by implementing pneumatic levitation, and the resulting changes in the transmission response are characterised.<br><br>The resonant frequency of a SRR is dependent on the orientation of the incident electromagnetic waves. Pneumatic levitation is firstly proposed to allow free rotation of a SRR in the azimuthal plane resulting in continuous resonant frequency variations. The inclusion of another identical SRR located below the spinning SRR forms a broad-side coupled architecture. Depending on whether the static SRR is placed parallel or perpendicular to the electric field, the coupled SRRs can achieve 10% (2.66GHz to 2.39 GHz) or 12% (2.67 GHz to 2.38 GHz) continuous frequency sweep respectively. The levitation platform which holds the SRR is demonstrated to provide different spinning speed profiles and hence frequency sweep rates for the SRR response based on various platform designs.<br><br>An advanced pneumatic levitation system is devised to allow discrete on-demand resonant frequency control of broad-side coupled SRRs utilizing the rotation angle and separation of SRRs. The pneumatic structure stops the upper SRR at desired locations to achieve an associated resonant frequency response. The coupled SRRs can realise a 35% tunable frequency range (3.236 GHz to 2.11 GHz) over 180 degrees of rotation. The separation of SRRs, driven by the applied pneumatic pressure, demonstrates a tunable frequency range from 0.7% to 11.3% depending on the set rotation angle.<br><br>The horizontal arrangement of SRRs introduces another dimension for structure tuning based on the lateral space between two resonators. A pneumatic levitation system which enables the manipulation of the horizontal placement of a SRR leads to a smooth conversion between edge coupled and broad-side coupled SRRs. The transition affects the mutual capacitance of the structure resulting in changes to the transmission response. A 28% frequency reduction from 3.2 GHz results during the transition from edge coupled to broad-side coupled mode if two gaps of the SRRs are initially facing each other. When the gaps are facing outwards at the start, a second resonant frequency appears in the examined band and mirrors the shift of the first resonance in the opposite direction, increasing from 3.2 GHz. The investigation of the lateral control of a SRR using pneumatic levitation is further explored with the integration of an SRR with a CPW and monopole antenna for proof of concept reconfigurable RF device functionality.<br><br>The integration of pneumatic systems as an approach to tune the structure of SRRs exhibits tremendous potential for the physical modification of coupled SRRs, and possibly also any small resonant devices or components. Both simulation and experiments has demonstrated the possibilities to manipulate frequency shift between 2.1 GHz to 3.24 GHz. Furthermore its key advantages are its non-metallic structure which has minimal impact on the resonant properties and incident field, the near frictionless operation, and the control over the degrees of freedom of structural variation.