Burak Ozbey

Continuously tunable terahertz metamaterial employing magnetically actuated cantilevers

Terahertz metamaterial structures that employ flexing microelectromechanical cantilevers for tuning the resonance frequency of an electric split-ring resonator are presented. The tuning cantilevers are coated with a magnetic thin-film and are actuated by an external magnetic field. The use of cantilevers enables continuous tuning of the resonance frequency over a large frequency range. The use of an externally applied magnetic field for actuation simplifies the metamaterial structure and its use for sensor or filter applications. A structure for minimizing the actuating field is derived. The dependence of the tunable bandwidth on frequency is discussed.

Wireless Displacement Sensing Enabled by Metamaterial Probes for Remote Structural Health Monitoring

We propose and demonstrate a wireless, passive, metamaterial-based sensor that allows for remotely monitoring submicron displacements over millimeter ranges. The sensor comprises a probe made of multiple nested split ring resonators (NSRRs) in a double-comb architecture coupled to an external antenna in its near-field. In operation, the sensor detects displacement of a structure onto which the NSRR probe is attached by telemetrically tracking the shift in its local frequency peaks. Owing to the NSRRs near-field excitation response, which is highly sensitive to the displaced comb-teeth over a wide separation, the wireless sensing system exhibits a relatively high resolution (<1 μm) and a large dynamic range (over 7 mm), along with high levels of linearity (R2 > 0.99 over 5 mm) and sensitivity (>12.7 MHz/mm in the 1–3 mm range). The sensor is also shown to be working in the linear region in a scenario where it is attached to a standard structural reinforcing bar. Because of its wireless and passive nature, together with its low cost, the proposed system enabled by the metamaterial probes holds a great promise for applications in remote structural health monitoring.

Wireless Sensing in Complex Electromagnetic Media: Construction Materials and Structural Monitoring

In this paper, wireless sensing in the presence of complex electromagnetic media created by combinations of reinforcing bars and concrete is investigated. The wireless displacement sensing system, primarily designed for use in structural health monitoring (SHM), is composed of a comb-like nested split-ring resonator (NSRR) probe and a transceiver antenna. Although each complex medium scenario is predicted to have a detrimental effect on sensing in principle, it is demonstrated that the proposed sensor geometry is able to operate fairly well in all scenarios except one. In these scenarios that mimic real-life SHM, it is shown that this sensor exhibits a high displacement resolution of 1 μm, a good sensitivity of 7 MHz/mm in average, and a high dynamic range extending over 20 mm. For the most disruptive scenario of placing concrete immediately behind NSRR, a solution based on employing a separator behind the probe is proposed to overcome the handicaps introduced by the medium. In order to obtain a one-to-one mapping from the measured frequency shift to the displacement, a numerical fit is proposed and used. The effects of several complex medium scenarios on this fit are discussed. These results indicate that the proposed sensing scheme works well in real-life SHM applications.

Wireless Measurement of Elastic and Plastic Deformation by a Metamaterial-Based Sensor

We report remote strain and displacement measurement during elastic and plastic deformation using a metamaterial-based wireless and passive sensor. The sensor is made of a comb-like nested split ring resonator (NSRR) probe operating in the near-field of an antenna, which functions as both the transmitter and the receiver. The NSRR probe is fixed on a standard steel reinforcing bar (rebar), and its frequency response is monitored telemetrically by a network analyzer connected to the antenna across the whole stress-strain curve. This wireless measurement includes both the elastic and plastic region deformation together for the first time, where wired technologies, like strain gauges, typically fail to capture. The experiments are further repeated in the presence of a concrete block between the antenna and the probe, and it is shown that the sensing system is capable of functioning through the concrete. The comparison of the wireless sensor measurement with those undertaken using strain gauges and extensometers reveals that the sensor is able to measure both the average strain and the relative displacement on the rebar as a result of the applied force in a considerably accurate way. The performance of the sensor is tested for different types of misalignments that can possibly occur due to the acting force. These results indicate that the metamaterial-based sensor holds great promise for its accurate, robust and wireless measurement of the elastic and plastic deformation of a rebar, providing beneficial information for remote structural health monitoring and post-earthquake damage assessment.

A Wireless Passive Sensing System for Displacement/Strain Measurement in Reinforced Concrete Members.

In this study, we show a wireless passive sensing system embedded in a reinforced concrete member successfully being employed for the measurement of relative displacement and strain in a simply supported beam experiment. The system utilizes electromagnetic coupling between the transceiver antenna located outside the beam, and the sensing probes placed on the reinforcing bar (rebar) surface inside the beam. The probes were designed in the form of a nested split-ring resonator, a metamaterial-based structure chosen for its compact size and high sensitivity/resolution, which is at µm/microstrains level. Experiments were performed in both the elastic and plastic deformation cases of steel rebars, and the sensing system was demonstrated to acquire telemetric data in both cases. The wireless measurement results from multiple probes are compared with the data obtained from the strain gages, and an excellent agreement is observed. A discrete time measurement where the system records data at different force levels is also shown. Practical issues regarding the placement of the sensors and accurate recording of data are discussed. The proposed sensing technology is demonstrated to be a good candidate for wireless structural health monitoring (SHM) of reinforced concrete members by its high sensitivity and wide dynamic range.

An Equivalent Circuit Model for Nested Split-Ring Resonators

In this paper, an equivalent circuit model for nested split-ring resonators (NSRRs) is proposed. NSRRs are an emerging class of split ring resonators, preferred in a range of areas from sensing in biomedical or civil engineering applications to antenna design, due to their more compact size and enhanced sensitivity/resolution characteristics over the conventional SRRs. In the proposed model, the NSRR structure is treated as a combination of basic elements, i.e., strips and gaps, and the electromagnetic characteristics of the whole geometry are expressed in terms of capacitances and inductances of each of these elements. The outputs of the model are compared with those obtained via full-wave simulations using the package programs as well as measurements. The variation of NSRR resonance frequency (

Multi-Point Single-Antenna Sensing Enabled by Wireless Nested Split-Ring Resonator Sensors

f_{\text {res}}

RF displacement and strain sensing system for wireless structural health monitoring

) with all important design parameters is also compared with full-wave simulations. In all comparisons, the results demonstrate agreement, showing that the proposed model can correctly explain the electromagnetics of the NSRR structure and that it provides an intuitive way for a better and easier analysis and a preliminary design of normally complex structures.

Feasibility study of installation of solar panels on a high power HF antenna land

In this paper, simultaneous multi-point wireless sensing is proposed and demonstrated via multiple sensors in nested split-ring resonator (NSRR) geometry coupled to a single illuminator antenna. In this passive multi-point sensing system, each probe in the sensor array is assigned a non-overlapping spectral interval for frequency shift in response to local mechanical loading around a unique operating resonance frequency in the band of the antenna. Here, it is shown that the antenna is capable of capturing the responses from all probes in a single frequency sweep. Furthermore, the inter-coupling between the array elements and the effect of antenna illumination on the coupling are experimentally investigated in a systematic way. In addition, as a proof-of-concept real-life application in structural health monitoring, two NSRR sensors are located inside a concrete beam to monitor the strain forming on reinforcing bars, and this dual-probe system is demonstrated to record strain simultaneously via both of the embedded probes.

A Wireless Metamaterial-Inspired Passive Rotation Sensor With Submilliradian Resolution

Structural health monitoring (SHM) is a technology with worldwide interest that is vital to ensure the reliability of any structure while also protecting the safety of human life. Over the years, a lot of research has been conducted on this topic, proposing SHM methods that may be instrumental in understanding the condition of critical parts of a structure. These methods generally rely on wired and/or active technologies, which are not preferable since the wires disallow telemetric measurements and mean increased weight and space, while the active technologies require electric power in order to operate. Two of the most important damage indices of a building structure such as a reinforcing bar (rebar) are the strain and displacement forming either with time or a sudden impact like an earthquake.