Amir Ebrahimi

High-Sensitivity Metamaterial-Inspired Sensor for Microfluidic Dielectric Characterization

A new metamaterial-inspired microwave microfluidic sensor is proposed in this paper. The main part of the device is a microstrip coupled complementary split-ring resonator (CSRR). At resonance, a strong electric field will be established along the sides of CSRR producing a very sensitive area to a change in the nearby dielectric material. A micro-channel is positioned over this area for microfluidic sensing. The liquid sample flowing inside the channel modifies the resonance frequency and peak attenuation of the CSRR resonance. The dielectric properties of the liquid sample can be estimated by establishing an empirical relation between the resonance characteristics and the sample complex permittivity. The designed microfluidic sensor requires a very small amount of sample for testing since the cross-sectional area of the sensing channel is over five orders of magnitude smaller than the square of the wavelength. The proposed microfluidic sensing concept is compatible with lab-on-a-chip platforms owing to its compactness.

Metamaterial-Inspired Rotation Sensor With Wide Dynamic Range

A rotation sensor with a wide dynamic range is designed based on tapered U-shaped resonators. The proposed device is composed of a rounded microstrip transmission line that couples to two meandered resonators that are stacked on top of each other. By rotating the upper resonator, the overlapping area between the two resonators is increased causing a stronger coupling that shifts down the resonance frequency of the device. This frequency shift can be read out in the transmission response from which the rotation angle is determined. The operation principle of the sensor is explained in detail by using a circuit model. A sensor prototype is designed for the microwave frequency range and an experiment is presented for validating the proposed sensing approach. This sensing device is well suited for further miniaturization using microelectromechanical systems technology.

Second-Order Terahertz Bandpass Frequency Selective Surface With Miniaturized Elements

In this paper, a second-order frequency selective surface (FSS) made of miniaturized elements is proposed and designed for terahertz applications. The FSS is composed of two layers of metallic arrays separated from each other by a polymer dielectric spacer. The unit cells on the front and back layers are smaller than λ0/5, where λ0 is the free space wavelength. The operation principle of the proposed FSS is described through a circuit model, and a synthesis procedure is presented for designing a desired filtering response. A prototype of the FSS is synthesized to operate at a center frequency of 0.42 THz with 45% fractional bandwidth. The designed FSS is fabricated by using microfabrication process. The performance is evaluated by using terahertz time-domain spectroscopy. Measurement results show a low sensitivity of the FSS response to oblique angles of incidence for both of the TE and TM polarizations.

Microwave microfluidic sensor for determination of glucose concentration in water

In this paper, a compact microfluidic biosensor is designed based on a complementary electric-LC resonator coupled with a microstrip line. It is shown that by flowing water-glucose solutions with different concentrations to the sensing area, the resonance property of the resonator is modified. This measurable change in the electromagnetic property is then used to quantify the glucose concentration. A prototype of the designed sensor is fabricated and tested to verify the biosensing concept.

Interlayer tuning of X-band frequency-selective surface using liquid crystal

In this paper, a new concept of a voltage-controlled tunable frequency-selective surface (FSS) is introduced based on liquid crystal technology. The designed FSS consists of two periodically patterned metallic layers, separated by a thin dielectric substrate. Tunability is achieved by integrating liquid crystal cells within the substrate for each unit cell, producing interlayer capacitors. By applying a bias voltage between the front and back metallic arrays, the anisotropy axis of the liquid crystal molecules can be re-oriented, and thus the effective relative permittivity of the liquid crystals can be modified to cause a frequency shift in transmission response. Electromagnetic simulations predict 5.6% of continuous frequency tuning for this multi-layer FSS.

Compact Dual-Mode Wideband Filter Based on Complementary Split-Ring Resonator

This letter proposes a microstrip filter based on a dual-mode complementary split-ring resonator (DMCSRR). For the input/output coupling, a dual C-shaped feed structure is implemented together with the DMCSRR to acheive a wideband response. The resonator offers a wide fractional bandwidth of 62% at the central frequency of 2.23 GHz and a very compact structure with a footprint of 0.0625λg×0.18λg, where λg is the guided wavelength at the midband frequency. A comprehensive lumped element circuit analysis accompanies the simulation and measurement results.

Varactor-Tunable Second-Order Bandpass Frequency-Selective Surface With Embedded Bias Network

A varactor-tunable second-order bandpass frequency-selective surface (FSS) for microwave frequencies is presented in this article. The FSS is composed of three stacked metallic layers. The wire grid in each layer in combination with metallic vias provides the bias for the varactors. This configuration eliminates the need for a dedicated bias network for the varactors, and thus avoids undesirable responses associated with the added bias grid. An equivalent circuit model together with an analytical design method is provided to simplify the design procedure of the FSS. The performance of the proposed structure is experimentally validated in a parallel-plate waveguide setup. Measurements show that by changing the varactor capacitance from 0.12 to 0.38 pF, the center frequency of the filter is tuned from 5.2 to 3.7 GHz with a consistent fractional bandwidth of 9% and with an insertion loss between 3 and 6 dB.

Dual-mode behavior of the complementary electric-LC resonators loaded on transmission line: Analysis and applications

This article presents an analysis of metamaterial resonators coupled with microstrip transmission line. The behavior of complementary electric-LC resonators loaded on a microstrip line is analyzed using the equivalent circuit model. In this paper, it is shown that a special type of these resonators show a dual-mode behavior when excited through the electromagnetic field around the microstrip transmission lines. The bandstop and bandpass configurations of these dual mode resonators loaded with microstrip lines are introduced and analyzed. Their potential applications are highlighted through designing a displacement sensor and a dual-mode bandpass filter prototypes.

Design of dual-band frequency selective surface with miniaturized elements

A new dual-band frequency selective surface (FSS) is introduced in this paper. By having a miniaturized unit cell size, the proposed FSS transmission response shows minimal sensitivity to the angle of the incident electromagnetic wave. The two passband frequencies of the proposed configuration can be controlled independently by tunning the unit cell geometrical parameters appropriately. An equivalent circuit model analysis is presented to provide an insightful synthesis procedure for the filter. Full-wave numerical electromagnetic simulations are used to confirm the analysis and synthesis method presented based on the circuit model.

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.