Model Of Coupled Resonators Research Articles

Analyzing Binding Specificity in a Microparticle-Based DNA Displacement Assay Using Multiharmonic QCM-D.

Employing particles as a label is a common approach for signal amplification in various surface-based biosensors. However, the size dependency of adhesive forces can increase the likelihood of nonspecific interactions between the particles and surface. Hence, using microscale particles in surface-based sensors requires both developing surface chemistries with enhanced antifouling properties and precise methods for evaluating these properties. Here we employ a quartz crystal microbalance with dissipation monitoring (QCM-D) to investigate the binding specificity of microparticles anchored multivalently to DNA-functionalized surfaces. We design a competitive particle displacement assay by implementing toehold-mediated strand displacement as an actuator in the microparticle-substrate interface, in which specifically anchored particles dissociate from the surface upon DNA displacement. We evaluate the efficiency of particle displacement in various modified surfaces by measuring the dissipation change (ΔD) following the addition of invader single-strand DNA. We further show that, prior to the particle displacement step, the specificity of particle binding can be inferred from comparing QCM-D harmonics in the particle binding step. Our results suggest that the frequency of zero crossing in the coupled-resonator model, fZC, can be used to characterize the specificity of particle binding. In combination, fZC in the particle binding step and ΔD in the particle displacement step can be considered synergic measures for evaluating the specificity of particle binding on DNA-coated surfaces.

Investigation of Three-Dimensional Bacterial Adhesion Manner on Model Organic Surfaces Using Quartz Crystal Microbalance with Energy Dissipation Monitoring.

Bacterial biofilms reduce the performance and efficiency of biomedical and industrial devices. The initial step in forming bacterial biofilms is the weak and reversible attachment of the bacterial cells onto the surface. This is followed by bond maturation and secretion of polymeric substances, which initiate irreversible biofilm formation, resulting in stable biofilms. This implies that understanding the initial reversible stage of the adhesion process is crucial to prevent bacterial biofilm formation. In this study, we analyzed the adhesion processes of E. coli on self-assembled monolayers (SAMs) with different terminal groups using optical microscopy and quartz crystal microbalance with energy dissipation (QCM-D) monitoring. We found that a considerable number of bacterial cells adhere to hydrophobic (methyl-terminated) and hydrophilic protein-adsorbing (amine- and carboxy-terminated) SAMs forming dense bacterial adlayers while attaching weakly to hydrophilic protein-resisting SAMs [oligo(ethylene glycol) (OEG) and sulfobetaine (SB)], forming sparse but dissipative bacterial adlayers. Moreover, we observed positive shifts in the resonant frequency for the hydrophilic protein-resisting SAMs at high overtone numbers, suggesting how bacterial cells cling to the surface using their appendages as explained by the coupled-resonator model. By exploiting the differences in the acoustic wave penetration depths at each overtone, we estimated the distance of the bacterial cell body from different surfaces. The estimated distances provide a possible explanation for why bacterial cells tend to attach firmly to some surfaces and weakly to others. This result is correlated to the strength of the bacterium-substratum bonds at the interface. Elucidating how the bacterial cells adhere to different surface chemistries can be a suitable guide in identifying surfaces with a more significant probability of contamination by bacterial biofilms and designing bacteria-resistant surfaces and coatings with excellent bacterial antifouling characteristics.

A planar metamaterial based on metallic rectangular-ring pair for narrow electromagnetically induced transparency-like effect

We design numerically and demonstrate experimentally a planar metamaterial with a narrow band electromagnetically induced transparency (EIT)-like resonance at microwave frequencies. The meta-molecule, consisting of a pair of metallic rectangular rings connected by a top metallic strip, is mirror symmetric with respect to the exciting electric field of the normally incident wave. The coupling between a broad bright mode (electric dipole) of the whole meta-molecule and a sharp dark mode (electric quadrupole) belonging only to the rectangular-ring pair can efficiently induce an ultra-narrow EIT-like resonance. By using a coupled-resonator model that shows good accordance with the numerical and experimental results, the observed effect can be well explained. Our design provides another way to realize the sharp EIT-like behavior with strong dispersion and the slow-wave effect, which may find potential applications in constructing the slow-wave devices, filters, and sensors.

Coupled-Resonator Theory of Isolation in Multi-Mode Antennas

The literature currently maintains the assumption that mutual coupling is the mechanism that leads to the degradation of isolation between the active ports of antenna arrays. However, this paper shows that a coupled-resonator model with series-coupled mutual coupling breaks down when applied to multi-mode/multi-port antenna arrays and limits the achievable isolation. An improved model based on parallel-coupled modes is presented. This model suggests that poor isolation is more accurately caused by unbalanced antenna modes. Using this model, several novel examples of simple and compact dual- and triple-mode antennas show how to maximize isolation in multi-mode antennas by balancing the modes’ resonant frequencies and radiation bandwidths. For comparison, the mutually coupled assumption limits isolation to around 20 dB in the proposed novel structures, whereas 40–70 dB is possible when parallel-coupled modes are considered. Based on the developed concept, a compact triple-mode two-pole-filtering antenna is fabricated at 3500 MHz with 160 MHz of bandwidth and more than 40 dB of isolation between the antenna ports.

Monochromatic Multimode Antennas on Epsilon‐Near‐Zero Materials

AbstractOptical antennas couple propagating optical fields into confined modes. The spectral position and spatial extent of the confined modes are most often engineered via the design of the antenna. However, while often relegated to a secondary role, the dielectric environment can drastically alter the optical response of antennas. Here, antennas on an epsilon‐near‐zero material—a material with a vanishing permittivity—are fabricated and characterized, demonstrating pinning of the fundamental antenna mode and the two subsequent harmonics to a narrow wavelength range. The spectral pinning of multiple modes results in what is a nearly monochromatic, yet multimode, response for the system. Coupling of these modes to the epsilon‐near‐zero Berreman mode supported by the thin epsilon‐near‐zero material is also observed. The response of the coupled system is observed experimentally and simulated using finite element methods. A coupled resonator model is developed to intuitively model the optical response of the system. The results presented here offer a mechanism for engineering the optical response of antenna systems by engineering the local dielectric environment, with potential applications in sensing, imaging, infrared optoelectronics, and thermal emission control.

High extinction ratio electromagnetically induced transparency analogue based on the radiation suppression of dark modes

A high extinction ratio (ER) electromagnetically induced transparency (EIT) analogue based on single-layer metamaterial is designed and experimentally demonstrated in this paper. This design involves four mirror-like symmetrically coupled split ring resonators (SRRs) that exhibit a bright-dark-dark-bright mode configuration. The EIT-like effect is realized by coupling between the bright resonators and dark resonators. The high ER feature is achieved from the suppression of radiative losses, due to opposite directions of electric and magnetic dipoles of two dark modes in the unit cell. Classical coupled resonator model is used to theoretically analyze the device transmission performances and to characterize parameter influence of the ER. Both numerical simulation and experiment results demonstrate that the ER of this device can reach more than 21 dB, which is 11 dB higher than that of conventional bright-dark coupling SRR arrangement. Finally, the potential multi-channel sensing utility of this device is demonstrated to show the importance of high ER feature.

Quantification of the viscoelasticity of the bond of biotic and abiotic particles adhering to solid-liquid interfaces using a window-equipped quartz crystal microbalance with dissipation

The quartz-crystal-microbalance-with-dissipation (QCM-D) has become a powerful tool for studying the bond viscoelasticity of biotic and abiotic colloidal particles adhering to substratum surfaces. A window-equipped QCM-D allows high-throughput analysis of the average bond viscoelasticity, measuring over 106 particles simultaneously in one single experiment. Other techniques require laborious analyses of individual particles. In this protocol, the quantitative derivation of the spring-constant and drag-coefficient of the bond between adhering colloidal particles and substratum surfaces using QCM-D is explained for bacteria and silica particles, using the particle-mass derived for validation. Bond viscoelasticity is calculated using a coupled resonator model, paying special attention to the protocol for mathematical fitting needed to obtain reliable quantitative output. Knowledge of the viscoelasticity of the bond between colloidal particles and substratum surfaces facilitates development of new strategies to detach adhering particles from or retain them on a surface.

Optically active Babinet planar metamaterial film for terahertz polarization manipulation

AbstractA planar Babinet‐inverted dimer metamaterial possessing strong optical activity is proposed and characterized. An original fabrication method to produce large area (up to several cm2) freely suspended flexible metallic membranes is implemented to fabricate the metamaterial. Its optical properties are characterized by terahertz time‐domain spectroscopy, revealing anisotropic transmission with high optical activity. A simple coupled resonator model is applied to explain the principal optical features of the dimers, with predictive power of positions and number of resonances through a parametrical model. The model is validated for correct polarization‐dependent quantitative results on the optical activity in transmission spectra. The fabrication method presented in this work as well as the slit dimer design has great potential for exploitation in terahertz optics.

A generalized strategy for designing 19F/1H dual‐frequency MRI coil for small animal imaging at 4.7 Tesla

To propose and test a universal strategy for building (19) F/(1) H dual-frequency RF coil that permits multiple coil geometries. The feasibility to design (19) F/(1) H dual-frequency RF coil based on coupled resonator model was investigated. A series capacitive matching network enables robust impedance matching for both harmonic oscillating modes of the coupled resonator. Two typical designs of (19) F/(1) H volume coils (birdcage and saddle) at 4.7T were implemented and evaluated with electrical bench test and in vivo (19) F/(1) H dual-nuclei imaging. For various combinations of internal resistances of the sample coil and secondary resonator, numerical solutions for the tunable capacitors to optimize impedance matching were obtained using a root-seeking program. Identical and homogeneous B1 field distribution at (19) F and (1) H frequencies were observed in bench test and phantom image. Finally, in vivo mouse imaging confirmed the sensitivity and homogeneity of the (19) F/(1) H dual-frequency coil design. A generalized strategy for designing (19) F/(1) H dual-frequency coils based on the coupled resonator approach was developed and validated. A unique feature of this design is that it preserves the B1 field homogeneity of the RF coil at both resonant frequencies. Thus it minimizes the susceptibility effect on image co-registration.

Bistability, multistability and non-reciprocal light propagation in Thue–Morse multilayered structures

The nonlinear properties of quasi-periodic photonic crystals based on the Thue–Morse sequence are investigated. The intrinsic spatial asymmetry of these one-dimensional structures for odd generation numbers results in bistability thresholds, which are sensitive to the propagation direction. Along with resonances of perfect transmission, this feature allows us to achieve strongly non-reciprocal propagation and to create an all-optical diode. The salient qualitative features of such optical diode action are readily explained through a simple coupled resonator model. The efficiency of a passive scheme that does not necessitate an additional short pump signal is compared to an active scheme where such a signal is required.

The theory of planar Bragg resonators

The reflecting properties of one-dimensional planar Bragg gratings are studied. A coupled resonator model for studying the diffraction of electromagnetic waves in an arbitrarily corrugated waveguide is suggested. It is based on exact relationships that follow from the two-dimensional boundary-value problem stated in terms of the Helmholtz equation. The specific relationships for the rectangular corrugation of the grating-forming plates are presented. The reflection coefficients of the Bragg gratings vs. corrugation length and incident radiation frequency are calculated. An analytical solution for the “narrow” corrugation is obtained.

A coupled resonator model of the detection of nuclear magnetic resonance: Radiation damping, frequency pushing, spin noise, and the signal‐to‐noise ratio

Magnetic resonance involves two coupled resonating systems: the spins and the tuned receiver coil. We simulate the spin system by an equivalent electrical resonator. An analysis of coupled resonators leads to a straightforward derivation of properties such as radiation damping, frequency pushing, and spin noise. The theory is applied to recent experiments (M. Guéron and J. L. Leroy, J. Magn. Reson. 85, 209-215 (1989]. The sensitivity of the spin noise experiment is shown to be T2/tau 0, where 1/tau 0 is the rate of radiation damping. This result leads directly to a fundamental formulation of the usual signal-to-noise ratio, (SNR)2 = (m0 B/tau 0)/(4Fk theta delta v), where m0 is the equilibrium magnetic moment, theta is the temperature, and F is the noise figure of the receiver. An equivalent electrical resonator can also be used to describe the active medium of masers.

Disk-and-washer cavities for an accelerator

Studied is the behavior of disk-and-washer accelerator cavities, in which the single radial stem support is adopted. The support leads about 70% larger and 20% smaller rf power loss than that of the calculated value in the normal cell and in the end cell, respectively. The distortion of the field is limited in the region of the so-called coupling cells. The properties of the coupled cavities, as the dispersion curve or the effect of tuners on the relative axial field is measured and well explained by the biperiodic coupled resonator model. The manufacturing of the actual cavity is also described, in which electroplating and welding methods are developed. The transverse coupling impedance calculated for a multiple-cell cavity are comparable with the instability experiments made in the TRISTAN accumulation ring.

Coupled Resonator Model for Standing Wave Accelerator Tanks

The behavior of standing wave accelerator tanks, made up of chains of resonant cavities, is investigated using a coupled resonator model. This model gives accurate predictions of the behavior of such a cavity chain, including tolerances to errors in manufacture, cavity feed distributions, and transient response. The parameters necessary in the theory, the cavity couplings, Q's, and frequencies, may easily be determined by experiment. Extension of the simple chain to a more complex chain with double periodicity and second nearest neighbor coupling is demonstrated. Advantages of operating such accelerators in the π/2 mode are shown.