Frequency-dependent Coupling Coefficient Research Articles

Predicting the frequency-dependent effective excess charge density: A new upscaling approach for seismoelectric modeling

The seismoelectric method is based on the capacity of seismic waves to generate measurable modifications of the electrical field in porous media. Even though it combines the advantages of seismic and geoelectrical methods, it remains largely underused in hydrogeophysics. Its signal results from an electrokinetic coupling that can be modeled using either the coupling coefficient or the effective excess charge density. The traditional approach is based on the frequency-dependent coupling coefficient, which relates the pressure drop with the change in the electrical potential. A more recent approach consists of describing the excess charge that is effectively dragged by water flowing within the pores. We have developed a new model for the frequency-dependent effective excess charge density. For this, we make use of a mechanistic upscaling of the electrokinetic coupling in a capillary. This novel approach introduces inertial effects arising within the pore space in the flux-averaging procedure to explain the frequency dependence of the effective excess charge density. The presented model is successfully compared to previous models and published data. This new frequency-dependent upscaling approach has the potential of fundamentally improving our current understanding of the seismoelectrical signal in more complex environments, such as partially saturated and fractured media.

Simulation Analysis of the Filter with Frequency Dependent Coupling Coefficients

This paper illustrates a general approach to the simulation of the filter with frequency dependent coupling coefficients. Based on the frequency transformation formulas from lowpass to bandpass domain, circuit parameters can be determined and schematic model can be built to analyse the effects of frequency-dependent coupling coefficients on filter. A filter example is given finally to validate the proposed approach and the simulation results are in good agreement with the theory which verifies the correctness of the theory.

Investigation of the special features of the coupling coefficients for microstrip asymmetric hairpin resonators at frequencies of the second passband

3 UDC 537.621; 621.317.023 The behavior of the frequency-dependent coupling coefficients is investigated for a pair of microstrip resonators formed by conductors shaped as an asymmetrical hairpin. It is demonstrated that the total coupling coefficient of the resonators in a two-pole filter becomes close to zero in the region of the frequency of the second resonance due to mutual compensation for inductive and capacitive interactions. This allows a device for protection against high-power radio pulse to be developed based on such resonators with additional hairpin resonator containing control element manufactured from high-temperature superconductor (HTS) film. High-speed power limiters - protection devices (PD) - are necessary to protect input receiver circuits from high-power radio pulses. It is obvious that the electric PD strength is determined by the portion of power absorbed by the device from that incident on its input. Therefore, in addition to high speed, such devices must also possess high reflectivity in the off-state of the device. Microstrip resonant structures whose control element is manufactured from a high-temperature superconductor (HTS) film are promising for such devices actively investigated nowadays (1-3). The high speed of these protection devices is caused by small times of phase transition of the HTS material from the superconducting to normal state when current exceeding the critical threshold flows through it. The high reflectivity of the device in the off-state is caused practically by broken coupling between its input and output when the state of the HTS film changes from superconducting to normal one. The principle of PD operation consists in the following. The third resonator with the strip conductor completely or partially manufactured from the HTS material film is added to two microstrip resonators (MSR) with configurations of the conductor strips that provide mutual compensation for the inductive and capacitive interactions near resonant frequencies (4). This resonator provides required coupling between the MSR, thereby forming the desired passband of the device. When the HTS film goes to the normal (high-resistance) state under the influence of a radio pulse of sufficient power, coupling between the resonators is broken, and the device operates in the regime of limitation. The level of signal suppression in the limitation regime is one of the main specifications of protection devices. As demonstrated investigations (3), this level decreased with increasing central frequency of the working band of the device. In many respects, this is due to a decrease in sizes of resonators and devices as a whole accompanied by a decrease of the distance between the input and output of the device and by the corresponding increase of the directly transmitted signal.

Manipulating optical polarization by stereo plasmonic structure

We theoretically study a particular plasmonic structure with stereo nanoholes array in metallic film, which has remarkable abilities to manipulate the optical polarizations at optical frequencies. The main property is that any linear polarization states including a complete 90° optical rotation can be obtained in transmission by proper structural design in combination of enhanced transmission efficiency. Together with the polarization change, surface plasmon propagation bounded on the surface of transmission side also can be modulated. Furthermore, an analytical Coupled Mode Method (CMM) is developed by introducing a frequency dependent coupling coefficient to describe such optical rotation property in stereo plasmonic systems.

Analysis of the coupling coefficients of stripline resonators in the designs of suspended-substrate filters

Expressions for the frequency-dependent coupling coefficients of stripline resonators in miniature designs of suspended-substrate filters are obtained. The effect of the design parameters of such filters on the coupling coefficients of their resonators is theoretically studied and frequency-selective properties of the device are analyzed. It is shown that interaction between resonators at frequencies of the filter passband is predominantly inductive in the presence of small capacitive interaction and the attenuation poles of the amplitude-frequency response (AFR) observed beyond the passband are caused by the mutual cancellation of inductive and capacitive interactions. Frequency dependences of coupling coefficients can be used to explain features of the AFRs of suspended-substrate filters. It is shown that experimental AFRs agree well with theoretical AFRs calculated in quasi-static approximation with the use of 1D models.

Nanolamellar magnetoelectric BaTiO3–CoFe2O4 bicrystal

Here, we report a spontaneously formed nanolamellar BaTiO3–CoFe2O4 bicrystal. (11¯0) interfaces join the BaTiO3 and CoFe2O4 single crystalline periodically arranged lamellae that have a common [111] direction. The superlattice of approximately 2 nm wavelength is magnetoelectric with a frequency dependent coupling coefficient of 20 mV/Oe cm at 100 Hz. The BaTiO3 component is a ferroelectric relaxor with a Vogel–Fulcher temperature of 311 K. The relaxor behavior gives rise to a magnetic tunability of the relative dielectric constant ⟨εr⟩−1dεr/dH≈10−2. Since the material can be produced by standard ceramic processing methods, the discovery represents great potential for magnetoelectric devices.

Investigation of the coupling coefficients of stripline resonators in combline filters on a suspended substrate

Expressions for the frequency-dependent coupling coefficients of codirectional resonators used in a miniature design of a stripline filter on a suspended substrate are derived. The obtained expressions fully reflect the specific features of the frequency response of the analyzed structure. It is shown that the numerical analysis of a 1D model of this device performed in the quasi-static approximation provides sufficiently good agreement with experimental results. The influence of the design parameters of the analyzed structure on the frequency-selective properties of band-pass filters designed on the basis of this structure is theoretically investigated, and the capabilities for a substantial improvement of the selectivity of such devices are demonstrated.

Force on an ion in solution due to an oscillating electric field

We consider an ion immersed in a polar fluid under the influence of an oscillating electric field. The frequency dependent coupling coefficient, defined as the ratio of the force to the product of charge and field, is studied from both a microscopic and a macroscopic point of view. In the micro-scopic theory we derive a correlation function expression. We evaluate the coupling coefficient in the macroscopic theory by use of linear electrohydrodynamics.

Quantum relaxation, the shape of lattice absorption and inelastic neutron scattering lines

The fundamental optical lattice vibrations are treated as the system, the remaining lattice vibrations as the reservoir, and the anharmonic interactions as the coupling in a general density matrix theory of relaxation processes. An immediate result of this theory are expressions for frequency dependent level shifts and damping coefficients as well as corresponding frequency dependent coupling coefficients between the optical modes. If the coupling coefficients are neglected, and if in our expressions for the shift and damping coefficients anharmonic interactions in the reservoir are neglected our expressions simplify to those obtained by Wallis and Maradudin by summing an infinite ladder of diagrams. By treating an arbitrary mode as the system and using the fluctuation-dissipation theorem, we derive the relation between the lifetime and shift of the mode and its contribution to the one-phonon inelastic neutron scattering line shape. The relaxation theory we use is based on a systematic improvement of the Hartree approximation in which the system and reservoir are treated in a symmetric fashion.