Zero Phase Delay Research Articles

A Fully Symmetrical Uni-Planar Microstrip Line Comparator Network for Monopulse Antenna

In this letter, a fully symmetrical uni-planar comparator network is proposed for monopulse antenna feeding. To break through the fundamental limitation of a conventional 180 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{\circ}$</tex-math> </inline-formula> coupler (crossing between input and output ports and amplitude imbalance), a novel symmetric ports coupler is designed by cascading two identical 90 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{\circ}$</tex-math> </inline-formula> couplers with two-phase delay lines, where the total phase delay of two lines is 180 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{\circ}$</tex-math> </inline-formula> . To realize in planar structure, a zero-phase delay planar crossover is designed to resolve signal crossing between two stage couplers in a comparator network. To verify our design concept, a prototype monopulse array operating at 5.7 GHz is designed, fabricated, and measured, and results are aligned well with simulation and theory.

An ultra-narrow-band optical filter based on zero refractive index metamaterial

Owing to the photonic band gap effect and defect state effect, photonic metamaterials have received much attention in the design of narrow bandpass filters, which are the key devices of optical communication equipment such as wavelength division multiplexing devices. In this work, based on zero-index metamaterial (ZIM), a compact filter with both high peak transmission coefficient and ultra-narrow bandwidth is proposed. The photonic metamaterial with conical dispersion and Dirac-like point is achieved by optimizing the structure and material component parameters of dielectric rods with square lattice in air. It is demonstrated that a triply degenerate state can be realized at the Dirac-like point, which relates this metamaterial to a zero-index medium with effective permittivity and permeability equal to zero simultaneously. Electromagnetic (EM) wave can propagate without any phase delay at this frequency, and strong dispersion occurs in the adjacent frequency cone, leading to dramatic changes in optical properties. We introduce a ZIM into photonic metamaterial defect filter to compress the bandwidth to the realization of ultra-narrow bandpass filter. The ZIM is embedded into the resonant cavity of line defect filter, which is also composed of dielectric rods with square lattice in air. In order to increase the sensitivity of the phase change with frequency, the Dirac-like frequency is adjusted to match the resonant frequency of the filter. We study the transmission spectrum of the structure through the COMSOL Multiphysics simulation software, and find that the peak width at half-maximum of the filter decreases as the thickness of ZIM increases, and the peak transmittance is still high when bandwidth is greatly compressed. The zero phase delay inside the slab can be observed. Through field distribution analysis, the zero-phase delay and strong coupling characteristics of electromagnetic field are observed at peak frequency. The comparison with conventional photonic metamaterials filter is discussed. We believe that this work is helpful in investigating the realization of ultra-narrow bandpass filters.

Tunable zero-phase delay of one-dimensional photonic crystals containing InSb material

In this paper, by introducing a variety of the new semiconductor material InSb, the broadband zero-phase delay has been realized, which is based on one-dimensional photonic crystals (PCs). It has been found that the tunable effects of the zero-phase delay can be obtained in the zero-effective-phase gap (denoted as zero- φ e f f gap). Under these circumstances, the phases of the TE and TM waves switch smoothly across the stop band in the PCs and the difference between the phase shift of both polarized waves could remain constant inside the band. The results reveal that when satisfying the condition of zero-averaged (volume) refractive index (zero- n ¯ ), zero- φ e f f delay within the gap 10.06–11.85 THz can be switched precisely by the magnetic influx density 2–4 T. Meanwhile, the temperature of 220–290 K and the incident angle of 0° to 90° can manipulate the bandwidth of zero- φ e f f delay about 180° precisely in the 10.02–11.9 THz regime. In addition, we think the zero- φ e f f gap can be applied in manufacturing tailored broadband phase retarders or wave plates.

Band-Limited Chirp-Evoked Compound Action Potential in Guinea Pig: Comprehensive Neural Measure for Cochlear Implantation Monitoring.

Patients with severely impaired high-frequency hearing and sufficient residual low-frequency hearing can be provided with a cochlear implant (CI), thereby facilitating ipsilateral electric and acoustic stimulation with established advantages over electric stimulation alone. However, partial or complete hearing loss often occurred after implantation due to, inter alia, acute mechanical trauma to cochlear structures during electrode insertion. Possibilities of intraoperative monitoring using electrocochleography (ECochG) have recently been studied in CI patients, primarily using the ongoing response to low-frequency tone bursts consisting of the cochlear microphonic (CM) and the auditory nerve neurophonic. By contrast, the transient neural response to tone bursts, that is, compound action potential (CAP), was generally less detectable or less sensitive as a monitoring measure, thus falling short of providing useful contribution to electrocochleography analysis. In this study, we investigate using chirps to evoke more robust CAP responses in a limited frequency band by synchronizing neural firing, and thereby improving CAP sensitivity to mechanical trauma in a guinea pig model of cochlear implantation. Stimuli were band-limited between 100 Hz and 10 kHz to investigate their frequency range selectivity as a preliminary model for low-frequency hearing. They were constructed by adding a harmonic series either with zero phase delay (click) or by adjusting the phase delay at a rate that is inversely related to a traveling wave delay model (chirp), with three different parameters to examine level-dependent delay compression. The amplitude spectrum was thus identical between stimuli with differences only in phase. In Experiment 1, we compared input-output functions recorded at the round window in normal-hearing guinea pigs and implemented a high-pass noise masking paradigm to infer neural contribution to the CAP. In Experiment 2, guinea pigs were implanted with a custom-built CI electrode using a motorized micromanipulator. Acute mechanical trauma was simulated during the electrode insertion. At each insertion step, CAP and CM responses were measured at the round window for the following stimuli: broad-band click, band-limited click, and band-limited chirps (3 parameters), and tone bursts at frequencies 1, 2, 4, and 8 kHz. Chirps compared with the equal-band click showed significantly lower thresholds and steeper slopes of sigmoid-fitted input-output functions. The shorter chirp evoked significantly larger amplitudes than click when compared at equal sensation level. However, the click evoked larger amplitudes than chirps at higher levels and correspondingly achieved larger saturation amplitudes. The results of the high-pass noise masking paradigm suggest that chirps could efficiently synchronize neural firing in their targeted frequency band, while the click recruited more basal fibers outside its limited band. Finally, monitoring sensitivity during electrode insertion, defined as relative amplitude change per unit distance, was higher for chirp-evoked CAP and tone burst-evoked CM, but smaller for CAP responses evoked by clicks or tone bursts. The chirp was shown to be an efficient stimulus in synchronizing neural firing for a limited frequency band in the guinea pig model. This study provides a proof of principle for using chirp-evoked CAP as a comprehensive neural measure in CI patients with residual hearing.

Interaural Coherence Estimation for Speech Processing in Reverberant Environment

Interaural coherence is used to quantify the effects of reverberation on speech, and previous studies applied the conventional method using all previous time data in the form of an infinite impulse response filter to estimate interaural coherence. To consider a characteristic of speech that continuously changes over time, this paper proposes a new method of estimating interaural coherence using time data within a finite length of speech, which is called the quasi-steady interval. The length of the quasi-steady interval is determined with various frequency bands, reverberation times, and short-time Fourier transform (STFT) variables through numerical experiment, and it decreased as reverberation time decreased and the frequency increased. In this interval, a diffuse speech, which is an infinite sum of reflected speeches of different propagating paths, is uncorrelated between two microphones apart from each other; thus, the coherence is close to zero. However, a direct speech measured at the two microphones has steady amplitude and phase difference in this internal; thus, the coherence is close to one. Moreover, the new method is the form of a finite impulse response filter that has a linear phase delay or zero phase delay with respect to speech to frequency; thus, the same or zero time delay for each frequency is applied to the power spectral density. Therefore, the coherence estimation of the new method is closer to the ideal value than the conventional one, and the coherence is accurately estimated at the time–frequency bins of direct speech, which is time-varying according to speech variation.

드룹 제어 기반 병렬운전 인버터의 동특성 개선을 위한 Third-order Generalized Integrator 기반의 전력계산 알고리즘

In this paper, a novel power calculation algorithm is proposed based on third-order generalized integrator for improving dynamics characteristics in droop control. Power calculation algorithm is important in droop control because it affects the characteristics of droop control. Conventionally, the power calculation method using low-pass filter has been widely used, but there is a problem because the phase delay necessarily occurs due to the dynamics of low-pass filter. Therefore, this paper proposes a novel power calculation method with zero-phase delay at fundamental frequency by utilizing third-order generalized integrator. By using the proposed calculation method, it can achieve to have strong noise rejection about high-order harmonics and dc offset with no phase delay at fundamental frequency.

Efficient light redirection via stretched field resonance in dielectric meta-resonator.

Light redirection plays an important role in photonic integrated circuit system, which attracts much attention on account of thriving application prospects from microwave to visible frequency. By treating a two-dimensional photonic crystal array as a dielectric resonator with low effective index neff << 1, a new strategy of one-direction semi-enclosed meta-resonator is proposed for light redirection and splitting with a high efficiency beyond 90%. Instead of zero-index material, the phenomenon of significant collimating radiations with zero phase delay can also be achieved through a meta-resonator of low effective index to stretch the internal resonant field with a wavelength much longer than that in air. The geometrical dimensions and structural parameters of the meta-resonator offer a great design flexibility for modulating the operating frequency. The numerical simulation and experimental results perfectly coincide with the theoretical predictions. This strategy can also be extended to other artificial metamaterials and three-dimensional cases, which may offer fantastic possibilities to the development of integrated photonics.

Zero-phase propagation in realistic plate-type acoustic metamaterials

We theoretically, numerically, and experimentally analyze the Density-Near-Zero (DNZ) regime of a one-dimensional acoustic metamaterial. This acoustic metamaterial is composed of thin elastic plates periodically clamped in an air-filled waveguide, and the effective dynamic zero mass density is obtained from the strong dispersion around the bandgaps associated with the resonances of the plates. We emphasize the importance of the impedance mismatch between the acoustic metamaterial and the surrounding waveguide at the frequency of the zero effective density in addition to the consequences of the inherent losses. As a result, the frequency of the zero phase propagation, i.e., the acoustic propagation with zero phase delay, is not exactly the frequency of the zero density and lies in the frequency bandgap where the effective density is negative. Considering these limitations, the zero phase propagation is still experimentally observed and a subwavelength acoustic dipole is numerically designed, thus demonstrating the possible realistic implementations of DNZ acoustic metamaterials.

Brewster effect when approaching exceptional points of degeneracy: Epsilon-near-zero behavior

We reveal that the phenomenon of full transmission without phase accumulation commonly associated with epsilon-near-zero (ENZ) materials for a plane-wave does not require vanishing of permittivity. We theoretically connect the phenomenon with condition of the Brewster effect satisfied at the edges of stop bands (so called exceptional points of degeneracy) and show that the full transmission without phase accumulation can be observed in various one-dimensional periodic structures. Particularly, exploiting the manifold of exceptional points of degeneracy in one-dimensional all-dielectric periodic lattices, we demonstrate that these structures not only offer a lossless and extremely simple, CMOS compatible alternative for some applications of ENZ media, but exhibit new properties of all-angle full transmission with zero phase delay.

A Novel Dual-Band Zero-Phase True Crossover With Arbitrary Port Impedance

A novel dual-band true crossover that can match with any impedance presented at its input and output ports is proposed in this letter. To break through the conventional 50- $\Omega $ reference port impedance constraint, a planar crossover with a zero-phase delay in the transmission is designed first at a single operating frequency. The proposed single-band zero-phase crossover consists of outer branch lines and inner crossed lines, and the design parameters for each line are obtained by applying the even-odd mode analysis method. Second, the dual-band function is implemented on the proposed zero-phase crossover by replacing each line with dual-band transmission line, which has two series sections and one shunt section. A prototype of dual-band zero-phase crossover operating at 2.15 and 4.1 GHz is designed, fabricated, and measured. The simulation and measurement results agree well with each other to prove the design concept.

A Zero Phase Delay Power Divider Using Zero Phase Impedance Transformer

The 3-dB power divider is one of the most common three-port device in microwave systems, which equally splits the signal at its two output ports. In previous Wilkinson power divider design, the phase delay between the input and output ports is not considered into the design requirements. However, the zero-phase shifting power divider attracts great interest in modern microwave systems. In this letter, a 3-dB power divider with zero-phase delay is designed based on a zero-phase impedance transformer. Instead of metamaterial transmission line, a transmission line stub is added to connect the isolation resistor, and a capacitor is insert between the output ports and the end of main branch to cancel out the imaginary part of even–odd mode impedances. With this new design, it releases the layout restriction that the two branches route around to connect to lumped element resistor. Closed-form design equations are derived and a prototype device is then simulated and measured. The measurement results agree well with the simulation results.

Optimal Power Control Strategy for Wind Farm with Energy Storage System

The use of energy storage systems (ESSs) has become a feasible solution to solve the wind power intermittency issue. However, the use of ESSs increases the system cost significantly. In this paper, an optimal power flow control scheme to minimize the ESS capacity is proposed by using the zero-phase delay low-pass filter which can eliminate the phase delay between the dispatch power and the wind power. In addition, the filter time constant is optimized at the beginning of each dispatching interval to ensure the fluctuation mitigation requirement imposed by the grid code with a minimal ESS capacity. And also, a short-term power dispatch control algorithm is developed suitable for the proposed power dispatch based on the zero-phase delay low-pass filter with the predetermined ESS capacity. In order to verify the effectiveness of the proposed power management approach, case studies are carried out by using a 3-MW wind turbine with real wind speed data measured on Jeju Island.

Tailorable Zero-Phase Delay of Subwavelength Particles toward Miniaturized Wave Manipulation Devices.

Adjustable zero-phase delay and equiphase control are demonstrated in single and multilayer dielectric particle arrays with high index and low loss. The polarization-independent near-zero permeability is the origin of the wave control near the first Mie magnetic resonance. The proposed design paves the way for subwavelength devices and opens up new avenues for the miniaturization and integration of THz and optical components.

Manipulation of electromagnetic wavefront based on zero index magnetic metamaterial

In this work, a zero index magnetic metamaterial (ZIMM) is designed based on the two-dimensional array of ferrite rods periodically arranged in the air. By calculating the photonic band structures within the framework of multiple scattering theory and retrieving the effective electric permittivity εeff and effective magnetic permeability μeff, the structure parameters can be optimized and then the effectively matched zero index with εeff = μeff = 0 is achieved. Within this matched ZIMM, electromagnetic (EM) wave can propagate without any phase delay, resulting in the manipulation of phase pattern in space. By simulating the electric field patterns of a Gaussian beam incident on ZIMM slabs with different thickness, zero phase delay inside the slab can be observed. By designing various outgoing interfaces a plane EM wavefront can be transformed into a cylindrical one, or even into a more general wavefront. In addition, the focusing and beam splitting effects are demonstrated as well. Besides, since the permeability of magnetic materials can be controlled by an external magnetic field or a temperature, the EM features of ZIMM can be flexibly tuned, enabling a promising prospect in designing EM devices and potential applications.

Zero phase delay in metamaterials

Metamaterials with zero phase delay can guide light over hundreds of wavelengths without introducing phase variations so as to reduce the unwanted effects of frequency dispersion, which has been widely studied by researchers in the world. Based on the research works of our group, in this paper we summarize and review the latest theoretical and experimental researches and progress of metamaterials with zero phase delay. The mechanisms of phase modulations to realize zero phase delay in various metamaterials are classified and concluded. Further analyses are carried out on the characteristics and present research problems of various methods to realize zero phase delay, and the prosperous future are forecasted. We believe the related investigations are of great significance to the development of fundamental physics and the design of optical devices.

Metamaterials with Zero Phase Delay

During the early years of research into metamaterials, some interest has shifted towards the realization of materials that exhibit zero or near-zero refractive index. A refractive index of zero implies that light enters a state of quasi-infinite phase velocity and infinite wavelength. Instead of strong resonance mechanism in metamaterials, the physical phenomenon of PhC is based on the special dispersion relations of photonic bands with weak loss. Several different metamaterials to realize zero phase delay are introduced in this paper. Their remarkable properties should have significant technological applications in photon delay lines with zero phase difference, information-processing devices, new optical phase control and measurement techniques.

Zero phase delay with relax incident condition in photonic crystals

Based on the wavefront modulation of photonic crystal (PhC), zero phase delay of propagating electromagnetic wave (EMW) can be realized with a relaxed incident condition in the PhC. The phase velocity is modulated perpendicular to the group velocity with wavefronts extending along the direction of energy flow, which lead to the phenomenon of zero phase delay with a finite spatial period. This effect can be realized simultaneously in both positive and negative refracted waves. The phase difference between the incident and transmitted waves are measured within a wide incident angle region to demonstrate zero phase delay can be realized easily instead of zero-n or zero-averaged-n materials. Further investigations prove that the phenomena of zero phase delay induced by this way can also be realized easily in various PhC configurations and can be accurately manipulated by changing the incident angle or the flexible design of PhC configuration.

A Novel Method to Realize Zero Phase Delay of Electromagnetic Wave

Zero phase delay of electromagnetic wave (EMW) transmission can be realized based on the wavefront modulation of photonic crystals (PhCs). When the phase velocity is controlled perpendicular to the group velocity with wavefronts (or phasefronts) parallel to the direction of energy flow, the phase will keep constant in transmission process despite of the increase of propagating length. The phase different between the incident and transmitted waves is measured to demonstrate that the phase can remain invariable in PhCs instead of zero-index materials or zero-averaged-index PhC superlattices. This effect can be extended to other artificially engineered materials, and will open a new route to obtain perfect zero-phase delay propagation for EMW.

Zero phase delay induced by wavefront modulation in photonic crystals

A new mechanism for the generation of efficient zero phase delay of electromagnetic wave propagation based on wavefront modulation is investigated in this paper. Both numerical simulations and experiments have demonstrated the zero phase delay behaviors of wave propagation in a two-dimensional triangular photonic crystal. The zero phase delay propagation, independent of the propagating distance, is attributed to an invariable wavefront modulation in a photonic crystal in the direction of wave propagation where the phase velocity is perpendicular to the group velocity with parallel wavefronts (or phasefronts) extending along the direction of the energy flow. This effect can be extended to the three-dimensional cases or other artificially engineered materials and may open a new route for obtaining perfect zero phase delay propagation for an electromagnetic wave instead of using zero-index or zero-averaged-index materials and may have significant potential in many applications.

THE SERIAL RESONANT ANTENNA FOR THE LARGE FIELD OF VIEW MAGNETIC RESONANCE IMAGING

A serial resonant antenna for the large fleld of view (FOV) magnetic resonance imaging (MRI) is presented. It consists of metallic patches cascaded through lumped capacitors in serial on the top layer of a grounded dielectric substrate. The theoretical analysis show that at the resonant frequency, uniformly distributed current with zero phase delay is produced independent of the antenna length, hence a uniform magnetic fleld for large FOV MRI can be achieved. Integrated with the L-shaped tunable matching network, the antenna can be tuned easily to operate rigorously at the working frequency of the MRI system. The numerical modeling, physical fabrication and measurement, as well as the phantom imaging are carried out to design, characterize and verify the performance of the proposed antenna for MRI.