Frequency Splitter Research Articles

Unidirectional mode interference in magneto-optical photonic heterostructure

We investigate a unidirectional mode interference effect based on one-way coupled topological edge states (CTESs), which originate from the coupling of topological edge states (TESs) in magneto-optical photonic crystal (MOPC) heterostructure. By using the finite element method, the self-imaging phenomenon in the MOPC heterostructure is predicted. As an example of applications, a one-way tunable frequency and power splitter based on unidirectional mode interference is designed, which is reflectionless. Besides, the splitting ratio can be tuned by adjusting the external magnetic field. Moreover, the splitter is robust against common disorders, including the radius- and position-fluctuations of pillars and nonuniform magnetizations, which keep the bandgap open. Our findings provide a new, to the extent of our knowledge, way of designing integrated photonic circuit applications such as reflectionless filters, couplers, multiplexers, switches, or even nonreciprocal devices, and so on.

Tunable anisotropic parameters realized by metal-dielectric hybrid meta-atoms.

Rational design of the structure enables metamaterials to go beyond the ingredients and achieve unprecedented material properties. However, the realization of complicated and anisotropic electromagnetic parameters relies on the elaborate design of building blocks, and the mutual coupling between the anisotropic responses makes precise control of material parameters even more difficult. Here, we propose a metal-dielectric hybrid metamaterial, not only realizing the decoupling between anisotropic electromagnetic responses, but also establishing a one-to-one correspondence between independent geometric dimensions and anisotropic parameter components. Moreover, a tuning theoretical paradigm applied to an anisotropic and resonant system is further suggested, which proves that the operating frequency of this hybrid metamaterial can be easily adjusted by changing external fields. As prototypes, two typical and tunable microwave meta-devices, a transformation-optics cloak and a frequency splitter, are constructed with Ba-Sm-La-Ti ferroelectric ceramic and flexible printed circuit board, which successfully demonstrate our proposed design theory. This work provides a simple strategy for the design and fabrication of tunable anisotropic metamaterials, and boost the development of meta-devices toward practical application.

A case study on the assessment of RF switch and splitter options for coupling of transceiver modules to bidirectional antennas employed in linear wireless sensor networks

AbstractRecently, a concept of linear wireless sensor networks (LWSNs) has attracted much attention. For such networks, one of the key challenges in sensor node design is to couple transceiver modules with bidirectional antennas placed back‐to‐back for opposite radiation. As is known, simply, this can be achieved by using well‐known coupling options like radio frequency (RF) switch or splitter. However, it is important to decide between two seemingly equally good options according to the system requirements such as RF performance, power consumption, and cost. Therefore, this study aims to comparatively assess these options from the system level point of view to find out what advantages or disadvantages either provides as per the other from widespread use of them in a LWSN‐based cathodic protection monitoring of oil and natural gas pipelines in extreme environments. Preliminary field tests are also conducted to validate the efficiency of coupling options for LWSN links. Results show that RF splitter offers low power consumption and cost whereas RF switch has advantages of low loss. Thus, it is believed that this study may provide useful insights to design bidirectional sensor links for LWSNs.

Resonant excitation of surface plasma modes in a dielectric core-plasma antenna with arbitrary structure

In this letter, we theoretically investigate how the surface manipulation method can be used for the resonant excitation of the surface plasma waves (SPWs) in the new proposed dielectric core-plasma antenna with any arbitrary structure parameters. Results show the high efficiency of terahertz TM mode/SPW conversion for a “typical” plasma antenna even up to more than 50 percent. We emphasize that the present results for the new proposed experimental accessible structures can be used in many laboratory applications such as generation of high-order harmonics, designing a new laser frequency splitter as well as photodetectors, and so on.

Dual‐output quasi‐Yagi antenna for out‐of‐band RF energy harvesting

Aiming to improve the SWIPT (Simultaneous Wireless Information and Power Transfer) technologies, this work proposes a novel Dual-Output quasi-Yagi antenna (DOQY), designed by combining a single classic quasi-Yagi antenna (QY) and a dedicated frequency splitter in order to behave as two distinct antennas, one operating at 1.8 GHz mobile communication band for data communication and another at 2.4 GHz ISM band for out-of-band energy harvesting. To validate the proposal, the results of the DOQY are compared to those presented by a reference quasi-Yagi antenna (QYref) with the same dimensions. Additionally, for analysis of the energy harvesting capacity and the corresponding necessary RF design criteria, the antennas are connected to a well-established rectifier system and its performances were compared. The novel architecture presents a antenna gain performance of 70%, in comparison with QYref in both central frequency bands, presenting, however, the same performance in energy harvesting. At 1.8 GHz the antenna gain performance is increased to 81% of the QYref, adding the rectifier circuit in their respective port. These satisfactory results endorse the operability of the DOQY for SWIPT application, adding a new port without compromising the system performance.

Compact effective surface plasmon polariton frequency splitter based on substrate integrated waveguide

In this paper, we present a compact effective surface plasmon polariton (ESPP) frequency splitter induced by structural dispersion in substrate integrated waveguide (SIW). The frequency splitter consists of three SIW layers. Periodic wire arrays are placed on the interface of layers with relative effective permittivity in the opposite sign to support ESPP propagation, which can introduce transmission zero. By properly placing the substrates, the two passbands are spatially isolated from each other. The designed frequency splitter is numerically simulated and analysed. The numerical results demonstrate that the two passbands can be flexibly tuned by changing the relative permittivities of substrates and the lateral dimensions of SIW. The sample design achieves tunable dual passbands split and has a low profile and compact size.

Laser-induced defects in optical multilayer coatings by the spatial resolved method

The spatial resolved method, which measures the laser-induced damage fluence by identifying the location of the damage point in the Gaussian beam three-dimensional direction, is demonstrated. The advantages and practicality of this method have been explained. Taking a triple frequency beam splitter as an example, the defect damage fluence can be accurately calculated by the spatial resolved method. The different defect damage performance of the triple frequency splitter is distinguished under irradiations of only the 355 and 532 nm lasers. The spatial resolved method provides a way to obtain precise information of optical film defect information.

Frequency splitter based on spoof surface plasmon polariton transmission lines

We propose a frequency splitter based on spoof surface plasmon polariton (SSPP) transmission lines (TLs). The device consists of two bent domino SSPP TLs with different geometric parameters, leading to different passbands, forming two frequency band branches. A transition from a rectangular waveguide to the two SSPP TLs is designed for frequency splitting. To achieve efficient transition for both branches in their respective frequency bands, different transition lengths of the two branches and a shifted placement from the center are adopted. Furthermore, for the high frequency band branch, to obtain satisfactory out-of-band rejection below the lower cut-off frequency, an SSPP bandstop structure is introduced by placing SSPP TL sections along the main SSPP TL. A prototype is designed, fabricated, and evaluated. The results prove the feasibility of the proposed SSPP frequency splitter.

Hybrid Newmark-conformal FDTD modeling of thin spoof plasmonic metamaterials

The aim of this paper is to present a new efficient and accurate semi-implicit finite-difference time-domain (FDTD) method for modeling thin plasmonic metamaterials supporting spoof surface plasmons. The presented method is formulated by combining Yu–Mittra's conformal FDTD technique for dielectrics, the simplified conformal finite integration technique for perfectly electric conductors (PECs) and the Newmark-Beta method. The resultant scheme is magnetically implicit, has a more relaxed stability condition than that of Yee's FDTD scheme, and allows for accurate modeling of both PEC and dielectric curved surfaces. Energy conservation and stability of the presented scheme is theoretically proved with the energy inequality method. Its formulation can be generalized to a class of magnetically implicit FDTD schemes with weakly conditional and unconditional stability in a unified manner. The presented scheme is used to simulate thin structures supporting spoof surface plasmon polaritons and spoof localized surface plasmons, and also applied to recent plasmonic devices such as planar frequency splitter, ultrathin rainbow trapping device and compact planar metadisk with split-ring resonators. The accuracy and efficiency of the presented scheme are assessed in comparison with the conventional explicit and implicit FDTD methods, and their conformal variants.

Stochastic Control of Predictive Power Management for Battery/Supercapacitor Hybrid Energy Storage Systems of Electric Vehicles

This paper presents a neural network (NN) based methodology for power demand prediction and a power distribution strategy for battery/supercapacitor hybrid energy storage systems of pure electric vehicles. To develop an efficient prediction model, driving cycles are first grouped and distinguished as three different driving patterns. For each driving pattern, characteristic parameter data that could better featured driving cycles are extracted effectively and used to train NN. The predictive information combined with its error is subsequently used for power distribution. Then, to deal with different dynamics of battery and supercapacitor systems, a frequency splitter is used and its frequency is further optimized by a particle swarm optimization algorithm to minimize the total cost including battery degradation and system energy for each driving pattern. Based on these efforts, a real-time predictive power management control strategy is finally proposed. To verify its effectiveness, simulation has been conducted to compare with the state-of-the-art control strategy under a speed profile composing of five standard driving cycles. Results show that obviously enhanced performance can be achieved by the proposed control strategy.

3D correlation NMR spectrum between three distinct heteronuclei for the characterization of inorganic samples: Application on sodium alumino-phosphate materials

We report here an original NMR sequence allowing the acquisition of 3D correlation NMR spectra between three distinct heteronuclei, among which two are half-integer spin quadrupolar nuclei. Furthermore, as two of them exhibit close Larmor frequency, this experiment was acquired using a standard triple-resonance probe equipped with a commercial frequency splitter. This NMR technique was tested and applied to sodium alumino-phosphate compounds with 31P as the spin-1/2 nucleus and 23Na and 27Al as the close Larmor frequencies isotopes. To the best of our knowledge, such experiment with direct 31P and indirect 27Al and 23Na detection is the first example of 3D NMR experiment in solids involving three distinct heteronuclei. This sequence has first been demonstrated on a mixture of Al(PO3)3 and NaAlP2O7 crystalline phases, for which a selective observation of NaAlP2O7 is possible through the 3D map edition. This 3D correlation experiment is then applied to characterize mixing and phase segregation in a partially devitrified glass that has been proposed as a material for the sequestration of radioactive waste. The 31P-{23Na,27Al} 3D experiment conducted on the partially devitrified glass material conclusively demonstrates that the amorphous component of the material does not contain aluminum. The as-synthesized material thus presents a poor resistance against water, which is a severe limitation for its application in the radioactive waste encapsulation domain.

NMR crystallography to probe the breathing effect of the MIL-53(Al) metal-organic framework using solid-state NMR measurements of 13C-27Al distances.

The metal-organic framework MIL-53(Al) (aluminium terephthalate) exhibits a structural transition between two porous structures with large pore (lp) or narrow pore (np) configurations. This transition, called the breathing effect, is observed upon changes in temperature or external pressure, as well as with the adsorption of guest molecules, such as H2O, within the pores. We show here how these different pore openings can be detected by observing the dephasing of 13C magnetization under 13C-27Al dipolar couplings using Rotational-Echo Saturation-Pulse Double-Resonance (RESPDOR) solid-state NMR experiments with Simultaneous Frequency and Amplitude Modulation (SFAM) recoupling. These double-resonance NMR experiments between 13C and 27Al nuclei, which have close Larmor frequencies, are feasible thanks to the use of a frequency splitter. The experimental SFAM-RESPDOR signal fractions agree well with those simulated from the MIL-53(Al)-lp and -np crystal structures obtained from powder X-ray diffraction analysis. Hence, these 13C-27Al solid-state NMR experiments validate these structures and confirm their rigidity. A similar agreement is reported for the framework ligands in the as-synthesized (as) MIL-53(Al), in which the pores contain free ligands. Furthermore, in this case, 13C-{27Al} SFAM-RESPDOR experiments allow an estimation of the average distance between the free ligands and the 27Al nuclei of the framework.

Local measure of the electromagnetic field in magnetic resonance coils: How do simulations help to disentangle the contributions of the electric and magnetic fields?

The development of probes for Nuclear Magnetic Resonance (NMR) spectroscopy of metabolites, biomolecules or materials requires the accurate determination of the radio-frequency (RF) magnetic field strength, B1, at the position of the sample since this RF-field strength is related to the signal sensitivity and the excitation bandwidth. The Ball Shift (BS) technique is a commonly employed test bench method to measure the B1 value. Nevertheless, the influence of the RF electric field, E1, on BS is often overlooked. Herein, we derive, from Maxwell equations, an analytical expression of the BS, which shows the contribution of both the electric and magnetic energies to the BS value. This equation shows that the BS allows quantifying the B1 field strength only in regions where the electric energy is small with respect to the magnetic one. The numerical simulations of electromagnetic (EM) field and energy prove that this condition is fulfilled at 100.5MHz inside the electrically balanced coil of a double-resonance 1H/X 4mm Magic Angle Spinning (MAS) probe since for that circuit, the center of the coil is an antinode for the B1 standing wave and a node for the E1 one. We also show that the simulated BS values agree well with the experimental ones. Conversely, NMR experiments show that the contribution of the electric energy to BS becomes significant when the X channel of this probe is connected to a frequency splitter. In that case, the use of BS method to estimate the B1 value is compromised.

Frequency splitter based on the directional emission from surface modes in dielectric photonic crystal structures.

We demonstrate the numerical design and the experimental validation of frequency dependent directional emission from a dielectric photonic crystal structure. The wave propagates through a photonic crystal line-defect waveguide, while a surface layer at the termination of the photonic crystal enables the excitation of surface modes and a subsequent grating layer transforms the surface energy into outgoing propagating waves of the form of a directional beam. The angle of the beam is controlled by the frequency and the structure operates as a frequency splitter in the intermediate and far field region.

Adaptive frequency-separation-based energy management system for electric vehicles

This paper deals with an adaptive frequency-based power sharing method between batteries and ultracapacitors (UC) as power sources within an electric vehicle. An adaptive frequency splitter is used for routing the low-frequency content of power demand into the battery and its high-frequency content into the UC system, taking profit from the UC as a peak power unit. Autonomy may thus be increased while preserving battery state of health and ensuring that UC voltage variations remain confined within certain desired range. Results obtained by real-time experiments on a dedicated test rig validate the proposed energy management approach and recommend it to be applied as power source coordination method to microgrids in general.

Spoof surface plasmon polaritons supported by ultrathin corrugated metal strip and their applications

AbstractIn this review, we present a brief introduction on the spoof surface plasmons supported on corrugated metallic plates with nearly zero thickness. We mainly focus on the propagation characteristics of spoof surface plasmon polaritons (SPPs), excitation of planar SPPs, and several plasmonic devices including the bending waveguide, Y-shaped beam splitter, frequency splitter, and filter. These devices are designed and fabricated with either planar or conformal plasmonic metamaterials, which are validated by both full-wave simulations and experiments, showing high performance. We also demonstrate that an ultrathin textured metallic disk can support multipolar spoof localized surface plasmons, either with straight or curved grooves, from which the Fano resonances are also observed.

Planar surface plasmonic waveguide devices based on symmetric corrugated thin film structures.

Recently, a conformal surface plasmon (CSP) structure has been successfully proposed, which is very promising for application of planar plasmonic devices in the frequency ranging from microwave to mid-infrared [Proc. Natl. Acad. Sci. U.S.A. 110, 40-45 (2013)]. Here we investigated the dispersions and electromagnetic (EM) field patterns of a symmetric CSP structure in which the two sides of the planar metal strip are symmetrically corrugated by groove arrays. The symmetric CSP structure can support both the symmetric mode (even mode) and the anti-symmetric mode (odd mode) of surface wave propagation. Based on the even mode, we analyzed the EM wave coupling between two adjacent symmetry CSP strips, and then designed and analyzed two planar CSP waveguide devices in the terahertz frequency: a frequency splitter and a 3 dB directional coupler. To verify the functionality and performance of these waveguide devices, we scaled down the working frequency to microwave and designed similar devices with scaled geometry. We implemented microwave experiments on the fabricated prototypes, and the tested device performances have clearly validated the functionality of our designs. The symmetric CSP structure is believed to be very applicable in future design of novel planar plasmonic device and circuitry.

A multidirectional frequency splitter with band-stop plasmonic filters

We propose a multidirectional frequency splitter with band-stop plasmonic filters, in which a double-period grating structure is adopted to produce band-stop filtering features. The multidirectional frequency splitter consists of three specially designed metallic gratings with finite thickness. Better isolation between different metallic gratings is achieved at the lower frequencies. The experimental verification of the frequency splitter is implemented at the microwave frequencies with excellent agreements to full-wave simulations. A four-way THz frequency splitter excited by the cylindrical wire is also proposed and simulated to show how the design can be scaled down to the THz frequencies for the potential applications.

MIM plasmonic waveguide splitter with tooth-shaped structures

A plasmonic splitter based on subwavelength metal–insulator–metal (MIM) waveguides with tooth-shaped structures is proposed and numerically researched by using the finite-difference time-domain (FDTD) method in visible and near infrared frequencies. The splitter is regarded as two zigzag-shaped MIM waveguides, which naturally stretch out two tooth structures in bending corners. Each tooth forms a resonant cavity. The transmission of the zigzag-shaped waveguide is close to zero at some resonant wavelength of the tooth cavity. The same-order resonant wavelength has an approximately linear relationship with the depth of the tooth. When the geometric parameters of the two zigzag-shaped waveguides of teeth are suitably initialized, both frequency splitter and power splitter can be simply achieved.

Time domain topology optimization of 3D nanophotonic devices

We present an efficient parallel topology optimization framework for design of large scale 3D nanophotonic devices. The code shows excellent scalability and is demonstrated for optimization of broadband frequency splitter, waveguide intersection, photonic crystal-based waveguide and nanowire-based waveguide. The obtained results are compared to simplified 2D studies and we demonstrate that 3D topology optimization may lead to significant performance improvements.