Frequency Tuning Research Articles

Two-dimensional FePS3 nanoelectromechanical resonators with local-gate electrostatic tuning at room temperature

Nanoelectromechanical systems (NEMS) enabled by two-dimensional (2D) magnetic materials are promising candidates for exploring ultrasensitive detection and magnetostrictive phenomena, thanks to their high mechanical stiffness, high strength, and ultralow mass. The resonance modes of such vibrating membrane NEMS can be probed optically and also manipulated mechanically via electrostatically induced strain. Electrostatic frequency tuning of 2D magnetic NEMS resonators is, thus, an important means of investigating magneto-mechanical coupling mechanisms. Toward realizing magneto-mechanical coupled devices, we build circular drumhead iron phosphorus trisulfide (FePS3) NEMS resonators with different diameters (3–7 μm). Here, we report on experimental demonstration of tunable antiferromagnet FePS3 drumhead resonators with the highest fractional frequency tuning range up to Δf/f0 = 32%. Combining experimental results and analytical modeling of the resonance frequency scaling, we attain quantitative understanding of the elastic behavior of FePS3, including the transition from “membrane” to “plate” regime, with built-in tension (γ) ranging from 0.1 to 2 N/m. This study not only offers methods for investigating mechanical properties of ultrathin membranes of magnetic 2D materials but also provides important guidelines for designing future high-performance magnetic NEMS resonators.

Proof‐of‐Concept for Selective Magnetization Switching for Microfabricated Exchange‐Spring Magnets by Spin Wave Excitation

AbstractThis paper presents a proof‐of‐concept for selective magnetization switching in microfabricated elements with L10‐FePt/Ni81Fe19 (permalloy; Py) exchange‐coupled bilayers, known as exchange‐spring magnets, by exciting spin wave dynamics. Although the resonance frequency of the perpendicular standing spin wave mode definitely can be tuned by varying the Py layer thickness or the aspect ratio of the element, considering the requirements of selective magnetization switching, it is found that the frequency tuning by varying the aspect ratio is suitable. The spin wave‐assisted magnetization switching (SWAS) experiments for the different aspect ratios reveal the condition for the switching field reduction for each aspect ratio. Thanks to the different resonance frequencies between the different aspect ratios, the selective nature of SWAS method is experimentally demonstrated. The findings involve the contribution of higher‐order spin wave dynamics, and emphasize the significance of adjusting the aspect ratio of elements to realize selective magnetization switching, offering potential applications in multilevel recording media.

A mixed-mode on-chip automatic frequency tuning technique for biopotential amplifiers

A mixed-mode on-chip automatic frequency tuning technique for biopotential amplifiers

Deterministic Parity‐Time Symmetry Single‐Mode Oscillation in Filterless Multimode Resonators

AbstractParity‐time symmetry has great potential for mode selection in multimode resonators. However, in a PT‐symmetry system with saturable absorption mechanisms, the random background noise can initiate single‐mode oscillation at any of the maxima within the gain spectrum, that is, potential PT frequencies. Such randomness impedes the acquisition of high‐quality signals at desired frequencies. Here, this work proposes a method to obtain deterministic PT‐symmetry single‐mode oscillation in a filterless multimode resonator through one‐shot injection. With this technique, this work changes the system's gain spectrum and enhances the gain discrepancy. Utilizing the frequency domain saturable absorption of the resonator, oscillation at desired mode can maintain its frequency after the withdrawal of the injection signal. To validate the concept, this work establishes a polarization‐division multiplexed dual‐loop optoelectronic oscillator (OEO) with a 1‐km long cavity operated under PT‐symmetry conditions. By one‐shot injecting the PT‐OEO, this work effectively eliminates the randomness arising from the relatively flat gain spectrum, facilitating oscillation at any desired potential PT frequencies from 1.8 to 9 GHz without requiring elaborate frequency tuning structures. Moreover, the one‐shot injection technique produces ultra‐low phase noise performance, achieving a remarkable −158.6 dBc Hz−1@10 kHz. This performance level stands in close comparison with the best phase noise values recorded for OEOs.

Interface mechanism of photon–magnon–phonon conversion in an epitaxial ferrite–dielectric structure

Abstract It is shown that in the transition layer of an epitaxial yttrium iron garnet (YIG) film, there are effects of intense power conversion and redistribution between electromagnetic waves (EMW), exchange spin waves (ESW) and acoustic waves (AW). These interconversion occurs during the casсade of double hybridization of EMW-ESW and secondary hybridization of ESW-AW. The necessary phase synchronism condition for this is ensured by the smooth distortion of the ESW dispersion within the thickness direction of the transition layer. The secondary hybridization of ESW-AW manifests itself in the intense excitation of AW, which are radiated into the depth of the gadolinium gallium garnet (GGG) substrate. In this case, magnetoacoustic resonances are excited in the YIG-GGG bilayer structure, for the observation of which strict parallelism and optical polishing of the reflecting surfaces of the YIG-GGG structures are required. An important advantage of magnetoacoustic resonances is the record high quality factor in the microwave range and high resistance to external atmospheric influences, which is of significant interest for the fabrication of highly stable magnetoacoustic microwave generators with discrete frequency tuning.

Low noise InGaAs/InP single-photon detector with DC to 1 GHz tunable gate frequency

An InGaAs/InP single-photon detector (SPD) typically operates in gated mode, but the capacitive response of a single-photon avalanche diode introduces spike noise, obscuring the avalanche signal. Most avalanche signal discrimination schemes cannot completely eliminate spike noise, resulting in residual noise. Limited by residual noise, these schemes have large noise and a limited frequency tuning range. However, for applications like quantum key distribution and laser ranging, a low noise, frequency-tunable InGaAs/InP SPD is crucial for enhancing system performance. Here, we propose a (residual noise assisted) discrimination method that aligns the maximum amplitude of the avalanche signal with the peak of the residual noise. This method turns the residual noise from adversity into an advantage for signal discrimination. With this method, we achieve tunable gating frequency from DC to 1 GHz. Additionally, this method enables the discrimination of weak avalanche signals, allowing effective single-photon detection at low avalanche gain. Across the entire tuning range, at a 20% detection efficiency, the dark count rate is approximately 5.0×10−7 per gate, and the afterpulse probability is less than 1.0%, significantly lower than in previous experiments. The proposed SPD exhibits low noise and a wide tunable gating frequency range, providing a reliable foundation for various applications.

Frequency agile photonic integrated external cavity laser

Recent advances in the development of ultra-low loss silicon nitride integrated photonic circuits have heralded a new generation of integrated lasers capable of reaching fiber laser coherence. However, these devices are presently based on self-injection locking of distributed feedback laser diodes, increasing both the cost and requiring tuning of laser setpoints for their operation. In contrast, turn-key legacy laser systems use reflective semiconductor optical amplifiers (RSOAs). While this scheme has been utilized for integrated photonics-based lasers, so far, no cost-effective RSOA-based integrated lasers exist that are low noise and simultaneously feature fast, mode-hop-free, and linear frequency tuning as required for frequency modulated continuous wave (FMCW) LiDAR or for laser locking in frequency metrology. Here we overcome this challenge and demonstrate a RSOA-based, frequency agile integrated laser, that can be tuned with high speed, with high linearity at low power. This is achieved using monolithic integration of piezoelectrical actuators on ultra-low loss silicon nitride photonic integrated circuits in a Vernier filter-based laser scheme. The laser operates at 1550 nm, features a 6 mW output power and a 400 Hz intrinsic laser linewidth, and allows ultrafast wavelength switching within 7 ns rise time and 75 nW power consumption. In addition, we demonstrate the suitability for FMCW LiDAR by showing laser frequency tuning over 1.5 GHz at 100 kHz triangular chirp rate with a nonlinearity of 0.25% after linearization and use the source for measuring a target scene 10 m away with a 8.5 cm distance resolution.

Graphene based THz filter design using open-loop resonator for space applications

This paper introduces a graphene-based tunable terahertz bandpass filter with a dual-mode open-loop resonator, designed to operate at a resonant frequency of 6.35 THz. Leveraging a graphene layer between the conductor and dielectric layers, the filter enables the propagation of surface plasmons, allowing dynamic tunability essential for terahertz applications. Key advantages of this design include precise bandwidth control, achieved by manipulating the resonator's physical parameters, and adaptable center frequency tuning through variations in graphene's chemical potential, providing a tuning range of approximately 0.16 THz. These reconfigurable properties make the filter highly suitable for integration into terahertz space communication systems, where adaptability and high performance are critical. The proposed design's ability to fine-tune both bandwidth and center frequency establishes it as a versatile and efficient solution for emerging terahertz-based applications, demonstrating significant potential for enhancing the flexibility and functionality of future communication technologies.

Research on miniaturized frequency steering system based on atomic clock

In order to generate a high-performance RF signal, by analyzing the traditional frequency steering system, and aiming at the goal of miniaturization and engineering, this paper designs a miniaturized frequency steering system based on dual-atomic clock. In addition, we have carried out research on key technologies such as high-precision frequency deviation measurement and precision frequency regulation. On this basis, a frequency deviation measurement and correction system is designed. And according to the theoretical analysis, the measuring accuracy of the frequency deviation measurement approach can reach 1.0 × 10-14, besides, the step frequency tuning can also reach 1.125 × 10-14. What's more, some related experiments, the RF signal synthesized from a Rb clock and a master has an accuracy of 2.26 × 10-13, and also the frequency stability of 104 s in terms of the Allan deviation reaches 2.36 × 10-14, suggesting that the overall performance of the rubidium atomic clock has been greatly improved.

High-selectivity fully tunable wideband bandpass filter with adaptive transmission zeros

This paper presents a compact fully tunable wide-band bandpass filter based on the varactors loaded quadruple mode coupled resonator. Triple adaptive transmission zeros (TZs) have achieved by reasonably setting the identical shifting mechanism architecture of transmission poles and adjacent TZs, which dramatically improve the selectivity. Meanwhile, it realized the tunable center frequency (CF) with a constant absolute bandwidth, resulting in the CF tuning range of 26.7 %, 25.8 %, and 15.6 % from 1.5 to 1.95 GHz. The bandwidth tuning range of 42.7 % can be achieved from 180 to 920 MHz with a fixed CF. The test results match well with the theoretical simulation so as to successfully validate the correctness of the proposed design approach.

Tuning of the Cut-Off Frequency in Effective Medium Approximation and Long Range Surface Plasmon Excitation in Graphene and Black Phosphorus

Tuning of the Cut-Off Frequency in Effective Medium Approximation and Long Range Surface Plasmon Excitation in Graphene and Black Phosphorus

Compartmentalized pooling generates orientation selectivity in wide-field amacrine cells

Orientation is one of the most salient features in visual scenes. Neurons at multiple levels of the visual system detect orientation, but in many cases, the underlying biophysical mechanisms remain unresolved. Here, we studied mechanisms for orientation detection at the earliest stage in the visual system, in B/K wide-field amacrine cells (B/K WACs), a group of giant, nonspiking interneurons in the mouse retina that coexpress Bhlhe22 (B) and Kappa Opioid Receptor (K). B/K WACs exhibit orientation-tuned calcium signals along their long, straight, unbranching dendrites, which contain both synaptic inputs and outputs. Simultaneous dendritic calcium imaging and somatic voltage recordings reveal that individual B/K dendrites are electrotonically isolated, exhibiting a spatially confined yet extended receptive field along the dendrite, which we term "compartmentalized pooling." Further, the receptive field of a B/K WAC dendrite exhibits center-surround antagonism. Phenomenological receptive field models demonstrate that compartmentalized pooling generates orientation selectivity, and center-surround antagonism shapes band-pass spatial frequency tuning. At the microcircuit level, B/K WACs receive excitation driven by one contrast polarity (e.g., "ON") and glycinergic inhibition driven by the opposite polarity (e.g., "OFF"). However, this "crossover" inhibition is not essential for generating orientation selectivity. A minimal biophysical model reproduced compartmentalized pooling from feedforward excitatory inputs combined with a substantial increase in the specific membrane resistance between somatic and dendritic compartments. Collectively, our results reveal the biophysical mechanism for generating orientation selectivity in dendrites of B/K WACs, enriching our understanding of the diverse strategies employed throughout the visual system to detect orientation.

Semi-Active Vibration Control for Wind Turbines: A Variable Tuned Mass Damper Approach Utilizing 1st Modal and 3P Tuning

Vibration in wind turbine towers poses a significant threat to the service life and structural integrity of wind turbines. Dampers have been identified as a pivotal strategy for alleviating such vibrations. Despite this, the dynamic behavior of large-scale offshore wind turbines is frequently swayed by wind shear, the tower shadow effect, and the Rotor-Nacelle Assembly (RNA) control system, typically manifesting as responses to the blade passing frequency (3P). To mitigate these vibrations, this study introduces a 3P tuning method for tuned mass dampers (TMDs), alongside a sophisticated design approach that targets optimal frequency and damping ratios. The integration of a semi-active variable-tuned mass damper (SA-V-TMD) offers a dual-mode control solution: The “3P tuning mode” adeptly manages vibrations across a spectrum of operating conditions, while the “1st modal frequency tuning mode” stabilizes the structure during parked states. Simulations substantiate the 3P tuning method’s enhanced efficacy over standard methods under operational conditions. Furthermore, the SA-V-TMD demonstrates superior effectiveness and stability in comparison to traditional TMDs, underscoring its potential as a preeminent solution in wind turbine vibration management.

A dynamic event-triggered approach for observer-based formation control of multi-agent systems with designable inter-event time

This paper addresses the leader-following formation control problems for generic linear multi-agent systems under directed topology with designable inter-event time. A synthesis approach combining controller and observer design is developed under a dynamic event-triggered communication and control scheme. The proposed feedback control, state estimation, and event-triggered rules are distributed, and only local information is required for each agent to implement these algorithms. The proposed dynamic event-triggered protocol incorporates model-based estimation and clock-like auxiliary dynamic variables to prolong the inter-event time and economize the network resources. Furthermore, the inter-event time is designable, which allows more flexible tuning of communication frequency with only minor performance degradation. Sufficient conditions for formation control are established by linear matrix inequalities. The proposed method exhibits significant improvement over the dynamic event-triggered control methods described in the existing literature. Compared to the existing static event-triggered strategy, the proposed approach significantly reduces the utilization of communication resources while preserving asymptotic convergence to the desired formation. Comparative simulations demonstrate the validity and effectiveness of the proposed theoretical results.

Strong hole-photon coupling in planar Ge for probing charge degree and strongly correlated states

Semiconductor quantum dots (QDs) in planar germanium (Ge) heterostructures have emerged as front-runners for future hole-based quantum processors. Here, we present strong coupling between a hole charge qubit, defined in a double quantum dot (DQD) in planar Ge, and microwave photons in a high-impedance (Zr = 1.3 kΩ) resonator based on an array of superconducting quantum interference devices (SQUIDs). Our investigation reveals vacuum-Rabi splittings with coupling strengths up to g0/2π = 260 MHz, and a cooperativity of C ~ 100, dependent on DQD tuning. Furthermore, utilizing the frequency tunability of our resonator, we explore the quenched energy splitting associated with strong Coulomb correlation effects in Ge QDs. The observed enhanced coherence of the strongly correlated excited state signals the presence of distinct symmetries within related spin functions, serving as a precursor to the strong coupling between photons and spin-charge hybrid qubits in planar Ge. This work paves the way towards coherent quantum connections between remote hole qubits in planar Ge, required to scale up hole-based quantum processors.

Exciton Fine Structure in Axially Symmetric Quantum Dots and Rods of III-V and II-VI Semiconductors.

Both absorption and emission of light in semiconductor quantum dots occur through excitation or recombination of confined electron-hole pairs, or excitons, with tunable size-dependent resonant frequencies that are ideal for applications in various fields. Some of these applications require control over quantum dot shape uniformity, while for others, control over energy splittings among exciton states emitting light in different polarizations and/or between bright and dark exciton states is of key importance. These splittings, known as exciton fine structure, are very sensitive to the nanocrystal shape. Theoretically, nanocrystals of spheroidal shape are often considered, and their nonsphericity is treated perturbatively as stemming from a linear uniaxial deformation of a sphere. Here, we compare this treatment with a nonperturbative model of a cylindrical box, free of any restrictions on the cylinder's aspect ratio. This comparison allows one to understand the limits of validity of the traditional perturbative model and offers insights into the relative importance of various mechanisms controlling the exciton fine structure. These insights are relevant to both colloidal nanocrystals and epitaxial quantum dots of III-V and II-VI semiconductors.

6.7-8.1 µm tunable single-frequency difference frequency generation in ZGP for high-resolution spectroscopy.

Difference frequency generation (DFG) based tunable single-frequency mid-infrared (MIR) light sources are desirable for high-resolution spectroscopy, sensing, and imaging. In this work, we demonstrate a continuous-wave (CW) single-frequency DFG in a ZnGeP2 (ZGP) crystal driven by all-fiber near-infrared (NIR) fiber lasers, for the first time to our knowledge. The all-fiber NIR laser sources consist of a 1.5 µm erbium-doped fiber amplifier seeded by a CW tunable fast scanning single-frequency laser and a 1.9 µm CW tunable single-frequency thulium-doped fiber laser. Taking advantage of the high nonlinear coefficient and large birefringence of the ZGP crystal, single-frequency DFG in ZGP achieves a broad spectral tuning range from 6.7 to 8.1 µm, with an output power at the 10 µW level. Precise detection of C2H2 gas by continuously scanning the DFG source across a spectral range of 1.1 THz (∼34 cm-1) is also presented, highlighting the potential of the tunable DFG source for high-resolution optical spectroscopy applications. We anticipate this work will provide what we believe to be a new platform for spectroscopy in the molecular fingerprint spectral region.

Machine Learning Enabled Compact Frequency‐Tunable Triple‐Band Hexagonal‐Shaped Graphene Antenna for THz Communication

ABSTRACTIn this article, a compact triple‐band frequency‐tunable (FT) hexagonal‐shaped graphene antenna through a machine learning (ML) approach for terahertz (THz) application is presented. The proposed THz antenna is designed on a polyamide () substrate with a thickness of 10 μm, and graphene is used as an antenna radiator. The size of the substrate is 38 × 46 μm2. The FT is achieved by changing the chemical potential of graphene material. The performance of the proposed THz antenna has been investigated, and the impacts of several conducting materials like gold, aluminum, copper, and graphene and dielectric materials like Rogers RT/duroid 5880, polyamide, quartz, and SiO2 are explored. The proposed THz antenna provides three operating bands. The frequency of operation in Band‐1 is 2.51–5.05 THz, Band‐2 is 5.99–7.43 THz, and Band‐3 is 7.94–9.63 THz. The bandwidth in Band‐1, Band‐2, and Band‐3 are 2.54, 1.44, and 1.69 THz, respectively. The % of impedance bandwidth in Band‐1, Band‐2, and Band‐3 are 67.19%, 24.02%, and 21.28% respectively. The proposed antenna has a maximum peak gain of 5 dBi. The proposed antenna is optimized through various ML algorithms like random forest (RF), extreme gradient boosting (XGB), K‐nearest neighbor (KNN), decision tree (DT), and artificial neural network (ANN). The RF algorithm gives more than 99% accuracy compared to other ML algorithms and accurately predicts the S11 of the proposed antenna. The proposed THz antenna would be suitable for applications related to imaging, medical, sensing, and ultra‐speed short‐distance communication applications in the THz region.

Dynamically tunable terahertz metamaterial absorber based on the composite structure of graphene/shape memory alloy

The equipment that can actively adjust the frequency and intensity of terahertz wave absorption peaks is a key link in the future development of terahertz wave intelligence. However, there was relatively little research on devices that can actively tune the absorption peak intensity of terahertz waves at this stage, which limits the development of intelligent terahertz wave devices. This thesis designs a three-dimensional tunable terahertz wave absorber. By bending the shape memory alloy or adjusting the Fermi level of graphene, the dual tuning of THz wave frequency and intensity can be realized. The absorber can achieve three perfect absorption peaks at 0.708, 1.929, and 2.334 THz, with absorption peak intensities of 99.99%, 99.57%, and 94.13%, respectively. The simulation results of this thesis provide data and references for the development of future smart terahertz devices.

Wind-Induced Vibration Control of High-Rise Buildings with Double-Skin Façades Using Distributed Multiple Tuned Façade-Dampers-Inerters

To address the shortcomings of tuned mass dampers (TMD), such as excessive internal space occupation and overlarge physical mass, this paper proposes a tuned façade damper inerter (TFDI) that utilizes parts of the outer façades of double-skin façades (DSF) as damping mass, capitalizing on the lightweight and efficient characteristics of inerters. The TFDI effectively resolves the challenge of multi-layer connections of inerters in high-rise buildings by utilizing corridor space. By vertically distributing TFDIs, a distributed multiple TFDI (d-MTFDI) system is formed. The configuration and motion of equations of this system are presented, and the control effectiveness is validated using wind tunnel test data. Two tuning modes are further proposed: unified tuning mode and distributed tuning mode. For the unified tuning mode, analytical expressions for optimal tuning frequency and damping ratio are derived; for the distributed tuning mode, numerical optimization methods are employed to determine the optimal tuning frequency range and damping ratio. Comparative results indicate that the distributed tuning mode achieves higher control efficiency than the unified tuning mode, with a significant reduction in the required optimal damping ratio. Furthermore, comparisons with d-MTMD demonstrate that d-MTFDI significantly enhances wind-induced vibration control performance.