Resonant Frequency Tuning Research Articles

High performance piezoelectric vibration energy harvesting by electrical resonant frequency tuning

Extending the frequency bandwidth (BW) of vibration energy harvesters (VEH) that power wireless sensor nodes is of scientific and industrial interest. In this aim, electrical methods to tune the resonant frequency of piezoelectric harvesters with strong electromechanical coupling coefficients have been developed. In this work, we provide guidelines for designing such strongly coupled VEH and present a broadband harvester with high normalized power density (NPD). Through an analytical model, we explain how the coupling coefficient and the quality factor of a cantilever can be jointly maximized, thereby maximizing the figure of merit . The proposed cantilever prototype made of PZN-5.5PT and aluminum offers one of the best coupling coefficients among the state-of-the-art (k 2= 49.8%) and a high quality factor (Qm = 140). Associated to an appropriate tunable electrical interface (short-circuit synchronous electric charge extraction (SECE) in our case), the prototype exhibits a NPD of 12.0 mW g−2 cm−3 and a frequency BW of 36.0% (56.5 Hz around 157 Hz) at 0.34 m s−2 with a tunable electrical interface: the short-circuit SECE. This represents the highest product NPW × BW from state of the art.

Nonlinear effects and applications for piezoelectric materials

The requirements of high quality factor, low power consumption, easy design techniques and compatibility with the main standard fabrication processes of integrated circuits (IC) make the tunable piezoelectric resonators a suitable option for the new technologies of fifth generation of telecommunication (5G) and Internet of Things (IoT). In this work the nonlinear state equations for piezoelectric effect are presented. From these equations we may deduce which materials can be used in applications where a hysteresis behavior or resonance frequency tunability are required, additionally, it is shown which crystals have the nonlinear tensor’s symmetry compatible with each application field. A novel model for the tunable piezoelectric devices is shown taking into account the consequences of voltage tuning. Finally, three different ways to design and implement the nonlinear behavior of piezoelectric materials to tune devices are introduced.

Spin-Echo Silencing Using a Current-Biased Frequency-Tunable Resonator

The ability to control microwave emission from a spin ensemble is a requirement of several quantum memory protocols. Here, we demonstrate such ability by using a resonator whose frequency can be rapidly tuned with a bias current. We store excitations in an ensemble of rare-earth ions and suppress on demand the echo emission ("echo silencing") by two methods: (1)detuning the resonator during the spin rephasing, and (2)subjecting spins to magnetic field gradients generated by the bias current itself. We also show that spin coherence is preserved during silencing.

Silicon Photonic Integrated Fano Resonator With Increased Slope Rate for Microwave Signal Processing

A tunable silicon photonic (SiP) integrated Fano resonator with an increased slope rate for microwave signal processing is proposed, fabricated, and experimentally demonstrated. A grating-based Fabry-Perot (FP) cavity-coupled micro-ring resonator (MRR) joint with a Mach-Zehnder Interferometer (MZI) is used to form the proposed Fano resonator. Since the resonant modes of the FP cavity and the MZI interfere with that of the MRR, a Fano resonator with an ultra-sharp asymmetric line shape is realized. A microheater is placed on top of the MRR to achieve thermal tuning of the Fano resonance frequency. The proposed Fano resonator is fabricated and experimentally evaluated. A high slope rate (SR) of 379.08 dB/nm and an extinction ratio (ER) of 22.97 dB are obtained. Thanks to its ultra-sharp asymmetric line shape, the applications of the proposed Fano resonator for microwave signal processing are discussed and experimentally demonstrated, including instantaneous frequency measurement with an improved resolution of ±0.2 GHz in a 7 GHz frequency measurement range, and optical temporal differentiation with an increased differentiation gain.

Stretchable three-dimensional tunable frequency selective fabric of U-shaped units and its electromagnetic response mechanism

Three-dimensional frequency selective fabric, based on textile or textile composite materials, is formed by adding another dimension in the longitude along the two-dimensional (2D) plane, and has the characteristics of miniaturization and multi-resonant frequency compared to the traditional 2D frequency selective fabric. In this paper, tunable three-dimensional frequency selective fabric (3D TFSF) forming a U-shaped array is proposed. The U-shaped unit is composed of two velvets and a dipole at the bottom. Through analysis of the physical samples, the geometric model of the 3D TFSF stretched along the x-axis and the y-axis during the stretching process was established. The velvets of the 3D TFSF were studied in both oblique and upright states during stretching. The 3D TFSF has good tunability, while the velvets remain upright when stretched, and it has the characteristics of stable resonance frequency under small strain and adjustable resonance frequency under large strain. By stretching, because the shape and size of the U-shaped conductive units can be changed, the equivalent inductance ( L) and capacitance ( C) of 3D TFSF can change during stretching to realize the tuning of resonant frequency. The 3D TFSF offers more design freedom and possibilities. Significant effects of wave absorption or selective filtering by the periodic structure can be achieved by regulating the structural parameters and material parameters together.

Measuring Interaction Bandwidth During Physical Human-Robot Collaboration

An assistive robot can augment human performance by providing physical assistance or motion guidance. In human-robot collaboration, it is important to know the bandwidth of an individual's ability to generate motion in response to external stimuli, such as visual or haptic cuing. This becomes particularly relevant in timing-sensitive tasks, such as walking or catching a falling object. In this work, we propose a frequency-based assessment of motion that enables us to measure the bandwidth of physical human-robot interaction (pHRI)—quantifying how fast individuals can respond to stimuli on a continuous basis. We introduce a robot-assisted virtual dynamic task with a tunable resonant frequency. A human subject study with seven participants shows that our task can elicit a dynamic response in a participant at frequencies of 0.5 Hz, 1 Hz, 1.5 Hz and 2.5 Hz at the arm. Using the virtual task, we test whether haptic cues improve motion timing. At all tested frequencies, we find that haptic stimuli help guide timing of dynamic movement and improve performance compared to visual-only cuing. By quantifying the interaction bandwidth for other pHRI systems—particularly when the human collaborators have neuromotor impairments—our method can help assistive robots adapt to an individual. Moreover, our results highlight the importance of incorporating haptic feedback into pHRI for dynamic tasks—haptics can provide guidance around motion timing, such as in assistive robots used for assessment and physical rehabilitation.

Actively tunable electromagnetically induced transparency on the solid-state plasma metamaterial

A hybrid metamaterial based on a metal-solid-state plasma (SSP) structure has been demonstrated, which actively controls the transparency window by introducing the SSP. The unit cell consists of square patch with a slot and metal cut wire (CW) with SSPs embedded. The designing of a resonant frequency tuning is intrinsically more difficult than amplitude modulation, which has been extensively researched. By introducing SSP and sophisticated structural design, the frequency shifts 403 GHz when the structure switches between two states. The transmission window is switched by changing the state of SSP, allowing for a dynamical group delay of the terahertz frequency. The linearly coupled Lorentz oscillator model is utilized to explore the underlying mechanism of the actively tunable electromagnetically induced transparency behavior between the bright and bright modes. We provide fascinating possibilities for innovative optical components in certain areas, including ultrafast switching, sensing, and terahertz active filtering.

A Bridge-Shaped Vibration Energy Harvester with Resonance Frequency Tunability under DC Bias Electric Field.

A vibration piezoelectric energy harvester (PEH) is usually designed with a resonance frequency at the external excitation frequency for higher energy conversion efficiency. Here, we proposed a bridge-shaped PEH capable of tuning its resonance frequency by applying a direct current (DC) electric field on piezoelectric elements. A theoretical model of the relationship between the resonance frequency and DC electric field was first established. Then, a verification experiment was carried out and the results revealed that the resonance frequency of the PEH can be tuned by applying a DC electric field to it. In the absence of an axial preload, the resonance frequency of the PEH can be changed by about 18.7 Hz under the DC electric field range from −0.25 kV/mm to 0.25 kV/mm. With an axial preload of 5 N and 10 N, the resonance frequency bandwidth of the PEH can be tuned to about 13.4 Hz and 11.2 Hz, respectively. Further experimental results indicate that the output power and charging response of the PEH can also be significantly enhanced under a DC electric field when the excitation frequency deviates from the resonance frequency.

Fingerprinting the Hidden Facets of Plasmonic Nanocavities.

The optical properties of nanogap plasmonic cavities formed by a NanoParticle-on-Mirror (NPoM, or patch antenna) are determined here, across a wide range of geometric parameters including the nanoparticle diameter, gap refractive index, gap thickness, facet size and shape. Full understanding of the confined optical modes allows these nanocavities to be utilized in a wide range of experiments across many fields. We show that the gap thickness t and refractive index n are spectroscopically indistinguishable, accounted for by a single gap parameter G = n/t0.47. Simple tuning of mode resonant frequencies and strength is found for each quasi-normal mode, revealing a spectroscopic “fingerprint” for each facet shape, on both truncated spherical and rhombicuboctahedral nanoparticles. This is applied to determine the most likely nanoscale morphology of facets hidden below each NPoM in experiment, as well as to optimize the constructs for different applications. Simple scaling relations are demonstrated, and an online tool for general use is provided.

Effects of Electric Bias on Different Sc-Doped AlN-Based Film Bulk Acoustic Resonators

Film bulk acoustic resonators (FBARs) based on aluminum nitride (AlN) and scandium-doped aluminum nitride (AlScN) exhibit tremendous application aspects in the radio frequency front-end due to achievable high-frequency characteristics, superior thermal performances and compatibility with harsh environments. Delicately controlling the resonant frequency (fs) of FBAR is essential for integrating filters or modules. In this work, we provide a practical feasibility in adjusting fs of AlN and AlScN FBAR using external direct current electric bias (EDC). When applying a negative EDC (the direction along the reversed c-axis), fs shifts to a lower frequency, whereas a positive EDC brings a higher fs. In order to extract the equivalent values of the stiffness coefficient (c33), piezoelectric coefficient (e33) and dielectric constant (εzz) of AlN and AlScN piezoelectric materials, we adopted the electromechanical equivalent Mason model. The results show that the equivalent values of c33 increase with the change of EDC from negative to positive, and, on the other hand, those of e33 and εzz decrease. Our work provides a systematic investigation on the electric field-influenced stiffening effect of AlN and AlScN piezoelectric films and opens a feasibility for frequency-tunable resonators.

Design of tunable low-frequency acoustic energy harvesting barrier for subway tunnel based on an optimized Helmholtz resonator and a PZT circular plate

This paper presents a tunable, low-frequency acoustic energy harvesting barrier, which contains the following four parts: the noise acquisition input module, the Helmholtz resonator optimization module, the resonant frequency tuning module, and the electricity generation module. The aim of this study is to make rational use of the huge noise energy inside the subway tunnel and convert it into electric energy to power the sensing and detecting equipment and lighting equipment along the railway. In this work, the optimal harvester unit and resonant frequency tuning part were pertinently designed to increase the output power of the unit. Experimental results show that one unit of the system can generate 317.5 mV instantaneous voltage and 100.8 μW instantaneous maximum power at 100 dB, and it verifies the efficiency and practicability of the proposed acoustic energy harvesting noise barrier. The device has a broad application prospect and can be adapted to different tunnel environments, including high-speed railway tunnels, highway tunnels, urban subway tunnels, etc., with excellent conversion efficiency. These results can provide valuable ideas for the design and practical application of new multi-functional noise barriers in the future.

Varactor-graphene-based multi-reconfigurable triplet filter with independent tuning of frequency and amplitude

In this paper, a multi-reconfigurable filter which consists of three identical varactor-graphene-loaded coaxial substrate integrated waveguide (SIW) resonators is presented. The center frequency and transmission amplitude of the proposed filter is independently reconfigurable by means of electrically controlling the values of the varactor capacitance and the graphene resistance, respectively. Tuners and their bias circuits are mounted on the surfaces of the SIW resonator to adjust the tuning of resonant frequency and unloaded quality factor, which enable to realize the frequency and amplitude of the presented multi-reconfigurable filter. In addition, the proposed filter applies a cascaded triplet topology to generate a transmission zero at the upper side in order to enhance skirt selectivity and out-of-band rejection. The circular shape of the resonator provides great flexibility and produces an additional compactness of the filter. The proposed multi-reconfigurable coaxial SIW filter is designed and fabricated, with high-Q varactors and graphene thin sheets as frequency and amplitude tuning elements, respectively, exhibiting the following reconfigurable characteristics: (a) a wide tuning range of 0.58–1.01 GHz with a constant 1 dB fractional bandwidth of 2 ± 0.2%. (b) A continuous tuning range of amplitude at any center frequency in the achievable frequency band. For instance, the proposed filter can be tuned with an amplitude range of 3.02–19.8 dB by varying the value of the graphene sheet resistance at 1.01 GHz. (c) Free combination of the arbitrary center frequency and attenuation level. The proposed filter with tunable filtering and attenuating responses has widely potential in reconfigurable wireless communication systems and radar systems due to its high integration and versatility.

A Giant Dual‐Resonant in Magnetoelectric Composite Based on Electrical and Electromechanical Coupling Towards Enhanced Working Bandwidth and Frequency Tuning

Expanding the resonance bandwidth and achieving tunable frequency are crucial for applying magnetoelectric (ME) composites in variable environments to realize their application, including magnetic and current sensors, tunable microwave devices, energy harvesters, etc. Herein, a dual‐coupling mode of combining electrical and electromechanical to implement wide bandwidth and frequency tuning in a ME laminated composite connected to an external inductor is investigated. Furthermore, this dual‐coupling mode is theoretically and experimentally studied and two resonances based on an equivalent circuit method are predicted. When the ME composite is connected to an inductor of 0.5 mH with an internal resistance of 31.74 Ω, the experimental result shows that the bandwidth increased by 429.32% compared with the original. In contrast, while the ME composite is connected to an inductor of 0.5 mH with an internal resistance of 12.16 Ω, two ME voltage coefficients (αV) are dramatically increased by 302.29% and 356.80% at resonance peaks, and the resonance frequencies are proportionally tuned of 6.84% (Δf1 = 6.24 kHz) and 4.74% (Δf2 = 4.32 kHz), respectively. These experimental results are significantly in agreement with the theoretical analysis. Therefore, the proposed method effectively achieves bandwidth expansion, ME coupling coefficient enhancement, and resonance frequency tuning.

Tunable plasmon-induced transparency in graphene-based plasmonic waveguide for terahertz band-stop filters

Terahertz (THz) tunable filters have great advantages in miniaturizing integrated and multiband communication systems. Here, THz band-stop filter with switchable single/double plasmon-induced transparency (PIT) based on metal-dielectric-metal waveguide consisting of a ring-stub cavity and two graphene ribbons (GRs) on stub sidewalls is proposed. The switchable characteristics of single and dual-PIT are investigated numerically and theoretically by the finite-difference time-domain and the radiating multi-oscillator theory, displaying good correspondence. The single-PIT is excited by the destructive interference between bright mode and dark mode, which possesses significant tunability of resonant frequency and transmission amplitude due to the existence of GRs. When independently regulating chemical potentials of GRs on the left and right sidewalls, the dual-PIT emerges. And the filter based on dual-PIT switches from single stopband to dual-stopband or even multi-stopband filtering. Besides, the band-stop filtering performance of the tunable PIT can be further optimized by increasing the number of ring-stub cavities. The tunable PIT in graphene-based plasmonic waveguide holds potential for THz multiband communications and subwavelength plasmonic devices, such as filters, switches, modulators.

Resonance Frequency Tuning of a 200 GHz Band Absorber by an External Magnetic Field

Resonance Frequency Tuning In article number 2100319, Shin-ichi Ohkoshi and co-workers investigate the effect of the external magnetic field on the millimeter-wave absorption of rhodium-substituted epsilon iron oxide, a 200-GHz band absorber, and achieve tuning of the resonance frequency.

Full 2\u03c0 tunable phase modulation using avoided crossing of resonances

Active metasurfaces have been proposed as one attractive means of achieving high-resolution spatiotemporal control of optical wavefronts, having applications such as LIDAR and dynamic holography. However, achieving full, dynamic phase control has been elusive in metasurfaces. In this paper, we unveil an electrically tunable metasurface design strategy that operates near the avoided crossing of two resonances, one a spectrally narrow, over-coupled resonance and the other with a high resonance frequency tunability. This strategy displays an unprecedented upper limit of 4π range of dynamic phase modulation with no significant variations in optical amplitude, by enhancing the phase tunability through utilizing two coupled resonances. A proof-of-concept metasurface is justified analytically and verified numerically in an experimentally accessible platform using quasi-bound states in the continuum and graphene plasmon resonances, with results showing a 3π phase modulation capacity with a uniform reflection amplitude of ~0.65.

Encapsulated Microbubble Fiber-Tip Fabry-Perot Cavity With Tunable Bandwidth for Sensitive Acoustic Detection

A photothermally generated microbubble on a single-mode fiber tip with tunable frequency bandwidth was demonstrated for sensitive detection of acoustic waves. The microbubble with spherical gas-water interface formed a flexible Fabry-Pérot cavity at the fiber tip and detected the acoustic waves by interferometric readout of the bubble deformation. To work in different liquids besides water, the sensor was encapsulated into a water-filled tube and the effects of the encapsulation process on the optical and acoustic characteristics of the sensor were investigated. A 40 μm-diameter microbubble based sensor exhibited a noise-equivalent pressure level of ∼1.0 mPa/Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> at the frequency of ∼100 kHz. The bubble diameter was photothermally changed from 20 μm to 60 μm, which enabled online tuning of the sensor resonant frequency from 100 kHz to 300 kHz. This tunable feature is attractive to applications that requires the detection of acoustic waves covering different frequency bands. The encapsulated microbubble sensor with advantages of high sensitivity, tunable bandwidth and low-cost would be interesting for applications in biomedical and industrial areas involving various liquid environments.

Design of a Compact Dual-Band Textile Antenna Based on Metasurface.

This paper presents a compact textile antenna design based on a metasurface for wearable applications. It operates in the 2.45 GHz and 5.5 GHz industrial, scientific, and medical bands. A two-dimensional equivalent circuit model is proposed to provide insight into the working principle of the metasurface. The tuning of the radiator's resonant frequencies can be easily performed by adjusting the dispersion curve of the metasurface unit cell. The metasurface in this work consists of a 4 × 4 array of unit cells fed by a printed coplanar waveguide structure with a slot in its reverse side to maintain its low profile structure. The main innovations of this work are: (i) the -2nd mode is employed to significantly miniaturize the antenna dimensions; (ii) the simultaneous excitation of the +1st mode to enable dual-band operation; (iii) an integrated back reflector to reduce back radiation and lower SAR; and (iv) the use of full textile materials to guarantee user comfort, ease of fabrication and low cost. The proposed antenna's footprint is 44.1 × 44.1 mm2 (0.12 λ2 at 2.45 GHz), with an impedance bandwidth of 10.2% centered at 2.45 GHz and 22.5% at 5.5 GHz. The maximum gain is -0.67 dBi and 7.4 dBi in free space, and 9% of power gain attenuation is generated when used on the body, and is suitable as a miniaturized antenna for wearable applications.

Development of a simple resonance frequency tuning method for magnetostrictive vibration energy harvesters

A fine-tuning method of the resonance frequency for a magnetostrictive vibration energy harvester by changing the magnetization state, namely using the ΔE effect of Young’s modulus, is proposed. Adjusting magnetization strength by changing the distance between the magnet for magnetization and the magnetostrictive vibration energy harvester in ten-millimeters revealed to tune the resonance frequency in 0.1 Hz order. A plot of the resonant frequency against the change in the flux density on the magnetostrictive material showed good agreement with a quadratic function approximation. A magnetostrictive vibration energy harvester tuned using this fine-tuning method could generate electricity stably for eleven days, suggesting the possibility of this fine-tuning method for long-term use.

Resonance Frequency Tuning of a 200 GHz Band Absorber by an External Magnetic Field

The effect of the external magnetic field on the millimeter‐wave absorption of rhodium‐substituted epsilon iron oxide, ε‐Rh0.13Fe1.87O3 (1) and ε‐Rh0.19Fe1.81O3 (2) nanomagnets, is investigated. Terahertz time‐domain spectroscopy (THz‐TDS) shows that 1 and 2 display a zero‐field ferromagnetic resonance (the so‐called natural resonance) at 201 GHz with a linewidth of 20 GHz and at 210 GHz with a linewidth of 30 GHz, respectively. The ferromagnetic resonance is measured under an external magnetic field (H ex). Applying +3.5 kOe parallel to the remnant magnetization and −3.5 kOe antiparallel to the remnant magnetization shifts the resonance frequency at 201 GHz in 1 by +6 and −4 GHz and that in 2 by +4 and −4 GHz, respectively. Simulations of the ferromagnetic resonance using the Landau−Lifshitz−Gilbert model reproduce the magnetic field‐induced shifts of the resonance frequencies. The 220 GHz band millimeter wave is the highest frequency with a high transparency for “atmospheric windows” and is expected to be a carrier frequency for sixth‐generation mobile communication systems (6 G) or 7 G. This study may help realize applications for millimeter‐wave isolators, circulators, or shutters.