Resonant Frequency Tuning Research Articles

Static and dynamic characteristics of electrostatically coupled MEMS beams under asymmetric actuation conditions

Abstract Electrostatically actuated microbeams have gained prominence due to their applications as micro-actuators and ultrasensitive sensors. In this study, we investigate the dynamic behavior of electrostatically coupled microbeams, specifically focusing on the effects of asymmetric actuation conditions. Our investigation encompasses both static and dynamic characteristics of the coupled microbeam system, considering various gap ratios between the beams and the fixed electrodes. Within the coupled system, two doubly clamped microbeams are positioned between two fixed electrodes. We develop a reduced-order model (ROM) to investigate static and dynamic responses of the coupled system. To validate the ROM, we rigorously compare its results with finite element (FE) simulations. Our findings reveal that the gap ratios play a pivotal role in shaping the system’s response. Notably, first two natural frequencies are important for design of micro-resonators and they exhibit complex variation with respect to the applied DC voltage. Moreover, we explore resonance frequency tunability and investigated interplay between geometric nonlinearity and nonlinear electrostatic actuation forces. These insights contribute significantly to the efficient design of MEMS resonators.

Combining Magnetostriction with Variable Reluctance for Energy Harvesting at Low Frequency Vibrations

In this paper, we explore the benefits of using a magnetostrictive component in a variable reluctance energy harvester. The intrinsic magnetic field bias and the possibility to utilize magnetic force to achieve pre-stress leads to a synergetic combination between this type of energy harvester and magnetostriction. The proposed energy harvester system, to evaluate the concept, consists of a magnetostrictive cantilever beam with a cubic magnet as proof mass. Galfenol, Fe81.6Ga18.4, is used to implement magnetostriction. Variable reluctance is achieved by fixing the beam parallel to an iron core, with some margin to create an air gap between the tip magnet and core. The mechanical forces of the beam and the magnetic forces lead to a displaced equilibrium position of the beam and thus a pre-stress. Two configurations of the energy harvester were evaluated and compared. The initial configuration uses a simple beam of aluminum substrate and a layer of galfenol with an additional magnet fixing the beam to the core. The modified design reduces the magnetic field bias in the galfenol by replacing approximately half of the length of galfenol with aluminum and adds a layer of soft magnetic material above the galfenol to further reduce the magnetic field bias. The initial system was found to magnetically saturate the galfenol at equilibrium. This provided the opportunity to compare two equivalent systems, with and without a significant magnetostrictive effect on the output voltage. The resonance frequency tuning capability, from modifying the initial distance of the air gap, is shown to be maintained for the modified configuration (140 Hz/mm), while achieving RMS open-circuit coil voltages larger by a factor of two (2.4 V compared to 1.1 V). For a theoretically optimal load, the RMS power was simulated to be 5.1 mW. Given the size of the energy harvester (18.5 cm3) and the excitation acceleration (0.5 g), this results in a performance metric of 1.1 mW/cm3g2.

Integrated Wired/Wireless Charging System for Electrical Vehicles With Resonant Frequency Tuning Function

Integrated Wired/Wireless Charging System for Electrical Vehicles With Resonant Frequency Tuning Function

Triangular-shaped two-dimensional vibrational electromagnetic energy harvester

Energy harvested from vibrations can be used to power e.g. wearables and Internet-of-things devices. Here we investigate a two-dimensional triangular-shaped electromagnetic vibration energy harvester with tunable resonance frequency. The harvester has rotatable arrays of fixed magnets, that can be turned to adjust the magnetic forces, a free-to-move structure with three cylindrical magnets, and a set of coils to generate a current. Using an experimental 2D shaker, the power produced by the harvester is measured as function of a vibrational frequency in the x-direction from 1 Hz to 11 Hz in steps of 0.25 Hz and in the y-direction from 1 Hz to 10 Hz in steps of 1 Hz, both at 2 mm amplitude, and at five different angles of the fixed magnets. The harvester produces up to 30 mW of power, and the resonance frequency in both the x- and y-directions shifts from around 7 Hz to around 11 Hz as the fixed magnets are rotated, clearly demonstrating that the resonance frequency can be tuned.

Stabilized conformal planar cavity with continuous adjustable resonant frequency

A conformal planar cavity with filling dielectrics is conformally transformed from a concave cavity by transformation optics. The proposed conformal planar cavity offers remarkable advantages, including high stability, high Q factor, tunable resonant frequency, and small mode volume. In contrast to concave cavities, it offers a significant advantage by being integrable onto a chip. Additionally, when compared to planar cavities based on metasurfaces, which lack the capability for continuous resonant frequency adjustment, the proposed conformal cavity offers a tunable resonant frequency that can be continuously adjusted by simply changing the cavity length without the need for redesigning the filling dielectrics. Only dielectrics with permittivity ranging from 1 to 1.7 are required inside the conformal cavity, which can be easily obtained at various frequency bands. The tunability and stability of the conformal planar cavity is numerically verified, and experimental demonstrations at microwave band are performed.

Electromagnetic vibrational energy harvester with targeted frequency-tuning capability based on magnetic levitation

Electromagnetic vibrational energy harvester with targeted frequency-tuning capability based on magnetic levitation

Smart reconfigurable electromagnetic metamaterials based on thermadapt shape memory Poly(ethylene–vinyl acetate)

Smart reconfigurable metamaterials can better adapt to changing electromagnetic environments and broaden the range of applications. However, constructing electromagnetic reconfigurable metamaterials, especially those with large areas or applied to complex surfaces via a universal approach, is still a challenge. Here, we introduce a smart reconfigurable metamaterial consisting of a thermadapt shape memory polymer ethylene vinyl acetate copolymer (EVA) matrix and a flowable liquid–metal resonant unit. Based on the excellent self-healing properties of EVA, large-area metamaterials can be constructed by thermal assembly of metamaterial units. In addition, the original shape of the metamaterial can be reprogrammed to apply to complex three-dimensional surfaces with the reprocessing properties of EVA. Moreover, by utilizing the shape memory performance of the EVA, the temporary resonant frequency of the metamaterial can be set by programming and the resonant frequency tuning of the metamaterial can be controlled under external temperature stimulation, achieving noncontact tuning. In the future, this concept can be broadly applied in fields such as complex structure stealth layers and multifunction filters.

Design and simulation of a tunable comb-drive actuator with a wide frequency tuning range and low pull-in voltage

The presented paper describes the design, simulation, and analysis of a novel tunable comb-drive actuator that aims to increase the range of tuning resonance frequency while reducing the pull-in voltage. The conventional comb resonator has a limited resonant frequency tuning range, and hence, modifying the spring stiffness of the structure is crucial to obtaining a tunable comb resonator. The proposed design includes eight flexible beams on each side that support a set of comb finger parts. The actuator achieves the goal of shifting the resonance frequency both downwards and upwards by utilizing Serpentine nested-folded beams. A triangular comb with non-uniform varied finger lengths combined with variable gap fingers is designed to adjust the frequency downwards, while a comb with constant finger lengths combined with variable gap fingers is designed to adjust the frequency upwards. To simulate and design the structure, the IntelliSuite software is utilized. The results show that the actuator has a primary resonant frequency of 3052 Hz, which can be lowered to 335 Hz by applying a tuning voltage of 74 V to the downward tuning part. Similarly, the resonant frequency can be increased to 3159 Hz by applying a tuning voltage of 60 V to the upward tuning part. The resonator achieves a maximum frequency tuning range of 90%, and the simulation results are in good agreement with the theoretical predictions. However, it is worth noting that the size of this resonator is relatively small, approximately 1077 × 328 μm2. This innovative design offers potential applications in various fields, including micro-electromechanical systems (MEMS), micro-optics, and microsensors. Overall, the presented work demonstrates the feasibility of achieving a tunable comb resonator with a significantly improved resonant frequency tuning range and reduced pull-in voltage.

Graphene metamaterials-based plasmon-induced terahertz modulator for high-performance multiband filtering and slow light applications.

We proposed multilayered graphene (Gr)-based surface plasmon resonance-induced high-performance terahertz (THz) modulators with tunable resonance frequencies. Previously reported Gr metamaterials-based THz plasmonic modulators had small group delay, low extinction ratio (ER), and difficult-to-tune resonant frequency without changing structural parameters in the THz range. A comprehensive investigation employing the finite-difference time-domain (FDTD) simulation technique revealed high group delay, broad tunability independent of structural parameters, and large ER for our proposed quadband and pentaband plasmonic modulators. We obtained tunable group delays with a maximum of 1.02 ps and 1.41 ps for our proposed quadband and pentaband plasmonic modulators, respectively, which are substantially greater compared to previously reported Gr-based metamaterial structures. The maximum ER of 22.3 dB was obtained, which was substantially high compared to previous reports. Our proposed modulators were sensitive to the polarization angle of incident light; therefore, the transmittance at resonant frequencies was increased while the polarization angle varied from 0° to 180°. These high-performance plasmonic modulators have emerging potential for the design of optical buffers, slow light devices, multistop band filters, integrated photonic circuits, and various optoelectronic systems.

A 1.33–1.88 GHz microfluidically tunable filter with controllable coupling

AbstractIn this article, a continuously microfluidically tunable filter using two microstrip resonators is proposed. By injecting different amount of water into the tubes, the resonant frequency as well as coupling intensity between two resonators can be controlled. As a result, the fractional bandwidth (FBW) of the proposed band can keep constant when tuning the frequency. As far as the authors know, most of the state‐of‐the‐art microfluidics tunable filters are discontinuous, and the tuning range is limited. In this article, the wide tuning capacity of the frequency is realized by placing some tubes between the microstrip resonators and the ground. By increasing or decreasing the amount of water in the pipes, the local dielectric constant and the equivalent electrical length of the transmission line are changed simultaneously. Therefore, it plays a key role in resonant frequency tuning. In the other hand, the coupling coefficient can be controlled by injecting the amount of water into the tube between the two resonators. Finally, through the analysis of computer simulation technology simulation and measurement, it can be seen that the tuning range of resonant frequency is up to 41.3%, with the central frequency varying from 1.33 to 1.88 GHz. The insertion loss is less than 3.09 dB and the return loss is higher than 15 dB, while the FBW is 3.4% ± 0.2%. The measurement matches well with the simulation results, verifying the proposed design methodology.

Efficiency of a cluster of underwater low-frequency sources

The efficiency of underwater low-frequency sound sources can be improved by using tunable high-quality resonators, increasing the emission aperture, or using source clusters. A very low frequency tunable resonator is hard to build. Large aperture sources are difficult to deploy. This study shows that the efficiency of a cluster of sources can be much higher than that of each source. Low frequency sources separated by distance operate independently, the sources add up the pressure, and the emitted pressure is proportional to the number of elements in the cluster. As a result, the radiated power of the cluster increases according to the quadratic law of the number of its elements, and the efficiency of the cluster increases in proportion to this number. To prove this, finite element modeling of an array of underwater sources was carried out. The simulation included the internal structure of each sound source with Helmholtz bubble resonators driven by standard audio 2 kW subwoofers. Indeed, the cluster efficiency increases when the distance between the sources exceeds several of their diameters. Simulations showed that a cluster of 32 broadband sources with a frequency of 10– 100 Hz could produce sound pressure levels equal to a standard air gun.

Investigation of ambient vibration sources for direct energy harvesting by optimizing resonant frequency using proof mass

Ambient mechanical sources typically vibrate below the frequency of 200 Hz, posing challenges for thin film piezoelectric sensors, including low power, high resonant frequency, and small bandwidth. To optimize the electrical energy harvesting from the ambient sources, it is crucial to reduce the resonant frequency of the energy harvester to match that of the ambient sources. In this study, the energy harvester’s resonant frequency dependency on proof mass is thoroughly investigated using the finite element method (FEM). Further, the FEM results are experimentally validated through a custom-designed vibration set-up. Different ambient vibration energy sources, their vibrating frequencies, and accelerations are examined to harness direct mechanical energy and convert it into electric energy using the piezoelectric sensor. Further, the effective proof mass and position are determined to achieve the targeted frequency obtained from ambient sources. Consequently, the harvester is utilized for direct energy harvesting from the ambient sources. The addition of proof mass can lower the resonant frequency of the harvester from 160 Hz to 40 Hz allowing the harvester to vibrate at maximum amplitude to obtain maximum output voltage. Significant enhancement of output power is observed after the tuning of harvester resonant frequency, harvesting a maximum output power of 19.29 μW when mechanically sourced from the bike mirror, measured at an acceleration of 4.50 g at 43 Hz.

Scaling of self-stimulated spin echoes

Self-stimulated echoes have recently been reported in the high cooperativity and inhomogeneous coupling regime of spin ensembles with superconducting resonators. In this work, we study their relative amplitudes using echo-silencing made possible by a fast frequency tunable resonator. The highly anisotropic spin linewidth of Er3+ electron spins in the CaWO4 crystal also allows to study the dependence on spin-resonator ensemble cooperativity. It is demonstrated that self-stimulated echoes primarily result from a combination of two large control pulses and the echo preceding it.

Origami-Inspired Vibrotactile Actuator (OriVib): Design and Characterization.

The use of vibrotactile feedback, in place of a full-fledged force feedback experience, has recently received increased attention in haptic communities due to their clear advantages in terms of cost, expressiveness, and wearability. However, designers and engineers are required to trade off a number of technical challenges when designing vibrotactile actuators, including expressiveness (a wide band of actuation frequency), flexibility, and the complexity of the manufacturing process. To address these challenges, we present the design and characterization of an origami-inspired flexible vibrotactile actuator, named OriVib, with a tunable resonance frequency (expressiveness), an origami-inspired design (flexible, soft contact with the human body), and a streamlined manufacturing process (low-cost). Based on its characterization, the fabricated OriVib actuator with 54 mm diameter can produce up to 1.2 g vibration intensity where the vibration intensity increases linearly from 6-11 V input. The resonance frequency is tunable through the characteristic diameter (the resonance frequency decreases in an almost inversely proportional fashion as the diameter increases). As for the thermal signature, the OriVib actuator maintains its temperature below 38 oC when actuated within 6-8 V. In terms of repeatability, the OriVib maintained an average vibration intensity of 0.849 g (standard deviation 0.035 g) for at least 2 million cycles. These results validate the effectiveness of the OriVib actuator to offer an expressive, low-cost, and flexible vibrotactile actuator.

A QMSIW Cavity-Backed Self-Diplexing Antenna With Tunable Resonant Frequency Using CSRR Slot

A QMSIW Cavity-Backed Self-Diplexing Antenna With Tunable Resonant Frequency Using CSRR Slot

Electric Field Assisted Resonance Frequency Tuning in Free Standing Nanomechanical Devices for the Application in Multistate Switching using Phase Change Material

VO2 possesses a unique property of solid-state phase transition near room temperature wherein it transforms from monoclinic (M1) to tetragonal phase (R) which alters its various physical properties such as...

Investigation of the SERS application of gold films deposited on uncured polydimethylsiloxane with tunable LSPR

We present an approach to investigate the localized surface plasmon resonance and surface-enhanced Raman scattering of gold films deposited on uncured polydimethylsiloxane via thermal evaporation. Differing from solid substrates, the liquid surface of uncured polydimethylsiloxane can serve as an isotropic substrate on which gold atoms nucleate and disperse to form characteristic microstructures in a controlled manner. By adjusting experimental parameters during film deposition, the absorption of resonant plasmon modes can be tuned in the visible spectral range due to the control of particle size and distribution in Au films. Furthermore, Raman measurements are conducted to investigate the enhancement of Raman signals in these films, and the experimental results are verified by simulation analysis. This work exhibits tunability of surface plasmon resonance frequency and enhanced Raman detection capability by depositing metal films on liquid surfaces, thus providing potential applications of these films in flexible biosensors and chemical detection.

A drum-like piezoelectric rotational energy harvester via magnetic beating

In this Letter, an indirectly excited approach of introducing an air-filled separation chamber is proposed to develop a drum-like piezoelectric rotational energy harvester (DL-PREH) via magnetic beating. The harvester delivers the external excitation to the piezoelectric transducer via the intermediate air chamber, and the electric output of transducer is induced by the air pressure inside the chamber. Thus, a high reliability can be guaranteed for the harvester under an unexpected excessive impact due to the air-filled separation zone. Moreover, the harvester can easily implement a resonant frequency tuning by altering the drum height to improve the rotation speed adaptability. Its potential applications as a sustainable power source to charge different capacitors and power commercial light-emitting diodes (LEDs) are demonstrated experimentally. The fabricated DL-PREH device can achieve a maximum output power of 10.63 mW with a drum height of 6 mm at the matching resistance of 24 kΩ. Also, it can light up at least 100 blue commercial LEDs in parallel. The designed harvester exhibits its good power generation capability and resonance frequency tunability.

Vibration Energy Harvesting for Aerospace Applications

The aerospace industry is actively seeking to employ wireless sensors for various data collection and structural health monitoring applications. While continued development of wireless sensors and sensor networks holds promise in the aerospace industry, the challenge of powering these sensors must still be addressed. Vibration energy harvesting is one possible approach in this regard, and is particularly promising for aerospace applications due to the ubiquitous presence of vibration energy. In this review paper the generic design considerations and challenges involved in harvesting energy from vibration energy are described. The paper also highlights recent progress addressing current challenges in adapting a vibration energy harvesting approach in a practical application, including resonance frequency tuning and design considerations for optimal energy harvesting performance. Recent progress in adapting this approach to the microscale using MEMS technology is also highlighted.

A frequency tunable resonator using liquid crystals on flexible substrates

ABSTRACT Liquid crystals have already been widely used in reconfigurable microwave devices through external electrically controlled dielectric properties. The traditional method is to sandwich liquid crystals between two metal layers etched on hard substrates. However, this method of adding external electric fields tends to cause short-circuiting between the upper and lower electrodes of liquid crystals in the bending state for the case of electrodes on flexible substrates. In this paper, a novel method is proposed to realise a frequency tunable resonator using liquid crystal fabricated on flexible substrates. The resonator is composed of coplanar waveguide structures. Since the metal layers of the coplanar waveguide placed on the same horizontal plane do not touch each other when bending, it allows the controlled electric field direction to be parallel to the electrode layers. Liquid crystals are placed under the coplanar metals for the electric field control. In order to maximise tunability, the structural parameters of the proposed structure were analysed in detail. The test results agree with the theory and simulation to verify the reliability of this frequency tunable resonator. Furthermore, the test results also illustrate that the applied electric field method can achieve the frequency continuous electrically tunable function when the flexible resonator is bending.