Megahertz Frequencies Research Articles

Extending radiowave frequency detection range with dressed states of solid-state spin ensembles

Quantum sensors using solid-state spin defects excel in the detection of radiofrequency (RF) fields, serving various applications in communication, ranging, and sensing. For this purpose, pulsed dynamical decoupling (PDD) protocols are typically applied, which enhance sensitivity to RF signals. However, these methods are limited to frequencies of a few megahertz, which poses a challenge for sensing higher frequencies. We introduce an alternative approach based on a continuous dynamical decoupling (CDD) scheme involving dressed states of nitrogen vacancy (NV) ensemble spins driven within a microwave resonator. We compare the CDD methods to established PDD protocols and demonstrate the detection of RF signals up to ~85 MHz, about ten times the current limit imposed by the PDD approach under identical conditions. Implementing the CDD method in a heterodyne/synchronized protocol combines the high-frequency detection with high spectral resolution. This advancement extends to various domains requiring detection in the high frequency (HF) and very high frequency (VHF) ranges of the RF spectrum, including spin sensor-based magnetic resonance spectroscopy at high magnetic fields.

Evaluating the Removal of Polystyrene Latex Particles Using the Quartz Transducer Ultrasonic Cleaners in the Megahertz Frequency Range

The removal of nanometer-sized particles is necessary along with a shift to microfabrication and highly integrated semiconductor chips. Spray-type ultrasonic cleaning methods are currently used to clean semiconductors. However, this method has the problem of collapsing wiring patterns due to severe fluctuations in the sound pressure impinging on the substrate surface. We developed a quartz transducer ultrasonic cleaner (QTC) to solve the problem of constant variations in sound pressure. In this study, we conducted experiments on the removal polystyrene latex particles from the surface of silicon wafers using QTC and elucidated the physical particle removal mechanism.

Acoustically controlled bubble nucleation

Fundamental studies of single bubble heat transfer are crucial to improve our understanding of boiling phenomena and develop modeling and simulation tools for the design and optimization of boiling systems. However, conducting these kinds of experiments over a wide range of conditions is challenging and may involve expensive and complicated experimental techniques (e.g., lasers) to isolate and control bubble nucleation. In this work, we introduce a new technique to control nucleation with an ultrasonic beam. A low-cost and widely available piezoelectric disc driven at megahertz frequencies directed at a heated surface can increase the time-averaged pressure and suppress evaporation until the moment the transducer is turned off, allowing us to control the incipience of boiling to within 150 µs. We demonstrate this technique by measuring the physical and thermal footprint of natural and acoustically controlled bubbles with high-resolution infrared thermometry and phase detection diagnostics. We were able to raise the bubble nucleation temperature by over 30 K compared to a reference case with no acoustic control, which significantly changes bubble growth rate, microlayer formation and evaporation and departure diameter. We highlight the potential of this new low-cost and easy-to-use technique in a variety of different boiling heat transfer studies.

Electrically tunable space-time metasurfaces at optical frequencies.

Active metasurfaces enable dynamic manipulation of the scattered electromagnetic wavefront by spatially varying the phase and amplitude across arrays of subwavelength scatterers, imparting momentum to outgoing light. Similarly, periodic temporal modulation of active metasurfaces allows for manipulation of the output frequency of light. Here we combine spatial and temporal modulation in electrically modulated reflective metasurfaces operating at 1,530 nm to generate and diffract a spectrum of sidebands at megahertz frequencies. Temporal modulation with tailored waveforms enables the design of a spectrum of sidebands. By impressing a spatial phase gradient on the metasurface, we can diffract selected combinations of sideband frequencies. Combining active temporal and spatial variation can enable unique optical functions, such as frequency mixing, harmonic beam steering or shaping, and breaking of Lorentz reciprocity.

4H silicon carbide bulk acoustic wave gyroscope with ultra-high Q-factor for on-chip inertial navigation

Inertial navigation on a chip has long been constrained by the noise and stability issues of micromechanical Coriolis gyroscopes, as silicon, the dominant material for microelectromechanical system devices, has reached the physical limits of its material properties. To address these challenges, this study explores silicon carbide, specifically its monocrystalline 4H polytype, as a substrate to improve gyroscope performance due to its low phonon Akhiezer dissipation and its isotropic hexagonal crystal lattice. We report on low-noise electrostatic acoustic resonant gyroscopes with mechanical quality factors exceeding several millions, fabricated on bonded 4H silicon carbide-on-insulator wafers. These gyroscopes operate using megahertz frequency bulk acoustic wave modes for large open-loop bandwidth and are tuned electrostatically using capacitive transducers created by wafer-level deep reactive ion etching. Experimental results show these gyroscopes achieve superior performance under various conditions and demonstrate higher quality factors at increased temperatures, enabling enhanced performance in an ovenized or high-temperature stabilized configuration.

Deformation state of a graphene sheet within the framework of the continuum moment-membrane theory of elasticity

The paper proposes an approach to finding the stress-strain state (SSS) of structures containing graphene, a novel nanomaterial that has currently found а wide range of practical applications in nanoelectromechanical systems. Graphene is a 2D basic building block for other carbon structures such as membranes, sheets, nanotubes, etc. To describe the SSS of a graphene sheet, the phenomenological continuum moment-membrane theory of plates is used, from which, due to the fact that graphene is an ultrathin material, the concept of thickness is excluded. The physical elasticity relationships of a graphene sheet are expressed through its rigidity characteristics, determined using the harmonic potential of interatomic interactions in carbon. A differential formulation and the corresponding variational formulation are given for the problem of static deformation and determination of the natural frequencies and modes of vibration of a graphene sheet. The variational formulation is based on the Lagrange principle and is implemented numerically using the finite element method. Finite element relations are constructed taking into account moment effects of the behavior of a graphene sheet. For approximation, a 4-node rectangular finite element is used. Numerical solutions to several problems of static deformation of a graphene sheet under conditions of a plane stress state and transverse bending are presented, and the analysis of its natural vibrations is also performed. Good convergence of numerical simulation results in all considered problems is demonstrated. The obtained numerical solutions are essential in designing and calculating resonators in which ultrathin nanostructures are used. The establishment of the fact that a graphene sheet has a high intrinsic frequency falling in the GHz region (for example, quartz resonators are characterized by megahertz frequencies) opens up new prospects for using graphene itself as an ultrasensitive nanomechanical resonator for detecting small masses and ultrasmall displacements.

High-performance CeFeCo/FeSiAl soft magnetic composites for megahertz power devices

Soft magnetic composites (SMCs) play a crucial role in modern electronics and electrical devices, for which challenges remain in maintaining magnetic performance and reducing loss at megahertz (MHz) frequencies. Here, CeFeCo/FeSiAl@ polyurethane (PU) SMCs have been rationally designed with the simultaneous achievement of large relative permeability, high domain-wall resonance frequency, and low power loss. As a rare-earth soft magnetic alloy, the CeFeCo is promising for high-frequency applications due to its easy-plane anisotropy, whereas FeSiAl is advantageous with increased electrical resistivity as well as approaching-zero magnetocrystalline anisotropy and magnetostriction. Hot pressing has been adopted to achieve a dense and homogeneous distribution of CeFeCo and FeSiAl powders in the PU for reduced magnetic dilution and eddy current loss. The resultant SMCs exhibit optional soft magnetic performance with large relative permeability of 21.0, low power loss of 3677.5 kW·m−3 at 5 MHz, and high domain-wall resonance frequency of 386.1 MHz. As such this work provides insights into the design of high-frequency SMCs incorporating novel rare-earth soft magnetic alloys.

Polarization-insensitive wide-angle resonant acousto-optic phase modulator.

Phase modulators are commonly used devices in optics. Free-space phase modulators are typically constructed from optically anisotropic crystals exhibiting the Pockels effect. To preserve the light's polarization state as it propagates through the crystal, it is essential to align the polarization and the angle of incidence of the light with respect to the crystal. In this study, we demonstrate the feasibility of constructing free-space resonant phase modulators with a broad acceptance angle and minimal dependence on the polarization state of light using an acousto-optic approach. These modulators operate in the megahertz frequency range, require modest power levels, have aperture sizes exceeding 1 cm2, and feature sub-millimeter thickness.

Ultrasound generation in water via quasi-periodically snapping polymeric core–shell micro-bead excited with radiowaves

This work reports the results of a theoretical and numerical study showing the occurrence of stochastically resonating bistable dynamic in polymeric micro-bead of sub-micrometric size with stiff core and soft shell. The system, submerged in water, is excited with a pulsed laser working in the Mega-Hertz frequency range and tuned to match both an optical and acoustic resonance of the system. The laser interacts with the carbon nanotubes embedded in the shell of the polymeric micro-bead generating heat. The concurrent action of the generated heat with the standing acoustic oscillations, gives rise to a stochastically resonating bistable system. The system in fact is forced to switch between two states (identifiable with the creation and organized disruption of a quasi-hexagonal tessellation) via a snap-through-buckling mechanism. This phenomenon results in the unprecedented generation of pressure oscillations. These results open the way to develop a new type of core–shell micro-transducers for radioacoustic imaging applications able to work in the Mega-Hertz frequency range. From a more general thermodynamic perspective, the reported mechanism shows a remarkable periodicity and energy conversion efficiency.

Optically isotropic longitudinal piezoelectric resonant photoelastic modulator for wide angle polarization modulation at megahertz frequencies

Polarization modulators have a broad range of applications in optics. The acceptance angle of a free-space polarization modulator is crucial for many applications. Polarization modulators that can achieve a wide acceptance angle are constructed by attaching a piezoelectric transducer to an isotropic material, and utilizing a resonant transverse interaction between light and acoustic waves. Since their demonstration in the 1960s, the design of these modulators has essentially remained the same with minor improvements in the following decades. In this work, we show that a suitable single crystal with the correct crystal orientation, functioning as both the piezoelectric transducer and the acousto-optic interaction medium, could be used for constructing a highly efficient free-space resonant polarization modulator operating at megahertz frequencies and exhibiting a wide acceptance angle. We construct the modulator using gallium arsenide, an optically isotropic and piezoelectric crystal, and demonstrate polarization modulation at 6 MHz with an input aperture of 1 cm in diameter, acceptance angle reaching ±30∘, and modulation efficiency exceeding 50%. Compared to state-of-the-art resonant photoelastic modulators, the modulator reported in this work exhibits greater than 50-fold improvement in modulation frequency for the same input aperture, while simultaneously reducing the thickness by approximately a factor of 80. Increasing the modulation frequency of photoelastic modulators from the kilohertz to the megahertz regime and substantially reducing their thickness lead to significant performance improvements for various use cases. This technological advancement also creates opportunities for utilizing these devices in new applications.

Power loss measurement system for soft magnetic materials in megahertz frequencies

Soft magnetic materials play a key role in developing integrated and miniaturized power electronics. However, it is still challenging to accurately evaluate the high-frequency (MHz) power loss of soft magnetic materials, which determines the energy efficiency of power electronics. In this paper, we firstly trace the high-frequency error origination in traditional electrometric method and propose a two-step calibration method for the system to compensate the phase angle discrepancy between exciting current and induced voltage. The first-step calibration eliminates the phase angle discrepancies caused by propagation delay of current and voltage probes, while the second-step calibration compensates residual phase angle discrepancies. A calibration factor k is defined to determine whether the second-step calibration is needed. The experimental results demonstrate that the system’s phase discrepancy is compensated within 0.13°, enabling power loss measurement frequency up to 20 MHz that much higher than present apparatus. Our results will facilitate the development of high-frequency soft magnetic materials and promote the miniaturization of power electronics.

Frequency dependence of ultrasonic effects on the kinetics of hen egg white lysozyme fibrillation

Our study aimed to investigate the effects of ultrasound on the fibrillation kinetics of HEWL (hen egg white lysozyme) and its physicochemical properties. Ultrasound, a mechanical wave, can induce conformational changes in proteins. To achieve this, we developed an ultrasound exposure system and used various biophysical techniques, including ThT fluorescence spectroscopy, ATR-FTIR, Far-UV CD spectrophotometry, Fluorescence microscopy, UV-spectroscopy, and seeding experiments. Our results revealed that higher frequencies significantly accelerated the fibrillation of lysozyme by unfolding the native protein and promoting the fibrillation process, thereby reducing the lag time. We observed a change in the secondary structure of the sonicated protein change to the β-structure, but there was no difference in the Tm of native and sonicated proteins. Furthermore, we found that higher ultrasound frequencies had a greater seeding effect. We propose that the effect of frequency can be explained by the impact of the Reynolds number, and for the Megahertz frequency range, we are almost at the transition regime of turbulence. Our results suggest that laminar flows may not induce any significant change in the fibrillation kinetics, while turbulent flows may affect the process.

Laser-Generated Ultrasonic Vortex in the Megahertz Frequency Range

Laser-Generated Ultrasonic Vortex in the Megahertz Frequency Range

Ultrasonic imaging based on pulsed Airy beams.

In ultrasonic imaging, high impedance obstacles in tissues may lead to artifacts behind them, making the examination of the target area difficult. Acoustical Airy beams possess the characteristics of self-bending and self-healing within a specific range. They are limited-diffracting when generated from finite aperture sources and are expected to have great potential in medical imaging and therapy. In this paper, pulsed Airy (pAiry) beams are employed for ultrasonic imaging at megahertz frequency, and the protocol is demonstrated via both simulations and experiments. Firstly, the generation of pAiry beams using a linear array is simulated, and the pulsed beams inherit some characteristics of continuous wave Airy beams, such as propagating along curved paths and self-healing. In experiments where obstacles are present at the beam paths, the image quality in pAiry-based imaging is superior to that in classical iso-depth imaging. The results demonstrate the feasibility and benefits of ultrasonic imaging based on pAiry beams and provide an important basis for developing imaging techniques employing non-diffracting acoustic beams.

Reservoir water flooding evaluation based on electromagnetic wave logging permittivity and conductivity inversion

Electromagnetic wave logging at the measurement frequency of megahertz provides two kinds of information namely conductivity and permittivity, which is helpful to solve the problem of identifying water flooding situation of oil layers after long-term water displacement development. The electromagnetic wave combination logging tool in Daqing Oilfield measures two phase difference curves at frequencies of 60 MHz and 2 MHz. At present, there is still a lack of permittivity and conductivity inversion methods for this tool that are suitable for the interpretation of water flooding situation. Based on the magnetic dipole theory of uniform medium, the study found that for the combination logging tool, the 60 MHz phase difference is affected by both the permittivity and conductivity of the formation, while the 2 MHz phase difference is mainly affected by the conductivity. The reasonable and conveniently procedure for calculating the permittivity and conductivity from the inversion of the phase difference curves is constructed. Firstly, the shale content and porosity parameters of the layers are calculated from the curves of natural gamma and acoustic time difference, while the permittivity is calculated by a formula linearly constrained by shale content based on the permittivity of mudstone and oil-bearing clean sandstone. Secondly, for 2 MHz phase difference curve, a formula for calculating conductivity with known permittivity is established. Thirdly, set the calculated permittivity as the known parameter, a formula for inversion of the 2 MHz phase difference curve to calculate the conductivity is derived. Fourthly, using the inversion calculation of the conductivity as a known input, establish a formula for inversion of the 60 MHz phase difference curve to calculate the permittivity. In the process, the permittivity calculated by the shale content constraint method is used as the initial value of the iteration, which weakens the influence of mudstone on the permittivity and ensures the accuracy of the iteration. Finally, the permittivity and conductivity calculated by inverse calculation for two sealed coring wells can reflect the flooding situation of layers. The identification standard of flooding levels was established by using the conductivity and permittivity of inversion calculation, and the coincidence rate reached 90.7%, which is suitable for the effective identification of remaining oil in the long-term fresh water displacement layers. At the same time, based on the simplified theoretical model, the inversion of 3 combination of (2 MHz, 20 MHz), (60 MHz, 20 MHz), (2 MHz, 100 MHz) is carried out respectively, and the calculated values of remaining oil saturation are consistent with the injected water sweeping area, so the universality of the research method is verified.

Resonant driving scheme for p-doped gallium nitride high electron mobility transistor to reduce driving power loss

In high-frequency power electronics applications, gallium nitride high electron mobility transistors (GaN HEMTs) can switch at frequencies of several megahertz. In this case, the driving loss of transistors becomes one of the important reasons that affect the entire conversion efficiency of the system. p-doped GaN (p-GaN) as a new GaN HEMT structure has achieved commercial success in recent years, but due to its special structure, traditional resonant driving schemes designed for Si-MOSFETs have poor applicability to p-GaN HEMTs. Therefore, according to the structure characteristics and the driving requirements of p-GaN HEMTs, an improved resonant driving scheme is proposed. In the proposed driving scheme, the gate charge energy is recycled to the resonant capacitor when the p-GaN HEMT is turned off, and released when it is turned on, thus reducing the driving power loss. The working principle of the driving circuit and the design method of component parameters are given in this paper. The experimental results show that for high-frequency applications with switching frequencies exceeding several megahertz, the power loss of the proposed resonant driving scheme is significantly lower than that of non-resonant driving scheme, which verifies the effectiveness and feasibility of the proposed scheme.

Binary Volume Acoustic Holograms

In recent years, high-resolution additive manufacturing has enabled a diverse range of low-cost methods for ultrasonic wave-front shaping. Acoustic holograms, in particular, allow for the generation of arbitrary diffraction-limited acoustic fields at megahertz frequencies from single-element transducers. These are phase plates that function as direct acoustic analogs to thin optical holograms. In this work, it is shown that, by using multiple polymer three-dimensional (3D) printing, two-material (binary) acoustic analogs to ``thick'' or volume optical holograms can also be generated. First, an analytic approach for designing a volume hologram that diffracts a set of input fields onto a desired set of output fields is briefly summarized. Next, a greedy-optimization approach based on random downhill binary search able to account for the constraints imposed by the chosen fabrication method is introduced. Finally, an experimental test case designed to diffract the field generated by a 2.54-cm planar lead zirconate titanate (PZT) transducer onto eight distinct patterns dependent on the direction of the incident field is used to validate the approach and the design method. Field scans of the eight target fields demonstrate that acoustic analogs of optical volume holograms can be generated using multipolymer printing and that these allow the multiplexing of distinct fields onto different incident field directions.

A Comprehensive Review on Wireless Power Transfer Systems for Charging Portable Electronics

Wireless power transfer (WPT) for portable electronic applications has been gaining a lot of interest over the past few decades. This study provides a comprehensive review of the recent advancements in WPT technology, along with the challenges faced in its practical implementation. The modeling and design of WPT systems, including the effect of cross-coupling in multiple receivers, have been discussed and the techniques for efficiency improvement have been highlighted. The challenges of coil design, EMI shielding, and foreign object detection have been pointed out and various cutting-edge solutions have been presented. With improvements in wide bandgap technology, there is a push to operate WPT systems at mega-hertz frequencies. The reason for this is twofold: the miniaturization of the system and the ability to achieve a better magnetic link efficiency. However, with higher frequency comes the challenge of operating the power electronic components efficiently by using soft-switching techniques. Hence, an in-depth discussion on soft-switched topologies such as the Class D and Class E converters and their variations has been provided. Finally, the effects of magnetic field exposure on humans along with safety standards have been discussed.

A PVDF Receiver for Acoustic Monitoring of Microbubble-Mediated Ultrasound Brain Therapy.

The real-time monitoring of spectral characteristics of microbubble (MB) acoustic emissions permits the prediction of increases in blood-brain barrier (BBB) permeability and of tissue damage in MB-mediated focused ultrasound (FUS) brain therapy. Single-element passive cavitation detectors provide limited spatial information regarding MB activity, greatly affecting the performance of acoustic control. However, an array of receivers can be used to spatially map cavitation events and thus improve treatment control. The spectral content of the acoustic emissions provides additional information that can be correlated with the bio-effects, and wideband receivers can thus provide the most complete spectral information. Here, we develop a miniature polyvinylidene fluoride (PVDF thickness = 110 μm, active area = 1.2 mm2) broadband receiver for the acoustic monitoring of MBs. The receiver has superior sensitivity (2.36-3.87 V/MPa) to those of a commercial fibre-optic hydrophone in the low megahertz frequency range (0.51-5.4 MHz). The receiver also has a wide -6 dB acceptance angle (54 degrees at 1.1 MHz and 13 degrees at 5.4 MHz) and the ability to detect subharmonic and higher harmonic MB emissions in phantoms. The overall acoustic performance of this low-cost receiver indicates its suitability for the eventual use within an array for MB monitoring and mapping in preclinical studies.

Enhanced Power Conversion Capability of Class-E Power Amplifiers With GaN HEMT Based on Cross-Quadrant Operation

Class-E power amplifiers are widely used in megahertz frequency power conversion systems due to their high efficiency, which can further be enhanced by virtue of wide-bandgap devices such as GaN high-electron-mobility transistors. Here, a GaN-based cross-quadrant mode Class-E amplifier is proposed, which addresses one of the major challenges for such amplifiers, i.e., to achieve both high power and high efficiency with low-voltage-rating devices. By utilizing the reverse conduction of GaN transistors, a cross-quadrant mode Class-E amplifier with small dc-feed inductance is constructed, whose circuit model is derived by virtue of the Laplace transform technique. We demonstrate an experimental prototype operating at 3.11 MHz with a 100-V GaN transistor, achieving an output power of about 6 W with the efficiency being almost 90% when the input voltage is 10 V and the load resistance is 28 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathrm{\Omega }$</tex-math></inline-formula> . Compared with conventional Class-E amplifiers, the power conversion capability of the proposed amplifier is increased up to three times from 0.49 to 1.69 with a slight reduction in efficiency. Such cross-quadrant mode amplifiers can be used to improve the power conversion capability and to reduce the peak switch voltage at the same output power level.