Wide Range Of Resonant Frequencies Research Articles

Adiabatic leaky integrate and fire neurons with refractory period for ultra low energy neuromorphic computing

In recent years, the in-memory-computing in charge domain has gained significant interest as a promising solution to further enhance the energy efficiency of neuromorphic hardware. In this work, we explore the synergy between the brain-inspired computation and the adiabatic paradigm by presenting an adiabatic Leaky Integrate-and-Fire neuron in 180 nm CMOS technology, that is able to emulate the most important primitives for a valuable neuromorphic computation, such as the accumulation of the incoming input spikes, an exponential leakage of the membrane potential and a tunable refractory period. Differently from previous contributions in the literature, our design can exploit both the charging and recovery phases of the adiabatic operation to ensure a seamless and continuous computation, all the while exchanging energy with the power supply with an efficiency higher than 90% over a wide range of resonance frequencies, and even surpassing 99% for the lowest frequencies. Our simulations unveil a minimum energy per synaptic operation of 470 fJ at a 500 kHz resonance frequency, which yields a 9x energy saving with respect to a non-adiabatic operation.

A Unified Active Damping for Grid and Converter Current Feedback in Active Front End Converters

The Active Front End (AFE) is interconnected to the grid with an LCL filter to reduce the switching harmonics. Possible resonances induced by the LCL filter can be damped using Active Damping (AD). In AFE applications, the current sensor can be placed on either the grid-side or the converter-side, resulting in different frequency responses. This paper presents a novel active damping approach that is universally applicable to all active front end converters regardless of whether the current sensor is placed on the grid side or the converter side. At the heart of the proposed approach is a practically implementable fourth-order filter that dampens the resonance whilst being capable of mitigating the challenges associated with both grid current feedback and converter current feedback. These include amplifications associated with derivatives in active damping term with grid current feedback and high susceptibility to instability with converter current feedback due to digital delay. The proposed active damping is thoroughly investigated in terms of practical implementation issues such as different LCL filter parameters, different sampling methods, grid impedance, and digital delay. The approach is experimentally validated on motor drives consisting of 2 two-level three-phase converters interfaced with a dSPACE rapid control prototyping system across a wide range of resonant frequencies and PWM sampling methods. Stability analysis is performed on both current control methods to validate that active damping assures stable operation for a wide range of resonant frequencies and grid impedance.

High-resolution measurement of atomic force microscope cantilever resonance frequency

The atomic force microscope (AFM) is widely used in a wide range of applications due to its high scanning resolution and diverse scanning modes. In many applications, there is a need for accurate and precise measurement of the vibrational resonance frequency of a cantilever. These frequency shifts can be related to changes in mass of the cantilever arising from, e.g., loss of fluid due to a nanolithography operation. A common method of measuring resonance frequency examines the power spectral density of the free random motion of the cantilever, commonly known as a thermal. While the thermal is capable of reasonable measurement resolution and speed, some applications are sensitive to changes in the resonance frequency of the cantilever, which are small, rapid, or both, and the performance of the thermal does not offer sufficient resolution in frequency or in time. In this work, we describe a method based on a narrow-range frequency sweep to measure the resonance frequency of a vibrational mode of an AFM cantilever and demonstrate it by monitoring the evaporation of glycerol from a cantilever. It can be seamlessly integrated into many commercial AFMs without additional hardware modifications and adapts to cantilevers with a wide range of resonance frequencies. Furthermore, this method can rapidly detect small changes in resonance frequency (with our experiments showing a resolution of ∼0.1 Hz for cantilever resonances ranging from 70 kHz to 300 kHz) at a rate far faster than with a thermal. These attributes are particularly beneficial for techniques such as dip-pen nanolithography.

Tunable, multi-modal, and multi-directional vibration energy harvester based on three-dimensional architected metastructures

Conventional vibration energy harvesters based on two-dimensional planar layouts have limited harvesting capacities due to narrow frequency bandwidth and because their vibratory motion is mainly restricted to one plane. Three-dimensional architected structures and advanced materials with multifunctional properties are being developed in a broad range of technological fields. Structural topologies exploiting compressive buckling deformation mechanisms however provide a versatile route to transform planar structures into sophisticated three-dimensional architectures and functional devices. Designed geometries and Kirigami cut patterns defined on planar precursors contribute to the controlled formation of diverse three-dimensional forms. In this work, we propose an energy harvesting system with tunable dynamic properties, where piezoelectric materials are integrated and strategically designed into three-dimensional compliant architected metastructures. This concept enables energy scavenging from vibrations not only in multiple directions but also across a broad frequency bandwidth, thus increasing the energy harvesting efficiency. The proposed system comprises a buckled ribbon with optional Kirigami cuts. This platform enables the induction of vibration modes across a wide range of resonance frequencies and in arbitrary directions, mechanically coupling with four cantilever piezoelectric beams to capture vibrations. The multi-modal and multi-directional harvesting performance of the proposed configurations has been demonstrated in comparison with planar systems. The results suggest this is a facile strategy for the realization of compliant and high-performance energy harvesting and advanced electronics systems based on mechanically assembled platforms.

Passive wideband concentric rings resonator for vocal cords abnormalities detection: Application on larynx cancer pathologies.

This work addresses the study and design of a diagnostic device consisting of a thin-film sensor array based on 8-mm concentered rings, acting as an autonomous acoustic sensor covering a wide range of resonance frequencies (0.1 KHz-2 MHz). In addition to its advantageous shape, this device integrates both the active vibratory element and the embedded electronics dedicated to coding, control, and analysis. The results show that the experimental device could be the basis of a telemedical platform for the objective assessment and monitoring of chronic laryngeal dysphonia through the spectro-temporal analysis of the vibration of the vocal cords. Furthermore, this non-invasive, non-intrusive protocol does not require the physical cooperation of the patient.

Multi-Tuned Radiofrequency Coil Using Microfluidically Tunable Capacitor for Magnetic Resonance Imaging/Spectroscopy at 7-Tesla

Multi-nuclear magnetic resonance imaging and spectroscopy are considered valuable tools due to their capability of diagnosis and monitoring of several diseases. They require multi-nuclear Radiofrequency coils in order to interrogate the proton (1H) and other nuclei (X-nuclei) in the human body. Such coils provide anatomical images by acquiring (1H) spectra and metabolites information by acquiring spectra of X-nuclei. In addition, the high signal received from proton (1H) is used for B0 shimming purposes. However, the signal strength for these X-nuclei is too low. Hence, the signal-to-noise-ratio is low. The main advantages of using multinuclear Radiofrequency coils are that they speed up the imaging process and reduce the spatial positioning error that might arise when replacing the Radiofrequency coil in order to perform imaging of different nuclei. In addition, comfortable environment will be provided for patients by avoiding any inconvenience of moving out and asking to replace the coils. In this paper, a multi-tunable microstrip transmission line Radiofrequency coil has been designed by using microfluidically tunable Radiofrequency capacitor. This capacitor offers a wide range of capacitance tuning which extends between Cmin=1.76 pF and Cmax=48.7 pF. Hence, a wide range of resonant frequencies (fmin=75 MHz - fmax=298 MHz) can be offered by this coil in order to excite several nuclei at a field strength of 7-Tesla.

A Design of Wide-range Frequency-tracking Ultrasonic Power Supply

Aiming at the problem that the frequency tracking range of commercial ultrasonic power supply on the market is narrow, which makes the load of ultrasonic power supply, a structure of transducer-horn-tool, difficult to match. This paper presents a kind of ultrasonic power supply based on TMS320F28335, which can track the frequency in a wide range(15-21kHz). The advantages, theory, software and hardware structure of the power supply are introduced, which can realize the functions of wide range frequency tracking, power regulation, human-computer interaction and so on. Experiments show that the power supply can well match the ultrasonic vibration load with a wide range of resonant frequencies, and has good human-computer interaction function.

Creating localized plasma waves by ionization of doped semiconductors.

Localized plasma waves can be generated by suddenly ionizing extrinsic semiconductors with spatially periodic dopant densities. The built-in electrostatic potentials at the metallurgical junctions, combined with electron density ripples, offer the exact initial condition for exciting long-lasting plasma waves upon ionization. This method can create plasma waves with a frequency between a few terahertz to subpetahertz without substantial damping. The lingering plasma waves can seed backward Raman amplification in a wide range of resonance frequencies up to the extreme ultraviolet regime. Chirped wave vectors and curved wave fronts allow focusing the amplified beam in both longitudinal and transverse dimensions. The main limitation to this method appears to be obtaining sufficiently low plasma density from solid-state materials to avoid collisional damping.

A Two State Feedback Active Damping Strategy for the LCL Filter Resonance in Grid-Connected Converters

A novel active damping strategy for the LCL filter resonance is proposed using the grid current and the capacitor voltage. The proposed technique is deduced in the continuous time domain and a discussion for its discrete implementation is presented. According to the proposed technique, instability of the open loop system, which results in non-minimum phase behavior, can be avoided over wide range of resonant frequencies. Moreover, straightforward co-design steps for both the fundamental current regulator and the active damping loops can be used. A numerical example along with experimental results are introduced to validate the proposed strategy performance over wide range of resonant frequencies.

Experimental Investigation of the Cross-Sensitivity and Size Effects of Polyvinylidene Fluoride Film Sensors on Modal Testing

Due to advantages such as light weight, flexibility, and low cost, polyvinylidene fluoride (PVDF) films have been widely used in engineering applications as sensors for detecting strain, pressure, or micro-force. However, it is known that PVDF strain sensors have strain cross-sensitivity in mutually orthogonal directions. Furthermore, the size of the PVDF film sensor would also affect the dynamic strain sensing performance. In this paper, to investigate the cross-sensitivity and size effects experimentally, we employ PVDF film sensors to perform dynamic measurements on a cantilever beam. Since the vibrations of the cantilever beam are excited by impacts of a steel ball, the induced highly repeatable transient responses contain a wide range of resonant frequencies and thus can be used to investigate both the size and cross-sensitivity effects of the PVDF film sensors in a dynamic sensing environment. Based on the experimental results of the identified resonant frequencies compared with results obtained from a strain gauge, finite element calculations, and theoretical predictions, suggestions for the use of the PVDF strain sensor in modal testing are given in this paper.

Adaptive control of force microscope cantilever dynamics

Magnetic resonance force microscopy (MRFM) and other emerging scanning probe microscopies entail the detection of attonewton-scale forces. Requisite force sensitivities are achieved through the use of soft force microscope cantilevers as high resonant-Q micromechanical oscillators. In practice, the dynamics of these oscillators are greatly improved by the application of force feedback control computed in real time by a digital signal processor (DSP). Improvements include increased sensitive bandwidth, reduced oscillator ring up/down time, and reduced cantilever thermal vibration amplitude. However, when the cantilever tip and the sample are in close proximity, electrostatic and Casimir tip-sample force gradients can significantly alter the cantilever resonance frequency, foiling fixed-gain narrow-band control schemes. We report an improved, adaptive control algorithm that uses a Hilbert transform technique to continuously measure the vibration frequency of the thermally-excited cantilever and seamlessly adjust the DSP program coefficients. The closed-loop vibration amplitude is typically 0.05 nm. This adaptive algorithm enables narrow-band formally-optimal control over a wide range of resonance frequencies, and preserves the thermally-limited signal to noise ratio (SNR).

Nonlinear precession of magnetization in a ferrite-garnet film of the (100) type

The dynamics of stationary resonance precession during perpendicular biasing of a ferrite-garnet film of the (100) type in a wide range of resonance frequencies and amplitudes of an alternating field is studied on the basis of numerical solution of the magnetization motion equations. The influence of the crystallographic and growth anisotropy on the trajectories of precession motion is studied. A new type of symmetric precession trajectories is found and the states of dynamic bistability are revealed.

Adsorbate aggregation and relaxation of low-frequency vibrations

We present a study of resonant vibrational coupling between adsorbates and an elastic substrate at low macroscopic coverages. In the first part of the paper we consider the situation in which adsorbates form aggregates with high local coverage. Based upon our previously published theory, we derive formulas describing the damping rate of adsorbate vibrations for two cases of such aggregation: (i) adsorbates attached to step edges and (ii) adsorbates forming two-dimensional islands. We have shown that damping is governed by local coverage. Particularly, for a wide range of resonant frequencies, the damping rate of adsorbates forming well-separated islands is described by the damping rate formula for a periodic overlayer with the coverage equal to the local coverage in the island. The second part of the paper is devoted to facilitating the evaluation of damping rates for a disordered overlayer. The formula describing the damping rate involves the parameter β, which is related to the local density of phonon states at the substrate surface and does not allow a closed-form representation. For substrates of isotropic and cubic symmetries, we have developed a good analytical approximation to this parameter. For a vast majority of cubic substrates the difference between the analytical approximation and numerical calculation does not exceed 4%.

Hydrogen in the A15 compounds Nb 3Sn and Nb 3Al: a nuclear magnetic resonance study

Nuclear magnetic resonance measurements of the 119Sn, 27Al Knight shifts and the 119Sn, 27Al and 1H spin-lattice relaxation rates in the A15-type compounds Nb 3SnH x (D x ) ( x = 0, 0.7 and 1.2) and Nb 3AlH x ( x = 0, 2.3) have been performed over the temperature range 10–460 K. The low temperature 119Sn Knight shift and spin-lattice relaxation data indicate that indicate that in Nb 3SnH x (D x ) the density of electron states at the Fermi level decreases strongly with increasing x. The hydrogen mobility in Nb 3Al is found to be much higher than that in Nb 3Sn. The behaviour of the proton spin-lattice relaxation rate for NB 3AlH 2.3 in a wide range of resonance frequencies (9–90 MHz) can be described by the model using a double-peak distribution of activation energies.

RF ion linacs for applied research and industrial applications

The development of the radio-frequency quadrupole (RFQ) structure has made rf ion linacs practical for applications in research and industry requiring energetic ions. Since the RFQ can be designed to operate over a wide range of resonant frequencies, it can be used for a variety of accelerated ions, beam currents and output energies. This compact accelerator is simple to operate and can be used alone or with other structures to achieve even higher energy or lower momentum spread in the ion beam than is available from the RFQ alone. The inherent flexibility of the RFQ, together with its present commercial development worldwide, has resulted in its increased use for applications such as high energy ion implantation, isotope production, and neutron and gamma production for nondestructive examination and testing of materials. Potential applications that have been proposed for rf ion linacs include accelerator mass spectrometry, changed particle activation and heavy ion backscattering spectrometry. This paper will discuss these applications and describe several representative rf ion linac systems.

Pulse shaping to improve performance of NMR multiple-pulse sequences: 2-D solvent-suppressed cosy of vitamin B 1 in water

Grafted “narrow reject” pulse shapes, whicch were shown previously to be capable of uniformly exciting a wide range of resonance frequencies with a sharp null directly on resonance for solvent suppression, are combined to generate multiple-pulse sequences. In particular, we show that two-dimensional solvent-suppressed spectra can be obtained with such pulses. This is the first application of pulse Grafting to high-resolution, multiple-pulse NMR spectroscopy.

Transition metal NMR spectroscopy - a probe into organometallic structure and catalysis

Abstract

Variable frequency heavy-ion linac, RILAC: I. Design, construction and operation of its accelerating structure

A variable frequency linear accelerator at RIKEN (IPCR), which is named RILAC, is designed to accelerate ions of almost every element in the periodic table. In this report, the design, construction and performance of the resonator cavities of this linac are described. A new accelerating structure was developed for the variable frequency scheme. The principal aim of the development was to obtain a configuration within the cavity to keep a uniform voltage distribution along the accelerating axis over the wide range of resonant frequencies required. The final form adopted is a coaxial quarter-wave type resonator with a race-track-like cross section for its coaxial inner and outer conductors. It has a movable shorting device as a frequency tuner and its open end is enlarged and loaded with drift tubes, connected to the inner and outer conductors alternatingly. The structure can maintain the required uniformity of the accelerating voltage within 10% in spite of resonant frequency tuning between 17 and 45 MHz. A relatively modest accelerating gradient was chosen so that cw operation could be realized. The RILAC is composed of six such cavities which are independently excited and it succeeded in the acceleration of a beam through all the cavities in 1981.

Variable pulse width piezoelectric ultrasonic transducer driver

Requirements of ceramic piezoelectric ultrasonic transducer drive circuits are discussed in the light of today's advanced non-destructive testing techniques. A new drive circuit based upon power MOSFET devices, which overcomes many of the shortcomings of capacitor discharge circuits, is described. This driving technique enables transducers of a wide range of resonant frequencies to be driven from a single drive unit. It also enables transducer characteristics to be optimized for particular applications by control of the drive pulse shape.