Showing papers on "Fundamental frequency published in 2012"

Steady-State Analysis of Interaction Between Harmonic Components of Arm and Line Quantities of Modular Multilevel Converters

Abstract: The fundamental frequency component in the arm currents of a modular multilevel converter is a necessity for the operation of the converter, as is the connection and bypassing of the submodules. Inevitably, this will cause alternating components in the capacitor voltages. This paper investigates how the arm currents and capacitor voltages interact when the submodules are connected and bypassed in a sinusoidal manner. Equations that describe the circulating current that is caused by the variations in the total inserted voltage are derived. Resonant frequencies are identified and the resonant behaviour is verified by experimental results. It is also found that the effective values of the arm resistance and submodule capacitances can be extracted from the measurements by least square fitting of the analytical expressions to the measured values. Finally, the analytical expression for the arm currents is verified by experimental results.

Joint DOA and multi-pitch estimation based on subspace techniques

Abstract: In this article, we present a novel method for high-resolution joint direction-of-arrivals (DOA) and multi-pitch estimation based on subspaces decomposed from a spatio-temporal data model. The resulting estimator is termed multi-channel harmonic MUSIC (MC-HMUSIC). It is capable of resolving sources under adverse conditions, unlike traditional methods, for example when multiple sources are impinging on the array from approximately the same angle or similar pitches. The effectiveness of the method is demonstrated on a simulated an-echoic array recordings with source signals from real recorded speech and clarinet. Furthermore, statistical evaluation with synthetic signals shows the increased robustness in DOA and fundamental frequency estimation, as compared with to a state-of-the-art reference method.

An Adaptive Synchronous-Reference-Frame Phase-Locked Loop for Power Quality Improvement in a Polluted Utility Grid

Abstract: The proper operation of grid-connected power electronics converters needs using a synchronization technique to estimate the phase of the grid voltage. The performance of this synchronization technique is related to the quality of the consumed or delivered electric power. The synchronous-reference-frame phase-locked loop (SRF-PLL) has been widely used due to its ease of operation and robust behavior. However, the estimated phase can have a considerable amount of unwanted ripple if the grid voltage disturbances are not properly rejected. The aim of this paper is to propose an adaptive SRF-PLL which strongly rejects these disturbances even if the fundamental frequency of the grid voltage varies. This is accomplished by using several adaptive infinite-impulse-response notch filters, implemented by means of an inherently stable Schur-lattice structure. This structure is perfectly suited to be programmed in fixed-point DSPs (i.e., it has high mapping precision, low roundoff accumulation, and suppression of quantization limit cycle oscillations). The proposed adaptive SRF-PLL has been tested by means of the TI TMS320F2812 DSP. The obtained experimental results show that the proposed synchronization method highly rejects the undesired harmonics even if the fundamental harmonic frequency of a highly polluted grid voltage abruptly varies.

A 0.28 THz Power-Generation and Beam-Steering Array in CMOS Based on Distributed Active Radiators

Abstract: In this paper, we present a scalable transmitter architecture for power generation and beam-steering at THz frequencies using a centralized frequency reference, sub-harmonic signal distribution, and local phase control. The power generation and radiator core is based on a novel method called distributed active radiation, which enables high conversion efficiency from DC to radiated terahertz power above fmax of a technology. The design evolution of the distributed active radiator (DAR) follows from an inverse design approach, where metal surface currents at different harmonics are formulated in the silicon chip for the desired electromagnetic field profiles. Circuits and passives are then designed conjointly to synthesize and control the surface currents. The DAR consists of a self-oscillating active electromagnetic structure, comprising of two loops which sustain out-of-phase currents at the fundamental frequency and in-phase currents at the second harmonic. The fundamental signal, thus gets, spatially filtered, while the second harmonic is radiated selectively, thereby consolidating signal generation, frequency multiplication, radiation of desired harmonic and filtration of undesired harmonics simultaneously in a small silicon footprint. A two-dimensional 4×4 radiating array implemented in 45 nm SOI CMOS (without high-resistivity substrate) radiates with an EIRP of +9.4 dBm at 0.28 THz and beam-steers in 2D over 80° in both azimuth and elevation. The chip occupies 2.7 mm × 2.7 mm and dissipates 820 mW of DC power. To the best of the authors' knowledge, this is the first reported integrated beam-scanning array at THz frequencies in silicon.

Widely Linear Adaptive Frequency Estimation of Unbalanced Three-Phase Power Systems

Abstract: A novel technique for online estimation of the fundamental frequency of unbalanced three-phase power systems is proposed. Based on Clarke's transformation and widely linear complex domain modeling, the proposed method makes use of the full second-order information within three-phase signals, thus promising enhanced and robust frequency estimation. The structure, mathematical formulation, and theoretical stability and statistical performance analysis of the proposed technique illustrate that, in contrast to conventional linear adaptive estimators, the proposed method is well matched to unbalanced system conditions and also provides unbiased frequency estimation. The proposed method is also less sensitive to the variations of the three-phase voltage amplitudes over time and in the presence of higher order harmonics. Simulations on both synthetic and real-world unbalanced power systems support the analysis.

Energy harvesting in the super-harmonic frequency region of a twin-well oscillator

Abstract: Nonlinear dynamical systems exhibit super-harmonic resonances that can activate large-amplitude motions at fraction integers of the fundamental frequency of the system. Such resonances offer a unique and untapped opportunity for harnessing vibratory energy from excitation sources with low-frequency components. To that end, this paper exploits the super-harmonic frequency bands of a nonlinear twin-well (bi-stable) oscillator for harvesting energy from low-frequency excitations. Theoretical and experimental studies are performed on an axially loaded clamped-clamped piezoelectric beam harvester with bi-stable potential characteristics. Voltage- and power-frequency bifurcation maps are generated near the super-harmonic resonance of order two. It is shown that, for certain base acceleration levels, the harvester can exhibit responses that are favorable for energy harvesting. These include a unique branch of large-orbit periodic inter-well oscillations, coexisting branches of large-orbit solutions, and a bandwidth of frequencies where a unique chaotic attractor exists. In these frequency regions, the harvester can produce power levels at half its fundamental frequency that are comparable to those obtained near the fundamental frequency.

Estimating Bridge Fundamental Frequency from Vibration Response of Instrumented Passing Vehicle: Analytical and Experimental Study

Abstract: Driving velocity, natural frequency of vehicle and natural frequency of bridge are the main contributing factors to vibration of a vehicle when passing a bridge By separating contributions of the first two factors, one can estimate the natural frequency of a bridge indirectly from vehicle acceleration response when it crosses a bridge In this paper, we apply this concept to estimate the bridge fundamental frequency indirectly using the response of a passing instrumented vehicle The paper first describes analytical formulation and finite element simulation to demonstrate the feasibility of the method Afterwards, it describes an experimental verification as a proof-of-concept of the method on a full-scale simply-supported short span bridge by using a light commercial vehicle instrumented with accelerometer Dynamic responses of the vehicle while passing the bridge are recorded and analyzed Spectra analysis of the vehicle responses reveal that the first natural frequency of the bridge can be estimated w

Digital Filters for Fast Harmonic Sequence Component Separation of Unbalanced and Distorted Three-Phase Signals

Abstract: In this paper, two methods for determining the fundamental frequency and harmonic positive- and negative-sequence components of three-phase signals are investigated. Many aspects of the space-vector discrete Fourier transform and generalized delayed signal cancellation (GDSC) such as response time for different possible implementations, frequency adaptation schemes, stability of recursive implementation, and rounding error effects are discussed. A new design procedure for GDSC transformations is presented. New indices for characterizing three-phase unbalanced and distorted signals are proposed. Simulations and experiments are included in order to verify the performances and illustrate the theoretical conclusions.

Frequency Adaptive PLL for Polluted Single-Phase Grids

Abstract: This paper proposes a frequency adaptive phase-locked loop (PLL) for use in single-phase systems. The main objective is to obtain a reliable synchronization signal even in polluted grids, where the fundamental frequency is contaminated with harmonics, or present variations in phase, amplitude, and/or frequency. The proposed PLL is based on the concept of a variable sampling period technique, already implemented in a three-phase digital synchronization method proposed by the authors. This single-phase method allows us to automatically adjust the sampling frequency to be an integer multiple of the line frequency. In this case, the phase error is calculated just by one multiplication, thereby reducing implementation. A sliding Goertzel transform-based filter is also used in the loop to reject the undesired effects of this phase error detector and line disturbances, such as harmonics. To stabilize the loop, a controller that maximizes the bandwidth with an acceptable transient is introduced. The characteristics of the proposed single-phase PLL are described and the experimental results obtained from a DSP implementation are presented. A set of comparative simulations between the proposed PLL and some single-phase PLL described in the literature are conducted to validate the method. The advantages of the proposed system over other methods analyzed are also dealt with. The robustness of the system is verified by the experimental tests conducted as well as by the harmonic filtering properties. The system is also characterized by its simple architecture, which allows us to provide a high dynamic response with a very much reduced number of calculations.

Goertzel algorithm generalized to non-integer multiples of fundamental frequency

Abstract: The article deals with the Goertzel algorithm, used to establish the modulus and phase of harmonic components of a signal. The advantages of the Goertzel approach over the DFT and the FFT in cases of a few harmonics of interest are highlighted, with the article providing deeper and more accurate analysis than can be found in the literature, including the memory complexity. But the main emphasis is placed on the generalization of the Goertzel algorithm, which allows us to use it also for frequencies which are not integer multiples of the fundamental frequency. Such an algorithm is derived at the cost of negligibly increasing the computational and memory complexity.

Frequency Adaptive Least-Squares-Kalman Technique for Real-Time Voltage Envelope and Flicker Estimation

Abstract: This paper presents real-time implementation of a new frequency adaptive least-squares-Kalman (LSK) technique to monitor voltage flicker and fluctuations in power system. The proposed method is based on a two-level mathematical model of a voltage waveform. A simple low computation frequency tracking method is also introduced. The least-squares (LS) optimization algorithm extracts the fundamental frequency component of the voltage and updates its internal model based on the estimated frequency of the voltage waveform. The Kalman filter, which works in combination with the LS algorithm, is developed to predict the instantaneous voltage flicker level. The proposed method is robust and adaptive and is evaluated experimentally through real-time implementation with a widely available digital control board.

Harmonic lasing in x-ray free electron lasers

Abstract: Harmonic lasing in a free electron laser with a planar undulator (under the condition that the fundamental frequency is suppressed) might be a cheap and efficient way of extension of wavelength ranges of existing and planned x-ray free electron laser (FEL) facilities. Contrary to nonlinear harmonic generation, harmonic lasing can provide much more intense, stable, and narrow-band FEL beam which is easier to handle due to the suppressed fundamental frequency. In this paper we perform a parametrization of the solution of the eigenvalue equation for lasing at odd harmonics, and present an explicit expression for FEL gain length, taking into account all essential effects. We propose and discuss methods for suppression of the fundamental harmonic. We also suggest a combined use of harmonic lasing and lasing at the retuned fundamental wavelength in order to reduce bandwidth and to increase brilliance of x-ray beam at saturation. Considering 3rd harmonic lasing as a practical example, we come to the conclusion that it is much more robust than usually thought, and can be widely used in the existing or planned x-ray FEL (XFEL) facilities. In particular, Linac Coherent Light Source (LCLS) after a minor modification can lase to saturation at the 3rd harmonic up to the photon energy of 25--30 keV providing multigigawatt power level and narrow bandwidth. As for the European XFEL, harmonic lasing would allow one to extend operating range (ultimately up to 100 keV), to reduce FEL bandwidth and to increase brilliance, to enable two-color operation for pump-probe experiments, and to provide more flexible operation at different electron energies. Similar improvements can be realized in other x-ray FEL facilities with gap-tunable undulators like FLASH II, SACLA, LCLS II, etc. Harmonic lasing can be an attractive option for compact x-ray FELs (driven by electron beams with a relatively low energy), allowing the use of the standard undulator technology instead of small-gap in-vacuum devices. Finally, in this paper we discover that in a part of the parameter space, corresponding to the operating range of soft x-ray beam lines of x-ray FEL facilities (like SASE3 beam line of the European XFEL), harmonics can grow faster than the fundamental wavelength. This feature can be used in some experiments, but might also be an unwanted phenomenon, and we discuss possible measures to diminish it.

Probing colloid-substratum contact stiffness by acoustic sensing in a liquid phase.

Abstract: In a quartz crystal microbalance, particles adhering to a sensor crystal are perturbed around their equilibrium positions via thickness-shear vibrations at the crystal’s fundamental frequency and overtones. The amount of adsorbed molecular mass is measured as a shift in resonance frequency. In inertial loading, frequency shifts are negative and proportional to the adsorbed mass, in contrast with “elastic loading”, where particles adhere via small contact points. Elastic loading in air yields positive frequency shifts according to a coupled resonance model. We explore here the novel application of a coupled resonance model for colloidal particle adhesion in a liquid phase theoretically and demonstrate its applicability experimentally. Particles with different radii and in the absence and presence of ligand–receptor binding showed evidence of coupled resonance. By plotting the frequency shifts versus the quartz crystal microbalance with dissipation overtone number, frequencies of zero-crossing could be infe...

Frequency comb generation at terahertz frequencies by coherent phonon excitation in silicon

Abstract: By exciting few-cycle femtosecond laser pulses at 397 nm in near-resonance with the direct bandgap of silicon, researchers experimentally demonstrate coherent phonon generation in silicon at a fundamental frequency of 15.6 THz and all-optical >100 THz frequency comb generation.

Free vibration analysis of sandwich plates with functionally graded face sheets and temperature-dependent material properties: A new approach

Abstract: Improved high-order sandwich plate theory is used to analyze the free vibration of sandwich plates with functionally graded (FG) face sheets in various thermal environments. The material properties of FG face sheets are assumed to be temperature-dependent by a third-order function of temperature and vary continuously through the thickness according to a power-law distribution in terms of the volume fractions of the constituents. Also, the material properties of the core are assumed to be temperature-dependent by a third-order function of temperature. The governing equations of motion in free natural vibration are derived using Hamilton's principle. A new approach is used to reduce the equations of motion and then solved them for both un-symmetric and symmetric sandwich plates. In-plane stresses of the core that usually are ignored in the vibration characteristics of the sandwich structures are considered in this formulation. The results show that the fundamental frequency parameter increases and decreases with increasing the volume fraction index for soft core and hard core sandwich plates, respectively. The results indicate that as the side-to-thickness ratio, the core-to-face sheet thickness ratio and the temperature are changed, a significant effect on the fundamental frequency parameter is observed. Good agreement is found between the theoretical predictions of the fundamental frequency parameters and the results obtained from other references for simply supported sandwich plates with functionally graded face sheets in the literature.

A Current-Source-Converter-Based High-Power High-Speed PMSM Drive With 420-Hz Switching Frequency

Abstract: In this paper, a current-source-converter (CSC)-based high-power high-speed (HPHS) permanent-magnet synchronous motor drive is proposed for high-speed compressor applications. The most important feature of the proposed CSC-fed HPHS drive is that the switching frequency is limited to 420 Hz at 200-Hz fundamental frequency. In the drive system, the whole operation range is divided into three regions, namely, the high-, medium-, and low-speed regions, where different modulation strategies and control schemes are used with the requirement of switching frequency and output filter. In particular, a two-pulse space vector modulation with dynamic capacitor voltage control is proposed for the high-speed region to achieve better dynamic and harmonic performance. Both simulation and experiments verify the proposed control strategy.

Nonlocal Timoshenko beam theory for vibration of carbon nanotube-based biosensor

Abstract: This article studies vibration of carbon nanotube (CNT)-based biosensor A CNT-based biosensor is modeled as a nonlocal Timoshenko beam made of multiwall CNT carrying a spherical nanoscale bio-object at the free end, and the influence of the rotary inertia of the bio-object itself is considered The fundamental frequencies are computed via the transfer function method The effects of the attached spherical bio-object's rotary inertia and mass, the length-to-diameter of the CNT on the natural frequencies are discussed If the nonlocal parameter is neglected, the frequencies for four possible cases are compared Obtained results show that the rotary inertia decreases the fundamental frequency, while an increase in the diameter of the attached bio-object reduces the natural frequency, but causes frequency shift to rise The mass sensitivity of biosensor can be improved for short CNTs used The rotary inertia of the attached bio-object has a strong effect on the natural frequencies and cannot be simply neglected The nonlocal Timoshenko beam model is more adequate than the nonlocal Euler-Bernoulli beam model for short CNT biosensors Obtained results are helpful to the design of micro-cantilevered resonator as atomic-resolution mass sensor or biosensor

Accurate Measurement of Fault Currents Contaminated With Decaying DC Offset and CT Saturation

Abstract: Decaying dc offset and current-transformer (CT) saturation are the main obstacles to accurate measurement of the fundamental frequency component of fault currents. So far, most of the research works have focused exclusively on only one of these obstacles. However, very recently, research has been directed toward new current measurement algorithms which can deal with both of these issues simultaneously. Using least error squares technique and a simple offline lookup table, this paper introduces a novel method to filter out the decaying dc component and the effects of CT saturation. The proposed algorithm provides the fundamental sinusoidal component of current accurately. This method can respond using only five current samples. Meanwhile, the window size could also be increased to provide more immunity against noise and harmonics. High speed and accuracy, together with the simplicity and noise immunity of the proposed method, can make it a practical solution to address the decaying dc offset and CT saturation problems. Numerous simulated and real fault currents as well as real-time hardware implementation verify the effectiveness of the proposed algorithm.

Energy harvesting from a multifrequency response of a tuned bending-torsion system

Abstract: We investigate the benefits of tuning the frequencies of an energy harvester to extract more energy from a base excitation that comprises three frequency components. The energy harvester is composed of a unimorph cantilever beam with asymmetric tip masses. By adjusting the asymmetry of the tip masses, we can tune this beam–mass structure to harvest energy from multifrequency components of a base excitation. We model the beam using the Euler–Bernoulli beam theory and use the first three global mode shapes of the harvester in a Galerkin procedure to derive a reduced-order model describing its response. We derive an exact analytical solution for the tip deflection, twisting angle, voltage output, and harvested electrical power. Using this solution, we investigate the advantages of harvesting energy from a response that contains multifrequencies in comparison to a response that contains a single frequency by tuning only the fundamental frequency. The advantages of this bending–torsion energy harvester and the effect of its tuning are investigated for different short- and open-circuit configurations. The results show that, through a proper tuning of this bending–torsion harvester, the harvested power can be increased significantly and it can be made to cover a wide range of electrical load resistances.

The effect of the driving frequencies on the electrical asymmetry of dual-frequency capacitively coupled plasmas

Abstract: In capacitively coupled radio frequency discharges driven by two consecutive phase-locked harmonics, the electrical asymmetry effect (EAE) allows one to generate a dc self-bias as a function of the phase shift, θ, between the driving harmonics. If the two frequencies are chosen to be 13.56 and 27.12 MHz, the mean ion energy at both electrodes can be varied by a factor of about 2 by tuning θ at nearly constant ion flux. Until now the EAE has only been investigated in discharges operated at a fundamental frequency of f = 13.56 MHz. Here, we study the effect of changing this fundamental frequency on the performance of the EAE, i.e. on the electrical generation of a dc self-bias, the control range of the mean ion energy, and on the ion flux at both electrodes as a function of θ, by kinetic particle-in-cell/Monte Carlo simulations and theoretical modelling. We use argon gas and cover a wide range of fundamental frequencies (0.5 MHz ⩽ f ⩽ 60 MHz) and secondary electron yields. We find that the performance of the EAE is significantly worse at lower frequencies, i.e. the control range of the dc self-bias and, thus, the control range of the mean ion energy are strongly reduced. Based on the analytical model (i) the enhanced charged dynamics at lower frequencies and (ii) the transition of the electron heating mode induced by changing f are found to be the reasons for this effect.

Dual-Pitch Processing Mechanisms in Primate Auditory Cortex

Abstract: Pitch, our perception of how high or low a sound is on a musical scale, is a fundamental perceptual attribute of sounds and is important for both music and speech. After more than a century of research, the exact mechanisms used by the auditory system to extract pitch are still being debated. Theoretically, pitch can be computed using either spectral or temporal acoustic features of a sound. We have investigated how cues derived from the temporal envelope and spectrum of an acoustic signal are used for pitch extraction in the common marmoset (Callithrix jacchus), a vocal primate species, by measuring pitch discrimination behaviorally and examining pitch-selective neuronal responses in auditory cortex. We find that pitch is extracted by marmosets using temporal envelope cues for lower pitch sounds composed of higher-order harmonics, whereas spectral cues are used for higher pitch sounds with lower-order harmonics. Our data support dual-pitch processing mechanisms, originally proposed by psychophysicists based on human studies, whereby pitch is extracted using a combination of temporal envelope and spectral cues.

Harmonic reduction in capacitive micromachined ultrasonic transducers by gap feedback linearization

Abstract: The nonlinear relationship between the electrical input signal and electrostatic force acting on the capacitive micromachined ultrasonic transducer (CMUT) membrane limits its harmonic imaging performance. Several input shaping methods were proposed to compensate for the nonlinearity originating from the electrostatic force's dependence on the square of the applied voltage. Here, we analyze harmonic generation in CMUTs with a time-domain model. The model explains the basis of the input shaping methods and suggests that the nonlinearity resulting from gap dependence of the electrostatic force is also significant. It also suggests that the harmonic distortion in the output pressure can be eliminated by subharmonic ac-only excitation of the CMUT in addition to scaling the input voltage with the instantaneous gap. This gap feedback configuration can be approximated by the simple addition of a series impedance to the CMUT capacitance. We analyze several types of series impedance feedback topologies for gap feedback linearization. We show that for subharmonic ac excitation, although resistive and capacitive impedances result in a trade-off between input voltage and harmonic distortion for a desired pressure output, harmonic generation can be suppressed while increasing the Pa/V transmit sensitivity for proper series inductance and resistance feedback. We experimentally demonstrate the feedback method by reducing harmonic generation by 10 dB for the same output pressure at the fundamental frequency by using a simple series resistor feedback with a CMUT operating at a center frequency of 3 MHz. The proposed methods also allow for utilization of the full CMUT gap for transmit operation and, hence, should be useful in high-intensity ultrasonic applications in addition to harmonic imaging.

Stacking sequence optimization of composite plates for maximum fundamental frequency using particle swarm optimization algorithm

Abstract: The paper illustrates the application of the particle swarm optimization (PSO) algorithm to the lay-up design of symmetrically laminated composite plates for maximization of fundamental frequency. The design variables are the fiber orientation angles, edge conditions and plate length/width ratios. The formulation is based on the classical laminated plate theory (CLPT), and the method of analysis is the semi-analytical finite strip approach which has been developed on the basis of full energy methods. The performance of the PSO is also compared with the simple genetic algorithm and shows the good efficiency of the PSO algorithm. To check the validity, the obtained results are compared with those available in the literature and some other stacking sequences, wherever possible.

Harmonic Ultrasound Imaging of Nanosized Contrast Agents for Multimodal Molecular Diagnoses

Abstract: The aim of the present work was to demonstrate the possibility of selective detection of nanoparticle contrast agents (NPCAs) on diagnostic echographic images by exploiting the second harmonic component they introduce in the spectra of corresponding ultrasound signals, as a consequence of nonlinear distortion during ultrasound propagation. We employed silica nanospheres (SiNSs) of variable diameter (160 nm, 330 nm, and 660 nm) dispersed in different volume concentrations (range 0.07-0.8%) in agarose gel samples that were automatically scanned through a digital ecograph using narrow-band ultrasound pulses at 6.6 MHz and variable mechanical index (MI range 0.2-0.6). In the first part of the study, the intensity peaks of four different spectral components of the backscattered signal were considered: fundamental (detected in correspondence of the incident ultrasound frequency), subharmonic (detected at half of the fundamental frequency), ultra harmonic (detected at 1.5 times the fundamental frequency), and second harmonic (detected at twice the fundamental frequency). Subsequently, based on the experimental results of the first part of the study and on our recently reported findings, the focus was moved to a detailed comparison between subharmonic and second harmonic trend, which were determined as a function of nanoparticle composition, sample concentration, and MI. The experiments were also repeated on different agarose samples, containing SiNSs covered by an outer shell of smaller magnetic nanoparticles, made of either iron oxide (IO) or FePt-IO nanocrystals. Obtained results show that this new ultrasound-based method for NPCA imaging has a detection sensitivity similar to that of our previously introduced subharmonic-based technique in the presence of 330-nm SiNSs, but performs significantly better in the detection of both the types of “dual mode” NPCAs. The fact that the reported detection method was optimized for identification of 330-nm SiNSs (a sort of “ideal” size for the development of novel tumor-targeting NPCAs) and that the magnetically coated particles are detectable also through magnetic resonance imaging makes the presented second harmonic ultrasound method a valuable solution for the introduction of new protocols for multimodal molecular diagnoses employing only nonionizing radiations.

Sleep EEG alterations: effects of pulsed magnetic fields versus pulse-modulated radio frequency electromagnetic fields.

Abstract: Studies have repeatedly shown that electroencephalographic power during sleep is enhanced in the spindle frequency range following radio frequency electromagnetic field exposures pulse-modulated with fundamental frequency components of 2, 8, 14 or 217 Hz and combinations of these. However, signals used in previous studies also had significant harmonic components above 20 Hz. The current study aimed: (i) to determine if modulation components above 20 Hz, in combination with radio frequency, are necessary to alter the electroencephalogram; and (ii) to test the demodulation hypothesis, if the same effects occur after magnetic field exposure with the same pulse sequence used in the pulse-modulated radio frequency exposure. In a randomized double-blind crossover design, 25 young healthy men were exposed at weekly intervals to three different conditions for 30 min before sleep. Cognitive tasks were also performed during exposure. The conditions were a 2-Hz pulse-modulated radio frequency field, a 2-Hz pulsed magnetic field, and sham. Radio frequency exposure increased electroencephalogram power in the spindle frequency range. Furthermore, delta and theta activity (non-rapid eye movement sleep), and alpha and delta activity (rapid eye movement sleep) were affected following both exposure conditions. No effect on sleep architecture and no clear impact of exposure on cognition was observed. These results demonstrate that both pulse-modulated radio frequency and pulsed magnetic fields affect brain physiology, and the presence of significant frequency components above 20 Hz are not fundamental for these effects to occur. Because responses were not identical for all exposures, the study does not support the hypothesis that effects of radio frequency exposure are based on demodulation of the signal only.

Designing maximum power output into piezoelectric energy harvesters

Abstract: Energy harvesting from vibrational sources has been the focus of extensive research in the last decade, but fundamental questions remain concerning the design of these harvesters. We consider a piezoelectric bimorph energy harvester and seek to translate design requirements, such as mass and target natural frequency, into beam dimensions that maximize power output. Our method centers around optimizing the thickness of the piezoelectric layers of a beam relative to the total beam thickness, otherwise known as the thickness ratio. This method uses approximations for the fundamental frequency and mode shape. This allows for the development of algebraic expressions for the modal parameters required for the prediction of power output. The resulting expression for power is fully defined by the fixed system level requirements and the only unknown parameters, the piezoelectric thickness ratio and the damping ratio. We show in an example case that, for typical damping ratio values, the ideal thickness ratio is not significantly affected by changes in the damping ratio. As such, the method requires a simple sweep of the thickness ratio in order to determine the beam design which maximizes the power. We develop the design method for both systems where the piezoelectric material is continuous and where the thickness is selected from a discrete set of values. Because our method produces a single algebraic expression for the power, the resulting beam design can be developed extremely quickly from a set of design requirements, and thus does not require optimization algorithms. We also show that our design method achieves more power output and requires less piezoelectric material than an approach which maximizes the coupling coefficient.

Optimization of laminated composite plates for maximum fundamental frequency using Elitist-Genetic algorithm and finite strip method

Abstract: In the present paper, fundamental frequency optimization of symmetrically laminated composite plates is studied using the combination of Elitist-Genetic algorithm (E-GA) and finite strip method (FSM). The design variables are the number of layers, the fiber orientation angles, edge conditions and plate length/width ratios. The classical laminated plate theory is used to calculate the natural frequencies and the fitness function is computed with a semi-analytical finite strip method which has been developed on the basis of full energy methods. To improve the speed of the optimization process, the elitist strategy is used in the Genetic algorithm. The performance of the E-GA is also compared with the simple genetic algorithm and shows the good efficiency of the E-GA algorithm. A multi-objective optimization strategy for optimal stacking sequence of laminated box structure is also presented, with respect to the first natural frequency and critical buckling load, using the weighted summation method to demonstrate the effectiveness of the E-GA. Results are corroborated by comparing with other optimum solutions available in the literature, wherever possible.

CMOS THz Generator With Frequency Selective Negative Resistance Tank

Abstract: This paper reports a CMOS terahertz oscillator with a novel frequency selective negative resistance (FSNR) tank to boost its operating frequency. The demonstrated oscillator can operate at a fundamental frequency of about 0.22 THz, exceeding the CMOS device cutoff frequency of fT. The proposed architecture suppresses undesired 2nd and odd harmonics and boosts the fourth-order harmonic (0.87 THz), which radiates through an on-chip patch antenna. The THz oscillator's output spectrum is profiled by using a Michelson interferometer. The oscillator circuit consumes 12 mA from a 1.4 V supply and occupies a 0.045 mm2 die area in a 65 nm CMOS technology.