2nd Harmonic Component Research Articles

Sensitivity, Pole-Zero and Distortion Analysis of State Variable Filter with Multiple Faults

In this paper the fault diagnosis of multiple faults in linear circuits is studied for distortion analysis for 2nd and 3rd harmonic components by considering a state variable filter circuit. To study the testability of the circuit the distortion analysis is plotted for various fault conditions. The sensitivity of the output signal with respect to the faults along with pole-zero analysis is obtained. The transfer function of the state variable filter considered for the analysis is given by: ▪

Turn-on optomagnetic bacterial DNA sequence detection using volume-amplified magnetic nanobeads

Detection of a Vibrio cholerae DNA-sequence using an optomagnetic read-out exploiting the dynamic behavior of magnetic nanobeads along with two turn-on data analysis approaches is demonstrated. The optomagnetic method uses a weak uniaxial AC magnetic field of varying frequency applied perpendicular to the optical path and measures the modulation of laser light passing through a cuvette containing the sample with oligonucleotide-tagged magnetic beads and macromolecular coils of single-stranded DNA. The DNA coils are formed upon a padlock probe ligation followed by rolling circle amplification (RCA). The presence of target gives rise to a change of the 2nd harmonic component, V2=V2'+iV2'', of the transmitted light. We demonstrate that by using the phase angle ξ defined as ξ=arctanV2'/V2'' in the low-frequency region we obtain a limit of detection of 10pM for an RCA time of only 20min corresponding to a total assay time of 60min. Moreover, we show that the approach based on ξ is significantly more robust than the analysis based on a turn-off of the signal due to free magnetic nanobeads used in previous work (Donolato et al., submitted for publication), where a limit of detection of 10pM was obtained for an RCA time of 60min. The increased robustness and the reduction in total assay time constitute significant steps towards the realization of a low-cost, rapid and sensitive biosensor platform suitable for pathogen detection in both human and veterinary medicine settings.

2D hall sensor array for measuring the position of a magnet matrix

Hall sensor array is used to measure the position of a magnet array and needs compensation of errors caused by manufacturing tolerances as well as harmonic components of the magnetic flux of the magnet array. This paper presents a 2D hall sensor array to measure the position of a magnet matrix by filtering harmonic components. First, 1D sensor array to filter out arbitrary number of harmonic signals is proposed and extended to 2D sensor array for the position measurement of a magnet matrix. A 2D hall sensor array for filtering both fundamental and 2nd harmonic components of the magnetic flux and its conditioning circuit board are built to measure the position of the magnet matrix for a planar motor. Finally, performances of filtering harmonics and measuring position of the magnet matrix are experimentally verified with a XY linear motion stage. The proposed 2D hall sensor array is compatible to a sine encoder and is directly applicable to commercial motion controllers.

The glycemic index of a mid morning snack modifies the body temperature rhythm

The structure of a circadian rhythm depends on the activity of the suprachiasmatic clock, on the presence of zeigebers, and on the presence of masking factors. Regarding body temperature, a clear circadian rhythm is well recognized, with maximal values approaching dusk and minimal in the small hours, near dawn. However, masking factors can enhance or reduce the amplitude of the circadian rhythms. Food eating is a masking factor on the body temperature rhythm, probably related to the Thermal Effect of Food (TEF), a measure of the energy spent for the digestion, absorption, and disposal of a given amount and type of food. Also, the Glycemic Index (GI) shows how quickly blood glucose rises after eating a given amount and type of food. As high GI foods require lower digestive processing, their TEF should be lower than that of lower GI. The present study aims at recording the consequences of modifying the GI of a mid morning snack on the whole 24 h body temperature cycle in young human subjects. The study was conducted on 15 university students (8 female, 7 male, 19–25 years old). Each subject was provided with an activity meter and a wrist temperature holder during two non consecutive periods of 5 days. During the experimental days, each subject ingested between 10.30–11.30 AM one of two snacks of precise composition with low and high GI. Each participant was blind to the GI of the snack ingested. Significant differences were found between the averaged peripheral temperature of the subjects during light and dark periods. Also, the 2nd harmonic component (12 h) was modified. From the well known phase opposition between central and peripheral temperature, the results point to changes in the central temperature cycle. Arguably, TEF dependent changes in the peripheral dissipation could occur without real changes in the core temperature. However, the TEF consequences does not extend beyond 6 h after ingestion, while the recorded changes in peripheral temperature showed long term effects, being extended up to the whole 24 h cycle. Therefore, the body temperature seems to have been modified as a consequence of the nutritional properties of a small mid morning snack. The body temperature cycle shows a high sensitivity to the GI of a minor meal.

Enhanced coherent terahertz Smith-Purcell superradiation excited by two electron-beams

This paper presents the studies on the enhanced coherent THz Smith-Purcell superradiation excited by two pre-bunched electron beams that pass through the 1-D sub-wavelength holes array. The Smith-Purcell superradiation has been clearly observed. The radiation emitting out from the system has the radiation angle matching the 2nd harmonic frequency component of the pre-bunched electron beams. The results show that the two electron beams can be coupled with each other through the holes array so that the intensity of the radiated field has been enhanced about twice higher than that excited by one electron beam. Consequently superradiation at the frequency of 0.62 THz can be generated with 20A/cm(2) current density of electron beam based on above mechanism. The advantages of low injection current density and 2nd harmonic radiation promise the potential applications in the development of electron-beam driven THz sources.

비선형 경사 균열면에서의 고조파 발생 특성 해석

Based on the nonlinear spring model coupled with perturbation method, 2nd harmonic waves generated by oblique incident ultrasound on nonlinear crack interface were calculated and investigated. Reflected and transmitted waves from the interface were determined and analyzed at various angle of incidence for the cracks with different interfacial stiffness in order to estimate the 2nd harmonic generation of incident ultrasound. It was shown in computer simulation that the 2nd harmonic components changed much with the increase of incidence angle in both reflected and transmitted wave, but became very small when the incident angle approached toward 90 degree. It can be concluded that the 2nd harmonic component of reflected wave has a meaningful amplitude as much as the transmitted 2nd harmonic wave from partly closed crack.

Development of scattering near-field optical microspectroscopy apparatus using an infrared synchrotron radiation source

We report the status of a scattering near-field microspectroscopy apparatus developed at SPring-8 using an infrared synchrotron radiation (IR-SR) source. It consists of a scattering type scanning near-field optical microscope and a Fourier transform infrared spectrometer. The IR-SR is used as a highly brilliant and broad-band IR source. This apparatus has potential for application in near-field spectroscopy with high spatial resolution beyond the diffraction limit. In order to eliminate background scatterings from the probe shaft and/or sample surface, we used higher harmonic demodulation method. The near-field spectra were observed by 2nd harmonic components using the lock-in detection. The spatial resolution of about 300nm was achieved at around 1000cm−1 (10μm wavelength).

Mapping nanomechanical properties of live cells using multi-harmonic atomic force microscopy

The nanomechanical properties of living cells, such as their surface elastic response and adhesion, have important roles in cellular processes such as morphogenesis, mechano-transduction, focal adhesion, motility, metastasis and drug delivery. Techniques based on quasi-static atomic force microscopy techniques can map these properties, but they lack the spatial and temporal resolution that is needed to observe many of the relevant details. Here, we present a dynamic atomic force microscopy method to map quantitatively the nanomechanical properties of live cells with a throughput (measured in pixels/minute) that is ∼10-1,000 times higher than that achieved with quasi-static atomic force microscopy techniques. The local properties of a cell are derived from the 0th, 1st and 2nd harmonic components of the Fourier spectrum of the AFM cantilevers interacting with the cell surface. Local stiffness, stiffness gradient and the viscoelastic dissipation of live Escherichia coli bacteria, rat fibroblasts and human red blood cells were all mapped in buffer solutions. Our method is compatible with commercial atomic force microscopes and could be used to analyse mechanical changes in tumours, cells and biofilm formation with sub-10nm detail.

Technical procedures to select basic parameters of a fluxgate magnetometer

In fluxgate magnetometers, the external magnetic field is generally measured from the second harmonic induced voltage in the pick-up coil. Thus, toimprove the performance of a fluxgate magnetometer design, careful considerations should focus on some operational parameters and how to calibrate them to attainan optimal performance with a minimum intrinsic noise at the output. Basically, two main factors are considered: i) the output dependence on variations of the evenharmonics amplitudes with the excitation current; and ii) adjustments for a perfect timely match between the core saturation and the time-width of the sampling. Thebest sensitivity of the magnetometer is obtained in a portion of the hysteresis curve where the 2nd harmonic component predominates. Since this region depends on theamplitude of the excitation, it becomes necessary to calibrate the excitation amplitude in order to get the highest 2nd harmonic amplitude in the pick-up coil. When theamplitude of the excitation current is modified, the amplitude of the even harmonics also changes, and consequently the magnetometer will operate below its optimalsensitivity, depending on how much the current has changed. Similar result is observed when the core is built with a different inductance (different number of wraps)which requires operational tests to be carried out to verify the level of the core saturation by adjusting the amplitude and the frequency to get the best performancefrom the magnetometer. Changes in the amplitudes of the excitation current generally occur with changes in the excitation current waveform, affecting the timing ofthe core saturation. To avoid bad synchronization between the excitation current and the sampling, the phase shift circuit is locked with the excitation current circuitin order to work together and variations on the excitation current phase is automatically corrected in the sampling circuit. In summary, finding the moment whenthe 2nd harmonic has its greatest value, adjusting the time-width of the synchronous detector and avoiding phase’s shifts between excitation and detection circuitscan produce a magnetometer performing at its lowest noise output.

In vitro microemboli classification using neural network models and RF signals

Emboli classification is of high clinical importance for selecting appropriate treatment for patients. Several ultrasonic (US) methods using Doppler processing have been used for emboli detection and classification as solid or gaseous matter. We suggest in this experimental study exploiting the Radio-Frequency (RF) signal backscattered by the emboli since they contain additional information on the embolus than the Doppler signal. The aim of the study is the analysis of RF signals using Multilayer Perceptron (MLP) and Radial-Basis Function Network (RBFN) in order to classify emboli. Anthares scanner with RF access was used with a transmit frequency of 1.82 MHz at two mechanical indices (MI) 0.2 and 0.6. The mechanical index is given as the peak negative pressure (in MPa) divided by the square root of the frequency (in MHz). A Doppler flow phantom was used containing a 0.8 mm diameter vessel surrounded by a tissue mimicking material. To imitate gas emboli US behaviour, Sonovue microbubbles were injected at two different doses (10μl and 5μl) in a nonrecirculating at a constant flow. The surrounding tissue was assumed to behave as a solid emboli. In order to mimic real clinical pathological situations, Sonovue concentration was chosen such that the fundamental scattering from the tissue and from the contrast were identical. The amplitudes and bandwidths of the fundamental and the 2nd harmonic components were selected as input parameters to the MLP and RBFN models. Moreover the frequency bandwidths of the fundamental and the 2nd harmonic echoes were approximated by Gaussian functions and the coefficients were used as a third input parameter to the neural network models. The results show that the Gaussian coefficients provide the highest rate of classification in comparison to the amplitudes and the bandwidths of the fundamental and the 2nd harmonic components. The classification rates reached 89.28% and 92.85% with MLP and RBFN models respectively. This short communication demonstrates the opportunity to classify emboli based on a RF signals and neural network analysis.

Quadrature and eight‐phase VCOs implemented with SiGe injection locked frequency dividers

AbstractThis article proposes a new technique for designing multi‐phase voltage controlled oscillators (VCOs), which were implemented in the standard TSMC 0.35 μm SiGe 3P3M BiCMOS process. The quadrature voltage‐controlled oscillator (QVCO) consists of two direct‐ injection locked frequency dividers (ILFDs) with a tail MOSFET. The 2nd harmonic frequency component at the drain node of tail transistor in one ILFD is injected to the gate of injection MOSFET in the other ILFD to couple the two independent ILFDs. The eight‐phase VCO is also designed with similar technique to couple four differential VCOs. At the supply voltage of 3.0 V, the output phase noise of the QVCO is −118.22 dBc/Hz at 1 MHz offset frequency from the carrier frequency of 2.28 GHz, and the figure of merit is −173.25 dBc/Hz. At the supply voltage of 3.0 V, the total power consumption is 14.4 mW. At the supply voltage of 3.0 V, the output phase noise of the eight‐phase VCO is −116.14 dBc/Hz at 1 MHz offset frequency from the carrier frequency of 2.92 GHz, and the figure of merit is −171.3 dBc/Hz. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 395–398, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24053

VEP indices of cortical lateral interactions in epilepsy treatment

We extend Spekreijse’s strategy for analyzing lateral interactions in visual evoked potentials (VEPs) to clinical neurophysiologic testing of patients with epilepsy. Stimuli consisted of the radial windmill/dartboard pattern [Ratliff, F., & Zemon, V. (1982). Some new methods for the analysis of lateral interactions that influence the visual evoked potential. In: Bodis-Wollner (Ed.), Evoked potentials, Vol. 388. (pp. 113–124). New York: Annals of the New York Academy of Sciences.] and conventional checkerboards. The fundamental and 2nd-harmonic components of the steady-state responses were used to calculate indices reflecting facilitatory (FI) and suppressive (SI) cortical interactions. We carried out two studies. In the first, VEPs in 38 patients receiving antiepileptic drug (AED) therapy were compared to those of age-matched controls. For three AEDs (tiagabine, topiramate, and felbamate), addition of the drug did not change the FI and SI compared to baseline values or those of normal controls. However, the addition of gabapentin was associated with an increase of the FI, and this change was reversed when the medication was withdrawn. This suggested a medication-specific change in cortical lateral interactions. The second study focused on the effects of neurostimulation therapy. Eleven epilepsy patients receiving chronic vagus nerve stimulation (VNS) treatment were tested. By comparing VEPs recorded with the stimulator on (Stim-ON) and turned off (Stim-OFF) in the same session, we determined that VNS did not have a short-acting effect on lateral interactions. However, when compared with normal controls, the VNS patients had a significantly smaller SI ( p < .05), but no difference in the FI, demonstrating the presence of a chronic effect. We conclude that with the appropriate stimuli, VEPs can be used as a measure of cortical lateral interactions in normals and epileptic patients, and demonstrate specific changes in these interactions associated with certain treatment modalities.

UBVRI polarimetry of the massive interacting binary SX Cassiopeiae: modeling the electron-scattering circumstellar envelope

Aims. We perform a study of the structure, density, and distribution of ionized circumstellar gas in the strongly interacting binary SX Cas. Methods. We apply our new model codes for electron scattering in circumstellar matter to analyze a previously unpublished, extensive linear polarization data set for SX Cas, collected during four successive observing periods in 1981–84 at the Crimean Astrophysical Observatory. These data are complemented by our polarization observations carried out in 2000 and 2005 with the KVA-60 telescope at La Palma. Results. A clear, phase-locked pattern of polarization variations over the 36.6-day orbital period is revealed in each season, showing significant 1st and 2nd harmonic Fourier components and pronounced effects in the U and B bands at the primary eclipse, when the hot component and the surrounding circumstellar matter are obscured by the companion star. Seasonal variability is also found, but the major features of the polarization curves are well explained by a model with an extended scattering region on the trailing side of the accreting star, where the stream from the companion hits the accretion disk. No significant polarized flux is detected from the disk. We interpret this as being due to multiple scattering and strong absorption effects in the optically thick medium, which reduce the polarization of the light emerging from the disk to low levels. The modeled scattering region is above the orbital plane by about 10 ◦ ,a s seen from the center of the mass gainer. We attribute this to dominant electron scattering taking place on the upper side of an optically and geometrically thick accretion disk seen at an inclination i ∼ 78 ◦ by the observer.

Investigation on phase-coded third harmonic imaging for normal and pathological tissues in transmission mode in vitro

In this paper, a phase-coded pulse technique is proposed to improve the signal-to-noise ratio (SNR) in the 3rd harmonic imaging in transmission mode, where three pulses with initial phases of 0°, 120° and 240° are transmitted and their corresponding received signals are linearly summed. By means of simulations and measurements, we show that the 3rd harmonic is enhanced by 9.5 dB, whereas the fundamental or the 2nd harmonic components are suppressed; the axial and lateral beam profiles of the processed 3rd harmonics are superior to those of the fundamental or 2nd harmonic components. In addition, this technique is applied to obtain the 3rd harmonic images for two normal and pathological biological tissues in transmission mode. This technique yields a dramatically cleaner and sharper contrast than the images obtained by the traditional fundamental imaging and the 2nd harmonic imaging, which helps distinguish the normal and pathological states of tissues.

Corona enhancement in ultrasonographical post-vascular phase images with microbubble contrast agent: A novel specific sign for hepatocellular carcinomas

In 1.5 Harmonic Imaging ultrasonography (1.5 HI US), images are obtained in a band intermediate between the fundamental and 2nd harmonic components, resulting in stronger contrast enhancement than in conventional harmonic imaging. We attempted to assess the hemodynamics of hepatocellular carcinomas (HCC) with special attention to blood drainage using 1.5 HI US. Forty-two HCC nodules, metastatic liver tumors and hepatic hemangiomas were studied. In contrast studies, intermittent ultrasound transmission was performed for a period of up to 45 sec after the injection of contrast agent, which was regarded as the vascular phase. The time point of 5 min later was specified as the post-vascular phase, and images were obtained by single manual transmission for comparison of contrast enhancement with surrounding hepatic parenchyma. In addition, histological examination was performed. 1.5 HI US clearly demonstrated the strong tumor vessels in most HCCs. Corona enhancement, in which the areas surrounding the tumor are enhanced, was observed in 71.4% (30/42) of HCC nodules during the post-vascular phase. This sign was not observed in any other tumors. Histological findings revealed that CD34-positive-endothelial cells were prominent in the surrounding area of HCC. In conclusion, 1.5 HI US is an effective tool for evaluating hemodynamics in both early- and post-vascular phase. Corona enhancement may be due to the trapping of contrast agent in the endothelial cells in the surround of HCC nodules and be a novel specific sign for HCC.

The usefulness of 1.5 harmonic imaging ultrasonography with Levovist in the diagnosis of focal hepatic tumors

In contrast-enhanced 1.5 harmonic imaging sonography, images are obtained in a band intermediate between the fundamental and the 2nd harmonic components. In the present study, we investigated the usefulness of 1.5 harmonic imaging sonography with the use of the contrast agent Levovist for the diagnosis of hepatocellular carcinoma (HCC), metastatic hepatic tumor, and hepatic hemangioma. The subjects in this study were 64 patients with 70 nodules of hepatic tumors (42 nodules in 36 cases of hepatocellular carcinoma, 20 nodules in 20 cases of metastatic hepatic tumor, and 8 nodules in 8 cases of hepatic hemangioma). Contrast enhancement of tumors acquired in the early, portal, and late phases with 1.5 harmonic imaging sonography were compared to classify the tumors. 1.5 harmonic imaging sonography of HCC showed contrast enhancement of 36 nodules (85.7%). Hypervascular enhancement in the early phase, which was maintained in the portal phase, changed to images with no contrast enhancement with partial persistence of contrast enhancement in the late phase. 1.5 harmonic imaging sonography of metastatic hepatic tumor showed hypervascular enhancement of the margin of 20 nodules (100%) in the early and portal phases, which changed to images with no contrast enhancement in the late phase. 1.5 harmonic imaging sonography of hepatic hemangiomas maintained hypervascular enhancement on the tumor margin of 5 nodules (62.5%) in the early and portal phases. When early phase 1.5 harmonic imaging sonography did not show hypervascular enhancement in 3 nodules (37.5%), and late-phase images confirmed that these 3 nodules were hypervascular enhancement on the tumor margin. 1.5 harmonic imaging sonography of hepatic tumors (hepatocellular carcinoma, metastatic hepatic tumor and hepatic hemangioma) provided characteristic findings of contrast enhancement in the early, portal, and late phases, and will contribute to differential diagnosis.

Contrast-Enhanced Harmonic EUS: A Method to Visualize Microcirculation in Digestive Organs

Introduction: EUS is superior to any other imaging modalities with respect to the spatial resolution, but of limited value in producing parenchymal perfusion images with the use of the contrast agents. Recent discoveries of ultrasound have shown intravenous perfluorocarbon-containing microbubbles such as Definity produce harmonic signals at a low acoustic pressure. These contrast agents may be suitable for EUS that produces low acoustic pressure. In the present study, we observed microcirculation of digestive organs in dogs after the injection of Definity by means of a newly developed EUS probe. Methods: Contrast-enhanced harmonic sonography was conducted in 12 beagle dogs under anesthesia. The abdomen was opened by midline incision. An experimental EUS probe with a convex array was attached to stomach, small intestine, gallbladder or pancreas. The images were analyzed by ALOKA ProSound SSD 6500. E-PHD mode that sensitively depicts signals from microbubbles by the combination of filtered fundamental components and 2nd harmonic components was used. Each organ was sequentially observed after intravenous infusion of different doses of Definity. In some experiments, a part of the pancreas was ablated by radiofrequency after observing normal pancreas, and 1 ml of saline was injected into gastric submucosa. Results: After the injection of Definity, signals from microbubbles appeared from the area around the main pancreatic duct and subsequently branched off in the pancreas. The signals were finally distributed homogenously in the pancreatic tissue 10 seconds later. After the radiofrequency ablation, the contrast-enhanced harmonic sonography visualized the ablated lesion as a hypovascular perfusion defect. After vessels appeared flowing into the gallbladder, the muscle layer and the mucosal layer were sequentially observed. In stomach and small intestine, signals from microbubbles appeared as perforating vessels in the proper muscle layer and transverse vessels in the submucosal layer. Subsequently, signals were distributed in the mucosal layer. In the saline-injected lesion of gastric wall, some stretched vessels flowing between serosal and luminal sides were visualized. Conclusion: Contrast-enhanced harmonic sonography with the use of EUS probe successfully visualized microcirculation in digestive organs and would be a convincing method for depiction of small lesions, comprehension of detailed structure and differential diagnosis of digestive diseases. Introduction: EUS is superior to any other imaging modalities with respect to the spatial resolution, but of limited value in producing parenchymal perfusion images with the use of the contrast agents. Recent discoveries of ultrasound have shown intravenous perfluorocarbon-containing microbubbles such as Definity produce harmonic signals at a low acoustic pressure. These contrast agents may be suitable for EUS that produces low acoustic pressure. In the present study, we observed microcirculation of digestive organs in dogs after the injection of Definity by means of a newly developed EUS probe. Methods: Contrast-enhanced harmonic sonography was conducted in 12 beagle dogs under anesthesia. The abdomen was opened by midline incision. An experimental EUS probe with a convex array was attached to stomach, small intestine, gallbladder or pancreas. The images were analyzed by ALOKA ProSound SSD 6500. E-PHD mode that sensitively depicts signals from microbubbles by the combination of filtered fundamental components and 2nd harmonic components was used. Each organ was sequentially observed after intravenous infusion of different doses of Definity. In some experiments, a part of the pancreas was ablated by radiofrequency after observing normal pancreas, and 1 ml of saline was injected into gastric submucosa. Results: After the injection of Definity, signals from microbubbles appeared from the area around the main pancreatic duct and subsequently branched off in the pancreas. The signals were finally distributed homogenously in the pancreatic tissue 10 seconds later. After the radiofrequency ablation, the contrast-enhanced harmonic sonography visualized the ablated lesion as a hypovascular perfusion defect. After vessels appeared flowing into the gallbladder, the muscle layer and the mucosal layer were sequentially observed. In stomach and small intestine, signals from microbubbles appeared as perforating vessels in the proper muscle layer and transverse vessels in the submucosal layer. Subsequently, signals were distributed in the mucosal layer. In the saline-injected lesion of gastric wall, some stretched vessels flowing between serosal and luminal sides were visualized. Conclusion: Contrast-enhanced harmonic sonography with the use of EUS probe successfully visualized microcirculation in digestive organs and would be a convincing method for depiction of small lesions, comprehension of detailed structure and differential diagnosis of digestive diseases.

Control scheme studies of voltage source type superconducting magnetic energy storage (SMES) under asymmetrical voltage

Symmetry of system voltage is very important to the performance of superconducting magnetic energy storage (SMES). Both theoretical analysis and simulation results show that, negative sequence current and 2nd harmonic power will be injected into the system, when conventional symmetrical fire is used in power conditioning system (PCS) of SMES. Two indices are used to evaluate the performance of PCS of SMES: the relative error of average value and 2nd harmonic component of active power supplied by SMES. To improve the performance of SMES, symmetrical vector control is put forward in this paper. According to the objective, there are three kinds of symmetrical vector control: positive sequence voltage control, zero negative sequence current control and constant active power control. Their principles are presented and improvements on the performance of SMES are verified by electromagnetic transient simulation. It shows that all those three methods decrease the relative error of average value of active power supplied by SMES. Zero negative sequence current control and constant active power control can also limit the relative error of 2nd harmonic component of active power supplied by SMES effectively.

Finite Element Simulation of Nonlinear Acoustic Behavior at Minute Cracks Using Singular Element

A finite element method (FEM) simulation of wave propagation is performed for a model plate which includes minute cracks nucleated by spallation. The minute cracks are modeled by singular elements which express nonlinear stress-strain at the crack surfaces. The transmitted wave through these cracks is simulated and the 2nd harmonic amplitude is processed by fast fourier transform (FFT). The ratio of the 2nd harmonic component to the fundamental one increases with an increase in the incident wave of amplitude for the incident wave of amplitude 5–20 nm. The simulated results qualitatively confirm the measured nonlinear acoustic response on spalled samples.

Estimation of Nonlinear Acoustic Parameter Using Bispectral Analysis.

The fact that material degradation can be calculated by measuring nonlinear acoustic effect has been proposed by previous studies. They reported that the most conventional method to measure nonlinear acoustic effect is to measure the absolute magnitude of the fundamental and 2nd order harmonic frequency component in the propagated ultrasonic wave. For this aim, power spectral analysis technique has been used widely. However, there is a fatal disadvantage in using power spectrum in that the gaussian additive noise superimposed in the wave signal remains in the power spectrum domain, Moreover, the magnitude of the 2nd order harmonic frequency component generated by nonlinear effect is so small that it may be suppressed by the noise remaining in the power spectrum domain. This paper proposes the bispectrum analysis method to overcome this problem. In order to evaluate the performance of our proposed bispectrum method, several sham signals with different SNR (Signal-to-Noise Ratio) were generated in a computer based on the nonlinear wave signal model, and the nonlinear parameter β was estimated in both methods of power spectrum and bispectrum to compare the accuracy. Simulation results showed that the bispectrum method was more stable and could estimate closer nonlinear parameter to the true value than the power spectrum method. Also, in order to verify that our method is applicable to the actual signal the bispectrum method was applied to the actual experimental signals that were obtained from the transmission test in several SS41 specimens with different degrees of degradation.