The lack of soft magnetic composites with high power density in MHz frequency range has become an obstacle in the efficient operation of the electrical and electronic equipments.Here,a promising method to increase the...The lack of soft magnetic composites with high power density in MHz frequency range has become an obstacle in the efficient operation of the electrical and electronic equipments.Here,a promising method to increase the cut-off frequency of iron-based soft magnetic composites to hundreds of MHz is reported.The cut-off frequency is increased from 10 MHz to 1 GHz by modulating the height of the ring,the distribution of particles,and the particle size.The mechanism of cut-off frequency and permeability is the coherent rotation of domain modulated by inhomogeneous field due to the eddy current effect.An empirical formula for the cut-off frequency in a magnetic ring composed of iron-based particles is established from experimental data.This work provides an effective approach to fabricate soft magnetic composites with a cut-off frequency in hundreds of MHz.展开更多
As is well known, there exists a tradeoff between the breakdown voltage BVcEO and the cut-off frequency fT for a standard heterojunction bipolar transistor （HBT）. In this paper, this tradeoff is alleviated by collec...As is well known, there exists a tradeoff between the breakdown voltage BVcEO and the cut-off frequency fT for a standard heterojunction bipolar transistor （HBT）. In this paper, this tradeoff is alleviated by collector doping engineering in the SiGe HBT by utilizing a novel composite of P＋ and N- doping layers inside the collector-base （CB） space-charge region （SCR）. Compared with the single N-type collector, the introduction of the thin P＋ layers provides a reverse electric field weakening the electric field near the CB metallurgical junction without changing the field direction, and the thin N layer further effectively lowers the electric field near the CB metallurgical junction. As a result, the electron temperature near the CB metallurgical junction is lowered, consequently suppressing the impact ionization, thus BVcEO is improved with a slight degradation in fT. The results show that the product of fTXBVcEo is improved from 309.51 GHz.V to 326.35 GHz.V.展开更多
In SPECT, noise is one of the major limitations that degrade image quality. To suppress the noisy signals in an image, digital filters are most commonly applied. However, in SPECT image reconstruction, selection of an...In SPECT, noise is one of the major limitations that degrade image quality. To suppress the noisy signals in an image, digital filters are most commonly applied. However, in SPECT image reconstruction, selection of an appropriate filter and its functions has always remained a difficult task. In this work an attempt was made to investigate the effects of varying cut-off frequencies and in keeping the order of Butterworth filter constant on detectability and contrast of hot and cold re-gions images. A new insert simulating hot and cold regions which provides similar views in a reconstructed image was placed in the phantom’s cylindrical source tank and imaged. Tc-99m radionuclide was distributed uniformly in the phantom. SPECT data were collected in a 20% energy window centered at 140 keV by a Philips ADAC Forte dual head gamma camera mounted with a LEHR collimator. Images were generated by using the filtered backprojection technique. A Butterworth filter of order 5 with cut-off frequencies 0.35 and 0.45 cycles·cm<sup>-1</sup> was applied. Images were examined in terms of hot and cold regions, detectability and contrast. Results show that the hot and cold regions’ detectability and contrast vary with the change of cut-off frequency. With a 0.45 cycles·cm<sup>-1</sup> cut-off frequency, a significant enhancement in contrast of cold regions was achieved as compared to a 0.35 cycles·cm<sup>-1</sup> cut-off frequency. Furthermore, the detectability of hot and cold regions improved with the use of a 0.45 cycles·cm<sup>-1</sup> cut-off frequency. In conclusion, image quality of hot and cold regions affected in a different way with a change of cut-off frequency. Thus, care should be taken in selecting the filter cut-off frequency prior to reconstruction of images;particularly, when both types of regions are expected in the reconstructed image.展开更多
The extraordinary mode(X-mode)lower cut-off frequency is proposed for use in the reflectometry diagnostic on ITER for the electron density profile measurement,which is a trade-off between extreme plasma parameters and...The extraordinary mode(X-mode)lower cut-off frequency is proposed for use in the reflectometry diagnostic on ITER for the electron density profile measurement,which is a trade-off between extreme plasma parameters and the accessible probing frequency.In contemporary experiments,the lower cutoff frequency can be identified at the probing frequency below the electron cyclotron frequency(f_(ce)) under certain plasma conditions.We provide here,for the first time,the experimental validation of the use of the lower cut-off frequency for the density profiles via the reflectometry measurement on EAST.The corresponding group delay of the lower cut-off frequency evolves continuously with the upper one,revealing a reasonable radial coverage extension of reflectometry measurement toward the plasma core.It is concluded that the lower cut-off frequency can be used as a supplement to the upper one in the density profile inversion process,which is of particular interest in the high magnetic field and/or density discharge to extend the radial coverage of reflectometry measurement.展开更多
The availability of ideal conditions like anechoic chamber to characterize some sound parameters, like sound intensity and sound power necessities the determination of free field and cut off frequency measurements. In...The availability of ideal conditions like anechoic chamber to characterize some sound parameters, like sound intensity and sound power necessities the determination of free field and cut off frequency measurements. In this article, full experiment was executed at Wayne State University (Detroit-Michigan), to determine the cut off frequency in all directions;the obtained results showed that the free field can be determined for a specified space. So other tests can take place in this space avoiding regions where reflections and consequently noise can be found. Upon these results tests related to noise abatement in vehicles can be done in such environment.展开更多
In view of the influence and harm of low frequency vibration environment on the structure of spaceflight products,a low frequency dynamic study method for piezoelectric sensor based on the dynamic system of sinusoidal...In view of the influence and harm of low frequency vibration environment on the structure of spaceflight products,a low frequency dynamic study method for piezoelectric sensor based on the dynamic system of sinusoidal pressure is proposed.This method uses a sinusoidal pressure dynamic system with two-way dual channel import and export synchronization technology to study the low frequency characteristics of a piezoelectric sensor of PCB company,and its lower cut-off frequency is 0.26 Hz.It is also studied that when the frequency of the measured vibration or shock signal is 1-200 kHz,the error range of signal positive pressure action time is 4.87%-0.03%.The dynamic compensation for the low frequency of the vibration sensor is carried out,and the compensation effect is good.展开更多
Graphene is a new promising candidate for application in radio-frequency （RF） electronics due to its excellent elec- tronic properties such as ultrahigh carrier mobility, large threshold current density, and high sa...Graphene is a new promising candidate for application in radio-frequency （RF） electronics due to its excellent elec- tronic properties such as ultrahigh carrier mobility, large threshold current density, and high saturation velocity. Recently, much progress has been made in the graphene-based RF field-effect transistors （RF-FETs）. Here we present for the first time the high-performance top-gated RF transistors using millimeter-scale single graphene domain on a SiO2/Si substrate through a conventional microfabrication process. A maximum cut-off frequency of 178 GHz and a peak maximum os- cillation frequency of 35 GHz are achieved in the graphene-domain-based FET with a gate length of 50 nm and 150 nm, respectively. This work shows that the millimeter-scale single graphene domain has great potential applications in RF devices and circuits.展开更多
This work proposes a new strategy to improve the rotor position estimation of a permanent magnet synchronous motor(PMSM) over wide speed range. Rotor position estimation of a PMSM is performed by using sliding mode ob...This work proposes a new strategy to improve the rotor position estimation of a permanent magnet synchronous motor(PMSM) over wide speed range. Rotor position estimation of a PMSM is performed by using sliding mode observer(SMO). An adaptive observer gain was designed based on Lyapunov function and applied to solve the chattering problem caused by the discontinuous function of the SMO in the wide speed range. The cascade low-pass filter(LPF) with variable cut-off frequency was proposed to reduce the chattering problem and to attenuate the filtering capability of the SMO. In addition, the phase shift caused by the filter was counterbalanced by applying the variable phase delay compensation for the whole speed area. High accuracy estimation result of the rotor position was obtained in the experiment by applying the proposed estimation strategy.展开更多
Based on the linear viscoelastic differential constitutive law andcable structural model, the coupled longitudinal-transverse wavesthat propagate along a viscoelastic cable with small curvature isinvesti- gated. A mat...Based on the linear viscoelastic differential constitutive law andcable structural model, the coupled longitudinal-transverse wavesthat propagate along a viscoelastic cable with small curvature isinvesti- gated. A mathematical model is presented that describes thethree-dimensional nonlinear response of a vis- coelastic cable. Anasymptotic form of this model is obtained for the linear response ofcables having small equilibrium curvature.展开更多
基金the National Natural Science Foun-dation of China(Grant Nos.91963201 and 12174163)the 111 Project(Grant No.B20063).
文摘The lack of soft magnetic composites with high power density in MHz frequency range has become an obstacle in the efficient operation of the electrical and electronic equipments.Here,a promising method to increase the cut-off frequency of iron-based soft magnetic composites to hundreds of MHz is reported.The cut-off frequency is increased from 10 MHz to 1 GHz by modulating the height of the ring,the distribution of particles,and the particle size.The mechanism of cut-off frequency and permeability is the coherent rotation of domain modulated by inhomogeneous field due to the eddy current effect.An empirical formula for the cut-off frequency in a magnetic ring composed of iron-based particles is established from experimental data.This work provides an effective approach to fabricate soft magnetic composites with a cut-off frequency in hundreds of MHz.
基金supported by the National Natural Science Foundation of China(Grant Nos.60776051,61006059,and 61006044)the Beijing Municipal Natural Science Foundation,China(Grant Nos.4142007,4143059,4082007,and 4122014)the Beijing Municipal Education Committee,China(Grant Nos.KM200710005015 and KM200910005001)
文摘As is well known, there exists a tradeoff between the breakdown voltage BVcEO and the cut-off frequency fT for a standard heterojunction bipolar transistor （HBT）. In this paper, this tradeoff is alleviated by collector doping engineering in the SiGe HBT by utilizing a novel composite of P＋ and N- doping layers inside the collector-base （CB） space-charge region （SCR）. Compared with the single N-type collector, the introduction of the thin P＋ layers provides a reverse electric field weakening the electric field near the CB metallurgical junction without changing the field direction, and the thin N layer further effectively lowers the electric field near the CB metallurgical junction. As a result, the electron temperature near the CB metallurgical junction is lowered, consequently suppressing the impact ionization, thus BVcEO is improved with a slight degradation in fT. The results show that the product of fTXBVcEo is improved from 309.51 GHz.V to 326.35 GHz.V.
文摘In SPECT, noise is one of the major limitations that degrade image quality. To suppress the noisy signals in an image, digital filters are most commonly applied. However, in SPECT image reconstruction, selection of an appropriate filter and its functions has always remained a difficult task. In this work an attempt was made to investigate the effects of varying cut-off frequencies and in keeping the order of Butterworth filter constant on detectability and contrast of hot and cold re-gions images. A new insert simulating hot and cold regions which provides similar views in a reconstructed image was placed in the phantom’s cylindrical source tank and imaged. Tc-99m radionuclide was distributed uniformly in the phantom. SPECT data were collected in a 20% energy window centered at 140 keV by a Philips ADAC Forte dual head gamma camera mounted with a LEHR collimator. Images were generated by using the filtered backprojection technique. A Butterworth filter of order 5 with cut-off frequencies 0.35 and 0.45 cycles·cm<sup>-1</sup> was applied. Images were examined in terms of hot and cold regions, detectability and contrast. Results show that the hot and cold regions’ detectability and contrast vary with the change of cut-off frequency. With a 0.45 cycles·cm<sup>-1</sup> cut-off frequency, a significant enhancement in contrast of cold regions was achieved as compared to a 0.35 cycles·cm<sup>-1</sup> cut-off frequency. Furthermore, the detectability of hot and cold regions improved with the use of a 0.45 cycles·cm<sup>-1</sup> cut-off frequency. In conclusion, image quality of hot and cold regions affected in a different way with a change of cut-off frequency. Thus, care should be taken in selecting the filter cut-off frequency prior to reconstruction of images;particularly, when both types of regions are expected in the reconstructed image.
基金supported by the National Key R&D Program of China(Nos.2017YFE0301205 and 2019YFE03040002)National Natural Science Foundation of China(Nos.11875289,11975271,11805136,12075284,and 12175277)China Postdoctoral Science Foundation(No.2021M703256)。
文摘The extraordinary mode(X-mode)lower cut-off frequency is proposed for use in the reflectometry diagnostic on ITER for the electron density profile measurement,which is a trade-off between extreme plasma parameters and the accessible probing frequency.In contemporary experiments,the lower cutoff frequency can be identified at the probing frequency below the electron cyclotron frequency(f_(ce)) under certain plasma conditions.We provide here,for the first time,the experimental validation of the use of the lower cut-off frequency for the density profiles via the reflectometry measurement on EAST.The corresponding group delay of the lower cut-off frequency evolves continuously with the upper one,revealing a reasonable radial coverage extension of reflectometry measurement toward the plasma core.It is concluded that the lower cut-off frequency can be used as a supplement to the upper one in the density profile inversion process,which is of particular interest in the high magnetic field and/or density discharge to extend the radial coverage of reflectometry measurement.
文摘The availability of ideal conditions like anechoic chamber to characterize some sound parameters, like sound intensity and sound power necessities the determination of free field and cut off frequency measurements. In this article, full experiment was executed at Wayne State University (Detroit-Michigan), to determine the cut off frequency in all directions;the obtained results showed that the free field can be determined for a specified space. So other tests can take place in this space avoiding regions where reflections and consequently noise can be found. Upon these results tests related to noise abatement in vehicles can be done in such environment.
文摘In view of the influence and harm of low frequency vibration environment on the structure of spaceflight products,a low frequency dynamic study method for piezoelectric sensor based on the dynamic system of sinusoidal pressure is proposed.This method uses a sinusoidal pressure dynamic system with two-way dual channel import and export synchronization technology to study the low frequency characteristics of a piezoelectric sensor of PCB company,and its lower cut-off frequency is 0.26 Hz.It is also studied that when the frequency of the measured vibration or shock signal is 1-200 kHz,the error range of signal positive pressure action time is 4.87%-0.03%.The dynamic compensation for the low frequency of the vibration sensor is carried out,and the compensation effect is good.
基金supported by the National Basic Research Program of China(Grant Nos.2011CBA00600,2011CBA00601,and 2013CBA01604)the National Natural Science Foundation of China(Grant No.60625403)the National Science and Technology Major Project of China(Grant No.2011ZX02707)
文摘Graphene is a new promising candidate for application in radio-frequency （RF） electronics due to its excellent elec- tronic properties such as ultrahigh carrier mobility, large threshold current density, and high saturation velocity. Recently, much progress has been made in the graphene-based RF field-effect transistors （RF-FETs）. Here we present for the first time the high-performance top-gated RF transistors using millimeter-scale single graphene domain on a SiO2/Si substrate through a conventional microfabrication process. A maximum cut-off frequency of 178 GHz and a peak maximum os- cillation frequency of 35 GHz are achieved in the graphene-domain-based FET with a gate length of 50 nm and 150 nm, respectively. This work shows that the millimeter-scale single graphene domain has great potential applications in RF devices and circuits.
基金Project(2012(PS-2012-090))supported by the Pukyong National University Research Abroad Fund,Korea
文摘This work proposes a new strategy to improve the rotor position estimation of a permanent magnet synchronous motor(PMSM) over wide speed range. Rotor position estimation of a PMSM is performed by using sliding mode observer(SMO). An adaptive observer gain was designed based on Lyapunov function and applied to solve the chattering problem caused by the discontinuous function of the SMO in the wide speed range. The cascade low-pass filter(LPF) with variable cut-off frequency was proposed to reduce the chattering problem and to attenuate the filtering capability of the SMO. In addition, the phase shift caused by the filter was counterbalanced by applying the variable phase delay compensation for the whole speed area. High accuracy estimation result of the rotor position was obtained in the experiment by applying the proposed estimation strategy.
基金the National Natural Science Foundation of China(No.59635140)
文摘Based on the linear viscoelastic differential constitutive law andcable structural model, the coupled longitudinal-transverse wavesthat propagate along a viscoelastic cable with small curvature isinvesti- gated. A mathematical model is presented that describes thethree-dimensional nonlinear response of a vis- coelastic cable. Anasymptotic form of this model is obtained for the linear response ofcables having small equilibrium curvature.
