Global energy and environmental issues are becoming increasingly problematic,and the vibration and noise problem of 110 kV transformers,which are the most widely distributed,have attracted widespread attention from bo...Global energy and environmental issues are becoming increasingly problematic,and the vibration and noise problem of 110 kV transformers,which are the most widely distributed,have attracted widespread attention from both inside and outside the industry.DC bias is one of the main contributing factors to vibration noise during the normal operation of transformers.To clarify the vibration and noise mechanism of a 110 kV transformer under a DC bias,a multi-field coupling model of a 110 kV transformer was established using the finite element method.The electromagnetic,vibration,and noise characteristics during the DC bias process were compared and quantified through field circuit coupling in parallel with the power frequency of AC,harmonic,and DC power sources.It was found that a DC bias can cause significant distortions in the magnetic flux density,force,and displacement distributions of the core and winding.The contributions of the DC bias effect to the core and winding are different at Kdc=0.85.At this point,the core approached saturation,and the increase in the core force and displacement slowed.However,the saturation of the core increased the leakage flux,and the stress and displacement of the winding increased faster.The sound field distribution characteristics of the 110 kV transformer under a DC bias are related to the force characteristics.When the DC bias coefficient was 1.25,the noise sound pressure level reached 73.6 dB.展开更多
Carbon nitride films were deposited on Si (100) substrates using plasma-enhanced chemical vapor deposition (PECVD) technique from CH4 and N2 at different applied dc bias voltage. The microstructure, composition and ch...Carbon nitride films were deposited on Si (100) substrates using plasma-enhanced chemical vapor deposition (PECVD) technique from CH4 and N2 at different applied dc bias voltage. The microstructure, composition and chemical bonding of the resulting films were characterized by Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). The mechanical properties such as hardness and elastic modulus of the films were evaluated using nano-indentation. As the results, the Raman spectra, showing the G and D bands, indicate the amorphous structure of the films. XPS and FTIR measurements demonstrate the existence of various carbon-nitride bonds in the films and the hydrogenation of carbon nitride phase. The composition ratio of N to C, the nano-hardness and the elastic modulus of the carbon nitride films increase with increasing dc bias voltage and reach the maximums at a dc bias voltage of 300 V, then they decrease with further increase of the dc bias voltage. Moreover, the XRD analyses indicate that the carbon nitride film contains some polycrystalline C3N4 phase embedded in the amorphous matrix at optimized deposition condition of dc bias voltage of 300 V.展开更多
IEC TS 60076-23,the first IEC standard on DC bias suppression devices approved by IEC/TC 14 in November 2017,is expected to be published and put into force in 2018,overcoming the lack of such IEC standards in the fiel...IEC TS 60076-23,the first IEC standard on DC bias suppression devices approved by IEC/TC 14 in November 2017,is expected to be published and put into force in 2018,overcoming the lack of such IEC standards in the field.The Shanghai branch of SGCC has carried out studies and researches on DC bias effect for more than 10 years,and it has led the standard development based on its R&D and the application of DC bias suppression devices in China.展开更多
Effect of direct current negative bias on diamond nucleation in microwave plasma assisted chemical vapor deposition system was discussed. The influence of the magnitude of negative bias value,bias duration and methane...Effect of direct current negative bias on diamond nucleation in microwave plasma assisted chemical vapor deposition system was discussed. The influence of the magnitude of negative bias value,bias duration and methane concentration in the gas mixture on nucleation density of diamond films was studied respectively. It is demonstrated that direct current negative bias can drastically enhance the diamond nucleation at a suitable value.Long bias duration and high methane concentration are helpful for diamond nucleation.展开更多
With the increasing demand for high torque density in motors,more and more new topologies emerge.Furthermore,the magnetic field modulation principle is widely concerned and has evolved into an effective analysis metho...With the increasing demand for high torque density in motors,more and more new topologies emerge.Furthermore,the magnetic field modulation principle is widely concerned and has evolved into an effective analysis method for studying the new motor topology.This paper introduces the principle of magnetic field modulation.And the research on high torque density in recent years is reviewed from the perspective of magnetic field modulation,including permanent magnet vernier machine(PMVM),flux reverse machine(FRM),flux switching machine(FSM),dual permanent magnet(DPM)machine,and DC biased machine.The principle of magnetic field modulation makes it possible to propose higher torque density topologies in the future.展开更多
A theoretical model was proposed to describe the effects of external bias electric field on terahertz(THz)generated in air plasma.The model predicted that for a plasma in a bias electric field,the amplification effect...A theoretical model was proposed to describe the effects of external bias electric field on terahertz(THz)generated in air plasma.The model predicted that for a plasma in a bias electric field,the amplification effect of the THz wave intensity increases with the increase of the excitation laser wavelength.We experimentally observed the relationship between the THz enhancement effect and the electric field strength at different wavelengths.Experimental results showed a good agreement with the model predictions.These results enhance our understanding of the physical mechanism by which femtosecond lasers excite air to generate THz and extend the practical applications of THz generation and modulation.展开更多
Fe73. 5 Cu1 Nb3 Si15.5B7 nanocrystalline powder cores with different particle sizes ranging from 10 to 125 9m were fabricated by cold-pressing techniques. The cores exhibited increased core loss P cv and decreased ini...Fe73. 5 Cu1 Nb3 Si15.5B7 nanocrystalline powder cores with different particle sizes ranging from 10 to 125 9m were fabricated by cold-pressing techniques. The cores exhibited increased core loss P cv and decreased initial permea- bility μi with addition of fine powders below 50 μm in size, and the content should be less than 40 mass%. It was thought to be closely related to the high coercive force H c due to the stresses generated during the crushing process and high demagnetization fields of small powders. Furthermore, modifying the alloy compositions by adding defined amount of Ni could improve the soft magnetic properties, including superior characteristics of permeability under high direct current （DC） bias field and comparable low core loss at high frequency.展开更多
Yttria-stabilized zirconia (YSZ) thin films with the c-axis texturing were successfully deposited onpolycrystalline metallic tape (Hastelloy-C) by a dc bias rf magnetron sputtering. X-ray measurements re-vealed that t...Yttria-stabilized zirconia (YSZ) thin films with the c-axis texturing were successfully deposited onpolycrystalline metallic tape (Hastelloy-C) by a dc bias rf magnetron sputtering. X-ray measurements re-vealed that the resulting YSZ films exhibited pure c-axis texturing. YBCO films deposited by using demaguetron sputtering on Hastelloy tape with YSZ buffer layer were c-axis oriented with △ω(FWHM of apeak in the rocking curve) = 5. 9° . T_c_o of 91 K and J_c of 2. 0 × 10￣3 A/cm￣2(77 K, OT) were obtained.展开更多
Stray currents from DC metro systems intrude into the grounded neutrals of large power transformers,posing a major threat to the differential relay protection of transformer.In this paper,the performance of harmonic b...Stray currents from DC metro systems intrude into the grounded neutrals of large power transformers,posing a major threat to the differential relay protection of transformer.In this paper,the performance of harmonic blocking based differential relay protection considering neutral stray currents(NSCs)from DC metro systems is thoroughly investigated.The findings reveal that relays may fail to clear internal faults in some scenarios because they are blocked due to NSC-induced harmonic currents.To improve the reliability of differential relay protection,a method for preventing incorrect operation is proposed using a skewness-based criterion to detect the presence of NSCs.Then,the relay is unblocked when an internal fault is simultaneously detected by the novel internal fault detection block.The proposed method is resistant to current transformer saturation and accounts for NSC fluctuations.Various time-domain simulations conducted in PSCAD/EMTDC verify the effectiveness of the proposed method.展开更多
The DC bias will lead to maloperation of the second harmonic restraint when entering the power system,which causes the failure of transformer differential protection.Therefore,this paper explores the impact of DC bias...The DC bias will lead to maloperation of the second harmonic restraint when entering the power system,which causes the failure of transformer differential protection.Therefore,this paper explores the impact of DC bias on differential protection and proposes a DC bias detection algorithm based on harmonic components.Firstly,the theoretical mechanism by which DC bias causes transformer differential protection failure is analyzed,exploring the influence of different magnitudes of DC bias and different fault types on differential protection.Subsequently,under the conditions of DC bias or inrush current,this study simulated the root mean square(RMs)value and phase angle characteristics of the second harmonic of transformer differential current,and established a DC bias detection algorithm using two criteria:RMS value identification and phase angle identification.When the algorithm detects DC bias,it will block the second harmonic restraint to ensure the normal operation of differential protection during internal transformer faults.The proposed method is validated through simulations using typical protection failure scenarios,demonstrating its effectiveness in resolving the refusal issue of transformer differential protection under DC bias conditions.展开更多
The longitudinal piezoelectric response of[001]poled rhombohedral and orthorhombic Pb(In_(1/2)Nb_(1/2))O_(3)-Pb(Mg_(1/3)Nb_(2/3))O_(3)-PbTiO_(3)crystals were investigated with respect to DC bias electric field,being i...The longitudinal piezoelectric response of[001]poled rhombohedral and orthorhombic Pb(In_(1/2)Nb_(1/2))O_(3)-Pb(Mg_(1/3)Nb_(2/3))O_(3)-PbTiO_(3)crystals were investigated with respect to DC bias electric field,being in the range of-2-15 kV/cm.For rhombohedral crystals with compo-sitions far away from morphotropic phase boundary(MPB),the piezoelectric response generally decreased with increasing positive DC bias field,while for crystals with MPB compositions,the piezoelectric response firstly decreased and then increased as function of DC bias.The piezo-electric response was found to decrease drastically when DC bias larger than phase transition feld.On the other hand,the piezoelectric response was slightly enhanced for all the crystals as function of negative DC bias prior to the depolarization.To explain the obtained results,the field dependent piezoelectric cofficients in domain engineered crystals were analyzed based on ther-modynamic approach.展开更多
To clarify the electromagnetic,vibration,and loss characteristics of the internal components of a converter transformer under DC bias conditions and their influencing mechanisms,a series of studies are conducted using...To clarify the electromagnetic,vibration,and loss characteristics of the internal components of a converter transformer under DC bias conditions and their influencing mechanisms,a series of studies are conducted using the finite element method and model experiments.This paper quantifies the influence of different DC contents on the magnetic flux density,force,and displacement distribution characteristics of the iron core and winding and analyzes the internal relationship between various indicators.The inflection point of the DC bias coefficient on the vibration is obtained and the contribution mechanism of the different responses of the iron core and winding to this inflection point is explained.The value of the DC bias coefficient for changing the main vibration frequency is determined.When the DC bias coefficient is 1.0 and 1.5,the main frequency of vibration moves to the right to 250 Hz and 350 Hz.Based on the principle of similarity,a DC bias vibration experimental platform for converter transformers is developed,and DC bias magnetic experiments are conducted to verify the reliability of the simulation results.展开更多
Capacitive micromachined ultrasonic transducer(CMUT)technology is a potential candidate to implement an ultrasonic power receiver for implantable medical devices(IMDs)because CMUT technology employs photolithography-b...Capacitive micromachined ultrasonic transducer(CMUT)technology is a potential candidate to implement an ultrasonic power receiver for implantable medical devices(IMDs)because CMUT technology employs photolithography-based microfabrication techniques amenable to miniaturization,integration with electronics,and biocompatibility.Pre-charged CMUTs operating in constant-charge mode eliminate the DC bias and this mode of operation is more suitable for ultrasound power transfer to IMDs.We designed and fabricated a novel pre-charged CMUT structure with a built-in charge storage capacitor.This new configuration features a floating electrode between the upper and lower electrodes.Charges are stored on this floating electrode prior to implantation by directly bringing the floating electrode into contact with the bottom electrode while applying a DC bias between the top and bottom electrodes of the CMUT.After pre-charging the CMUT,the charges are retained without any leakage,as confirmed by occasional measurements over the course of about two years.We have also demonstrated that this device allows operation without a DC bias and can be used as a power receiver in an IMD.In the presented design,the CMUT can be pre-charged at a desired precise charge level.The amount of trapped charge can be controlled by holding the floating electrode in contact with the bottom electrode by applying external ultrasound pressure and simultaneously maintaining a DC bias.The maximum received power was 10.1 mW,corresponding to a received power density of 3.1 mW/mm2,with a 14.5%efficiency.We have achieved an acoustic-toelectrical power conversion efficiency as high as 29.7%at lower input power levels.展开更多
Constant fraction discriminator （CFD） is one of theoretic method which can locate timing point at same fraction of echo pulse in pulsed time-of-flight （TOF） laser rangefinding. In this paper, the theory of CFD met...Constant fraction discriminator （CFD） is one of theoretic method which can locate timing point at same fraction of echo pulse in pulsed time-of-flight （TOF） laser rangefinding. In this paper, the theory of CFD method was analyzed in reality condition. The design, simulation and printed-circuit-board （PCB） performance of CFD circuit were shown. Finally, an over amplified method was introduced, by which the influence of direct-current （DC） bias error could be reduced. The experimental results showed that timing discriminator could set the timing point to a certain point on echo pulse, which did not depend on the amplitude of echo pulse.展开更多
It is now recognized that nanoscale particulate matter(PM)represents a substantial health hazard for our society,including PM from restaurant smoke.In this study,we explored the use of a transient pulsed plasma in con...It is now recognized that nanoscale particulate matter(PM)represents a substantial health hazard for our society,including PM from restaurant smoke.In this study,we explored the use of a transient pulsed plasma in conjunction with an applied DC bias to treat oil aerosols that closely resemble restaurant(i.e.,charbroiler)smoke emissions.For polyaromatic olefin PAO-4 and soybean oil,we found that a three-order-of-magnitude reduction in particulates(i.e.,99.9%remediation)could be achieved with this system.Here,the plasma discharge was produced in a 4-in.-diameter cylindrical reactor with a 5-10 ns high voltage(30 kV)pulse generator together with applied DC bias voltages up to 10 kV.The distribution of nanoparticle sizes was measured using a scanning mobility particle sizer(SMPS)with diameter centered around 225 nm.Here,the main mechanism of remediation occurs in a two-step process in which the oil nanoparticles are first ionized by the free electrons and free radicals in the plasma and then the charged particles are swept out to the sidewalls of the reactor by the applied DC potential.We believe this general approach opens up new degrees of freedom in the design of electrostatic oil aerosol pollution control devices.展开更多
Based on the Gummel-Poon model of BJT, the change of the DC bias as a function of the AC input signal in RF linear power amplifiers is theoretically derived, so that the linearity of different DC bias circuits can be ...Based on the Gummel-Poon model of BJT, the change of the DC bias as a function of the AC input signal in RF linear power amplifiers is theoretically derived, so that the linearity of different DC bias circuits can be interpreted and compared. According to the analysis results, a quantitative adaptive DC bias circuit is proposed, which can improve the linearity and efficiency. From the simulation and test results, we draw conclusions on how to improve the design of linear power amplifier.展开更多
Isolation-dependent applications require a transformer with high efficiency,low magnetizing current,and anti-DC bias capability.The kilohertz planar negative magnetic reluctance structure is used to achieve this targe...Isolation-dependent applications require a transformer with high efficiency,low magnetizing current,and anti-DC bias capability.The kilohertz planar negative magnetic reluctance structure is used to achieve this target with its magnetic-frequency variation property,which reduces the magnetic reluctance of the fundamental component.However,this design cannot be applied to low-frequency transformers owing to the high loss caused by its limited self-inductance and quality factor.To solve this problem,a pole-wrapped negative equivalent magnetic reluctance(PNEMR)structure is presented.The proposed design employed a copper-based PNEMR structure wrapped around the magnetic poles to enhance the fundamental flux and suppress the DC component of flux.Accordingly,the magnetizing current is reduced,and the isolation transformer is less susceptible to the DC bias.The proposed design can simultaneously improve the anti-DC magnetic bias capability,efficiency,and power factor of the transformers.To verify the effectiveness of the proposed design,a 10 kW C-core PNEMR structure-based transformer for isolation-dependent applications was constructed and compared to the generalized structures and transformers with planar negative magnetic reluctance structures.Results indicate that the PNEMR-based transformer can enhance the efficiency and power factor from 96.1%and 0.87 to 96.6%and 0.93,respectively,under full load conditions.展开更多
基金supported by the Key R&D Program of Shandong Province(2021CXGC010210).
文摘Global energy and environmental issues are becoming increasingly problematic,and the vibration and noise problem of 110 kV transformers,which are the most widely distributed,have attracted widespread attention from both inside and outside the industry.DC bias is one of the main contributing factors to vibration noise during the normal operation of transformers.To clarify the vibration and noise mechanism of a 110 kV transformer under a DC bias,a multi-field coupling model of a 110 kV transformer was established using the finite element method.The electromagnetic,vibration,and noise characteristics during the DC bias process were compared and quantified through field circuit coupling in parallel with the power frequency of AC,harmonic,and DC power sources.It was found that a DC bias can cause significant distortions in the magnetic flux density,force,and displacement distributions of the core and winding.The contributions of the DC bias effect to the core and winding are different at Kdc=0.85.At this point,the core approached saturation,and the increase in the core force and displacement slowed.However,the saturation of the core increased the leakage flux,and the stress and displacement of the winding increased faster.The sound field distribution characteristics of the 110 kV transformer under a DC bias are related to the force characteristics.When the DC bias coefficient was 1.25,the noise sound pressure level reached 73.6 dB.
基金Projects(59925513 50323007) supported by the National Natural Science Foundation of China+2 种基金 project(G1999065005) supported by the National Basic Research Program of China project(2003AA305670) supported by the Hi-tech Research and Development Program of China and supported by "Top Hundred Talents Program" of Chinese Academy of Sciences
文摘Carbon nitride films were deposited on Si (100) substrates using plasma-enhanced chemical vapor deposition (PECVD) technique from CH4 and N2 at different applied dc bias voltage. The microstructure, composition and chemical bonding of the resulting films were characterized by Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). The mechanical properties such as hardness and elastic modulus of the films were evaluated using nano-indentation. As the results, the Raman spectra, showing the G and D bands, indicate the amorphous structure of the films. XPS and FTIR measurements demonstrate the existence of various carbon-nitride bonds in the films and the hydrogenation of carbon nitride phase. The composition ratio of N to C, the nano-hardness and the elastic modulus of the carbon nitride films increase with increasing dc bias voltage and reach the maximums at a dc bias voltage of 300 V, then they decrease with further increase of the dc bias voltage. Moreover, the XRD analyses indicate that the carbon nitride film contains some polycrystalline C3N4 phase embedded in the amorphous matrix at optimized deposition condition of dc bias voltage of 300 V.
文摘IEC TS 60076-23,the first IEC standard on DC bias suppression devices approved by IEC/TC 14 in November 2017,is expected to be published and put into force in 2018,overcoming the lack of such IEC standards in the field.The Shanghai branch of SGCC has carried out studies and researches on DC bias effect for more than 10 years,and it has led the standard development based on its R&D and the application of DC bias suppression devices in China.
文摘Effect of direct current negative bias on diamond nucleation in microwave plasma assisted chemical vapor deposition system was discussed. The influence of the magnitude of negative bias value,bias duration and methane concentration in the gas mixture on nucleation density of diamond films was studied respectively. It is demonstrated that direct current negative bias can drastically enhance the diamond nucleation at a suitable value.Long bias duration and high methane concentration are helpful for diamond nucleation.
基金supported in part by the National Natural Science Foundation of China(NSFC)under Project No.51737010the National Key R&D Program of China under Grant 2020YFA0710500。
文摘With the increasing demand for high torque density in motors,more and more new topologies emerge.Furthermore,the magnetic field modulation principle is widely concerned and has evolved into an effective analysis method for studying the new motor topology.This paper introduces the principle of magnetic field modulation.And the research on high torque density in recent years is reviewed from the perspective of magnetic field modulation,including permanent magnet vernier machine(PMVM),flux reverse machine(FRM),flux switching machine(FSM),dual permanent magnet(DPM)machine,and DC biased machine.The principle of magnetic field modulation makes it possible to propose higher torque density topologies in the future.
基金Natural Science Foundation of Beijing,China(Grant No.JQ18015),the National Natural Science Foundation of China(Grant Nos.61935001 and 61905271).
文摘A theoretical model was proposed to describe the effects of external bias electric field on terahertz(THz)generated in air plasma.The model predicted that for a plasma in a bias electric field,the amplification effect of the THz wave intensity increases with the increase of the excitation laser wavelength.We experimentally observed the relationship between the THz enhancement effect and the electric field strength at different wavelengths.Experimental results showed a good agreement with the model predictions.These results enhance our understanding of the physical mechanism by which femtosecond lasers excite air to generate THz and extend the practical applications of THz generation and modulation.
基金Sponsored by National High-tech Research and Development Program(863 Program)of China(2013AA030802)
文摘Fe73. 5 Cu1 Nb3 Si15.5B7 nanocrystalline powder cores with different particle sizes ranging from 10 to 125 9m were fabricated by cold-pressing techniques. The cores exhibited increased core loss P cv and decreased initial permea- bility μi with addition of fine powders below 50 μm in size, and the content should be less than 40 mass%. It was thought to be closely related to the high coercive force H c due to the stresses generated during the crushing process and high demagnetization fields of small powders. Furthermore, modifying the alloy compositions by adding defined amount of Ni could improve the soft magnetic properties, including superior characteristics of permeability under high direct current （DC） bias field and comparable low core loss at high frequency.
文摘Yttria-stabilized zirconia (YSZ) thin films with the c-axis texturing were successfully deposited onpolycrystalline metallic tape (Hastelloy-C) by a dc bias rf magnetron sputtering. X-ray measurements re-vealed that the resulting YSZ films exhibited pure c-axis texturing. YBCO films deposited by using demaguetron sputtering on Hastelloy tape with YSZ buffer layer were c-axis oriented with △ω(FWHM of apeak in the rocking curve) = 5. 9° . T_c_o of 91 K and J_c of 2. 0 × 10￣3 A/cm￣2(77 K, OT) were obtained.
基金supported by National Natural Science Foundation of China(No.U2166212)。
文摘Stray currents from DC metro systems intrude into the grounded neutrals of large power transformers,posing a major threat to the differential relay protection of transformer.In this paper,the performance of harmonic blocking based differential relay protection considering neutral stray currents(NSCs)from DC metro systems is thoroughly investigated.The findings reveal that relays may fail to clear internal faults in some scenarios because they are blocked due to NSC-induced harmonic currents.To improve the reliability of differential relay protection,a method for preventing incorrect operation is proposed using a skewness-based criterion to detect the presence of NSCs.Then,the relay is unblocked when an internal fault is simultaneously detected by the novel internal fault detection block.The proposed method is resistant to current transformer saturation and accounts for NSC fluctuations.Various time-domain simulations conducted in PSCAD/EMTDC verify the effectiveness of the proposed method.
基金supported in part by the National Natural Science Foundation of China(No.51977173)Northwest Branch of State Grid Corporation of China(SGNW0000DKJS2310091).
文摘The DC bias will lead to maloperation of the second harmonic restraint when entering the power system,which causes the failure of transformer differential protection.Therefore,this paper explores the impact of DC bias on differential protection and proposes a DC bias detection algorithm based on harmonic components.Firstly,the theoretical mechanism by which DC bias causes transformer differential protection failure is analyzed,exploring the influence of different magnitudes of DC bias and different fault types on differential protection.Subsequently,under the conditions of DC bias or inrush current,this study simulated the root mean square(RMs)value and phase angle characteristics of the second harmonic of transformer differential current,and established a DC bias detection algorithm using two criteria:RMS value identification and phase angle identification.When the algorithm detects DC bias,it will block the second harmonic restraint to ensure the normal operation of differential protection during internal transformer faults.The proposed method is validated through simulations using typical protection failure scenarios,demonstrating its effectiveness in resolving the refusal issue of transformer differential protection under DC bias conditions.
基金supported by the National Basic Research Program of China(973 Program)under Grant No.2009CB623306International Science and Technology Cooperation Program of China under Grant No.2010DFR50480National Nature Science Foundation of China(Grant Nos.10976022 and 50632030).
文摘The longitudinal piezoelectric response of[001]poled rhombohedral and orthorhombic Pb(In_(1/2)Nb_(1/2))O_(3)-Pb(Mg_(1/3)Nb_(2/3))O_(3)-PbTiO_(3)crystals were investigated with respect to DC bias electric field,being in the range of-2-15 kV/cm.For rhombohedral crystals with compo-sitions far away from morphotropic phase boundary(MPB),the piezoelectric response generally decreased with increasing positive DC bias field,while for crystals with MPB compositions,the piezoelectric response firstly decreased and then increased as function of DC bias.The piezo-electric response was found to decrease drastically when DC bias larger than phase transition feld.On the other hand,the piezoelectric response was slightly enhanced for all the crystals as function of negative DC bias prior to the depolarization.To explain the obtained results,the field dependent piezoelectric cofficients in domain engineered crystals were analyzed based on ther-modynamic approach.
基金supported by the Key R&D Program of Shandong Province(No.2021CXGC010210).
文摘To clarify the electromagnetic,vibration,and loss characteristics of the internal components of a converter transformer under DC bias conditions and their influencing mechanisms,a series of studies are conducted using the finite element method and model experiments.This paper quantifies the influence of different DC contents on the magnetic flux density,force,and displacement distribution characteristics of the iron core and winding and analyzes the internal relationship between various indicators.The inflection point of the DC bias coefficient on the vibration is obtained and the contribution mechanism of the different responses of the iron core and winding to this inflection point is explained.The value of the DC bias coefficient for changing the main vibration frequency is determined.When the DC bias coefficient is 1.0 and 1.5,the main frequency of vibration moves to the right to 250 Hz and 350 Hz.Based on the principle of similarity,a DC bias vibration experimental platform for converter transformers is developed,and DC bias magnetic experiments are conducted to verify the reliability of the simulation results.
基金supported by the NSF under Grant 1160483 as part of a Centreto-Center collaborative partnership with NUI Galway,Ireland and Queen’s University,Belfast,Northern Irelandperformed in part at the NCSU Nanofabrication Facility(NNF),and Duke University Shared Materials Instrumentation Facility(SMIF),all of which are members of the North Carolina Research Triangle Nanotechnology Network(RTNN)which is supported by the National Science Foundation(Grant ECCS-2025064)as part of the National Nanotechnology Coordinated Infrastructure(NNCI).
文摘Capacitive micromachined ultrasonic transducer(CMUT)technology is a potential candidate to implement an ultrasonic power receiver for implantable medical devices(IMDs)because CMUT technology employs photolithography-based microfabrication techniques amenable to miniaturization,integration with electronics,and biocompatibility.Pre-charged CMUTs operating in constant-charge mode eliminate the DC bias and this mode of operation is more suitable for ultrasound power transfer to IMDs.We designed and fabricated a novel pre-charged CMUT structure with a built-in charge storage capacitor.This new configuration features a floating electrode between the upper and lower electrodes.Charges are stored on this floating electrode prior to implantation by directly bringing the floating electrode into contact with the bottom electrode while applying a DC bias between the top and bottom electrodes of the CMUT.After pre-charging the CMUT,the charges are retained without any leakage,as confirmed by occasional measurements over the course of about two years.We have also demonstrated that this device allows operation without a DC bias and can be used as a power receiver in an IMD.In the presented design,the CMUT can be pre-charged at a desired precise charge level.The amount of trapped charge can be controlled by holding the floating electrode in contact with the bottom electrode by applying external ultrasound pressure and simultaneously maintaining a DC bias.The maximum received power was 10.1 mW,corresponding to a received power density of 3.1 mW/mm2,with a 14.5%efficiency.We have achieved an acoustic-toelectrical power conversion efficiency as high as 29.7%at lower input power levels.
基金This work was sponsored by the National Natural Science Foundation of China （Grant No. 40801123）.
文摘Constant fraction discriminator （CFD） is one of theoretic method which can locate timing point at same fraction of echo pulse in pulsed time-of-flight （TOF） laser rangefinding. In this paper, the theory of CFD method was analyzed in reality condition. The design, simulation and printed-circuit-board （PCB） performance of CFD circuit were shown. Finally, an over amplified method was introduced, by which the influence of direct-current （DC） bias error could be reduced. The experimental results showed that timing discriminator could set the timing point to a certain point on echo pulse, which did not depend on the amplitude of echo pulse.
文摘It is now recognized that nanoscale particulate matter(PM)represents a substantial health hazard for our society,including PM from restaurant smoke.In this study,we explored the use of a transient pulsed plasma in conjunction with an applied DC bias to treat oil aerosols that closely resemble restaurant(i.e.,charbroiler)smoke emissions.For polyaromatic olefin PAO-4 and soybean oil,we found that a three-order-of-magnitude reduction in particulates(i.e.,99.9%remediation)could be achieved with this system.Here,the plasma discharge was produced in a 4-in.-diameter cylindrical reactor with a 5-10 ns high voltage(30 kV)pulse generator together with applied DC bias voltages up to 10 kV.The distribution of nanoparticle sizes was measured using a scanning mobility particle sizer(SMPS)with diameter centered around 225 nm.Here,the main mechanism of remediation occurs in a two-step process in which the oil nanoparticles are first ionized by the free electrons and free radicals in the plasma and then the charged particles are swept out to the sidewalls of the reactor by the applied DC potential.We believe this general approach opens up new degrees of freedom in the design of electrostatic oil aerosol pollution control devices.
文摘Based on the Gummel-Poon model of BJT, the change of the DC bias as a function of the AC input signal in RF linear power amplifiers is theoretically derived, so that the linearity of different DC bias circuits can be interpreted and compared. According to the analysis results, a quantitative adaptive DC bias circuit is proposed, which can improve the linearity and efficiency. From the simulation and test results, we draw conclusions on how to improve the design of linear power amplifier.
基金Supported by the Research Grant Council of the Hong Kong SAR Government under projects PolyU PolyU152180/19E.
文摘Isolation-dependent applications require a transformer with high efficiency,low magnetizing current,and anti-DC bias capability.The kilohertz planar negative magnetic reluctance structure is used to achieve this target with its magnetic-frequency variation property,which reduces the magnetic reluctance of the fundamental component.However,this design cannot be applied to low-frequency transformers owing to the high loss caused by its limited self-inductance and quality factor.To solve this problem,a pole-wrapped negative equivalent magnetic reluctance(PNEMR)structure is presented.The proposed design employed a copper-based PNEMR structure wrapped around the magnetic poles to enhance the fundamental flux and suppress the DC component of flux.Accordingly,the magnetizing current is reduced,and the isolation transformer is less susceptible to the DC bias.The proposed design can simultaneously improve the anti-DC magnetic bias capability,efficiency,and power factor of the transformers.To verify the effectiveness of the proposed design,a 10 kW C-core PNEMR structure-based transformer for isolation-dependent applications was constructed and compared to the generalized structures and transformers with planar negative magnetic reluctance structures.Results indicate that the PNEMR-based transformer can enhance the efficiency and power factor from 96.1%and 0.87 to 96.6%and 0.93,respectively,under full load conditions.
