We report the design of three frequency selective surface （FSS） filters used on the FengYun-4 （FY-4） microwave satellite, which separate five-frequency bands in the frequency range of 50-429 GHz with the insertion...We report the design of three frequency selective surface （FSS） filters used on the FengYun-4 （FY-4） microwave satellite, which separate five-frequency bands in the frequency range of 50-429 GHz with the insertion loss less than 0.4 dB, and separation between adjacent channels more than 20 dB for either TE or TM incidence. Firstly, we briefly introduce the disadvantages of two types of FSS filter： waveguide-array FSS and printed FSS, which are commonly employed in the millimeter and sub-millimeter wave band. In order to meet the insertion loss requirement and specified spectral transmission response, we adopt a filter composed of two closely spaced freestanding metal plates, which con- tains an array of resonant ring slot elements. Computer simulation technology （CST） is used to optimize the structural dimensions of the resonant unit and interlayer separation. Numerical results show that these FSS filters exhibit trans- mission loss of less than 0.4 dB and separation between adjacent channels of more than 20 dB. Simulated transmission coefficients are in close agreement with the required specification, and even exceed the performance specifications.展开更多
In conventional High Power Microwave(HPM)waveguide arrays of longitudinal shunt slots,the mutual coupling of slots in different waveguide can badly decrease the capability of wide-angle scanning of array.For this reas...In conventional High Power Microwave(HPM)waveguide arrays of longitudinal shunt slots,the mutual coupling of slots in different waveguide can badly decrease the capability of wide-angle scanning of array.For this reason,an L-band HPM waveguide array of longitudinal shunt slots was designed.The choke groove was adopted to restrain the mutual coupling of slots of the HPM array antenna.The results of simulation are:the scanning angle of array without choke groove structure with the gain of antenna decreased 3 dB is only 24.7°,and it is 33.0°for array with choke groove structure;the wideband of active reflection of array have been improved with choke groove structure,the bandwidth of VSWR≤3 of array with choke groove is 6.6%,and that is 5.0%without choke groove;the power-handling capacity of array antenna with scanning angle of 35°can reach 957 MW,which is a little less than that of array without scanning(1008MW).展开更多
Based on the hot electron effect in a semiconductor, an overmoded resistive sensor for 0.3-0.4 THz band is investi-gated. The distribution of electromagnetic field components, voltage standing wave ratio （VSWR）, and...Based on the hot electron effect in a semiconductor, an overmoded resistive sensor for 0.3-0.4 THz band is investi-gated. The distribution of electromagnetic field components, voltage standing wave ratio （VSWR）, and the average electric field in the silicon block are obtained by using the three-dimensional finite-difference time-domain （FDTD） method. By adjusting several factors （such as the length, width, height and specific resistance of the silicon block） a novel sensor with optimal structural parameters that can be used as a power measurement device for high power terahertz pulse directly is proposed. The results show that the sensor has a relative sensitivity of about 0.24 kW 1, with a fluctuation of relative sensitivity of no more than ±22%, and the maximum of VSWR is 2.74 for 0.3-0.4 THz band.展开更多
Based on the concepts of fast polarization, effective electric field and electron impact ionization criterion, the effect of polymer type on electric breakdown strength （EBD） on a nanosecond time scale is investigat...Based on the concepts of fast polarization, effective electric field and electron impact ionization criterion, the effect of polymer type on electric breakdown strength （EBD） on a nanosecond time scale is investigated, and a formula that qualitatively characterizes the relation between the electric breakdown strength and the polymer type is derived. According to this formula, it is found that the electric breakdown strength decreases with an increase in the effective relative dielectric constants of the polymers. By calculating the effective relative dielectric constants for different types of polymers, the theoretical relation for the electric breakdown strengths of common polymers is predicted. To verify the prediction, the polymers of PE （polyethylene）, PTFE （polytetrafluoroethelene）, PMMA （organic glass） and Nylon are tested with a nanosecond-pulse generator. The experimental result shows EBD （PTFE） 〉 EBD （PMMA） 〉 EBD （Nylon） 〉 EBD （PE）. This result is consistent with the theoretical prediction.展开更多
The airborne cross-track three apertures MilliMeter Wave (MMW) Synthetic Aperture Radar (SAR) side-looking three-Dimensional (3D) imaging is investigated in this paper. Three apertures are distributed along the cross-...The airborne cross-track three apertures MilliMeter Wave (MMW) Synthetic Aperture Radar (SAR) side-looking three-Dimensional (3D) imaging is investigated in this paper. Three apertures are distributed along the cross-track direction, and three virtual phase centers will be obtained through one-input and three-output. These three virtual phase centers form a sparse array which can be used to obtain the cross-track resolution. Because the cross-track array is short, the cross-track resolution is low. When the system works in side-looking mode, the cross-track resolution and height resolution will be coupling, and the low cross-track resolution will partly be transformed into the height uncertainty. The beam pattern of the real aperture is used as a weight to improve the Peak to SideLobe Ratio (PSLR) and Integrated SideLobe Ratio (ISLR) of the cross-track sparse array. In order to suppress the high cross-track sidelobes, a weighting preprocessing method is proposed. The 3D images of a point target and a simulation scene are achieved to verify the feasibility of the proposed method. And the imaging result of the real data obtained by the cross-track three-baseline MMW InSAR prototype is presented as a beneficial attempt.展开更多
The nanocrystalline samarium substituted Co-Zn ferrites with chemical formula Co0.7Zn0.3SmyFe2-yO4(where y=0,0.01,0.02,0.03,0.04) were synthesized by sol-gel autocombustion route.The analysis of Xray diffractograms(XR...The nanocrystalline samarium substituted Co-Zn ferrites with chemical formula Co0.7Zn0.3SmyFe2-yO4(where y=0,0.01,0.02,0.03,0.04) were synthesized by sol-gel autocombustion route.The analysis of Xray diffractograms(XRD) reveals the formation of cubic spinel structure.The planes indexed from XRD analyses were confirmed in the selected area electron diffraction(SAED) image of the sample.Nanocrystalline nature of the particles in the ferrite samples was confirmed by TEM.The morphology was analyzed by scanning electron microscopy(SEM).Magnetic measurements show an increase in the magnetization for x ≤0.03.The decrease in magnetization due to spin canting is observed for x=0.04.The coercivity depends on Sm3+doping concentration,grain size and saturation magnetization.The complex permeability of the ferrites was analyzed as the function of frequency and Sm3+composition(y).The real part of complex permeability varies linearly with the grain size.展开更多
By investigating the interaction of an n-type silicon sample with the TM01 mode millimeter wave in a circular waveguide, a viable high-power TM01 millimeter wave sensor is proposed. Based on the hot electron effect, t...By investigating the interaction of an n-type silicon sample with the TM01 mode millimeter wave in a circular waveguide, a viable high-power TM01 millimeter wave sensor is proposed. Based on the hot electron effect, the silicon sample serving as a sensing element（SE） and appropriately mounted on the inner wall of the circular waveguide is devoted to the on-line measurement of a high-power millimeter wave pulse. A three-dimensional parallel finite-difference time-domain method is applied to simulate the wave propagation within the measuring structure. The transverse electric field distribution, the dependences of the frequency response of the voltage standing-wave ratio（VSWR） in the circular waveguide, and the average electric field amplitude within the SE on the electrophysical parameters of the SE are calculated and analyzed in the frequency range of 300–400 GHz. As a result, the optimal dimensions and specific resistance of the SE are obtained,which provide a VSWR of no more than 2.0, a relative sensitivity around 0.0046 kW-1 fluctuating within ±17.3%, and a maximum enduring power of about 4.3 MW.展开更多
A megawatt-level subterahertz surface wave oscillator （SWO） is proposed to obtain high conversion efficiency by using separated overmoded slow wave structures （SWSs）. Aiming at the repetitive operation and practic...A megawatt-level subterahertz surface wave oscillator （SWO） is proposed to obtain high conversion efficiency by using separated overmoded slow wave structures （SWSs）. Aiming at the repetitive operation and practical applications, the device driven by electron beam with modest energy and current is theoretically analyzed and verified. Then, the functions of the two SWS sections and the effect of the drift tube are investigated by using a particle-in-cell code to reveal how the proposed device achieves high efficiency. The mode analysis of the beam-wave interaction region in the device is also carded out, and the results indicate that multi-modes participate in the premodulation of the electron beam in the first SWS section, while the TM01 mode surface wave is successfully and dominantly excited and amplified in the second SWS section. Finally, a typical simulation result demonstrates that at a beam energy of 313 keV, beam current of 1.13 kA, and guiding magnetic field of above 3.5 T, a high-power subterahertz wave is obtained with an output power of about 70 MW at frequency 146.3 GHz, corresponding to the conversion efficiency of 20%. Compared with the results of the previous subterahertz overmoded SWOs with integral SWS and similar beam parameters, the efficiency increases almost 50% in the proposed device.展开更多
Plasma immersion ion implantation （PI） overcomes the direct exposure limit of traditional beam- line ion implantation, and is suitable for the treatment of complex work-piece with large size. Pm technology is often ...Plasma immersion ion implantation （PI） overcomes the direct exposure limit of traditional beam- line ion implantation, and is suitable for the treatment of complex work-piece with large size. Pm technology is often used for surface modification of metal, plastics and ceramics. Based on the requirement of surface modification of large size insulating material, a composite full-directional PHI device based on RF plasma source and metal plasma source is developed in this paper. This device can not only realize gas ion implantation, but also can realize metal ion implantation, and can also realize gas ion mixing with metal ions injection. This device has two metal plasma sources and each metal source contains three cathodes. Under the condition of keeping the vacuum unchanged, the cathode can be switched freely. The volume of the vacuum chamber is about 0.94 m3, and maximum vacuum degree is about 5 x10-4 Pa. The density of RF plasma in homogeneous region is about 109 cm-3, and plasma density in the ion implantation region is about 101x cm-3. This device can be used for large-size sample material PHI treatment, the maximum size of the sample diameter up to 400 mm. The experimental results show that the plasma discharge in the device is stable and can run for a long time. It is suitable for surface treatment of insulating materials.展开更多
A sub-nanosecond pulse discharge tube is a gas discharge tube which can generate a rapid high-voltage pulse of kilo-volts in amplitude and sub-nanoseconds in width. In this paper, the sub-nanosecond pulse discharge tu...A sub-nanosecond pulse discharge tube is a gas discharge tube which can generate a rapid high-voltage pulse of kilo-volts in amplitude and sub-nanoseconds in width. In this paper, the sub-nanosecond pulse discharge tube and its working principles are described. Because of the phenomenon that the deformation process of the mercury film on the electrode surface lags behind the charging process, the mercury film deformation process affects the dynamic breakdown voltage of the tube directly. The deformation of the mercury film is observed microscopically, and the dynamic breakdown voltage of the tube is messured using an oscillograph. The results show that all the parameters in the charging process, such as charging resistance, charging capacitance and DC power supply, affect the dynamic breakdown voltage of the tube. Based on these studies, the output pulse amplitude can be controlled continuously and individually by adjusting the power supply voltage. When the DC power supply is adjusted from 7 kV to 10 kV, the dynamic breakdown voltage ranges from 6.5 kV to 10 kV. According to our research, a kind of sub-nanosecond pulse generator is made, with a pulse width ranging from 0.5 ns to 2.5 ns, a rise time from 0.32 ns to 0.58 ns, and a pulse amplitude that is adjustable from 1.5 kV to 5 kV.展开更多
The time-dependence evolution of the extinction spectra of the silver nanoplates is studied to analyze the underlying physical mechanism of the growth process. As the synthesis cycles increase, the wavelength of the a...The time-dependence evolution of the extinction spectra of the silver nanoplates is studied to analyze the underlying physical mechanism of the growth process. As the synthesis cycles increase, the wavelength of the absorption peak is first blue-shifted and then is followed by the red shift, attributing to the mode alteration of the longitudinal surface plasmon resonance of the silver nanoplates. The capping agents are also optimized for the convenient and speedy growth of the large integrated Ag nanostructure. These observations expand the comprehensive understanding of plasmon resonance of the Ag nanoplates, and give a better manipulation of their applications in the plasmonie nanodevices.展开更多
This paper proposes a quasi-static conformal mapping analysis to analytically evaluate the input resistance of Archimedean spiral antenna at its radiation region. The deviation from the original constructs of band the...This paper proposes a quasi-static conformal mapping analysis to analytically evaluate the input resistance of Archimedean spiral antenna at its radiation region. The deviation from the original constructs of band theory for two-wire spiral antennas leads to the concept of common slot-line mode radiation. The per-unit-length capacitance and the characteristic impedance of the quasi-TEM fundamental propagating mode in periodic coplanar waveguide (PCPW) structure are obtained in terms of spiral parameters including substrate properties. This formula enables little computational effort on the computation of input resistance at the radiation mode of balanced-excited two-arm Archimedean spiral antennas. The numerical simulation demonstrates the accuracy of derived formulas both in free space and when a dielectric layer is presented.展开更多
The sub-micron（of the order of 150 nm） thick core–shell composite fibers of magnesium ferrite-polyvinylidene fluoride are prepared by electrospinning.The loading of magnesium ferrite is varied from 1 to 10 wt%.The ...The sub-micron（of the order of 150 nm） thick core–shell composite fibers of magnesium ferrite-polyvinylidene fluoride are prepared by electrospinning.The loading of magnesium ferrite is varied from 1 to 10 wt%.The study results by X-ray diffraction,scanning electron microscope,and infra-red spectroscopy indicate the formation of core–shell structure and an enhancement in the amount of b-phase compared to a-phase in the polyvinylidene fluoride.The particle size of the magnesium ferrite in the fiber is evaluated to be 30 nm.The low frequency dielectric studies indicate that the addition of the magnesium ferrite increases the polarization resulting in the increase in the dielectric constant but decreases the dielectric loss.The magnetization measurements indicate an increased value of coercivity compared to bulk due to the nano-size of the magnesium ferrite.The microwave absorption at the ferromagnetic resonance increases with the increase in the concentration of magnesium ferrite.The resonance field is found to vary with the loading of MFO.展开更多
With ever-increasing operating frequencies and complicated artificial structures, loss effects become more and more important in applications of metamaterials. Based on circuit theory and transmission line principle, ...With ever-increasing operating frequencies and complicated artificial structures, loss effects become more and more important in applications of metamaterials. Based on circuit theory and transmission line principle, the design equations for effective electromagnetic (EM) parameters (attenuation constant α, phase constant β, characteristic impedance Z0) of general active and passive metamaterial are compared and derived from the equivalent lumped circuit parameters (R, G, LL, CL, LR, CR). To verify the design equations, theα, βand Z0 indifferent cases, including balanced, unbalanced, lossless, passive and active, are shown by numerical simulations. The results show that using the active method can diminish the loss effects. Meantime, it also has influence on phase constant and real part of characteristic impedance.展开更多
Formation of a quasi-stationary discharge or quasi-stationary emission mode in the explosive-emission electron sources is related to the current limitation resulting from the emissive ability saturation of cathode pla...Formation of a quasi-stationary discharge or quasi-stationary emission mode in the explosive-emission electron sources is related to the current limitation resulting from the emissive ability saturation of cathode plasma with its expansion. The paper shows that in the process of the discharge current stabilization in the explosive-emission sources with the point- or blade-type emitters the essential role belongs to the electron beam space charge. Availability of the space charge results in limitation of the current growth velocity at the initial discharge phase and, hence, restricts the emissive ability of the cathode plasma and contributes to its saturation. In the vacuum diodes with multiemitter cathodes, the space charge availability increases the cathode operation stability and can provide obtaining of quasi-stationary beam current values or close to them resulting in formation of a plasma emission surface at the cathode close to the continuous one.展开更多
Breakdown formation in the explosive-emission sources is related to the interelectrode gap filling with the cathode and anode plasma generated at the anode and in the gap under the beam influence. Under conditions of ...Breakdown formation in the explosive-emission sources is related to the interelectrode gap filling with the cathode and anode plasma generated at the anode and in the gap under the beam influence. Under conditions of saturation of the cathode plasma emissive ability as well as when the measures on the emission boundary stabilization are taken, the anode plasma has the deciding part in the formation of the electron source breakdown. The paper presents the results of the anode plasma investigations obtained to solve the problem of the electron beam length increase in the explosive-emission sources. The data concerning the gas release from the anode, the mechanism of the anode plasma formation and the anode plasma influence on the parameters of the generated electron beam are presented as well.展开更多
Breakdown formation in an explosive-emission electron source is related to the interelectrode gap filling with plasma propagating from the cathode and formed at the anode and in the interelectrode gap under the electr...Breakdown formation in an explosive-emission electron source is related to the interelectrode gap filling with plasma propagating from the cathode and formed at the anode and in the interelectrode gap under the electron beam action. Plasma anode is used to increase the beam current density. Preliminary interelectrode gap filling with plasma in the explosive-emission source decreases the influence of uncontrolled plasma arrival from the anode on the diode processes, promotes current density increase and duration of generated electron beams. The paper considers the influence of the cathode geometry on the breakdown formation in the plasma-anode explosive-emission electron source. The data on obtaining of microsecond electron beams with current density of 30 A/cm^2 and 1.5-2 kA/cm^2 are presented.展开更多
Quasistationary discharge mode setting in the explosive-emission sources is related to the saturation of the cathode plasma emissive ability resulting in the decrease of the velocity of plasma propagation into the int...Quasistationary discharge mode setting in the explosive-emission sources is related to the saturation of the cathode plasma emissive ability resulting in the decrease of the velocity of plasma propagation into the interelectrode gap. It was shoran previously that the electron beam space charge providing the current rise slowing-down is of great importance in the process of the discharge mode stabilization. The paper considers a possibility of the discharge protraction at the expense of decrease of the ion charge order in the plasma composition and application of the directed plasma flows. The data concerning obtainig of micro- and millisecond electron beams in the explosive-emission sources are presented as well.展开更多
Investigations are directed to the development of high-power sources ofUWB （ultrawideband） radiation based on excitation of anterma arrays with bipolar voltage pulses. In the previously designed high-power UWB sourc...Investigations are directed to the development of high-power sources ofUWB （ultrawideband） radiation based on excitation of anterma arrays with bipolar voltage pulses. In the previously designed high-power UWB sources only one bipolar pulse former and different feeder systems for pulse distribution through the array elements were used. By means of this approach, a number of UWB sources were created with the bipolar voltage pulse length ranging from 0.2 to 2 ns and effective potential of radiation ranging from 0.4 to 3 MV. The approach has got a restriction related to the electrical breakdown in a bipolar voltage pulse former. A new approach to the creation of high-power UWB sources based on a multicharmel bipolar pulse former is suggested： the number of bipolar pulse formers is equal to the number of antennas in the array. The main problem in realization of this approach is a stable operation of bipolar pulse formers in order to ensure a coherent summation of radiated pulses in the far-field zone. The result of this work is the instability of-150 ps at the pulse length of 3 ns obtained in a one-channel bipolar pulse former indicating that the suggested approach is realizable.展开更多
Dielectric studies were carried out on a lead free Sodium Bismuth Titanate,NBT,(Na_(0.5)Bi_(0.5)TiO_(3))composition.The material was synthesized by conventional ceramic method(CS)and microwave sintering(MS).The presen...Dielectric studies were carried out on a lead free Sodium Bismuth Titanate,NBT,(Na_(0.5)Bi_(0.5)TiO_(3))composition.The material was synthesized by conventional ceramic method(CS)and microwave sintering(MS).The presence of single phase has been confirmed by X-ray diffraction and scanning electron microscopy of NBT ceramic.The later technique(MS)resulted in material with high density,dielectric properties and improved microstructure.The transition temperature was observed slightly higher for microwave sintered(MS)material.Longitudinal modulus measurements are very sensitive property to identify the phase transitions in ceramics.Longitudinal modulus(L)measurements were also employed on these samples in the frequency 136 kHz and can be studied in the wide temperature range 30℃to 400℃.The elastic behavior(L)showed a break at two temperatures(~200℃and 350℃)in both the conventional and microwave sintered ceramics.In NBT ceramics,permittivity anomalies are connected to modulus anomalies.The results are correlated with the dielectric measurements.This behavior explained in the light of structural phase transitions in the ferroelectric ceramics.展开更多
文摘We report the design of three frequency selective surface （FSS） filters used on the FengYun-4 （FY-4） microwave satellite, which separate five-frequency bands in the frequency range of 50-429 GHz with the insertion loss less than 0.4 dB, and separation between adjacent channels more than 20 dB for either TE or TM incidence. Firstly, we briefly introduce the disadvantages of two types of FSS filter： waveguide-array FSS and printed FSS, which are commonly employed in the millimeter and sub-millimeter wave band. In order to meet the insertion loss requirement and specified spectral transmission response, we adopt a filter composed of two closely spaced freestanding metal plates, which con- tains an array of resonant ring slot elements. Computer simulation technology （CST） is used to optimize the structural dimensions of the resonant unit and interlayer separation. Numerical results show that these FSS filters exhibit trans- mission loss of less than 0.4 dB and separation between adjacent channels of more than 20 dB. Simulated transmission coefficients are in close agreement with the required specification, and even exceed the performance specifications.
文摘In conventional High Power Microwave(HPM)waveguide arrays of longitudinal shunt slots,the mutual coupling of slots in different waveguide can badly decrease the capability of wide-angle scanning of array.For this reason,an L-band HPM waveguide array of longitudinal shunt slots was designed.The choke groove was adopted to restrain the mutual coupling of slots of the HPM array antenna.The results of simulation are:the scanning angle of array without choke groove structure with the gain of antenna decreased 3 dB is only 24.7°,and it is 33.0°for array with choke groove structure;the wideband of active reflection of array have been improved with choke groove structure,the bandwidth of VSWR≤3 of array with choke groove is 6.6%,and that is 5.0%without choke groove;the power-handling capacity of array antenna with scanning angle of 35°can reach 957 MW,which is a little less than that of array without scanning(1008MW).
基金Project supported by the National Natural Science Foundation of China(Grant No.61231003)
文摘Based on the hot electron effect in a semiconductor, an overmoded resistive sensor for 0.3-0.4 THz band is investi-gated. The distribution of electromagnetic field components, voltage standing wave ratio （VSWR）, and the average electric field in the silicon block are obtained by using the three-dimensional finite-difference time-domain （FDTD） method. By adjusting several factors （such as the length, width, height and specific resistance of the silicon block） a novel sensor with optimal structural parameters that can be used as a power measurement device for high power terahertz pulse directly is proposed. The results show that the sensor has a relative sensitivity of about 0.24 kW 1, with a fluctuation of relative sensitivity of no more than ±22%, and the maximum of VSWR is 2.74 for 0.3-0.4 THz band.
文摘Based on the concepts of fast polarization, effective electric field and electron impact ionization criterion, the effect of polymer type on electric breakdown strength （EBD） on a nanosecond time scale is investigated, and a formula that qualitatively characterizes the relation between the electric breakdown strength and the polymer type is derived. According to this formula, it is found that the electric breakdown strength decreases with an increase in the effective relative dielectric constants of the polymers. By calculating the effective relative dielectric constants for different types of polymers, the theoretical relation for the electric breakdown strengths of common polymers is predicted. To verify the prediction, the polymers of PE （polyethylene）, PTFE （polytetrafluoroethelene）, PMMA （organic glass） and Nylon are tested with a nanosecond-pulse generator. The experimental result shows EBD （PTFE） 〉 EBD （PMMA） 〉 EBD （Nylon） 〉 EBD （PE）. This result is consistent with the theoretical prediction.
基金Supported by the National Basic Research Program (973) of China (No. 2009CB72400)
文摘The airborne cross-track three apertures MilliMeter Wave (MMW) Synthetic Aperture Radar (SAR) side-looking three-Dimensional (3D) imaging is investigated in this paper. Three apertures are distributed along the cross-track direction, and three virtual phase centers will be obtained through one-input and three-output. These three virtual phase centers form a sparse array which can be used to obtain the cross-track resolution. Because the cross-track array is short, the cross-track resolution is low. When the system works in side-looking mode, the cross-track resolution and height resolution will be coupling, and the low cross-track resolution will partly be transformed into the height uncertainty. The beam pattern of the real aperture is used as a weight to improve the Peak to SideLobe Ratio (PSLR) and Integrated SideLobe Ratio (ISLR) of the cross-track sparse array. In order to suppress the high cross-track sidelobes, a weighting preprocessing method is proposed. The 3D images of a point target and a simulation scene are achieved to verify the feasibility of the proposed method. And the imaging result of the real data obtained by the cross-track three-baseline MMW InSAR prototype is presented as a beneficial attempt.
基金Project supported by the Minor Research Project sanctioned by the supported by the Dnyanopasak Shikshan Mandal’s Arts,Commerce and Science College,Jintur,431509,Maharashtra,India (47-766/13)。
文摘The nanocrystalline samarium substituted Co-Zn ferrites with chemical formula Co0.7Zn0.3SmyFe2-yO4(where y=0,0.01,0.02,0.03,0.04) were synthesized by sol-gel autocombustion route.The analysis of Xray diffractograms(XRD) reveals the formation of cubic spinel structure.The planes indexed from XRD analyses were confirmed in the selected area electron diffraction(SAED) image of the sample.Nanocrystalline nature of the particles in the ferrite samples was confirmed by TEM.The morphology was analyzed by scanning electron microscopy(SEM).Magnetic measurements show an increase in the magnetization for x ≤0.03.The decrease in magnetization due to spin canting is observed for x=0.04.The coercivity depends on Sm3+doping concentration,grain size and saturation magnetization.The complex permeability of the ferrites was analyzed as the function of frequency and Sm3+composition(y).The real part of complex permeability varies linearly with the grain size.
基金Project supported by the National Natural Science Foundation of China(Grant No.61231003)
文摘By investigating the interaction of an n-type silicon sample with the TM01 mode millimeter wave in a circular waveguide, a viable high-power TM01 millimeter wave sensor is proposed. Based on the hot electron effect, the silicon sample serving as a sensing element（SE） and appropriately mounted on the inner wall of the circular waveguide is devoted to the on-line measurement of a high-power millimeter wave pulse. A three-dimensional parallel finite-difference time-domain method is applied to simulate the wave propagation within the measuring structure. The transverse electric field distribution, the dependences of the frequency response of the voltage standing-wave ratio（VSWR） in the circular waveguide, and the average electric field amplitude within the SE on the electrophysical parameters of the SE are calculated and analyzed in the frequency range of 300–400 GHz. As a result, the optimal dimensions and specific resistance of the SE are obtained,which provide a VSWR of no more than 2.0, a relative sensitivity around 0.0046 kW-1 fluctuating within ±17.3%, and a maximum enduring power of about 4.3 MW.
基金Project supported by the National Natural Science Foundation of China(Grant No.61231003)
文摘A megawatt-level subterahertz surface wave oscillator （SWO） is proposed to obtain high conversion efficiency by using separated overmoded slow wave structures （SWSs）. Aiming at the repetitive operation and practical applications, the device driven by electron beam with modest energy and current is theoretically analyzed and verified. Then, the functions of the two SWS sections and the effect of the drift tube are investigated by using a particle-in-cell code to reveal how the proposed device achieves high efficiency. The mode analysis of the beam-wave interaction region in the device is also carded out, and the results indicate that multi-modes participate in the premodulation of the electron beam in the first SWS section, while the TM01 mode surface wave is successfully and dominantly excited and amplified in the second SWS section. Finally, a typical simulation result demonstrates that at a beam energy of 313 keV, beam current of 1.13 kA, and guiding magnetic field of above 3.5 T, a high-power subterahertz wave is obtained with an output power of about 70 MW at frequency 146.3 GHz, corresponding to the conversion efficiency of 20%. Compared with the results of the previous subterahertz overmoded SWOs with integral SWS and similar beam parameters, the efficiency increases almost 50% in the proposed device.
文摘Plasma immersion ion implantation （PI） overcomes the direct exposure limit of traditional beam- line ion implantation, and is suitable for the treatment of complex work-piece with large size. Pm technology is often used for surface modification of metal, plastics and ceramics. Based on the requirement of surface modification of large size insulating material, a composite full-directional PHI device based on RF plasma source and metal plasma source is developed in this paper. This device can not only realize gas ion implantation, but also can realize metal ion implantation, and can also realize gas ion mixing with metal ions injection. This device has two metal plasma sources and each metal source contains three cathodes. Under the condition of keeping the vacuum unchanged, the cathode can be switched freely. The volume of the vacuum chamber is about 0.94 m3, and maximum vacuum degree is about 5 x10-4 Pa. The density of RF plasma in homogeneous region is about 109 cm-3, and plasma density in the ion implantation region is about 101x cm-3. This device can be used for large-size sample material PHI treatment, the maximum size of the sample diameter up to 400 mm. The experimental results show that the plasma discharge in the device is stable and can run for a long time. It is suitable for surface treatment of insulating materials.
基金supported by the National Key Laboratory Foundation of China (No.9140C530103110C5301)
文摘A sub-nanosecond pulse discharge tube is a gas discharge tube which can generate a rapid high-voltage pulse of kilo-volts in amplitude and sub-nanoseconds in width. In this paper, the sub-nanosecond pulse discharge tube and its working principles are described. Because of the phenomenon that the deformation process of the mercury film on the electrode surface lags behind the charging process, the mercury film deformation process affects the dynamic breakdown voltage of the tube directly. The deformation of the mercury film is observed microscopically, and the dynamic breakdown voltage of the tube is messured using an oscillograph. The results show that all the parameters in the charging process, such as charging resistance, charging capacitance and DC power supply, affect the dynamic breakdown voltage of the tube. Based on these studies, the output pulse amplitude can be controlled continuously and individually by adjusting the power supply voltage. When the DC power supply is adjusted from 7 kV to 10 kV, the dynamic breakdown voltage ranges from 6.5 kV to 10 kV. According to our research, a kind of sub-nanosecond pulse generator is made, with a pulse width ranging from 0.5 ns to 2.5 ns, a rise time from 0.32 ns to 0.58 ns, and a pulse amplitude that is adjustable from 1.5 kV to 5 kV.
基金Supported by the Natural Science Foundation of Hubei Province under Grant No 2014CFB554
文摘The time-dependence evolution of the extinction spectra of the silver nanoplates is studied to analyze the underlying physical mechanism of the growth process. As the synthesis cycles increase, the wavelength of the absorption peak is first blue-shifted and then is followed by the red shift, attributing to the mode alteration of the longitudinal surface plasmon resonance of the silver nanoplates. The capping agents are also optimized for the convenient and speedy growth of the large integrated Ag nanostructure. These observations expand the comprehensive understanding of plasmon resonance of the Ag nanoplates, and give a better manipulation of their applications in the plasmonie nanodevices.
文摘This paper proposes a quasi-static conformal mapping analysis to analytically evaluate the input resistance of Archimedean spiral antenna at its radiation region. The deviation from the original constructs of band theory for two-wire spiral antennas leads to the concept of common slot-line mode radiation. The per-unit-length capacitance and the characteristic impedance of the quasi-TEM fundamental propagating mode in periodic coplanar waveguide (PCPW) structure are obtained in terms of spiral parameters including substrate properties. This formula enables little computational effort on the computation of input resistance at the radiation mode of balanced-excited two-arm Archimedean spiral antennas. The numerical simulation demonstrates the accuracy of derived formulas both in free space and when a dielectric layer is presented.
文摘The sub-micron（of the order of 150 nm） thick core–shell composite fibers of magnesium ferrite-polyvinylidene fluoride are prepared by electrospinning.The loading of magnesium ferrite is varied from 1 to 10 wt%.The study results by X-ray diffraction,scanning electron microscope,and infra-red spectroscopy indicate the formation of core–shell structure and an enhancement in the amount of b-phase compared to a-phase in the polyvinylidene fluoride.The particle size of the magnesium ferrite in the fiber is evaluated to be 30 nm.The low frequency dielectric studies indicate that the addition of the magnesium ferrite increases the polarization resulting in the increase in the dielectric constant but decreases the dielectric loss.The magnetization measurements indicate an increased value of coercivity compared to bulk due to the nano-size of the magnesium ferrite.The microwave absorption at the ferromagnetic resonance increases with the increase in the concentration of magnesium ferrite.The resonance field is found to vary with the loading of MFO.
文摘With ever-increasing operating frequencies and complicated artificial structures, loss effects become more and more important in applications of metamaterials. Based on circuit theory and transmission line principle, the design equations for effective electromagnetic (EM) parameters (attenuation constant α, phase constant β, characteristic impedance Z0) of general active and passive metamaterial are compared and derived from the equivalent lumped circuit parameters (R, G, LL, CL, LR, CR). To verify the design equations, theα, βand Z0 indifferent cases, including balanced, unbalanced, lossless, passive and active, are shown by numerical simulations. The results show that using the active method can diminish the loss effects. Meantime, it also has influence on phase constant and real part of characteristic impedance.
文摘Formation of a quasi-stationary discharge or quasi-stationary emission mode in the explosive-emission electron sources is related to the current limitation resulting from the emissive ability saturation of cathode plasma with its expansion. The paper shows that in the process of the discharge current stabilization in the explosive-emission sources with the point- or blade-type emitters the essential role belongs to the electron beam space charge. Availability of the space charge results in limitation of the current growth velocity at the initial discharge phase and, hence, restricts the emissive ability of the cathode plasma and contributes to its saturation. In the vacuum diodes with multiemitter cathodes, the space charge availability increases the cathode operation stability and can provide obtaining of quasi-stationary beam current values or close to them resulting in formation of a plasma emission surface at the cathode close to the continuous one.
文摘Breakdown formation in the explosive-emission sources is related to the interelectrode gap filling with the cathode and anode plasma generated at the anode and in the gap under the beam influence. Under conditions of saturation of the cathode plasma emissive ability as well as when the measures on the emission boundary stabilization are taken, the anode plasma has the deciding part in the formation of the electron source breakdown. The paper presents the results of the anode plasma investigations obtained to solve the problem of the electron beam length increase in the explosive-emission sources. The data concerning the gas release from the anode, the mechanism of the anode plasma formation and the anode plasma influence on the parameters of the generated electron beam are presented as well.
文摘Breakdown formation in an explosive-emission electron source is related to the interelectrode gap filling with plasma propagating from the cathode and formed at the anode and in the interelectrode gap under the electron beam action. Plasma anode is used to increase the beam current density. Preliminary interelectrode gap filling with plasma in the explosive-emission source decreases the influence of uncontrolled plasma arrival from the anode on the diode processes, promotes current density increase and duration of generated electron beams. The paper considers the influence of the cathode geometry on the breakdown formation in the plasma-anode explosive-emission electron source. The data on obtaining of microsecond electron beams with current density of 30 A/cm^2 and 1.5-2 kA/cm^2 are presented.
文摘Quasistationary discharge mode setting in the explosive-emission sources is related to the saturation of the cathode plasma emissive ability resulting in the decrease of the velocity of plasma propagation into the interelectrode gap. It was shoran previously that the electron beam space charge providing the current rise slowing-down is of great importance in the process of the discharge mode stabilization. The paper considers a possibility of the discharge protraction at the expense of decrease of the ion charge order in the plasma composition and application of the directed plasma flows. The data concerning obtainig of micro- and millisecond electron beams in the explosive-emission sources are presented as well.
文摘Investigations are directed to the development of high-power sources ofUWB （ultrawideband） radiation based on excitation of anterma arrays with bipolar voltage pulses. In the previously designed high-power UWB sources only one bipolar pulse former and different feeder systems for pulse distribution through the array elements were used. By means of this approach, a number of UWB sources were created with the bipolar voltage pulse length ranging from 0.2 to 2 ns and effective potential of radiation ranging from 0.4 to 3 MV. The approach has got a restriction related to the electrical breakdown in a bipolar voltage pulse former. A new approach to the creation of high-power UWB sources based on a multicharmel bipolar pulse former is suggested： the number of bipolar pulse formers is equal to the number of antennas in the array. The main problem in realization of this approach is a stable operation of bipolar pulse formers in order to ensure a coherent summation of radiated pulses in the far-field zone. The result of this work is the instability of-150 ps at the pulse length of 3 ns obtained in a one-channel bipolar pulse former indicating that the suggested approach is realizable.
文摘Dielectric studies were carried out on a lead free Sodium Bismuth Titanate,NBT,(Na_(0.5)Bi_(0.5)TiO_(3))composition.The material was synthesized by conventional ceramic method(CS)and microwave sintering(MS).The presence of single phase has been confirmed by X-ray diffraction and scanning electron microscopy of NBT ceramic.The later technique(MS)resulted in material with high density,dielectric properties and improved microstructure.The transition temperature was observed slightly higher for microwave sintered(MS)material.Longitudinal modulus measurements are very sensitive property to identify the phase transitions in ceramics.Longitudinal modulus(L)measurements were also employed on these samples in the frequency 136 kHz and can be studied in the wide temperature range 30℃to 400℃.The elastic behavior(L)showed a break at two temperatures(~200℃and 350℃)in both the conventional and microwave sintered ceramics.In NBT ceramics,permittivity anomalies are connected to modulus anomalies.The results are correlated with the dielectric measurements.This behavior explained in the light of structural phase transitions in the ferroelectric ceramics.
