All‐superconducting rotating machines have the potential for meeting the high power density and high efficiency required for electrical aircraft applications.However,very high AC loss encountered in superconducting a...All‐superconducting rotating machines have the potential for meeting the high power density and high efficiency required for electrical aircraft applications.However,very high AC loss encountered in superconducting armature windings could hinder their development.Multifilamentary MgB_(2) wires are one of the promising candidates for the stator windings,due to their potentially low AC loss properties with small filament size and twist pitches.As the first step,the dependence of critical current and n‐value on magnetic fields and temperatures I_(c)(B,T)and n(B,T),which are basic input parameters for AC loss simulation,needs to be measured.In this work,we present transport I_(c)measurements in three non‐magnetic multifilamentary MgB_(2) wires(MgB_(2)/Nb/CuNi/CuZn):one large wire with a 0.70 mm diameter and 25 mm twist pitch,and two small wires with a 0.48 mm diameter each and a 10 mm and 30 mm twist pitch respectively.A four‐probe direct current method is used to measure I_(c) of the MgB_(2) wires with variations in temperature(15-35 K)and magnetic field(0-5.5 T).Full I_(c) data for the small wire with 10 mm twist pitch was obtained,and the n‐values were mostly less than 20.While the I_(c) data for the large wire at low fields was more limited due to heating,the n‐values were higher and could be up to around 100.The difference is attributed to the different filament sizes.Experiments also found that there is no significant hysteresis in the transport critical current measured by decreasing or increasing magnetic fields due to the non‐magnetic sheaths.This non‐hysteretic characteristic is critical for lowering AC loss because the additional losses from magnetic sheaths can be eliminated.From the magnetic‐field dependence of critical current density,an empirical expression has been developed that provides suitable extrapolations to lower fields for the large wire.展开更多
The four-probe technique is widely used in the characterization of electrical properties of solids and thin films. To investigate the influence of finite size probes with non-planar contact on the standard four-probe ...The four-probe technique is widely used in the characterization of electrical properties of solids and thin films. To investigate the influence of finite size probes with non-planar contact on the standard four-probe method, we have proposed an image method to simulate the potential distribution within the specimen. The numerical results show that for infinitely thick samples, the standard method can only provide accurate determination of resistivity （relative error below 1%） when the ratio of the average inter-electrode spacing to the diameter of the probe is greater than 3. We have also found that disregarding the probe size brings a less dominate error than that introduced by the approximate formula, when the sample＇s thickness is close to the inter-electrode spacing.展开更多
By mixing various concentrations of poly (ethylene glycol), a series of poly(3,4-ethylenedioxythiophene)- poly(styrenesulfonate) composite thin films were prepared. The electrical conductivity of the PEDOT-PSS/PEG thi...By mixing various concentrations of poly (ethylene glycol), a series of poly(3,4-ethylenedioxythiophene)- poly(styrenesulfonate) composite thin films were prepared. The electrical conductivity of the PEDOT-PSS/PEG thin films was measured by the four-probe method. Experimental results showed that the inclusion of poly(ethylene glycol) influenced the electrical conductivity of PEDOT-PSS film significantly. With the increase of PEG concentrations, the electrical conductivity sharply increased to reach a maximum and then slowly decreased down. Furthermore, the PEG molecular weight and environment temperature also played important roles on the electrical conductivity of PEDOT-PSS/PEG thin films. A good linear relationship was found between ln sDC and T -1/2 within the entire temperature range detected.展开更多
基金supported by CSC(Chinese Scholarship Council)and was partly supported by the New Zealand Ministry of Business,Innovation and Employment under the Advanced Energy Technology Platform program.This program is the“High power electric motors for large scale transport contract number RTVU2004”supported by the Royal Society of New Zealand Catalyst:Seeding New Zealand-Japan Joint Research Project Programme contract number E4153.
文摘All‐superconducting rotating machines have the potential for meeting the high power density and high efficiency required for electrical aircraft applications.However,very high AC loss encountered in superconducting armature windings could hinder their development.Multifilamentary MgB_(2) wires are one of the promising candidates for the stator windings,due to their potentially low AC loss properties with small filament size and twist pitches.As the first step,the dependence of critical current and n‐value on magnetic fields and temperatures I_(c)(B,T)and n(B,T),which are basic input parameters for AC loss simulation,needs to be measured.In this work,we present transport I_(c)measurements in three non‐magnetic multifilamentary MgB_(2) wires(MgB_(2)/Nb/CuNi/CuZn):one large wire with a 0.70 mm diameter and 25 mm twist pitch,and two small wires with a 0.48 mm diameter each and a 10 mm and 30 mm twist pitch respectively.A four‐probe direct current method is used to measure I_(c) of the MgB_(2) wires with variations in temperature(15-35 K)and magnetic field(0-5.5 T).Full I_(c) data for the small wire with 10 mm twist pitch was obtained,and the n‐values were mostly less than 20.While the I_(c) data for the large wire at low fields was more limited due to heating,the n‐values were higher and could be up to around 100.The difference is attributed to the different filament sizes.Experiments also found that there is no significant hysteresis in the transport critical current measured by decreasing or increasing magnetic fields due to the non‐magnetic sheaths.This non‐hysteretic characteristic is critical for lowering AC loss because the additional losses from magnetic sheaths can be eliminated.From the magnetic‐field dependence of critical current density,an empirical expression has been developed that provides suitable extrapolations to lower fields for the large wire.
基金Project supported by the Innovation Project of the Shanghai Institute of Technical Physics,CAS(No.CXJJ-Q-DX-57)
文摘The four-probe technique is widely used in the characterization of electrical properties of solids and thin films. To investigate the influence of finite size probes with non-planar contact on the standard four-probe method, we have proposed an image method to simulate the potential distribution within the specimen. The numerical results show that for infinitely thick samples, the standard method can only provide accurate determination of resistivity （relative error below 1%） when the ratio of the average inter-electrode spacing to the diameter of the probe is greater than 3. We have also found that disregarding the probe size brings a less dominate error than that introduced by the approximate formula, when the sample＇s thickness is close to the inter-electrode spacing.
文摘By mixing various concentrations of poly (ethylene glycol), a series of poly(3,4-ethylenedioxythiophene)- poly(styrenesulfonate) composite thin films were prepared. The electrical conductivity of the PEDOT-PSS/PEG thin films was measured by the four-probe method. Experimental results showed that the inclusion of poly(ethylene glycol) influenced the electrical conductivity of PEDOT-PSS film significantly. With the increase of PEG concentrations, the electrical conductivity sharply increased to reach a maximum and then slowly decreased down. Furthermore, the PEG molecular weight and environment temperature also played important roles on the electrical conductivity of PEDOT-PSS/PEG thin films. A good linear relationship was found between ln sDC and T -1/2 within the entire temperature range detected.
