Contactless Conductivity Measurement - Revision history

E0732931: /* Experiment Set up */

2022-04-30T15:16:36Z

Experiment Set up

← Older revision		Revision as of 15:16, 30 April 2022
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	The measuring circuit consists of a detecting coil, a compensating coil with equal turns of copper wire and a primary coil. The primary coil is connected to the Lock-in Amplifier output. An ac current flows through primary coil and gives rise to magnetic field. The detecting coil and the compensating coil are connected to Lock-in Amplifier input so that we can measure the voltage. The compensating coil is used to compensate the voltage in detecting coil without samples. We connect the detecting coil to one port(A) in Lock-in Amplifier and compensating coil in another port(B). The resultant voltage is the difference between two coils which is the voltage induced by ~~the Eddy current in~~ the sample. Of course, the sample is placed in the middle of detecting coil and the sample length is short compare to the length between detecting coil and compensating coil so that the Eddy current in the sample has little effect on the compensating coil. In literature, secondary coil is adjusted by position and voltage offset so that voltage without sample is zero. The combination of detecting coil and compensating coil in our set up is analogous to the secondary coil used in literature.		The measuring circuit consists of a detecting coil, a compensating coil with equal turns of copper wire and a primary coil. The primary coil is connected to the Lock-in Amplifier output. An ac current flows through primary coil and gives rise to magnetic field. The detecting coil and the compensating coil are connected to Lock-in Amplifier input so that we can measure the voltage. The compensating coil is used to compensate the voltage in detecting coil without samples. We connect the detecting coil to one port(A) in Lock-in Amplifier and compensating coil in another port(B). The resultant voltage is the difference between two coils which is the voltage induced by the sample. Of course, the sample is placed in the middle of detecting coil and the sample length is short compare to the length between detecting coil and compensating coil so that the Eddy current in the sample has little effect on the compensating coil. In literature, secondary coil is adjusted by position and voltage offset so that voltage without sample is zero. The combination of detecting coil and compensating coil in our set up is analogous to the secondary coil used in literature.

	Figure 4 shows the schematic of coils set up. For method one, a and c contact points are connected to port A and b and c points are connected to port B for balancing voltage. For method 2, only a and c contact points are used to be connected with voltmeter measuring root mean square voltage. d and e points are for ac current in.		Figure 4 shows the schematic of coils set up. For method one, a and c contact points are connected to port A and b and c points are connected to port B for balancing voltage. For method 2, only a and c contact points are used to be connected with voltmeter measuring root mean square voltage. d and e points are for ac current in.
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	[[File:connect3.jpeg\|center\|thumb\|Figure 7. A picture of wires connecting SR830 Lock-in Amplifier]]		[[File:connect3.jpeg\|center\|thumb\|Figure 7. A picture of wires connecting SR830 Lock-in Amplifier]]

	Figure 8 shows the panel of the Labview program we built and Figure 9 is the source code. First, We do one measurement without samples, the program will give us some x, y and theta values. Ideally, the theta value would be 0 because we have the compensating coil. But in reality, the coils are not perfect so that we need to calibrate the system to cancel the phase. The calibration is done by giving some offsets so that theta becomes 0. This is automatically done when we choose the "calibrate" option in the program for the first measurement. Then we insert our samples and measure with calibrate option off. The "x from sample" and "y from sample" in the program will give us the final results which correspond to real and imaginary part of the EMF induced ~~by the sample~~.		Figure 8 shows the panel of the Labview program we built and Figure 9 is the source code. First, We do one measurement without samples, the program will give us some x, y and theta values. Ideally, the theta value would be 0 because we have the compensating coil. But in reality, the coils are not perfect so that we need to calibrate the system to cancel the phase. The calibration is done by giving some offsets so that theta becomes 0. This is automatically done when we choose the "calibrate" option in the program for the first measurement. Then we insert our samples and measure with calibrate option off. The "x from sample" and "y from sample" in the program will give us the final results which correspond to real and imaginary part of the EMF induced.

	[[File:labviewpanel.png\|center\|thumb\|Figure 8. A screenshot of the Labview program panel we built to calibrate and measure]]		[[File:labviewpanel.png\|center\|thumb\|Figure 8. A screenshot of the Labview program panel we built to calibrate and measure]]

E0732931: /* Experiment Set up */

2022-04-30T15:14:20Z

Experiment Set up

← Older revision		Revision as of 15:14, 30 April 2022
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	Figure 4 shows the schematic of coils set up. For method one, a and c contact points are connected to port A and b and c points are connected to port B for balancing voltage. For method 2, only a and c contact points are used to be connected with voltmeter measuring root mean square voltage. d and e points are for ac current in.		Figure 4 shows the schematic of coils set up. For method one, a and c contact points are connected to port A and b and c points are connected to port B for balancing voltage. For method 2, only a and c contact points are used to be connected with voltmeter measuring root mean square voltage. d and e points are for ac current in.

	Figure 5 shows our coils and different terminals. Two terminals on the right are the positive and negative terminals for primary coil. The magnetic field induced by this coil is calculated to be 14.073 * I which I is the applied current controlled by the Lock-in Amplifier. There are three terminals on the left. We connect upper two to for the detecting coil and lower two for the compensating coil. They are connected to different input ports in Lock-in Amplifier. We put tissues in the bottle so that the sample lies in the range of detecting coil		Figure 5 shows our coils and different terminals. Two terminals on the right are the positive and negative terminals for primary coil. The magnetic field induced by this coil is calculated to be 14.073 * I Oe which I is the applied current controlled by the Lock-in Amplifier. There are three terminals on the left. We connect upper two to for the detecting coil and lower two for the compensating coil. They are connected to different input ports in Lock-in Amplifier. We put tissues in the bottle so that the sample lies in the range of detecting coil

	[[File:Schematic of coils.png\|center\|thumb\|Figure 4. A schematic of coils set up]]		[[File:Schematic of coils.png\|center\|thumb\|Figure 4. A schematic of coils set up]]

E0732931: /* Experiment Set up */

2022-04-30T15:11:28Z

Experiment Set up

← Older revision		Revision as of 15:11, 30 April 2022
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	The measuring circuit consists of a detecting coil, a compensating coil with equal turns of copper wire and a primary coil. The primary coil is connected to the Lock-in Amplifier output. Ac current flows through primary coil and gives rise to magnetic field. The detecting coil and the compensating coil are connected to Lock-in Amplifier input so that we can measure the voltage. The compensating coil is used to compensate the voltage in detecting coil without samples. We connect the detecting coil to one port(A) in Lock-in Amplifier and compensating coil in another port(B). The resultant voltage is the difference between two coils which is the voltage induced by the Eddy current in the sample. Of course, the sample is placed in the middle of detecting coil and the sample length is short compare to the length between detecting coil and compensating coil so that the Eddy current in the sample has little effect on the compensating coil. In literature, secondary coil is adjusted by position and voltage offset so that voltage without sample is zero. The combination of detecting coil and compensating coil in our set up is analogous to the secondary coil used in literature.		The measuring circuit consists of a detecting coil, a compensating coil with equal turns of copper wire and a primary coil. The primary coil is connected to the Lock-in Amplifier output. An ac current flows through primary coil and gives rise to magnetic field. The detecting coil and the compensating coil are connected to Lock-in Amplifier input so that we can measure the voltage. The compensating coil is used to compensate the voltage in detecting coil without samples. We connect the detecting coil to one port(A) in Lock-in Amplifier and compensating coil in another port(B). The resultant voltage is the difference between two coils which is the voltage induced by the Eddy current in the sample. Of course, the sample is placed in the middle of detecting coil and the sample length is short compare to the length between detecting coil and compensating coil so that the Eddy current in the sample has little effect on the compensating coil. In literature, secondary coil is adjusted by position and voltage offset so that voltage without sample is zero. The combination of detecting coil and compensating coil in our set up is analogous to the secondary coil used in literature.

	Figure 4 shows the schematic of coils set up. For method one, a and c contact points are connected to port A and b and c points are connected to port B for balancing voltage. For method 2, only a and c contact points are used to be connected with voltmeter measuring root mean square voltage. d and e points are for ac current in.		Figure 4 shows the schematic of coils set up. For method one, a and c contact points are connected to port A and b and c points are connected to port B for balancing voltage. For method 2, only a and c contact points are used to be connected with voltmeter measuring root mean square voltage. d and e points are for ac current in.

E0732931: /* Sample Preparation */

2022-04-30T15:10:41Z

Sample Preparation

← Older revision		Revision as of 15:10, 30 April 2022
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	For this experiment, we have tested three samples, copper metal rod (Cu), Teflon and sodium doped lanthanum manganite (La<sub>1-x</sub>Na<sub>x</sub>MnO<sub>3</sub>). We choose copper and Teflon because we have them in the workshop and the theoretical values of some necessary parameters like susceptibility and dc conductivity of copper and Teflon are easy to obtain online so that we can calculate and verify our results. We also choose La<sub>1-x</sub>Na<sub>x</sub>MnO<sub>3</sub> especially La<sub>0.95</sub>Na<sub>0.05</sub>MnO<sub>3</sub> because we have measured its resistivity value through standard four probes method in our MPT projects. Due to its property of changing Curie temperature with respect to the level of doping, La<sub>0.95</sub>Na<sub>0.05</sub>MnO<sub>3</sub> at room temperature shows semi conductor like resistivity behavior.		For this experiment, we have tested three samples, copper metal rod (Cu), Teflon and sodium doped lanthanum manganite (La<sub>1-x</sub>Na<sub>x</sub>MnO<sub>3</sub>). We choose copper and Teflon because we have them in the workshop and the theoretical values of some necessary parameters like susceptibility and dc conductivity of copper and Teflon are easy to obtain online so that we can calculate and verify our results. We also choose La<sub>1-x</sub>Na<sub>x</sub>MnO<sub>3</sub> especially La<sub>0.95</sub>Na<sub>0.05</sub>MnO<sub>3</sub> because we have measured its resistivity value through standard four probes method in our MPT projects. Due to its property of changing Curie temperature with respect to the level of doping, La<sub>0.95</sub>Na<sub>0.05</sub>MnO<sub>3</sub> at room temperature shows semi conductor like resistivity behavior.

	The copper rod we cut and polished is presented in Figure 1. The radius of the rod is 0.003 meters and the length is 0.0082 meters. The theoretical volume susceptibility we found online is -9.63 * 10<sup>-6</sup> and the conductivity is about 58.7 * 10<sup>6</sup> siemens/meter. We will use these parameters as well as our measured voltages to compute our experimental conductivity. Teflon is cut with the same dimension ~~with~~ theoretical conductivity about 10<sup>-24</sup> siemens/meter.		The copper rod we cut and polished is presented in Figure 1. The radius of the rod is 0.003 meters and the length is 0.0082 meters. The theoretical volume susceptibility we found online is -9.63 * 10<sup>-6</sup> and the conductivity is about 58.7 * 10<sup>6</sup> siemens/meter. We will use these parameters as well as our measured voltages to compute our experimental conductivity. Teflon is cut with the same dimension, it has theoretical conductivity about 10<sup>-24</sup> siemens/meter.

	[[File:copper.jpg\|center\|thumb\|Figure 1. A picture of our copper rod sample]]		[[File:copper.jpg\|center\|thumb\|Figure 1. A picture of our copper rod sample]]

E0732931: /* Conclusion */

2022-04-30T15:09:33Z

Conclusion

← Older revision		Revision as of 15:09, 30 April 2022
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	The set up we made has the configuration with detecting coil surrounding samples which will also lead to inaccuracy in the measurements. The detecting coil around samples is associated to an additional magnetic flux from primary coil irrespective of the presence of the sample. While using tube shape sample, the detecting coils will be more sensitive to magnetic field screened by the tube outside if it's placed in the tube.		The set up we made has the configuration with detecting coil surrounding samples which will also lead to inaccuracy in the measurements. The detecting coil around samples is associated to an additional magnetic flux from primary coil irrespective of the presence of the sample. While using tube shape sample, the detecting coils will be more sensitive to magnetic field screened by the tube outside if it's placed in the tube.

	In our experiment, the sample we use has lengths slightly larger than their diameters so that edge effect may contribute a lot here. Further improvements can be made if we use a longer rod which we do not have access to for this time.		In our experiment, the sample we use has lengths only slightly larger than their diameters so that edge effect may contribute a lot here. Further improvements can be made if we use a longer rod which we do not have access to for this time.

	==Team Members==		==Team Members==

E0732931: /* Sample Preparation */

2022-04-30T15:07:25Z

Sample Preparation

← Older revision		Revision as of 15:07, 30 April 2022
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	For this experiment, we have tested three samples, copper metal rod (Cu), Teflon and sodium doped lanthanum manganite (La<sub>1-x</sub>Na<sub>x</sub>MnO<sub>3</sub>). We choose copper and Teflon because we have them in the workshop and the theoretical values of some necessary parameters like susceptibility and conductivity of copper and Teflon are easy to obtain online so that we can calculate and verify our results. We also choose La<sub>1-x</sub>Na<sub>x</sub>MnO<sub>3</sub> especially La<sub>0.95</sub>Na<sub>0.05</sub>MnO<sub>3</sub> because we have measured its resistivity value through standard four probes method in our MPT projects. Due to its property of changing Curie temperature with respect to the level of doping, La<sub>0.95</sub>Na<sub>0.05</sub>MnO<sub>3</sub> at room temperature shows semi conductor like resistivity behavior.		For this experiment, we have tested three samples, copper metal rod (Cu), Teflon and sodium doped lanthanum manganite (La<sub>1-x</sub>Na<sub>x</sub>MnO<sub>3</sub>). We choose copper and Teflon because we have them in the workshop and the theoretical values of some necessary parameters like susceptibility and dc conductivity of copper and Teflon are easy to obtain online so that we can calculate and verify our results. We also choose La<sub>1-x</sub>Na<sub>x</sub>MnO<sub>3</sub> especially La<sub>0.95</sub>Na<sub>0.05</sub>MnO<sub>3</sub> because we have measured its resistivity value through standard four probes method in our MPT projects. Due to its property of changing Curie temperature with respect to the level of doping, La<sub>0.95</sub>Na<sub>0.05</sub>MnO<sub>3</sub> at room temperature shows semi conductor like resistivity behavior.

	The copper rod we cut and polished is presented in Figure 1. The radius of the rod is 0.003 meters and the length is 0.0082 meters. The theoretical volume susceptibility we found online is -9.63 * 10<sup>-6</sup> and the conductivity is about 58.7 * 10<sup>6</sup> siemens/meter. We will use these parameters as well as our measured voltages to compute our experimental conductivity. Teflon is cut with the same dimension with theoretical conductivity about 10<sup>-24</sup> siemens/meter.		The copper rod we cut and polished is presented in Figure 1. The radius of the rod is 0.003 meters and the length is 0.0082 meters. The theoretical volume susceptibility we found online is -9.63 * 10<sup>-6</sup> and the conductivity is about 58.7 * 10<sup>6</sup> siemens/meter. We will use these parameters as well as our measured voltages to compute our experimental conductivity. Teflon is cut with the same dimension with theoretical conductivity about 10<sup>-24</sup> siemens/meter.

E0732931: /* Theory */

2022-04-30T15:06:28Z

Theory

← Older revision		Revision as of 15:06, 30 April 2022
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	</div>		</div>

	~~And~~ D and d are the outer and inner diameter of the sample because this approach chooses tube sample. When we express it in terms of voltages, the expression becomes		D and d are the outer and inner diameter of the sample because this approach chooses tube sample. When we express it in terms of voltages, the expression becomes

	<div class="center" style="width:auto; margin-left:auto; margin-right:auto;">		<div class="center" style="width:auto; margin-left:auto; margin-right:auto;">

E0732931: /* Introduction */

2022-04-30T15:04:22Z

Introduction

← Older revision		Revision as of 15:04, 30 April 2022
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	==Introduction==		==Introduction==

	In our Spintronics Lab, when we want to analyze a sample, conductivity or resistivity as a electrical property is almost always necessary. Normally, we use a Voltmeter or standard four probes method to take a measurement. However, surface preparation and contamination have great effects on the electrical properties of the samples. Thus, a contactless technic would be a better way to carry out the conductivity measurement. When we were doing the ac magnetic susceptibility measurement, we learn from literature that there is connection between the electrical conductivity and the ac magnetic susceptibility. We would like to build the set up described in the literature, take a measurement on the conductivity of our samples and compare them with the results from literature or standard four probes measurement.		In our Spintronics Lab, when we want to analyze a sample, conductivity or resistivity as a electrical property is almost always necessary. Normally, we use a Voltmeter or standard four probes method to take a measurement. However, surface preparation and contamination have great effects on the electrical properties of the samples. Thus, a contactless technic would be a better way to carry out the conductivity measurement. When we were doing the ac magnetic susceptibility measurement, we learn from literature that there is connection between the electrical conductivity and the ac magnetic susceptibility. We would like to build the set up described in the literature, take a measurement on the conductivity of our samples and compare them with the results from literature or from standard four probes measurement.

	==Theory==		==Theory==

A0236240R: /* Conclusion */

2022-04-30T11:24:28Z

Conclusion

← Older revision		Revision as of 11:24, 30 April 2022
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	The set up we made has the configuration with detecting coil surrounding samples which will also lead to inaccuracy in the measurements. The detecting coil around samples is associated to an additional magnetic flux from primary coil irrespective of the presence of the sample. While using tube shape sample, the detecting coils will be more sensitive to magnetic field screened by the tube outside if it's placed in the tube.		The set up we made has the configuration with detecting coil surrounding samples which will also lead to inaccuracy in the measurements. The detecting coil around samples is associated to an additional magnetic flux from primary coil irrespective of the presence of the sample. While using tube shape sample, the detecting coils will be more sensitive to magnetic field screened by the tube outside if it's placed in the tube.

	In our experiment, the sample we use has lengths ~~smaller~~ than their diameters so that edge effect may contribute a lot here. Further improvements can be made if we use a longer rod which we do not have access to for this time.		In our experiment, the sample we use has lengths slightly larger than their diameters so that edge effect may contribute a lot here. Further improvements can be made if we use a longer rod which we do not have access to for this time.

	==Team Members==		==Team Members==

A0236240R: /* Conclusion */

2022-04-30T11:22:58Z

Conclusion

← Older revision		Revision as of 11:22, 30 April 2022
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	It comes out that the response of voltage is quite small compared to calibration voltage which indicate the response coming from copper coils not wound well and environment may influence greatly on the final result. To make a improvement, we may better design a support for copper wires to wind them tightly and uniformly and put the whole set up in the vacuum chamber with temperature controller to eliminate the influence of environment.		It comes out that the response of voltage is quite small compared to calibration voltage which indicate the response coming from copper coils not wound well and environment may influence greatly on the final result. To make a improvement, we may better design a support for copper wires to wind them tightly and uniformly and put the whole set up in the vacuum chamber with temperature controller to eliminate the influence of environment.

	Skin depth is a very important factor for eddy current distribution in material. For magnets with large permeability, the decreasing of skin depth will lead to inaccuracy in conductivity and no more satisfy the condition that skin depth should be far larger than sample diameters. As well from the formula provided below, we see for high frequency measurement, accurate data are hard to obtain.		Skin depth is a very important factor for eddy current distribution in material. For magnets with large permeability, the decreasing of skin depth will lead to inaccuracy in conductivity and no more satisfy the condition that skin depth should be far larger than sample diameters. As well from the formula provided below, we see for high frequency measurement, accurate data are hard to obtain due to the decreasing in skin depth.

	<div class="center" style="width:auto; margin-left:auto; margin-right:auto;">		<div class="center" style="width:auto; margin-left:auto; margin-right:auto;">