Ultrasensitive technique to measure kinetic inductance has test specimen included as part of the inductance of a tank circuit of a tunnel diode oscillator. Frequency counter measures shift in frequency of oscillator, caused by changes in inductance. Frequency shift in tank circuit is proportional to change in kinetic inductanc

Meservey, R. H.

Tedrow, P. M.

English

NASA Technical Reports Server

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November 1970
	
Brief 70-1049 1
 
NASA TECH BRIEF 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage commercial 
application. Tech Briefs are available on a subscription basis from the National Technical Information Service, Springfield, 
Virginia 22151. Requests for individual copies or questions relating to the Tech Brief progam may be directed to the Tech-
nology Utilization Division, NASA, Code UT, Washington, D.C. 20546. 
Kinetic Inductance Measured in a Superconducting Wire 
Liquid Helium Dewar 
•__ - -------
Oscillator Circuit Senses Inductance Change 
The capability of metal in a superconducting state 
(i.e. cooled to a few degrees Kelvin) to transport an 
enormous current density has stimulated a widespread 
interest in developing practical applications for this 
phenomenon; e.g., a commercial power generating 
station could transmit electrical power in a super-
conducting transmission line that would carry thou-
sands of amperes at a low voltage. 
A research program has been initiated for the pur-
pose of developing the experimental techniques and 
theoretical foundation to further the understanding 
of the physical process. An important physical param-
eter investigated in the program is the kinetic induc-
tance, LK., associated with the inertial mass of the elec-
tron in a superconducting metal. Even in a metal, LK 
has a very small value; for example, in a 1-meter 
length of 0.25-mm diameter superconducting wire well 
below its transition temperature, LK., is approximately 
10- 10
 henry. To measure the small values, the test spec-
imen is included as part of the inductance of the tank 
circuit of the tunnel diode oscillator shown in the 
figure. A shift in the frequency of the oscillator, caused 
by changes in the inductance, is sensed by a frequency 
counter. Experimental data has verified that a fre-
(continued overleaf)
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17'^
https://ntrs.nasa.gov/search.jsp?R=19700000473 2020-03-17T00:31:01+00:00Z
quency shift in the oscillator tank circuit is propor-
tional to a change in kinetic inductance. The simplicity 
of the technique makes the measurement of LK par-
ticularly useful'in determining the critical field and cur-
rent of high-field superconductors. Also, the measure-
ment technique is ultrasensitive; in fact, frequency 
shifts observed with a thin-film aluminum wire have 
been used to detect changes in temperature of 5x 10-70K, 
a change in magnetic field of 10 5 gauss, and a change 
in current associated with one quantum in a flux 
magnetometer. 
Potential applications would be its use as a trans-
ducer that measures a magnetic field and as the sensing 
element in a flux quantization magnetometer. 
Note: 
The following documentation may be obtained 
from:
Technical Information Service 
American Institute of Aeronautics 
and Astronautics, Inc. 
750 Third Avenue 
New York, New York 10017 
Single document price $3.00 
(or microfiche $0.50)
Reference: 
N69-33783, Measurements of the Kinetic In-
ductance of Superconducting Linear Structures 
Patent status: 
Inquiries about obtaining rights for the commercial 
use of this invention may be made to NASA, Code 
GP, Washington, D.C. 20546. 
Source: 'R. H. Meservey and P. M. Tedrow of

Massachusetts Institute of Technology

under contract to

Electronics Research Center

(ERC- 10305)
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Kinetic inductance measured in a superconducting wire

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