The temperature dependence of fluxoid quantization in a superconducting loop. The sensitivity of the device is expected to surpass that of other superconducting- based bolometric devices, such as superconducting transition-edge sensors and superconducting nanowire devices. Just as important, the proposed device has advantages in sample fabrication

Bonetti, Joseph A.

Day, Peter K.

Kenyon, Matthew E.

Leduc, Henry G.

NASA Technical Reports Server

30 NASA Tech Briefs, July 2010
The temperature dependence of flux-
oid quantization in a superconducting
loop. The sensitivity of the device is ex-
pected to surpass that of other supercon-
ducting-based bolometric devices, such
as superconducting transition-edge sen-
sors and superconducting nanowire de-
vices.  Just as important, the proposed
device has advantages in sample fabrica-
tion.  Two challenges of transition edge
sensor fabrication are the reproducibil-
ity of the superconducting transition
temperature, Tc , and the sharpness of
the transition. In the proposed device,
unlike in other devices, the sample
would remain in the superconducting
state at all times during operation. That
is to say it would be maintained at an ab-
solute temperature, T, below its super-
conducting Tc. Thus, the sharpness of
the transition does not directly come
into play.  Also, the device can operate
over a relatively wide temperature span
of about 0.70 Tc to 0.95 Tc. Therefore,
reproducibility of Tc is not important
from sample to sample.  These two ad-
vantages eliminate major challenges in
device fabrication.  
The proposal is based on the theory of
fluxoid quantization in a superconduct-
ing loop (see figure) with a track width
(w) less than the temperature-depend-
ent characteristic depth of supercurrent
penetration (λ) of the material. The the-
ory has been shown to lead to the follow-
ing equation: 
where Is is the temperature-dependent
supercurrent, t is the thickness of the su-
perconducting ring, Φ0 is the magnetic-
flux quantum, n is an integer denoting
the number of fluxoid quanta, ΦA is the
magnetic flux applied to the ring, r is the
radius of the ring, and λ0 is the charac-
teristic depth of penetration of super-
current at absolute zero temperature.
The applied magnetic flux (ΦA)
would serve as a bias that could be ad-
justed to select the mode of operation.
I T
wt n
rµ
T Ts
A
c( ) = −( ) − ( )Φ Φ0
0 0
2
4
2
1
π λ
[ / ]
A Superconducting Ring would support a temperature-dependent supercurrent Is in the presence of
an applied magnetic flux ΦA.
Bolometric Device Based on Fluxoid Quantization 
This device offers extremely high sensitivity for radiometric applications. 
NASA’s Jet Propulsion Laboratory, Pasadena, California
t
w
Superconducting
Ring of Radius r Supercurrent Is
table in the design is that residual phase-
wander between the locked radio fre-
quency (RF) and local oscillator (LO) K-
band source synthesizers is canceled at an
intermediate 450 MHz IF stage before
final conversion to baseband through an
IQ mixer. 
To implement the FMCW chirp, a 2–4
GHz low-phase-noise commercial YIG
synthesizer is used with a tuning band-
width of 5 kHz, typically ramping over
350 MHz (subsequently multiplied by 36
to 12.6 GHz) in 50 ms. The chirp signal
is up-converted onto the CW synthesiz-
ers’ signals before multiplication. De-
ramping of the FMCW waveform occurs
at the 600 GHz receiver mixer. While
high multiplication factors should be
generally avoided in FMCW radar sys-
tems to minimize the impact of phase
noise in the transmitted signal, in this
case, the short standoff ranges produce
a phase noise floor that lies below the
thermal noise except for the brightest,
mirrorlike specular targets.
The submillimeter power is transmitted
first through a silicon wafer beam splitter
and then a plano-convex Teflon lens with
a diameter of 20 cm. This lens focuses the
THz beam to a spot size of ≈2 cm at a
standoff range of 4 m. To achieve scanned
images, a flat mirror on a two-axis rota-
tional stage deflects the beam in the de-
sired direction
This innovation is an improvement
over an earlier submillimeter high-reso-
lution radar. First, a faster frequency-
sweeping method consisting of a wide-
band YIG oscillator has been
implemented. Second, the data acquisi-
tion and signal processing software has
been updated in order to deal with the
faster radar pulse repetition rate.
The improvements mean that the 580-
GHz imaging radar can now acquire
three-dimensional images of people in
about five minutes. It is also feasible to
detect objects concealed by clothing.
This capability is possible because of the
improved speed and functionality of the
imaging radar’s hardware and software. 
This work was done by Robert Dengler, Ken
Cooper, Goutam Chattopadhyay, Peter Siegel,
Erich Schlecht, Imran Mehdi, Anders
Skalare, and John Gill of Caltech for NASA’s
Jet Propulsion Laboratory. 
In accordance with Public Law 96-517,
the contractor has elected to retain title to this
invention. Inquiries concerning rights for its
commercial use should be addressed to:
Innovative Technology Assets Management
JPL
Mail Stop 202-233
4800 Oak Grove Drive
Pasadena, CA 91109-8099
E-mail: iaoffice@jpl.nasa.gov
Refer to NPO-45156, volume and number
of this NASA Tech Briefs issue, and the
page number.
https://ntrs.nasa.gov/search.jsp?R=20100024431 2019-08-30T10:11:59+00:00Z
NASA Tech Briefs, July 2010 31
This flux could be generated by any con-
venient means — such as those used to
flux bias DC-SQUIDS. To obtain one of
two distinct modes of operation, one
would adjust ΦA to obtain nΦ0 – ΦA ≈
Φ0/2, placing the device in the middle
of the n-fluxoid quanta branch. This
mode would be a radiometric one, in
which the device would function simi-
larly to a superconducting-transition-
edge sensor (TES) bolometer. Assuming
the proposed device would be mounted
on a low-thermal-conductance mem-
brane similar to that used for TES
bolometers, it has been estimated that
the responsivity would be an order of
magnitude greater than that of a typical
TES bolometer.
To obtain the other distinct mode of
operation, one would adjust ΦA to place
the device extremely close to the transi-
tion between the n- and (n – 1)-fluxoid-
quanta branches. In this mode, the de-
vice would function as a threshold-type
sensor having potential utility in applica-
tions that involve photon counting and
other counting-type detections. 
This work was done by Joseph A. Bonetti,
Matthew E. Kenyon, Henry G. Leduc, and
Peter K. Day of Caltech for NASA’s Jet Propul-
sion Laboratory. Further information is con-
tained in a TSP (see page 1).
In accordance with Public Law 96-517,
the contractor has elected to retain title to this
invention. Inquiries concerning rights for its
commercial use should be addressed to:
Innovative Technology Assets Management
JPL
Mail Stop 202-233
4800 Oak Grove Drive
Pasadena, CA 91109-8099
E-mail: iaoffice@jpl.nasa.gov
Refer to NPO-45655, volume and number
of this NASA Tech Briefs issue, and the
page number.


Bolometric Device Based on Fluxoid Quantization

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