here is a bit of research that suggests cheaper low field machines will come along after Aurora... Please hurry caprius you are in the horse race of your life...
rfglobalnet.com
As a way to diversify outside of military applications, the
Consortium for Superconducting Electronics was founded in
1989 for HTS research purposes, notably in cellular base
stations and medical instruments.2 The group, which includes
Lincoln Labs, MIT, AT&T, IBM, Conductus (Sunnyvale, CA),
and CTI-Cryogenics (Mansfield, MA), is also supported by
ARPA.
At present, companies working on and supplying HTS filters for
cellular base-station applications include Conductus, Illinois
Superconductor Corp. (Evanston, IL), Superconductor
Technologies, Inc. (Santa Barbara, CA), Superconductor Core
Technologies (Golden, CO), and DuPont. This past December,
for example, Superconductor Technologies delivered a receiver
filter subsystem to a manufacturer of GSM base stations. The
subsystem design can integrate as many as six thin-film HTS
filter pairs along with a closed-cycle Stirling cryocooler.
Superconductor Technologies' filter subsystem promises to
improve the performance of cellular and other wireless systems
(see Microwaves & RF, December 1994, p. 226). Similar in
performance to the filter developed by K&L Microwave
(Salisbury, MD) and partners (see p. 38), Superconductor
Technologies' filter exhibits less than 0.15-dB insertion loss at
its center frequency of 2.245 GHz, with return loss of better
than 25 dB. The lumped-element filter incorporates
carefully-processed YBCO and TlBaCuCuO substrate
materials with minimal nonlinear properties to achieve the
widest possible dynamic range. The compact design of the HTS
filter/cryocooler combination results in a filter package that is
about one-sixth the size of conventional cellular cavity filters.
The company's REACH receiver front end has been
field-tested by QUALCOMM (San Diego, CA) and exhibited
base-station-receiver noise-figure improvement of as much as 6
dB. This improvement could reduce the number of base stations
required for PCS deployment of a
code-division-multiple-access (CDMA) network by as much as
50 percent.
This past month, Illinois Superconductor Corp. (ILSC)
announced the successful completion of a major field trial of the
company's SpectrumMaster cellular filter. The filter, which is
equipped with a closed-cycle gas cooling system, is housed in a
standard 19-in. rack (see Microwaves & RF, November 1995,
p. 132). The field trial precedes commercial use of ILSC's
filters by a major East Coast cellular provider. Tested in
Cincinnati, OH by cellular and PCS carrier Ameritech Cellular
Services, the HTS filter provided considerably greater rejection
of out-of-band noise and interference than conventional
room-temperature filters.
The HTS filter reduced the effective cellular system noise floor,
resulting in an extension of coverage area, higher voice quality,
more usable channels, and less background noise. Located in
the cell-site building between the cellular system antenna and
receiver preamplifier, the compact filter subsystem saves a
tremendous amount of space compared to conventional cellular
filters. According to Ameritech's Vice President of Customer
and Network Services, Evan Richards, "The ILSC filter has
shown that it can provide the customer benefits we're after."
Conductus demonstrated a low-noise filter subsystem at the
Wireless World Expo in San Francisco this past November,
following successful system-level testing by base-station
manufacturer Peninsula Wireless Communications. With the
HTS filter subsystem, the noise figure for Peninsula's MRC-800
base station dropped from 4 dB to only 0.4 dB. The lower
noise figure could mean an extension of cellular coverage of
more than 70 percent. The Conductus filter assembly combines
an HTS bandpass filter and cryogenic low-noise amplifier.
While wireless filters and other low-loss components may
represent the largest future market for HTS electronics, medical
systems such as magnetic resonance imaging (MRI) and nuclear
magnetic resonance (NMR) offer the greatest present
opportunities for superconducting technology. The growing
interest in low-field MRI and the need for lower-cost medical
systems drives the development of HTS coil technology for
MRI, which is currently the biggest commercial application for
superconducting technology.3
For example, in August 1994, Conductus entered into an
agreement with Varian Associates (Palo Alto, CA) to develop
HTS receiver coils (thin films of YBCO patterned as a spiral on
a substrate) for Varian's NMR spectrometers. In March 1995,
the two companies announced a successful HTS NMR probe
for Varian's 400-MHz spectrometer. In conjunction with
Intermagnetics General, DuPont just received a $5.8 million
award from the Advanced Technology Program to develop
HTS sensing systems for incorporation into MRI systems.
Both Conductus and Superconductor Technologies, Inc. (STI)
have developed low-noise receivers to replace the copper
antenna in low-field MRI devices. In most standard MRI
devices based on relatively-high magnetic fields, the noise from
the body limits the resolution. If one works with a lower field or
smaller MRI devices using receivers with enhanced sensitivity,
the noise is limited by the sensor itself.
Conductus recently announced a joint project with the
Magnetic Resonance Systems Research Laboratory at Stanford
University (Stanford, CA) to develop a new mammography
scanner which combines the manufacturer's HTS receiver-coil
technology and the school's MRI expertise. The project is being
underwritten by a $4.39 million contract from the Naval
Research Laboratory (NRL) and ARPA under the Defense
Department's Focused Research Initiative.
The goal of the research is to develop an MRI mammographic
scanner with reduced costs compared to conventional MRI
mammography systems. Stanford's imaging instrument uses two
inexpensive pulsed electromagnets instead of the single,
expensive, superconducting magnet of conventional MRI
scanners. To maintain high image quality with the low
magnetic-field strengths, low-noise cryogenic electronics are
needed, including HTS receiving coils and low-noise amplifiers.
MRI involves the application of a high-frequency alternating
magnetic field to a sample in the presence of an orthogonal
static magnetic field. The combination of fields causes nuclei in
the sample to precess (spin) about the static field. The nuclear
precession creates an alternating magnetic field, generating low
levels of RF energy. An MRI system employs sensitive
receiving electronics to detect these low-level signals. Imaging
can be improved by increasing the receiver signal-to-noise ratio
(SNR) or increasing the signal strength of the RF signals. The
former can be achieved with HTS electronics; the latter can be
achieved by increasing the static magnetic field.
The receivers make use of tuned coils that are similar to
antennas. Usually the system noise is dominated by the noise of
the receiver coil. The noise of these coils scales with its
resistance as well as with ambient temperature. By lowering the
temperature and the resistance, as is done with HTS coils, the
overall SNR of the MRI receiver improves drastically,
compared to room-temperature copper receiver coils.
Data-collection time is related directly to the MRI or NMR
SNR, and is generally proportional to the square of the SNR. If
the SNR is doubled, data collection is four times faster.
FORMING PARTNERSHIPS
Because the number of companies performing superconducting
work in this country is small, partnerships are vital to the
proliferation of HTS technology. Just last month, DuPont and
Superconducting Core Technologies, Inc. (SCT) signed an
exclusive two-year, $7 million purchase and supply agreement
for superconducting thin films. Under the agreement, SCT is
guaranteed an exclusive supply of superconducting thin films
and patterned components for commercial wireless
communications applications from DuPont. According to
DuPont's General Manager of Superconductivity, Alan Lauder,
"DuPont and SCT share a common vision in the widespread
introduction of superconducting technology and look forward to
additional collaborations in the communications field." In
addition, in a partnership with Com-Dev (Cambridge, Canada),
DuPont recently received a Technology Reinvestment Program
(TRP) award to develop high-power HTS components for
satellite-communications systems.
Last August, STI and Conductus announced the formation of
the HTS Thin-Film Manufacturing Alliance (HTMA), a
consortium to develop cost-effective manufacturing technology
for the production of superconducting thin-film components.
Formation of the alliance coincides with an HTMA agreement
with ARPA for three years of funding totalling $5.6 million.
Participating organizations in HTMA will contribute similar
amounts over the life of the project, for an overall effort of
$11.2 million. Initial goals of the consortium include
development of industry standards for substrates, thin films, and
test procedures. Additional participants in HTMA include
Stanford University and Georgia Tech University (Atlanta, GA).
Once considered a laboratory curiosity, superconductors have
found a firm (and potentially large) niche in medical
applications. Should cellular and other wireless systems
designers fully adopt HTS filters in their base-station designs,
the handful of companies manufacturing HTS components is
sure to grow.
REFERENCES
1. Zhi-Yuan Shen, High-Temperature Superconducting
Microwave Circuits, Artech House, Norwood, MA, 1994.
2. Gloria B. Lubkin, "Applications of High-Temperature
Superconductors Approach the Marketplace," Physics Today,
March 1995, p. 20.
3. Randy Simon, "NMR: The First Big Market for HTS
Technology," Superconductor Industry, Summer, 1995.
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