IEEE Spectrum November, 2014 - 61

decade designing portable cryogenic systems, including an
ingenious Stirling-cycle refrigerator no bigger than a bicycle
pump. Made largely of plastic, it could still cool a niobium
SQUID to 8.5 K. Later, after he retired in 1985, he and his
grandson devised a liquid-helium cryostat that could main-
tain temperatures of 1 millikelvin. Now known as the Z cryo-
stat ("Z" for Zimmerman), it is a standard piece of equipment
in many high-temperature superconductivity labs.
fIfTy years afTer ITs InvenTIon, The sQUId Is only
now coming into its own. Two companies currently manu-
facture the devices, and dozens of research groups around
the world are investigating new applications for them. The
Swedish company Elekta, for instance, makes neurological
"stations" that each incorporate 306 SQUID circuits for veri-
fying the abnormal magnetic activity associated with epi-
lepsy and other conditions. Aided by high-speed computer
processing, the apparatus yields a three-dimensional mag-
netic field map of a patient's brain that can be used to guide
surgical treatment of the condition.
The SQUID is also a principal building block for numerous
electronics applications, including analog-to-digital converters
and both traditional and quantum computing. In nondestruc-
tive testing, the devices have been used to detect aluminum
corrosion in aircraft. Such anomalies would otherwise be
nearly impossible to detect without dismantling or otherwise
damaging the components, and the magnetic fields produced

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by such corrosion are exceedingly weak compared with those
from other components on the plane, such as the steel fasteners.
Researchers are also considering the SQUID as a tool for
measuring the effectiveness of magnetically activated drug
delivery; this technique involves dispersing drugs through
the blood using magnetic nanoparticles. SQUID arrays offer
a way to noninvasively detect where the nanoparticles have
dispersed and where the drug has been delivered. There have
even been reports of nanoSQUIDs, which their inventors claim
can measure the magnetic field of a single atom.
If the SQUID continues on its way to a glorious future, it
will be a testament to Zimmerman's energy and persistence.
Building on those fragile lab curiosities devised in Dearborn,
he doggedly refined and improved them over the course of
several decades. Along the way, he spread the SQUID gospel,
collaborating eagerly with researchers outside his own dis-
cipline and enthusiastically tackling the hard engineering
problems to ensure its success. What the story of the SQUID
elegantly shows is that the moment of invention-however
surprising, revelatory, and exciting-is but the first small step
in the long road to reality. It is also a poignant reminder of
what's been lost. As today's corporations move away from
unfettered basic research, we should not forget the crucial
role of the 20th century's industrial labs and the ingenious
ideas and inventions that emerged from them. n
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Table of Contents for the Digital Edition of IEEE Spectrum November, 2014
