IEEE Spectrum December, 2007 - 49

RESOURCES
have gotten 3 centimeters per second.
back to the envelope. The ideal coilgun
uses the interplay between the currentinduced magnetic field pulse inside the coil
and the movement of the ferrous projectile
to maximize the energy transferred from
wire to slug. but that requires the slug to zip
through the coil in a fraction of a second. My
energy transfer was abysmal, as I could tell
by the spark when I closed the contact for
a second time. Essentially all the energy of
the current pulse was winding up right back
in the capacitor.
I needed to put more turns in my coils and
to compress my magnetic field to a smaller volume. That way, I could get the projectile moving

fast enough to play effectively with the emerging magnetic field.
The right approach would have been to
find another tube and wind my wire carefully around it or even to get wire better
suited for winding solenoid coils. Instead,
I just took a fresh spool, unwound a few
inches from the outside, and soldered a
few inches of heavy-gauge wire onto the
nib that projected into the hollow core of
the spool. The projectile is smaller, but now
when I close the connection it hits the other
side of the desk with a satisfying tink.
It's not going to shoot down an incoming
ballistic missile or even seriously annoy our
cat, but it'll do as proof of concept. If I add a

The Foreign Patent
Money Trap
you may well need patents in
many countries, but that doesn't
mean you can afford them

invention

A lot of people simply assume that
a U.S. patent provides protection
outside of the United States or that
there is some kind of a "European
patent" or even a "world patent." These beliefs are dead wrong.
Your U.S. patent gives you no legal
recourse should a company based
overseas sell your invention overseas; in
fact, it even provides that competitor with
a free blueprint of your technology.
A recent U.S. Supreme Court decision
not only showed how short the arm of
U.S. patent law can be, it shortened it a bit
more. AT&T had alleged that Microsoft
had violated its U.S. patent for speechprocessing software. While the question
inside the United States was uninteresting-Microsoft's U.S. sales were indeed
found to be a violation-the real issue
was Microsoft's supplying the code to
non-U.S. manufacturers for installation
on computers sold abroad. Those non-U.S.
activities, the Supreme Court held, were
beyond the reach of AT&T's U.S. patent.
The upshot is that your U.S. patent provides you essentially no protection beyond
U.S. borders. Other countries' patents also

have little force outside their own domains.
So, you say, why not just go out and
get a passel of international patents? The
catch is the cost. A 2002 report by the U.S.
Government Accountability Office, supplemented in 2003, estimated that getting
a single patent in the United States and
maintaining it for 20 years would cost a
small business about US $10 000, and that
extending that same patent to nine other
countries would add between $160 000
and $360 000. That's why an engineering
manager has to know how patent laws
vary between countries.
The first key point has to do with filing deadlines. Most countries don't let you
publicly disclose your invention before filing for a patent on it. International treaties,
however, allow you to file in the United
States, then disclose your invention or sell
a product based on it, and then take up to
a year to file in other countries.
The second point is the cost of filing
and when it will be incurred. You have
to know this before beginning the process, or you may find out too late that you
can't afford to complete it. Typically, the
costs are low to moderate at the begin-

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MIck WIggINS

By KirK tesKA

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Table of Contents for the Digital Edition of IEEE Spectrum December, 2007