Magnetics Business & Technology - September/October 2019 - 13

FEATURE ARTICLE

romagnetic materials in the vicinity of the magnetic field source.
Modeling software is the simplest way to visualize this effect
and show the resultant fields.

A Case Study - Rotational Direction Gauge

We were challenged to build a surgical medical device with an
end effector that knew where the end was in 3D-space at all
times. Though not too hard on its own, we wanted a device that
was fast, easy to use, and could be subject to liquid spray and
intense cleaning. We choose to use an arm with both an "elbow" joint and a "shoulder" joint, both of which needed to read
their angles. The elbow wasn't too difficult - we used bearing
system to provide the single degree of freedom with a magnetic
Hall Effect encoder, and a disposable, sterile sleeve overtop.
However, the shoulder has an extra degree of freedom, so we
chose to use a stainless steel ball that sat in a shallow cup
which had a disc magnet hidden under it. The cup was moulded
right into the plastic of the base to be totally watertight. It was
very successful - the ball was very tightly coupled to the base
via the hidden magnet but could move freely in rotation (just
like a real shoulder). The location was measured by an optical
encoder. The base and arm were easy to separate and clean.
We chose 440C series stainless steel for the ball because it's
both corrosion resistant and magnetic.

(mixing tiny amounts of substances or activating tiny valves);
numerous EMI shields to isolate precision sensors used in
diagnostic medical devices; as well as similar applications to
the arm system described above for connecting parts together
through a waterproof barrier.
Overall, magnetics play an essential role in medical devices in
many ways, but most commonly they are found in EMI shielding or where parts need to be coupled though a sterilisable or
cleanable barrier.
About the author: Nigel Syrotuck is Engineering Team Lead of Starfish Medical in Victoria, BC, Canada, a medical device design
company which provides design, development and manufacturing services to help
companies create products for a number
of medical specialty areas. Prototype and
volume production are delivered in an ISO
13485 certified facility with FDA registration
and class 100,000 clean room capabilities.
For more information, see www.starfishmedical.com.

Other medical device applications where we've chosen magnets include: a small magnet to trigger a present/not present
Hall Effect sensor through a waterproof shield to indicate that a
refill cartridge in a handheld device was fully inserted; a magnetic system for mixing liquids within a closed container (similar
to commercial magnet mixers); various microfluidic applications

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September/October 2019 * Magnetics Business & Technology

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Magnetics Business & Technology - September/October 2019

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