The reduction in size of medical
electronics is a benefit of component suppliers across the board making their
products smaller with lower power requirements. This article looks at the
benefits achieved from the miniaturization of magnetic reed switches and the
specific applications in which they are used.
The reduction in size of medical electronics can be critical in
allowing new medical devices and equipment that advance diagnostic ability
while increasing overall patient comfort during the testing process to come to
market. Over the past few years, the ability of manufacturers of magnetic reed
switches to substantially reduce the size of these switches has allowed
widespread use in hearing aids and heart pacemakers, as well as in several
additional new applications in diagnostic devices.
Magnetic reed switches are hermetically sealed switches that
are normally backfilled with an inert gas, such as nitrogen, to allow reliable
operation over many years and millions of operations. They are non-contact
devices that do not require any power until they are actuated (closed). For
these (and other) reasons, they are ideal for use within medical devices.
Within the past 10 years, the glass length of available
magnetic reed switches has been reduced from about 12.7 to 3.7 mm (e.g., Standex
GR150 series), which is currently the shortest reed switch available (Figure 1).
This represents a component reduction of 70% in length and commensurate width –
a significant contribution towards reducing overall size of medical devices that
use these components.
Imaging
One such medical device is a pill-shaped camera that is swallowed by the
patient (Figure 2). These devices take digital photographs as the camera moves
through the patient’s intestinal track. In this instance, the magnetic reed switch
is an integral part of the pill-shaped camera. The external camera packaging
contains a magnetic source that triggers the magnetic reed switch to activate
the battery operated camera as the camera is removed from its packaging for use
by a medical professional. Reducing the size of the pill shaped camera is
essential for patient comfort in both ingesting the device and as it moves
through the intestinal tract. Ingesting a smaller capsule can induce less
stress upon the patient than a larger device, which diagnostically may be
relevant with normal vital signs, like heart rate and blood pressure. While
micro-miniature devices are highly desired, the quality of the device cannot be
compromised to accommodate the smaller size.
Monitoring
Other new applications under development include use of similar battery
operated devices to allow remote monitoring of certain conditions within a
person’s body from microminiaturized instruments placed temporarily within the
body. Again, microminiaturization is a key element of success here, as smaller
devices are less intrusive when they reside within the body.
Hearing Aids
In hearing aids, magnetic reed switches are commonly used to automatically
detect the patient’s use of a telephone (or cell phone) and enables automatic
adjustment of the device for optimum sound. Additional hearing aid applications
of magnetic reed switches include remote manual stepping of hearing aid
amplifier gain. The reduced size of magnetic reed switches has allowed use in
in-the-ear as well as behind-the-ear hearing aid applications.
Surface Mount
Technology
While 3.7-mm long switches are a dramatic breakthrough, ultra miniature medical
devices can sometimes better use SMT (Surface Mount Technology) based devices.
This can increase reliability, reduce production cost, and sometimes, reduce
overall size of the medical device. The Standex SR4M series is a surface mount
version of the GR150 3.7-mm long magnetic reed switch in a molded SMT
configuration with a package length of 5.13 mm (Figure 3).
Conclusion
While medical device manufacturers would like smaller components, reducing the
size can be a complicated task. To manufacture the GR150 for high volume
production, Standex had to develop a totally new microelectronics based
manufacturing system for both the manufacturing and test processes. That
investment is yielding benefits, however, not only for the company and the
medical device manufacturers, but also for the doctors who perform the
procedures and the patients who undergo them.
Paul Linsley is a senior product manager at Standex
Electronics. He has over 30 years of experience designing magnetic technology
based fluid level and proximity sensor systems used in medical, automotive,
appliance, and security applications. Linsley can be reached at PLinsley@standexelectronics.com.