Staying Connected - June 2009

Cable and Leadwire Shielding Options

Because medical cables and lead wires can act as unintended antennas to both receive and radiate electromagnetic interference (EMI) signal shielding is often necessary and is an important consideration of cable design.  Shields are additional conductors added to wire or cable to help isolate electromagnetic fields of conductors within the shield from those outside of the shield.  Shields may be placed over individual conductors, groups of conductors, or the entire bundle of conductors with the cable.  It is often necessary to incorporate multiple shields, in which case, they are typically electrically isolated from each other.


Cable cross section showing inner
spiral shield and outer braided shield

Physiological signals are analog by their nature and are generally very low in signal strength, making interference problematic and effective shielding an important consideration.

The most common location for a shield is immediately below the cable jacket.  However, more complex cables may be made up of several components (sub-cables) with one or more shields.

Shielding helps prevent unwanted external interference but is often used to prevent internal signals (cross talk) from interfering with each other within the cable.  This becomes a more significant issue when a cable carries both power and signal lines which is not uncommon for medical applications.

Each type of shielding has its own advantages and disadvantages to be considered when selecting the most effective option for a particular medical cable application.

Braided Shields

Braided shields provide excellent protection from low frequency interference while maintaining good flexibility and flex life. The higher the percentage of braid coverage, the more effective the EMI shielding.  Braided shields are typically made up of groups of fine copper strands and usually tinned.  Groups of strands are woven “Maypole” fashion and then wrapped in opposite directions around the cable. Most medical cables incorporating a braided shield specify 80 to 95% shield coverage.  Coverage of 100% is not possible with a braided shield.


Tinned copper braided shield
with 95% coverage

Bare copper braided shield
with 85% coverage

In addition to the percentage of coverage, the tightness of the braid affects performance.  A tight braid with a high percentage of coverage does a better job of shielding but makes the cable or wire less flexible.  A loose braid offers greater flexibility but with reduced effectiveness of the shield.

Braided shields can be more difficult to terminate because the braid is commonly “combed out and pigtailed.”  The extra labor to terminate a braided shield can add cost to the cable assembly.


Spiral shield with 95% coverage
under Teflon wrap is very flexible

Spiral Shields

A spiral shield, also known as a serve shield, consists of wire (usually tinned copper) wrapped in a single-layer spiral around one or more insulated conductors.  A spiral shield offers increased flexibility and flex life as compared with a braided shield.  Spiral shields typically offer 90 to 95% coverage.  They are also easier to terminate and are most effective at providing low frequency protection.

Foil Shields


Foil shield with drain wire. Drain
wire facilitates terminating shield

A foil shield consists of metallic foil, typically aluminum, laminated to a film such as polyester or polypropylene.  Foil shields provide 100% coverage with the foil typically wrapped in overlapping layers around the cable core.  The 100% coverage is a physical property and does not mean that a foil shield provides 100% EMI shielding.  Foil shields are generally most effective at shielding higher frequencies. Foil shields are lighter weight, less bulky, and typically add less cost to a cable or wire assembly than braided shields.

Foil shields may be more flexible than a braided shield but typically have a shorter flex life. A drain wire, which runs the length of the cable in contact with the foil shield, makes a reliable electrical termination of the shield possible.

Combination Shields


Example of a complex multi-core
cable with an inner foil shield
and an outer braided shield

Combination shields consist of more than one layer or type of shielding and provide maximum shield efficiency across a wider frequency spectrum. The combination braid-over-foil combines the strength and flexibility of a braided shield with the advantages of 100% coverage of a foil shield.

Full shielding of medical cables is impossible because the shield can not be effectively terminated at the patient.  This generally means that some type of electronic filtering is needed even when shielded cables and lead wires are used.


Ferrite attenuator
molded over cable

Ferrite EMI Attenuators

Cable design can include a ferrite attenuator.  These are placed around a cable to absorb extraneous and unwanted energy traveling on the cable.  Low frequency and DC signals see only the conductor and are unimpeded, but higher frequency signals are suppressed and dissipated reducing EMI interference.

Summary

Cables designed for medical electronic applications present some unique problems, partly because of the need for patient safety and partly because of the sensitive nature of physiological signal levels.

EMI and RF interference can degrade signals carried by medical cables making diagnosis more difficult or even impossible. Effective shielding can reduce unwanted interference and reduce the need for electronic filtering with the device.  Affinity’s engineering team can assist you in designing medical cable assemblies with appropriate and adequate shielding for your specific application.

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Meet Brian Schwenke – Affinity Project Engineer


Brian Schwenke – Affinity’s
newest Project Engineer

One of the newest members of the Affinity team is Brian Schwenke, Project Engineer.   Brian joined Affinity Medical Technologies in October of 2008 and “hit the ground running” by leading several new product development projects.  His experience, skills, and personality have blended well within the engineering group and the entire Affinity team.

Before joining Affinity, Brian worked for B. Braun, a large international medical manufacturing company.   At B. Braun, Brian was involved in tool design, new process validation and many other aspects of engineering.   Before he began his engineering career, Brian was in the U.S. Navy for 11 ½ years.


Brian working in Affinity
engineering lab

Navy Posts included Hawaii and Coronado Island in San Diego California.  He received his Bachelor of Engineering degree while serving in the U. S. Navy in addition to being trained and serving as a Survival Instructor.

As Project Engineer, Brian’s role at Affinity Medical includes custom cable and tool design, validation testing, manufacturing process engineering and new product production support.  He interacts regularly with customers during engineering project conference calls.  Leading a new product development project he is also responsible for identifying raw materials, components and obtaining quotes from vendors.  Brian reports to Bob Frank, Director of Engineering, and works closely with the other project engineers.  He also interacts daily with Sales, Customer Care and Production Planning in order to complete customer projects on time.  


Brian demonstrating new production
tool to other Affinity engineers

When asked what he liked most about his job at Affinity Medical, Brian said, “The diversity of my daily tasks makes every day interesting.  I also was impressed with how helpful the other team members were in getting me acclimated when I first came on board.   It was nice to be part of Affinity Medical’s 12 year Anniversary Party, and our monthly birthday celebrations show that CEO Mary Phillipp and the other management members really take a personal interest in everyone here at Affinity.”

Brian, an avid surfer, commutes daily from Northern San Diego County where he lives with his wife, Amy and three sons, Jeremy, Brian Jr. and Kai.  They are proud to report that Brian, Jr. will be leaving home to attend California State University at Berkeley this July on a full football scholarship.  The Schwenke family’s eldest son, Jeremy, is in the U.S. Army and will be deployed to Afghanistan in July.  Their youngest son, Kai, who is just 3½ years old will keep Brian and his wife busy while their older sons are away!

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Lunch and Learn – An Affinity Program For You

Our Lunch and Learn program is another way we can stay connected and help our friends and customers.  Choose from one of our three programs and gain additional insight and perspective about custom medical cable assemblies and connectors.

Our programs last about forty-five minutes, with the time divided between learning and lunch.  Affinity will provide lunch for your group.  There is no cost or obligation, other than your commitment for three or more of your team members to attend and a meeting room with a digital projector.  Each of your team members that attend will also receive a copy of the training material.

  • Off-The-Shelf or Custom Medical Connectors – A discussion of three connector options: off-the-shelf, custom, or hybrid.  We’ll discuss the advantages and disadvantages of each including performance, cost, and availability.
  • ANSI/AAMI EC53 Compliance – the basis for establishing medical cable and leadwire specifications.  We’ll discuss the standard, its intent, and how it can be applied to medical cable design and connector design.
  • Strain Reliefs – A discussion of how strain reliefs affect both electrical and mechanical performance of medical cables.  We’ll show samples of off-the-shelf and custom strain reliefs and discuss the advantages and disadvantages of each.

Lunch and Learn sessions are offered free of charge and are conducted by Bob Frank or Hank Mancini, both with over 20 years experience manufacturing medical devices and cable assemblies.

For more information or to schedule a Lunch and Learn session for your team, contact Hank Mancini at 949-477-9495 or email to hmancini@affinitymed.com.

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Announcements and Information


Fourth of July fireworks
behind Washington Monument
Public Domain photo
by SSGT. Lono Kollars

Independence Day Holiday

Affinity will be closed Friday, July 3rd in observance of Independence Day.


Trivia

June is the sixth month of our year and is named after the Roman goddess Juno, the wife of Jupiter.  It is also the month with above average number of marriages.  Juno was the goddess of marriage and many consider it good luck to be married in June.

June is the month in which summer officially begins on the 21st.  In the Northern Hemisphere, it is the month with the longest daylight hours of the year.


Statue of Roman goddess Juno
– image source Wikipedia

National Catfish Day
yes, there really
is a National Catfish Day!


Catfish – image source Wikipedia

President Ronald Reagan issued Presidential Proclamation 5672 in 1987 designating June 25th as National Catfish Day.  The day honors farm raised catfish.  In his proclamation, Reagan said, “I call upon the people of the United States to observe this day with appropriate ceremonies and activities.”  The proclamation does not list what “appropriate ceremonies and activities” are.




Suzann Sitka and Candy Golding
the Affinity Customer Care team

Affinity Customer Care - Hours of Operation

Affinity Medical Technologies customer care specialists are available to assist you from 7:00 A.M. until 4:00 P.M. Pacific time, except holidays.

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Affinity Medical Technologies

1732 Reynolds Ave
Irvine, CA 92614  USA
Phone: +1 949 477 9495
Fax: +1 949 477 9499
Email: CustomerCare2@affinitymed.com
Website: www.affinitymed.com