Staying Connected - February 2011

Shielding Options for Medical Cables

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 medical cable design.

Shields are additional conductors added to wire or cable to help isolate the 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 within 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 foil and 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 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 common for many 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 both high and low frequency interference while maintaining good flexibility and flex life.

Braided shields are typically made up of groups of fine copper strands and are usually tinned.  Braided shield usually consists of two groups woven in opposite directions; one group is applied in a left-hand lay and other in a right-hand lay.  Because of this design, a braided shield offers good flexibility, approaching that of a spiral shield.

Most medical cables incorporating a braided shield specify 80 to 95% shield coverage.  The higher the percentage of braid coverage, the more effective the EMI shielding is.  Coverage of 100% is not possible with a braided shield because leakage will always occur at points where the strands cross each other.


Tinned copper braided shield
with 95% coverage


Bare copper braided shield
with 95% 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.


A drain wire running the length of
the shield facilitates termination

Braided shields can be 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.  Occasionally a drain wire running the length of the shield is used to make termination of the shield easier.

For applications requiring a very high number of flex cycles, a braided shield may not be the best choice.  The braid will occasionally break down due to the cross lapping strands abrading each other.  When this happens the broken strands can damage insulation with continued flexing.



Spiral shield with 95% coverage
under Teflon wrap offers
excellent flexibility and flex life

Spiral Shields

A spiral shield, also known as a serve shield, consists of wire (usually tinned copper) wrapped in a single-layer spirally around one or more insulated conductors.  A spiral shield typically 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


A foil shield requires a drain wire
to facilitate terminating the 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 effective at shielding both high and low frequency interference. 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.



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

Combination Shields

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.

Comparison of Types of Shielding

The following chart offers a comparison of the three types of shielding discussed and a summary of electrical and mechanical performance for each:

Cable Shielding Characteristics

Type of Shield

Percent Coverage

Low Frequency Effectiveness

High  Frequency Effectiveness

RFI/EMI Effectiveness

Flexibility

Flex Life

Braided

80-95%

Excellent

Excellent

Good

Good

Good

Spiral

80-95%

Good

Fair

Poor

Excellent

Excellent

Foil

100%

Excellent

Excellent

Poor

Good

Fair



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, both because of the need for patient safety and also because of the nature of physiological signals.

EMI and RF interference can degrade signals carried by medical cables making diagnosis difficult or even impossible. Effective shielding can reduce unwanted interference and reduce the amount of electronic filtering needed within the device.

The Affinity engineering team has the experience and expertise to assist you in designing medical cable assemblies with appropriate and adequate shielding for your specific application.

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Meet Matt Pathmajeyan – Senior Project Engineer



Matt Pathmajeyan
Senior Project Engineer

“Affinity’s engineering team was strengthened significantly when Matt joined our team,” said Affinity Director of Engineering, Bob Frank.  “Matt brought a lot of skill and experience to Affinity.  He has an excellent knowledge of materials and processes and interfaces well with our OEM partners and suppliers.”

Matt became acquainted with and acquired skills in mold design at a young age while working at his father’s company during high school.  He attended Cal State Long Beach where he pursued a degree in Mechanical Engineering.  After university, Matt was hired by Gish Biomedical as an R & D Engineer.  He later joined B. Braun Medical as a Project Engineer where he worked until he joined the Affinity engineering team in February 2008.

As a Project Engineer at Affinity Medical, Matt interfaces with customers daily.  “Our projects generally involve getting regular input from our customers and feeding design concepts back to them,” said Matt.  His extensive background in tool design enables him to not only design the components, but the tooling also.

When asked what he likes most about his job at Affinity, Matt replied; “I enjoy the creative side of design where I envision, develop and produce the product.  Since Affinity Medical Technologies is a small, family owned business, I feel right at home.  It reminds me a bit of working for my Dad many years ago. I look forward to a long and productive career at Affinity Medical.”


Matt plays and loves guitars

Besides project engineering, Matt was responsible for writing and executing the Master Validation Plan for Affinity’s new facility.  “Every customer who reviewed the validation plan for our new facility was impressed,” said Business Development Manager, Hank Mancini.  “Matt’s plan was comprehensive and gave our OEM partners confidence in our ability to move the company without negatively affecting production of their products.”

Matt spends much of his personal time involved in music. He plays multiple instruments and enjoys building and repairing guitars, amplifiers, and effects pedals. “I probably love the guitar so much because of its perfect blend of engineering and art; the way the strings and the wood interact with the electro-magnetics of the pickups all the way through to the glowing tubes of the amplifier and all the spots in between.”  Matt enjoys vintage guitars and amplifiers and is continuing to grow his collection.

Aside from music, Matt feels fortunate to live nearby to his family and enjoys traveling and spending time with his girlfriend Sara and their Dalmatian, Puka. He enjoys watching sports and supporting the LA Lakers and Angels.

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Nameplates and Inserts



High quality multi-colored nameplates
provide necessary information
and meet regulatory requirements

Medical cables and wires require labeling and marking for identification and to comply with regulatory standards.  One of the most common methods to label cable assemblies or custom connectors is to use high quality multi-colored nameplates.

Nameplates are generally designed to fit into recessed pockets molded into the cable yoke or connector.  Nameplate labels are printed on a durable material such as polycarbonate which resists cleaning agents and scratching.  The recessed pocket helps prevent the nameplate from being removed either accidentally or intentionally.  When attached using an appropriate adhesive, the nameplate is virtually permanent.


High quality nameplates allow company
Logo to be prominently shown

One of the advantages of a nameplate system is the ability to print brands and logos with intricate detail and in multiple colors.  The material and process used to produce nameplates lends itself to high quality printing.  A well designed nameplate can not only convey necessary information, but can help associate the cable assembly with the manufacturer’s brand.

The Affinity team has helped our OEM partners properly and effectively label cables and connectors.  If you would like to see examples or samples of high quality nameplates, contact Affinity at customercare2@affinitymedical.com or call us at 949-477-9495.

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Announcements, Information, and Trivia



Wearing green is a tradition
for Saint Patrick’s Day

Saint Patrick’s Day

While March has no official U.S. holidays, Saint Patrick’s Day is celebrated mid March.

Saint Patrick's Day is actually a religious holiday celebrated internationally on March 17th. It is named after Saint Patrick (c. AD 387–461), a patron saints of Ireland. It originated as a Catholic holiday but has become more of a secular celebration of Irish culture.

Since 1991, March has been proclaimed Irish-American Heritage Month by the U.S. Congress or the President. Saint Patrick's Day is widely celebrated in the U.S. by Irish and non-Irish alike. It is one of the leading days for consumption of alcohol in the United States, and is typically one of the busiest days of the year for bars and restaurants. Many people, regardless of ethnic background, wear green clothing or other green items. Traditionally, those who are caught not wearing green are likely to be pinched.


The Saint Patrick’s Day parade in
New York City is the largest
civil parade in the world

Saint Patrick’s Day is celebrated with parades around the globe.  The New York parade is the largest Saint Patrick's Day parade in the world.  In a typical year, 150,000 marchers participate in the parade and up to two million spectators line the streets for the five hour procession.  The parade marches up a 1.5 mile route along 5th Avenue in Manhattan and is always led by the U.S. 69th Infantry Regiment.




Suzann Sitka, Cesar Jara and Candy Golding
- the Affinity Customer Care Team

Affinity Customer Care and
Hours of Operation

At Affinity Medical, we don’t have a customer service department.  In place of customer service, we have Customer Care Coordinators.  While our Customer Care Coordinators perform many of the same functions that customer service representative would, we strive to offer our OEM partners more than that.  The job of our Customer Care Coordinators is to take care of our OEM customer partners.

Affinity’s Customer Care team consists of Candy Golding, Suzann Sitka and Cesar Jara.  Candy is the team supervisor and has over twenty years experience working with medical cables.  Suzann joined Affinity over five years ago.  She has extensive experience having worked for several medical device manufacturers before joining Affinity.  Cesar is the newest member of the team, joining Affinity in mid 2009.

Affinity Medical Technologies Customer Care specialists are available to assist you from 7:00 A.M. until 4:00 P.M., Monday through Friday, U.S. Pacific Time, except holidays.

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Affinity Medical Technologies

New Address:
3545 Harbor Boulevard, Suite 150
Costa Mesa, CA 92626 USA
Phone: +1 949 477 9495
Fax: +1 949 477 9499

Email: Customercare2@affinitymedical.com
Website: www.affinitymedical.com
Blog: http://blog.affinitymed.com