Staying Connected - September 2007

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 an important consideration of cable design.

The strength of physiological signals carried by medical cables is often very low, making EMI interference problematic and proper shielding an important consideration.

A cable shield is typically placed between the core or conductors of a cable and the outer jacket.  More complex cables may be made up of several sub-cables, each being shielded.

Shielding not only keeps unwanted external interference out of the signal, but is often used to prevent internal signals (cross talk) from interfering with each other within the cable.  This is a often a significant consideration when the cable is carrying both power and signal lines.

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

Braided Shields


Braided Shield with 95% Coverage

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 shield.  Most medical cables incorporating a braided shield specify 80 to 95 percent shield coverage.  Coverage of 100% is not possible with a braided shield.

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

Braided shields can be harder to terminate because the braid must be combed out and pigtailed.  The extra labor can add cost to the cable or wire assembly.


Spiral Shield with 95% Coverage

Spiral Shields

A spiral shield, also known as a serve shield, consists of wire (usually copper) wrapped in a 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

A foil shield consists of metallic foil, typically aluminum, laminated to a film such as polyester or polypropylene.  Foil shields provide 100 percent coverage.  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 cost less than braided shields.

Foil shields may be more flexible than braid but typically have a shorter flex life. A drain wire which runs the length of the cable is generally used with foil shields to facilitate termination.

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 foil/braid combines the advantages of 100 percent foil coverage with the strength and flexibility of a braided shield.

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

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

Medical electronics involve some unique problems. These concerns are partly because of the need for patient safety and partly because of the sensitive nature of physiological signal levels.

EMI and RF interference can have a negative effect on the signals carried by medical cables and leadwires. Effective shielding can reduce unwanted interference and reduce the need for electronic filtering.  Let Affinity’s engineering team assist you in designing medical cables or wires with appropriate and adequate shielding.

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Mike Schubert – More than just designing cables


Mike spends many of his
working hours on the
production floor at Affinity

Although Michael Schubert only recently celebrated his one year anniversary at Affinity Medical Technologies, he has taken on his role as Project Engineer with gusto.  When Mike came on board a year ago, he was immediately thrust into several major engineering projects and became an integral part of the Affinity Medical team very quickly.

Before coming to Affinity, the majority of Mike’s professional experience had been in plastics manufacturing. With degrees in Engineering and Business Management, he has held various positions including Plant Manager, Supervisor and Manufacturing Engineer.  However, Mike Schubert has always been ready to assist wherever needed in the workplace.  For example, at previous companies Mike was instrumental in implementing the ISO certification process and also set up an entire Human Resources Department.  But his willingness to help out is not limited as Mike has worked at one time or another in shipping, customer service and production.  Mike Schubert’s working philosophy can be summed up as; ”Whatever needs to be done, whenever it needs to be done!”

 When away from his desk, Mike is usually out on the production floor conferring with management and team members.  His diligence and excellent work ethic are reflected in his early arrival and late departure from the Affinity Medical office every day. Mike is quoted as saying,” I do not think of a work day as consisting of only 8 hours.”


Mike enjoys the Affinity
10-Year Anniversary
Picnic in May

Mike’s major responsibility at Affinity Medical is working directly for Bob Frank, Director of Engineering as a Project Engineer.  He welcomes a challenge and truly takes ownership of his job while learning as much as possible about the entire company.  When asked what he likes most about his position at Affinity Medical Technologies Mike answered, “I enjoy the daily variety and learning Solid Works, the computer based design tool that I use every day as well as becoming familiar with the medical manufacturing industry.”

or the first six months of his employment, Mike’s family was still living in Northern California and he commuted 60 miles each way from his temporary residence.  Recently, after both of his daughters were married in the same year, he and his wife moved into their brand new home in Southern California. Mike is a member of several professional societies related to manufacturing. He appreciates all types of music from Sinatra to Schubert and also collects one of a kind and out of print classic comic books.

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Bonded Leadwires

One of the capabilities of Affinity Medical Technologies is offering our OEM customers a variety of choices in leadwires.  One of the options that has gained in popularity is bonded leadwires.

Bonded leadwires help eliminate wire tangle that is common when individual leadwires are used on Holter, event, or telemetry monitors.  Tangled leadwires can lead incomplete monitoring, patient discomfort.

Affinity Medical Technologies offers both shielded and unshielded bonded leadwires and in various configurations from two to ten conductors.  Almost any length lead is possible with the bonded wires typically separated 12 to 15” from the patient.


Example of 10-lead Bonded Cable

Example of 3-lead Bonded Cable

Affinity has expertise and experience in designing connectors and bonded leadwire systems for medical monitoring.  If you would like to see examples of cables incorporating bonded leadwires, contact Affinity Medical Customer Care at
949-477-9495 or email to customercare2@affinitymed.com.

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Announcements and Information

Tribute in Light

The "Tribute in Light" memorial is in remembrance of the events of Sept. 11, 2001, in honor of the citizens who lost their lives in the World Trade Center attacks. The two towers of light are composed of two banks of high wattage spotlights that point straight up from a lot next to Ground Zero.




Rosh Hashanah and Yom Kippur

September 13th is Rosh Hashanah, the Jewish New Year festival which commemorates the creation of the world. Rosh Hashanah lasts 2 days. Yom Kippur, on September 22nd is the Jewish holiday known as the Day of Atonement. It is considered to be one of the holiest and most solemn days of the year.  With Rosh Hashanah, Yom Kippur forms the Jewish High Holy Days.
           
            "L'shanah tovah" ... for a good New Year!



Suzann Sitka and Candy Golding
the Affinity Customer Care team

Affinity Customer Care - Hours of Operation

Affinity Medical Technologies customer care specialists are available from 7:00 A.M. until 4:00 P.M. Pacific time.

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Affinity Medical Technologies

1732 Reynolds Ave
Irvine, CA 92614  USA
Phone: 949-477-9495
Fax: 949-477-9499
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