Choosing the Right Connector Keeps Medical Equipment Shock-Free
By Dan Cronch, 3M Electronic Solutions Division

Planning for effective electromagnetic shielding ranks high on the list of the medical product designer’s considerations. Not only is proper shielding necessary for safe, effective products, but international standards demand it. The International Electrotechnical Commission (IEC) 60601-1 standard, Medical Electrical Equipment—Part 1: General Requirements for Safety, prescribes requirements to alleviate risks such as electrical shock and radiation hazards. The IEC 60601-1-2 standard, effective as of 2004, is a collateral standard that prescribes new, stricter electromagnetic compatibility (EMC) characteristics and more rigorous immunity testing requirements for medical equipment.

Shielding is necessary for four main reasons: to prevent the device from releasing electromagnetic interference (EMI) or radio frequency interference (RFI), which can disrupt and skew the accuracy of other electronic medical devices; to block ambient EMI and RFI noise emitted from other devices; to drain away electrostatic charges so electronics inside the device itself are not damaged; and to safeguard patients and users from electrical shock.

These considerations are essential to ensure the precision, reliability, and safety of any electronic device. However, nowhere is it more important than in hospitals, medical imaging labs, and doctor’s offices. EMI/RFI interference can, among other things, result in equipment failure and inaccurate results, potentially resulting in misdiagnosis, improper treatment or worse.

The level of shielding in a device is only as good as the sum of its parts. When it comes to interconnect components, designers must be careful to choose the right connectors and cables to ensure a high level of shielding if required for their application. Here are some features to consider when choosing interconnect products for medical equipment:

• Look for a connector that is fully shielded (360 degrees) with a conductive metal, such as plated steel or copper, to ensure high-quality shielding.

• Choose a connector with a low impedance path to ground to enable proper grounding for protection from shock hazards as well as electromagnetic interference.

• Consider a connector with an early mate/late break feature. In this type of connector, the shield mates before the signal mates and disconnects after the signal disconnects, preventing electrostatic charge from entering the signal path and damaging sensitive electronic components.

• Low-voltage differential signaling (LVDS) has been used successfully for years in medical image capture and display applications due to its excellent common-mode noise rejection, inherently low emissions, and very low power operation. If using LVDS technology, choose a connector with a proven track record in LVDS applications. The mini delta ribbon (MDR) connector, for example, has worked well with LVDS systems for many years.

• Shielded controlled impedance (SCI) connectors (3M’s products are shown at right) are well suited for clock lines in nuclear imaging units, including SPECT and PET. SCI is a unique solution for EMC in which designers may choose to use coax or twin-ax cables with an RF-style connector. SCI meets data rate requirements, is fully shielded, and has a smaller footprint than most RF connectors.

Choosing connectors that are compatible with a number of specialty cables offers the most flexibility in design. Because of their relative length, cables are highly susceptible to interference, so pay close attention to shielding features when shopping for cables.

One bad connector can cause an entire system to fail. To ensure the highest level of performance, reliability, and safety, choose the highest quality connectors and cables from a well-respected manufacturer.

Fortunately for the designer, proper shielding provides several ancillary benefits. One of them is a better signal. High-quality shielding keeps the signal path clear, resulting in a strong, clean signal while providing a low-impedance path to ground to drain static charges and prevent shock hazards. With the right connectors and cabling, designers can enhance the safety, performance, and accuracy of electronic medical devices.

Dan Cronch is a product development specialist with 3M’s Electronic Solutions Division, based in Austin, Texas. 3M Company manufacturers a broad range of EMC products, including connectors, cables, tapes, films, gaskets, and testing equipment. For more information, call 800.225.5373; email interconnectsinquirey@mmm.com; or visit www.3MInterconnects.com.