Features

Connectors are getting smaller and denser. The question is, how small can connectors go? To answer this question, it is important to remember that the applications that use connectors demand a number of performance and reliability requirements, particularly in medical devices.

The limpness and feel of a cable that complements the connector can assist in assuring patients that they are being served in a quality environment.

Application-specific connectors — and reduced-size connectors in particular — have come on quickly during the last five years. This is now fueling the rapid change in a combination of technological advances, starting with new solid model design and performance prediction software that help new advances in circuit chip technology. These changes have aided in driving increased performance and improved capabilities. These evolving circuit chips demand much lower voltages and current flow but run much faster and store and process significantly more data, while yielding a longer battery life. New software too has enabled designers the ability to model much smaller connector options that can be manufactured from a simple CAD rendering to a reality. New shell sizes and shapes can quickly be altered and cut out with CNC machines within minutes. These changes provide a faster prototype cycle at a reasonable price to designers that need to squeeze every last millimeter of space out of their interconnection systems. Oftentimes, designers select a standard connector to begin their circuit testing, but eventually find they need a custom design variation.

Determining Size Requirements

Connector size requirements are often based on a few key application factors and performance constraints, including electrical current load, signal integrity, environmental conditions, and circuit mobility. Many additional factors include awareness and compliance to biological protection, minimal open gaps and creep in connected mated pairs that can hoard contamination as well as a specific material selection to allow for sterilization.

Omnetics IP68 Nano-Circular series is housed in one of the smallest form factors available and remains sealed.

Electrical signal noise in operating rooms must also be shielded to allow many electronic systems to run simultaneously without interference to each other. Even the limpness and feel of a cable that complements the connector is considered a characteristic that can assist in assuring patients that they are being served in a quality environment.

A miniature cable that is ruggedized and overmolded with medical-grade silicone has a connector at the end that mates to a disposable catheter.

Electrical Current Load

Each connector contact must offer a low resistance interface with its mate and carry enough electrical current to satisfy the circuit it is serving. Fortunately, advances in chip technology have reduced the current flow rate, which enables the shrinking of interconnecting elements as long as they stay within a safe range for good performance (with some variations for power and signal surges). Current limits are often set by the diameter of the wire in the cabling itself, because wire length times resistance will set the performance and thermal capabilities of the interconnection system.

Using a low-resistance wire option that handles enough electrical current to run the equipment is often critical. So many machines are often running simultaneously, that high resistance can slow down the signal processing units or delay the triggering of emergency alarms. When connectors are designed with matched impedance, it also provides significant clarity in displays in the room.

Signal Integrity

As connectors and circuit modules squeeze into tighter spaces, circuits must still function independent of adjacent circuits. Designs must include protection against signal cross talk, as well as protection from electromagnetic emissions or reception of other signal noise in and about the system. Some modern shielding tricks are often built into the connector.

New shield materials often combine braided wire and aluminum foil that are wrapped around the length of the cable, inside the jacket material. Also, small ceramic filter discs can be included inside the connector housing that selects which frequency signal can pass through the cable and which are bled off to ground.

Environmental Conditions

Ruggedized connector designs for performance in extreme environments are often controlled by specifications that ensure continuous signal flow during high shock and vibration, as well as performance during extreme temperature cycles. Blood perfusion monitors, for example, sit near the patient during operations to assure the surgeon that there is no internal bleeding that can't be seen from the operating table.

A miniature cable that is ruggedized and overmolded with medical-grade silicone has a connector at the end that mates to a disposable catheter. The catheter rests inside the brain and is small and delicate. In this case, the main cable protects the small catheter from being accidently moved or pulled on during its use. Eventually the catheter is removed and disposed of, while the connector and cable assembly goes off to the rigors of sterilization and cleaning.

In some portable applications, such as neonatal monitors, electrocardiogram systems, and other skin-sensitive detectors, connectors often face some additional challenges. Ingress protection (IP) ratings, such as waterproof sealing and resistance can be critical in portable cable and equipment. Omnetics Connector Corporation's IP68 Nano-Circular series is an example of how this problem is solved in today's market. These connectors are housed in one of the smallest form factors available and remain sealed.

Selecting the proper materials and processing can also produce connectors that exceed specifications in IEC 60601 and prevent any electrical leakage or shorting to the patient being treated. Elastomeric seal rings are often built into connectors to ensure that neither moisture nor dust penetrate through the connector and enter the circuitry. Smaller and smaller seals will be needed as connectors continue to miniaturize.

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