Connector Technology: Rising to the Challenge

2012.01.18 // Posted by: Murray Slovick // Posted in: Articles, New Technology

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The connector designer is faced with ever-growing challenges: electrical connectors must withstand the rigors of harsh EMI, thermal and mechanical stress environments in automotive engine compartments, on welding machines, in remote cell tower locations and even on the human body. At the same time connectors must also support applications adhering to a myriad of military, computer, telecom, medical, appliance and automotive industry standards and specifications.

To meet all of these customer requirements suppliers churn out a bewildering array of contacts, materials, plating, moldings, assemblies and packages for board-to-board, wire-to-board, wire- to-wire, power, backplanes, I/Os and numerous other interconnects of all sorts.

But while the number of variants is impressive the major test for all of them remains the same: a successfully designed electrical connector must ensure predictable, reproducible and satisfactory field performance while also meeting industry demand for increased speed, smaller size, greater capacity and enhanced design flexibility.

Taken together it should not, then, be surprising that connector technology is the basis for a great deal of academic and industrial research. Let’s look at a few developments and trends that attracted my attention over the past few weeks.

Confirmed Seating

On at least two occasions the U.S. Space Shuttle program suffered serious time delays and incurred excessive costs simply because a plug was not seated well within a receptacle. The first of these occurred in a connector that allowed the Orbiter to send a signal to fire the solid rocket booster hold-down bolts, releasing the Shuttle from the launch pad. The belief was that the Orbiter pulled away from the plug as fueling occurred, resulting in a break in the connection.

The second occurred in the connector on the external tank that routes the lines to the engine cutoff sensors. This connector had an electrical disconnect during chill-down on several occasions, leading to a number of launch aborts. The belief here was that thermal contraction led to a separation of the plug and receptacle leading to a break in the connection.

After examining these failures Ellen Arens, Janine Captain and Robert Youngquist of the Kennedy Space Center proposed a sensor that provides a measurement of the degree of seating of an electrical connector (see NASA Tech Support Document KSC-13210/559). In other words, this sensor provides the distance which a plug is inserted into a socket or receptacle.

These sockets make contact with their corresponding pins by use of a small piece of metal that is extended by the presence of the pin. When the pin is inserted into the socket, a normal pin should make good electrical contact resulting in a low impedance connection.

In their concept the authors propose that a standard pin in a male connector would be replaced with a modified pin on which a resistive material is coated. This material provides a uniform resistivity along the pin’s length. As the pin is inserted into the socket, the sliding contact moves down the pin and the resistance is lowered, in proportion to the depth to which the pin has been inserted. Put another way the resistance across this pin changes as the point of contact between the pin and socket changes. Monitoring the resistance value then allows for correlation to a displacement value.

A user could monitor the resistance of this pin/socket, or by supplying a known voltage monitor the current (or by supplying a known current monitor the voltage) to determine the position of the pin relative to the socket. The authors (the resistive pin approach was conceptualized by Robert Youngquist and developed and tested by Ellen Arens and Janine Captain) assert that at the time of their reporting this is the only seating sensor ever demonstrated that can be located within a connector, i.e., an external element is not needed.

Designing a “Smart” Connector

When it comes to locating damaged or deteriorating telecommunications cable conventional wisdom has always been that pinpointing the exact location of failure required system or cell tower shutdown, even though that results in lost revenue and service. In an attempt to rectify this shortcoming, researchers at the Rochester Institute of Technology (RIT), working with Syracuse-based PPC Corp., have developed what they call the Smart Connector, a sensor device that once installed in the connecting units of coaxial cables can provide real-time information about equipment damage failure modes in RF cables.

The Smart Connector is smaller than a quarter and can be powered by harnessing miniscule amounts of RF energy from the coaxial cables it monitors. The technique used to monitor critical conditions and report on the sensor status is backscatter telemetry, which may be familiar to some engineers as it is also employed by RFID tag readers. In that application a reader transmits a continuous carrier wave to the tag, which when interrogated by an RF excitation then reflects -or backscatters - some of the signal back to the reader in an amplitude modulated form, corresponding to the tag’s data. In the case of the Smart Connector each sensor has a distinctive designation, so the system can be used to pinpoint problems it detects.

Beyond cellular connectors, the researchers envision this technology finding a place in other high value, or ‘can’t fail’ applications such as internal networks in spacecraft or aircraft. Both parties are in the process of final testing and technology transfer, according to Robert Bowman, professor of electrical and microelectronic engineering at RIT’s Kate Gleason College of Engineering.

Composites Fly

Two trends are driving a lot of product research and development in the aerospace/military connector industry. First, as airframe builders put more sophisticated electronic systems in every new aircraft − including fly-by-wire controls, sensors for closely monitoring aircraft systems, multimedia IFE (in-flight entertainment) and Internet access for passengers – they’re generating demand for higher data speeds and increased bus bandwidth. Second, with the high cost of aviation fuel there is a critical need for lightweight materials to reduce overall system weight and thereby lower fuel burn rates.

As an example consider the new Boeing 787, which entered commercial service with Japan’s All Nippon Airways (ANA) a couple of months ago. Strong, lightweight composite materials such as the carbon fiber laminate used in the 787’s wing and fuselage make up about 50 percent of the aircraft’s construction. Similarly, Boeing’s principal competitor Airbus is expected to make a larger commitment to composites (as well as to high-throughput fiber optics) in its A350 medium capacity, long-range widebody aircraft now under development.

As a supplier to the aerospace industry, connector manufacturers have had to embrace composite construction, too, as reducing weight and thereby improving fuel consumption is a principal issue among airlines, so even small aircraft components have to go on a diet.

Composites are plastic so they have greater corrosion resistance as compared to conventional metal materials and, due to their lighter weight (according to Glendale, CA based interconnect supplier Glenair, for most applications, composite connectors and accessories enjoy 40% weight savings over aluminum and 80% over stainless steel), threaded polymer plastic components are less likely to rattle loose.
Beyond that, composite housings and fiber optic filaments are not conductive (even though the composite materials are plated with conductive finishes) so EMI should not be an issue. Still, that benefit − composites are not conductive − could also be a hindrance. Here’s why: this new migration to composite materials for the external structures of airplanes exposes all the internal flight systems to severe environmental condition such as lightning strikes, which induce extremely high currents in the internal cable harnesses.

Where traditional metal-skinned aircraft act as a lightning rod, providing the lowest resistance for electrical discharges traveling from the sky to the ground, composite aircraft do not. Essentially, when you change to composites you do not have a Faraday cage (a conducting cage or enclosure designed to block out external electric fields to protect systems against lightning or EMI influences).

But progress has been made and supplier tests have shown that properly designed metal plated composite connectors can withstand to show that the connectors survive a lightning-like current pulse of 10,000 Amps for 500 µs.

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