Can Connectors Be Created Without Contacts?

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Contacts have long been the key component of every connector, delivering power and data. But the contact is also the most vulnerable element of connector design, subject to repeated use and damage during operation. In this blog, we consider why contacts are potentially a connector’s biggest point of weakness, if there any alternatives to conventional physical contact design, and why engineers would need them.

Contact Conductivity and Strength

Once mated, connectors have no moving parts. They remain in place until they are removed, but the very act of mating and unmating is the source of damage. Electrical contacts are commonly manufactured from alloys that combine good conductivity with mechanical strength. They also need to be easy to manufacture, whether using stamping techniques or machining. While pure copper is an excellent conductor, it is too soft and lacks the spring properties required. To achieve the performance needed, copper alloys are used, typically brass or beryllium copper.

Damage Caused by Contact

Alongside conductivity and strength, contact construction needs to ensure they remain in physical contact during use. This is achieved by creating a normal force between the two elements of the pair to ensure that vibration or shock does not cause the contact to become unmated. However, the force required to mate the connectors can also cause damage to the surface. After even a few cycles, the mating surface of the contact can become damaged. Under a microscope, the mating face of a contact will resemble the surface of a glacier with peaks and crevices.

Damage to the contact’s mating surface has a direct impact on the performance of the connector. Instead of the smooth surface of a new contact, the damage reduces the surface area that remains in contact with its mating face. This reduced area increases the electrical resistance of the connector system. In a power connector, this creates unwanted heat. For high-speed data connectors, reduced conductivity affects signal integrity, potentially causing critical data loss.

The movement of two unplated metal surfaces is a leading cause of connector failure, both during the mating cycle and the subsequent damage caused by fretting, which is the micro-vibration of the metals during normal operation. This is why the metal surfaces of a connector are plated. Gold is both a good conductive surface and self-lubricating, reducing the amount of force required to mate a connector and consequently reducing damage and extending the connector’s lifetime.

Designers in the connector industry have developed many innovative designs to reduce the damage caused by connector operation. The goal of these innovations is to maintain positive electrical contact between the two halves of a connector pair while minimizing mating force.

Unconventional Contact Design

Traditional connectors use a pin-and-socket configuration, in which a solid male pin is housed within the receptacle. Connectors like this must remain securely mated even when subjected to vibration. Pin-and-socket configurations offer 360° mating and are well suited to high-vibration applications. However, these are often accompanied by thick gold plating to achieve the reliability demanded by harsh conditions.

Another commonly used design is a USB connector that uses a wiping-style contact. Instead of a pin-and-socket arrangement, wiping contacts feature two spring surfaces that glide over each other as they mate. This design keeps the normal force to a minimum and extends the lifespan of the connector. Modern USB connectors are expected to perform many thousands of mating cycles, which is remarkable when we consider that MIL-Spec circular connectors are often rated at just 500 mating cycles.

Even with its high life cycle, the USB connector is not a solution for all applications. Industrial applications illustrate this challenge well. Industrial robots move constantly and require connections to deliver power and data from one part to another. Creating a reliable joint that will last the lifecycle of a robot is tricky. Cables that flex constantly will break, and connectors will wear out. Rotational connectors do exist, but they are both highly specialized and quite expensive. How can designers solve this complicated challenge?

Doing Away with Connectors?

With the availability of wireless communication systems, from 5G to Bluetooth^®, some designers have contemplated whether the connector could be removed completely. After all, the latest generation of wireless communications rivals conventional wired alternatives in speed. However, there are a few considerations preventing the demise of connectors.

Power Transmission

A major obstacle of a connector-free design is power. While data can be transmitted wirelessly, the power these devices need is harder to deliver without wires. Engineers and science fiction writers have, for many years, suggested that power can be sent via microwaves, lasers, or even radio waves. While these schematics might present an alternative to today's power grid, there are practical limitations. At a time when we are all being encouraged to reduce energy use, converting energy to microwaves impacts system performance. Current microwave systems deliver typical efficiencies between 30 and 60 percent,^[1] not including the losses incurred by transmitting energy through the atmosphere.

Another significant issue with relying on wireless power transmission is safety. Any system powerful enough to send energy over useful distances is also powerful enough to cause harm to any organism that intercepts the beam. At the short range of a factory floor, keeping an energy delivery beam focused on a moving robot while keeping workers safe is complicated. Therefore, for power at least, some kind of physical connection is preferred.

Interference and Security

Interference also presents a critical hurdle to doing away with connectors. The environment where connectors typically operate is already awash with electromagnetic radiation. Some is intentional, some is unwanted. With every wireless system emitting yet more radiation, the danger is that they overwhelm an already crowded electromagnetic spectrum. One person’s wireless signal is another person’s interference. Furthermore, with cybersecurity more relevant today than ever, an intercepted signal could potentially present a security weak spot.

Physical connectors can be shielded to prevent the emission of unwanted EMI and protect against interference from the environment. They also provide an element of security since cables and connectors can only be intercepted if they are accessible.

With these considerable constraints, it is safe to say connectors will be with us for some time.

Contactless Connector Technologies

Since connectors are here to stay, the question becomes, can we remove the contact from the system? Well, there are possibilities. While it is impractical to transmit power wirelessly over long distances, there are highly successful short-range alternatives. Inductive coupling is a technology already in use for wireless charging. It requires proximity to be effective, and it is a highly efficient system at close range. Moreover, inductive coupling does not pollute the electromagnetic environment in the same way as RF signals. A two-part connector that uses inductive coupling to transfer data or power would not need to make physical contact. Simply being close would be enough.

Another technology employs radio frequency communication using a near-field loop antenna. Just as in inductive coupling, this technology requires the two halves of the connector to be close, but they do not need to touch. Connectors that combine both technologies in the same connector housing offer power and signal delivery without physical contact.

The system still requires a pair of connectors, but without the need for physical contact, there is no material wear and tear. The lifespan of such a connector system is no longer limited by mating cycles, making it ideal for dynamic applications such as robotics or manufacturing. The two halves of the connector can even be separated by a pane of glass. This makes it useful for any application in which devices are inside a sealed container, such as a vacuum chamber or medical isolation unit.

Conclusion

Conventional connectors will continue to stay in designs. Despite the challenges posed by mechanical and environmental damage, their simplicity and availability make them unlikely to be replaced soon. Wireless communication will continue to be popular, but even in the latest 5G infrastructure, conventional connectors are essential.

However, contactless connectors have also found a place. Doing away with the need for physical contact provides enormous benefits for durability in tough conditions. In applications that demand security, reliability, and performance, the latest generation of contactless connectors offers designers a worthy alternative.

Sources

[1]

 https://www.sciencedirect.com/topics/engineering/microwave-power-transmission