As a member of IEEE I receive several tech journals and magazines and usually glance through them with something less than the rigor that the horse racing enthusiast perched at the rail uses to examine a copy of the Daily Racing Form. Nevertheless, every once in a while something catches my eye and that was the case recently when I came upon an article in the January 2014 issue of the IEEE Consumer Electronics magazine. The paper, entitled “ A New Trend in Connectivity” was written by Joshua Benjestorf, president and CEO of NMC Corp. , an engineering startup company focusing on non-mating connectors (hence the name NMC).
As you know, standard electronic connectors are used to physically connect devices to each other allowing signal data to flow through a mated pair of male and female receptacles. These contacts however, are exposed to the environment so connectors on devices such as smartphones or tablets can act as entry ports for water. While special insulating cases can be designed to keep water out, they usually do not completely seal standard connector ports and thus these contacts can be subject to fretting corrosion, resulting in signal loss. Beyond corrosion and oxidation, insufficient down force between the two metal contacts as well as dust particles that build up on them can, over time, also contribute to losses by increasing contact resistance.
During the operation of high-speed circuits, losses in signal quality further can be caused by signal reflections due to impedance mismatches between the source impedance, transmission line impedance and load impedance. In theory at least, using impedance matching can result in zero signal loss in system-to-system communication but despite the best efforts of connector designers to try and match impedance as best as possible we don’t live in a perfect world and every electromechanical device has some signal loss. In addition, electromechanical interference (EMI) from drives, motors and other nearby noise-producing equipment can cause loss or unreliable signal transmission but solutions to this potential hurdle are well in hand via shielded connectors and cabling that eliminates EMI concerns.
To prevent fretting corrosion, two primary methods are employed; using “high” contact forces or using costly materials such as gold which has good electrical properties and is not subject to corrosion issues.
In his article Benjestorf suggests another approach: his company’s patent pending Non-Mating Connector (NMC) designs eliminate the need for metal-to-metal ohmic contacts. Non mating connectors are different in that they propagate signal data using capacitive and/or magnetic coupling instead of conduction current. There are two types of NMCs. One deals with signal transfer using capacitive coupling, and the other deals with power transfer using inductive coupling (since capacitive coupling does not work for power transfer). The inductive coupling NMC is not unlike wireless chargers now on the market, functioning like a transformer with primary and secondary coils.
According to Benjestorf, to transmit data signals NMC connectors work by using electric fields between metal plates (that are insulated) rather than metal-to-metal wire contacts. The electric fields are concentrated in the dielectric material which also insulates the two plates from any water or dust. Completely sealed in a polymer the connector is said to be completely waterproof due to the lack of exposed ohmic contacts, eliminating the connector as a means of entry for water.
Electric fields between two plates of the NMC pass the data signal. In the IEEE article Benjentorf describes a proof of concept NMC connector that is deliberately and strikingly similar in design to standard USB 3.0 connectors. This was done for USB 3.0 compatibility and testing purposes.
NMC engineers, Benjestorf said, have also developed a way to transmit USB power, so the NMC connectors will be fully functional USB connectors.
Since it is designed to be compatible with the USB 3.0 standard the first NMC connector is symmetric about the horizontal axis, so you can no longer insert USB devices upside down, a common complaint about USB. An adapter to convert from NMC USB to regular USB is expected to allow for easy adoption of the connector with any device currently on the market.
In terms of its ability to transmit signals, the NMC proof of concept device demonstrated from test results that it, “exceeded the standard.” Benjestorf noted that three different values for capacitance were tested and all of them “were within 1% of each other.” NMC Corp. has observed elsewhere that test results showed performance 84.5% above the USB standard. What is more, the company has found that unlike that of traditional USB connectors, insertion loss with the NMC connector improves with higher frequency and data rates.
NMC connectors also eschew the use of standard mechanical latches that mechanically hold the two connector parts together; instead magnets are employed.
NMC engineers still have a lot to work to do before the product is ready for commercial introduction. The company admits it has to refine its working designs to reduce costs and it needs to develop procedures to manufacture the NMC connectors and adapters on a large scale (and acquire the machines to do so) a task that is going to present financial as well as technical challenges for the startup company.