Are non-magnetic connectors in your future?

Many years ago, I overheard an engineer, with whom I had some project contact, make a casual remark about an RF connector situation, asking “what’s the big deal, it’s just a connector?” That statement was enough to make me wonder about his overall professional judgment.

Connectors may look simple but they are not, of course, as they must combine electrical requirements with mechanical issues and incorporate suitable materials for both body and contact. The materials and platings of their contacts are especially intricate as they blend metallurgical chemistry with other factors such as manufacturability, flexibility, resilience, and resistance objectives.

In recent years, there’s been an added demand on connectors: the need to be non-magnetic. Technically, this means the connector’s materials exhibit extremely low magnetic susceptibility, as they neither generate magnetic fields nor interact with external ones in any significant way.

Note that the term “magnetic connector” is also used for a connector/cable that relies on a magnetic force to both make and maintain a connection. In this arrangement, the plug and the socket have corresponding magnets or magnetic faces to make a self-aligning connection. They are designed for quick, easy, and, often, “break-away” disconnection to protect ports from wear and damage. But the magnetic/non-magnetic connectors here are not these.

Is it easy to visually distinguish a magnetic connector from a non-magnetic one? Maybe, maybe not. Some non-magnetic connectors have a different surface sheen or glow compared to conventional connectors, while others have different color (Figure 1). Of course, some magnetic ones also have a different color depending on the finish, so it’s not a certainty. Fortunately, magnetism is easy enough to test.

Figure 1 These two RF connectors are non-magnetic; other than their color, they look like magnetic connectors. So, color alone is not a definitive indicator. Source: Rosenberger Group

Even minute amounts of magnetic “interference” can have significant consequences in high-frequency or magnetically sensitive systems. Therefore, the objective of non-magnetic component design is to make these parts “magnetically invisible”. So, they don’t distort the surrounding field or interfere with nearby sensors or measurement instruments.

This is especially crucial in environments where magnetic fields play an active role, such as MRI systems, particle accelerators, and quantum computers:

• In MRI systems, magnetic components can distort the magnetic field lines, leading to degraded system performance, measurement inaccuracies, and artifacts in imaging results. In contrast, non-magnetic components minimize these disturbances by maintaining field uniformity.
• In precision RF and microwave metrology, magnetic components can bias sensor readings or create unpredictable phase errors. For example, a magnetic connector near a current probe could influence the magnetic coupling, altering the measured waveform.
• In systems such as scanning electron microscopes, where magnetic fields steer and direct the electrons to supercolliders, where superconducting magnets keep the particle centered as they are being accurate, the magnetic field must be precisely shaped and controlled.
• In the “hot” field of quantum computing, the qubits—the quantum bits that carry computational information—are extremely sensitive to external magnetic fields. Even minor magnetic impurities in nearby materials can cause decoherence, leading to computational errors or reduced qubit lifetime.

Non-magnetic connectors provide low–loss signal transmission and maintain stable performance across temperature cycles—without contributing to unwanted magnetic noise. In these cryogenic systems, even small amounts of magnetic interaction could invalidate experimental results.

A non-magnetic connector will typically have a low magnetic susceptibility of less than 10^-5 (think back Electromagnetics 101: susceptibility is a dimensionless ratio) and a magnetic field strength of less than 0.1 milligauss. That’s at least one to two orders of magnitude less than standard connectors.

Making the non-magnetic connector

It may seem that all that’s required to make a non-magnetic connector is to use non-magnetic material such as copper. If only it were that easy, as non-magnetic materials have very different mechanical and electrical attributes, which affect connector performance and consistency.

A connector has three elements: the body, usually made of nylon or an engineered plastic and not a magnetic consideration; the contact or terminal pin, usually phosphor bronze, beryllium copper, or brass; and the surface plating(s), which can be copper, nickel, gold, tin, silver, palladium, or other metal.

The plating is the largest challenge, as it’s critical to long-term performance of the contact surfaces. The magnetic metals that are the concern here are iron, cobalt, and nickel, notes the Samtec video “Exploring Non-Magnetic Interconnects” (Figure 2).

Figure 2 Trouble zone in the periodic table: these three elements are the source of most of the magnetic problems. Solid-state physics analysis explains why this is so. Source: Samtec Inc.

The simple solution would be to avoid using these metals and instead use brass or aluminum for connector bodies with silver or gold plating. However, that’s often undesirable for performance reasons.

There are other options. For example, Samtec uses a nickel-phosphorus electrodeposited coating that works as a barrier layer between the copper-alloy base metal and subsequent outer layers. This barrier is needed to prevent migration of the copper to the surface-layer gold or tin of the connector pins, which would degrade the performance of that layer.

But wait—isn’t nickel one of the troublesome metals? Yes, but that’s where metallurgists bring some technical “magic” to the story. By adding phosphorus to the nickel, the ferromagnetism associated with high-purity nickel is reduced. This is because the added phosphorus interrupts the nickel’s atomic dipoles, causing the metal to become non-magnetic.

This is not the only option for going non-magnetic. Palladium provides a non-magnetic layer but is a costly alternative to nickel. Associated fasteners can be made of austenitic stainless steel (grades 304 or 316), which is non-magnetic due to its unique crystalline structure.

Other possibilities are eliminating the nickel completely, but this requires thicker copper and gold layers to slow the migration; use of a copper/tin/zinc alloy (Cu/Sn/Zn) called Tri-M3 as a barrier layer; or use of nickel-tungsten (Ni/W—tradename Xtalics). The goal is to reduce to grain size to nanoparticles and so disrupt the possibilities for alignment of the magnetic domains.

There are several ways to devise and fabricate non-magnetic connectors. It requires pure materials, deep-physics insight, metallurgical expertise, and precise control of production process. Assessing the non-magnetic characteristics involves sophisticated instrumentation to measure the magnetic permeability of the materials and connectors.

Each vendor has its own approach and a set of trade-offs regarding connector performance. Designers have many connector parameters to consider with respect to performance, solderability, number of mating cycles, supply-chain risk, and more.

The good news is that the increasing need for such connector means they are not items only available from one or two specialty suppliers. Nearly every manufacturer of RF connectors also offers non-magnetic versions, so users have many options for their connector needs and bill of materials.

What’s the price difference between magnetic and non-magnetic connectors? A quick, unscientific sampling showed that the non-magnetic ones were two to three times the price of their magnetic counterparts. It’s trivial to say that cost is a secondary concern in the applications where they are needed, but that is likely true.

Have you ever used non-magnetic connectors? Was the need for them identified in advance, or was it recognized after regular connectors were used, with problems identified and then linked to the magnetic connectors?

Certainly, the next time someone says, “it’s just a connector,” you can offer them firm evidence that’s not the case at all.

Related Content

• Consumer connectors get ruggedized
• Be aware of connector mating-cycle limits
• Giving Connector Contacts Adequate Consideration
• Through-hole connector resolves surface-mount dilemma
• Give Me Back My External Wi-Fi Antenna Connector, Please

The post Are non-magnetic connectors in your future? appeared first on EDN.