How smoother surfaces and rounder edges help keep us all safer and more connected.
Making the impossible possible with advanced technology is a frequently recurring theme in advertising today. It seems the wider world has finally “got” science; well-known high-tech brands are comfortable explaining how their technologies are enabling new and fantastic smartphone features, more immersive gaming and TV viewing experiences, safer more relaxing travel in our increasingly autonomous vehicles, among others.
Of course, we in the electronics industry are intimately familiar with the underlying innovations enabling these previously unimaginable new experiences. As digital computing capabilities advance at the speed of Moore’s Law – or, in some cases, even faster – system capabilities are making incredible gains, while at the same time physical size, power consumption and cost are reduced, resulting in new generations of products at once more user-friendly and affordable.
Automotive autonomous-driving systems provide a great example. Advanced safety features in particular have a habit of quickly transitioning from high-end options to mandatory fitments, as governments pursue the vision of zero road fatalities. Autonomous driving modes like pedestrian detection, collision avoidance, lane assist and adaptive cruise control can significantly reduce accident rates, and will be more in demand. Automotive radar will be critical for many of these systems, providing one of the most important senses alongside modes like visual sensing and lidar.
Once a high-end option, operating in the 24GHz band and supporting limited functionality, the latest 77GHz technology permits greater distance, speed and angular resolution suitable for mandatory safety systems within the tight space and power constraints of today’s vehicles.
There are already moves to use even higher frequency bands, such as 120GHz, in the future. The higher-frequency systems can also handle close-up work like parking assist or even monitoring passengers inside the vehicle to support features like gesture control. On the other hand, moving and manipulating the data from high-frequency radar, at multi-Gb/s rates, requires serious attention to engineering details all the way down to the physical properties of cables, interconnects and
circuit boards.
The cellular world is facing similar challenges, as 4G-LTE and 5G standards evolve to meet ever-growing bandwidth demands from increasing numbers of subscribers. And, of course, the impact of communications with the tens of billions of smart “things” we expect to see connected to the Internet is yet to be fully felt. 5G is expected to take off in the US and China this year, although economic factors will likely dampen European operators’ enthusiasm for a while yet.
These advanced cellular technologies, based on dual frequency-division multiplexing and operating at 6GHz antenna frequency to support the channel density and data rates demanded by modern digital lifestyles, can be highly vulnerable to background noise and distortion caused by unwanted effects such as passive intermodulation (PIM).
PIM is a key concern for network operators, infrastructure suppliers, installers and test-equipment manufacturers. The causes can be minute factors, such as unbalanced concentrations of electrons at sharp edges, or magnetic hysteresis in materials near the signal path. Even a rusty metal structure in the vicinity of an LTE mast is a potential cause of PIM distortion that can result in dropped connections, missed calls, or bit errors that waste data bandwidth – ultimately translating into lost revenue for operators.
Overcoming the challenges to signal integrity in the multi-GHz world demands minute attention to detail, including aspects such as the properties of materials that make up connectors and cables, and even the surface finish of conductors. It’s an environment plagued by anomalous effects, like skin effect and transverse electromagnetic mode (TEM), that have a profound effect on signal propagation. Above a few GHz, the skin depth for copper is significantly less than one micron, so a poor or inconsistent surface finish can cause disruptive losses and reflections. The resistivity and magnetic permeability of conductors also have an important effect on signal transmission, as do the effects of dielectric materials associated with the transmission lines.
The challenges to signal integrity are intensifying, but are not entirely unforeseen. It’s been heading this way for some time, and countermeasures like low-PIM cables and connectors are already in the market. As far as printed circuit materials and processes are concerned, standard substrates are known to be unsuitable at signal frequencies above about 500MHz. Low dissipation factor (Df), low dielectric constant (Dk) laminates and prepregs have evolved with moves toward generally higher signal frequencies throughout electronics applications. Low Df and Dk give designers more freedom to optimize copper trace widths, spacing, and PCB thickness to maintain signal integrity and meet other design constraints such as size and cost.
The stability of substrate parameters over time and temperature is extremely important to ensure repeatable performance. In addition to setting new benchmarks for Dk and Df, further innovations such as Hyper Very Low Profile (HVLP) copper give conductors a consistent surface finish for near-perfect PIM performance compared with standard HTE copper foils.
As our industry continues to redefine the limits of possibility, we can expect to face even more exacting engineering challenges – wherever in the signal chain our expertise may lie. These challenges will likely demand even more inventive and thoughtful solutions. But we are consumers, as well as inventors, and we all share the desire to discover what comes next.
Martin Cotton is director OEM projects at Ventec International Group (ventec-group.com); This email address is being protected from spambots. You need JavaScript enabled to view it..
