The other day, while browsing through an engineering magazine (one of my favorite activities for learning via serendipity), I saw an ad from a vendor of litz wire.
I thought, “There's a term I hadn’t seen in many years.” In this case, it was an ad from New England Wire, although there are other vendors, of course.
If you're not familiar with it, litz wire is not named after a person or a place. It's short for Litzendraht , the German term for braided, stranded, or woven wire. It's a very clever solution to the problems and inefficiencies caused by the skin effect — as the frequency of the current that a wire carries increases, the current tends to go to the outside of the wire.
The faster the electronics zip back and forth, the more they repel one another. As they try to stay farther away from one another, the effective resistance of the wire increases, and so do the losses. More and more of the wire's cross-section is rendered ineffective. Due to the skin effect, you are paying for copper and associated physical bulk, yet it is doing you little good and is actually counterproductive to effective signal conduction and component performance. The problem is most apparent and debilitating in components with lots of wire (think inductors or transformers).
Litz wire is effective at minimizing the skin effect up to about 500kHz. Above that, it is less effective for various reasons.
To make litz wire, the vendors abandon the single strand of wire. Instead, they use multiple strands of finer wires. With conventional stranded wire, the strands are meant to provide more bending flexibility, but thin strands alone won't reduce the skin effect. There are two additional characteristics of litz wire: The individual strands are insulated from one another, and they are woven together in various patterns to manage the electromagnetic fields of the wires at higher frequencies (different patterns can provide variations in performance characteristics). Thus the overall cable is composed of many fine, insulated wires in a precise braid.
I can only imagine what the production facility must look like. Since it must handle hair-thin wires that have very little strength, the pulling tension must be kept low, yet the braiding machine must also do its magic as the wires are pulled through the system. How do these machines keep the strands from breaking? How do they keep the whole thing from become an impossible tangle? Those production machines must be fairly impressive, and the people who designed them must be pretty clever.
Whether or not you have ever heard of litz wire or used a component made of it, you've undoubtedly run into other components that were cleverly designed to overcome or work around some physical limitations. There are capacitors, for example, in which the internal layers are fabricated in a way that reduces parasitic inductance or lowers equivalent series resistance.
These are just two examples, of course. Are there any other such design workarounds that caught your attention when you first saw them?