The history of inductors

2023-11-30

Today, we want to delve into the captivating history of inductors and take you on an informative journey through their evolution. Inductors, a fundamental component in electronic circuits, have a rich backstory that has contributed significantly to the development of technology.

Inductors, also known as coils or chokes, were discovered and studied by numerous scientists throughout history. However, the principles behind them were truly established by Michael Faraday in the 19th century through his experiments with electromagnetic induction. Faraday's brilliant insights laid the foundation for the modern understanding of inductors and electromagnetic fields.

Over time, various pioneers expanded upon Faraday's work to enhance the effectiveness and practicality of inductors. The introduction of iron cores to increase magnetic flux density by Joseph Henry and improvements made by Charles Proteus Steinmetz further revolutionized the field. These advancements paved the way for inductors to be widely used in applications such as transformers, electronic filters, energy storage, and more.

As technology progressed, inductors found their way into various industries, including telecommunications, automotive, aerospace, and renewable energy sectors. With their ability to store energy in magnetic fields and manipulate electrical currents, inductors have become indispensable in modern electronics.

I would like to share the story of inductors:

It is from approximately 30 years ago, when high-frequency chip inductors were developed. Mobile communications at that time referred to car telephones, which were so large that storage required the entire center console of a luxury car.

One day we received a request from a particular customer, "Do you have any high-frequency chip inductors with inductance up to 1 GHz, a high Q and a small inductance tolerance?" To be honest, my first thought was "What!? G- Gigahertz?"

At the time, our company had only one PC per section, with an 8-inch floppy-disk drive whirring and clicking as an external memory device. This was the era when documents were hand-written, copies were blue print, and ashtrays could still be seen on desks. The biggest obstacle was "How can we guarantee inductance values with narrow deviations for all units at high frequencies?"

High-frequency coils have been around for a long time. Spring coils were also used in mechanical tuners (the dials turned while clicking to change the channels of old TVs), and work by soldering the terminals and then deforming the coil with a spatula to tune the frequency. However, the specifications of those spring coils simply defined the physical dimensions such as the wire diameter, number of windings, and coil length, and did not guarantee the inductance value (nH ±x%) or other characteristics. This was right after Murata had started mass production of wire wound-type chip inductors, when we had the ability to make high-frequency inductors, but we worried about how to quickly and automatically measure the inductance and Q at high frequencies. Impedance analyzers (measuring instruments) capable of measuring up to 1 GHz existed, but at the time these instruments were not suitable speed-wise or mechanically for high-speed automated equipment.

We made some prototypes and the performance satisfied the customer's specifications, so adoption was decided and we started receiving orders. At first we relied on sheer force of numbers and measured each product by hand, but we were worried about how to cope as orders increased in the future.

While measuring and worrying in the shipping inspection room, an old Q meter (*1) off to the side caught my eye. The sight brought to mind nostalgic memories of my student days, but the Q meter would be of no use as it measured only up to 25.2 MHz, not to mention using analog tuning operation (turning a dial).

At that moment,  a second thought struck me, "A Q meter is a reactance resonance bridge (*2), isn't it? That's right! We don't need to measure the inductance itself." And once I had that thought, the rest was easy. I went and got a high-stability capacitor (after all, Murata is a capacitor manufacturer) and made a Colpitts oscillation circuit (*3). Next, I connected a power supply and a frequency counter, and conducted some tests. As expected, the oscillation frequency and the inductance correlated beautifully. I then made some modifications so that oscillation stopped when the Q value was low and finally connected the frequency counter output to a comparator (*4) to complete a high-speed automatic measurement and taping machine for high-frequency chip inductors. This provided prospects for mass production, enabling supply of sufficient quantities.

Mass production initially started up with two machines based on this measurement system. Some time thereafter, high-speed high-frequency impedance analyzers became available, which enabled direct high-speed measurement of inductance and Q from the third machine onward. Our first high-frequency chip inductor (LQN2A type: 3225 [mm]) was favored by many customers for many years. Since then, mobile communications have evolved at a tremendous pace, and the lineup has expanded accordingly and grown into the LQW series of wire wound-type high-frequency chip inductors.

High-frequency chip inductor series

*1 Q meter:

 An old analog measuring instrument used to measure the electrical characteristics of coils and capacitors. Wireless technicians with many years of experience may have nostalgic memories of using Q meters.

*2 Reactance resonance bridge:

 The principle of electrical balance for high frequencies. This system enables calculation of the value for an unknown coil when there is a resonator for which the value is already known and a balance can be achieved between the two.

*3 Colpitts oscillation circuit:

 A typical high-frequency oscillation circuit. Incidentally, the reason why I chose this oscillation circuit is that I was new on the job and this was the only oscillation circuit I knew at the time.

*4 Comparator:

 A device that sorts measured values into pass and fail and sends these results to machinery. A flag raiser.

At Hongda capacitors, we acknowledge the importance of staying up-to-date with the latest advancements in inductor technology. Our team of experts is dedicated to developing cutting-edge solutions that meet your specific requirements. From miniature surface-mount inductors to large power inductors, we offer a wide range of high-quality products to fulfill your diverse needs.

If you are interested in learning more about the history of inductors or seeking innovative inductor solutions, please don't hesitate to contact us. Visit our website or reach out to our friendly customer support team, who will be ready to assist you.

Thank you for your time, and we look forward to serving you soon.