A graph of current versus time for circuits with and without inductors

A Deep Dive Into Inductors

February 5, 2026 by John Elliot V No comments

[Prof MAD] runs us through The Hidden Power of Inductors — Why Coils Resist Change.

The less often used of the passive components, the humble and mysterious inductor is the subject of this video. The essence of inductance is a conductor’s tendency to resist changes in current. When the current is steady it is invisible, but when current changes an inductor pushes back. The good old waterwheel analogy is given to explain what an inductor’s effect is like.

There are three things to notice about the effect of an inductor: increases in current are delayed, decreases in current are delayed, and when there is no change in current there is no noticeable effect. The inductor doesn’t resist current flow, but it does resist changes in current flow. This resistive effect only occurs when current is changing, and it is known as “inductive reactance”.

After explaining an inductor’s behavior the video digs into how a typical inductor coil actually achieves this. The basic idea is that the inductor stores energy in a magnetic field, and it takes some time to charge up or discharge this field, accounting for the delay in current that is seen.

There’s a warning about high voltages which can be seen when power to an inductor is suddenly cut off. Typically a circuit will include snubber circuits or flyback diodes to help manage such effects which can otherwise damage components or lead to electric shock.

[Prof MAD] spends the rest of the video with some math that explains how voltage across an inductor is proportional to the rate of change of current over time (the first derivative of current against time). The inductance can then be defined as a constant of proportionality (L). This is the voltage that appears across a coil when current changes by 1 ampere per second, opposing the change. The unit is the volt-second-per-ampere (VsA^-1) which is known as the Henry, named in honor of the American physicist Joseph Henry.

Inductance can sometimes be put to good use in circuits, but just as often it is unwanted parasitic induction whose effects need to be mitigated, for more info see: Inductance In PCB Layout: The Good, The Bad, And The Fugly.

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Big Heat Pumps Are Doing Big Things

February 5, 2026 by Lewin Day 31 Comments

The heat pump has become a common fixture in many parts of modern life. We now have reverse-cycle air conditioning, heat pump hot water systems, and even heat pump dryers. These home appliances have all been marketed as upgrades over simpler technologies from the past, and offer improved efficiency and performance for a somewhat-higher purchase price.

Heat pumps aren’t just for the home, though. They’re becoming an increasingly important part of major public works projects, as utility providers try to do ever more with ever less energy in an attempt to save the planet. These days, heat pumps are getting bigger, and will be doing ever grander things in years to come. Continue reading “Big Heat Pumps Are Doing Big Things” →

Detecting Helium Leaks With Sound In A Physics-Based Sensor

February 4, 2026 by Donald Papp 10 Comments

Helium is inert, which makes it useful in a lot of different industries. But helium’s colorless and odorless non-reactivity also means traditional gas sensing methods don’t work. Specialized detectors exist, but are expensive and fussy. Thankfully, researcher [Li Fan] and colleagues found a physics-based method of detecting helium that seems as elegant as it is simple.

The new sensor relies on a topological kagome structure, and doesn’t depend on any chemical reaction or process whatsoever. The cylinders in the structure are interconnected; air can flow in and speakers at the three corners inject sound.

Sound waves propagate through the air within the structure at a fixed rate, and as helium enters the sensor it changes how fast the sound waves travel. This measurable shift in vibration frequency indicates the concentration of helium. It’s stable, calibration-free, doesn’t care much about temperature, and resets quickly. Even better, the three corners act as separate sensors, making it directional. It’s even quite rugged. Just as a basket weaved in a kagome pattern is stable and resistant to damage or imperfections in the individual strips that make up the pattern, so too is this sensor only marginally affected by physical defects.

The sensor design has been tested and shown to work with helium, but could possibly be applied to other gases. More detail is available at ResearchGate, with some information about the math behind it all in a supplemental paper.

Optical Combs Help Radio Telescopes Work Together

February 3, 2026 by Maya Posch No comments

Very-long baseline interferometry (VLBI) is a technique in radio astronomy whereby multiple radio telescopes cooperate to bundle their received data and in effect create a much larger singular radio telescope. For this to work it is however essential to have exact timing and other relevant information to accurately match the signals from each individual radio telescope. As VLBI is used for increasingly higher ranges and bandwidths this makes synchronizing the signals much harder, but an optical frequency comb technique may offer a solution here.

In the paper by [Minji Hyun] et al. it’s detailed how they built the system and used it with the Korean VLBI Network (VLB) Yonsei radio telescope in Seoul as a proof of concept. This still uses the same hydrogen maser atomic clock as timing source, but with the optical transmission of the pulses a higher accuracy can be achieved, limited only by the photodiode on the receiving end.

In the demonstration up to 50 GHz was possible, but commercial 100 GHz photodiodes are available. It’s also possible to send additional signals via the fiber on different wavelengths for further functionality, all with the ultimate goal of better timing and adjustment for e.g. atmospheric fluctuations that can affect radio observations.

Thomas Edison May Have Discovered Graphene

January 31, 2026 by Al Williams 13 Comments

Thomas Edison is well known for his inventions (even if you don’t agree he invented all of them). However, he also occasionally invented things he didn’t understand, so they had to be reinvented again later. The latest example comes from researchers at Rice University. While building a replica light bulb, they found that Thomas Edison may have accidentally created graphene while testing the original article.

Today, we know that applying a voltage to a carbon-based resistor and heating it up to over 2,000 °C can create turbostratic graphene. Edison used a carbon-based filament and could heat it to over 2,000 °C.

This reminds us of how, in the 1880s, Edison observed current flowing in one direction through a test light bulb that included a plate. However, he thought it was just a curiosity. It would be up to Fleming, in 1904, to figure it out and understand what could be done with it.

Naturally, Edison wouldn’t have known to look for graphene, how to look for it, or what to do with it if he found it. But it does boggle the mind to think about graphene appearing many decades earlier. Or maybe it would still be looking for a killer use. Certainly, as the Rice researchers note, this is one of the easier ways to make graphene.

Building Natural Seawalls To Fight Off The Rising Tide

January 30, 2026 by Lewin Day 36 Comments

These days, the conversation around climate change so often focuses on matters of soaring temperatures and extreme weather events. While they no longer dominate the discourse, rising sea levels will nonetheless still be a major issue to face as global average temperatures continue to rise.

This poses unique challenges in coastal areas. Municipalities must figure out how to defend their shorelines, or decide which areas they’re willing to lose. The City of Palo Alto is facing just this challenge, and is building a natural kind of seawall to keep the rising tides at bay.

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Rare-Earth-Free Magnets With High Entropy Borides

January 29, 2026 by Maya Posch 15 Comments

Map of the calculated magnetic anisotropy. (Credit: Beeson et al., Adv. Mat., 2025)

Although most of us simultaneously accept the premise that magnets are quite literally everywhere and that few people know how they work, a major problem with magnets today is that they tend to rely on so-called rare-earth elements.

Although firmly in the top 5 of misnomers, these abundant elements are hard to mine and isolate, which means that finding alternatives to their use is much desired. Fortunately the field of high entropy alloys (HEAs) offers hope here, with [Beeson] and colleagues recently demonstrating a rare-earth-free material that could be used for magnets.

Although many materials can be magnetic, to make a good magnet you need the material in question to be both magnetically anisotropic and posses a clear easy axis. This basically means a material that has strong preferential magnetic directions, with the easy axis being the orientation which is the most energetically favorable.

Through experimental validation with magnetic coercion it was determined that of the tested boride films, the (FeCoNiMn)₂B variant with a specific deposition order showed the strongest anisotropy. What is interesting in this study is how much the way that the elements are added and in which way determines the final properties of the boride, which is one of the reasons why HEAs are such a hot topic of research currently.

Of course, this is just an early proof-of-concept, but it shows the promise of HEAs when it comes to replacing other types of anisotropic materials, in particular where – as noted in the paper – normally rare-earths are added to gain the properties that these researchers achieved without these elements being required.