interference

16 Articles

Setup of a small lightbulb passing light through a thin film

Experimenting With Interference On Thin Layers

August 26, 2024 by No comments

[Stoppi] has taken on a fascinating project involving the interference of thin layers, a phenomenon often observed in everyday life but rarely explored in such depth. This project delves into the principles of interference, particularly focusing on how light waves interact with very thin films, like those seen in soap bubbles or oil slicks. The post is in German, but you can easily translate it using online tools.

Interference occurs when waves overlap, either reinforcing each other (constructive interference) or canceling each other out (destructive interference). In this project, [Stoppi] specifically examines how light behaves when passing through thin layers of air trapped between semi-transparent mirrors. When light waves reflect off these mirrors, the difference in path length leads to interference patterns that depend on the layer’s thickness and the wavelength of the light.

To visualize this, [Stoppi] used an interferometer made from semi-transparent mirrors and illuminated it with a bulb to ensure a continuous spectrum of light. By analyzing the transmitted light spectrum with a homemade spectrometer, he observed clear peaks corresponding to specific wavelengths that could pass through the interferometer. These experimental results align well with theoretical predictions, confirming the effectiveness of the setup.

If you like pretty patterns, soap bubbles are definitely good for several experiments. Don’t forget: pictures or it didn’t happen.

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Reggaeton-Be-Gone Disconnects Obnoxious Bluetooth Speakers

February 23, 2024 by 29 Comments

If you’re currently living outside of a Spanish-speaking country, it’s possible you’ve only heard of the music genre Reggaeton in passing, if at all. In places with large Spanish populations, though, it would be more surprising if you hadn’t heard it. It’s so popular especially in the Carribean and Latin America that it’s gotten on the nerves of some, most notably [Roni] whose neighbor might not do anything else but listen to this style of music, which can be heard through the walls. To solve the problem [Roni] is now introducing the Reggaeton-Be-Gone. (Google Translate from Spanish)

Inspired by the TV-B-Gone devices which purported to be able to turn off annoying TVs in bars, restaurants, and other places, this device can listen to music being played in the surrounding area and identify whether or not it is hearing Reggaeton. It does this using machine learning, taking samples of the audio it hears and making decisions based on a trained model. When the software, running on a Raspberry Pi, makes a positive identification of one of these songs, it looks for Bluetooth devices in the area and attempts to communicate with them in a number of ways, hopefully rapidly enough to disrupt their intended connections.

In testing with [Roni]’s neighbor, the device seems to show promise although it doesn’t completely disconnect the speaker from its host, instead only interfering with it enough for the neighbor to change locations. Clearly it merits further testing, and possibly other models trained for people who use Bluetooth speakers when skiing, hiking, or working out. Eventually the code will be posted to this GitHub page, but until then it’s not the only way to interfere with your neighbor’s annoying stereo.

Thanks to [BaldPower] and [Alfredo] for the tips!

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Hackaday Links: June 4, 2023

June 4, 2023 by 9 Comments

A report released this week suggests that 50 flights into its five-flight schedule, the Mars helicopter might be starting to show its age. The report details a protracted communications outage Ingenuity’s flight controllers struggled with for six sols after flight 49 back in April. At first attributed to a “communications shadow” caused by the helicopter’s robotic buddy, Perseverance, moving behind a rocky outcrop and denying line of sight, things got a little dicey once the rover repositioned and there was still no joy. Since the helicopter has now graduated from “technology demonstration” to a full-fledged member of the team tasked with scouting locations for the rover while respecting the no-fly zone around it, it was essential to get it flying again. Several attempts to upload a flight plan failed with nothing but an acknowledgment signal from the helicopter, but a final attempt got the program uploaded and flight 50 was a complete if belated success. So that’s good, but the worrying news is that since Sol 685, the helicopter has been switching in and out of nighttime survival mode. What that portends is unclear, but no matter how amazing the engineering is, there’s only so much that can be asked on Ingenuity before something finally gives.

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Mon Dieu! French Parent Kills Cell Service For An Entire Town To Stop Kids Surfing

February 19, 2022 by 34 Comments

It used to be that having technical skills meant that fixing the computer problems of elderly relatives was a regular occurrence. Over the last few years this has been joined by another request on our time; friends with teenage children requesting help configuring their routers such that Internet access is curtailed when the kids should sleeping. In France a desperate parent took more extreme measures, buying a wideband frequency jammer to ensure les petits anges can’t waste the night away on social media sites through their cellular connections. It had the intended effect, but sadly it also interrupted cellular coverage over a wide area The French spectrum regulator ANFR sent in their investigators (French, Google Translate link), and now the unfortunate parent faces the prospect of up to 6 months imprisonment and €30,000 fine for owning and using a device that’s illegal in France.

A cursory search of everybody’s favourite online electronics bazaars will find plenty of these devices, so perhaps what’s surprising is that we don’t see more of these devices even if it’s not the first tale of interference tracking that we’ve seen. Judging by the strategies our friends with kids take, we’d suggest meanwhile to the unfortunate French person, that they simply equip their kids with restricted data plans.

Interference Patterns Harnessed For Optical Logic Gates

January 16, 2021 by 16 Comments

The basics of digital logic are pretty easy to master, and figuring out how the ones and zeroes flow through various kinds of gates is often an interesting exercise. Taking things down a level and breaking the component AND, OR, and NOR gates down to their underlying analog circuits adds some complexity, but the flow of electrons is still pretty understandable. Substitute all that for photons, though, and you’ll enter a strange world indeed.

At least that’s our take on [Jeroen Vleggaar]’s latest project, which is making logic gates from purely optical components. As he himself admits in the video below, this isn’t exactly unexplored territory, but his method, which uses constructive and destructive interference, seems not to have been used before. The basic “circuit” consists of a generator, a pair of diffraction patterns etched into a quartz plate, and an evaluator, which is basically a pinhole in another plate positioned to coincide with the common focal point of the generator patterns. An OR gate is formed when the two generators are hit with in-phase monochromatic light. Making the two inputs out of phase by 180° results in an XOR gate, as destructive interference between the two inputs prevents any light from making it out of the evaluator.

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Duality Of Light Explored By Revisiting The Double-Slit Experiment

October 18, 2020 by 41 Comments

We’ve all seen recreations of the famous double-slit experiment, which showed that light can behave both as a wave and as a particle. Or rather, it’s likely that what we’ve seen is the results of the double-slit experiment, that barcode-looking pattern of light and dark stripes, accompanied by some handwaving about classical versus quantum mechanics. But if you’ve got 20 minutes to invest, this video of the whole double-slit experiment cuts through the handwaving and opens your eyes to the quantum world.

For anyone unfamiliar with the double-slit experiment,  [Huygens Optics] actually doesn’t spend that much time explaining the background. Our explainer does a great job on the topic, but suffice it to say that when coherent light passes through two closely spaced, extremely fine openings, a characteristic pattern of alternating light and dark bands can be observed. On the one hand, this demonstrates the wave nature of light, just as waves on the ocean or sound waves interfere constructively and destructively. On the other hand, the varying intensity across the interference pattern suggests a particle nature to light.

To resolve this conundrum, [Huygens] jumps right into the experiment, which he claims can be done with simple, easily sourced equipment. This is belied a little by the fact that he used photolithography to create his slits, but it should still be possible to reproduce with slits made in more traditional ways. The most fascinating bit of this for us was the demonstration of single-photon self-interference using nothing but neutral density filters and a CCD camera. The explanation that follows of how it can be that a single photon can pass through both slits at the same time is one of the most approachable expositions on quantum mechanics we’ve ever heard.

[Huygens Optics] has done some really fascinating stuff lately, from variable profile mirrors to precision spirit levels. This one, though, really helped scratch our quantum itch.

Wearable Cone Of Silence Protects You From Prying Ears

February 17, 2020 by 36 Comments

Careful,  the walls have ears. Or more specifically, the smart speaker on the table has ears, as does the phone in your pocket, the fitness band on your wrist, possibly the TV, the fridge, the toaster, and maybe even the toilet. Oh, and your car is listening to you too. Probably.

How does one fight this profusion of listening devices? Perhaps this wearable smart device audio jammer will do the trick. The idea is that the MEMS microphones that surround us are all vulnerable to jamming by ultrasonic waves, due to the fact that they have a non-linear response to ultrasonic signals. The upshot of that is when a MEMS hears ultrasound, it creates a broadband signal in the audible part of the spectrum. That creates a staticky noise that effectively drowns out any other sounds the microphone might be picking up.

By why a wearable? Granted, [Yuxin Chin] and colleagues from the University of Chicago have perhaps stretched the definition of that term a tad with their prototype, but it turns out that moving the jammer around does a better job of blocking sounds than a static jammer does. The bracelet jammer is studded with ultrasonic transducers that emit overlapping fields and result in zones of constructive and destructive interference; the wearer’s movements vary the location of the dead spots that result, improving jamming efficacy. Their paper (PDF link) goes into deeper detail, and a GitHub repository has everything you need to roll your own.

We saw something a bit like this before, but that build used white noise for masking, and was affixed to the smart speaker. We’re intrigued by a wearable, especially since they’ve shown it to be effective under clothing. And the effect of ultrasound on MEMS microphones is really interesting.

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