36C3: Phyphox – Using Smartphone Sensors For Physics Experiments

December 29, 2019 by Sven Gregori 7 Comments

It’s no secret that the average smart phone today packs an abundance of gadgets fitting in your pocket, which could have easily filled a car trunk a few decades ago. We like to think about video cameras, music playing equipment, and maybe even telephones here, but let’s not ignore the amount of measurement equipment we also carry around in form of tiny sensors nowadays. How to use those sensors for educational purposes to teach physics is presented in [Sebastian Staacks]’ talk at 36C3 about the phyphox mobile lab app.

While accessing a mobile device’s sensor data is usually quite straightforwardly done through some API calls, the phyphox app is not only a shortcut to nicely graph all the available sensor data on the screen, it also exports the data for additional visualization and processing later on. An accompanying experiment editor allows to define custom experiments from data capture to analysis that are stored in an XML-based file format and possible to share through QR codes.

Aside from demonstrating the app itself, if you ever wondered how sensors like the accelerometer, magnetometer, or barometric pressure sensor inside your phone actually work, and which one of them you can use to detect toilet flushing on an airplane and measure elevator velocity, and how to verify your HDD spins correctly, you will enjoy the talk. If you just want a good base for playing around with sensor data yourself, it’s all open source and available on GitHub for both Android and iOS.

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Building Your Own Tensegrity Structure

November 29, 2019 by Sharon Lin 37 Comments

It seems that tensegrity structures are trending online, possibly due to the seemingly impossible nature of their construction. The strings appear to levitate without any sound reason, but if you bend them just the right way they’ll succumb to gravity.

The clue is in the name. Tensegrity is a pormanteau of “tension” and “integrity”. It’s easiest to understand if you have a model in your hand — cut the strings and the structure falls apart. We’re used to thinking of integrity in terms of compression. Most man-made structures rely on this concept of engineering, from the Empire State Building to the foundation of apartment building.

Tensegrity allows strain to be distributed across a structure. While buildings built from continuous compression may not show this property, more elastic structures like our bodies do. These structures can be built on top of smaller units that continuously distribute strain. Additionally, these structures can be contracted and retracted in ways that “compressionegrities” simply can’t exhibit.

How about collapsing the structure? This occurs at the weakest point. Wherever the load has the greatest strain on a structure is where it will likely snap, a property demonstrable in bridges, domes, and even our bodies.

Fascinated? Fortunately, it’s not too difficult to create your own structures.

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A Single-Digit-Micrometer Thickness Wood Speaker

November 27, 2019 by Sharon Lin 22 Comments

Researchers have created an audio speaker using ultra-thin wood film. The new material demonstrates high tensile strength and increased Young’s modulus, as well as acoustic properties contributing to higher resonance frequency and greater displacement amplitude compared to a commercial polypropylene diaphragm in an audio speaker.

Typically, acoustic membranes have to remain very thin (on the micron scale) and robust in order to allow for a highly sensitive frequency response and vibrational amplitude. Materials made from plastic, metal, ceramic, and carbon have been used by engineers and physicists in an attempt to enhance the quality of sound. While plastic thin films are most commonly manufactured, they have a pretty bad impact on the environment. Meanwhile, metal, ceramic, and carbon-based materials are more expensive and less attractive to manufacturers as a result.

Cellulose-based materials have been making an entrance in acoustics research with their environmentally friendly nature and natural wooden structure. Materials like bagasse, wood fibers, chitin, cotton, bacterial cellulose, and lignocellulose are all contenders for effective alternatives to parts currently produced from plastics.

The process for building the ultra-thin film involved removing lignin and hemicellulose from balsa wood, resulting in a highly porous material. The result is hot pressed for a thickness reduction of 97%. The cellulose nano-fibers remain oriented but more densely packed compared to natural wood. In addition, the fibers required higher energy to be pulled apart while remaining flexible and foldable.

At one point in time, plastics seemed to be the hottest new material, but perhaps wood is making a comeback?

[Thanks Qes for the tip!]

How To Build The Strongest Arches

October 15, 2019 by Sharon Lin 13 Comments

When it comes to architectural features, there are probably not many as quintessentially memorable as arches. From the simplicity of the curved structure to the seemingly impossible task of a supposedly collapsable shape supporting so much weight in mid-air, they’ve naturally fascinated architects for generations.

For civil engineers, learning to calculate the forces acting on an arch, the material strength and properties, and the weight distribution across several arches may be familiar, but for anyone with only a basic physics and CAD background, it’s easy to take arches for granted. After all, they grace the Roman aqueducts, the Great Wall of China, and are even present in nature at Arches National Park. We see them in cathedrals, mosques, gateways, and even memorialized in the case of the St. Louis Gateway Arch. Even the circular construction of watch towers and wells, as well as our own rib cages, are due to the properties of arches.

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Bent Electric Field Explains Antenna Radiation

October 2, 2019 by Al Williams 15 Comments

We all use antennas for radios, cell phones, and WiFi. Understanding how they work, though, can take a lifetime of study. If you are rusty on the basic physics of why an antenna radiates, have a look at the very nice animations from [Learn Engineering] below.

The video starts with a little history. Then it talks about charges and the field around them. If the charge moves at a constant speed, it also has a constant electric field around it. However, if the charge accelerates or decelerates, the field has to change. But the field doesn’t change everywhere simultaneously.

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The March Toward A DIY Metal 3D Printer

July 26, 2019 by Sharon Lin 20 Comments

[Hyna] has spent seven years working with electron microscopes and five years with 3D printers. Now the goal is to combine expertise from both realms into a metal 3D printer based on electron-beam melting (EBM). The concept is something of an all-in-one device that combines traits of an electron beam welder, an FDM 3D printer, and an electron microscope. While under high vacuum, an electron beam will be used to fuse metal (either a wire or a powder) to build up objects layer by layer. That end goal is still in the future, but [Hyna] has made significant progress on the vacuum chamber and the high voltage system.

The device is built around a structure made of 80/20 extruded aluminum framing. The main platform showcases an electron gun, encased within a glass jar that is further encased within a metal mesh to prevent the glass from spreading too far in the event of an implosion.

Vacuum chamber enclosed in mesh (new gasket shown)

Mold for making silicone gasket

The design of the home-brewed high-voltage power supply involves an isolation transformer (designed to 60kV), using a half-bridge topology to prevent high leakage inductance. The transformer is connected to a buck converter for filament heating and a step up. The mains of the system are also connected to a voltage converter, which can be current-fed or voltage-fed to operate as either an electron beam welder or scanning electron microscope (SEM). During operation, the power supply connects to a 24V input and delivers the beam through a Wehnelt cylinder, an electrode opposite an anode that focuses and controls the electron beam. The entire system is currently being driven by an FPGA and STM32.

The vacuum enclosure itself is quite far along. [Hyna] milled a board with two outputs for a solid state relay (SSR) to a 230V pre-vacuum pump and a 230V pre-vacuum pump valve, two outputs for vent valves, and inputs from a Piranni gauge and a Cold Cathode Gauge, as well as a port for a TMP controller. After demoing the project at Maker Faire Prague, [Hyna] went back and milled a mold for a silicone gasket, a better vacuum seal for the electron beam.

While we’ve heard a lot about different metal 3D printing methods, this is the first time we’ve seen an EBM project outside of industry. And this may be the first to attempt to combine three separate uses for an HV electron beam into the same build.

The Physics Behind Antennas

July 11, 2019 by Al Williams 34 Comments

If you have done any sort of radio work you probably have a fair idea about what antennas do. It is pretty easy to have a cursory understanding of them, too. You probably know there’s something magic about antennas that are a quarter wave long or a half wave long and other multiples. But do you know why that matters? Do you understand the physics of why wire in a special configuration will cause signals to propagate through space? [Learn Engineering] does, and their new video is one of the best graphical explanations of what’s really going on in an antenna that we’ve seen. You can watch the video below.

If you tackle antennas using math, it is a long discussion. However, this video is about 8 minutes long and uses some great graphics to show how moving charges can produce a propagating electromagnetic field.

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