The Questionable Benefits Of Paying More For Air Quality Monitors

September 28, 2023 by Maya Posch 12 Comments

Does paying more for air quality monitors (AQMs) make sense? This was the question which [Achim Haug] at the Air Gradient project sought to answer, with the answer being a rather revealing ‘not at all’. Using data from the independent South Coast Air Quality Management District agency (South Coast AQMD), a plot was created of a range of commercially available AQMs for PM2.5 pollutants and their performance against a reference monitor. Here a value of 1.00 would mean performance equal to the (expensive, calibrated) reference.

R2 vs Price. Data Source: South Coast AQMD Data

This plot shows clearly that paying more for an AQM does not get you better performance, with the reason for this explored in a follow-up article by [Achim], where a range of AQMs are checked for which PM2.5 sensors they actually use. Perhaps unsurprisingly, most AQMs use the same PM2.5 sensors, with the sensor module not really affecting the cost of the AQM as they all cost about $10-20 in bulk.

Rather it seems that the other sensors (for CO₂, NO₂ and other measurements) along with features such as WiFi, LoRa determine much of the price tag. For getting good measurements, properties such as airflow over the sensors, the implemented compensation algorithms are probably the main things you want to look at when purchasing (or building) an AQM.

(Heading image: particulate matter sizes, relative to a human hair. Credit: California ARB)

Investigating The Fourth Passive Component

September 27, 2023 by Bryan Cockfield 45 Comments

When first learning about and building electronic circuits, the first things all of us come across are passive components such as resistors, capacitors, and inductors. These have easily-understandable properties and are used in nearly all circuits in some way or another. Eventually we’ll move on to learning about active components like transistors, but there’s a fourth passive circuit component that’s almost never encountered. Known as the memristor, this mysterious device is not quite as intuitive as the other three, so [Andrew] created an Arduino shield to investigate their properties.

Memristors relate electric charge and magnetic flux linkage, which means that their resistance changes based on the current that passes through them. As their name implies, this means they have memory, and retain their properties even after power is removed. [Andrew] is testing three different memristors, composed of tungsten, carbon, and chromium, using this specialized test set. The rig is based on an Arduino Uno and has a few circuit components that can be used as references and generates data on the behavior of the memristors under various situations.

The memristors used here do exhibit expected behavior when driven with positive voltage signals, but did exhibit a large amount of variability when voltage was applied in a negative direction. [Andrew] speculates that using these devices for storage would be difficult and would likely require fairly bespoke applications for each type. But as the applications for these seemingly bizarre circuit components increase, we expect them to improve much like any other passive component.

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A modern recreation of von Guericke's electrostatic generator

Electrostatic Generator Project Starts With Molten Sulfur

September 23, 2023 by Robin Kearey 38 Comments

Although the basic concept of electrostatic attraction has been known since ancient times, it was only in the 17th century that scientists began to systematically investigate electrostatics. One of the first to explore this new field was Otto von Guericke, who constructed an electrostatic generator to help with his experiments. [Markus Bindhammer] has reconstructed this machine, which formed the basis for later work by the likes of Wimshurst and Van de Graaff. [Markus] kept his machine in an almost period-correct fashion.

Von Guericke’s machine consists of a sulfur ball mounted on a spindle that allows it to be rotated and rubbed against a piece of cloth. By doing so, the ball gains a charge that can be used to attract small pieces of material. [Markus] built a neat wooden frame with faux-antique carved legs and installed a handle, a spindle, and a belt-drive system to rotate whatever’s mounted on the spindle at high speed.

All of this is beautifully documented in [Markus]’s video, but by far the most interesting part of his project is the process of manufacturing the sulfur ball. If you’ve always wanted one, here’s how to make one: first, melt some pieces of pure sulfur in a round-bottom flask using an oil bath. Then, turn on your vacuum pump to remove any air or water vapor trapped inside the liquid. Once the liquid is nice and clear, let it cool down and solidify very slowly; the sulfur ball can then be released from its container by breaking the glass with a hammer.

While it sounds simple, we can imagine it took a bit of experimenting to get all those steps just right. The end result is a simple but useful machine to demonstrate basic electrostatics, which [Markus] is planning to use in science lectures. There are lots of interesting experiments you can do with static electricity, including building a basic motor.

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Bending Light To Fit Technology

September 22, 2023 by Bryan Cockfield 3 Comments

Solar power is an excellent way of generating electricity, whether that’s for an off-grid home or for the power grid. With no moving parts maintenance is relatively low, and the downsides of burning fuel are eliminated as well. But as much as it’s revolutionized power generation over the last few decades, there’s still some performance gains to be made when it comes to the solar cells themselves. A team at Stanford recently made strides in improving cell efficiency by bending the properties of sunlight itself.

In order to generate electricity directly from sunlight, a photon with a specific amount of energy needs to strike the semiconductor material. Any photons with higher energy will waste some of that energy as heat, and any with lower energy won’t generate electricity. Previous methods to solve this problem involve using something similar to a prism to separate the light out into colors (or energies) that correlate to specific types of cells calibrated specifically for those colors. This method does the opposite: it changes the light itself to an color that fits the semiconductor material. In short, a specialized material converts the energy from two lower-energy photons into a single higher-energy photon, which then strikes the solar panel to create energy.

By adding these color-changing materials as a layer to a photovoltaic solar panel, the panel can generate more energy with a given amount of light than a traditional panel. The major hurdle, as with any research, is whether or not this will be viable when produced at scale, and this shows promise in that regard as well. There are other applications for these materials beyond photovoltaics as well, and the researchers provide an excellent demonstration in 3D printing. By adding these color-change materials to resin, red lasers can be used instead of blue or ultraviolet lasers to cure resin in extremely specific locations, leading to stronger and more accurate prints.

Aluminum Battery Is Sustainable

September 20, 2023 by Al Williams 27 Comments

If you think of metals in a battery, you probably think of lithium, mercury, lead, nickel, and cadmium. But researchers in Australia and China want you to think about aluminum. Unlike most battery metals, aluminum is abundant and not difficult to dispose of later.

Their battery design uses water-based electrolytes and is air-stable. It is also flame retardant. The battery can provide 1.25V at a capacity of 110 mAh/g over 800 charge cycles. The idea of using aluminum in a battery isn’t new. Aluminum is potentially more efficient since each aluminum ion is equivalent to three lithium ions. The batteries, in theory, have higher energy density compared to lithium-ion, but suffer from short shelf life and, so far, practical devices aren’t that close to the theoretical limits of the technology.

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Scientists Call Out Apollo 17 After Investigating Moonquakes Past

September 19, 2023 by Lewin Day 35 Comments

In the vast realm of space exploration, new discoveries often emerge from old data. Thanks to advanced algorithms and keen observers, the seismic activities of our closest celestial neighbor, the Moon, have recently been thrust back into the limelight.

Thanks to the effort of the NASA crew involved in the Apollo 17 mission, it’s possible investigate these phenomena today with datasets from the past. Recently, researchers working with this data turned up some intriguing findings, and published them in a new paper. It reveals that one unexpected source of moonquakes could be the very equipment that Earth’s astronauts left behind. Continue reading “Scientists Call Out Apollo 17 After Investigating Moonquakes Past” →

Multispectral Imaging Shows Erased Evidence Of Ancient Star Catalogue

September 18, 2023 by Donald Papp 43 Comments

Ancient Greek astronomer Hipparchus worked to accurately catalog and record the coordinates of celestial objects. But while Hipparchus’ Star Catalogue is known to have existed, the document itself is lost to history. Even so, new evidence has come to light thanks to patient work and multispectral imaging.

Hipparchus’ Star Catalogue is the earliest known attempt to record the positions of celestial bodies (predating Claudius Ptolemy’s work in the second century, which scholars believe was probably substantially based on Hipparchus) but direct evidence of the document is slim. Continue reading “Multispectral Imaging Shows Erased Evidence Of Ancient Star Catalogue” →