Piezomagnetic Trick Shrinks 2.5 GHz Antennas

To a ham radio operator used to “short”-wave antennas with lengths listed in tens of meters, the tiny antennas used in the gigahertz bands barely even register. But if your goal is making radio electronics that’s small enough to swallow, an antenna of a few centimeters is too big. Physics determines plausible antenna sizes, and there’s no way around that, but a large group of researchers and engineers have found a way of side-stepping the problem: resonating a nano-antenna acoustically instead of electromagnetically.

Normal antennas are tuned to some extent to the frequency that you want to pick up. Since the wavelength of a 2.5 GHz electromagnetic wave in free space is 120 cm mm, most practical antennas need a wire in the 12-60 cm mm range to bounce signals back and forth. The trick in the paper is to use a special piezomagnetic material as the antenna. Incoming radio waves get quickly turned into acoustic waves — physical movement in the nano-crystals. Since these sound waves travel a lot slower than the speed of light, they resonate off the walls of the crystal over a much shorter distance. A piezoelectric film layer turns these vibrations back into electrical signals.

Ceramic chip antennas use a similar trick. There, electromagnetic waves are slowed down inside the high-permittivity ceramic. But chip antennas are just slowing down EM waves, whereas the research demonstrated here is converting the EM to sound waves, which travel many orders of magnitude slower. Nice trick.

Granted, significant material science derring-do makes this possible, and you’re not going to be fabricating your own nanoscale piezomagnetic antennas any time soon, but with everything but the antenna getting nano-ified, it’s exciting to think of a future where the antennas can be baked directly into the IC.

Thanks [Ostracus] for the tip in the comments of this post on antenna basics. Via [Science Magazine].

Antenna Basics by Whiteboard

Like a lot of people, [Bruce] likes radio controlled (RC) vehicles. In fact, many people get started in electronics motivated by their interest in RC. Maybe that’s why [Bruce] did a video about antenna basics where he spends a little more than a half hour discussing antennas. You can see the video below.

[Bruce] avoids any complex math and focuses more on intuition about antennas, which we like. Why does it matter that antennas are cut to a certain length? [Bruce] explains it using a swing and a grandfather clock as an analogy. Why do some antennas have gain? Why is polarization important? [Bruce] covers all of this and more. There’s even a simple experiment you can do with a meter and a magnet that he demonstrates.

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Doppler Module Teardown Reveals the Weird World of Microwave Electronics

Oscillators with components that aren’t electrically connected to anything? PCB traces that function as passive components based solely on their shape? Slots and holes in the board with specific functions? Welcome to the weird and wonderful world of microwave electronics, brought to you through this teardown and analysis of a Doppler microwave transceiver module.

We’ve always been fascinated by the way conventional electronic rules break down as frequency increases. The Doppler module that [Kerry Wong] chose to pop open, a Microsemi X-band transceiver that goes for about $10 on eBay right now, has vanishingly few components inside. One transistor for the local oscillator, one for the mixer, and about three other passives are the whole BOM. That the LO is tuned by a barium titanate slug that acts as a dielectric resonator is just fascinating, as is the fact that PB traces can form a complete filter network just by virtue of their size and shape. Antennas that are coupled to the transceiver through an air gap via slots in the board are a neat trick too.

[Kerry] analyzes all this in the video below and shows how the module can be used as a sensor. If you need a little more detail on putting these modules to work, we’ve got some basic circuits you can check out.

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OpenEMS Makes Electromagnetic Field Solving… Merely Difficult

To ordinary people electronics is electronics. However, we know that the guy you want wiring your industrial furnace isn’t the guy you want designing a CPU. Neither of those guys are likely to be the ones you want building an instrumentation amplifier. However, one of the darkest arts of the electronic sects is dealing with electromagnetic fields. Not only is it a rare specialty, but it requires a lot of high-powered math. Enter OpenEMS, a free and open electromagnetic field solver.

We would like to tell you that OpenEMS makes doing things like antenna analysis easy. But that’s like saying Microsoft Word makes it easy to write a novel. In one sense, yes, but you still need to know what you are doing. In fairness, though, the project does provide a good set of tutorials, ranging from a simple wave guide to a sophisticated phased array of patch antennas. Our advice? Start with the waveguide and work your way up from there.

The software uses Octave or MATLAB for scripting, plotting, and support. You can download it for Windows or Linux.

If you want to start with something more intuitive for electromagnetic field visualization, this might help. If you prefer your models more concrete and less abstract, perhaps you should work at Lincoln Lab.

Long Range Wireless Internet

While most of you reading this have broadband in your home, there are still vast areas with little access to the Internet. Ham radio operator [emmynet] found himself in just such a situation recently, and needed to get a wireless connection over 1 km from his home. WiFi wouldn’t get the job done, so he turned to a 433 MHz serial link instead. (Alternate link)

[emmynet] used an inexpensive telemetry kit that operates in a frequency that travels long distances much more easily than WiFi can travel. The key here isn’t in the hardware, however, but in the software. He went old-school, implemending peer-to-peer TCP/IP connection using SLIP — serial line Internet protocol. All of the commands to set up the link are available on his project page. With higher gain antennas than came with the telemetry kit, a range much greater than 1 km could be achieved as well.

[Editor’s note: This is how we all got Internet, over phone lines, back in the early Nineties. Also, you kids get off my lawn! But also, seriously, SLIP is a good tool to have in your toolbox, especially for low-power devices where WiFi would burn up your batteries.]

While it didn’t suit [emmynet]’s needs, it is possible to achieve extremely long range with WiFi itself. However this generally requires directional antennas with very high gain and might not be as reliable as a lower-frequency connection. On the other hand, a WiFi link will (in theory) get a greater throughput, so it all depends on what your needs are. Also, be aware that using these frequencies outside of their intended use might require an amateur radio license.

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An Antenna that Really Cooks–Really

[9A4OV] set up a receiver using the HackRF board and an LNA that can receive the NOAA 19 satellite. Of course, a receiver needs an antenna, and he made one using a cooking pot. The antenna isn’t ideal – at least indoors – but it does work. He’s hoping to tweak it to get better reception. You can see videos of the antenna and the resulting reception, below.

The satellite is sending High-Resolution Picture Transmission (HRPT) data which provides a higher image quality than Automatic Picture Transmission (APT). APT is at 137 MHz, but HRPT is at 1698 MHz and typically requires a better receiver and antenna system.

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3D Printed Radiation Patterns

Radiation patterns for antennas can be utterly confusing, especially when presented in two dimensions, as they usually are. Fear not, [Hunter] has your back with 3D printed and color-coded radiation patterns.

In the field of antenna design, radiation patterns denote the relationship between the relative strength of radio waves emitted from antennas and the position of a receiver/transmitter in 3D space. In practice, probes can be used to transmit/receive from documented locations around an antenna while recording signal intensity, allowing researchers and engineers to determine the characteristics of arcane antennas. These measurements are normally expressed as two-dimensional slices of three-dimensional planes. Naturally, this sometimes (often) complex geometry is difficult for all but the most spatially inclined to mentally conceptualize with only the assistance of a 2D drawing. With computers came 3D models, but [Hunter] wasn’t satisfied with a model on a screen: they wanted something they could hold in their hands.

To that end, [Hunter] simulated several different antenna structures, cleaned up the models for 3D printing, and 3D printed them in color sandstone, and the end result is beautiful. By printing in colored sandstone through Shapeways, [Hunter] now has roughly walnut-sized color-coded radiation patterns they can hold in their hand. To save others the work, [Hunter] has posted his designs on Shapeways at Ye Olde Engineering Shoppe. So far, he has a horn antenna, dipole, inset fed patch antenna and a higher order mode of a patch antenna, all of which are under 15.00USD. Don’t see the antenna radiation pattern of your dreams? Fret not, [Hunter] is looking for requests, so post your ideas down in the comments!

Further, beyond the immediate cool factor, we can see many legitimate uses for [Hunter’s] models, especially in education. With more and more research promoting structural rather than procedural learning, [Hunter’s] designs could easily become a pedagogical mainstay of antenna theory classes in the future. [Hunter] is not the only one making the invisible visible, [Charles] is mapping WiFi signals in three dimensions.

Video after the break.

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