Author Topic: How to design antenna below 1khz with antenna design software like HFSS?  (Read 4518 times)

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Offline cdev

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I have some 20 cm x 1 cm ferrite rods that I bought some time ago from a Ukraine seller on ebay.

Intended for this purpose, These make fine LF antennas. Just as-is. With a couple of turns of enameled wire around it. They pick up all sorts of stuff. Ive also used a wooden clothes hanger that I have had for years that I used to use for drying laundry in the bathtub before I owned a dedicated "dryer"

If one wraps a very few (even just three or four) turns of wire around it it makes a substantial sized loop. Thats what matters. The space that is enclosed. It can be used as a magnetic loop for HF with a variable capacitor.   Ive also used a wooden palatte which some fencing material came on as a big loop. It makes a huge armature for wiring of any kind. Placed on its side it made a good ( square) directional loop. A very good HF antenna.

Which could likely be moved down in frequency to whatever one needed with some decent variable capacitors.  The large size means that it woud capture a lot of signal.  My experience doing this for HF was that lots of voltage is developed at the resonant frequency. More than 0.5 volt so it can be rectified very easily and turned into DC to power stufff. This is also easy to do with unused coax and that 50 feet of coax makes a good low frequency antenna. (if you add a capacitor)

Experiment a bit, you'll be surprised at how well all different sorts of ad-hoc antennas can work.
« Last Edit: May 01, 2022, 03:52:47 pm by cdev »
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Offline youta556Topic starter

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Is there anyone DIY piezoelectric antenna?reference:https://hackaday.com/2019/04/16/piezoelectric-antennas-for-very-very-low-frequencies/
 

Offline cdev

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I would suspect you'd have better luck with electromagnetic  focus in an antenna. Maxwell's equations define radio waves and antennas and how they work.

I have piezo disks and they almost certainly fail as antennas.

It would be a different story if you were trying to use them as microphones which they do very well as.

Every little vibration, boy do they pick them up well. On the other hand the high dielectric constant means that many ceramics are very useful for the size reductions they make possible with antennas. They may be subject to phenomena quite similar to piezo effects, but they are not piezoelectric.   The biggest and most long distance piezo effect I have ever seen was during the huge earthquake in Eureka California in the 1980s. It was a very large earthquake, and its a miracle more people were not killed or injured. Only one person was, a bank manager who was traveling in his car wityh his family. During the earhquake very bright flashes lit up the early morning sky very brightly. It was thought that these blue-green flashes may have been caused by tremendous piezoelectric charges.. In the surrounding mountains which contained a lot of quartz.. But who knows.. ? Similar flashes have been seen during other earthquakes and are shown on youtube.


Okay now I have reada bit more about this ide but not the actual paper yet. Who knows, I am curious what other people here think.


This is called a small antenna because of the very large wave length. Because of this, this doesnt seem to fit in to what I know so far. But who knows.. The people at SLAC are physicists who do high voltage stuff for fun.. too.

Is there anyone DIY piezoelectric antenna?reference:https://hackaday.com/2019/04/16/piezoelectric-antennas-for-very-very-low-frequencies/
« Last Edit: May 20, 2022, 12:49:34 am by cdev »
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Offline MarkMLl

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Okay now I have reada bit more about this ide but not the actual paper yet. Who knows, I am curious what other people here think.

I think that if it's piezo it's not antenna.

I've known people who've worked on things like that in the context of sonar, but it was a long time ago and modern DSP techniques etc. have improved things enormously... Hackaday's featured several projects which make good reading, although the power levels are miniscule compared with the stories I've heard...

There are several more useful articles, a good start is using Hackaday's search facility for "phased array". However the one I appreciated most is https://hackaday.com/2020/02/15/wall-panels-with-3760-antennas-can-increase-wireless-range/ which is useful even without following through to the main paper... I wonder what a minimal ("Arduino-compatible") switching circuit would look like?

MarkMLl
 

Online coppercone2

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https://physicstoday.scitation.org/do/10.1063/pt.6.1.20190530a/full/

there is this too, for low frequencies.

But it looks like its low power for local communications, because when you need to go for longer range you need a traditional antenna.
 

Offline MarkMLl

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Hmm... "Whereas a metal antenna’s equivalent circuit is just a resistor, the equivalent circuit for a piezoelectric antenna is an RLC circuit, and the values for the capacitance and inductance can be tuned using the antenna’s mechanical properties."

So I wonder whether that has to literally be an external force, or whether it can be done using a DC signal?

MarkMLl
 

Offline T3sl4co1l

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To the extent C varies with V (which it usually does for piezo materials), sure. :)

Tim
Seven Transistor Labs, LLC
Electronic design, from concept to prototype.
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Offline MarkMLl

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To the extent C varies with V (which it usually does for piezo materials), sure. :)

Does C vary with V if the material is unconstrained, or is the whole point that C varies as strain is built up in the material by a V to which it cannot respond by a change of dimension?

MarkMLl
 

Offline cdev

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Is this something hams, for example, could experiment with to make better use of the low frequency bands?
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Offline T3sl4co1l

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Mechanical bias I don't know.  Could be they have equivalent effect.

If nothing else, there's a small effect from material strain (somewhat, assuming K is constant under compression I guess), but that's more or less a basic electrostriction effect, much smaller than piezo- or ferro-electric effects.

Tim
Seven Transistor Labs, LLC
Electronic design, from concept to prototype.
Bringing a project to life?  Send me a message!
 

Offline radiolistener

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What can be used to design antenna below 1khz?[/size]

1 kHz full size antenna is about 150 km length. It's too long and almost impossible to build.

So, the only way is to use shortened antenna. It needs some radiator and matching device. If you don't expect to transfer high power into this antenna you can try to use magnetic antenna on ferrite rods.

Recently I hear about using piezo-crystal as antenna for a low frequency, it uses mechanical resonance effect in the piezo-crystal instead of electric resonance in LC contour as a matching, but it can be complicated for a ham because it requires a special crystal. I have no idea where to find it.
 


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