Novel Compact Antenna for VLF

My conclusion is that the piezo-crystal is solely used as a coupling device, offering a real resistance at resonance frequency. There's a field shaping toroid on the top of the crystal. What would happen if this would be extended to a longer wire/capacitance hat (length<lambda/4). Would the mechanism cancel out the added capacitive resistance? If this is the case I would understand what could be interesting about it: efficiency compared to lumped element tuners.

 

"Pocket size" for 2200m - odd, but that's not even remotely on my list........

Nathan's got it straight. Big difference between an antenna and a excited resonator.

 

A different piezoelectric material can demonstrate the concept. However, we chose LN because of its exceptional Q, high breakdown strength, and high mechanical strength. PZT is an alternative, but would limit Q to 1,000 or 2,000 or so. The whole point is that we must get much higher Q and lower system volume than what is possible with a same electrical size "conventional" transmitter and antenna. Our customer has specifications for which we are working to meet, not necessarily as a direct 1-1 replacement for what's already out there.

We claim the LN itself behaves as a Hertzian dipole. The same disadvantages of extremely short conventional electrical dipoles apply here, except the input impedance is now ~150 Ohms rather than >-j*10^6 Ohm @ 30 kHz with an enormous inductance to provide a match.

Not all resonators will radiate. We designed this resonator geometry to be a very short electric dipole. If there is data or analysis to the contrary to what we presented, I'm happy to attempt to address. The whole reason we presented this as open access was to welcome comments and analysis from those that might not have access behind the paywall of some of these journals.

-Mark

 

To me this is the most important statement.

 

Alexanderson was the inventor of the "multiple tuned antenna"
which first was described in the 1919 paper "Transatlantic Radio Communication", Trans. AIEE.

He was the first to utilise the distributed nature of ground system losses, and the improvement in antenna efficiency possible by using multiple tuning. In theory, the antenna efficiency of an electrically very small antenna improves with the square of the number of tuned circuits.

73/
Karl-Arne
SM0AOM

 

Good day Mark,

Am I correct in understanding the principle that, for the wavelengths involved, impedance matching to mechanically accelerate charge is much more efficient than impedance matching to electrically accelerate the same amount of charge?

Thanks,

-Bob

 

That might be one way of saying it. With the piezoelectric material as the radiating element, designed appropriately, there doesn't need to be any impedance matching at resonance. Therefore, compared to a same-length of wire, you won't have any losses associated with the needed matching network (a big inductor).

The losses associated with a conventional copper radiating element versus a piezoelectric radiating element are fairly similar. In the first case, the dominant loss is ohmic, in the second, it is elastic losses. By trying to get a high of a mechanical Q as possible, we reduce elastic losses. Unfortunately might be behind a paywall, but the group here did a nice job of analyzing this from first principles: https://aip.scitation.org/doi/pdf/10.1063/1.4975030?class=pdf

Mark

 

Thanks Mark,
If anyone would like to read and does not have an account,
I found a web accessible copy at:
https://sci-hub.se/https://doi.org/10.1063/1.4975030
I get the advantage over matching to a conductor. There
is still a need to couple energy in order to induce motion.
That would be the mechanical matching I asked about.
The other bane of short antennas, high potential gradient,
lives on.
73, -Bob

 

"Ya canna break the laws of physics, Jim" [McCoy]

 

My very limited knowledge of the Piezo effect is that if you apply a voltage the device moves physically and if you apply a physical pressure the device outputs a voltage. Resonating such a device is the basis of all crystal oscillators, so nothing new there. Stimulating a Piezo rod with a frequency equal to the rod's resonant frequency would therefore cause a physical vibration. In other words it would seem that this "antenna" is radiating sound waves and not electromagnetic waves. I may be wrong, but I don't believe that there is any kind of breakthrough in antenna design here.

 

Correct. The authors never made any claims about antennas. That comes from a misleading and incorrect headline that is being repeated.

 

The criticism of the word "antenna" in the phys.org article is probably fair. The actual paper published by study's authors is a better source.

However, please do note that this device is radiating RF, not sound. See quote from one of the authors of the study:

"A quick note: we are not sending sound. For many tests we have the piezo in vacuum. This is an electromagnetic transmitter."

I am still excited about the potential use of a similar device in amateur radio, at least in the 2200m band.