RF Energy Harvesting Banking

[Joel Shearon]

My project team is working on energy harvesting RF so here is what we have so far: a 5.8 GHz source which has 27dBm out of the transmitting antenna, 20-100mV out of a rectenna RF-DC circuit connected to the receiving antenna. That being said, we were planning on banking with super caps but the problem is that the super cap matches the source voltage which for un-boosted rf is way too low. We have looked into ultra low booster by Linear Tech but we also wanted to see if anyone on here had any suggestions.

I have been told to look into charging battery packs up to capacity but I was currently unaware of how that would work out so if anyone has an idea on that then please advise or otherwise if you have an idea of how to bank ultra-low DC converted RF then please advise.

 

[Gryd3]

20-100mV out of a rectenna RF-DC circuit connected to the receiving antenna.

Do you know how much 'current' you can source from that?
Any storage solution you employ will have self-discharge... and any boost converters you employ will eat up any net gains you hope to accomplish.
Not saying it can't be done, but there needs to be a lot of thought put into this. How far is the transmitter from the antenna?

 

[Joel Shearon]

Current measurements are currently on the order of ~30uA so yes I understand the issue and I also understand the issue of straight boosting which makes our current even weaker.
Distance is relatively local until proven to work. We have done everything from inch apart (100mV) to a foot or two away (15-30mV).

Any ideas?

 

[Gryd3]

Current measurements are currently on the order of ~30uA so yes I understand the issue and I also understand the issue of straight boosting which makes our current even weaker.
Distance is relatively local until proven to work. We have done everything from inch apart (100mV) to a foot or two away (15-30mV).

Any ideas?

Unfortunately not... I think the best you can do is look into directional antenna, and components with very low self-discharge. Unfortunately, the inverse square law is going to dictate what kind of distance you can get.
If anyone else has any ideas they will chime in, but most RF harvest circuits end up the same way the dodo bird did.

 

[Joel Shearon]

Unfortunately not... I think the best you can do is look into directional antenna, and components with very low self-discharge. Unfortunately, the inverse square law is going to dictate what kind of distance you can get.
If anyone else has any ideas they will chime in, but most RF harvest circuits end up the same way the dodo bird did.

I appreciate it. We actually are possibly going to look into directional antennas and waveguides today for extra help. Thanks again and yeah I hope more wonderful people chime in.

 

[hevans1944]

There is another thread here on this topic with an interesting self-published paper. You might want to give it look. The conclusions (at least for GHz frequencies from WiFi wireless router as a power source) are rather pessimistic.

 

[dorke]

Here is another paper on energy harvesting in the RFID field.

 

[davenn]

It really is a waste of time ... as was suggeste3d to you on the other forum
You like all others before you really don't understand how very low the radiated power level is. 27dBm ( 0.5W (500mW)) at even a few ft from the source isn't going to generate anything useful at the receive end

And also, per other comments are as equally valid you are generating 0.5W transmit and probably wasting several watts achieving that to recover a few microwatts .... can you see how pointless that is ?

Dave