Welcome
Username:

Password:


Remember me

[ ]
[ ]
Online
Guests: 19, Members: 2 ...
Weston viewing forum.php
Dave Marshall viewing forum.php

most ever online: 333
(Members: 3, Guests: 330) on 06 Jun : 15:15

Members: 2586
Newest member: Ray1214
Members Birthdays:
All today's birthdays', congrats!
Desmogod (38)
Alex Smith (21)


Next birthdays
04/25 Desmogod (38)
04/25 Alex Smith (21)
04/26 Bead (31)
Support 4hv.org!
Donate:
4hv.org is hosted on a dedicated server. Unfortunately, this server costs and we rely on the help of site members to keep 4hv.org running. Please consider donating. We will place your name on the thanks list and you'll be helping to keep 4hv.org alive and free for everyone. Members whose names appear in red bold have donated within the last three months. Green bold denotes those who have donated to keep the server carbon neutral.


Special Thanks To:
  • Aaron Holmes
  • Aaron Wheeler
  • Adam Horden
  • Alan Scrimgeour
  • Andre
  • asabase
  • Austin Weil
  • barney
  • Barry
  • Bert Hickman
  • Bill Kukowski
  • Brandon Paradelas
  • Bruce Bowling
  • BubeeMike
  • Byong Park
  • Cesiumsponge
  • Chris F.
  • Chris Hooper
  • Corey Worthington
  • Derek Woodroffe
  • Dalus
  • Dan Strother
  • Daniel Uhrenholt
  • datasheetarchive
  • Dave Billington
  • Dave Marshall
  • David F.
  • Dennis Rogers
  • drelectrix
  • Dr. John Gudenas
  • Dr. Spark
  • eastvoltresearch
  • Eirik Taylor
  • Erik Dyakov
  • Erlend^SE
  • Finn Hammer
  • Firebug24k
  • GalliumMan
  • Gary Peterson
  • George Slade
  • GhostNull
  • Grant
  • GreySoul
  • Henry H
  • IamSmooth
  • In memory of Leo Powning
  • Jacob Cash
  • James Howells
  • James Pawson
  • Jeff Greenfield
  • Jesse Frost
  • Jim Mitchell
  • jlr134
  • Joe Mastroianni
  • John Forcina
  • John Oberg
  • John Willcutt
  • Jon Newcomb
  • klugesmith
  • Leslie Wright
  • Lutz Hoffman
  • Mads Barnkob
  • Martin King
  • Mats Karlsson
  • Matt Gibson
  • Matthew Guidry
  • Michael D'Angelo
  • Mikkel
  • mileswaldron
  • mister_rf
  • Neil Foster
  • Nick de Smith
  • Nick Soroka
  • Nik
  • Norman Stanley
  • Patrick Coleman
  • Paul Brodie
  • Paul Jordan
  • Paul Montgomery
  • Ped
  • Peter Krogen
  • Peter Terren
  • PhilGood
  • Richard Feldman
  • Robert Bush
  • Royce Bailey
  • Scott Fusare
  • Scott Newman
  • Stella
  • Steven Busic
  • Steve Conner
  • Steve Jones
  • Steve Ward
  • Sulaiman
  • Thomas Coyle
  • Thomas A. Wallace
  • Timo
  • Torch
  • Ulf Jonsson
  • Vaxian
  • Weston
  • William Kim
  • William N.
  • William Stehl
  • Wesley Venis
The aforementioned have contributed financially to the continuing triumph of 4hv.org. They are deserving of my most heartfelt thanks.
Forums
4hv.org :: Forums :: Projects
<< Previous thread | Next thread >>   

Miniature wireless power demonstrator

Go to page  [1] 2 3 4 5 6 7
Author Post
Marko
Mon Aug 10 2009, 11:03PM Print View
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3144
20. 04. 2010 - update:

I added little FAQ summarizing the questions I've been most frequently asked about the project. I may update it with time and feel free to post a question you think might be suitable for me to add.

**FAQ**

- Are there kits or complete models available for sale?

Not yet as I'm currently unable to build any. I might make some this summer if I find increased interest, although I'm not promising anything as I have a number of hurdles to overcome regarding sales.

- I can't find the WIMA FKP capacitors like you used. Can I use ceramic/MKP/other type of capacitors available in my store?

No. Other types of capacitors, if they work at all are most likely going to be very lossy and overheat and melt in minutes.
Capacitors don't really even need to be WIMA brand, pretty much any polypropylene capacitors should work well.
This includes CDE942 caps generally used by tesla coilers here, as well as various brands of 'MKP' and similar caps. MKP is somewhat more lossy than FKP but worked fine in my first designs.

- I want to use the circuit to charge a mobile phone. Can I have schematics/plans?

I just don't have time to write about it now, and if you built the circuit I think it's straightforward enough for you to figure it out yourself.
Hint: a rectifier of suitable high speed diodes and a DC/DC converter chip.

- What is the diameter of transmitting and receiving loops?

Not sure why does everyone need to know this exactly, since I don't really remember the diameter I used myself. A larger loop is going to help transmit the power somewhat farther at cost of devices being about proportionally larger. Larger loop with same capacitor will result in lower resonant frequency.

- I can't find the copper tube and wire you used for the loops, what can I do?

Choice of the conductor used is really not critical as long as there is enough surface area to keep conductivity high and avoid overheating. A 6mm copper tube is OK for the transmitter and it should be easy to find in air conditioner stores. Receiver doesn't need to use wire, copper tube is fine too. If you have a large amount of thinner wire you could make a litz conductor by twisting several of them in parallel. 15-20mm width of copper strip should also make excellent conductor for the purpose.
Having equal loops on both transmitter and receiver will make the tuning easier.

- The transmitter circuit does not oscillate, instead it shorts the power supply and one mosfet and inductor heat up rapidly, what to do?

Firstly, if you are using a version without the relay, this is a common problem, and is caused by power supply voltage rising too slowly on powerup. To fix make sure you use a switch on low voltage side, that is immediately between your power supply and the circuit, to turn the circuit ON.

If it'+s still happening, make sure:
1. that the mosfet that suffered the condition is still working
2. check for connections of your circuit, misplaced components, directions of the diodes...
3. The circuit won't run without the loop attached!

Hope this helps.

- The transmitter oscillates but I get very little power on the secondary side. What can I do to improve?

There are two problems (or two parts of a same problem, more precisely); tuning and load impedance match.

Firstly, we want both LC circuits to resonate at about the same stand-alone f0 - the best starting point is to make them both with identical loops and capacitances.

But, to achieve maximum power throughput, we will need to fine-tune the system, prefferably during runtime. This can be done by increasing or decreasing the stand-alone resonant frequency of either the receiver or the transmitter. Some of ways to acheive that are -

1. Changing the diameter of loops - may be difficult to impossible depending on the construction, probably easier on receiver. Should not be done on the transmitter while it's operating, and it's loop should be soldered down anyway.
2. Changing the tank capacitance.
3. Much more convenient to do while system is running - is to insert a large ferrite core (AM radio ferrite rod, or a TV flyback transformer core) into a loop which we want to decrease f0.
4. Alternatively, we can bring a copper or aluminium plate behind the targeted loop to do the opposite.

Secondly we want to match the load impedance to the best possible way to the ''transmission line'' we created with coupled LC circuits. Playing with the circuit you will notice that the ''tuning'' methods described above also work to match the system to different loads! There are some reasonable limits we need to follow with the load if we want best power throughput. We can't use unreasonably low (like a car headlight) nor unreasonably high load resistances (25W 230V incadescent bulb?).
I found a 24V 5W bulb to be a decent load, although I suspected 3x 12V/2W bulbs in series might have performed better.

- I want to supersize the circuit/increase the input voltage/transmit the power over a few meters?

None of those are really practical with this design. The best shot for increasing the power throughput would be to use a ferrite transformer between the active section and LC tank - I tried it and it works but at cost of even greater mosfet heatage... if you are already at this point then you probably already understand that this circuit sucks and have better ideas than it anyway.
Just increasing the voltage to the circuit as it is beyond 18V is most likely to cause it to blow up. And using higher voltage mosfets is actually just going to make the problem worse.

Transmitting power this way on a scale of meters with sub-metre sized devices at any reasonable efficiency is pretty much science fiction as of today.

- Have you been developing any new ideas on wireless power? When may we see updates?

Yes, but I'm keeping it top secret as of now. It's not going to be simple and I don't have time to explain it anyway. ANd builds are unlikely to start before this summer.

- I built the circuit, but I measured a different frequency at the transmitter than your 1.5Mhz. What is wrong with my circuit?

Nothing may be wrong, you might just have used a larger loop diameter or more capacitance than me. If parts are really closely matching mine, thenthere might be a problem. Some things to try:

1.Just try powering something if you have the receiver - if not build one from a piece of wire and a light bulb, capacitor isn't even required for proof of concept.
If you get any incadescence on the bulb then your circuit is working already! Just proceed to tune up the receiver then.

2. Look for the current drawn from the power supply. If it's less than 0.5A or more than 1A without load then something is wrong. It's recommended to use a current limited supply for initial tests.

3. Try measuring the LC tank voltage with an oscilloscope, not a frequency counter - this also has to show the peak voltage which has to be about pi*supply voltage (37V for 12V supply). Some precautions are required while doing this - the power supply must not have grounded " - " (like a PC power supply does) because placing an oscilloscope ground clip to one of 'hot' ends of LC tank will cause short circuit. In that case we need to measure with scope input set to DC input and measure between ground and one ''hot end''. This will yield a ''halfwave rectified'' waveform but the peak voltage value should remain the same.



....that's about it for now.




Update 16. 9. 2009.
Eagle files of the new PCB


wirelesspower.zip

New update 24. 8. 2009. :

I designed a new PCB with goal of ease of replication by newbies. Including schematic with explanations. Preliminary board, may be subject to change.


through_hole_wireless.pdf
through_hole_wireless-schematic.pdf
through_hole_wireless-components.pdf


I also modified the old, prototype PCB (without the relay) a bit to make it more practical to use. All components are intended to be surface mounted on the copper side so there is no drilling involved.

pcb_old.pdf
pcb_old_parts.pdf

******


A number of people has expressed interest into this project, and I decided it would be best to post it up here as a project thread.

The idea behind the project was to create a small tabletop demonstrator of magnetically coupled wireless power transfer, resembling a miniature version of the MIT 'witricity' device. The goal was to keep the circuit simple with easily obtainable parts, and to keep voltage and power levels low so the device is safe for handling and doesn't require special methods of cooling.

The basic idea is to feed a parallel LC tank circuit from an AC voltage source at it's resonant frequency, which allows large reactive current to circulate in the circuit while only real power is being drawn from the source. This sets up a large alternating magnetic field in the inductor, which is designed as a single conductive loop in this case.
Now, another LC tank with load attached is brought in proximity to the excited LC circuit, significant amounts of power can be transferred via weak magnetic coupling between them. This is because AC current itself in the transmitting loop is very large, and inductive reactance of the receiver loop is canceled out by the capacitor.

For a practical device, the AC voltage source had to be substituted with an appropriate oscillator, which would take feedback from the tank circuit itself and hence always drive it at it's resonant frequency.

The circuit of choice was a slightly modified royer oscillator, such as popularly used in CCFL inverters and for flyback drivers.
Input voltage was limited to 15V for safety and because the circuit tends to become unstable at higher voltages.

The idea of the prototype circuit is rather simple.






Mosfets I used were IRFZ44, but any similar ones will do. A small piece of Aluminum for a heatsink is recommended, although in prototype I just soldered the mosfets onto the PCB.

Rg were at first 50, but later increased to 100 ohms which is enough and wastes less power. Resistors need to be rated 1 watt at least and they get quite hot.

Radio frequency chokes were 100uH, at first iron powder cores, but later switched to ferrite which produced much better results.
Powdered iron cores tended to heat up from magnetic flux they picked up from the transmitting loopas well.

Diodes - 1N4148's. Similar small high-speed diodes are ok.

The LC tank circuit is the part where heavy current circulates, and is required to be sturdy. The copper pipe used as conductor heats up significantly under ~20A it's passing continuously. To handle the current while keeping losses tolerable, capacitor consists of 6 paralleled 6.8nF 1000V wima FKP1 capacitors. It's important that capacitors are polypropylene dielectric and foil or foil+film based - other types will heat up and melt in this application.
The transmitter still oscillated at relatively high frequency and had to be tuned by insertion of a ferrite core into the loop, as shown on the picture. This lowered the frequency to about 1.5Mhz without load.
Alternatively a copper or aluminum plate can be brought near the loop to increase frequency, by decreasing inductance.
Number of capacitors was later increased to 8, removing the need of additional tuning.

On the receiver side only a single capacitor and a loop of 3mm solid copper wire was used. The wire heats up significantly, though.
You can notice I used a small matching inductor in series with the load, which is a 24V 5W. It's choice was guessed at 6uH and it improved performance somewhat at larger distances.

This prototype, though, had one problem - if the supply voltage rose too slowly, such as while DC filter capacitance is charging, it tended to fail to oscillate and just keep shorting the power supply with one mosfet ON. In the final design this was solved with a relay, which acts as undervoltage lockout of sorts, applying Ugg power rapidly after supply voltage rose high enough.

Jumpers in the schematic are to allow connection of a step up autotransformer between the mosfet amplifiers and the LC tank circuit.

I provided the schematic of the finished circuit, but not the PCB since it's a fairly odd design with odd components (SMT inductors) which I thought might not be too useful for most people. PM me if the PCB layout is desired.


PCB layout and part layout for the final circuit shown in the bottom picture, along with schematic:

parts_top.pdf
pcb_bottom.pdf






Cheers,

Marko
Back to top
MRacerxdl
Mon Aug 10 2009, 11:24PM
Registered Member #989
Joined: Sat Sep 08 2007, 02:15AM
Location: São Paulo, Brazil
Posts: 476
Very impressive! Sometime ago I thought to made something like that as my Electronic Technician Conclusion Work, but I opted to made a Plasma Speaker instead.

But I will try someday to made one of that!
Very good work!
Back to top
Website
Marko
Mon Aug 24 2009, 03:57PM
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3144
Updated with a new PCB...

Back to top
strider
Mon Sep 07 2009, 12:22PM
Registered Member #2341
Joined: Mon Sep 07 2009, 12:16PM
Location:
Posts: 9
Really nice work, but I have a question about the copper tube you used in the transmitter; what is the diameter of it? Is it 3AWG (6.35mm)...? I am working on a wireless electricity project also and had successfully transferred a 27 AC 10MHz signal with an efficiency of about 68% over 3 ft. and I'll be more than happy if you can offer me some of your time to talk about this project... Also if you want I can post pictures of my work
Back to top
Mates
Mon Sep 07 2009, 01:58PM
Registered Member #1025
Joined: Sun Sep 23 2007, 07:53PM
Location: Czech Rep.
Posts: 566
Nice "litle" project Marko!
Honestly, I liked your SSTC based wireless project more and I'm still expecting some progress, but this is also very impressive.

strider wrote ...

Also if you want I can post pictures of my work


We all want...

Back to top
strider
Mon Sep 07 2009, 02:31PM
Registered Member #2341
Joined: Mon Sep 07 2009, 12:16PM
Location:
Posts: 9
Here some pictures of my work (they are not that new), I post more new 1s soon... my current work is to charge a moble phone (700m A, 3.3V) and then I'll try to go for a notebook (20V 2A)

Thanks everyone and hope to have some nice chat with you guys (my msn:striderules@hotmail.com, skype:striderrules)





Back to top
GeordieBoy
Mon Sep 07 2009, 05:12PM
Registered Member #1232
Joined: Wed Jan 16 2008, 10:53PM
Location: Doon tha Toon!
Posts: 863
So you are using Helical antennas to direct the energy from a transmitter loop to the receiver loop?

It's a nice proof of principal but it looks a little bulky for the average laptop or mobile...



These people have pretty much nailed it technology-wise and showed me some real neat demo's of various devices like PC cooling fans, lamps, mobile phones, I-pods etc being powered by placing them anywhere on the charging pad in any orientation. The funny thing is that market uptake of this technology is very slow, that is seems nobody is really THAT interested in wireless charging afterall!

In fact the only wireless chargers that seem to be in common household appliances are those electric toothbrush and shaver chargers that enable the bathroom appliance (and it's charger) to be totally sealed to meet IP ratings for water ingress. I guess in that case the added expense of the hi-tech wireless power is justified because it solves a problem, but otherwise most consumer electronics is far too cost sensitive to include wireless power.

-Richie,
Back to top
Website
strider
Mon Sep 07 2009, 08:45PM
Registered Member #2341
Joined: Mon Sep 07 2009, 12:16PM
Location:
Posts: 9
The pics I included above were upon 1 of my validation stages of the concept, this is why I stuck with bulky coil at the receiver side although I am tring now to go with high power, I am also trying to go smaller with the receiver side but I can't go with that easy cause I need more help and time that's why I am trying to gather all the info I can and talk with guys like you here to get more info...
Back to top
GeordieBoy
Mon Sep 07 2009, 09:12PM
Registered Member #1232
Joined: Wed Jan 16 2008, 10:53PM
Location: Doon tha Toon!
Posts: 863
The technology section of this site has some information:



At the high power end of the scale you will find that the technology exists to fill a room full of enough wireless power to run laptops, light lamps and charge phones etc. The problem is that the required field strength is many many times greater than recommended human exposure levels in safety standards. It also causes serious interference problems to equipment that doesn't contain the necessary screening to make it wireless power tolerant! Not to mention induction heating of pretty much anything conductive in the field!

-Richie
Back to top
Website
strider
Mon Sep 07 2009, 09:28PM
Registered Member #2341
Joined: Mon Sep 07 2009, 12:16PM
Location:
Posts: 9
Up to my testing I had reached good levels of safety according to IEEE standards however my main problem resides with efficiency as the distance increases (low tail strength) and resonance disturbance (specially at the oscillator)... Also the transmitter i am working on consists of a vacuum tube oscillator however I am trying to find high voltage high freq. oscillator using mosfets. So my work needs alot more time and readings and I cant reach high levels so fast
Back to top
Lucifer
Wed Sep 09 2009, 02:54PM
Registered Member #2351
Joined: Wed Sep 09 2009, 02:43PM
Location:
Posts: 2
Hye Marko & strider,
I am new here...I am working same project with strider on a wireless electricity project for my final year project but using router 802.11g as a transmitter (2.4Ghz). Any idea? The receiver can receive the frequency 2.4Ghz ? How can i build the receiver for frequency from the router? can someone help me...please...
Back to top
strider
Thu Sep 10 2009, 12:18AM
Registered Member #2341
Joined: Mon Sep 07 2009, 12:16PM
Location:
Posts: 9
Lucifer you need to receive your signal using a router? what amount of power you are sending and what type of devices you are looking to use as load? please give more details so we can have better view to see how we can help
Back to top
Lucifer
Thu Sep 10 2009, 05:24AM
Registered Member #2351
Joined: Wed Sep 09 2009, 02:43PM
Location:
Posts: 2
is it possible to build the receiver which can receive the signal from router ? i need the power to charge a moble phone...
Back to top
strider
Thu Sep 10 2009, 11:13AM
Registered Member #2341
Joined: Mon Sep 07 2009, 12:16PM
Location:
Posts: 9
you need a harvesting circuit cause router power level is very low (micro to pico Watt).. Try to see Powercast Technology it will give you some help, also if you need further help you can reach me through my msn and skype posted on the post with pics above
Back to top
Curtis
Thu Sep 10 2009, 07:27PM
Registered Member #883
Joined: Sat Jul 07 2007, 01:02PM
Location:
Posts: 16
I think that this technology is in use ore than we think about in our everyday lives. It is the principal used in rfid tags used for loss prevention in stores. Just yesterday i say an induction charger for wii remotes where you just set the controller on the charging pad in any orientation to charge it.
Back to top
Scott Fusare
Fri Sep 11 2009, 02:37PM
Registered Member #531
Joined: Sat Feb 17 2007, 10:51AM
Location: Burlington, Vermont
Posts: 120
A quick prototype I put together at work as a concept demonstrator a year or so ago.










The low Q obtained with the printed planar inductor limited the overall range to ~30cm when using a third "repeating" resonator. This is running 2 watts at 1 MHZ input from a tiny class E oscillator. A larger high Q system was eventually built that delivered 10s of watts at ~70% transfer efficiency over a 20 cm gap.

Personally I don't understand why the MIT team and everyone who has followed believes this is anything new or innovative. Loosely coupled high Q resonators are quite venerable. All the MIT team did was re-describe the process in terms normally reserved for optical processes. Heck, they even won a MacArthur grant for demonstrating something Tesla was photographed doing more than a century ago!
Back to top
big5824
Fri Sep 11 2009, 03:45PM
Registered Member #1687
Joined: Tue Sep 09 2008, 08:47PM
Location: UK, Darlington
Posts: 240
Can someone explain to me what the MIT team did to improve efficiency and transfer range so much other than ensuring a good frequency match with the recieving coil. (google isnt too consistent)
Back to top
Scott Fusare
Fri Sep 11 2009, 04:20PM
Registered Member #531
Joined: Sat Feb 17 2007, 10:51AM
Location: Burlington, Vermont
Posts: 120
Resonators had measured Q of 1000.

As I said, they really did nothing new.
Back to top
...
Fri Sep 11 2009, 05:49PM
Registered Member #56
Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2364
What the MIT did that was new was publish their findings with a bunch of buzzwords and let the media loose on it. They made no innovation that tesla/marconi/etc (and possibly some of the people before them) didn't think of, and hasn't been well tested/documented by anyone doing RF work.
Back to top
Website
strider
Fri Sep 11 2009, 08:14PM
Registered Member #2341
Joined: Mon Sep 07 2009, 12:16PM
Location:
Posts: 9
How about evanescent resonance?? its used but in wireless electricity, also MIT had already admit that the concept is not new however they had make use of it on a good fashion. so if you can do better or make use of good concept in a good project you will gain a lot of respect for that
Back to top
Scott Fusare
Fri Sep 11 2009, 10:36PM
Registered Member #531
Joined: Sat Feb 17 2007, 10:51AM
Location: Burlington, Vermont
Posts: 120
I am not quite sure what you mean Strider? Have you read the papers, they are indeed claiming novelty here. Certainly they think it novel enough to apply for a US patent, which hopefully will not be granted.

They never actually use the phrase "evanescent resonance", unless there is a new paper out there that I am unaware of. What they are claiming is "evanescent" mode coupling of the resonators. At the frequencies and distances we (and they) are talking about "evanescent" is the same as "near field" or "induction field" or "reactive field". They are playing games with semantics, whether it is intentional or not is a matter up for debate.

As for making use of "a good concept" in a "good project" I am all for that but one should not claim novelty or uniqueness were it does not exist. As an example - Look up remote powering of sub-cutaneous implants and you will find that the medical community has used this technique for power transfer for 3-4 decades now.

I realize I am ranting about this. I just find it shameful that the paper published in Science passed peer review. A less prestigious institution would have been (hopefully) taken to task over their re-invention of the wheel. All from the EE department of my country's (arguably) most prestigious engineering school and from a native Croat no less!

As an aside, to anyone who has read the paper, look at the equation presented for coupling and ponder the physical implications of it....

Back to top
strider
Fri Sep 11 2009, 11:23PM
Registered Member #2341
Joined: Mon Sep 07 2009, 12:16PM
Location:
Posts: 9
I have read all their papers about 50 times and know what they claim and said, and about patents they have already 2, yeah they claim uniqueness cause if you can find any other application that make use of evanescent field with magnetic resonance for wireless power we can say that its a shame for MIT.. by the way MIT concept comes from concepts which were ignored in the past like coupled mode theory, evanescent tunneling over mid range (not small ranges like in optics), near field non radiative region (which was ignored when designing antenna and we always try decrease its region to avoid interference)...So for me they did a very great job
Back to top
Marko
Sat Sep 12 2009, 12:40PM
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3144
Hi guys,

I really didn't expect this thread to receive so much attention. I thought a single project thread should be for a single person's project, but I don't really have anything against some hijacking myself :P

A larger high Q system was eventually built that delivered 10s of watts at ~70% transfer efficiency over a 20 cm gap.


Scott,
Could you post some more information and pics of this system?

I have read all their papers about 50 times and know what they claim and said, and about patents they have already 2, yeah they claim uniqueness cause if you can find any other application that make use of evanescent field with magnetic resonance for wireless power we can say that its a shame for MIT.. by the way MIT concept comes from concepts which were ignored in the past like coupled mode theory, evanescent tunneling over mid range (not small ranges like in optics), near field non radiative region (which was ignored when designing antenna and we always try decrease its region to avoid interference)...So for me they did a very great job


''Resonant induction, evanescent wave coupling/tunneling", etc, really just describe an air cored transformer. I see no point making it more complex than that.
We add power factor correcting capacitance to these transformers to compensate their extremely low magnetizing inductance, which would otherwise be very prohibitive to drive. The resulting LC circuit can be useful for a self resonant oscillator as well.

Marko

Back to top
Scott Fusare
Sat Sep 12 2009, 02:04PM
Registered Member #531
Joined: Sat Feb 17 2007, 10:51AM
Location: Burlington, Vermont
Posts: 120
Hi Marko,

It's probably obvious that this topic is one I like to go on about. I hadn't meant to hijack your thread,
please pardon the breech in etiquette. Should we move the discussion elsewhere?

This technique was well suited to a particular design problem I had at work, so I ended up
spending quite a bit of time looking at the MIT group's work as well as what preceded them.

Come Monday I'll dig up some pictures of the larger system but in the interim I can describe it
as best as my memory will allow. For EMC compliance reasons I lowered the operating frequency to 150 kHz.
The inductors were roughly 15 cm in diameter planar wound from medium gauge Litz wire. I measured
the unloaded Q of the resonators at ~330 as I recall. The tank circuit was completed with poly film capacitors.
A 20 watt class E oscillator was series coupled to the tank via a impedance transformer wound on
a ferrite binocular core. The "receiver" side was identical with the addition of a trimmer cap for fine tuning.
High efficiency demanded running with tighter than critical coupling. I don't recall exactly what is was,
I'll consult my notes on Monday.

I agree with your observation on terminology. I don't think I am doing a good job of presenting my case to Strider though. I'll have to post something more detailed.


Back to top
strider
Sat Sep 12 2009, 02:33PM
Registered Member #2341
Joined: Mon Sep 07 2009, 12:16PM
Location:
Posts: 9
First of all thank you all for this great discussions and I am sorry if my posts cause any misunderstanding as I mean no offense at all...

Marko can you please tell me the diameter of the copper tube you used at the transmitter side..

Also I had established some great analysis papers of my work which is mainly build upon MIT work and I had also some great simulation results (using Comsol 3.5a RF module) to support the theory and results, and as I stated before I am still working on the concept and every new idea and discussion I have will help me a lot as I am always learning new things and I am honored to have it with you guys here..

Back to top
Dkauf
Sun Oct 11 2009, 03:33AM
Registered Member #2421
Joined: Tue Oct 06 2009, 01:58AM
Location:
Posts: 2
Hey very cool project !
It seems you put 2 capacitors at the receiver coil (electrolytic "black" and polyester "blue"). Can you tell me their values ?

Thanks,
Back to top
Sulaiman
Sun Oct 11 2009, 09:09AM
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: England Union Flag without Scotland
Posts: 2201
Nice project.

Just a couple of 'warnings'

1) These devices contravene most regulations as they are deliberate radiators of significant rf power

2) Be sure not to have any important rfid devices nearby..e.g. in the back of my UK passport








Scott, if you removed the inner part of your pcb antenna leaving only the outer few turns you would have a much higher Q antenna, something like the photo above.
Back to top
Scott Fusare
Sun Oct 11 2009, 12:09PM
Registered Member #531
Joined: Sat Feb 17 2007, 10:51AM
Location: Burlington, Vermont
Posts: 120
Hi Sulaiman,

Agreed on the regulations, although using the word "radiator" contributes to the misunderstanding of the principal involved. Pardon my being pedantic. The fields generated in the high power, across the room demos (MIT) will make the authorities apoplectic!

As to your comment on the printed inductor - I guess you are right about the inner turns contributing little but loss. I must admit this wasn't well thought out but rather a quick demo for management. However, the frequency being fixed, it seems to me that as you eliminate inner turns you will pass through a maximum Q point and then begin to descend as your inductance drops. I would think that the "few outer turns" would be in this regime. An interesting optimization problem.

Ultimately my application would have needed field shaping magnetics and also been operated above critical coupling for reasonable efficiency, both will kill my loaded Q anyway.

Scott
Back to top
Marko
Sun Oct 11 2009, 04:57PM
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3144
Dkauf wrote ...

Hey very cool project !
It seems you put 2 capacitors at the receiver coil (electrolytic "black" and polyester "blue"). Can you tell me their values ?

Thanks,


There are no electrolytic capacitors anywhere in the circuit, the round object on the receiver side is a 6uH choke I mentioned before in my post. It's redudant if higher impedance load is chosen (like 3x 12V bulbs in series). The blue capacitor also isn't polyester but metallized polypropylene, chosen for suitable resonant frequency. In this case it's 47nF, if I recall.

Marko
Back to top
Dkauf
Mon Oct 12 2009, 07:55PM
Registered Member #2421
Joined: Tue Oct 06 2009, 01:58AM
Location:
Posts: 2
Marko wrote ...

Dkauf wrote ...

Hey very cool project !
It seems you put 2 capacitors at the receiver coil (electrolytic "black" and polyester "blue"). Can you tell me their values ?

Thanks,


There are no electrolytic capacitors anywhere in the circuit, the round object on the receiver side is a 6uH choke I mentioned before in my post. It's redudant if higher impedance load is chosen (like 3x 12V bulbs in series). The blue capacitor also isn't polyester but metallized polypropylene, chosen for suitable resonant frequency. In this case it's 47nF, if I recall.

Marko



OK Thanks and congrats again, very cool stuff.-

Back to top
Go to page  [1] 2 3 4 5 6 7

Moderators: Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Bjørn, Dave Billington, Steve Conner, Wolfram, Mads Barnkob

Jump:     Back to top

Powered by e107 Forum System
 
Legal Information
This site is powered by e107, which is released under the GNU GPL License. All work on this site, except where otherwise noted, is licensed under a Creative Commons Attribution-ShareAlike 2.5 License. By submitting any information to this site, you agree that anything submitted will be so licensed. Please read our Disclaimer and Policies page for information on your rights and responsibilities regarding this site.