RF energy harvesting project
in [Design]
|
From: rahulponna on 10 Jul 2010 04:51 rahulponna had written this in response to http://www.electrondepot.com/electrodesign/RF-energy-harvesting-project-481956-.htm : Hi Mike, I am a Master's student and as a part of my final year project, I am working on the same thing as you, viz. RF energy harvesting and using the harvested energy to drive a wireless sensor network. I just started working on this project, I am still in the literature survey part. I wondering if you could share any good links/documents you would have come across. I have lot of doubts as to how to go about it myself. Have just some untested ideas. If you can share any material you found really useful/insightful it would be really great. Thanks & Regards, Rahul MikeF wrote: ------------------------------------- ##-----------------------------------------------## Delivered via http://www.electrondepot.com/ Electronics Enthusiasts' Community of the Net Web and RSS access to your favorite newsgroup - sci.electronics.design - 397015 messages and counting! ##-----------------------------------------------##
From: a7yvm109gf5d1 on 10 Jul 2010 17:45 On Jul 7, 2:01 pm, MikeF <mike.fal...(a)gmail.com> wrote: > Hello, I am working on a senior design project that harvests energy > from a 45watt UHF Ham Radio transmitter. Currently I am getting 3.4v > peak-peak at the receiving antenna. When I attempt to rectify the > signal into a DC voltage across a Schottky diode I am losing nearly > all of my voltage (it drops to around 500mv). I believe this may be to > the fact that my impedance going from the 50ohm antenna to my circuit > are not properly matched. > > My question is, does anyone have any ideas or information on how to > better match the impedance from my antennas to my rectifying circuit? > Or any other ways of getting around this issue. Use back diodes.
From: Paul Keinanen on 11 Jul 2010 00:19 On Wed, 7 Jul 2010 12:01:17 -0700 (PDT), MikeF <mike.fallat(a)gmail.com> wrote: >Hello, I am working on a senior design project that harvests energy >from a 45watt UHF Ham Radio transmitter. What kind of antenna did that transmitter use ? Radiation pattern ? >Currently I am getting 3.4v >peak-peak at the receiving antenna. What did you use as the pick-up antenna ? Radiation pattern ? At what distance and orientation from the transmit antenna ? What kind of load impedance did you use to measure that 3.4 Vpp ? Was the measurement made in the Tx antenna near or far field ? While in the far field, the free space impedance is assumed to be 377 ohms (120 pi ohms) and antennas are generally designed to work correctly in that environment. However, the assumption of 377 ohm free space impedance is not valid in the near field, thus, an extra antenna designed to have a 50 ohm impedance and hence expecting a 50 ohm load, might not work well in the near field. For instance the impedance of a Yagi antenna changes radically when the dimensions and distances of parasitic elements are changed. >When I attempt to rectify the >signal into a DC voltage across a Schottky diode I am losing nearly >all of my voltage (it drops to around 500mv). I believe this may be to >the fact that my impedance going from the 50ohm antenna to my circuit >are not properly matched. 3.4 Vpp =1.7 Vp= 1.2 Vrms. If this was a high impedance measurement, so in the best case after a _half_ wave rectifier, only 1.7 V would be available. For the maximum power transfer theorem with equal load and source impedances, 0.85 V would be available. However, in the loaded condition, the rectified voltage would not reach full peak voltage all the time, so about half of the open circuit Rms voltage would be more reasonable or 0.6 V. If you got 0.5 Vdc, this is in fact a quite good value. A nominally "50 ohm" antenna placed in the near field of a transmitter antenna might not give the best power transfer when loaded with 50 ohms.
First
|
Prev
|
Pages: 1 2 3 Prev: Where is Archimedes Lever?? Next: bread boarding taken a little too far |