[General] Energy Harvesting via RF source; RECTENNA

Good Day Member,

I am working on a rectenna that harvest GSM energy at 900 MHz and converts it into DC Voltage for charging a cell phone battery. From various literature review, I have made a simple patch antenna in CST MWS and designed its relevant rectifier circuit in ADS. The questions I want to ask are following:

1. In most of the rectenna papers, the output results are mentioned in terms of DC Voltage but not current.Why is that? As we all know that Voltage is derived quantity, it is the actual current that charges the device.So why not discuss results on the basis of current rather than voltages?

2.With regards to any cell phone battery values i.e. Voltage=3.8 V, Current 3200mAh and Power 9.88Wh [hypothetical]. Should I design my circuit that meets these requirements or just DC output from rectifier in terms of Voltage would suffice as much of literature demonstrates?? Mostly batteries are represented with mAh values, so should I concentrate my result on current??

3.Is multiband RF rectenna realizable as I haven't seen any papers that were successful in doing so?

Awaiting your kind replies,

Regards

kela3kela said:

for charging a cell phone battery.

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Ok

kela3kela said:

Voltage=3.8 V, Current 3200mAh and Power 9.88Wh

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Ok, let's do the math.
Average input power to the rectanna -30dBm = 1µW.
If your circuit is ideal and lossless, and the battery charging is ideal and lossless, it will take 10Wh/1µW = 10E6 hours = 1141 years to charge the battery.

Conclusion: battery charging with rectanna is not a useful idea.

Many people dream about "harvesting" RF energy by rectennas and use the DC power for something.
The main problem is that for rectenna size suitable above say 500 MHz, most detector diodes are low-level Schottky diodes. They are suitable to make sensitive detectors for RF inputs < -10 dBm but they saturate above 0 dBm input. Therefore such detectors can be only loaded by a current not exceeding ~...10 mA under 0 dBm RF input.
One can use such rectenna to charge a 100 uF..10 000 uF capacitor over several hours, then to blink a LED or run a short program in a microprocessor-driven sensor but that is all.

Until someone invents a new rectifier device useful for UHF/microwave rectenna, the effort is rather futile.

Good luck!

volker@muehlhaus said:

If your circuit is ideal and lossless, and the battery charging is ideal and lossless, it will take 10Wh/1µW = 10E6 hours = 1141 years to charge the battery.

Click to expand...

Thanks for the wakeup call..

jiripolivka said:

They are suitable to make sensitive detectors for RF inputs < -10 dBm but they saturate above 0 dBm input. Therefore such detectors can be only loaded by a current not

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Ok Thnx. Lets say I want to charge a small sensor working at 2-3 V. What about this then. Will it work with 900 MHz band signal and a rectifier circuitry?
What is more important in simulation results of rectifiers, the Current or Voltage?