Introduction: Microwave Energy Detector & Wireless Energy Harvesting

Description

This article describes how to build a wireless harvesting device that will capture stray 2.5GHz energy from a microwave oven and convert it into a useable voltage that will light up a red light emitting diode (LED). Hobbyists can modify the antenna with longer wires and try to pick up other signals such as AM/FM radio, mobile phone signals and other wireless energy. The LED's light will be visible when the module picks up 1 milliwatt-10 milliwatts of microwave power. Usually the most power leaks out of the door seam of a microwave oven.

What you need:

1 RFD102A (RF-DC Converter) module available at

http://www.rfdiagnostics.com/product/rfd102a/

1 ¼ watt leaded resistor (any value) or two wires that are 1 1/8 inches long (28.6mm)

1 Kingbright Surface mount red LED (part number: APT1608EC) available at Digikey/Mouser/Newark

Fine tipped soldering iron

Solder paste or Fine Solder

Step 1: Assembly Instructions


Cut the resistor wires off next to the resistor. These are just the right size at 1 1/8” long for a 2.5GHz dipole. Throw away the resistor and keep the wires.

Put solder paste on the module at pins 1 & 8 and at pins 4 and 5.Place the wires on pins 4 and 5 and solder carefully using tweezers to hold the wires (it will burn you otherwise). Solder at the lowest soldering temperature possible to avoid damaging the module. If the iron is too hot then you may damage the internal connections inside the module. Use a minimum of time for soldering (<10secs). The wires work as a dipole antenna to collect the 2.5GHz energy into the RF (Radio Frequency) Input of the module.

Place the LED with the anode (positive side) onto pin 1 and the cathode (negative side) on pin 8 and solder carefully. For those not familiar with LEDs, the triangle symbol of the diode should point to the ground pin of the module (pin 8). Your final microwave harvester should look like figure 2

Step 2: Test on Your Microwave Oven

Now put some water in a mug and put it in the microwave oven and cook on high for 2 minutes. While the microwave is running, hold the module and move the module antenna around to find a hot spot on the microwave. Tape the module on the ground wire to the microwave to keep it in place. If all is well then you will see the LED light up and dim as the electric fields change while the mug rotates in the microwave oven. The above figures show the microwave energy harvester in action. Experiment with antenna shapes and sizes. If you go too big or too small with the antenna then less energy will be collected. You can also put the assembled module near an 802.11b/g/n wireless LAN router and watch it flicker as the router transmits and receives 2.4-2.5GHz energy. Enjoy!

Other Project Ideas:

- Harvest AM/FM Radio Signals

FAQ

- What is the maximum current this module can provide? Ans: Typical current is ~0.5-5mA. Max current is 18mA.

- What is the efficiency of converting RF energy to a DC voltage? Ans: If the input power to the module is around 10-50mW then the RFD102A can achieve >50% efficiency if the resistance seen by the DC output is ~10kOhm.

- I don't have a soldering iron and am all thumbs. Where can I get a detector like this already built up? Ans. The RFD102A-DET is available http://www.rfdiagnostics.com/product/microwave-oven-window-energy-harvesting-kit/

- What is the maximum output voltage this module can produce? Ans: With 0.5W input power the module can produce up to 37V at 915MHz.

- Can I charge my mobile phone with this? Ans: It is possible with 4 RFD102A modules and antennas to produce enough current to charge a mobile phone. The hard part is the wireless source would need to be so powerful that you wouldn't want to be in the same room during charging. You may hurt your eyes by cooking them.

Comments

author
ShamarY (author)2016-01-09

is it possible that instead of connecting the led a speaker is put in its place and a phone call can be listened in on, or the radio?

author
utg001 (author)2015-11-13

I had an explosion of ideas from this project, I had to make this account :p

1> you seem to use specific dimensions/material of wire to tune it to 2.5 GHz, whats going on here? Can I use a sheet of metal? Can I tune it to some other frequency on this module? If so, how?

2> What is the ideal output from this model you made under ideal conditions (V & I)? Is it versatile enough to be used as a small power source for something if I join enough of them in series and parallel? Say 1000 of them in 10x10 series and parallel connection harnessing a constant strong signal, can the module support a tiny load (bit more than LED)?

I'm sorry if it sounds too stupid, but I'm only wanting to know a bit more fine details before I head to the drawing board :)

author
tbudka (author)utg0012015-11-14

1. Dipole antennas are usually sized to be 1/2 of a wavelength so each wire in this dipole is 1/4 of a wavelength. At 2.5GHz the 1/4 wavelength (c/f) = 0.25 * (3.0E10cm/sec)/(2.5E9 Hz) = 3cm. The leaded resistor wires are 2.86 cm (1 1/8 inch) long so that checks out. Sheet metal could be used for a bow-tie antenna or a cross pattern to pick up the other polarization. Size does matter. A larger dipole will pick up lower frequencies. The RFD102A module is broadband and limited by the frequency response of the antenna.

2. I posted a photo at the end of an array of 30 detectors picking up the energy. Your idea of putting a 10x10 array is a good one to scale up the power harvested. Kind of like having a larger solar panel. That would be a cool project to make.

Thanks for your questions/comments.

author
ke8bg (author)2015-11-14

From the FDA website on leakage..

Use to work on microwave ovens.. We had to leakage check each one before they went back into service. Most likely leakage is around the door. A door out of adjustment can spew out all sorts of radiation. Redundant door safety switches are there for a reason. I've been 'dosed' a couple of times by a technician who had left off the brass Magnetron gasket and couldn't figure out why the control board would shut down right after he pushed the start button. 500 watts at 2.4 ghz will overwelm a CPU chip. Be careful. 2.4ghz can cook you too!!!

BTW as stated below the power level drops off 'inverse square of the distance'.

"A Federal standard limits the amount of microwaves that can leak from an
oven throughout its lifetime to 5 milliwatts (mW) of microwave
radiation per square centimeter at approximately 2 inches from the oven
surface. This limit is far below the level known to harm people.
Microwave energy also decreases dramatically as you move away from the
source of radiation. A measurement made 20 inches from an oven would be
approximately one one-hundredth of the value measured at 2 inches."

author
tbudka (author)ke8bg2015-11-14

Thanks for this information and it's nice to meet someone familiar with microwave leakage/exposure. The light from the detector definitely gets dimmer very quickly as I pull it away from the microwave door. 5mW is very small and is only seen with this detector close to the microwave oven (<2inches). This is why I think we can only harvest energy close to the microwave rather than at the kitchen table. I would need to add an amplifier to pick up the weak microwave energy from the microwave if I were >5ft away.

author
MarcoG6 (author)2015-11-08

there was a kickstarter that made a phone case to turn the stray signals from ur phone to charge the phone they claimed to get 3x the battery life in a iphone 5 but the case was like 100$ maby u can make a chaeper one

author

tbucka is right, it just doesn't seem... legit.

author

*tbudka sorry

author
tbudka (author)MarcoG62015-11-09

That claim doesn't seem realistic. If the charger is collecting a lot of power from the phone then it's probably hurting its transmission/reception. The RFD102A module is very sensitive to low input powers but didn't get much power from my phone with a log periodic antenna. At 0.04mW/915MHz the module produces 0.5V output into a voltmeter. When I was testing the RFD102A-TB (TB=test board) my phone while on a call to my answering machine, I got up to 4V output from the module but that is into a high impedance. I think my next instructable will document this tests with a phone and a base station. Thanks for your comment.

author
MichiganDave (author)2015-11-07

A BIG Thanks for sharing and a small question for you: If you can harvest this energy can you save it? I am imagining doing this in order to save the "free" energy until its useful. Will it take a thousand years to power a flashlight, or merely ten?

author
tbudka (author)MichiganDave2015-11-08

To answer your question about charging a flashlight, yes it is possible to charge a flashlight in a reasonable time with your microwave oven if you have ~10-20 of these detectors to generate 50-100mA to charge up the batteries. Please see my last photo with 30 detectors on a microwave all lighting up. Then you need to make sure the oven is on a lot (like at Subway). Unfortunately you need to be so close the microwave to get this power. So IMHO, if you are going to try to get free energy, you need a good source in mind. Stray cell phone and WiFi power aren't high enough. An array of antennas pointing at a base station may give you some small amount of power but it won't be cost effective.

author
tbudka (author)MichiganDave2015-11-07

Yes. You can save the energy but not indefinitely. There are always small leakage paths to rob you of this hard fought free energy. The RFD102A has 60kOhms resistance to GND so if you had been able to charge a supercap (1F) to 5V, it would take 60000secs (1000mins or 16.67hrs) to discharge the capacitor by 36.8% of its energy (RC time constant). Supercaps also have their own leakage resistance. So you need to make sure you understand your microwave source and the leakage resistances of your components. TinkerJim has a great instructable on a Solar Engine that is very useful with this module. I am planning on posting about an improved module with TinkerJim's design. Another great question. Thanks for your interest.

author
turbiny (author)2015-11-06

Is it possible to recharge a phone via wifi router?

author
tbudka (author)turbiny2015-11-06

No. Most WiFi routers are very low output power. If you have a WiFi Booster Amplifier (2W) then there is a chance to get some power from this system to charge your phone but I wouldn't want to stay in that room with all that power. Most WiFi signals are <0.05W coming out of the router. This detector will light up and flicker close to an 802.11b/g router (2.5GHz) but that's only a few milliamps of current at 1.5V. Sorry about this but I agree with Dave Jone's eeVblog #55 that you won't be able to charge your cell phone from WiFi unless the transmitted power gets raised. Great question.

author
whyjbe (author)2015-11-06

Thanks tbudka for the tips. It's good to know that the power level drops quickly with distance. My microwave is still 'new' since I do not use it.

author
tbudka (author)whyjbe2015-11-06

There is really not much to worry about with microwave ovens, cell phones and base stations for health issues. I tested this module with a broadband antenna around a base station and I got a very low voltage out (1.5V max) which would mean there is less than 0.0005W of power right next to a base station. The cell phone companies do a great job keeping that power low around the base stations. Also since the wavelengths are large (inches/cm) there can't be much if any damage at the cell level (microns). IMHO I don't see much of a chance for low power (<10mW) microwaves to cause any health problems. Just don't stare at the microwave popcorn right next to the window... :)

author
whyjbe (author)2015-11-06

Thanks tbudka for the tips. It's good to know that the power level drops quickly with distance. My microwave is still 'new' since I do not use it.

author
whyjbe (author)2015-11-06

So is this another way of saying that this module transmutes the harmful EMF (electromagnetic frequency) waves coming off the microwave since it converts it to electrical power? If so that's awesome!

author
tbudka (author)whyjbe2015-11-06

This detector helps give the average person a way to "see" the levels of microwave energy leaking out. The power level drops extremely quickly with distance from your microwave so usually there is no need to worry about it. As you move this detector more than a few inches from most microwave ovens you won't see any light from the LED. This indicates that the power is less than 1mW which is tiny for exposure. For microwave ovens, the main danger is for your eyeballs where heating could cause cataracts. I don't believe there are any other harmful effects than that from your microwave at powers <10mW. If you have a loose door then I would recommend getting a new microwave. Please don't put your eyes close to the window or door seam or side vent of your microwave.

About This Instructable

18,495views

278favorites

Bio: Microwave Engineer, Consultant, Design Contractor, Electronics Enthusiast, Power Amplifier Designer, Filter Design, Electromagnetic Simulations, Orcad PCB Editor Design
More by tbudka:Solar Engine Demo Using the RFD88A Energy Harvesting Engine ModuleRFD102A Inside the Microwave Oven LightsMicrowave Energy Detector & Wireless Energy Harvesting
Add instructable to: