Surface Based Wireless Power Transmission and Bidirectional Communication for Autonomous Robot Swarms  Publication

This paper from ICRA 2008 details the construction of a 60cm x 60 cm surface that provides wireless (battery-free) power and bidirectional communication to an initial swarm consisting of five line-following robots, each consuming 200 mW.  Power transmission in the system was achieved through magnetic flux coupling between a high Q L-C resonator placed beneath the operating surface and a non-resonant pickup coil on each robot.  The average power density demonstrated was 4.1mW/cm2 for a static load, and the paper demonstrates much greater peak power for dynamic loads via capacitor storage and power conditioning circuitry.

See the paper (and related blog post) by Travis Deyle (myself) for additional details. The slides from the ICRA 2008 presentation are also available here.  Finally, a video of the swarm operating battery-free on the surface is shown below.  Also shown in the video is an LED being powered by the surface.






This is the coolest thing I have seen in a long time. I am going to build my own gang of robots.  I am taking a class on UHF RFID systems and I think I can use this idea for my class project.

Q1: How do you calculate the interrogation zones and the distortion distance between tags/robots? 

Q2: Is the charging sequential (as in the Alien antenna and reader device)?

Before I ask more details, I am going to read the paper. 

Any suggestions?



Hey CT,

Thanks for the interest.  I should probably note that while the communication and power harvesting concepts  are similar to UHF RFID, the actual operating regime (magnetic coupling) is much more like HF and LF RFID.  A UHF RFID apparatus would need to be operating in a completely different regime (electromagnetic coupling between the transmit antenna and robot receive antennas -- where the antennas are generally dipoles or patches).

Because this is magnetic coupling, the "interrogation zone" falls off precipitously with distance from the secondary (resonant) transmit coil.  For the system we built, it is likely to be useful only up to ~10 cm (see paper), though this is largely a function of your robots' power consumption and the Q of the transmit coil.

As for charging, the robots are all powered in parallel by the changing magnetic flux through each robot's coil.  To prevent interference between robots (and thus allow simultaneous power transfer), the receive coils were intentionally made non-resonant.  Again, details are in the paper.


—Travis Deyle

Most interesting project! If it were possible to add localization and orientation as well You'd have created _the_ ultimate robotics tool :)

Even if one used the power surface just as an uncomplicated way to reload a robot's battery it would already be helpful. In this case it wouldn't even be necessary to encircle the whole floor with the coil. Instead one could introduce "feeding areas" for reloading (and debriefing) robots.

Very inspiring :)





—Christoph K.
Very interesting but given that batteries aren't needed to work it would be interesting to see even smaller robots, small enough that not haveing the batteries is a must.


You're absolutely right.  You should check out the micro robots on this page:

The MiCRoN project actually did extensive testing in wireless power, and was cited in the paper.  In the case of small robot swarms, wireless power seems to be an effective method of power distribution.  However, it seems that the I-Swarm project preferred to use solar...


—Travis Deyle

Hi, I saw ur project and liked it very much. I have a few questions regarding ur project.

1. What is literally bidirectional communication in ur project does/mean?

2. How do you strongly say that ur robot consumes 200mW of power? How do you calculate? 

3. In the PIC micro controller  section,  i think it does 2 operations 

1. step down frequency from 40MHz to 112kHz.

2.  program for robot to behave as line follower. Is it correct? 


@ Amjath

1.  The bidirectional communication refers to communication between the power surface (main large coil) to all the robots, and communication from an individual robot to the power surface.  The former is accomplished by modulating the coil voltage / current, while the latter is accomplished by load modulating each robot's receive coil.

2.  We used a multimeter to measure the approximate load current / voltage for the robots.  For the contour plots in the paper, the load was just a resistor.

3.  There are actually two PIC microcontrollers.  One of them is in the power surface and is responsible for generating the 125 kHz (measured 112kHz) excitation frequency.  The PIC's clock oscillates at ~40MHz, from which it generates the 125kHz drive signal via pulse-width modulation (PWM).  The second PIC microcontroller serves as the robot's "brain."  It is indeed responsible for the line-following behavior.

I hope this helps clear things up; however, I imagine that the paper is probably the most succinct source of information.

—Travis Deyle

Hi,I have gone through your paper and I would like to implement it with the exact specifications as in the paper. But each and every specification is not mentioned.Can you mail me all the specifications and design.



I'm sorry... that project is more than 5 years old.  Many of the circuits (especially on the transmit side) were breadboard-only or custom protoboards and never had a detailed BOM.  I just don't have the time to go back and build detailed schematics and a full BOM.  You'll have to do a bit of experimenting on your own -- there should be plenty of details in the paper.  ;-)

Actually, I encourage you to give it a try.  Undergrad-level EE expertise should be sufficient to reproduce the project, and (like I said) it can mostly be done on a breadboard.

—Travis Deyle

Sir, Me and Manikanta are working on this project. But unfortunately, my guide said to do the same for a mobile phone. Surface Based Wireless charger for a mobile Phone. I would appreciate if we can get help in designing the transmitter and receiver. Actually when it comes to mobiles.every thing will be minute in size. Right now we are in bewildered state. Please guide us for making a transmitter circuit and receiver circuit for surface based wireless charger for mobile phone. I would love to take your help for this. Thank You Sir.

—Rajasekhar Josyula


We actually did that... we build a wireless phone recharger in another paper:  PowerPACK: A Wireless Power Distribution System for Wearable Devices.  It was published in the 2008 IEEE Symposium on Wearable Computers (ISWC).

—Travis Deyle

Thank You Sir for your feedback..We will look through the paper.

—Rajasekhar Josyula

Its like you read my mind! You appear to know a lot about this, like you wrote the book in it or something. I think that you could do with a few pics to drive the message home a bit, but other than that, this is excellent blog. A great read. I'll definitely be back.

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