Physics 589 

Graduate Research in Alternative Energy

2 Jun 08

    The wind belt is a device which generates electrical power using moving air currents. This device was  invented by Shawn Frayne, who is from Mountain View, Ca.

-Link to Popular Mechanics website

-Link to the wind belt developer's website 

The following is an image of the wind belt generator:


Here are a few diagrams of various types of wind belt generators:


-Link to voice coil wind belt design

Materials and Descriptions

    What materials are used for the black belt of the wind belt?

- The original belt was made out of mylar coated taffeta, which is a kite making material.

 What is "aeroelastic flutter" and how is it related to the 1940 Tacoma Bridge collapse.

- Aeroelastic flutter: a self-starting vibration that occurs when a lifting surface bends under aerodynamic load. Flutter was the cause of Tacoma Narrows Bridge collapse.

-Link to video of the Tacoma Bridge collaspe

-Link to Wikipedia article on aeroelastic flutter

Project One

 3 Jun 2008

    We began our project on Jun 3, 2008, attempting to recreate the wind belt generator from scratch. We constructed one model using a peice of ribbon which was eighty cm in lenght (purple, in case you were curious), two rare earth magnets,  a coil of wires consisting of a little more than three thousand turns, an upright fan, a spring scale, and a stand. The stand was made out of three bars attached by two clamps, and the ribbon was simply tied to the top and bottom of the stand. We made our measurements using an oscilliscope connected to the coil of wires. We placed the magnets on the ribbon at the antinode of the ribbon and set the coil of wires as close as possible to the magnets.*

    Upon completing the construction we began to experiment. First we set the fan on high and adjusted the tension on the ribbon to see where the maximum amount of oscillation occured. However, during this exerpiment it began to be apparent that, to a certain extent, the tension in the belt did not matter!  We began to get an oscillation at around six newtons. The oscillation continued until I had maxed out the spring scale. (I will note, that without the scale in place I could indeed stop the flutter of the ribbon by placing a great deal of force on it. However, that was more tension than our scale could measure and is not important to this part of our experiment.)  The quantity that did change as the tension changed was the frequency. Because of the fact that the freqency also depended on the angle at which the ribbon was presented to the fan, this change in frequency is not readily visible in our data.  

    We made the assumption that the amplitude of the signal would be very dependent on the fan speed, but this was not the case. As can be seen from the data, the greatest amplitude occured when the fan was set on meduim. This again has led me to believe that the ribbon is much more sensitive to the angle at which it presented to the fan rather than the wind speed or tension. 

    The following measurements are the ones that we got from the o'scope while we adjusted the various parameters: 

Fan Speed Tension (Newtons) Frequency (Hz) Amplitude (Vpp)
  22N 25.00 5V
High 18N 20.00 4V
  16N 22.20 4.5V
  22N 23.81 6V
Medium 18N 22.20 7V
  16N 20.00 6.2V
  22N 22.73 4.2V
Low 18N 22.20 4.2V
  16N 20.83 5V

Dr. Bruton also managed to get some video footage of the wind belt.

-Link to video of our wind belt generator

    I was looking at an image of the wind belt generator in an attempt to see how many turns they used on their coils. Although the image is not the great, I estimate the coils have about two hundred turns. The following image is the one I was looking at:



10 Jun 08

    We have begun try to find the best possible configuration for the generators. What we will do first is look at the number of turns the wire makes. Starting with fifty turns, testing the voltage, and then increasing the number of turns. We also want to check to see if the gauge of wire used makes a noticable difference.

12 Jun 08

    We spent today in the machine shop learning how to use the lathe, and turning our coils. The website we visited recommended around one thousand turns of wire. The following is a link to that website:

-Link to instructions on creating coils.

    We ran the lathe at around two rotations per second in order to determine the number of loops we were laying down. We calculated that, at that speed, it would take around eight and one half minutes to lay down one thousand turns. However, since we layed the first layer down slowly, we ran the lathe for about ten minutes instead. This should give us around the desired one thousand turns. The dimensions are as follows: inner diameter, one inch; outer diameter two inches; resistance fifteen point seven ohms.

30 Jun 08

    We tried out different types of material today, in order to see which material performed to best.
   1.  Purple Ribbon
   2.  Clear Mylar
   3.  35mm Film
   4.  Gray Duct Tape
   5.  String
We set each of the various types to the tension which worked best for that material. All types of the material did fluctuat, although the string did not do so very well. In all the cases, except that of the string, we noticed that the lighter materials had a higher frequency of oscillation. After seeing the results I feel that that both the mylar and the 35mm film were the best material for belts operating under low or microwind condtions. The other material that I liked was the purple ribbon; I think that it would be a little more durable that the other two, although it did not have quite as good an oscillation.
   After testing each of the materials by themselves we then placed the magnets on the ribbon.  First we placed the magnet in the center of the ribbon, and then at a spot a little over three quarters of the way to the end. (The reason that we did not place the magnet at the very end of the ribbon is because that is a node and we would have no amplitude of motion at all.) We noted that in every case, when the magnet was at the center of the ribbon it had a higher amplitude of motion, and a lower frequency, but also at that postion, it had a rotational component to its motion. Although this rotational motion does not seem to have any beneficial effect on the flux through the loops I will attempt to add this element into the theoretical calcultion in order to see how much effect it really has.  

Other Projects

    Although our main project was the wind belt, we had a few other ideas that we wanted to try out. The first of this was a pendulum type genertaor (it's image is the first one on the homepage). Also, we wanted to try and build a flutter generator out of voice coils from an old computer hard drive.

Pendulum Generator

4 Jun 08

    I have begun working on the pendulum generator. The materials I am using are as follows: two pens, one wood block, a screw wrapped with about one hundred turns of wire, and magnet. I have glued the the coil of wires to the board, and created the support for the the magnet out of the pens. I did this by drilling a hole halfway though one of the pens, inserting the other and glueing it into place. I then drilled a hole into the block of wood and inserted the my frame into that and glued it in place. Right now I am having difficultes with the glue that is holding them in place. It does not seem to be firm enough to hold the magnet up off the coil of wires. Anyway, more of updates on this later.

9 Jun 08

    Okay, so I finally got the glue to hold the frame in place. I tested the the generator using an oscilloscope and managed to get a small amount of voltage out of the generator (on the order of millivolts). However, I could only get voltage out as long as I swung the pendulum by hand. As soon as I stopped controlling the magnet the swing became too eratic and any voltage generated became negligable. I believe the way to fix this problem is, instead of using string to hang to the magnet, use something rigid. That way the magnet would only be able to swing in the desired direction, with the desired orientation.

Voice Coil Generator

4 Jun 08

    The second project is going well. Using the voice coil, two notebook tab posts, and a block of wood I created a place where the voice coil can move freeing and still give me enough support for both the ribbon and the magnet. Let me expain how I mounted the voice coil. First I drilled a hole in the block of wood, cloes enough to the edge that the ribbon can be connected. Then I hammered the notebook tab posts into the hole so that it would fit tightly. I then drilled another hole into the block in order the mount the button magnet, positioning the hole so that the coils would pass directly over the magnet. I also had a second magnet that I wanted to use, the one left over from the original voice coil system. Luckly, it had a metal bracket already attached so I simply placed it over the voice coil and screwed it down. After doing that the coil was sandwiched between two magnets. I must admit that I have a problem here as well: the glue that is holding the magnet down in the block of wood does not appear to be strong enough to resist the magnet force applied by the other magnet. I have reglued it and am awaiting the results.

5 Jun 08

    Today, while waiting for the glue to dry I went ahead and finished the frame that the voice coil sits in. I used two long metal brackets, nailed them to the wood block, and used a second wood block for the far end. In the second block I drilled a hole one inch in diameter and set a bolt through the wood. I plan to use that bolt as the anchor for my ribbon. If all goes well with the glue, I should have this project complete and ready to test by the 9th of June.

9 Jun 08

    Well, the glue finally managed to hold the magnet down, so I continued with the construction. I needed a way to adjust the ribbon so I took my cross-bolt and flattened one side. Then I started trying to solder two wires to the voice coil. That project was a litte more difficult than I originally thought it would be. I broke the first voice coil I used because the soldering gun was so hot that it burned right through the tiny wires that the voice coil uses. Luckly, I had a spare voice coil, one that had a little bit sturdier design. Tomorrow, my goal will be to find someway of mounting the coil so that the wires will not impair its movement, and still allow me to connect to them.

10 Jun 08

    I have completed the construction and tested the model. I can only get about .4 volts from the device. This is not enough to light up the LED. The minimum voltage to light the diode is about .7V so I am a bit short.

17 Jun 08

    Although the generator did not work very well we went ahead and shot a video of it. Here it is.

-Link to voice coil generator

Motion Generator

11 Jun 08

    The motion generator is a coil of wire wrapped around a plastic core with a magnet in the center. When you shake the wires the magnet moves inside and induces a current in the coils. We made one of these today and tested it. It worked very well, the only problem is that you have to shake the thing about 5 times per second. As you can image you get tired pretty rapidly. Here is a link to some examples of these generators.

-Link to the motion generator

16 Jun 08 

   I would like to use this type of generator to light the led which is attached to the rectifier circuit shown below. I have made several attempts so far, and was able to charge the capacitor up to about one volt, but was not able to light the led.

17 Jun 08

    We also have video for this particular generator.

-Link to video of motion generator

Rectifier Circuits

11 Jun 08

    I also want to build a rectifier circuit for the first project we did. I will try the full wave rectifier first since that one seems the the most useful in our application. The full wave rectifer has an average load voltage of;

.6375 VL(pk)

The following is an image of the full wave rectifier circuit and its corresponding output waveform:

Here is a link to an other circuit which also includes a storage device as well.

-Rectifier and storage circuit

 16 Jun 08

    Built the rectifier circuit today and began to test it. I did not have the OA91 diodes that they used so I used 4148s instead. I also did not have a 10 millifarad capcaitor, so I test the circuit out with a one farad capacitor. It did work, but took a long time to charge up. I also tried using a 2.2 millifarad capacitor and it worked, but discharged very rapidly. My next goal will be to connect multiple capacitors in parallel in order to increase the capacitance to the recommended level.

17 Jun 08

    In order to get as close to 10 millifarads as possible I have calculated that five capacitors will need to be connected in parallel. The value of each capacitor will be 2.2 millifarad. I calculated the total capacitance using  this equation:

CT = C1 + C2 + C3 +…+CN


18 Jun 08

    I am attempting to recreate a circuit diagram that will charge up a battery. After looking at a solar powered lamp, we think it might be better to use a battery as the staorage device instead of a capacitor. The reason for doing so is that the capacitors lose their charge too quickly to be of much use. The battery, on the other hand, takes much longer to charge, but holds it's charge for longer as well.  


19 Jun 08

    I continued work on the circuit diagram today. I had never used this version of electronic workbench, so it was interesting. Hopefully, on Monday I can finish this project and get the diagram posted here.


23 Jun 08

   Finally finished the circuit diagram. I had a bit of trouble tracing the wiring on the circuit itself, but as they say, the third time is the charm. In any case, here it is:


-Link to circuit diagram




 24 Jun 08

    Today we began working on the theory of how the magnet produces the electric field in the wire. Actually, we were more interested in the electromotive force (EMF) produced in the wire as the magnet assumes various orientations. I have begun to put all the information we have worked on into word documents and spread sheets. Over the next few days I will be uploading those documents to this website.


-Link to calculation of EMF


25 Jun 08


     We went ahead and graphed the emf output for our calculations, and also graphed the the magnetic field with respect to displacment of the magnet. Those two links are below.


-Link to EMF output


-Link to graph of magnetic field vs. displacement


1 Jul 08




1.  What happens to the EMF if the radius of the loop is doubled?
It seem as if this would cause the EMF to decrease by a value proportional to one over R cubed.
2.  What happens to the EMF if the distance of the magnet is doubled?
The EMF decreases by 1/4.
3.  What happens to the EMF if the amplitude of vibration of the magnet is doubled?
The EMF again decreases by 1/4.
4.  Based on your findings from question 3, is it better to have magnet in the middle of the belt or  toward the fixed ends of the belts?
At first glance it seems as if it would be better at the ends of the belt.  However, our experiments have consistently shown that more EMF is produced when the magnet is in the center of the belt.
5.  What happens  to the EMF if the frequency of vibration is doubled?
The EMF doubles as well.
6.  In your opinion, changing which of the following will help us to best maximize the EMF:     d, A, or, R?
Decreasing A, d and R should maximize the EMF.

3 Jul 08

    I finished the calcultation of the EMF, adding the rotational component of the motion. It is rather ugly but I will try to work on simplifying the expression.