Tractor Beams are mysterious waves that can attract particles towards the source. Here, we will show you how to build an Acoustic Tractor Beam with components that can be bought directly on the Internet for less than 75$.

With this Instructable you will be able to get in your hands a device that it was only seen on SciFi movies such as Star Wars or Star Trek.

If you want more scientific background on Acoustic Tractor Beams, you can check our Open Access research papers:

Do not forget to watch the attached video in this Instructables.

Step 1: Gather the Parts and Tools

We present a list of the necessary components. I have tried to place links for different countries. However, the same parts can be found all around the world, some useful websites are http://www.findchips.com/ http://www.dx.com/ http://www.miniinthebox.com/http://www.lightinthebox.com/http://www.banggood.com/

The circuit is not complicated. Basically, an Arduino will generate 4 half-square signals at 5Vpp 40kHz with different phases. These signals get amplified to 25Vpp by the Motor Driver and fed into the transducers. A button pad can be used to change the phases so that the particle moves up and down. A battery (7.3V) powers the Arduino and the logic part of the Motor Driver. A DC-DC Converter steps-up the 7.3V to 25V for the Motor Driver.


  • 30x 16mm 40kHz Transducers The MSO-A1640H10T are the best but minimum order is 500, they are good so perhaps you can save them for future ultrasonic projects. Alternatively, others 16mm 40kHz transducers will serve (emitters and receivers are pretty much the same) for instance the MCUSD16P40B12RO.

Necessary Tools:

  • 3D printer -> you can use an online service
  • Soldering Iron, Tin and Flux.

  • Drill

  • Hot-glue gun

  • Multimeter

  • Cable Peeler

  • Screwdriver and Pliers.

Step 2: 3D Print the Bowl

The transducers will be mounted in this bowl. This shape allows to naturally focus the beam.

We used an Ultimaker Extended 2+ with a 0.4mm nozzle and the Normal settings. No support, only brim. It does not need to have a perfect finish so any regular printer should work.

Step 3: Solder Arduino Headers (upwards If Possible)

Step 4: Program Arduino

Upload the attached program in the Arduino Nano. If you are using a cheap Nano (totally recommendable) you will need to install new drivers, there are usually links in the webpage where you bought it.

Step 5: Charge the Battery

This way when you finish the project it will be at full charge.

Step 6: Cut the Handler

300x45x15mm rectangular piece of wood.

Step 7: Redrill the Bowl

Sometimes the holes are not perfect and are a little bit clogged, re-drill them if it were necessary.

Step 8: Attach the Bowl to the Handler

Drill an initial hole in the handler, attach the central screw and then you will be able to drill the two holes at the sides.

Deattach the bowl, it is more comfortable to attach and test all the components without the bowl. At the end of the Instructables we will reattach it.

Step 9: Screw the DCConverter and the Driver

Close the the drilled holes for the bowl we will place the DC-DC converter at one side and the Driver at the other. Put them and mark with a pen to drill later. Then pass a screw and a nut through the holes of the devices for being able to attach them properly to the wood.

It is very important to leave the OUT side of the Converter closer to the bowl.

Remove the indicated jumper of the Driver and keep it for later.

Step 10: Stick the Arduino

With Velcro tape, double sided tape or just hotglue stick the Arduino below the Driver with the USB port pointing to the right.

Put the jumper between the D10 and D11 pins.

Step 11: Drill Through Holes

Drill two through holes above the Driver.

Drill tree through holes below the Arduino.

We will pass wires through these holes.

Step 12: Solder Wires to the Power Switch

The central pins provides the current to the circuit, the right pins go to the DC barrel and the left ones to the battery connector pins.

Try to use red wires for (+) and black for ground (-) to keep things ordered. Pay attention to where the + and - of the DC barrel go and solder it appropriately.

For the battery connector pins we can use pin headers and a tiny piece of strip-board. Be sure that the wires are not touching each other (use a multimeter), and even put hotglue between them to make them safer.

The power switch provides current to the circuit either from a DC barrel or from the battery.

We can use any DC adaptor between 9V and 12V that can provide at least 2A if you do not want to use a battery.

Step 13: Stick the Battery

With double-sided or Velcro tape. Do not use hot-glue since it could damage the battery. Put it in the same orientation as the image.

Step 14: Connect the DCConverter With the Driver

These wires will pass the step-up voltage (25V usually) from the DCConverter to the Driver.

Step 15: Glue the Power Switch

Step 16: Connect Logic Supply

We will provide 7.4V to the DCConverter IN.

First connect the black ground wire (-) from the central pins of the Switch into the DCConverter IN(-), in the same hole connect the ground for the Arduino.

Then, connect the red (+) wire from the central pin of Switch into the DCConverter IN(+), in the same hole put the VIn of the Arduino and the logic supply for the converter (pins from where we removed the jumper, very important to connect it into the highlighted pin).

Tining the tips of the wires will facilitate putting several wires in the same hole.

It is also possible to get voltage for the Arduino from the DCConverter. Instead of connecting Converter.IN(+) to Arduino.VIn, we can use DCConverter(5V) to Arduino(V5).

Step 17: Connect Signal Wires

These four wires will transfer the signals from the Arduino into the Driver.

Connect Arduino.(A0,A1,A2,A3) to Driver.(IN1,IN2,IN3,IN4).

Step 18: Button Pad

The button pad is optional, but if you make one you will be able to levitate the particles up and down.

The idea is to have three button pads that when pressed they make contact with ground (the buttons are active low).

Get ground from the Arduino to the common terminal of the buttons. Then, connect each of the buttons to D2(up), D3(down) and D4 (reset position).

Step 19: Set the Voltage to 10V

First Connect the battery (be sure to use the right polarity).

Switch on the device.

Rotate the potentiometer counterclockwise until you see 10V in the display.

In the final device we will use 25V but it is safer for the test equipment to work at 10V. If you use X10 probes then it is alright to use 25V throughout the process.

Step 20: Test the Signals

This step is optional but it is about time to check that everything is working fine.

Get two probes and connect the grounds to a ground of the circuit, temporarily using the button pad ground is one of the easiest options. Remember to put it back when finished.

Before the driver the signals should be 5Vpp and after the driver 10Vpp.

Signals from the same side are in phase while signals from opposite sides should be out of phase.

Step 21: Mark the Transducers (hard Method)

The transducers have polarity and they need to be marked. Do not trust manufacturer marks since they can be wrong.

This method is the one contained in the video, but we have an alternative one that is much easier one in the next step.

First take ground and voltage from any of the Driver outputs. Connect them to a transducer and also connect one probe to the same transducer. This probe will capture the emitted signal.

Take another probe and connect it to the transducer that needs to be marked, this will be the received signal.

Put the transducers face to face and check the signals in the scope.

If the signals are in phase, mark the leg connected to ground. If they are out of phase, mark the other leg.

Mark all the transducers.

Step 22: Mark Transducers (Easy Method)

This method for marking transducers is much easier than the previous one.

Just connect one probe to the transducer.

With a metal wire poke gently and repeatedly the inside of the transducer. Check the signal in the scope, if the first spike goes up, mark the ground leg. If the spike goes down, mark the other leg.

Step 23: Mount the Transducers

Put the transducers in the sockets with the marked legs pointing upwards (towards the top).

You do not need to populate the bottom row.

Step 24: Wire the Transducers

We need to wire the transducers to deliver power into them.

Measure the needed length for the wire and give three extra hands for connecting it later.

With the cable peeler, partially peel at the correct distance, later these exposed parts will be twisted around the transducers legs.

Once that you have made the cuts with the peeler, redistribute the plastic to keep a uniform length of cooper exposed. Twist the cooper wires to make them more solid. Twist the exposed parts around the transducers legs, apply flux and solder.

Follow the pattern presented in the images. That is, all the grounds are connected together. The red wires of the same half go towards the same side.

Pay attention to the numbers, these numbers correspond to the driver numbers.

Step 25: Test the Transducers

This step is optional but it is convenient to check that all the transducers are connected correctly.

Connect the ground from the bowl into the driver ground (there will be another wire there).

Connect the 4 red wires from the bowl into the outputs of the Driver, respect the numbering.

Connect two extra marked transducers to the scope probes. Be sure to connect the ground into the marked leg (or at least connect the two transducers in the same way). With these transducers we can check the emitted signal of other transducers.

Transducers from the same half of the bowl should emit in phase. Transducers from opposite halves emit out of phase.

Transducers with the wrong polarity should be desoldered, rotated and resoldered.

Step 26: Set Voltage to 25v

Be sure to set the DC-DC converter to 25V using its potentiometer.

Step 27: Attach the Bowl

Now that all the components are in place, it is time to reattach the bowl into the handler.

Step 28: Connect the Wires

Connect the ground from the bowl into the driver ground (there is already another wire there).

Step 29: Switch on and Levitate

Switch on the device, you should be able to feel a little bit the sound, or hear it if you point it into a big chunk of expanded polystyrene or foam.

Using an acoustically transparent sheet or tweezers you can place particles in the centre of the bowl (above 1.8cm approx) and they will be levitated.

Push the buttons to move the particle up or down.

Depending on the size of the particle and how close it is to the bowl, you will be able to levitate it laterally or upside down. It is also possible to levitate particles that are resting on a surface.

Step 30: Building Other Sonic Devices (Optional)

We have presented how to build the most efficient device but there are others that require even less electronics although they are not as efficient in terms of levitation power to watts.

For the following devices you will need smaller transducers, wires and connectors, as well as a different version for the Arduino (that generates always a 40kHZ signal).

Step 31: Coils Device (Optional)

Print the attached STL file. The transducers are fit in the bottom holes and they are all driven with the same signal.

Step 32: Tubes Devices

Print the attached STL file. The transducers are fit in the bottom holes and they are all driven with the same signal.

Step 33: Miscellaneous Files

Raw design files (Inventor)

Do not be to hard on him, it is a common mistake. Hope that everything goes alright and if you enjoy the project, stay in touch. I have some more similar projects coming: a directional speaker and a single-axis levitator capable of levitating water and live insects.
<p>Hello Asier,</p><p>I am building your acoustic tractor beam for a professor and student who hope to use it to catch and levitate drops of urine from hummingbirds -a very unusual application! After reading your comment yesterday about a new project capable of levitating water, I'm wondering if you think the acoustic tractor beam in these instructions is capable of doing what we intend.</p>
Dear SwatBio,<br><br>Unfortunately, the tractor beam will not be very useful.<br><br>I am working in a simple single-axis levitator that would easily levitate small droplets of urine. As long as you inject them with a pipette or syringe. It would be complicated to catch them in mid-air.<br><br>Is that a research work for an university or research center. I am quite use to collaborate with them. I would be very willing to help you.<br><br><br>Best regards,<br>Asier.
<p>Thank you, Asier. Yes, the project is for a college research project. I will, no doubt, seek your advice at some point. It's very generous of you to offer your help!</p><p>-John (SwatBio)</p>
<p>My friend and I made this for a school project and we did everything almost exactly the same as yours, switched it on and could hear a high pitched sound when we put foam over the top. But it would not levitate anything. We later narrowed this down to the fact that the DC-DC booster wasn't &quot;boosting&quot; as such, as when We tried to change the output, it would go down but not up. Did we do something wrong? </p>
Could you check the model of the DC-DC converter? There step-ups and step-down.
Yeah, I'm sorry, we checked everything today and discovered that we did purchase a step down converter (Shh it was my friend, blame it on him). I think that was about our only problem but if anything else goes wrong I'll ask you, or since we're nearly done, the next time might be pictures of the finished product
Some shortcut with the buttons. If they are not pressed the transducers should not click. Do any of the lights blink?
<p>The button panel was indeed shorting, and it has been fixed. The ball is still being thrown out though. The water bowl shows the pattern you described, but at a certain point (the point that the ball is thrown) the water ripples violently in a circular wave. Is there a possiblity of connecting something the wrong way around?</p>
Would there be any possibility of powering the device from a regulated DC just to check how much current it is consuming.<br>
<p>Hey Asier,</p><p>sorry if this is a duplicate comment, I had logging in issues.</p><p>We have completed your project but the ball is being thrown out rather than held in.</p><p>I'm guessing it's to do with waves being in/out of phase, but I have no idea!<br>I have no current access to an osciliscope, but if it requires one I can do that in future.</p><p>In the mean time, is there any likely problem?</p><p>Awesome project by the way!</p><p>Thanks</p>
A quick way of testing what is being emitted is to point the bowl into a water bowl. You should be able to see a dimple in the surface. If the trap is correct, it should be a dimple split in two.<br><br>It is possible to make quite a decent scope with an Arduino Nano (200Ks and 10bits), the tutorials that I have seen on that are a little bit crap so I will try to upload one.
Could you put a picture of the signals that you see?
<p>Hi Asier,</p><p>We've got the project working, and it's making sound, but we can't make anything levitate. We've spent a couple days testing the transducers with the oscilloscope, and sometimes we'll find that one is exactly in between in phase and out of phase. Is there a reason that you can think of for this? </p>
Sometimes the transducers are very poorly manufactured and have a lot of phase deviation between them. However, only one should not hinder the rest of the device. What is the amplitude of the received signal?
<p>More than just one is half in and out. Quite a few of them are. When you say &quot;received signal&quot;, do you mean the signal that is being read by the oscilloscope? If so, it is 10 V. </p>
<p>Hi Asier,</p><p>The items list calls for 12AWG wire, but the link leads to 20AWG. I have both, but the 20AWG seems to be a better fit for the project. Does it make a difference? And which should we be using. Sorry for the naive questions. I don't know too much about wiring and am doing my homework on this now.</p>
yeah 20AWG should be fine. The device takes around 1A or so. Actually now for these kind of devices I use 24AWG. It works fine and it is much easier to handle.
It should be possible to control the phase change through Bluetooth, I have done it with serial and the functioning is the same. If you have problems just use another Nano that read the bluetooth and puts ground into the pins of the other arduino.<br><br>Transducers for the upcoming levitator that can levitate liquids (and also for the directional speaker) and that are any of these:<br>Manorshi Black 10mm - 0.34$ - MSO-P1040H07T<br>Ningbo Black 10mm - 0.38$ - FBULS1007P-T<br>Murata Black 10mm - 1$<br>- manorshi https://manorshi.en.alibaba.com/<br>- ningbo https://bestgroup.en.alibaba.com/product/987365133-800848321/dog_repeller_ultrasonic_transducer_40khz_black_plastic_ultrasonic_sensor_ultrasonic_depth_sensor.html?spm=a2700.7803228.1998738836.187.TSqSlZ<br>- Murata provider http://www.hklihengic.com/english
<p>Hi Asier</p><p>That is an awsome project and i am trying to built it with my son for his sience fair.</p><p>I would like to know can you use the 16mm for the project that you stated to lavitate liquids? the reason I am asking is i just purchase from Alibaba 500 of them for the bowl type project. </p><p>and if it can be used what would need to be done diffrently?</p><p>Thanks</p>
How many transducers should de get?
The water levitator uses 72 and the directional speaker around 150 I think.
<p>Hi, I just finnished the project. This is so far the largest object that I've been able to levitate. With smaller ones it doesn't bounce at all. I managed to hold it floating horizontally, with good stability. Still working with the &quot;upside down&quot; way</p><p>. I'd like to know the basics of the code, since it seems to be written in assembly, I used a DIY oscilloscope like this one: </p><p><a href="https://www.instructables.com/id/Use-Your-Laptop-as-Oscilloscope/" rel="nofollow">https://www.instructables.com/id/Use-Your-Laptop-a...</a></p><p>Thanks Asier, this has been fun. Looking forward to see the improvements you make.</p><p><a href="https://www.instructables.com/id/Use-Your-Laptop-as-Oscilloscope/" rel="nofollow">https://www.instructables.com/id/Use-Your-Laptop-a...</a></p>
Good work Andrea, I have some future projects upcoming such as directional speaker or a simple standing wave levitator that easily levitates liquids and heavy stuff.
<p>Hi Asier, </p><p>I have a bluetooth module and I would like to use blynk to control the movement of the ball. Could this affect in any way the performance of the code?</p><p>And, regarding the standing wave levitator for liquids, could you advance what tytpe of transducer/s are needed so we can order them on time?</p><p> Thanks a lot again, and best regards, </p>
<p>In case you made a version with the buttons and noticed that the animation seemed to roll over and reset the -- direction which makes the ball move up then here is a possible solution.</p><p>Firstly</p><p>if( frame &lt; 0 ) { frame = 0;}</p><p>Which takes (frame) which is an static byte and cannot be less than 0</p><p>(Frame) needs to be another type of variable. I used Int and it worked like a charm.</p><p>Be warned I tested this on a scope but not on one of the devices. It looks all good to me though.</p>
<p>Everything connected, can hear the high pitched sound. Everything seems fine except not levitating anything. Only major difference I used a 9v battery + used a different ultrasonic transducer. It can make objects move a bit but not levitate </p>
<p>these were the transducers I used </p><p>http://www.ebay.com/itm/192030717764</p>
They seem legit. Do you have a scope or a multimeter to do some tests?<br><br>Can you test to drive it from a DC adaptor? (anything from 9V to 12V 1A will do)<br><br>Cheers,<br>Asier.
<p>HI everyone,</p><p>So I finally got some time to put this together! Thanks Asier! I am having a problem levitating things though. I can 'push' small objects around on the bench, but they won't float... more investigation with a scope and my phases are correct in each half for the most part, but I noticed that some transmitters are slightly off in phase a few degrees. nothing major, but not exactly 180 degrees . Is this causing my problems? I also notice the outputs from transducers in opposite halves and position are not exact in amplitude either. I assume these need to be about the same to cancel each other. I'm afraid its the transducers I bought, but not sure. can this be my problem? or did I do something silly. :)</p><p><a href="http://www.ebay.com.au/itm/122241644178?_trksid=p2060353.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT" rel="nofollow">http://www.ebay.com.au/itm/122241644178?_trksid=p2...</a></p><p>Thanks for any input! </p><p>Wes</p>
Yeah some transducers have phase deviations (I guess because of imperfections in the manufacturing process). In any case, the system will tolerate some deviations. <br><br>Have you tried putting the bead from the top with a metallic grid (or paper teabag)? https://youtu.be/6YV0lou4L4c?t=7m57s
<p>Hi Asier,</p><p>I'm working with a set of students that are interested in building this awesome piece of technology. We are having a problem finding a place to purchase the transducers. We tried your recommend links and the item is back ordered. Any recommendations or suggestions? We are in Seattle, Washington, U.S..</p><p>I did try one of the other technology sites you recommended and found these. Do you think these will work?</p><p> <a href="http://www.dx.com/p/tct40-16r-t-rt-split-ultrasound-ultrasonic-sensor-probe-silver-436417#.WMNcUG8rKpp" rel="nofollow"> http://www.dx.com/p/tct40-16r-t-rt-split-ultrasou...</a></p><p>Thanks in advance!</p>
The ones that you link seem alright (and both emitters and receivers will work) but it is hard to say if they will have a big phase deviation.<br><br>The best I have found so far (value for money) are these: https://manorshi.en.alibaba.com/product/60175991283-800165597/Long_Range_15Meter_Aluminum_Plastic_Ultrasonic_Sensor_Detector_110dB_Sensor.html?spm=a2700.7803228.1998738836.186.LYgvHK
<p>Hello<br>Asier, </p><p>I&rsquo;d like to ask you a couple of questions:</p><p>1st.<br>I&rsquo;ve seen the videos where you show a 3D representation of the acoustic forces resulting<br>in your device, but I still don&rsquo;t understand how something like the image I<br>attached is possible. How come can the object fly so high. Are there like close<br>&ldquo;links of a chain&rdquo;?</p><p>Which leads<br>me to the 2nd question: The levitation seems incredibly stable. I&rsquo;ve<br>worked with magnetic levitation and I need a continuous loop using PID control<br>in order to keep the system stable. How can this be so still?</p><p>And 3rd:<br>Could you please explain or post the code in plain C++ or a flow diagram? I understand<br>the part needed in order to achieve<br>higher speed in the Arduino, timers, etc, but most of it is quite hard for me<br>to grab.</p><p>Many thanks<br>in advance, </p>
<p>1) That is a secondary trap created above the primary Twin trap. It could be a focal point or a bottle trap. We have seen similar stuff before: <a href="http://www.nature.com/article-assets/npg/ncomms/2015/151027/ncomms9661/extref/ncomms9661-s1.pdf">http://www.nature.com/article-assets/npg/ncomms/20...</a> Supplementary Figure 1.</p><p>2) In magnetic levitation the object can only be pushed or pulled so you need to use PWM to balance the forces with gravity or an opposite magnet. The control may not be as fast as it should and it is harder. In acoustic traps the forces are naturally converging towards the trapping point. Also the particles are very very light, when we levitate water droplets they are more wobbly.</p><p>3) I will post a more detailed version of the code, which is a simplification of a 64 channels board that we will publish soon.</p><p>Cheers,</p><p>Asier.</p>
<p>hi Asier, my friend and I are going to do this project as our final year projects. Would you like to advise us or give us some tips as a student to be able make this project successful ?</p>
<p>For marking the transducers use the method described in the text (not the one in the video). If you can use exposed wire to connect the transducers to save some time since you will not need to strip them. If you have a scope check the signals at different stages of the constructions to check if things are going as they should. Good luck.</p>
<p>hi again, I want to use a better chip than the L298N because mine is causing me trouble, I can only use it for about 30 mins before it breaks. I was wondering which one I should use and, more importantly, will I need to change anything in the arduino code (or other aspects)?</p>
<p>Can you tell me the specs of the power supply you are using? (volt &amp; amp). I think the L298N should work just fine.<br> <br> <br> <br> </p>
It overheats? I have been driving these guys for hours and they work like a charm. I do not think there is anything cheaper&amp;better.
<p>When I turn it on the DCDC display, and the LED's on the Arduino nano and the L298N blink repeatedly. What's wrong with this?</p>
Either some shortcut or flaky connection.
<p>My l298N is still frying when I use it for mire than an hour (in intervals) for testing with 10 volts. Does anyone know how to fix this. I tried connecting an external 5 volt logic supply but to no avail. Maybe can someone recommend a different driver. Also, what specs do I set on my oscilloscope to see if the transceivers are in phase using method 1?</p>
I did all the test with the USB port. I didn't use more than 10 v. Anyhow, I would not recomend It, I did It at my own risk with an old laptop ?
<p>Hi, I need help with my bowl. Do the transceivers have to fit perfectly in the bowl. Is it okay if I got the cheap ones from aliexpress?</p>
I used cheap ones from Aliexpress Android working fine. One of them at each end is a little out of place once but It doesn't seem to be a problem
<p>Hey, can I use an Arduino Mega instead of the Arduino Nano?</p>
With a UNO would be pretty much the same. But MEGA has different pin mappings, so it will be quite complex. Anyhow, you can get Nanos for just 2 pounds so no worth the effort.
<p>Andrea, I have the same problem as you with the transceivers. I'm assuming it is because they might be out of phase</p>
Check the jumpers at both sides in the L298N

About This Instructable




Bio: Researcher at Bristol University interesting in Ultrasound and in general any effects that waves can produce.
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