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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.


Components:

  • 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)

<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
<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>I don't know why, but I can't upload the video properly. Here is a link:</p><p>https://www.youtube.com/watch?v=yN8oNPYYBzs</p>
<p>... and I'll be glad to help anyone with his project ;)</p>
<p>hey, my driver board keeps on messing things up. The red one. It only lets through 0.10 volts out of its outputs. WHY is this happening. It is not working anymore because of this.</p>
<p>Hi Asier, thanks for sharing this great coment. I am testing the output<br> volt. and I get about 12 votls at OUT1 and OUT2, but OUT3 &amp; OUT4 <br>gives 0 volts. The regulator is set at 20 Volts. And the reads from A0 <br>to A3 in the Arduino are 2 volts each. Any idea about what this might <br>be? </p><p>Thanks in advance</p>
I think I can see one Jumper missing in the L298N. The jumpers that are the sides of the input signals should be connected (they are the enables), if they are not there that pair of signals will not emit. Apart from that everything seems ok.
<p>You are right! I didn't notice I removed that jumper. Thanks a lot.</p><p>Now both sides are fine. When I place the object it is pushed quite a bit outside the bowl, but each time jumps on a different direction.</p><p>Is it possible to test the polarity of the transducers the same way (with a metal wire the inside of the transducer) once they are placed in the bowl and soldered? I used a DIY oscilloscope that just reaches 8 KHz (it uses the PC sound card) and I can't use that techique</p><p>Regards, </p>
<p>Yeah, poking with a wire could do. All the transducer should have the same polarity since we invert the phase in the Arduino software. Could you double check that A0-&gt;In1, A1-&gt;In2... One way of testing is to connect the bowl point towards a tray with water (leave 2 or 3 cm gap) and check that the deformation that see in the surface looks (D) like http://www.nature.com/articles/ncomms9661/figures/3 if you get only a spot it means that you are getting a focal point instead of a twin trap and that a half of the array may be reserved.</p>
<p>* I meant project ;)</p>
<p>Hi, so I have everything ready and wired up. The transceivers are emitting some kind of sound and square wave signal. For some reason, whenever I try to levitate my foam, it goes flying into different directions. What could the problem be?</p>
If you have a scope and two spare transducers follow the steps in the https://youtu.be/6YV0lou4L4c?t=6m53s video where you check what each transducer is emitting and be sure that same halves are in phase and opposite ones are out of phase . What is the peak-to-peak of the waves that you read?
Hello, would these transducers work? The data sheets are very similar.<br><br>http://vi.raptor.ebaydesc.com/ws/eBayISAPI.dll?ViewItemDescV4&amp;item=131590233040&amp;category=36332&amp;pm=1&amp;ds=0&amp;t=1487787421761
Hard to say without a picture but the specs seem alright.
<p>A few questions...</p><p> - How effective would metal tranducers (like this <a href="http://www.ebay.com/itm/331415944083" rel="nofollow">http://www.ebay.com/itm/331415944083</a>) be compared to plastic ones?</p><p> - How would one scale this up so that it will levitate heavier objects?</p><p>Thank you for making releasing this project!</p>
You are welcome.<br><br>It is hard to say, I have tested several models for power and phase deviation; and even when they look the same, they are quite diverse.<br><br>I have a directional speaker coming and I will publish my comparisson of transducers, but the metal ones from Manroshi are the best I have tested so far.<br><br>Yeah, more transducers and more voltage equals to denser objects. Although it is a little bit strange, the size does not matter, only the density of the object. Although so far the objects cannot be bigger than half of the wavelenght, we are working on surpassing that limit. But if you want to levitate denser objects I recommend to use a standing wave. We are working in a robot that can pick and process samples in mid-air of densities up to 1.2, so it can deal with water and most of the stuff.
Thank you for answering quickly. If you do not mind here is one more question... <br><br>If (343.21 meters per second) / (40 khz) = 8.6 mm then the objects can be no bigger than 4.3 mm. If one were to use a tranducer that produced a lower frequency then how would that affect the project?<br><br>Once again thank you for contributing.<br><br>
<p>To be more specific, by how much will timer1 need to be adjusted for lower frequency, by how much do the delays between OUTPUTS be increased, and by how much do the phases need to be changed. Is there any mathematical method to calculate how the code should be changed? </p>
<p>25kHz transducers are rather pricey and in a tractor beam configuration they are not going to be that useful. But if you want to try a standing wave you may be able to levitate big particles.</p><p>I was preparing an optimized standing wave setup for levitating liquids and other heavy objects.</p><p>If you do not want to move the particle around, this code is much easier to select arbitrary frequencies:</p><p>#include &lt;avr/sleep.h&gt;</p><p>#include &lt;avr/power.h&gt;</p><p>//byte pattern = 0b00000000; //all the ports will output the same signal</p><p>byte pattern = 0b10101010; //consecutive ports will have an opposite signal</p><p>void setup()</p><p>{</p><p> DDRC = 0b11111111; //set pins A0 to A7 as outputs</p><p> PORTC = 0b00000000; //output low signal in all of them</p><p> // initialize timer1 </p><p> noInterrupts(); // disable all interrupts</p><p> TCCR1A = 0;</p><p> TCCR1B = 0;</p><p> TCNT1 = 0;</p><p> OCR1A = 319; // compare match register 16MHz / 319 = changes every 50kHz -&gt; 25kHz half-square wave</p><p> TCCR1B |= (1 &lt;&lt; WGM12); // CTC mode</p><p> TCCR1B |= (1 &lt;&lt; CS10); // 1 prescaler, no prescaling</p><p> TIMSK1 |= (1 &lt;&lt; OCIE1A); // enable timer compare interrupt</p><p> interrupts(); // enable all interrupts</p><p> // disable ADC</p><p> ADCSRA = 0; </p><p> // turn off everything we can</p><p> power_adc_disable ();</p><p> power_spi_disable();</p><p> power_twi_disable();</p><p> power_timer0_disable();</p><p> power_usart0_disable();</p><p> while(true); //avoid entering into the loop</p><p>}</p><p>ISR(TIMER1_COMPA_vect) // timer compare interrupt service routine</p><p>{</p><p> PORTC = pattern; //output portDV into ports A0 to A7</p><p> pattern = ~pattern; //invert all the bits</p><p>}</p><p>void loop(){</p><p>}</p>
<p>Today the transducers arrived! My son and I made this super-useless-thats-why-I-want-it project! Great!</p><p>I used these transducers from the German distributor Reichelt:</p><p><a href="https://www.reichelt.de/Ultraschall-Sensoren/A-16PT/3/index.html?ACTION=3&GROUPID=6682&ARTICLE=145924&OFFSET=16&" rel="nofollow">https://www.reichelt.de/Ultraschall-Sensoren/A-16P...</a></p><p>They are not combo transmitters/receivers. You get a pair of transeiver and receiver. However the transceiver just works. I have to try if the receivers could be misused as transceivers, too.</p><p>BTW. I would suggest to solder all wires in step 16 to the middle-pin of the switch instead of screwing them to the terminal of the inverter. </p>
<p>I ordered these transducers...</p><p><a href="http://www.ebay.com.au/itm/322221621215?_trksid=p2060353.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT" rel="nofollow">http://www.ebay.com.au/itm/322221621215?_trksid=p2...</a></p><p>...It appears the transducer shell is just marginally too big to seat properly in your hemisphere design. Could I have the .sldprt file to see if I can fix it? I will try suppressing them approx .5mm more and see if that helps. I will be happy to post the modified file here.</p>
I ordered the same transducers too. But haven't received them yet. Did they work ok for you? Besides fit?
<p>There you go. There are no holes in the base so you will have to drill them manually (it's an inventor file and I'm not very familiar with inventor). The transducers fit well from my printed file.</p>
Thank you!!
<p>Sorry it has taken me so long to reply. I have not received all the items I need to make the tractor beam yet. I have been experiencing issues with the postal service. I do strongly suggest recessing the driver points by .5mm though. I have tested the fitment of the drivers and they seat nicely. If you remind me tomorrow I will upload the edited STL (I am not on the correct computer at the moment).</p>
<p>I'd like to see the edited stl file. My transducers are too big as well. </p>
In step 33 there are some raw files.
<p>If anybody in Melbourne Australia is planning on making this device I have a spare print of the transducer shell (didn't fit the transducers I ordered). The outer finish of the print isn't great but it will work as intended. Message me if you want it and it's yours.</p>
<p>Mad respect for that! Very cool project!</p>
<p> Is there any chance of presenting the circuit in a schematic, rather than a block diagram form?</p>
Hello Mr. Marzo, I built this device for a school project. It is recieving power and I can hear the sound made by each tranducer however I am unable to levitate it. Are there any tips you could give me on how to check the device to ensure it is properly set up? I can send pictures of my device if you need it. Hopefully you are still replying to comments because I need some guidance!

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