Ultrasound gel does amazing things to sound waves

Ultrasound gel does amazing things to sound waves


[Music] when my wife was pregnant she had ultrasound scans that is not my wife by the way you can’t film inside NHS hospitals so that is stock footage which I really like because look at how the image of the baby isn’t really changing and yet this guy is going crazy look whew let’s let’s look all around the baby that guy’s no sonographer anyway sometimes I’m accused of not being in the moment but that’s not true I’m just in a different moment like instead of thinking wow I’m seeing my unborn child for the first time I’m thinking wow that machine is amazing I wonder how it works and I actually know a little bit about how ultrasound scanning machines work now what really struck me the last time was the gel that they squeezed onto your belly before they rub the ultrasound wand on it I remember after the scan during a moment of contemplative silence LeeAnn saying what are you thinking about and I said well I just wonder whether that gel is purely for lubrication or whether it serves some other purpose so next time he went in I snuck a look at the bottle the sonographer was dispensing the gel from and it specifically said ultrasound gel so it wasn’t just a generic lubricant it turns out that ultrasound gel is specifically formulated to do one job and that job is acoustic coupling and it’s really interesting and that’s what this video is about but first of all what is an ultrasound scan well it’s like sonar so you send out sound waves they bounce off various things and you listen out for the reflected waves coming back to you and you can use the timing to figure out how far away things are and you can use the direction to figure out where things are with a sophisticated device like your knobs and scanner you can use that information to build up quite a good picture in the case of a pregnancy scan it’s the baby that the sound waves up sing-off specifically the baby’s bones the purpose of the gel is to sonically merge the probe and the human body into a single acoustic entity and by doing so it removes unwanted reflections think about this if you stand in front of a wall and scream like I do for relaxation you’ll hear your scream coming back at you because walls reflect sound but sound also passes through walls like this aeroplane my studio is near City Airport in London which is annoying so the question is how much acoustic energy gets reflected and how much gets transmitted at the interface between two different substances and why that’s what we need to figure out and to do that I’ve got an analogous wave system so sound waves are longitudinal which means the vibrations go in the same direction as the wave is traveling these waves are transverse so the oscillations are perpendicular to the direction of wave travel but the physics is the same so look if I lock one of these rods in position then this is gonna be like a sound wave coming up against a really solid unmovable wall and you can see that the wave gets reflected completely and you can see why if you look at the rod that’s just next to it as the wave comes in that rod is pulled upwards that creates tension in these two cords here which pulls the rod back down again but it actually travels past the origin and goes much lower than it and that pulls on the road next to it which pulls on the road next to it and so the wave travels back in the direction it came from sound waves don’t reflect completely off of walls because walls have a little bit of give and we can simulate that by adding weights to the wave machine so the heavier rods represent the wall because like the atoms in the wall they’re harder to get moving in this case because of inertia look what happens when we send an impulse up to the boundary it’s partially reflected and it’s partially transmitted just by the way that the transmitted wave is traveling slower than the incoming wave that’s not true for a sound going from air to wall sound actually travels more quickly through the wall that’s because this analogy isn’t perfect if I add even more weights then even more of the wave is reflected and less is transmitted which makes sense because we’re getting closer to the situation where I was physically holding one of the rods in place so hopefully you can see that the more different two substances are the more reflection you getting the less transmission you get when I say more different I’m actually talking about something called acoustic impedance which is a measure of how much does a substance resist acoustic motion basically the the vibration of atoms and molecules that is sound it’s a bit like refractive index when you’re dealing with electromagnetic waves if you’re familiar with that the only difference is that refractive index is the inverse of wave impedance the human body has an acoustic impedance of about three thousand times that of air so if you want to work out how much sound that is produced outside the human body ends up inside the human body when it passes through the boundary between the two you put the two acoustic impedances into this equation and you get our answer about naught point one percent so hardly any and by the way you get the same problem in Reverse if you go from high acoustic impedance to low acoustic impedance you get refraction as well hopefully you can see that we would expect that intuitive if I show you what happens when you go from some impedance to zero impedance you see if I pinch these two cords together the cord is providing no torque to resist the twisting of that final rod this final rod actually travels higher than it would normally because it’s unimpeded on this side and so that pulls on the rod next to it and that pulls on the rod next to it and so you end up with a way of travelling backwards a reflected wave so without ultrasound gel naught point 1 percent of the acoustic energy would find its way into your body and then not point 1 percent of that would make its way back out again for the receiver to pick up not put 1 percent not point 1 percent is one ten thousandth of a percent completely useless what ultrasound gel does is remove the boundary between different acoustic impedances it removes the impedance mismatch it’s formulated to have the same acoustic impedance as the human body so that there’s no barrier between the speaker and the inside of the human body and the inside the human body and the microphone inside the probe I don’t know if speaking on microphone of the right words in this context but at least you know what I mean while we’re on the subject of ultrasound scans I want to tell you about a collaboration between art and science that I think is really interesting it’s called ode to the future and it’s a collaboration between a musician and people who are yet to be born and it uses the technology of ultrasound scans and I just think it’s a really interesting kind of artistic way of looking at how curiosity driven innovation will shape the future links in the description I hope you enjoyed this video if you did don’t forget to hit subscribe and I’ll see you next time [Music]

100 thoughts to “Ultrasound gel does amazing things to sound waves”

  1. I think your math was wrong. The transducer impedance and the body of the transducer are directly coupled to the skin and would have an impedance much closer to that of the body. The skin and fat will also have a much lower impedance than you mentioned. I think any old jelly would work to ensure direct contact and I think lowering friction is more important than any acoustic property the gel may have.
    Coupling high impedance devices to the air is done with regular loudspeakers and the horn is an example of an acoustic transformer.

  2. It's funny you had that thought about the gel. I used to work for a company that did NDT(Non Destructive Testing) and one of the tests they offered was Ultrasonic testing of materials and welds. And with the little testing apparatus we had to put that same gel on the metal rods in order to give a solid coupling of the apparatus and the materials. Without the gel, the vibrations of the apparatus moving across the metal could interfere with test and the gel helped smooth out the surface and remove those vibrations.

  3. The wave reflected back because of lower impedance is hard to imagine for sounds waves. Is it instead because of different vibrational harmonies that a wave would be reflected back into a higher impedance material? If so does matching harmony make the transfer 100%?

  4. Oh, you didn't prove it! I was going to give you 10 points. "Ultrasound gel removes the barrier between the machine and the human body." In fact, you didn't give any evidence at all – not even a study reference, link, quote. I was wondering how you were going to get your elaborate contraption to demo that one! (NOT!! Oh-well! MVP in video.)

  5. Nor did you explain the actual physics of ultrasound gel. So – guess I will. So it's called "ultrasound coupling gel." The secret to it is its mass and its willingness to vibrate and it's molecular (or atomic) -level contact with the substrate (skin, but hey.) This in effect describes the peculiar nature of the gel. It's made up of 99.5% water, and .5% "copolymer" – a plastic. So this turns the water into a "middle phase" which is molecularly very "elastic" because of the electrostatic bonding of water. I don't know the details of this, but it's a vital property of water.
    Sound waves find a minimal barrier upon striking this stuff because it has a high transference of vitrations. It's mass and volume then couple this energy to an enlarged surface area at the skin, eliminating any intermediate barrier of air (a secondary loss) and (this is the critical part) because of the virtual ADHESIVE quality of the gel to the skin, the energy is effectively ACTIVELY PUMPED via "STANDING WAVES" into the WATER CONTENT of human flesh BELOW THE SKIN. Hense – no barrier.

  6. I think, the "magic" is, that the "speaker" vibrates not in air, but in the gel, which has about the same acoustic impedance as the human body. So, there is almost no reflection at all.

  7. If ultrasound works on high frequency vibration and the Human inner ear works in high frequency vibrations and it's being directed at a baby's body mass then the baby is being subjected to an incredibility laud audible humming sound within its inner ear which is extremely uncomfortable especially for a delicate new lifeform. 😲 😖

  8. this video just reminded me with impedance matching circuits in electronics classes way years ago to college time, super excellent tutorial.

  9. I wonder just how accurate the dolphin's sonar is. I've heard before dolphins are capable of sending memorized ultrasound scans to other dolphins just like we send pictures or videos, except they don't need any devices. Say a dolphin sings (for a lack of a better word) its ultrasound and it bounces of a rock, then travels back to our flipper. The received ultrasound is processed in his/her brain's visual cortex. We could say the dolphins "imagine" or envision the ultrasound into an actual image. So now the dolphin knows both the specific ultrasound it recorded and the corresponding image and is able to recreate that exact ultrasound with his own "ultravoice" to another dolphin, which then should be able to see that same corresponding image.
    Consider also their intelligence, possible imagination and creativity… they could be using an actual language of images.

    OFFTOPIC SIDE NOTE: you should exercise your face muscles… your right side seems stronger and tenser and it pulls your mouth to the side. It looks very weird.

  10. So does that mean you could cover a wall with an ultrasound gel of similar impedance and more sound would then pass through it? The opposite of soundproofing.

  11. I said something like that to my girlfriend, she would be very angry. She sent me a photo of herself in the hospital. I could see the QR Code on your wrist band so I decided to look it up and told her what it said. She was mad because that was the first thing I replied back with. 😂

  12. Rather than adding weights, could you have spread the gap of your wires for “more rigid” bodies? In my head at least your demo remain analogous for speed of wave then too…

  13. An airplane took off outside just as he said just like this airplane and my mind was blowing up with chaos. Wow that's some good sound effects.

  14. @steve mould, ultrasound works on piezoelectric effect, there is no microphone or transmitter.
    Special crystals called piezoelectric crystals convert electricity into sound energy and vice versa.. Rest of your explanation was great.. Thanks 👌

  15. First time I imagined waves like that. And you've built it. As soon as I saw 2 strings I was like, wait a minute.. You're like my mind, always shuffling never gambling.

  16. Aloe Vera gel found at places like loblaws works exactly the same but is about 1/10th of the price. If you use your own at home, just use aloe Vera gel.

  17. i don't know, i thought you were an alternative Murdoc voice actor for the Gorillaz.. , amazing vids by the way!!

  18. Yeah, my mind is thinking about all kinds of stuff, at any time, I can be completely off topic!! Thinking about alot of things most would NOT!

  19. I’ve had those scans on my heart all my life. I had to have one a few days after having heart surgery during a stay in hospital and because of me being weakened and having to be careful, I got stuck by laying down. Fortunately there’s a button that makes it go up and down so I was helped to get back up. Funniest thing I’ve ever done

  20. i actually got an ultrasound today(im a dude btw but ill get to that.) I got a enlarged cystic spleen and they went to damn town with that gel

  21. Thanks for the great video Steve, as a musician I am always fascinated by your videos that touch the topic of acoustics (and so fourth), keep up the good work!

  22. I’m watching this at 3 a.m, I have no clue what this man is talking about, my girlfriend and I haven’t even talked about marriage let alone a Baby

    But I’m loving this

  23. You created an alternating current with rods and a couple of nuts (weight). Would it be like energy bumping into energy like in physics. This looks like a nuts idea for recreating computer switches. Like little seasaws. Be a transistor, and still keep the electricity flowing.

  24. yes i m having that moment a lot so the dolphins doesnt transmit sound from their head but from their mouth, so you should use better visuals 😀

  25. So, the idea that babies during the pregnancy will listen music from outside and maybe remember after is not true, I wonder. Even if they are capable of remember things, they will listen only 0.1% of everything from outside and those sounds need to compete with all the internal sounds of the body. Am I wrong?

  26. Excellent explanation and nice model with weights. I think the impedance matching gel has an impedance that is the geometric mean ( that is the square root of the impedance of transducer * impedance of body) of the two different impedances. This creates impedance match. See why camera lenses are coated and and looked colored ( coloured).

  27. How doesn’t this guy have 10 million subscribers???
    I love learning with my kids by watching Steve’s videos!
    So thanks Steve your not only teaching kids but I’m 35 and your teaching me too!!

  28. I thank SmarterEveryDay for bringing this channel into my life and i thank Steve Mould for all this array of content i have to back peddle through

  29. "Ultrasound gel is specifically formulated to perform one job, and that job is acoustic coupling".
    Well, first off, you need to develop a healthy cynicism for 'marketing horseshit'. "Ana Wiz Ltd. of Units 5-6 Chiltern Works…" only has to match the density of the human body (~985 kg/m3: which is slightly less than seawater) and KY Jelly is a ready substitute (source: https://sonosupplies.com/blogs/learn/what-can-you-use-instead-of-ultrasound-gel-alternatives). Ana's Wiz are, however, interested in de-genericizing (aka increasing the price) of a product that is mostly water. Secondly, "acoustic coupling" can have several meanings, including the one you are thinking of. So did you try it? Oh, I guess that is a dumb question… 🙂

  30. What effect does ultrasound have on the baby ?
    Can the sound waves damage or interfere with cellular functions and or growth of the cells of the unborn child (fetus) ?

  31. Apologies, I don’t know how to ask a question on you tube. So doing it here.please explaindifference between the various Anti that come with stero equiptment? Thank you.

  32. Could you imagine a material (paint) that what ever sound wave hits it, it translates it to the opposite of it's self? (noise cancelling). Homes would be so so quiet!

  33. I am extremely interested by the rod dynamics at 6:40 where the rods stay torqued upwards on the far side after reflecting the wave. what prevents them from leveling out?

  34. I use ultrasound for welds. Use an A scan. We don't use phased array yet, so our flaw detectors only produce signals, no images.

  35. Umm ., just a word of warning , do not use the gel in a lava lamp with UV Paint and glitter.. My bedroom could be entered into CSI Gay disco Holocaust. Very cool , but damn its still on teh curtains , and roof , and bed

  36. Would be nice to know how effective the gel is. If you were getting 0.1% without it, do you get 0.3% with it? 1.0%? 10%?

    I would think that having direct contact with the skin would be the most important aspect (akin to attaching a speaker/microphone directly to a wall) but to do that and move the probe would require lubrication. So I actually doubt that the primary purpose of the gel is acoustic coupling in the sense that the gel plays an active role, but rather that the primary purpose IS lubrication, which allows movement of the probe with contact.

  37. Love your show. Are you spirituality enlightened? Sorry i have to ask. Your insight are amazing. The words you use like living in the moment all point to enlightenment

  38. Ok. Im actually scared. I just mentioned how i got an ultrasound on my heart, to my gf. And now this video is being suggested.

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