Your use of the CD tracks to measure the movement was brilliant! I loved that. Great video overall, although I would have liked at least one close-up shot of the strips near the beginning. I'm sure they're basically featureless, but when you first took them out and were handling them I found myself wishing you would show a good macro shot of them.
This desperately needs close ups. Even if they are not live, just record the close up separately and overlay that video while you are explaining things.
Thanks for explaining how these little buggers work! Even just a little closer on the whole video. Do we really need to see the wired and how it is hooked up after you are done explaining the setup? Having the oscilloscope square and straight to the camera would make a difference too. Great video Content! Keep it up!
Nice opening shot. Very clean. But I like seeing a messy lab in the background just as much. I watch because it's about the science. And I have always been curious. Will have to re-activate one of thee things and take it through a store to try this out!
+Applied Science Everyone knows that there is a positive correlation between the amount of shit on your bench and the accuracy of scientific data collected.
Matthias, just make a (woodworking) contraption that magnetizes and demagnetizes it, so that it's turning on and off every couple of seconds, and then enter a store. This can be quite funny. And I'm wondering if it"s actually possible to set the alarm of from a big distance (50meters), it should be.
+Barack Lasagna | Why not use a small mirror lever and have it deflect a laser? You see the results on the wall where the beam hits. You wouldn't even need a microscope.
+Barack Lasagna Although I would be concerned about the field from the coil slightly attracting/repelling the hardware for the lever, causing movement that's confused with the magnetorestriction.
+Barack Lasagna I think you meant the lever solution is ingenious; Ben is Genius for sure. Only people can be genius. However people and things can be ingenious. All that to say, your screen name IS ingenious. Love it! He's been like a flat, wet noodle, covered in cheese as president.
+DRC Paintball I've had some look at the internals of sensormatic stuff and from what I remember they have equipment to also rearm tags right? Not sure how they do that... I remember all the sensormatic boxes I had with huge 400v capacitors in them. I also remember that not all tags are even deactivated, the long clothes tag just has a special tool to remove it (that tool has two of the sticker alarm tags inside ironically) but stays armed. There was an electronic one as well with a battery inside that'd alarm if someone tried to remove the tag without using the special tool (I've got a test tag), did shops ever start using them?
+DRC Paintball What do you mean by "in phase"? Do you mean the alternating transmit and listen phases should be in step at all gates in the store? Since there is no network between the different gates of the store, how would syncronization work? Also, what causes false alarming when the store is closed for the night?
+DRC Paintball Thank you. How often does the transmitter transmit? Do they get any sync help from the mains AC? Otherwise, it seems like you would need atomic clocks in each gate to have different gates independently keep in sync to the precision required.
Fascinating as always, Ben! I never knew how those strips worked (and I admit to opening them up to see what was inside). You gotta love all of the uses for Kapton tape...
I've never come across ones with exceptionally sharp edges. Tap on the tag so the strips fall to one end. Use scissors to snip-off the opposite end. Pour the two free shims out. The third strip isn't worth salvaging.
You must be the Lock Picking Lawyer, but you are under cover conducting research for your next video to shame lock companies! My lips re sealed ( wink, wink ). HAHAHA
Some anti-theft tags use an amorphous ribbon with a very square B-H loop and a very low coercivity, in fact the earths magnetic field is strong enough to magnetize them in one direction or the other. The transmitter coil generates a pair of fields at two different frequencies and the amorphous ribbon acts as a non-linear magnetic mixer generating fields at the sum and difference frequencies. Say the transmitter generates 5kHz and 8kHz then the sum and difference will be 13kHz and 3kHz respectively. The receiver coils pick up the 13kHz and sound the alarm. To deactivate the tags a small piece of steel adjacent to the ribbon is magnetised and that keeps the ribbon saturated.
Great video. One thing to think about: An amplified signal has more energy, yet the metal strip can't add energy to the system because it doesn't have a power source. So, where is the extra energy coming from?
think of it like a spring. if you oscillate it at its resonant frequency, it will have a higher amplitude. if you oscillate it at a different frequency, the natural frequency of the spring will interfere with the way you're oscillating it and it has less amplitude. it doesn't get extra energy from somewhere else, it just doesn't dissipate the energy as much as it would if it wasn't at that frequency.
+Physics Videos by Eugene Khutoryansky Wait a second, I'm pretty sure there's a video on youtube by this Eugene Kutoryansky guy that will explain it, I'll try and find the link.
+Physics Videos by Eugene Khutoryansky Hmmm, I thought about the higher amplitude while watching the video, and my thought is that the system does not actually have more energy, but rather that energy is stored as vibration in the tag, you can see that with the tag in place, the waveform has a more gradual buildup rather than the nearly square envelope it had without the tag, as the tag is resonant with the frequency of the exciter coil, it starts vibrating in phase with the field of that coil, so the re-emitted energy is also in phase and the two fields add together and you get a higher amplitude. I expect that the tag absorbs a small amount of energy from each period of the exciter coil, until it reaches the maximum it can store as vibration, at that point it only needs a little energy to keep resonating(to replace the energy lost as heat and the loading of the scope). The envelope of the signal when the tag is in place does look similar to a charge/discharge curve. The two coils are essentially an air core transformer, so adding some ferrous metal strips probably increases the coupling a little. Of course, there isn't much metal in these tag so the total energy coupling this "core" could provide wouldn't be very large, though it may be detectable on a high impedance instrument like the scope. Adding a DC magnetic field to a transformer, for example with a permanent magnet can, of course, strongly affect it's characteristics, though the magnet in the tag is probably too weak to significantly affect things.
Thanks! I really love your detailed explanations of stuff. I've watched your most recent videos since subscribing about 6 months ago, but still catching up on this older content. So, so nice and thorough. It isn't flashy or anything, just very clear explanations. Please keep it up.
Wow - These videos make me so happy! I studied electronics, electrical and telecommunications engineer for 10 years and you bring several concepts together in a very simple and beutiful way, like different sounds in a orchestra. Amazing!!! Congrats!
In the first minute you may think it;s not interesting, But you MUST SEE the complete lengh of the video,!! This guy is amazing, in his complete setup, Great setup and a great Research, Thanks for sharing !!!
Hi Ben. Thanks for the video, it was enjoyable as always. If your still interested in this topic you may want to try using a strain gauge to estimate the saturation magnetostriction. If you glue the strain gauge directly to the ribbon surface with any brand of cyanoacrylate and then monitor the change in resistance via a wheatstone bridge configuration while slowly rotating the sample/applied field you can quite accurately estimate the saturation magnetostriction using the know gauge factor. We use this method in the lab I work in and so I can assure you its possible to achieve sub ppm resolution. I wish I could point you in the direction of a few papers on the topic but its very poorly documented in the literature. If you have any questions about this, or on magnetic materials (especially nanocrystalline or amorphous materials) in general feel free to drop me a line. Richard
I just want to let you know that here in 2022, I am re-watching all of your content for probably the third time. Your videos could be 3 hours long and I would still be dismayed when they're over.
Hello, i worked in the industry that made these tags, the met-glass is a glass/ metal formula that can get magnetized and un magnetized REAL fast. And believe me..it cuts your skin REAL fast too... Any way .. the met-glass came in a roll that was cut to what ever length or width you dialed into the cutter machine. In a few hours we would have a entire box full. A super efficient high frequency transformer can be made with met-glass ; however it is expensive stuff..... wear cloth gloves.. or buy a box of bandages.. nice mini relay switches can be made also.. :)
Even though I don't understand half of what you're talking about, you present your findings in such a way that keeps me watching. Thank you for keeping me interested ;-)
I'm sure you diagrams and scope screens are clearly visible to you Ben, but could you Zoom in so viewers aren't struggling to see what amounts to 1/16th of OUR viewing screen size?
Hi Ben; Many years ago, mid '80s, ASIR, I had a magnitostrictive delay line. It was from a mid '60s Friden calculator. Unfortunately I have lost track of it now. This had a long steel wire carefully supported and coiled into a spiral. The transducers at each end had 2 tiny strips of the magnetostrictive material spot welded to the wire at right angles. There was a small coil around one of the strips and a small bias magnet in the coil. Both ends were made the same. When I pulsed the coil it would cause one strip to lengthan and the other to shrink. This applied a twist to the wore which propagated down the wire. Of course, at the other end the strips were forced to stretch and shrink inducing a magnetic field in the coil. You could easily see the delayed signal on a 'scope. I speculated that it could dynamically hold about 8k bits of data. Maybe more, probably less. I didn't have a micro yet so couldn't actually see if I could recirculate any data through it. I have there been any amateur attempts at making such a device? redrok redrok.com
I can't believe the people who disliked your great video. I can only assume that those were the ones who wanted you to tell them how to defeat the anti-theft tags and have no science background to figure it out themselves.
Your data suggests that the resonant frequency of the metal strip is narrowly defined by the dimensions and temperature. If you were to change the temperature significantly, you'd change the resonant frequency and thus the tag would fail to function normally.
+eformance That's a really good point! I hadn't thought about extreme temperatures causing the tag to malfunction. I wonder if the manufacturer has a spec on that. I'll have to try it with freeze-spray and a low-temp oven. Thanks!
+eformance Where's the data that, say, a 50K temperature change would alter the resonant frequency enough to cause a problem? The thermal expansion may look huge under the microscope, but it's still tiny compared to normal mechanical tolerances. The Q of the metal strip is not all that high, it dies out pretty quickly.
+eformance The reader does a frequency shift from cycle to cycle to shift the resonance through the tag response range. There is also a series of switches that alternately swap the transmit and receive aluminium strip coils so that the tag distance is not going to make a difference. The transmit power is pretty high, around 50W of power, it does make every metal thing within 5m of the coil have a circulating current, which means any CRT within 5m of the coil will have a very annoying beat on the image as it modulates the electron bean scan. The tags are pretty reliable in use, very few will get past without triggering the system.
+Hatagashira I've seen a video by Samy Kamkar on how to trick the motion detectors at glass shop doors with a gas duster, now I see just another reason to carry them with me on my next shopping tour haha :D
@6:06 this piece is called the "Bias Magnet" and it provides the Magnetic Bias to put the resonating Magnetorestrictive thin metal on the resonating point on the curve. If the magnet is not present (Deactivated Tag) then the Magnetorestrictive piece of metal is still the same but will be displaced to a non resonating state on the curve.
inademv it's a periodic pulse the energy was stored in the resonating metal strip which then continue to resonate in a dampened amplitude for a certain amount of time after the pulse ended. The anti-theft tag actually doesn't add any energy to the system it actually takes away from the energy transmitted in order to induce its own oscillation but the receiver isn't looking for that it's looking for the continued oscillation after each pulse goes quiet if the pulse stops and the receiver no longer hears anything and no tag is passing through but if the pulse stops and there is still a ringing coming out of the system then it must be from the tag
One thing you forget to consider is that under the 58kHz excitation, the strip is resonating. The amplitude of displacement is roughly Q times the displacement under static (DC) excitation. Here Q is the quality factor of the resonator. From the ring down, Q is not small (most certainly more than 100, possibly more than 1000). So in the end, it is indeed theoretically possible for the strip to develop 0.1% strain (1/1000 inch over 1 inch) at its resonance frequency (12 ppm * 100 = 0.12%). These being said, the lever setup is quite neat for static test!
you just keep going deeper and deeper into it...some of the topics you explain in detail and some other you brush off... overall it's amazing... and like your original intentions, these videos motivate me to try my own experiments....
Thank you for making these videos with so much care, I highly appreciate that you explain things so deeply! The video qualuty is also very good. Next improvement could be more close ups, I would like to see the small piece of metal, the graph and your measuring apparatus in more detail. If you have enough time to edit :)
5:26 The funny thing is: They are going for the inductor-cap combo a lot of the times, but they make it out of aluminium foil and between two plastic/canvas sheets and that's it. It's working, it's flexible and it's way cheaper than even these metal strips. It's just some spiral shape with the ends folded over each other while keeping those insulated to form the inductor and capacitor.
It is important to note that metal strips are of two different ferrous alloys. One is a type of steel, as this becomes a ‘permanent’ magnet when subjected to a magnetic field. The other is iron, in that it responds to a magnetic field but resists becoming a permanent magnet. The plastic container is water proof to prevent corrosion of the metals strips within. The device is ingenious and the presentation in this video of how it works is pure genius.
Great video! A quick note: While the maximum displacement under static field might be ~several microns, that is only under static field. Fluctuating the field at the resonant frequency of the metal plate will "ring the bell" and cause greater and greater displacements
Very interesting, I especially like the meter you made to measure such slight movements. I use the strips as shims in my home machine shop, because their thickness is between .0005 to .001, for example; when I have one of my lathes preoccupied with a four jaw set up, that I can't break down, I'll use another lathe that has a three jaw chuck, test run out with a workpiece in the jaws, and fill the high spots with two or three of those strips, to get as close to a four jaw reading, if at, times, even better. I was commissioned to build a micro wire straightener 2. Years ago, and, as you may know, the straightener parts had to mesh as perfect as a Swiss watch, suffice it to say, I placed at least ten of those strips through the machine, and when their assessor tested the little machine he certified it as passing, as a Swiss watch, not knowing of the security strips turned shims...rotfl 😃
My understanding was that the use of a strong magnet would saturate the adjacent hard steel where its coercivity would leave it in a permanent magnet state that was just right for generating the ring-down pulse. To deactivate you had to de-magneitze the hard steel strip, so at the checkout counter is actually a zebra stripe type magnet that will de-magnetize the strip when the tag is swiped past it. The reason for this is that many ne'er-do-wells would think think they could defeat the tags by magnetizing them., but would in fact, make sure the tags were fully activated. Also another part of the design is the plastic separator between strips is slippery Teflon, so that the strip can resonate without being too quickly damped.
dude ur amazing just dnt stop i know my generation is not interested in science and u deserve more i learned on ur channel compared to school . ur the best just keep it up.
Another great video! The curve of magnetic field vs mechanical output is the same as magnetic field vs recorded signal for audiotape. Tape recorders apply bias to the recorded signal to move the recordings into the linear portion of the curve. Some cheap cassette recorders use a magnet for DC bias, but most use AC bias around 45 khz.
Without DC bias, the magnetostrictive effect is a square-law effect, so the frequency is effectively doubled because you are riding across the tip of a parabola (which the bar is not tuned for). With the bias, the the effect is linear if the DC field is large compared to the AC field (you are riding on the relatively-straight side of the parabola), so there is no doubling.
So basically, you've taught us that you can carry an item out of a store with a small, strong neodymium magnet against the security strip and the alarm won't go off :p happy shoplifting everyone!
+Rizwan Awan (TheOnlyRizzy) No. Many products are source tagged in the factory to prevent you from doing anything. You also can't deactivate larger tags with inductors and capacitors in them.
In my university library, you could easily locate the location of the magnetic field if you walked through with headphones on. Very high pitched, probably around 15kHz in my case.
yes you can hear the horizontal 15khz and you can hear the vertical at 50hz or so, you can also hear the high voltage whine...but those drive nobody crazy unless you are part of the hyper sensitive snowflake millenial generation, if you hear it just turn the volume up...and flybacks dont have loose windings...vertical output transformers maybe but a flyback built like that would fry in seconds...
@@markgigiel2722 My hearing used to be so good I knew if a TV was being used nearby. Sadly now I have tinnitus that falls exactly around 15 KHz or more likely the sub-harmonic about 7 or 8 KHz where my hearing starts to fall off. I think that in my case being a passenger in turboprop planes did my hearing in. I started wearing ear plugs, but too late.
@@rhyoliteaquacade Mhm yeah. After being an aircraft tech and exposed to countless hours of various high Db frequencies and many cross country flights; after 20 years of that, I sustained NO hearing loss so pardon my skepticism at your claim of hearing loss as a turboprop passenger.
Libraries typically used a different alloy, mu-metal, and much longer strips and would usually bury the strips in the spine of the book. That way they didn't have to disassemble the book. I have some strips somewhere, but from memory they're about 2 or 2 1/2" long. Also they worked on a slightly different principle. The alloy would saturate very easily so the effect would be to generate 2nd harmonic signals that the system would then detect. Our local library years ago went to RFID tags so they could have individual serial numbers used on the book borrow and returns, automatically machjine sort them for which branch the book had to be sent to and to check it in against the library card used to check it out. So it's quite possible the frequency was quite a bit lower.
8 лет назад
You are doing an amazing job! Here in Brazil it's more common to see that heavy round plastic ones. That one I think that isn't by this method.
+Navarro Eletrônica Those big round ones (if they're the ones I am thinking of) typically have an inductor (usually ferrite cored) and a capacitor, forming a tuned circuit at the same frequency as these (58KHz). I've learned to my cost that some power supplies such as laptop chargers etc. have combinations of components resonant at the same frequency, and can set them off! It used to be walkman headphones in the late 80s that would do it!
Thanks for the wonderful video.before watching the video, Today i found one of this srtip and cut it apart to find what is inside. I found metal strip and three more strips i thought they were plastic but flame test confirmed that it is metal. I searched many videos but you explained the working principle. Thanks again ❤
Love the new setup, and I really love the quality content you're putting out. I check for updates daily and slightly bummed when there's non, but never disappointed by what you put out when you do upload something new :)
+Samy Kamkar Or how to destroy a hard drive. Take it with you on a shopping trip, go through the self checkout, and use their demagnetizer. (Especially if you're too lazy to have your own. :-) )
Samy Kamkar You can wrap them in aluminum foil, too. Or if you have the time, line the inside of a shopping bag with foil and then you can fill it up. Just make sure the top of the bag is closed when you walk through the sensors. It works with RFID, too.
I've wanted to know this for a couple of years now, I've really wondered how these works.. Wow, Thanks for taking your time to investigate and share the results with us! =D Great video!
That alloy strip is actually metallic glass. Little bits and pieces of it work great for tweaking RF stuff that needs a little inductance in a spot that is hard to put a bigger coil in.
Beautiful work (as always). MANY thanks for taking the time and trouble to research this topic, construct the apparatus, eliminate the bugs, record the video, edit and post it.
thanks for explaining magnetostriction, very clear and concisely! just noting that this is the most common tags used in retail. there are others, like the square ones with the metallic spiral. most made in China products will use the cheaper strip
Really cool! I have always wondered how those things workes when I see them (the tags are so small that it would be hard to put any electronics in them, haha), but have forgot to do any reseach.
@10:56 this fixture is good, for better results you may need to link the vibration to an arm and then use incident and reflected light beam to observe under the microscope or on the wall for example. This is because the spring in this fixture introduces lots of impedance to the vibrating Magnetorestrictive plate, and thus may not present the real variation in the length of the Magnetorestrictive plate. Your fixture is fun, and the light beam idea is more fun.
@8:45 you must move the magnet only in one direction and along the tag to transfer magnetism into the Bias Magnet and insure it provide the proper move on the curve into MAX response.
The new setup is a bit more clean but it looks like you're doing fewer perspectives as a result. As you were taking apart the tag would have been a great time for a change of perspective to get a good visual on the strip from over your shoulder or the table. Yet from the far away perspective it is a bit harder to see whats going on.
Great video! Question, if a tag was magnetized, would a puncture in the tag through the metal strip and magnets it’s sandwiched between be unmagnetized after piercing it?
A magnet will activate and/or deactivate it, depending on which side (polarity) you rub accross it. The ones that are designed to never deactivate, simply have a thin piece of plastic between the two metal strips to keep them from touching. I always assumed that it had a static discharge or that the strip actually bowed inward like a pop up cap on a juice bottle.....or both. You can use the same magnetic key that they open the clear plastic lock up boxes or "spider wrap" for merchandise with.
+Jesse Guerrero The rig was awesome, but it may be flawed. He may have not been measuring expansion/contraction. What about sideways movement from the electromagnet pulling the tag around at 58kHz?
+ddiddy666 That is a good question. I'm not exactly sure, but I believe the manufacturer uses two ribbons just to get more signal. Two oscillators will produce more signal than one. The ribbon cannot be made thicker because it is created by extremely rapid cooling to obtain the desired magnetic properties, and a double-thickness ribbon would cool rapidly enough at the edges, but not quickly enough in the center. So, two thin ribbons it is.
+Applied Science Perhaps it has something to do with different magnet-harmonic frequencies? i.e. half wave + full wave or 1/4 wave. Curious whether a small neo-d magnet or ferrite magnet on the device with one strip vs two produces different degradation in signal. I'm thinking out of phase frequencies might cancel attempts to bypass the security feature.
+Applied Science One strip is actually resonating a little high and the other is a little lower than 58kHz. It helps with system performance and reliability.
@15:05 that also depends on the fabric of the thin plate and the orientation of this thin plate relative to the Acoustomagnetic field, and of course to the Bias Magnet - the point of thin plate state on the curve.
I had a watch that you could charge up by shaking your hand which would set up store alarms all the time... must have had some matching frequency components or so... One goal for your patreon might be a second camera so you can zoom in to the DUT while in a second window have the scope, that way much more screen real estate is used.
Correction. There is sound being transmitted. But, number one, it's above the audible spectrum, and number two they aren't using mechanical audible means to detect it, they are using a magnet to detect it.
An interesting example of magnetostriction is the high pitched tone that is created whenever a CRT monitor is turned on. The scanning rate of old "tube" style TVs was about 16kHz, that is, the electron beam would sweep across the screen at about 16,000 times per second. The beam was directed by electromagnets, which would also stress ferrous materials in the set to oscillate at the same frequency, making a high pitched "whine". Unfortunately, as we age, we tend to lose the ability to hear high frequency sounds, and often by about age 30, most of us can no longer hear sounds that high.
I certainly don't miss the high pitched whine of CRT TVs. There the effect is more likely to be just the huge electromagnet on the CRT pulling on anything that is attracted to the magnets, sheet steel structural parts used to be common in TVs and for example speakers have large unshielded magnets on the back that could also potentially get vibrated by the CRTs deflection field. The effect is however believed to be quite prevalent in giving large mains transformers there loud buzzing sound.
I understand somehow the strip resonates with the surrounding oscillating field when nearby the magnetized strip. Are you saying the detectors are able to sense the field/signal emitted from the ringing strip when the surrounding field stops and the strip somehow emits a ringing signal/field on its own after the surrounding oscillating field is stopped?
Sounds similar to a metal detector. In a metal detector, a coil creates an electromagnetic field. When metal enters the field, the field makes the metal create its own field in response. That field created by the metal causes resistance to the field created by the detector, and the circuitry in the metal detector can measure that change in resistance. This is simplified, but that is the gist
Definitely true. That was a brilliant way of describing the anti theft device and a way to measure its movement. However even in it's simplicity, I don't think too many understood it. Great demonstration.:-)
I liked your messy lab, and down home look that I could relate to. It was like you and I were in the garage building incredible stuff. Please don't let fancy lights and microphones get in the way.
I vaguely remember an experiment in college physics lab where we were measuring very small motions. We used a mirror with highly colimnated light shining on a scale we placed on the wall several feet away. Today with lasers, that would be an interesting way to measure the length change in this experiment.
The resonance can actually cause more variation in length than the static value measured, depending of course on the Q factor, power and exposing time. But in the graphs of the scope I actually see how the grow quite a bit in the "burst" duration of 58khz signal
The magnet used to de-chooch the tags - (the two strips) shorts them in a way that changes their resonance frequency. One is more ferrous than the other strip.
The assertion that the ribbon moves a thousandth of an inch in response to magnetic forcing could still be correct. Remember that this is a resonant response: its amplitude can be much larger than the equilibrium response to a constant driving force.
