Ultrasound source: 14 kHz 90 dB

Discussion in 'Analog & Mixed-Signal Design' started by curro92, Sep 25, 2018.

  1. curro92

    Thread Starter Member

    Sep 29, 2012
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    Hello,
    I want to verify if it is true that ultrasound is effective against the varroa mite, currently the worst enemy of bees, which kills the hive in about two years if it is not treated with chemicals. I want to build an ultrasound source for that purpose.
    I have a signal source like this

    [​IMG]

    Now I need an amplifier and a speaker or tweeter. And a power source.
    The system should work for about 30 days. You have to optimize consumption, so you do not have to use very large batteries.

    My doubts are these:
    - what power (watts) must the amplifier have to obtain 90 dB to 30cm in a closed enclosure such as the hive?
    - What speaker would be suitable?

    My bees appreciate your suggestions :)
     
  2. BR-549

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    Sep 22, 2013
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    Are you sure that prolonged exposure won't hurt the bees?
     
  3. Alec_t

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    Sep 17, 2013
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    14kHz is not ultrasonic (though it would be inaudible to people with defective hearing). I share BR's concern that your bees won't appreciate being bombarded with 90dB of sound. They'd probably abandon the hive.
     
  4. DickCappels

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    Aug 21, 2008
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    It looks like there has been some research done. Apparently the bees don't notice it but it is devastating to the mite population. This guy says it works and has products based on it.
    https://www.varroa-killer-sound.com/en_GB

    I made something similar when neighbors moved in, bringing a couple of noisy barking dogs with them.

    upload_2018-9-25_17-23-41.png
    Note that the oscillator is the CMOS LMC555C not the bipolar NE555. The NE555 might work but the waveform will not be symmetric. This circuit was not designed as much as it was thrown together in a hurry. I think it would be good to add more bypass capacitance and to assure that the power supply is current limited because both the MOSFETs are on as the power supply rises.

    The transducer was a dynamic tweeter I bought at store that sold audio equipment.

    It must have worked because while I was checking it on the scope my wife came in and said "Will you please stop whatever it is that you are doing?"

    The 90 db spl is a problem.I guess you can buy, borrow, or rent a sound pressure level meter and take the measurement. Inside a closed space there are likely to be "dead zones" in which reflections partially or totally cancel incident sound waves.

    The higher the drive voltage the higher the battery drain. Here again an SPL meter can help you find tune performance.

    If you look through this forum long enough you sound be able to find solutions based on a Piezoelectric transducer. Probably a little more difficult to source the parts but may be worth investigating.
     
  5. ericgibbs

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    Jan 29, 2010
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    hi curro,
    I know its not an electronic solution, but Turkish bee keepers, give bees that are carrying mites, a really major dusting with icing sugar.
    Thats powered sugar, as the bees clean the sugar off each other, they knock off the mites.
    A lower tray in the hive, has small perforated holes which the mites fall into a tray, which catches the mites, ready for destroying.

    This is not a joke.


    E
     
  6. Janis59

    Active Member

    Aug 21, 2017
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    RE:""what power (watts) must the amplifier have to obtain 90 dB to 30cm""

    The closed room acoustics is rather complicated thing, at first You will calculate the room constant, then apply it to get the near field distance where it becomes a far field etc etc. Thus, I suggess to approximate it by near field, i.e. with open space formulas and keep in mind that the real Wattage will be needed slightly less.

    Thus the sound pressure in spherical distance from source is p(Pa)=sqrt(Q*ro*c*Pac/4/pi()/r^2) where
    Q is directivity, if high source then 1, if on-ground source then 2;
    ro is air density, summer 1.19, winter 1.33 kg/m3;
    c is sound speed, 340m/s winter 320 m/s summer;
    pi is 3.14;
    r is distance, in Your case 0.3(m) squared;
    and Pac is acoustic power (slightly lower than electrical power on loudspeaker).

    The same time, ANSI S1.1-1994 creates the pressure decibel as Lp=20log(P/20microPascals)
    So, Your wished 90 dB will turned to 0.65 Pa sound pressure, as any Excel will ease that calculation.

    For power in hemispheric (low altitude) model, my Excel shows You need 0.01 Watt (!!)

    Intuitively it sounds absurdly small power, so take better the 1 Watt and it will be more than sure.

    By the way, try the 20 cent worth piezoelectric lighter noodle in reverse regime. Normally You bend it and it give a spark. Here load it with high voltage and it will bend, creating the ultrasound.
     
    Last edited: Sep 26, 2018
  7. curro92

    Thread Starter Member

    Sep 29, 2012
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    Thank you all.

    Janis59's indication will be very useful for me, 1 Watt to start testing.

    Can you explain to me in more detail, perhaps with a drawing, that idea of the piezoelectric lighters? What frequency kHz do the ultrasounds obtained have?
     
  8. Janis59

    Active Member

    Aug 21, 2017
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    It depends on the producer. But all are rather high frequency thing where You can easily measure the response time with osciloscope.
    About lighter I mean the construction similar to this https://www.shopbic.com/products/lighters however there are zillions of similar producers and all are identic. The cheapest I seen costs 0,12 USD and expensivest 0,40 USD. The detail You need is inside this https://en.wikipedia.org/wiki/Piezo_ignition black plastic envelope. Just take it out with a care, its about 3mm thick round rod with 2 cm length. Material - polycristallic mix of different salts. At bending or shortening generates the high voltage. At exposing in high voltage and small current it bends or lengthens.
    Thus the first step is take it up from the trash bin and distract. Then second step is to measure the frequency, third is to find the right amplifier topology for right voltage and current. And never vice versa, I mean starting with circuit and trying to buy actuator what passes with this circuit.
    By the way, its very simle to slow it (decrease the resonance frequency) - just add the mass, and rather impossible to lift it up.
     
    Last edited: Sep 27, 2018
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  9. Janis59

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    Aug 21, 2017
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    Indications for resonance - lighter always give a solely one spark. Any spark is the short-life product, what time-span may be measured by ultrafast videocam (complicated) or by photoresistor and oscilloscope (simple). I think the timing of spark will well correlate with resonance, because the main mechanism there is the mechanical resonance in any quatzed device. The hammer is hitting the rod, rod is resonating at own frequency, and while it happens, the spark may be seen.
    Other technique is to measure electronically, switch the rod to Dirac delta pulse generator and measure the response function by oscillosope`s Fourier analizer part, or activate the oscilloscope sweep generator functionality and measure the current via this rod - at resonance there ought be sharp minimum. Probably are another methods (spectral analizer etc).
    Cardinally other method probably may be minded about, is COMSOL modelling for rod vibrations, but there will be plenty of constants unknown, thus better make a in vivo measurement

    P.S. Here one had been measured something out of this https://rimstar.org/materials/piezo/ignitor1.htm
     
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  10. Janis59

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    Aug 21, 2017
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    I find one much hevyer piezo with 4 kHz, but Your is no less than (12/3)^2=16-fold lighter, thus the frequency ought be at least 16*4=64 kHz or slightly higher. So, it seems it will anyway will work in non-rezonant regime. Its bad, as proportionally less will be the amplitude of off-resonant waves.
    Just try to realize what actuator has the higher frequency and use that. Logically, the power will be multiplied proportionally to distance to resonance.

    PS Any mechanical attaching of crystall to Your target of choice may be done by "superglue". At one of sources is said:""
    Good quality temporary bonds may be made with cyanoacrylate (e.g. "super
    glue"). An added benefit of cyanoacrylate bonds is that the bond easily achieves
    electrical contact. The length of time the bond will last will be application
    dependent, from seconds to years. For a short time the performance of the part is
    very close to that achieved using the best bonds, which makes it useful for
    exploratory work""
     
    Last edited: Sep 27, 2018
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  11. Janis59

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    Aug 21, 2017
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  12. Janis59

    Active Member

    Aug 21, 2017
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    Here are another doctor dissertation on theme, used 12mm and 37mm diameter 0,6mm platelet style actuators on 1,7MHz and 3.7MHz. Thus, seems they are not so lazy as those 4kHz one. Read it through for ideas. https://digitalcommons.odu.edu/cgi/viewcontent.cgi?article=1010&context=ece_etds

    P.P.S. At piezo.com is said
    What is the resonant frequency of a piezoceramic sheet? There is no one 'resonance'. There are many resonances. The number of them and their location in the frequency spectrum depend on the shape and thickness of the part. For a flat sheet as shipped, three obvious resonances are the ones associated with the length, width, and thickness of the sheet.
    Can I drive a piezo transducer with a 'square wave'? The answer is application dependent. If the square wave voltage is low (i.e., less than 30 V), then the answer is usually yes. If the square wave voltage is higher, there is a good chance for shockwave, damage, cracking, reduced life, or other failures. Careful control of the square wave rise time/fall time is the solution.

    PPPS From rageuniversity.org page
    ""There is no inherent frequency limit for a piezoceramic sheet. In practice the
    frequency limits of applications are usually determined by resonances associated
    with the shape and/or size of the transducer design. A typical 2.85" square, .0075"
    thick sheet of PSI-5A material has a thickness mode vibration in the neighborhood
    of 13 MHz and a planar dilatation mode at around 14 KHz. At ultrasonic
    frequencies large surface area parts draw considerable current and resistive
    heating of the electrodes becomes the limiting factor""

    The most of materials allow the 500 mictrostrains deformation (=500 micrometers to meter of length) thus there is said:
    ""Assuming that we stretch a PSI-5A (1.5" x 2.5" x .0075") sheet to ±500
    microstrains quasistatically at a frequency just below its fundamental longitudinal
    resonance of 15 KHz, and that we collect 100% of the stored electrical energy at
    its height twice per cycle we would get approximately 9 watts of electrical power
    from the sheet. The mechanical energy input under these assumptions would be
    in excess of 100 watts. Resonant designs can be considerably more efficient.""

    So... seems somewhen heard... parallel quartz resonance and serial one. Only in the quartz case them are rather near, while here are hardly far, one in kHz and another in MHz.
     
    Last edited: Sep 27, 2018
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  13. curro92

    Thread Starter Member

    Sep 29, 2012
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    Many thanks!
    I'm going to have to take a few hours to look at all this in detail :)
     
  14. curro92

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    Sep 29, 2012
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    I use powered sugar to count varroa mites. The problem is that of all the mites that are in the hive, only 25% are on the adult bees. The rest is inside the closed alveoli where the larvae develop.
     
  15. Alec_t

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    Sep 17, 2013
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    How? Why do you need to count them?
     
  16. Dodgydave

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    Jun 22, 2012
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    Here is one i used for a Cat/Dog pest alarm, it uses a sweeping frequency output centred on 3.5Khz, which can be retuned to suit, using a piezo transducer on a 12V supply , for higher power use the Tip41/42 output transistors with a tweeter speaker. DSC_0171.JPG
     
  17. curro92

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    Sep 29, 2012
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    It is to know the parasite load: three hundred bees are taken, powdered sugar is poured, that causes the varroas to fall off. The mites are counted and the rate of infestation calculated: how many mites per 100 bees. If the proportion is greater than 10 mites/100 bees, the infestation is serious, and a treatment must be carried out. If it is smaller, the situation is tolerable. There are other forms of the level of infestation, for example, counting the natural fall of mites to the bottom of the hive.
     
  18. ericgibbs

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    Jan 29, 2010
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    hi curro,
    If you get a working solution, that gets fair results, using 14kHz, I would be interested hearing the details.
    We have a few hives on our farm in South Africa, we could try out the 14kHz idea.
    E
     
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  19. AllanGH

    Member

    Oct 1, 2013
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    This, of course, and in my personal experience, is the best, and most entertaining, application for high sound pressure output ultrasonic devices.

    Strangely enough, my neighbours have developed the odd opinion that it's better to keep their dogs indoors.
     
    Last edited: Oct 21, 2018
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  20. oz93666

    Senior Member

    Sep 7, 2010
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    ordinary hi-fi tweeter
    [​IMG] [​IMG]
     
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