Tube Amplifiers
Ste P asked:

1.Can an ultrasonic transducer (inexpensive) commercial that has a frequency of 40kHz concentrate be used to generate ultrasonic waves of 18kHz to 2MHz. 2.The aim to generate ultrasonic waves through a transducer and an amplifier and I wear the `t know what it is best used as transducer. 3.Can a piezo-electric tweeter be used? 4.Can ultrasonic waves be concentrated using a parable? 5.I want to generate cavitation in a liquid in a tube and I thought that the best way was to use ultrasonic waves at high power. How do I calculate the correct length of a tube as a frequency specific? Thank you.


2 Comments so far

  1. Nikan on July 21, 2009 10:20 am

    For the first part of your question I should say that as far as I know (i’m using ultrasonic waves for a research) the frequency of the wave made by a transducer is constant. Cuz it is its very structure that create the wave and I haven’t seen any transducer which transmits selective waves. By the way, 18 kHz is not ultrasonic.

    Second Part: You should choose a frequency which best suits your research. Try other researches in the topic so that you’ll may find out that which frequency is better for such tasks. And you should know that the power of the transducer must be enough to go through the tube without completely fading away.

    Third: All of ultrasonic transducers are piezoelectric (As Far As I Know!) so I don’t think that there’ll be any trouble.

    Fourth: Sorry I don’t know.

    Fifth: I can’t get exactly what you mean but I think by knowing the energy loss of the wave in the tube you will be able to figure out the length of the tube.

    I know I haven’t said much but I hope these would help you 🙂

  2. on July 23, 2009 10:02 am

    O.K. what your talking about is the bandwidth of the transducer. A transducer will have a central frequency like you say (in this case 40khz) but it will also have a bandwidth. The bandwidth is the frequency range the transducer can operate within which will be less power output than the central frequency, however the power loss will only be limited. A transducer can usually operate outside of the bandwidth however the power loss will usually be more. The frequency range you are hoping to get from this 40khz transducer is quite high. I think it would be unlikely that it could do this range. If it can do this range, it would be very unlikely that the bandwidth would cover this range.
    *note – you are not always able to get this bandwidth information before purchasing a transducer especially with a cheap transducer.

    Choosing a transducer is very specific to the application which you are hoping to use it for. Some examples of questions to ask are; whether you need a water coupled transducer or an air coupled, whether the transducer will run in chirps/ pulses -ie. reduced duty cycle -(like for non destructive testing) or constant output, whether you require a narrow beam or a wider beam angle (like for distance measurement) or maybe you require the entire transducer to resonate (eg. bolted langevin transducer), how wide bandwidth you require, whether you will be attaching a horn (to concentrate and/or direct the output), whether it is a high output application or relatively low output, what the specific application is, what type of amplifier you are using (better to select the transducer before selecting the amp) – best if you can select a transducer that will run of a cheap amp like an pro audio amp if you want to save money, whether you require an industrial transducer or whether you could achieve your goals using a standard acoustic transducer like a loudspeaker.

    piezoelectric and magnetostrictive are two different types of transducers. You could use piezo, it tends to have a wider bandwidth also, and it can also be used for very high frequencies. A standard tweeter would be difficult to use because it is only designed to only cover the audio range of up to 20khz. Also the output graph is something to consider. For example a tweeter may be rated to 20khz with a power output (spl) of 130db, but the output graph or output may drop off substantially at only 14khz. It is still rated to 20khz, but the power is very low at this level. I think that the frequency range you are trying to get is very wide, and maybe you will need an industrial transducer. As you appear to be trying to save money, maybe you can find a small or cheaper industrial transducer which can cover your application.

    Do you mean a parabolic horn? Sometimes a horn is used to concentrate sound waves from a transducer. The transducer would have to be designed to accommodate a horn. A number of different types of horns are available. You would have to research this for your application. Professionally build horns can be very expensive. Maybe you can find a cheap copy somewhere, although it would be unethical to buy a direct copy of a more expensive design.

    If you are serious about this you will have to do some research more than yahoo answers.

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