jimmylovesni
Automotive
- Jul 13, 2010
- 35
Hello,
I have a 1 MHtz transducer, being driven in a high intensity pulsing fashion, that being that the 1MHtz signal is being pulsed at 1KHtz. The ultrasound signal is being applied to a borax plate (3”x4”x1.2mm). There is no wedge being used between the transducer and borax (glass) and I am letting the transducer either sit on the glass or otherwise, hold it on the end /edgeof the glass.
So I am trying induce flextural waves, specifically lamb waves. By using the oscilloscope, I can calculate the speed of sound to validate the type of wave I am seeing. This is done by comparing where the 1kthz turns on to where the received signals reach the hydrophone. So there is a very small pulse reaching the hydrophone which would correlate with a lamb wave, maybe about 20mv Peak to peak which corresponds to something in the Pascal range. The time it takes for this pulse to arrive computes out to about 2500m/s which is the typical propagation mode for the slower lamb mode to arrive (longitudinal is much faster). The problem is that after the desired lamb wave arrives, I get a much larger signal that arrives which I think is some type of vibration and has a large amplitude of almost 10x larger than the lamb wave. The speed of sound (propagation time) for this vibration does not seem to change when I put the hydrophone closer to the transducer where as the time for the the lamb wave to reach the hydrophone gets shorter. So it appear this vibration is something maybe like the natural frequency of the thin borax plate?
So how do I get rid of or reduce the amplitude of these vibrations so I can just have the pure lamb waves? Increasing the mass or length of the glass? Is there a way to damp it? I tried adding water under the glass so that borax is coupled to the table and it does reduce the amplitude alittle but also reduces the amplitude of the lamb way too. Really not sure how to fix this one. Any help is really appreciated.
Can anyone also explain the difference between a flextural wave and a vibration?
Thanks
Jim
I have a 1 MHtz transducer, being driven in a high intensity pulsing fashion, that being that the 1MHtz signal is being pulsed at 1KHtz. The ultrasound signal is being applied to a borax plate (3”x4”x1.2mm). There is no wedge being used between the transducer and borax (glass) and I am letting the transducer either sit on the glass or otherwise, hold it on the end /edgeof the glass.
So I am trying induce flextural waves, specifically lamb waves. By using the oscilloscope, I can calculate the speed of sound to validate the type of wave I am seeing. This is done by comparing where the 1kthz turns on to where the received signals reach the hydrophone. So there is a very small pulse reaching the hydrophone which would correlate with a lamb wave, maybe about 20mv Peak to peak which corresponds to something in the Pascal range. The time it takes for this pulse to arrive computes out to about 2500m/s which is the typical propagation mode for the slower lamb mode to arrive (longitudinal is much faster). The problem is that after the desired lamb wave arrives, I get a much larger signal that arrives which I think is some type of vibration and has a large amplitude of almost 10x larger than the lamb wave. The speed of sound (propagation time) for this vibration does not seem to change when I put the hydrophone closer to the transducer where as the time for the the lamb wave to reach the hydrophone gets shorter. So it appear this vibration is something maybe like the natural frequency of the thin borax plate?
So how do I get rid of or reduce the amplitude of these vibrations so I can just have the pure lamb waves? Increasing the mass or length of the glass? Is there a way to damp it? I tried adding water under the glass so that borax is coupled to the table and it does reduce the amplitude alittle but also reduces the amplitude of the lamb way too. Really not sure how to fix this one. Any help is really appreciated.
Can anyone also explain the difference between a flextural wave and a vibration?
Thanks
Jim
