jimmylovesni
Automotive
- Jul 13, 2010
- 35
Im having an odd problem with an ultrasound driver and transducer combination. The driver produces a an waveform output from 500hz to 5MHz (tested with 10ohm resistive load) which we are trying to use to drive transducers ranging 500khz too 3MHz (500KHz, 1MHz, 1.35Mhz, 2MHz, and 3MHz) at the resonant frequency. We are using a driving voltage from 5 to 35Volts on each. Each transducer has a capacitance of around 5nf and each is the same size except for thickness which of course, varies with frequency/wavelength, the slower frequencies needing to be thicker.
In a test water bath, the 1.35Mhz, 2MHz, and 3MHz transducers work great, producing a very powerful output which creates a force of around 1megapascal or larger as measured on a hydrophone. The output power can also be verified outside of the water bath as these transducers can levitate water. The output pressure wave of these transducers stays constant over time (ie 20min).
The unexpected problem is that for the lower frequency transducers cannot sustain their high energy output. The 1MHz produces a large amount of pressure but then this energy fades after about 5 seconds (at 30V). If I let the setup rest for about a minute and turn on the power again, it runs again for 5 seconds. If I run it at a lower voltage, the transducer will run at the higher power for a longer amount of time but eventually will fade out. With the 500KHz, the effect is even more pronounced, and it can be run less than half the time the 1 MHz can run. During the entire time that the transducer is failing, the voltage intput it stays constant as seen on an oscilloscope.
Im guessing that either the circuit is heating up or otherwise the transducers. I would have expected more heat loss at the circuit during high frequency operation though due to frequency response losses at the higher bandwidth. The lower frequency transducers, which are thicker, don’t feel hot so Im confused about what is going on. Im guessing they are not meant to be driven in a continuous fashion? Any ideas?
In a test water bath, the 1.35Mhz, 2MHz, and 3MHz transducers work great, producing a very powerful output which creates a force of around 1megapascal or larger as measured on a hydrophone. The output power can also be verified outside of the water bath as these transducers can levitate water. The output pressure wave of these transducers stays constant over time (ie 20min).
The unexpected problem is that for the lower frequency transducers cannot sustain their high energy output. The 1MHz produces a large amount of pressure but then this energy fades after about 5 seconds (at 30V). If I let the setup rest for about a minute and turn on the power again, it runs again for 5 seconds. If I run it at a lower voltage, the transducer will run at the higher power for a longer amount of time but eventually will fade out. With the 500KHz, the effect is even more pronounced, and it can be run less than half the time the 1 MHz can run. During the entire time that the transducer is failing, the voltage intput it stays constant as seen on an oscilloscope.
Im guessing that either the circuit is heating up or otherwise the transducers. I would have expected more heat loss at the circuit during high frequency operation though due to frequency response losses at the higher bandwidth. The lower frequency transducers, which are thicker, don’t feel hot so Im confused about what is going on. Im guessing they are not meant to be driven in a continuous fashion? Any ideas?