Видео

Certainly this is one of the Precision Acoustics 1 MHz HIFU transducers (60 mm diameter, 75 mm focal length). The drive system was a Keysight Technologies 33512B function generator producing a 1 MHz CW waveform which was then amplified by an Electronics & Innovation 2100L power amplifier.

acoustic impedance

Hi - there are a number of publications that have suggested strategies for choosing the acoustic impedance of the matching layer material (especially if you are using more than one material). For single matching layers this is oftens a material that is the geometric mean of the piezo-electric medium and the acoustic load (e.g. PZT and water). Once you have identified a material, you will know its wavespeed. Therefore you can identify the wavelength at the frequency of interest and from this the length required to achieve one quarter wavelength in that matching material

Glad you liked it. Thank for your comment!

As a starting point you should ask, is it possible to determine a frequency range is likely to be a deterrent for the pests of concern, yet not going to cause distress to those people and creatures that are not the intended target? Critically, the upper limit of human hearing deteriorates with age so even if you cannot hear the signals generated, young children may be able to. Furthermore, other animals (domestic and wild) may have hearing ranges that extend well beyond human hearing. High frequency signals may cause substantial distress to dogs and bats; this latter case is especially important since bats may be protected species (they are in the UK). The second issue is that the transducers need to be specifically designed to operate in air. All of the Precision Acoustics transducers are designed to operate in fluids and solids so would not radiate well into air. In summary then, one needs to be particularly careful when designing your transducer to minimise collateral harm. Expert advise from an airborne ultrasonics expert familiar with the hearing ranges of a wide variety of species is probably required

As you'll have seen the presentations use a lot of animation and therefore PDF printouts can look very cluttered as they contain all the objects regardless of whether they have appeared/disappeared at any one time. You are welcome to contact me via the Precision Acoustics Ltd website if I can be of any more asssistance

Sorry for that. We'll have a look at the upload and see if we can get the audio quality improved. Thanks for letting us know

Thanks - glad you liked it. This is currrently a very tricky question to answer not least of which due to the fundamental limitations of hydrophone metrology. There is only one national measurement institution offering calibrations above 60 MHz and the uncertainty levels at this frequency are substantial. Therefore, please consider these estimates as being VERY rough. For 0.4mm 16um with conventional preamplification, the noise floor of your DAQ is likely to be the limiting factor. Assuming this to be about 1mV noise pk-pk, I would expect NEP to be in the range 15-25 kPa (will vary from one device to another) For 0.4mm 16um with differential preamplification, there is a lot more gain in the preamp but has a higher internal noise floor. In this case I'd expect NEP to be more like 10 kPa (will varIy from one device to another). One final note, 0.4mm is likely to be highly direction at 63 MHz. You may be better off considering a small hydrophone, such as the 0.2mm diameter differentially amplified membrane hydrophone

Thanks

You are very welcome. Glad you found it to be of assistance

Glad to you like it. Two reasons: Firstly, highly resonant devices (as is often found in therapeutic devices) can be very dependent upon the impedance they are radiating into. When a wave is reflected back from an imperfectly absorbing target, there will be some effective pressure that arrives back at the source transducer, thus changing the instantaneous radiation impedance experienced by the transducer, and thus how much is radiated out into the fluid. Secondly, a portion of the reflected wave arriving back at the transducer will be converted by the piezo-electric crystal into an electrical signal within the transducer. This is unlikely to be fully in-phase with the electrical signal that is driving the transducer, and therefore there will be some level of destructive intereference and cancellation, so the output signal is reduced. In either case, less acoustic power is radiated from the transducer for the same power input, so radiation efficiency is reduced. Hope that helps!

Glad you liked it. We have plans for a number of additional videos in this series and measurements with hydrophones will feature heavily in several of these. Do have a look at the PA Tutorial on Basic setup for hydrophone measurements as this is the first to look at this topic, with more to follow