MadSci Network: Physics

Re: Can you sonicate liquid samples by applying the frequency to the air around

Date: Sat Sep 25 08:26:02 2004
Posted By: Gareth Evans, Industrial R&D practitioner and manager ( retired )
Area of science: Physics
ID: 1092238207.Ph

You asked whether it is possible to ďsonicateĒ several small liquid samples by applying ultrasound to the air around the samples. I have to disappoint you Iím afraid. The transfer of energy from the ultrasonic source to the object you wish to receive the energy requires strong coupling of the source to the object. Ultrasound is no different qualitatively from audible sound. Remember those tin cans connected by string ? They transmit sound a lot better than shouting across the gap. Wire works even better. The difference between air and wire is that air is compressible and the energy is dissipated by the air gap. At ultrasonic frequencies this loss process is severe. When pregnant women are scanned to reveal images of the unborn babies using ultrasound, a gel is used to ensure good coupling of the source and detector with the skin to minimise reflections and dissipation of the ultrasound waves. This also explains why baths of water are used to treat multiple samples. The incompressible water provides the coupling of the single source to the several objects. Your question implies that you want to avoid the use of baths. I donít know whether they exist but you might want to try a branched probe as an alternative. I acknowledge Dr H Adamís input to this answer. He spent some time as Head of the Dispersion Technology Laboratory at Eastman Kodak so I knew he was well qualified to advise

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