How many hertz use are used in ultra sound?

Answer 1

That depends upon the ultrasound. In simple terms, ultrasound is sound at frequencies (measured in hertz) beyond the upper range of human hearing. Conversely infrasound is sound at frequencies below the lower range of human hearing. For ultrasound, this starts at approximately 20,000 hertz (Hz) or 20 kilohertz (kHz) in humans, although some gender and age variation will allow hearing of sound above these in certain people.

The exact frequencies used in ultrasound depend upon what it is being used for, e.g. cleaning, therapy, diagnostics, etc. As they are large fields in themselves I will briefly give rough frequencies used in a few of them:

Ultrasonic Cleaners

- 20kHz to 40kHz

- Used for cleaning equipment, such as jewellery, surgical instruments, industrial components

Sonochemistry

- 20kHz to 100kHz

- breaks up compounds and cause extreme localised temperatures/pressures to trigger reactions (does not in itself cause chemical changes)

HIFU (High Intensity Focused Ultrasound)

- 250kHz to 2000kHz

- used for cyst and tumour treatment

Therapeutic Ultrasound (besides HIFU)

- 0.7 to 3.3 megahertz (MHz) (700,000 to 3,300,000 Hz) depending upon use

- Lithotripsy - breakdown of kidney and gall stones

- Physiotherapy - causes heating and possibly stretching of tissue; effectiveness of ultrasound in physiotherapy is somewhat unproven though

- Bone growth - can stimulate bone growth; animal studies only as far as I'm aware

- Thrombolysis - break down of blood clots

Diagnostic ultrasound

- 1 to 18 megahertz (MHz) depending upon depth (that's 1,000,000 to 18,000,000 Hertz)

- used for non-invasive (or invasive depending upon procedure) imaging of body tissues, particularly obstetrics (imaging pregnant women and their babies)