Putting Confidence in Ultrasound

Phantom gel

Membrane hydrophone

Choosing a Hydrophone

Click here for a comparison table of hydrophones and different amplifiers.

Sensitivity versus effective area: as with most sensors, voltage amplitude is proportional to the area of the active element. More sensitive devices have a larger sensing area, hence lower spatial resolution and narrower acceptance angle (directivity) with a specific frequency (or wavelength).

Interference with the acoustic field: in general, it is preferable to use a sensor that does not affect the parameter being measured. However, the choice of hydrophone depends on the nature of the acoustic field. Continuous wave fields are most affected by large reflecting structures in the neighborhood, so the needle type is preferred -- keeping in mind that the hydrophone may have a reflecting support structure. Pulsed fields are more forgiving because the reflections can be separated by time, so membrane types may be acceptable.

Fragility: Hydrophones are intrinsically fragile, especially near the sensing element, because their purpose is have high sensitivity to transient pressures. Different models have varying degrees of protection depending on construction.

Immersion: Although all Onda hydrophones are sealed, water is a relatively aggressive solvent, and it even migrates through plastics. For this reason we recommend that the hydrophone be taken out of the tank when it is not actively used.

Size: Needle hydrophones afford the smallest size, followed by the capsule design, and membrane types are extremely large compared to the sensing element.

Cost: In general, membrane devices are more costly, followed by capsule and then needle hydrophones. Within each type, the smallest devices are the most difficult to make and hence the most expensive.

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Hydrophones AIMS III - Scanning System
OptiSon - Schlieren System RFB - Radiation Force Balance
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