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Hydrophone Handbook

       2. Choosing a Hydrophone

 2.1 Applications
 There are many factors to consider when selecting a
 hydrophone. Sensitivity, frequency response, durability and cost
 must all be taken into account in making the best choice for a
 specific application.
 A list of general hydrophone requirements is given below:
 • Wide frequency range and flat frequency response
 • Wide dynamic range and low inherent noise
 • High spatial resolution
 • Minimal influence on the measured sound field
 Selection criteria should not be considered in isolation. Many of
 the parameters are inter-dependent. Understanding the trade-
 offs is key to determining the appropriate hydrophone.
 Hydrophones have been widely adopted for medical ultrasound
 applications for several reasons. They offer a combination of
 high temporal and spatial resolution, and are relatively compact
 and affordable to use.
 Water has been established as a good standard measuring
 medium because it is cheap, readily accessible, and simulates
 the acoustic properties of tissue.
 However, hydrophone measurements are not always
 representative of clinical conditions because of differences in
 attenuation, which varies as a function of frequency and
 distance from the transducer, between water and tissue. To
 account for this discrepancy, a derating factor or in-situ factor is
 commonly applied to the acoustic output measured in water for
 medical applications.


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