Ultrasonic sound velocity measurement in samples of soft materials through under-resonance excitation.

Ultrasound (US) velocity determination is a valuable characterization technique, providing important information on elastic properties of materials. Sound velocity can be obtained accurately in the pulsed method if the thickness of the specimen is precisely known. This is clearly not easily achievable for soft materials, such as biologic soft tissues or tissue-mimicking phantoms. From this consideration, previous works have established that sound velocity can be determined in through-transmission configuration without thickness measurement through the time-of-flight determination of specimen-reflected echoes in plane parallel-surfaced specimens. It is shown here that the amplitude and shape of these specimen echoes can be significantly improved by working in the tone-burst mode at an excitation frequency below the transducer resonance. This is particularly valuable for materials presenting a low acoustic contrast with the surrounding medium, usually water, such as tissue-mimicking materials and water-based phantoms, making the specimen echo time-of-flights and, consequently, the sound velocity determination, more reliable.