Medium Acoustic Property

• Air: Only low frequency ultrasound can propagate in air at a speed of 300m/s with a very high attenuation. The acoustic impedance of air near zeros.
• Water: Sound velocity in water is around 1500m/s at room temperature. Water has very little attenuation to ultrasound. The acoustic impedance of water is about 1.5MRayl.
• Soft tissue: Sound velocity in soft tissue is around 1540m/s. The attenuation of soft tissue is around 0.3 dB/cm/MHz. The acoustic impedance of soft tissue is around 1.5MRayl.
• Bone: Sound velocity in bone is much fast that in soft tissue. Bone also has a higher attenuation. Normally, ultrasound beam cannot penetrate bone.