Application of a voltage across a piezoelectric crystal causes the crystal either contract or expand depending upon the polarity of the voltage.

The acoustic impedance of a plastic matching layer for a transducer should be as close as possible to that of the piezoelectric crystal.

Signal-to-noise ratio can be improved by using higher ultrasound frequency.

Increasing the degree of transducer damping will reduce the lateral resolution.

The divergence angle of an ultrasound beam from an unfocused transducer decreases with decreasing the transducer diameter.

Ultrasound is a transverse, mechanical wave.

If the attenuation coefficient of an ultrasound beam is 1dB cm-1 MHz-1, the attenuation of an ultrasound at 2 MHz passing through a 1.5 cm thick tissue is

When an ultrasound beam is focused tighter, the depth of focus becomes larger.

An ultrasonic beam propagates from medium 1 into medium 2. If the incident angle is smaller than the refraction angle, the sound velocity in medium 1 is higher than that in medium 2.

The thinner the piezoelectric crystal, the higher the resonant frequency that may be created.