A method for measuring a mechanical property of a subject includes using an ultrasonic transducer to apply ultrasonic vibration pulses to a vibration origin in the subject in an on-off time sequence in order to impart a harmonic motion at a prescribed frequency to the subject, and when the vibration pulses are off, preferably using the same transducer to apply ultrasonic detection pulses to a motion detection point and to receive echo signals therefrom in order to sense the harmonic motion on the subject at the motion detection point The ultrasonic detection pulses are interspersed with the vibration pulses and can be applied in a non-uniform manner From the received ultrasonic echo signals, a harmonic signal is detected and a characteristic such as amplitude or phase of the detected harmonic signal is calculated using a Kalman filter or interpolation.