Depending on frequency and propagation speed of the ultrasound the wavelength determines the minimum duration of an ultrasound pulse and the thickness of an ultrasound beam. High ultrasound frequency thus brings high resolution but, unfortunately, low sensitivity i.e. weak reflected signals due to the fact that the absorbtion increases with the frequency. In order to get best performance out of an ultrasound based measuring system, despite the limiting factors above, the ultrasound transducer must not introduce distorsion or have any negative influence on the ultrasound signals. Sensitivity, pulse length and beam width are the major parameters in this respect and all three parameters are directly depending on the design and performance of the transducer. There is no optimal design for all applications.
Some applications require high resolution and others long measuring distance.
Measuring with ultrasound is common in solid material, in liquid or in air with applications within medicin as well as within industry. One application for example is measuring of gas flow in connection with the growing use of natural gas as well as in connection with medical gas flow. Another example is non-contact measuring of distance in robot applications and anthropometrical measurements for example screening of scoliosis. The active substance in an ultrasound transducer is a piezoelectric substance. Intens research is being performed in many laboratories world wide aiming at new materials with better performance.