where Zm, Zt and Zst are the acoustic impedance values of respectively the matching layer,
the transducer and the biological tissue. The matching layer thickness must be λ/4 to
produce destructive interference with the waves reflected back. For example, in the case of a
single porous matching layer, suitable for a PZT transducer working at a frequency of 50
MHz, with a speed of sonar wave propagation of v = 1882 m/s and acoustic impedance of
Zm = 9.64 [106 Kg / m2s], its thickness t would be: