Abstract: The orthotropic mechanical sensing units made from piezoelectric composite material are discussed in this paper. The electromechanical coupling equations of the OPCM sensing units are deduced, which can be used to monitor the strains along arbitrary directions in the fields of general planar strain. And the orthotropism of the piezoelectric effects of OPCM is verified through experiments. The experiments prove that only when the polarization direction of the piezoelectric phase is parallel to the plane on...