A. Gałka, B. Gambin, and J. Telega, “Variational bounds on the effective moduli of anisotropic piezoelectric composites”, Arch. Mech., vol. 50, no. 4, pp. 675–689, Jan. 1998, Accessed: Nov. 19, 2025. [Online]. Available: https://am.ippt.pan.pl/index.php/am/article/view/v50p675