Disclosed is a recombinant plasmid for expressing hepatitis B viral antigens in vivo, comprising an adeno-associated virus vector and a replication-competent hepatitis B virus genome fragment. According to certain aspects, the present invention significantly speeds up the convergence of the optimization by allowing direct computation of gradient of the cost function. When external energy is supplied to the insulating film, the insulating film contacts the piezoelectric structure and the piezoelectric structure is then deformed to generate electric energy.