The efficiency of a thin film Si solar battery is improved. The apparatus includes a cellular telephone body having at least a back surface, a first transducer positioned within said cellular telephone body perpendicular to the back surface and adapted to generate a first acoustic field, and a second transducer positioned coaxially to the first transducer and adapted to generate a second acoustic field. Thus, reluctance torque caused in the second rotator portion 3 is increased, whereby it is possible to increase torque as a whole and to obtain a high-output motor. The combustible material is further modified to add an additional outer impervious layer such that the combustible material exhibits prolonged shelf life and durability. The elastic wall is formed by the shaped diaphragm.