An ultrasonic transducer device comprising a casing which encloses a piezoelectric device , wherein the piezoelectric device comprises an internal ventilation path for the passage of cooling air from the outside of the piezoelectric device to the outside of the casing , wherein the device comprises a connection plate comprising a body which extends inside the casing and which has a mass calculated in accordance with the mass-spring-damper model, a hub centrally extending from the connection plate and protruding outside the casing , the hub being configured for the connection with an operating member, for example a sonotrode, wherein the connection plate comprises a seat comprising at least one threaded portion and wherein the piezoelectric device comprises: - a piezoelectric element sandwiched between the body of the plate and a countermass element , wherein the piezoelectric element and the countermass element comprise respective central holes aligned with the seat of the connection plate , - a fastening element inserted in the aligned holes of the countermass element and of the piezoelectric element and fastened into the seat of the connection plate by screwing, and - a plate made of metallic material, placed between the piezoelectric element and the countermass element so as to form a contact element connectible with an electric power source, the fastening element comprising a head , a central portion and an end portion , wherein: - the head has a diameter greater than the one of the central portion ; - the end portion is threaded and is sized so as to couple with the seat of the connection plate by screwing; - the central portion has a frustoconical shape, tapered towards the end portion , and has a diameter always smaller with respect to the internal diameter of the holes which pass through the countermass element , the piezoelectric element and a first part of the body of the connection plate , so as to form a toroidal spacing between the fastening element and the internal walls of the countermass and piezoelectric elements , wherein said toroidal spacing is flared passing from the countermass element to the body of the connection plate and comprises a section of smaller section at the countermass element and a section of greater section at the body . - a piezoelectric element sandwiched between the body of the plate and a countermass element , wherein the piezoelectric element and the countermass element comprise respective central holes aligned with the seat of the connection plate , - a fastening element inserted in the aligned holes of the countermass element and of the piezoelectric element and fastened into the seat of the connection plate by screwing, and - a plate made of metallic material, placed between the piezoelectric element and the countermass element so as to form a contact element connectible with an electric power source, the fastening element comprising a head , a central portion and an end portion , wherein: - the head has a diameter greater than the one of the central portion ; - the end portion is threaded and is sized so as to couple with the seat of the connection plate by screwing; - the central portion has a frustoconical shape, tapered towards the end portion , and has a diameter always smaller with respect to the internal diameter of the holes which pass through the countermass element , the piezoelectric element and a first part of the body of the connection plate , so as to form a toroidal spacing between the fastening element and the internal walls of the countermass and piezoelectric elements , wherein said toroidal spacing is flared passing from the countermass element to the body of the connection plate and comprises a section of smaller section at the countermass element and a section of greater section at the body . <EOS>