In order to go deeply into ultrasonic welding, it is necessary to previously explain what sound waves are and how they are created. First of all, they are mechanical vibrations that are comparable with the ones that are created by any musical instrument. They are called ultrasounds because their frequency is higher than the one that can be heard by the human ear. These pressure waves are created by piezoelectric ceramics, which are closed in the converter or transducer. Piezoelectric ceramics can create a tension difference between the two sides, if they are subject to a strong pressure. This phenomenon is usually used in piezoelectric lighters and microphones. In detail, this phenomenon is used contrariwise in ultrasounds. Voltage is sent to the ceramic and the latter lengthens or shortens according to voltage polarity. After having created the vibration, it will be necessary to amplify and transmit it to the items to be welded. Obviously, we would like to stress that every part of the acoustic or vibrating set cannot be tampered with or altered, as the latter is perfectly calibrated and tuned during manufacturing operations. This control operation allows the ultrasonic welder to work in a perfect way.