Filler: an inert substance added to a resin to modify its physical properties.

Frequency: the number of cycles per second, measured in hertz.

Gain: the ratio of output amplitude to input amplitude of a horn or booster.

Horn: an acoustical tool that transfers mechanical vibrations from the transducer and booster to the parts to be assembled.

Near field weld: refers to a weld where the contact surface of the horn is 1/4 inch or less away from the joint surface. It is important that the horn fits the exact contour of the part to be welded.

Nodal point: the point or points in a booster or horn where little or no linear motion occurs.

Staking: the melting and forming of a plastic stud to retain or lock another material (often dissimilar) in place.

Swaging: used to capture another component of an assembly by melting and reforming a ridge of plastic around the component. The ridge locks the second component in place without welding the two materials together.

Thermoplastic resins: material that can be repeatedly softened and reshaped with heat and pressure. They are ideal for ultrasonic welding.

Thermoset resins: material that cannot be melted or reformed. Hard and brittle, they are not suitable for ultrasonic welding.

Transducer: a piezoelectric device that converts high-frequency electrical energy into high-frequency mechanical vibrations.

Ultrasonic welding: an assembly process in which parts are joined by the local application of pressure and high-frequency vibratory energy.