An analytical model of a longitudinal-torsional ultrasonic transducer

The combination of longitudinal and torsional (LT) vibrations at high frequencies finds many applications such as ultrasonic drilling, ultrasonic welding, and ultrasonic motors. The LT mode can be obtained by modifications to the design of a standard bolted Langevin ultrasonic transducer driven by an axially poled piezoceramic stack, by a technique that degenerates the longitudinal mode to an LT motion by a geometrical alteration of the wave path. The transducer design is developed and optimised through numerical modelling which can represent the geometry and mechanical properties of the transducer and its vibration response to an electrical input applied across the piezoceramic stack. However, although these models can allow accurate descriptions of the mechanical behaviour, they do not generally provide adequate insights into the electrical characteristics of the transducer. In this work, an analytical model is developed to present the LT transducer based on the equivalent circuit method. This model can represent both the mechanical and electrical aspects and is used to extract many of the design parameters, such as resonance and anti-resonance frequencies, the impedance spectra and the coupling coefficient of the transducer. The validity of the analytical model is demonstrated by close agreement with experimental results

A strategy for delivering high torsionality in longitudinal-torsional ultrasonic devices

A composite longitudinal-torsional vibration mode has applications in ultrasonic motors, ultrasonic welding and ultrasonic drilling. There are two ways to obtain this vibration behaviour using a single transducer, namely (i) coupling of a longitudinal and a torsional mode, which is known to be difficult; and (ii) degenerating a longitudinal mode to deliver longitudinal-torsional behaviour at the horn tip. A mode-degenerating horn is achieved by incorporating helical or diagonal slits in an otherwise traditional exponential horn driven by a Langevin transducer. However, it is often difficult with this configuration to avoid coupling of unwanted bending modes, low responsiveness, and loss of ultrasonic energy due to boundaries between tuned components. Therefore, in this study the mode-degenerating characteristics are achieved by incorporating the helical slits and exponential geometry features in the front mass of the transducer itself. Finite element analysis and vibration experimental analysis show that this strategy prevents coupling of bending modes, increases responsiveness, and reduces energy losses. Most importantly the transducer delivers a very high torsionality

Trauma, gender and performance Theorizing the body of the survivor

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