Acoustical power
Why specify this parameter precisely

The capacity to generate a high level of acoustic power is one of the essential characteristics of a transducer for therapeutic applications.

One of the main factors limiting transducer’s power is the rise in internal temperature caused by the production of heat. This heat production results from losses during the conversion of the electric energy into acoustic energy.

Transducers for therapeutic applications are designed in such a way as to minimise losses and to evacuate the heat produced towards an external medium, directly or by the means of a coolant.

However, even after defining the design, the internal temperature of the transducer still depends on the configuration of the excitation cycle and the cooling conditions.

The influence of excitation conditions

The temperature of the active element increases during the ON excitation cycle, then cooling takes effect according to the environment of the transducer. The absolute and relative durations of these ON and OFF cycles therefore establish the maximum temperature during the ON cycle and thus determine the maximum acoustic power during that cycle.

Evolution of the temperature rise of the active element vs. duty cycle
(at a given acoustic power)

a/ Duty cycle at 100% leading to an unacceptable level and the destruction of the device
b/ Duty cycle at 50% (shorter time ON) leading to an acceptable situation
c/ Duty cycle at 25% leading to low heating

Evolution of the temperature rise of the active element vs. ON & OFF times
(at a given acoustic power and same duty cycle)

a/ Duty cycle at 50% (time ON 20s) leading to destruction of the device
b/ Same duty cycle at 50% (time ON 2s) leading to an acceptable situation