Sonic & ultrasonic transducers
Sonic & ultrasonic transducers are electro-mechanical or electro-acoustic converters. They transform electric energy in vibrations of a transducer part, which is used to generate mechanical, acoustic or even thermal power. Sonic transducers operate at audible frequencies, while ultrasonics operate at 20kHz or above. Transducers are often reciprocal devices: Most transducers can operate as sensors or generators exploiting mecano-electric conversion. This section introduces only actuation or emission modes. Conversion in such transducers are generally based on piezoelectric, magnetostrictive or magnetic forces.
The most convention approach consists in using such forces to excite a mechanical resonance. For the same electric excitation, the vibration at resonance is the low frequency vibration multiplied by the mechanical Quality factor at resonance. This allows to achieve a good efficiency and reduced excitation voltages. The alternative way is to generate forced vibrations. Forced vibrations lead to large frequency bandwidth and are much less sensitive to load variations.
Usual ultrasonic transducers also called industrial ultrasonic processors are resonant structures based on typically 3 half-wave length resonators : a piezo converter, a booster and a sonotrode. They are used for ultrasonic welding, milling, cleaning, nebulization or ultrasonic assistance in drilling, extrusion, homogeneisation, filter declogging… Cedrat can define solutions using standard transducers. Customisation is often required to adapt the sonotrode to the load as shown below.
A new approach consists in using new active materials such as multilayer piezo ceramics (MLA) or giant magnetostrictive materials (GMM). These are used for building low frequency resonant transducers in dual-mass Tonpilz structures. Based on pre-stressed MLA, Cedrat PPAs and APAs are relevant sources for ultra-compact resonant transducers because offer very large dynamic strains (more than 1%) at low voltage (<10V) as in the Water Tracker. In addition, PPAs and APAs offer also large strains outside resonance, which allows them to be used for forced vibrations, for example in tribometers, glass cutting or piezo shakers.
At last, magnetic actuators can be considered for low frequencies acoustic sources: Cedrat MICAs magnetic actuators offer an interesting alternative to voice coils for higher forces density and for 10 times less heating. Giant Magnetostrictive materials (GMM) are an alterventive to piezos for low frequency high power transducers (sonar).
Some examples are given hereafter or in our related publications on sonic or ultrasonic transducers.
