Sonic & ultrasonic transducers
Sonic & ultrasonic transducers are electro-mechanical or electro-acoustic converters. They transform electric energy into vibrations, which are used to generate mechanical, acoustic or even thermal power. Sonic transducers operate at audible frequencies, while ultrasounds 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 is generally based on piezoelectric, magnetostrictive or magnetic forces.
The most conventional 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.
The usual ultrasonic transducers also called industrial ultrasonic processors are resonant structures typically based on 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 to build 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 they offer very large dynamic strains (more than 1%) at low voltage (<10V) as in the Water Tracker. In addition, PPAs and APAs offer large strains outside resonance, what allows them to be used for forced vibrations, for example in tribometers, piezo shakers or various vibration assisted processes (glass / metal / composite cutting, drilling, edm ...).
Eventually, 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 alternative to piezos for low frequency high power transducers (sonar).
Some examples are given hereafter or in our related publications on sonic or ultrasonic transducers.
