Improvements in the performance of materials induced by advances in electronics, more efficient modelling and design tools and better knowledge of materials led to new perspectives in the use of ultrasound.
The Piezoelectric Effect:
Although a number of principles can be used to generate ultrasound, transducers mainly use the piezoelectric effect to convert electrical energy into mechanical movement.
In 1880 Pierre and Jacques Curie demonstrated the piezoelectric effect on a quartz sample, which becomes electrically charged when subjected to compressive stress. Conversely, when electrical voltage is applied to the quartz it causes a deformation in the crystal.
Ultrasound is produced by piezoelectric transducers. These transducers enable electrical energy to be converted into mechanical energy and vice versa.
It is a good idea to look at them according to their use:
- for emission: the properties sought are output and the capacity to emit a strong signal,
- for receiving: the sensitivity and signal/sound relationship are the characteristics which determine the performance of the transducer.
It is possible to use a transducer for emission/receiving, particularly for measurement systems or control techniques. In this case, the transducer should be a compromise between the criteria described above
There are many types of transducers which can be used for most applications, within the ultrasound frequency range. However, they can be classified according to their use and/or frequency range.
Two complementary technologies are in use :
- Low frequency:
The transducers are created by ceramics held between two metallic components which ensure the whole structure is tightly held in place (Langevin transducer) or from a disc which uses Poisson effect.
The power transducer is associated with two elements to adjust the transfer of energy as suited to the environment:
The sonotrode that transmits the mechanical vibration to the respective medium and whose shape determines the change in amplitude of the vibration produced by the transducer.
The booster, which is optional, is located between the transducer and the sonotrode. Its role is to ensure an amplification of the mechanical vibration.
- High frequency:
The transducers consist of a single ceramic produced from a homogenous or piezo-composite material. For measurement, adaptation layers enable the energy transfer to be optimised in the propagation medium, the whole transducer is then protected by a membrane which is acoustically transparent to the signal.
An ultrasound device consists of power electronics suitable for the transducer. The generator power supply is created using a network supply. For medium-range power, some of our generators are supplied with voltages that are as low as 24 VDC.
The generator has two major roles:
- Conversion of a network voltage into a voltage suitablefor the transducer (which can exceed 1kV). Controlling this voltage enables the power delivered to the transducer to be controlled. There are many strategies for controlling the equipment correctly. These very much depend on the the application. Our generators can be adapted to the different issues posed by the application.
- Conversion of the network frequency to the resonance frequencyof the transducer. The transducer supplies its optimal power when it is at its resonance (or antiresonance) frequency. The electronics should therefore be able to control the frequency of the transducer which the environment varies depending on the medium. There are many strategies for controlling the equipment correctly. These very much depend on the application.
Power generators can supply from a few W up to 5 kWatts. Power transducers for welding are often limited to 3kW – 4kW, during very short excitation periods. For applications in fluids, such as cleaning, the transducer power is around several dozen kW. In these applications, the transducers are mounted in groups.
Our current range of NexTgen equipment is entirely numeric. The control functionality has been developed to ensure superior performance efficiency. They are to be used with an Ethernet connection to enable the « remote control » functionality by means of which our customer care people can run diagnostics and updates from a distance.
Bibliographical Notes :
Power ultrasonics: Applications of high-intensity Ultrasound:
Gallego-Juarez and Karl F.Graff – WOODHEAD PUBLISHING
Handbook on Application of Ultrasound – Sonochemistry and Sustainability:
Dong Chen, Sanjay K. Sharma, Ackmez Mudhoo – CRC Press
Sonochemistry: From Basic Principles to Innovative Applications
Juan Carlos Colmenares, Gregory Chatel – Springer
Ultrasonics: Fundamentals, Technologies, and Applications, Third Edition:
Dale Ensminger, Leonard J.Bond