Simulation & Measurement
Modelling and simulation of piezoelectric systems
Beside analytical calculations and simplified numerical models, we use the finite element method (FEM) for the frequency-accurate design of ultrasonic resonators. In the modeling, we are able to represent very precisely:
- the „active“ piezoelectric material behavior (dielectricity, piezoelectricity, mass and compliance)
- the directional dependence of the material properties (anisotropy)
- the change of polarization direction in stack actuators
- material-specific damping properties
- the resonance characteristics of piezoelectric transducers
- piezoelectric actuators and sensors
Laser measurement of ultrasonic vibrations
Using our laser measurement technology, we are able to analyse dynamic processes with high precision and contactless, without affecting the sensitive behaviour of the sensors, actuators, or ultrasonic transducers. The use of this special measurement technology allows for example:
- the highly accurate visualisation of vibration distributions in the µm amplitude range
- the error analysis in our customers’ products (e.g. spurious resonances)
- the analysis of tolerance-related frequency and amplitude variations in production
- the validation of results of electromechanical simulations (FEM) by measurements
- the optimization of sensitive structural oscillators
Thermal simulation and temperature measurement
The temperature of piezoelectric ultrasonic transducers influences their characteristic properties. If temperatures are too high due to environmental influences or self-heating, this can lead to excessive aging of the system and thus premature failure. In addition, temperature-related frequency shifts can cause problems with the electrical control. We therefore consider the influence of temperature both in the model and experimentally in order to define suitable operating parameters and limits.
- Modelling of self-heating of ultrasonic converters in the design phase
- Experimental analysis of the operating point-dependent heating of ultrasonic converters by precise temperature measurements during operation
- Definition of design changes to avoid excessive heat generation
Here we show an example of electromechanical thermal simulation.
Thermomechanical simulation of piezoelectric converters
By application of our comprehensive simulation options, the electromechanical behavior can be calculated as a first step. The results obtained include:
- The values of the resonance and anti-resonance frequencies and associated impedance values
- Characteristic electrical parameters for the electrical control
- The amplitude distribution of the deflection for a given electrical excitation
- The distribution of mechanical stresses to optimize critically stressed components
- Influences of manufacturing inaccuracies on the frequency position or power requirement
Thermal simulation at the target amplitude in resonance
Based on the electromechanical results, thermal simulations can be carried out:
- The temperature distribution in the piezoelectric converter for the previously investigated target amplitude in resonance
- The power requirement integrally and for individual subcomponents (e.g. the piezo actuator)
- The distribution of heat sources due to internal damping
- Amplitude dependences of power demand and temperature
Measurements for validation
Using laser vibrometry and non-contact thermal sensors, we assess:
- The accuracy of our simulation results
- Amplitude dependencies of electromechanical and thermal material properties
- Numerical values of the electromechanical parameters and amplitude dependencies
- The long-term load capacity of the systems (endurance tests for Wöhler diagrams)
Further analyses
By combining different multiphysics simulations and measurements, many complex questions can be investigated very effectively already in the design phase:
- The dependence of the static bias voltage distribution in the piezo actuator on the temperature
- The temperature-dependent frequency drift (due to thermal expansion and material softening)
- The durability of metals, polymers and adhesives
- The thermomechanical behavior of lead-free piezoceramics compared to PZT ceramics
- Nonlinearities of piezoceramics and metals (damping and compliance behavior)
Application tests and construction of test benches
After simulating ultrasound systems, comprehensive and in-depth experimental analysis of the systems is of crucial importance in the development process in order to validate model results and to be able to investigate influences that are difficult to represent in the model. To test new ultrasound processes or to test ultrasound converters, sonotrodes and tools, we can rely on extensive measurement equipment as well as many years of experience and creativity in setting up measurement environments. In this context, we can offer the following services, among others:
- Short-term implementation of application tests for various ultrasound processes with existing ultrasound systems (various frequencies and power classes)
- Comprehensive characterisation of processes by a variety of measurement methods (laser measurement, precise temperature measurement, simultaneous measurement of electrical and mechanical quantities, process-accompanying measurements)
- Development and construction of suitable test benches for testing ultrasonic systems (e.g. defined loads, applications in water,…)
Material fatigue tests (ultrasonic Wöhler curves)
To record Wöhler curves, measurements with load cycle numbers in the three-digit million range are necessary. By using ultrasonic frequencies, high cycle numbers can be achieved within an hour, which would otherwise require weeks of testing. With existing ultrasonic actuators, our know-how for dimensioning suitable ultrasonic samples and our ATHENA ultrasonic generator, we have the perfect test environment to test your materials for fatigue strength.
Sound simulation, ultrasonic acoustics and cavitation measurement
There is always an interaction between the ultrasonic transducer and the sound field it generates. In particular, in processes involving liquids, the adjacent fluid influences the characteristics of the ultrasonic transducer. In other applications, the nature of the sound field generated is crucial for the application (distance sensors) and should be influenced by design measures.
We use the finite element method (FEM) to calculate sound fields in the ultrasonic range and their interaction with the sound generator. We also have measurement methods for the experimental analysis of ultrasonic acoustics, even in cavitations-based processes.
- FEM simulation of sound fields and their interaction with the ultrasonic transducer (fluid-structure interaction)
- Sound measurements in air and liquids in the ultrasonic range (ultrasonic microphone and hydrophone)
- Experimental analysis of cavitation activity (acoustic measurements, foil tests, sonoluminescence, cavitation noise)
- Analysis of damping effects (e.g. due to non-reflective edges, due to fluid viscosity or due to cavitation)
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