Electrical and electromechanical characterization methods for piezo-, ferro- and dielectrics

Various methods are used to characterize piezoelectric properties. The piezoelectric charge constants d₃₃ and d₃₁ can be determined quasistatically using a Berlincourt meter. For this purpose, a low-frequency load is applied to the piezo material and the electrical response is measured. To determine a complete set of linear piezoelectric material parameters, electrical impedance measurements are carried out on various disk- and cuboid-shaped test specimens in accordance with DIN 50324-2. Depending on the problem, various other methods such as acoustic time of flight measurements or laser vibrometric measurements are also used to characterize piezoelectric material properties.

• d₃₃-measurement up to 4000 pC/N, d₃₁-measurement up to 400 pC/N
• Impedance spectroscopy/measurement and evaluation according to DIN 50324-2
• Acoustic time of flight measurements
• Laser vibrometry

Piezoelectric transducers can be electrically/mechanically excited in various ways and the mechanical/electrical response measured. For an initial characterization, electrical impedance spectroscopy has proven to be the method of choice. However, more complex characterizations can also be carried out using laser vibrometers, for example. Spatially resolved sound field measurements in a water bath are also used to characterize ultrasonic transducers.

• Impedance spectroscopy
• Laser vibrometry
• Acoustic characterization (sound field measurement) with 5-axis measuring system in a water bath

The electrical volume and surface resistance of solid insulating materials are usually measured on suitably shaped test specimens (e.g. disk specimens). Electrodes are applied to these, and an electrical voltage of up to 1000 V DC is applied across the electrodes during the resistance measurement. The electrical resistance is determined from a simultaneous high-precision current measurement.

• Measurement of the electrical volume and surface resistance (1 MOhm to 200 TOhm at temperatures from -50 °C to 1000 °C, at room temperature up to > 1 POhm)
• Measurements according to DIN EN 62631

The dielectric strength of dielectric materials is usually measured on suitably shaped test specimens (e.g. disk specimens). Depending on the task, film electrodes are applied to the samples, and the latter are placed between two solid electrodes. An increasing electrical voltage (DC or AC) is applied to the electrodes until dielectric breakdown occurs, which manifests itself in the form of a sudden current flow. The highest electrical voltage reached is the breakdown voltage, from which the (nominal) dielectric strength is then determined via the geometry of the test specimen. In most cases, however, the dielectric strength depends on the specific setup (e.g. the thickness of a disk sample), so that it can also be useful to measure directly on the component and determine the corresponding component characteristics with regard to the dielectric strength.

• Measurement of dielectric strength DC (up to 100 kV) and AC (up to 12 kV)
• Measurements according to the standards ASTM D149, ASTM D3755 and DIN EN 60243
• Model-based assessment of electrical component failure due to electrical breakdown

The measurement of the complex electrical impedance or permittivity and loss angle is carried out on suitably shaped test specimens or components. Electrodes are usually applied beforehand in order to be able to apply harmonic alternating voltage signals to the test specimens. The current response is measured at different measurement frequencies and the complex electrical impedance is determined. On this basis, the permittivity and the loss angle are calculated.

• Measurement of complex electrical impedance, permittivity and loss angle in the frequency range from 20 Hz to 1 GHz (measurements at higher frequencies can be offered in cooperation with the Group Microsystems, LTCC and HTCC)
• Measurement according to the standards ASTM D150, DIN EN 62631-2-1 and DIN EN 62631-2-2

Laser Doppler vibrometers can be used to measure mechanical vibrations of test specimens and components on their surface without contact using a laser beam. In addition to point measurements, the vibration fields on extended surfaces can also be characterized and visualized. This method can be used, for example, to identify material parameters, characterize ultrasonic transducers and validate models.

• Point and area measurements of the vibration behavior of surfaces (spatially resolved vibration velocity and spatially resolved vibration displacement) and interpretation of the results

Charge and displacement measurements on ferroelectric and other test specimens under arbitrary transient large signal electrical excitation are offered. The temperature range from -50 °C to 250 °C is typically covered (extended temperature ranges are possible depending on the problem). High-voltage amplifiers up to 100 kV DC are available for the poling of ferroelectrics.

• Hysteresis measurement (charge and displacement or polarization and strain for material samples)
• Determination of tangent and secant capacitances in the large signal range
• Poling up to 100 kV, pulse poling

Both, a water bath and an air coupled acoustic chamber are available for acoustic characterization. A five-axis positioning system can be used to precisely position hydrophones and reflectors, for example. Depending on the problem, pulse-echo or transmitter-receiver arrangements can be implemented. A typical application for a transmitter-receiver arrangement is the characterization of the emitted three-dimensional sound pressure field of ultrasonic transducers in a water bath. For this purpose, sound is emitted from the transducer and received by means of a hydrophone. The hydrophone is moved step by step in space in order to capture the entire spatial sound field.

• Sound field measurements in water and in air with transient (pulse-shaped) or harmonic excitation
• Measurements of acoustic impedances, sound velocities and attenuation properties
• Characterization of the sound field according to DIN EN 61689

Laser Doppler vibrometers can be used to measure mechanical vibrations of test specimens and components on their surface without contact using a laser beam. In addition to point measurements, the vibration fields on extended surfaces can also be characterized and visualized. This method can be used, for example, to identify material parameters, characterize ultrasonic transducers and validate models.

• Concept, design and implementation of life tests and highly accelerated life tests (HALT)
• Application of lifetime prediction models, determination of Weibull parameters and failure probabilities
• Problem-adapted analysis of failure mechanisms

One of our main areas of work is the development of customer-specific measurement setups, particularly for electrical and electromechanical characterization. We offer our know-how and develop a test bench for your measurement task. We have access to a wide range of measuring equipment and our own mechanical workshop. Please do not hesitate to contact us!

Exampels

• Electrocaloric test bench
• Electrical characterization of thermally sprayed coatings