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Electromechanical and acoustical characterization of piezoceramic elements and NDT ultrasound transducers by using different types of excitation signals

In the construction phase of ultrasound NDT transducers the piezoceramic elements are usually characterized electromechanically by using vector/network analyzers and frequency sweeping signals around resonance frequency of interest with low level continuous electrical excitation signals. In the real operating conditions the NDT ultrasound transducer can be excited by using pulse (unipolar, bipolar, spike) or short burst signals with different amplitudes up to 400 V depending on the piezoceramic element thickness, pulse type and its duration. In this paper, different types of excitation signals with different excitation levels are used for characterization of piezoceramic elements and assembled NDT transducers. The electromechanical and acoustical characterization results are compared regarding the nonlinear effects at resonance frequencies and changed thermodynamical conditions. In addition, the pulse- echo responses in time and frequency domain of one NDT transducer is analyzed by using different types of excitation signals (unipolar, bipolar and bipolar asymmetric). It is observed that electromechanical characterization by using different types of excitation signals and their levels on the DUT (piezoceramic element or NDT transducers) gives different results for the impedance/admittance magnitude at resonances. When the impulse excitation is used the electrical impedance magnitude at resonance is increased compared to the measurements with impedance spectroscopy method. Also, when bipolar pulse is used as excitation the response from the same considered object in pulse-echo setup testing is with higher amplitude in comparison with unipolar pulse excitation. The losses at resonance are increased due to harder ferroelectric domain orientation switching when pulse excitation is used in comparison with continuous signals excitation

piezoceramic element ; non-destructive testing ultrasound transducer ; electromechanical characterization ; excitation signal types ; pulse-echo response duration and transducer sensitivity

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