Effect of 21.R-C filter on the slow transient half sine input waveform represents a slow half sine pulse input (feature many mechanical shock signal), although most of the high frequency components did not change, but its output waveform has a serious distortion, clearly shows the positive and negative two migration, while the input waveform is unipolar.
1) input waveform
2) input spectrum
3) filter characteristics
4) output spectrum
5) output waveform
Fig. 22., the influence of R-C filter on the transient input waveform of slow sawtooth wave indicates a sawtooth wave, which has a slow rising front and a sudden trailing edge. Many piezoelectric film switches are used to detect this mechanical process. From the output waveform, the front edge almost doesn't exist, but the rear edge of the drop almost keeps its original amplitude. The polarity of output pulse is relative to the input waveform.
1) input waveform
2) input spectrum
3) filter characteristics
4) output spectrum
5) output waveform
temperature effect
Many characteristics of a piezoelectric film vary with the excitation frequency and temperature. This characteristic is reversible and repeatable with the change of frequency or temperature.
In addition, the permanent decay of the PVDF piezo strain constant d33 can be seen from figure 23 at 70 C for a long time exposed to an elevated temperature.
When the stable temperature is reached, the properties of the material remain constant over time. The piezoelectric film can be annealed to a specific working (or maximum storage) temperature to achieve long-term stability in high temperature applications. Figure 24 shows the effect of PVDF reversible temperature on the coefficient of d31 and G31.
The effects of the temperature on the dielectric constant (epsilon / epsilon) and dissipation factor (tan delta E) of a polymer piezoelectric film are given in Figure 25a and 25B.
At very low (cryogenic) temperatures, the piezoelectric film has shown excellent sensor characteristics.
Diagram 25A, relation diagram of dielectric loss tangent and temperature 25B, relation between dielectric constant and temperature
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