Piezoelectric resonance electromechanical coupling factor

Fig. 11. (a) Equivalent series resistance of quartz and langasite single crystals as a function of resonator vibration modes, (b) electromechanical coupling factor of langasite series as a function of piezoelectric constant. 

In general, elastic coefficients, piezoelectric constants and electromechanical coupling factors are determined by the transportation line method, which was recommended as IRE standard (1957, 1958, 1961). This method is a dynamic method, because the measurement sample is made as a vibrator and measiued in a vibration state at a frequency near its intrinsic resonance frequency. When a small AC voltage is applied to a piezoelectric sample (poled single crystal, or poled bulk ceramic) having a pair of electrodes on opposite surfaces, the sample vibrates at a frequency near its resonance frequency, fr. Figure 22-12 shows a sample inserted in a transportation network. By changing the... 

The value of tand for PVDF is typically 0.1. This is 10 times greater than the value of 0.01 for ceramics (PZT 5). As discussed earlier, it is this high mechanical loss or damping that prevents measurement of the electromechanical coupling factors using the piezoelectric resonance method. 

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