Note 1 to entry: When the electromechanical coupling factor is low, an approximate value of the frequency is given by the expression

${\displaystyle f_{\text{p}}=\frac{1}{2\pi \sqrt{L_1\frac{C_1{C}_0}{C_1+C_0}}}}$

where C₀ represents the shunt capacitance and L₁ and C₁ the motional inductance and the motional capacitance respectively. The expression can be derived from Figure 2 by letting R₁ = 0.

X

Figure 2 – Equivalent circuit of a piezoelectric vibrator (one-port resonator)

Note 2 to entry: This entry was numbered 561-02-11 in IEC 60050-561:1991.