Identification of Geometric Parameters Influencing the Impedance Sensitivity of Piezoelectric Mass Sensors

For resonant mass sensors, a frequency sweeping procedure is usually required to identify the frequency shift in a relative frequency range, which is not suitable for detecting incremental mass. The impedance detection method can measure mass at a fixed frequency. To further explore such sensing mechanism, the main geometrical parameters influencing the impedance sensitivity have been carefully analyzed considering the electro-mechanical coupling effects, and a series of design rules have been proposed for improving sensitivity, e.g. increasing the cantilever length and piezoelectric thickness, which is contrary to the traditional method of minimizing the geometric size for frequency based sensors. Three macro-sized sensors with 21.0 mm, 26.0 mm and 30.0mm long cantilevers are fabricated, and the measured impedance sensitivities are
$212.7\Omega $
/mg,
$514.8\Omega $
/mg and
$737.4\Omega $
/mg that are increasing with the cantilever length, thus validating the design rules on cantilever length. However, the frequency sensitivities are 14.0 Hz/mg, 9.2 Hz/mg, and 7.2 Hz/mg that are decreasing with the cantilever length. Furthermore, the impedance sensitivity is much higher than the frequency sensitivity, and the design map of the sensor is presented as an overall guideline for structure optimization.