Liquid-Level Sensing by Trapped-Energy-Mode Thickness Vibration

Abstract

A new method is presented for detecting a small-scale variation in liquid level using an energy-trapping phenomenon in piezoelectric thickness-mode vibrators. In a piezoelectric plate operating in a trapped-energy mode, an evanescent field is created in the surrounding region of the plate. When this region is dipped in a liquid, a small leakage of vibration energy occurs. The amount of leakage varies depending on how deep the surrounding region is in the liquid. Therefore, small variations in liquid level are detected by observing the changes in the electric characteristics of the vibrators, such as quality factor and the electric conductance G. Preliminary experiments have shown that almost linear variations in G against dipping depth can be obtained within a few millimeter range.

Liquid-level sensing by trapped-energy mode of backward-wave-type thickness vibration

“…Figure 6 shows the characteristics obtained by resonator C (conventional trapped-energy resonator) at the antiresonance frequency. The variation is almost the same as that obtained at the resonance described in the former report [2], [3]. Figure 7 shows the results obtained by resonator B with a wider unelectroded gap.…”

“…III. EXPERIMENS [2], [3] Thickness-poled PbTiO 3 plates of 30 mm diameter and 1 mm thickness (Fuji Ceramics M-6) were employed as vibrator materials because their fundamental thickness-extensional vibration is the backward-wave mode. Experiments were carried out for the following two resonators with different electrode geometries: one with an inner electrode of 6 mm diameter and an unelectroded gap of 1 mm width (designated hereafter as "resonator A"), and the other with an inner electrode of 4 mm diameter and an unelectroded gap of 2 mm width ("resonator B").…”

“…The well-known pulse-echo method is inadequate for measurement in a very small distance range. As an alternative to the pulse-echo method, the authors have presented a new technique that employs a piezoelectric thickness vibrator operating in a trapped-energy mode [1] for detecting a small-scale variation in liquid level [2], [3]. The evanescent field created in the trapped-energy-mode resonator is effectively used as a range finder in a small distance range, such as that demonstrated in the authors' previous study [4].…”

Modeling and analysis of a liquid-level sensor utilizing an evanescent field of a trapped-energy vibrator

“…1(a) [2], [3]. A piezoelectric plate is supported vertically by clamping its top fringe and dipped in a liquid of which the surface level is measured.…”

“…A novel approach for detecting a small-scale variation in liquid level that employs a piezoelectric thickness vibrator operating in a trapped-energy mode [1] has been studied by the authors [2]- [6]. In a trapped-energy resonator, an evanescent field is created in the surrounding region in which the vibration amplitude decays exponentially.…”