Instrumentation & Measurement Magazine 26-4 - 49

Improvement of the Relative
Sensitivity for Obtaining a High
Performance Piezoelectric Sensor
Zine Ghemari, Salah Belkhiri, and Salah Saad
T
he purpose of a piezoelectric sensor is to measure the
vibratory movements of structures by the direct effect
of the piezoelectric material. In this paper, the operating
principle of the piezoelectric sensor is defined in detail,
and it is translated as a mathematical model (i.e., the modeling
of this type of sensors). This developed model relates the
accelerometer electrical parameters with their mechanical parameters,
and simulation of this model allows the appropriate
sensor damping rate to be chosen which minimizes error and
improves accuracy and sensitivity. The proposal of a new relation
links the relative frequency with the piezoelectric sensor
natural frequency that makes it possible to minimize the resonance
phenomenon effect, to facilitate the suitable choice of the
sensor and to protect it.
Preface
Rotating machines are widely present in many industrial installations.
The failures that can be encountered on a rotating
machine are numerous. Given the importance of these rotating
machines in certain devices, it is necessary investigate their
mechanical condition, in order to be able to take the appropriate
decisions about their mechanical condition at the right
time [1], [2].
One of the means of monitoring the mechanical state of a rotating
machine is the collection and analysis of its vibrations.
Vibrations are an integral part of our universe [3]. The slightest
movement causes vibrations of varying amplitude and duration,
from the slow oscillation of a suspension bridge excited
by the wind to the shock generated on landing by an airplane,
including the noise of the engines of our cars [4]. This vibratory
environment is felt by all of the equipment we use in everyday
life and can cause malfunctions going as far as the destruction
of the material in question [5], [6]. The moving parts generate
vibrations, and over time these vibrations degrade these parts.
The use of vibration analysis makes it possible to detect their
fatigue and faults at an early stage [7]-[10].
In recent years, piezoelectric sensors have played a much
different role from their conventional pressure sensing functions
for test and measurement applications [11]-[14]. Many
June 2023
works have been carried out to optimize the electrical performances
of the piezoelectric sensor [15]-[19].
To improve the relative sensitivity, the piezoelectric accelerometer
is modeled in this work to extract a relationship of the
measurement error as a function of the damping rate on the
one hand and the relative sensitivity as a function of the frequency
ratio and the damping rate on the other hand. The first
relationship makes it possible to choose an appropriate value
of the damping rate, and the second aims to improve the sensitivity
of the accelerometer. The first part of the paper presents
the piezoelectricity technology since our choice of the accelerometer
is the accelerometer with piezoelectric detection. In the
second section we illustrate the piezoelectric sensor application
in structural health monitoring. The third section is devoted to
the modeling of the piezoelectric accelerometer to develop new
models that facilitate the optimization of the accuracy and the
relative sensitivity of this type of sensor. We describe the simulation
of the developed models and the interpretation of the
results obtained. Finally, the effect of the resonance phenomenon
on the accelerometer operation is shown.
Piezoelectric Technology
A piezoelectric material is a material across which an electric
field forms when a force is applied to its ends. Likewise, if a
voltage is applied across the same material, it deforms. The
first effect is called the direct piezoelectric effect and the second
inverse piezoelectric effect (Fig. 1). These effects were discovered
by Pierre and Jacques Curie in 1880 [20].
Piezoelectric materials are particularly numerous. The best
known is probably quartz, still used today in watches to generate
clock pulses. But it is synthetic ceramics, PZTs, which are
currently most widely used in industry.
Many natural crystals exhibit piezoelectric properties. We
can cite quartz, topaz, tourmaline, berlinite (AlPO4) or sugar. In
practice, the materials used for the manufacture of the various
systems are synthetic materials which can be classified according
to their crystallographic structure or their chemical composition.
The core of a piezoelectric accelerometer is composed
of a lamella of piezoelectric material, usually an artificially
IEEE Instrumentation & Measurement Magazine
1094-6969/23/$25.00©2023IEEE
49
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