压电谐振传感器在流体密度测量中的研究

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摘要

流体（气体或者液体）密度测量在日常生活和工作中会常常遇到。传统密度测量

方法主要是根据密度公式 =m/V 或阿基米德原理来实现的，这两种测量方法要么

花费时间，要么测量精度较低。因此，近年来，人们提出了很多可快捷准确进行

密度测量的新方法，利用谐振式压电传感器来实现液体或气体密度的快捷及高精

度测量的方法就是其中之一。

本文研究的谐振式传感器采用玻璃作为谐振片，通过分别粘贴在薄玻璃片两

面的具有高压电常数、柔韧性好、易于加工的聚偏氟乙烯薄膜（PVDF），实现谐

振传感器的激发和测量。

本文，首先制作了谐振式压电传感器，并组建了谐振测试系统；其次，通过

在空气中测量谐振片的谐振频率，然后；将测得的频率与理论计算的谐振频率进

行比较，以确定谐振式传感器可满足使用；接下来，在谐振片上放置面粉颗粒，

并测量谐振频率变化，以确定传感器的灵敏度；最后通过分别测量谐振传感器在

不同气体压强下、不同油中以及不同液体深度下的谐振频率变化，得出谐振频率

和气体、液体压强的关系。

实验结果证明，PVDF 制成的谐振式传感器具有较高的灵敏度和精度，既可以

测量气体的密度也可以测量液体的密度。

关键词：气体液体密度测量谐振传感器 PVDF 压电效应

Abstract

Density measurement of fluid is commonly used in our daily life. Traditional

measurement mainly depends on the density formula ρ= m/V or Archimedes’ law.

These two methods either take a lot of time or can not get a high accuracy. So, in recent

years, many new quick and precise ways has been developed, one of which makes use

of mechanical resonator sensor based on piezoelectric effect. This is a very fast

measurement for fluids’ density with high accuracy.

In this paper, a very thin glass is used for vibration plate with two thin PVDF

(Polyvinylidene fluoride) films glued on both sides of the glass as excitation and

detection of the sensor. PVDF has very high piezoelectric coefficient and nice flexibility.

Moreover, it is very soft, easily to be made into all kinds of shapes according to the

applications.

First of all, a mechanical resonator sensor is produced. And then the resonance

measurement system is built. Second, do a measurement in the air to get the resonance

frequency. Calculate the theoretical value of the resonance frequency. Make a

comparison between the measured value and theoretical one to decide whether this

sensor can be used or not. Third, put some small flour particles on the vibration plate

and measure the variation of resonance frequency to confirm the sensitivity. At last,

some measurement under different pressure and in different oils as well as the different

depth below the oil level can be done to work out the relationship between the

resonance frequency and the density of gas or liquid.

The output of this experiment has proved that mechanical resonator sensor made of

PVDF films has very high sensitivity and accuracy. This sensor can not only used for

the density measurement of gas, but also for the liquid.

Key words: gas, liquid, density measurement, resonator sensor, PVDF,

piezoelectric effect

Content

摘要

Abstract

1. Introduction……………………………………………………………………….......1

1.1 Traditional measurement for the density of fluid…………………..……………. 1

1.2 Mechanical resonator sensor…………………………………………………...... 1

1.3 My Work……………………………………………………………….…………2

2 Piezoelectricity and PVDF……………………………………………………….........3

2.1 Piezoelectricity............................................................................................…........3

2.1.1 Brief introduction to the piezoelectricity……………………………………3

2.1.2 Explanation about the piezoelectricity……………………………………...3

2.1.3 Piezoelectric material…………………….……………….…….…………..7

2.2 Polyvinylidene fluoride (PVDF)……………………………………….….……...7

2.2.1 Brief introduction to PVDF……………………………………………........7

2.2.2 PVDF piezoelectric equations and working principle ………………….......8

2.2.3 Characteristics of PVDF……………………………………………...……9

3 Mechanical vibration and resonance…………………………………………...…….10

3.1 One degree of free system with damp ing………………………………………10

3.2 One degree of free system with harmonic motion……………………………...12

3.3 Quality factor……………………………………………………………….......13

4 Resonator sensor construction……………………………………………………......15

4.1 Idea about the sensor…………………………………………………………...15

4.2 Sensor Construction…………………………………………………………….15

4.3 working principle……………………………………………………………….17

4.4 Measurement system…………………………………………………………...18

4.5 Measurement content…………………………………………………………...18

5 Experiment result and analysis……………………………………………………….19

5.1 Measurement in the air…………………………………………………………19

5.2 Movement of small particles on the sensor…………………………………….21

5.3 Measurement in different pressure……………………………………………..23

5.4 Measurement in the cooking oils……………………………………………….25

5.5 Measurement in the mobilgear oil……………………………………………...27

5.6 Measurement in the mixture of gas and liquid…………………………………31

6 Conclusion and discussion……………………………………………………………34

Reference……………………………………………………………………………….35

在读期间公开发表的论文和承担科研项目及取得成果…………………………….37

Acknowledgements…………………………………………………………………….38

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摘要：

摘要流体（气体或者液体）密度测量在日常生活和工作中会常常遇到。传统密度测量方法主要是根据密度公式=m/V或阿基米德原理来实现的，这两种测量方法要么花费时间，要么测量精度较低。因此，近年来，人们提出了很多可快捷准确进行密度测量的新方法，利用谐振式压电传感器来实现液体或气体密度的快捷及高精度测量的方法就是其中之一。本文研究的谐振式传感器采用玻璃作为谐振片，通过分别粘贴在薄玻璃片两面的具有高压电常数、柔韧性好、易于加工的聚偏氟乙烯薄膜（PVDF），实现谐振传感器的激发和测量。本文，首先制作了谐振式压电传感器，并组建了谐振测试系统；其次，通过在空气中测量谐振片的谐振频率，然后；将测得的频率与理论计算的...

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