一种新型传感器测试表面液滴

VIP免费

3.0 陈辉 2024-11-19 4 4 4.08MB 59 页 15积分

侵权投诉

Development of a sensor for the detection of droplets on technical surfaces

摘要

摘要摘要

摘要

随着社会的发展，人们越来越重视生活水平和环境的质量，于是各种各样用来检测

环境的传感器得到了很大的发展和应用。SAW （表面声波）由于其体积小和价格低的

优点，被大量的研发和生产，例如：气体传感器用来检测大气中的分子，液体传感器

用来检测溶液，还有压力传感器，温度传感器，湿度传感器和生物传感器等等。

表面声波是一种在固体表面上所传递的弹性能量波，其传递的能量百分之九十都集

中在表面以下一个波长的深度，并随着纵深距离呈现指数关系的衰减。其高能量聚集以

及低散射的特性，使得 SAW 元件有相当高的灵敏度条件。当 SAW 元件操作在更高频

率下，由于声波能量的聚集更接近表面，因此元件对表面的扰动将更趋灵敏。而

Rayleigh wave 的波动形式，是由纵波与剪波耦合而成，当晶体在震荡状态时，基板表

面上任一粒子在空间中的连续运动轨迹为椭圆形。

另外一方面，

SAW 在感测技术的发展上，也具有相当的潜力，因为 SAW 元件的敏感

度高，当晶体受到扰动影响，所产生的频率漂移都在数百 KHz 之间，利用目前的量测仪

器，可精确侦测到 1Hz 的微小变化量，另外，由于元件的操作范围广体积小，且制程上

易与半导体技术整合，适合大量生产，进而提升了 SAW 元件的实用性。良好的信噪比，

也有助在资料的取得分析上，避免后续许多繁杂的转换处里过程。

液滴检测在环境监测，工业用夜，质量保证方面起了很大的作用。液滴检测的重要

意义是它能够测试液体的物理和化学性质，比如密度，粘度，蒸发等等。SAW 还能够在

非压电材料的表面被激发并传播，如果有液体存在于传播路径上，将会影响表面声波的

幅度和传播速度。Lamb 波作为表面声波的一种，能够被 IDT（叉指电极）激发在一个

厚度为 1mm 到 2mm 的平板，并能够在液体的另一面传播。这是 Lamb 波的一个很大的优

点，因为它将液体跟叉指电极有效的隔离，起到了保护压电晶体的作用，并且这个技术

将用来检测液滴。

当表面声波在固液表面传播时，会发生模式转换，即从表面声波 SAW 转换为 Leaky

SAW，这时声波将以一定的角度Ө

传入液体。基于这种技术研制成了一种波导 wave

guide，它能够使声波在波导的内测表面多次反射传播后，最终被接收端的 IDT 转换为

电信号，此信号携带了液体的许多物理特性和化学特性，通常用于检测液体的浓度。

相比于在声波波导中传播，表面声波在液滴中的传播表现更为复杂。因为波导的反

射面相互平行，声波也将在两个表面以一个可以计算出的角度进行多次反射并传播。但

是对于一个液滴，当声波传至液滴时，虽然也发生模式转换，但由于它的表面与平板的

表面不平行，所以经过反射后传到液滴表面将发生复杂的反射，目前还没有完整的数学

模型对这个机理进行描述。并且声波还会在液体与平板的边界产生发散。

但是对于一定的衰减系数，重复性的实验已经证明了液滴大小和声波衰减呈现出线性

References

的关系。在测试的过程中，液滴的形变导致了接收信号幅度的变化。实验已经证明了三

个主要的影响液滴形变速度的因数：

（1）液滴的粘度：当用水滴测试，接收的声波信号幅度变化非常慢，因为水滴的粘度

较小，形变速度比较慢；但是对于油滴，由于它的粘度比水滴大，所以形变非

常快，接收的声波信号变化也很快，更快的达到稳定状态。

（2）平板的光滑度：如果将液滴滴在光滑的平板表面，液滴的形变也相对较慢；但是

滴在一个相对粗糙的平板表面，液滴形变非常迅速，能够很快达到稳定状态。

（3）液滴的蒸发：对比水滴跟液滴，实验表明水滴的形变速度不仅受到以上两个因素

的影响，还有蒸发的影响，因为水滴的蒸发导致水滴的形变在同种条件下表现更

快。

虽然实验过程存在液滴形变的影响，但是通过数据分析和处理，依然可以计算出液

滴的大小和声波衰减的线性关系。

另外两个实验验证了在测试液滴大小过程中温度和位置的效应：

（1）位置效应：上面的实验都是将液滴滴在平板的中央位置，如果改变液滴的滴定位

置，也会影响声波的衰减变化。两组实验结果表明，液滴滴在平板的中央位置是

最为合理的，因为接收到的声波信号幅度最大，所以敏感度最高。越靠近 IDT

的地方，声波衰减越大，接收到的声波信号幅度也就越小。

（2）温度效应：在相同的条件下改变液滴的温度也会产生不同的声波效应。两组实验

表明，随着液滴温度的降低，接收到的声波信号幅度也随之增大，说明温度越高

的液体对声波传播表现为更大的阻抗。

最后一个实验验证了用声波反射原理测定液滴位置的可行性。在第一章里将会介绍

表面声波传到液滴边界的时候，除了发生模式转化，还有很小的一部分声波将在液滴和

平板的交界处被反射。这个实验只用了一个 IDT 同时作为激发和接收的作用，但是要用

到一个辅助电路。如果直接将信号发生器和 IDT 连接，当信号激励完以后，信号发生器

直接耦合到地，反射回来的声波转化为电信号后，也将直接被信号发生器拉到地，这时

候就无法测出反射波。所以必须在信号发生器和 IDT 之间耦合一个 510Ω的电阻。然后

通过数据处理，消除 IDT 产生的衰减信号，就能够很好的测到反射信号。利用这个反

射信号的传播时间和传播速度就可以计算出液滴到 IDT 之间的距离。但是数据处理过程

比较复杂，需进一步探讨更好的办法并改进实验装置。

关键词

关键词关键词

关键词：

：：

：表面声波

表面声波表面声波

表面声波，

，，

，液滴

液滴液滴

液滴，

，，

，形变

形变形变

形变，

，，

，大小

大小大小

大小，

，，

，位置

位置位置

位置，

，，

，反射声波

反射声波反射声波

反射声波。

。。

。

Development of a sensor for the detection of droplets on technical surfaces

Abstract

Along with the advantage of living, people pay more attention to the management of quality

of environment and various sensors have been developed. Especially, SAW (surface acoustic

wave) sensors are developed in large quality because of its advantages of small volume and

low price. For examples, gas sensors applied in detecting modules in the air, liquid sensors

applied in detecting solutions, pressure sensors, temperature sensors humidity sensors ,

biology sensors and so on. On the other hand, SAW have large potential in development of

sensor technology for its high sensitivity. Additionally, because of its wide work range, small

volume, and being easily connected with semiconductor technology, suitable being produced

in large quantity, the applications of SAW device have been grown considerably. Nice S/R

ratio can also improve the acquisition and analysis of the data, avoiding many trivial

transforming process.

The droplet detection plays a very important part in environment monitoring, industrial use

of liquid, and ensuring the quality of life. The significant of droplet detection is for testing

many physical and chemical properties of liquid, such as density, viscosity, evaporation and

so on. It has been demonstrated that SAW can also be excited on non-piezoelectric surfaces

and that the presence of liquid droplets on the propagation path of SAW on such a surface

will influence the wave amplitude and velocity. Lamb wave, one sort of SAW, can propagate

on technical plates with a thickness of 1mm to 2mm, and which can excited by the IDT

(Inter-Digital Transducer) on the rear side isolated from liquid. It’s a big advantage for

protection of IDT, and this allows the development of a sensor for the detection of droplets

on technical surfaces.

Compared to propagation in waveguide made of parallel plate, acoustic wave behaves

much more complex when transmitting to a droplet. For a constant damping coefficient,

experiments carried out repeatedly have testified the linear relativity of the attenuation of

acoustic wave and the size of droplet. During the measurement, droplet deformation result in

variable amplitude of signal for a certain size of droplet. Additional experiments have been

carried out to discuss the effections of position and temperature for size detection. Futher

more, employing another plate mounted with only one IDT, the author have found out the

reflected acoustic wave by a droplet, which illustrate the practicability of position detection.

The whole course of signal transformation have been measured by oscilloscope and recorded

through the software programed by Excel VBA.

Key words: Lamb wave, droplet, deformation, size, position, reflect SAW

References

Content

1. Introduction............................................................................................................................................... 1

1.1. Purpose and significant............................................................................................................... 1

1.2. Lamb wave.................................................................................................................................... 2

1.3. Mode conversion.......................................................................................................................... 3

1.4.Attenuation of acoustic wave with droplet................................................................................. 4

2. Experiment mechanism and equipment.............................................................................................. 6

2.1. Sensor fabrication........................................................................................................................ 6

2.1.1. Sensor for droplet size detection.................................................................................... 7

2.1.2. Sensors for detecting the position by wave reflection................................................. 8

2.2. Signal generation and detection.............................................................................................. 11

2.2.1. Function generator.......................................................................................................... 12

2.2.2. Ocilloscope...................................................................................................................... 12

2.3. Facilitated apparatus................................................................................................................. 13

3. Measurement and result....................................................................................................................... 16

3.1. Test for the stability of measurement system......................................................................... 16

3.2. Droplet size detection................................................................................................................ 18

3.2.1. Droplet deformation course monitered by acoustic wave......................................... 19

3.2.1.1. Influence of droplet viscosity.............................................................................. 20

3.2.1.2. Influence of substrate smoothness................................................................... 22

3.2.1.3. Influence of evaporation..................................................................................... 25

3.2.2. Droplet size detection by amplitude............................................................................. 26

3.2.2.1. Size detection for water droplet......................................................................... 26

3.2.2.2. Size detection for oil droplet............................................................................... 28

3.2.3. Droplet size detection by duration................................................................................ 29

3.2.3.1. Propagation duration measurement for water droplet................................... 29

3.2.3.2. Propagation duration measurement for oil droplet......................................... 30

3.2.4. The effect of position on droplet size measurement.................................................. 32

3.2.5. Temperature effect on droplet size detection.............................................................. 34

3.2.6. Error analysis and sensor limitation............................................................................. 38

3.3. Detection of droplet position by reflected acoustic wave..................................................... 39

3.3.1. Detection by Multi-plexer............................................................................................... 40

3.3.2. Detection of reflected acoustic wave........................................................................... 41

4. Measurement software......................................................................................................................... 45

4.1. About excel VBA......................................................................................................................... 45

4.2. Introduction to active DSO........................................................................................................ 46

4.3. Measurement program.............................................................................................................. 47

4.3.1. Interface of the software................................................................................................ 47

4.3.2. Program flow................................................................................................................... 48

5. Conclusions and outlook...................................................................................................................... 52

Ackownledgements................................................................................................................................... 53

References.................................................................................................................................................. 53

References

1. Introduction

1.1. Purpose and significant

The technology of droplet detection can be easily applied on line, which is usually

used in environment protection, pharmaceutical industry, food and drink field, and any

others involving liquid detection.

For the present, quantity of researches about surface acoustic wave have been done,

including the wave exciting, propagation and energy transversion. Studies about the

wave propagation bearing liquid are also grow up quickly, and based on these theories, a

lot of technologies have been applied in real life[1-4]. Due to the strong attenuation of

Rayleigh waves in liquid, it’s very convenient employing such waves to detect the

properties of liquid[5-7]. However, the research about acoustic wave interacting with

sprinkle of liquid, say one droplet in microlitre, is deficient. Conventional studies of

droplet are mostly involving the ananlysis of deformation and generation [8-12].

Employing traditional methods, more apparatus should be put to use, and the data

represent weak relativity, raising the difficult for judgement. It’s very important to

explore and develop the method for droplet detection.

It is well known that surface acoustic wave (SAW) devices have the potential for the

detection of droplets via the mode conversion effect at the solid liquid interface.

Understanding the acoustic characteristic of droplet directly relate to the applications

and developments of the measurement technologies. By means of the characteristic

acoustic parameters, we can carry out the studies which involve the absoption and

reflection. Then the detection of acoustic parameters for droplet become the essential

question of detecting the droplet parameters. The author have introduced a new

approach, involving detection for the size and position of droplet. In this paper, the

mechanism about Lamb wave and loading with liquid will elaborated, then the author

introduced the sensor for measuring the size and position of droplet. With the help of

experiments, conclutions for interreaction of acoustic wave and droplets are discussed.

Development of a sensor for the detection of droplets on technical surfaces

1.2. Lamb wave

If the thickness of the solid substrate is ﬁnite and decreases to dimensions comparable

to or smaller than the wavelength of an SAW, the mode of propagation changes into

Lamb waves in the case of an elastically isotropic plate [13]. As an example, Lamb

wave devices have been realized from thin membranes of silicon nitride etched from a

supporting silicon waver and covered by a thin piezoelectric ZnO layer and metallic

interdigital electrodes for wave excitation and detection [14-19].

Figure 1.1. Schematic drawing of the dispersion relation and the surface displacements

of the lowest-order Lamb wave modes S

and A

on SiN plates in comparison with the

Rayleigh wave velocity [20].

In contrast to Rayleigh waves, Lamb waves, which form two sets of modes exhibiting

symmetric or antisymmetric displacements with respect to the neutral plane of the plate,

respectively, are not free of dispersion. For thicknesses well below the wavelength,

for example not more than a few per cent of the wavelength of the bulk transverse wave

in the substrate, only the two lowest-order symmetric and antisymmetric modes can be

excited, whose dispersion relation is substantially different [21] (ﬁgure 1.1).

Whereas the propagation velocity of the symmetric mode increases with decreasing

thickness and approaches a value larger than the velocity of a Rayleigh wave, the

velocity of the antisymmetric mode monotonically decreases towards zero with

decreasing thickness.

文档加载中……请稍候！
如果长时间未打开，您也可以点击刷新试试。

下载文档到电脑，查找使用更方便

15 积分 4人已下载

立即下载 VIP免费下载

摘要：

Developmentofasensorforthedetectionofdropletsontechnicalsurfaces2摘要摘要摘要摘要随着社会的发展，人们越来越重视生活水平和环境的质量，于是各种各样用来检测环境的传感器得到了很大的发展和应用。SAW（表面声波）由于其体积小和价格低的优点，被大量的研发和生产，例如：气体传感器用来检测大气中的分子，液体传感器用来检测溶液，还有压力传感器，温度传感器，湿度传感器和生物传感器等等。表面声波是一种在固体表面上所传递的弹性能量波，其传递的能量百分之九十都集中在表面以下一个波长的深度，并随着纵深距离呈现指数关系的衰减。其高能量聚集以及低散射的特性...

展开>> 收起<<

一种新型传感器测试表面液滴.pdf

共59页,预览6页

还剩页未读，继续阅读

一种新型传感器测试表面液滴

相关推荐

开通VIP享超值会员特权

作者详情

相关内容

推荐作者

热门标签

举报选择: