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Using an immersion surface acoustic wave sensor for liquid testing
Pavol Koštial, Jaroslava Machalíková, František Černobila
To cite this version:
Pavol Koštial, Jaroslava Machalíková, František Černobila. Using an immersion surface acoustic wave sensor for liquid testing. Journal de Physique III, EDP Sciences, 1993, 3 (2), pp.355-362.
�10.1051/jp3:1993103�. �jpa-00248925�
Classification Physics Abstracts
06.60 43.35 62.60 62.80
Using an immersion surface acoustic wave sensor for liquid testing
Pavol Koltial (I), Jaroslava Machalikov6 (2) and Frantilek tlemobila (~)
(1) Department of Physics, Technical University of Transport and Communications, Vel'kf Diel, 01026 2ilina, Slovak Republic
(2) Department of Mechanical Technology, Technical University of Transport and Communi- cations, Vel'kf Diel, 01026 2ilina, Slovak Republic
(3) Department of Physics, Technical University of Transport and Communications, Vel'kf Diel, 01026 2ilina, Slovak Republic
(Received 25 February 1992, accepted 23 October 1992)
Abstract. The measurements of the SAW attenuation in different liquids are presented. A
specific immersion SAW sensor has been used for the liquid testing. The dependencies of the SAW attenuation as a function of : a) the viscosity ; b) the degree of the dissociation and c) a molecular structural arrangement, is discussed.
Introduction.
A large interest was recently devoted to the construction of surface wave acoustic microsensors. They are used for the measurement of a wide range of physical and chemical values.
The overview of the SAW sensor utilization is given in [I]. Oscillator techniques are used in the majority of SAW sensors [2]. A relatively smaller interest is devoted to the measurement of the SAW attenuation [3].
It is well known that the interaction of ultrasound with the liquid can give very important
information conceming the molecular liquid structure [4]. A physical parameter, very sensitive to these changes, is ultrasonic attenuation [5]. It seems to be reasonable to use the SAW
attenuation changes for the same type of experiments because of specific features of SAW
propagation, when SAW is in contact with liquid. Theoretical aspects of the SAW interaction with a liquid have been studied in [6]. Experimental evidence of a « square root » dependence
of the SAW attenuation versus viscosity is presented in [7].
In our work we deal with the utilization of immersion SAW sensor for the diagnostic of various liquids. The physical principles of the liquid sensor action are based on the following assumptions.
356 JOURNAL DE PHYSIQUE III N° 2 All types of surface waves in crystals are shear waves. That means that the particle displacement in the wave front has two or three components. In many cases, one component is perpendicular to the surface, and one or two « in-plane » components are presented. These
specific wave motions are the reason for energy losses, if SAW is in contact with a liquid. The
perpendicular component of the wave motion provokes the conversion of one part of the SAW energy to the compressional waves generated into a liquid volume, which is in the contact with the crystal surface.
The second reason for the SAW energy losses is connected with the « viscous coupling »
due to the fact that the SAW velocity along the crystal surface exceeds the velocity of ultrasound in the liquid.
The following relation describing the insertion losses due to « viscous coupling » has been derived for the leaky SAW [7].
L
=
A w~~~ I. (T. s)'~~ [dB], (1)
where A is the constant, I is the wave-liquid interaction length, w is the angular frequency, T is the viscosity.
For the horizontally polarized shear waves Ii, it has been shown that the SAW attenuation of ultrasonic energy is proportional to the square root of viscosity. The layer thickness of the
liquid which vibrates at the interaction with a SAW can be expressed by the relation [Ii d
= (2 T/s. w )'~~ (2)
The sense of used symbols is the same as above.
From the phenomenological theory of the ultrasound attenuation in liquids there is the well known relation describing the shear wave attenuation in liquids and gasses which has a form [8]
a = (2 T/s w )'~~ (3)
The dependence of the ultrasound attenuation on the square root of the viscosity is also present here.
Excluding numerical factors and the power of frequency dependencies, it seems to be natural, that the ultrasonic attenuation as a function of the viscosity has a « square root » form for the shear type of wave motion.
Experimental procedure.
The experimental arrangement is illustrated in figure I. The interdigital transducer (IDT) has been prepared on the polished surface of YZ LiNbO~. The opposite side of the same SAW-line has been plunged in to the investigated liquid. The Matec model 7700 has been used as a
generator and receiver respectively. Matec model 2470 A has been used for the measurements of the SAW attenuation. The advantage of such an experimental arrangement is in the very
easy application of the measured liquid to the sensor. The proper level of the SAW attenuation has been set by the depth of sensor immersion to the studied liquid. Because the SAW
attenuation depends on the immersion depth, the constant depth of a sensor draft has been used for the comparative measurements of the attenuation. The power value has been set constant
too. The temperature has been stabilized.
The measurements of the viscosity have been made at the same temperature with rotating
viscosimeter Rheotest 2.
absorber
MATEC
7700 2470 A
j~-~ tested
Fig. I. Experimental arrangement, sensor with one IDT plunged in the tested liquid.
Experimental results and discussion.
In our experiments we have tried to verify the « square root» dependence of the SAW attenuation mentioned above. In other experiments we have studied the relaxation phenomena
and dissociation degree in some water solutions of acids. The dependence of the SAW
attenuation versus the square root of the viscosity has been investigated on the water-glycerol
solution of different concentrations. The linear character of the dependence is clearly seen in the figure 2. This measurement has served as a test of used sensor and support for theoretical
assumptions mentioned above. We have also studied the « square root » dependence for the motor oil used in the diesel-electric locomotives. Results are shown in figure 3.
m
GLYCEROL in H,O
2.1 2.5 3.0 ~ j
Fig. 2. The dependence of the SAW attenuation in the aqueous solution of glycerol versus the square root of the viscosity.
358 JOURNAL DE PHYSIQUE III N° 2
fi~
m9a WZI~E~w
~
d
~ i
~
~
_,'©-
_=_=____-- ,' ,'
,'
l ~p',
I ,
I '
j '
I "
j '
I "
j '
I .
"
I ,'
j o
j "
i "
,'
oil oil
10 20 30
j ~j' j~
2 2, , ,
@ ~300
19 20 21 22 23 24 25 26
filmPa.sl~~~
Fig. 3. The dependence of the SAW attenuation divided by the square root of the density in a motor oil used in the diesel-electric locomotives versus the square root of the viscosity (left scale-solid line). The
dependence of the same oil viscosity versus « kilometer age » (right scale-dashed line).
Three interesting regions are observed during the 30 000 km traffic cycle. After a few thousand kilometers the viscosity falls strongly, then practically rises linearly and after about
20 000 km the slow curve bending begins (see Fig. 3). The reason of the viscosity fall is
probably in the presence of the diesel oil in the oil. This fact has been supported by decreasing
the oil flash point (above 20 °C).
The next increase of the viscosity is probably connected with the presence of high molecular
ingredients appearing in the process of oil aging. The oil stability during the traffic cycle has
been studied by the intensive ultrasound irradiation. In the decreasing and in the linear part of the viscosity curve in figure 3 no changes have been observed. The 2 dB attenuation change
h~~ been ob~erved after the irradiation (30 min) between irradiated and non-irradiated samples
for 34 000 km old oil.
The « square root » dependence of the attenuation has been supported for the investigated oil
excluding the initial and final point which are out of the linear dependence (see Fig. 3). The
type of observed dependence in figure 3 has been verified for the other locomotives and the results were the same.
The study of the dissociation degree of ionic liquids has been the next domain in which we have used immersion sensor.
For this type of experiment we test the aqueous solution of hydrochloric acid. The results are illustrated in figure 4. This solution is characterized by continuous dissociation, when the amount of the acid increases. High value of the dissociation coefficient supports such an
assumption (see Tab. I). It is clearly seen from figure 4, that the attenuation rises when the concentration of acid increases. Any maximum has not been observed in the investigated
concentration range. A further increase in the acid concentration was dangerous for IDT because of acid aggressivity.
~
idBi
HO
2 3 4 5 6 7
concentration IN
Fig. 4. The dependence of the SAW attenuation versus concentration (in the norrnality units N) in the aqueous solution of the hydrochloric acid.
For the other types of acids-water solutions, we have measured the SAW attenuation at the
same concentration (results are shown in Tab. I). The 2 N concentration of all investigated
acids has been measured at 23 °C. In the third column of table I, are given values of
dissociation constants [9]. From these results one can conclude that the final value of the SAW
360 JOURNAL DE PHYSIQUE III N° 2
Table I. The acid name, the chemical formula and dissociation constant.
acid chem. formula attenuation dissociation constant KD 18]
a [dB]
HO
~ O
sulphuric 'S ~ 24.0
X 103
/ "
_OH first degree 5.4 X 10-2
oxalic ~%O 24.4
/O second degree 5.4 X 10-5
~ OH
/ OH first degree 7.45 X 10-~
~i~~~ ~~~%O
38.6 second degree 1.7 X 10-5
~/ ~/ OH third degree 4.0 X 10-?
° +O
CHt~$~~
hydrochloric HCI 3 3. 8 0 X 10?
~ O
acetic CHr-C ~ 38.4 1.754 X 10-5
'OH
IO
HD-CHPC
~
tartaric ~~ 39.2 1.04
X 10-~
HD-CHPC'
' O
attenuation depends on the following factors :
a) relaxation phenomena (the size and the structure of the molecule, the number of bonds, and the configuration of functional groups) ;
b) the degree of the dissociation
c) the number of H+ components separated in the solution process per molecule.
The viscosity of the used solutions has been comparable in all cases.
Finally we will discuss the results obtained in the water-ethanol solution at 23 °C. The results are in figure 5. The maximum, which appeared at the 50 volume percent of ethanol, is
probably connected with the intemal structure of ethanol-water solution and namely with the existence of the hydrogen bond. The equilibrium between molecules bonded by the hydrogen
bond in a spatial net and « free » molecules is reached at the constant temperature. This maximum is shifted on the « bonded water » side.
The following addition of ethanol influences the location of molecules in the water net cavities. High polarity of O-H bonds improve the structure. This fact then can explain the attenuation rising (up to 50 volume percent of ethanol). It is probable to attain that this process
can be accompanied by relaxation effects in the ethanol molecule.
-1
o
I
o
o
io 50 70 eo go ioo
ethanol concentration [vol.%I
Fig. 5. The dependence of the SAW attenuation in the aqueous solution of ethanol versus a solution concentration in volume percents.
The addition of ethanol fulfills the cavities and the next increasing of its concentration
destroys the spatial net and increases the amount of « free » water molecules and attenuation falls.
Conclusion.
From presented results one can conclude that the immersion sensor can be used with success for the measurements of the viscosity of technical liquids and their wearing in the working cycle. It is proper for the study of the dissociation degree and relaxation phenomena
respectively. The advantage of used sensor is in a very easy application of measured liquid, good reproduction of results and quick measurements.
Acknowledgment.
This work was supported by a grant of Slovak ministry of the education, youth and sport No. 1/312/92.
References
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Sl.00 C 1987 IEEE.
[2] HAUDEN D., Ondes Electr. 68, n 4 (Juillet 1988).
[3] KOITIAL P. and SLABEYCIUS J., Phys. Status Solidi (a) K109 (1985).
362 JOURNAL DE PHYSIQUE III N° 2 [4] NISHIKAWA S., UEDA M., Bull. Chem. Sac. Jpn 65 (1992) 5.
[5] TUREKOVA I., Czech. J. Phys. B 23 (1973).
[6] CAMPBELL J. J. and JONES W. R., IEEE Trans.
on Sonics and Ultrasonics, SU 17 (1970) 71.
[7] SHIOKAWA S. and MORIIzUMI T., Jpn J. Appt. Phys. 27 Suppl. (1988) 27-1.
[8] MICHAILOV I. G., SoLovIov V. A. and SYRNIKOV J. P., Osnovy molekularnoj akustiky (NAUKA, Moskva, 1964).
[9] RABINOVIt V. A. and CHAVIN Z. J., Handbook of chemistry (in czech language), SNTL Praha (1985).
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