JP6266313B2 - QCM sensor - Google Patents

Description

  The present invention relates to a QCM (Quartz Crystal Microbalance) sensor for measuring physical properties using vibration of a crystal resonator.

  When trying to measure a minute physical quantity of a target measurement sample with a crystal resonator using a QCM sensor, it is difficult to ensure the measurement accuracy because the absolute value is very small. Therefore, means for grasping the physical quantity of the measurement sample by comparison with the measurement value of the reference sample is known (Patent Document 1). In Patent Document 1, a QCM sensor in which a crystal resonator that measures a measurement sample and a crystal resonator that measures a reference sample are arranged on the same support base is used, and the measured values of both are compared. .

JP 2004-205392 A

  By the way, in such a conventional QCM sensor, the external pressure applied to the measurement crystal resonator and the reference crystal resonator may fluctuate. In such a case, it may be difficult to ensure the accuracy of the comparative measurement. .

  The present invention has been made in consideration of the above-described circumstances, and its purpose is to reduce fluctuations in external pressure when attempting to measure a physical quantity of a sample in a sample atmosphere such as when immersed in the sample. Regardless, the object is to provide a QCM sensor capable of accurately detecting a minute physical quantity of a measurement sample.

In order to achieve the above object, the present invention provides the following means.
That is, the QCM sensor according to the present invention is a first electrode that can be contacted with a measurement sample to be detected in a QCM sensor that detects a physical quantity of the sample by contacting the sample with an electrode excited on the surface of a crystal resonator. A measurement crystal resonator having a first crystal substrate on which the first electrode is formed, a second electrode with which a reference sample serving as a reference when detecting a physical quantity of the measurement sample can be contacted, A casing for forming a reference crystal resonator having a second crystal substrate on which the second electrode is formed, and an internal chamber for isolating the reference electrode from the measurement sample and accommodating the reference sample therein The housing includes a volume changing portion that can change the volume of the internal chamber.
Due to this feature, the pressure applied to the first electrode of the first crystal substrate and the second electrode of the second crystal substrate can be made equal, so there is no need for an unnecessary connection between the measurement crystal resonator and the reference crystal resonator. A detection difference is unlikely to occur, and the accuracy of comparative measurement between the reference sample and the measurement sample can be ensured.

The QCM sensor according to the present invention includes a third electrode formed on a surface of the first crystal substrate opposite to a surface on which the first electrode is formed, and the third electrode of the second crystal substrate. A fourth electrode formed on a surface opposite to the surface on which the first electrode is formed, a partition wall that accommodates the third electrode and the fourth electrode inside, and defines a partition chamber partitioned from the inner chamber; It is characterized by having.
With this feature, the third electrode and the fourth electrode can be placed in the same environment, and the electrode on the side on which the measurement sample and the reference sample do not act is placed in the same environment. Therefore, an unnecessary detection difference between the measurement crystal resonator and the reference crystal resonator is less likely to occur, and the accuracy of comparative measurement can be ensured.

The QCM sensor according to the present invention is characterized in that the partition wall has a communication portion that connects the internal chamber and the partition chamber.
With this feature, the pressure difference that the reference crystal resonator receives from both sides can be reduced, and the accuracy of comparative measurement can be ensured.

In the QCM sensor according to the present invention, the housing includes a facing wall that faces the second electrode, and a side wall that is connected to the facing wall and covers the reference sample from a side. At least a part is formed by the volume fluctuation portion.
With such a feature, the rigidity of the housing in which the reference sample is accommodated is ensured, and the reference sample can be hardly subjected to unnecessary external pressure even in a sample atmosphere at high pressure.

Moreover, the QCM sensor according to the present invention is characterized in that the volume variation portion is formed of a bellows portion made of the same material as the side wall. Moreover, the QCM sensor according to the present invention is characterized in that the volume fluctuation portion is formed of a polymer material.
Due to the above features, the present invention can relieve excessive pressure applied to the reference sample, suppress changes in the reference sample, and ensure the accuracy of comparative measurement between the reference sample and the measurement sample. become able to.

Further, the QCM sensor according to the present invention is characterized in that the volume changing portion is constituted by a plunger member capable of moving back and forth toward the reference sample.
With this feature, a force equivalent to the external pressure can be transmitted to the second electrode surface of the second crystal substrate without generating a repulsive force such as an elastic force with respect to the pressure from the outside. Accordingly, since the pressure applied to the first electrode of the first crystal substrate and the second electrode of the second crystal substrate can be made equal, an unnecessary detection difference between the measurement crystal resonator and the reference crystal resonator is obtained. Therefore, comparative measurement between the reference sample and the measurement sample can be performed with higher accuracy.

It is a whole block diagram of the QCM sensor in 1st Embodiment of this invention. It is sectional drawing of the QCM sensor main body in 1st Embodiment of this invention. It is sectional drawing of the QCM sensor main body in 2nd Embodiment of this invention. It is sectional drawing of the QCM sensor main body in 3rd Embodiment of this invention.

Hereinafter, a first embodiment of a QCM sensor according to the present invention will be described with reference to FIGS. 1 and 2.
FIG. 1 is an overall configuration diagram showing a first embodiment of a QCM sensor 1 of the present embodiment, and FIG. 2 is a cross-sectional view of a QCM sensor main body. The QCM sensor 1 includes a QCM sensor main body 2, a first oscillator 3, a first counter 4, a second oscillator 5, a second counter 6, and a comparison unit 7. The QCM sensor 1 includes a measurement crystal resonator having a first crystal substrate 8 and a reference crystal resonator having a second crystal substrate 9, and the measurement crystal resonator is connected to the first oscillator 3. Yes. The reference crystal resonator is connected to the second oscillator 5. The first oscillator 3 is connected to the first counter 4, and the second oscillator 5 is connected to the second counter 6. Both the first counter 4 and the second counter 6 are connected to the comparison unit 7, and the vibration characteristics can be compared by comparing the output values from the measurement crystal resonator and the reference crystal resonator. Yes.

  The QCM sensor main body 2 includes a measurement crystal resonator 100 for measuring a measurement sample and a reference crystal resonator 200 for measuring a reference sample serving as a reference when detecting a physical quantity of the measurement sample. 10 is configured to be accommodated in the interior. The measurement crystal resonator 100 includes a first crystal substrate 8 and a first electrode 19 and a third electrode 20 formed on both surfaces thereof. The reference crystal resonator 200 includes the first crystal substrate 9 and the second electrode 22 and the fourth electrode 21 formed on both surfaces thereof. The first quartz substrate 8 and the second quartz substrate 9 are made of AT-cut quartz cut so as to excite thickness-thickness vibration.

  The measurement crystal unit 100 includes a first oscillator external to the QCM sensor body 2 via a first lead electrode 14 connected to the first electrode 19 and a third lead electrode 15 connected to the third electrode 20. 3 is connected. In addition, the reference crystal resonator 200 is connected to the second lead electrode 16 connected to the second electrode 22 and the fourth lead electrode 17 connected to the fourth electrode 21. Two oscillators 5 are connected.

  The measurement crystal unit 100 and the reference crystal unit 200 are further accommodated inside a partition wall 34 formed inside the housing 10. The partition wall 34 accommodates the measurement crystal resonator 100 and the reference crystal resonator 200 by fixing the first crystal substrate 8 and the second crystal substrate inside thereof. The first crystal substrate 8 may be fixed via the first lead electrode 14 and the third lead electrode 15, and the second crystal substrate 9 may be fixed via the second lead electrode 16 and the fourth lead electrode 17. It may be fixed. In this case, each lead electrode not only acts on the external continuity and the excitation of the vibrator, but also plays a role of fixing the measurement crystal vibrator 100 and the reference crystal vibrator 200 to the partition wall 34. become. Here, a space inside the partition wall 34 and sandwiched between the measurement crystal resonator 100 and the reference crystal resonator 200 is referred to as a partition chamber 26, and the measurement crystal resonator 100 is included in the partition chamber 26. The third electrode 20 and the fourth electrode 21 of the reference crystal resonator 200 face each other. Although not shown, the capacity of the compartment 26 may be defined by interposing a spacer between the measurement crystal resonator 100 and the reference crystal resonator 200.

  The casing 10 includes a lid portion 24 through which each of the lead wires described above is fixed, a side wall 42 that is connected to the lid portion 24 and forms a side surface of the housing 10, and a surface that is connected to the side wall 42 and opposite to the lid portion 24. It is comprised with the opposing wall 40 comprised by these. The facing wall 40 is disposed at a position facing the second electrode 22. A partition wall 34 is also connected to the lid portion 24. A space surrounded by the lid 24, the side wall 42, the facing wall 40, and the partition wall 34 is an internal chamber 30. The internal chamber 30 is filled with the reference sample 25. An O-ring 12a is interposed between the measurement crystal unit 100 and the inside of the lid 24, so that the measurement sample in the sample atmosphere and the inside of the housing 10 are kept liquid tight. . Similarly, an O-ring 12 b is interposed between the reference crystal resonator 200 and the inside of the partition wall 34, and the liquid tightness between the reference sample 25 in the internal chamber 30 and the inside of the isolation wall 34 is maintained. .

  Here, in the present embodiment, the partition wall 34 is formed with a communication portion 36 that connects the partition chamber 26 inside the partition wall 34 and the internal chamber 30 outside the partition wall 34. The communication part 36 is formed as a through-hole penetrating the partition wall 34, and the cross section thereof is formed so as not to overlap the first crystal substrate 8 and the second crystal substrate 9. Due to the communication portion 36 as the through hole, the reference sample 25 filled in the internal chamber 30 can freely move with the compartment 26 as shown by an arrow R in FIG. 2 through the communication portion. Yes. That is, the internal pressures of the internal chamber 30 and the compartment 26 are substantially equal. Here, when the reference sample 25 is not an insulator, the four electrodes 19 to 22 and the four lead electrodes 14 to 17 are preferably coated with an insulator thin film.

  In addition, a volume variation portion 38 is formed on the side wall 42 of the housing 10. In the present embodiment, the volume changing portion 38 has an elastic structure by a bellows portion having a bellows structure. Such an elastic structure functions as a pressure variation unit and a pressure adjustment unit that can vary and / or adjust the pressure applied to the reference crystal resonator. By this bellows part, the side wall 42 is formed so that it can expand and contract in the surface direction. The casing 10 is formed so that only the side wall 42 can be expanded and contracted. Therefore, even if a pressure change occurs in the reference sample 25 in the internal chamber 30, the pressure change is generated in the internal chamber 30 outside the partition wall 34 in which the measurement crystal resonator 100 and the reference crystal resonator 200 are accommodated. Can absorb. Further, even if a pressure change occurs in the first electrode 19 of the first crystal substrate 8 in the sample atmosphere, a similar pressure change is generated in the internal chamber 30 due to the expansion and contraction of the volume changing portion 38. Therefore, it is possible to reduce all pressure differences between the front and back of the first crystal substrate 8 and the front and back of the second crystal substrate 9. In addition, the volume fluctuation | variation part 38 may be a member of the same material as the side wall 42, and may be formed with a special polymer material. The elastic modulus that contributes to the fluctuation of the pressure fluctuation portion 38 is desirably a low elastic modulus. Since the low elastic modulus can suppress pressure transmission loss due to elastic force, it is possible to transmit pressure applied from the outside more directly. That is, the pressure from the outside of the facing wall 40 is P, the area of the outer surface of the facing wall 40 is S (the area receiving the pressure applied in the changing direction of the volume changing portion 38), and the elastic modulus (the volume changing portion 38 of the volume changing portion 38). If the sum is k, and the maximum displacement amount of the volume variation part 38 due to pressure is x, k << (PS / x) may be satisfied.

  Both the first electrode 19 and the third electrode 20 have the same shape, a circular shape with a rectangular shape added, and are formed at the same position with the first crystal substrate 8 interposed therebetween. In the present embodiment, the rectangular portions are stretched in opposite directions. The first electrode 19 and the third electrode 20 are formed of a gold film with a titanium thin film as a base. The constituent material of these electrodes is not limited to this, and any metal film can be used as long as it can stably vibrate the AT-cut quartz crystal resonator. Similarly, the second crystal substrate 9 includes a second electrode 22 on one surface and a fourth electrode 21 on the opposite surface, and the second crystal substrate 9 is attached by applying a voltage between both electrodes. It can be made to vibrate.

  The first lead electrode 14 is formed in a U-shape that sandwiches the measurement crystal resonator from both sides in the thickness direction, and similarly, the second lead electrode has the reference crystal resonator in the thickness direction. It is formed in a U shape sandwiched from both sides. The crystal lead for measurement is supported by the first lead electrode 14 and the third lead electrode 15 so as to be sandwiched from both the left and right side surfaces. Since the measurement crystal unit 100 is supported by the lead electrodes connected to the measurement crystal unit 100 with respect to the partition wall 34, the measurement crystal unit is not provided with a special support member. 100 can be supported with respect to the housing | casing 10 (partition wall 34). Therefore, the vibration of the measurement crystal resonator can be prevented as much as possible, and the electrical conduction of the measurement crystal resonator can be secured stably. The same applies to the reference crystal unit 200.

  Next, the operation of the QCM sensor 1 in this embodiment will be described. First, the QCM sensor body 2 is immersed in a measurement sample or placed in a sample atmosphere to prepare for measurement. The measurement sample exists as a liquid or gas sample atmosphere, and the QCM sensor body 2 of this embodiment is used in such a sample atmosphere. At this time, the reference sample 25 is already sealed in contact with the second electrode 22 of the second quartz substrate 9 in the internal chamber 30, and the measurement sample and the reference sample are completely isolated. Therefore, since the measurement sample and the reference sample are not mixed even in the sample atmosphere, the comparative measurement between the two can be performed with high accuracy. The measurement sample enters the surface of the first crystal substrate 8 where the first electrode 19 is located through the opening 24a of the lid 24, and the measurement sample and the first electrode 19 are in contact with each other. However, the O-ring 12a does not allow the measurement sample to enter further inside the housing 10 (isolation wall 34). Next, an alternating voltage is applied to the first crystal substrate 8 and the second crystal substrate 9 by the first oscillator 3 and the second oscillator 5, respectively. The comparison unit 7 compares the first output value and the second output value of the first crystal substrate 8 and the second crystal substrate 9 obtained by applying the voltage to obtain a comparison value.

  In the present embodiment, since the pressure change applied to the reference sample can be absorbed by the expansion and contraction of the volume variation portion 38 of the housing 10 filled with the reference sample 25, the accuracy of the comparative measurement between the reference sample and the measurement sample is ensured. Will be able to.

  Further, by defining the partition chamber 26 with the partition wall 34, the third electrode 20 and the fourth electrode 21 can be placed in the same environment, and the electrode on the side on which the measurement sample and the reference sample do not act is the same. It will be placed in the environment. Therefore, an unnecessary detection difference between the measurement crystal unit 100 and the reference crystal unit 200 is less likely to occur, and the accuracy of comparative measurement can be ensured.

  Further, by providing the partition wall 34 with the communication portion 36 that allows the internal chamber 30 and the partition chamber 26 to communicate with each other, the pressure difference that the reference crystal resonator 200 receives from both sides can be reduced, and the accuracy of the comparative measurement can be improved. It will be possible to secure.

  In addition, since the volume variation portion 38 is formed only on the side wall 42 of the housing 10 that accommodates the reference sample 25, the rigidity of the housing is ensured in the facing wall 40 where the volume variation portion 38 is not formed, and the sample at high pressure is obtained. Even in the atmosphere, the reference sample can be made difficult to receive unnecessary external pressure, and a pressure change similar to the pressure change applied to the first electrode 19 of the first crystal plate 8 is present in the internal chamber 30 and the compartment 26. Since it can be generated in the reference sample 25, the first electrode 19 surface of the first crystal plate 8 that is in contact with only the measurement sample, and the third electrode 20 surface of the first crystal plate 8 that is in contact with the reference sample 25, The pressure difference between the second electrode surface 22 and the fourth electrode surface 21 of the second crystal plate 9 can be reduced.

  Further, since the volume changing portion 38 is formed of the bellows portion made of the same material as the side wall, a complicated configuration can be eliminated.

  Next, a second embodiment of the present invention will be described based on FIG. FIG. 3 is a cross-sectional view of the QCM sensor main body 2 of the present embodiment. In addition, about the structure similar to 1st Embodiment, the same code | symbol is attached | subjected and description is abbreviate | omitted. This embodiment is different from the first embodiment in two points. One point is that the side wall, which is a part of the partition wall, is integrated with the housing 10, and only a portion that maintains the space between the first crystal plate 8 and the second crystal plate 9 is provided with a separate spacer 11. It is a point to use. Therefore, the compartment 26 is a closed space surrounded by the third electrode 20 of the first crystal plate 8, the spacer 11 (partition wall), and the fourth electrode 21 of the second crystal plate 9. In other words, there is no partition wall, and the portion that maintains the space between the first crystal plate 8 and the second crystal plate 9 is formed by the spacer 11 that is a part of the housing. Therefore, the compartment 26 is a closed space surrounded by the third electrode 20 of the first crystal plate 8, the spacer 11 (housing), and the fourth electrode 21 of the second crystal plate 9.

  Another difference from the first embodiment is that, in this embodiment, the internal chamber 30 in which the reference sample 25 is enclosed is formed by hollowing out the opposing wall 50 of the housing 10, and the reference sample 25 is minimized. The capacity is sufficient. The internal chamber 30 is formed inside the facing wall 50, one is closed by the second electrode 22, and the other is closed by the flange lid 13 with the volume varying portion 48 interposed therebetween. The flange lid 13 is fixed to the opposing wall 50 by a flange ring 23.

  The volume variation unit 48 also serves as a seal material between the flange lid 13 and the housing 10. Thus, by making the sealing material extendable / contractible with respect to the external pressure, the intrusion of the liquid in the external environment and the outflow of the reference sample are prevented, and the pressure change in the external environment transmitted through the flange lid 13 is second. It can be transmitted to the surface of the second electrode 22 of the quartz substrate 9. That is, even if a pressure change occurs on the surface of the first crystal substrate 8 on which the first electrode 19 is provided, the volume variation unit 48 causes the reference sample 25 to pass through the pressure applied to the flange lid 13 exposed to the same sample atmosphere. In order to transmit the pressure change to the surface of the second electrode 22 of the second crystal substrate 9, the first electrode 19 and the second electrode 22, which are electrodes on the side of measuring the sample in the first crystal substrate 8 and the second crystal substrate 9, respectively. The negative pressure can be made equal. Therefore, the influence of the external pressure can be canceled out in the measurement value comparison calculation of the comparative measurement, and the comparative measurement can be performed with high accuracy. The pressure deforming portion 48 is preferably a low elastic material having a sufficiently small elastic modulus with respect to the external pressure and the area of the outer surface of the flange lid 13. Further, the crushing white of the pressure deforming portion 48 is made thicker than originally used so as to be secured larger than usual. In addition, the flange ring 23 is designed to be tightened while leaving a margin for crushing.

  Next, a third embodiment of the present invention will be described based on FIG. FIG. 4 is a cross-sectional view of the QCM sensor body 2 of the present embodiment. The present embodiment is the same as the second embodiment, and differs from the second embodiment in the structure for sealing the reference sample 25. In addition, about the structure similar to 1st Embodiment and 2nd Embodiment, the same code | symbol is attached | subjected and description is abbreviate | omitted.

  In the present embodiment, the configuration for sealing the reference sample 25 is composed of a plunger 49 that can move back and forth, holding the O-ring 12c. The internal chamber 30 is formed inside the opposing wall 50, one of which is closed by the second electrode 22 and the other is closed by a plunger 49. In addition, the outer periphery of the side surface of the plunger 49 is partially recessed, and an O-ring 12c is provided. Thereby, it is possible to prevent the liquid from entering the external environment and the reference sample from flowing out. As described above, by using the plunger 49 as the sealing portion of the reference sample 25, even if the pressure of the external environment changes and the pressure change occurs on the surface of the first crystal substrate 8 on which the first electrode 19 is provided, the same applies. The plunger 49 is pushed and pulled by the pressure applied to the plunger 49 exposed to the sample atmosphere, and the pressure change can be transmitted to the second electrode 22 surface of the second crystal substrate 9 through the reference sample 25. Therefore, the pressures received by the first electrode 19 and the second electrode 22 that are the electrodes on the sample measurement side in the first crystal substrate 8 and the second crystal substrate 9 can be made equal. As a result, the influence of the external pressure can be canceled out in the measurement value comparison calculation of the comparative measurement, and the comparative measurement can be performed with high accuracy.

  The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the invention in the implementation stage.

DESCRIPTION OF SYMBOLS 1 QCM sensor 2 QCM sensor main body 8 1st crystal substrate (crystal oscillator for measurement)
9 Second crystal substrate (reference crystal resonator)
10 Housing 11 Spacer (partition wall) (Housing)
12a, 12b, 12c O-ring 13 Flange lid 14 First lead electrode 15 Third lead electrode 16 Second lead electrode 17 Fourth lead electrode 19 First electrode 20 Third electrode 21 Fourth electrode 22 Second electrode 23 Flange ring 24 Lid 24a Opening 25 Reference sample 26 Compartment chamber 30 Internal chamber 34 Compartment wall 36 Communication section 38, 48 Volume variation section 49 Plunger 40, 50 Opposite wall (housing)
42 Side wall (housing)
100 Crystal unit for measurement 200 Crystal unit for reference

Claims (7)

In the QCM sensor that detects the physical quantity of the sample by contacting the sample with the electrode excited on the surface of the crystal unit,
A measurement crystal resonator having a first electrode with which a measurement sample to be detected can contact, and a first crystal substrate on which the first electrode is formed;
A reference crystal resonator having a second electrode capable of contacting a reference sample serving as a reference when detecting a physical quantity of the measurement sample, and a second crystal substrate on which the second electrode is formed;
A housing that isolates the reference electrode from the measurement sample and forms an internal chamber in which the reference sample can be housed;
The QCM sensor, wherein the casing includes a volume changing unit capable of changing a volume of the internal chamber. A third electrode formed on a surface opposite to the surface on which the first electrode of the first crystal substrate is formed;
A fourth electrode formed on a surface opposite to the surface on which the second electrode of the second quartz substrate is formed;
2. The QCM sensor according to claim 1, further comprising: a partition wall that accommodates both the third electrode and the fourth electrode inside and defines a partition chamber partitioned from the internal chamber.  The QCM sensor according to claim 2, wherein the partition wall includes a communication portion that communicates the internal chamber with the partition chamber. The housing has a facing wall facing the second electrode, and a side wall connected to the facing wall and covering the reference sample from the side,
4. The QCM sensor according to claim 1, wherein at least a part of the side wall is formed by the volume changing portion. 5.  The QCM sensor according to claim 4, wherein the volume variation portion is formed of a bellows portion made of the same material as the side wall.  The QCM sensor according to claim 4 or 5, wherein the volume fluctuation portion is made of a polymer material.  The QCM sensor according to any one of claims 1 to 6, wherein the volume changing unit is configured by a plunger member that can move forward and backward toward the reference sample.

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