JP2006322887A - Sensing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To carry out sensing while keeping high stability, by using sealingly an oscillator in a case, and to attain high sensing feeling. <P>SOLUTION: This sensing device is provided with an oscillation circuit having the piezoelectric oscillator having a characteristic oscillation frequency and an external connection terminal with one portion of an oscillation loop formed in an outside of the circuit, and for conducting electric oscillation by the piezoelectric oscillator, and a detecting external unit having a pair of conductive plates, connected to the oscillation circuit by the external connection terminal, and for detecting a change of capacity between the conductive plates, a change of an electric impedance or an admittance of the detecting external unit is read into the oscillation loop to measure a change of a phase or a frequency output from the oscillation circuit. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a sensing device that performs physical quantity sensing.

  The chemical / medical information sensing device has a QCM (= Quartz Crystal Microbalance), that is, an adsorption film of a specific substance on the electrode surface of a crystal resonator, and is connected to an oscillation circuit to oscillate and measure the oscillation frequency. There is a method using a method of predicting the amount of a substance adsorbed on a film by the amount of change in frequency.

  The method was proposed by Sauerbery in 1959. When mass change: Δm [g] occurs due to a thin film that is sufficiently thin and uniform with respect to the thickness of the crystal resonator, the change in resonance frequency: ΔF [Hz] is given by equation (1).

ここで、F₀[MHz]は基本周波数、N[Hz・cm]は振動数定数、A[cm²]は電極面積、ρ[g・cm^-3]は水晶の密度を表す。

Here, F ₀ [MHz] represents a fundamental frequency, N [Hz · cm] represents a frequency constant, A [cm ² ] represents an electrode area, and ρ [g · cm ⁻³ ] represents a crystal density.

  Among such sensing devices, there is a crystal resonator microbalance device that measures a minute mass change of an adherend on the crystal resonator from a change in the resonance frequency of the crystal resonator (see, for example, Patent Document 1). FIG. 18 shows a crystal resonator microbalance device 100 described in Patent Document 1. The crystal resonator microbalance device 100 includes an overtone oscillator 112, an overtone At-Cut crystal resonator 113, a pressure film monitor main body 114, a diffusion vacuum pump 115, a vapor deposition board 116, and a bell jar 117.

  The crystal resonator microbalance device 100 shows a real-time monitor of the deposited film thickness in a vacuum device. As a high sensitivity QCM method, the quartz resonator 113 is overtone oscillated and the sensitivity is increased by increasing the detection frequency. Raised.

The quartz crystal resonator 113 is formed by depositing chromium / gold (thickness: 500 mm) electrodes on both surfaces of an AT-Cut quartz plate having a diameter of 9 mm and a thickness of 0.083 mm. In such a crystal oscillator 13, as shown by equation (1), the fundamental frequency: the frequency change as the F ₀ higher increases, i.e. the detection sensitivity is increased. The relationship between the fundamental frequency and the thickness of the vibrator is given by equation (2).

ここで、nはオーバートーン次数、K［MHz・mm］は振動子のカットアングルによって決まる定数、ｔ[mm]は振動子板の厚みを表す。

Here, n is the overtone order, K [MHz · mm] is a constant determined by the cut angle of the vibrator, and t [mm] is the thickness of the vibrator plate.

  Here, the overtone order n can be an odd number of 1, 3, 5,... In general, the vibrator can easily oscillate up to the fifth order. Depending on the frequency, oscillation up to the 9th order may be possible. A commonly used AT-Cut K constant is given by equation (3).

（3）式より10MHzの周波数でオーバートーン次数nを１として原発振で発振させた場合の厚みはt=0.166mmとなる。5次オーバートーン発振（n=5）では同一の厚みで約50MHzを得ることができる。このとき、質量変化に対する周波数変化量は（1）式より25倍となり、同検出感度も25倍となることを示している。

From the equation (3), the thickness when the overtone order n is set to 1 at the frequency of 10 MHz and the original oscillation is performed is t = 0.166 mm. In the fifth overtone oscillation (n = 5), about 50 MHz can be obtained with the same thickness. At this time, the frequency change amount with respect to the mass change is 25 times from the equation (1), and the detection sensitivity is also 25 times.

Patent Document 1 shows that detection sensitivity = 0.023 ng / cm ² · Hz is obtained by performing overtone oscillation using an At-Cut vibrator.
Japanese Patent No. 3003811

  However, the sensing device as described above adsorbs a measurement substance on the electrode surface that promotes vibration of the vibrator, oscillates the vibrator with an oscillation circuit, and measures its frequency to measure the amount of minute substance. Since the vibrator is left bare in the liquid phase, the stability of sensing is extremely reduced as compared with a communication vibrator that is used by sealing the vibrator in a case.

  Further, in the sensing device as described above, the vibrator is used as a consumable, resulting in high cost.

  The present invention has been made in view of such circumstances, and can be used for sensing while maintaining high stability by using a vibrator sealed in a case and obtaining high sensing sensitivity. Providing equipment.

  In order to achieve the above object, a sensing device of the present invention includes a piezoelectric vibrator having a specific oscillation frequency and an external connection terminal that forms part of an oscillation loop outside the circuit. An oscillation circuit that oscillates electrically, and a pair of conductor plates, connected to the oscillation circuit by the external connection terminals, and an external unit for detection that detects a change in capacitance between the conductor plates, A change in electrical impedance or admittance of the detection external unit is taken into an oscillation loop, and a change in phase or frequency output from the oscillation circuit is measured.

  In the sensing device of the present invention, it is preferable that the piezoelectric vibrator is a crystal vibrator.

  In the sensing device of the present invention, it is preferable that the piezoelectric vibrator is a SAW vibrator.

  In the sensing device of the present invention, it is preferable that the piezoelectric vibrator is a vibrator configured by a microstrip line or a micro electro mechanical system technology.

  Moreover, it is preferable that the sensing device of the present invention further includes a capacitance element or an inductance element connected in parallel to the detection external unit.

  Moreover, it is preferable that the sensing device of the present invention further includes a capacitance element or an inductance element connected in series to the detection external unit.

  In the sensing device of the present invention, it is preferable that one of the conductor plates of the detection external unit is grounded.

  According to the sensing device of the present invention, by using the vibrator sealed in a case, sensing can be performed while maintaining high stability, and the classification, mass, and physical quantity of chemical substances can be detected with high sensitivity. can do.

  In the conventional sensing device, the vibrator itself is placed in a gas or liquid to be measured while being bare, and is oscillated for measurement. Therefore, the stress applied to the vibrator is large and the measurement reliability is lowered. On the other hand, the sensing device of the present invention can store the vibrator in a case with a high degree of sealing, and is provided with an external unit made of metal for impedance measurement, etc., and the unit is coupled to an oscillation loop to change the impedance change in frequency. And measure. For this reason, the reliability of the vibrator in measurement can be made very high.

  By configuring the external unit with a highly reliable metal or the like, the reliability of the sensing device can be increased.

  Further, the external unit can freely select an optimal structure depending on the measurement target. As a result, the measurement object can be expanded as compared with the conventional QCM measurement method, and the measurement can be performed with high accuracy. This can greatly develop the chemical and physical measurement fields in the future.

  Next, embodiments of the present invention will be described with reference to the drawings. In order to facilitate understanding of the description, the same reference numerals are assigned to the same components in the drawings, and duplicate descriptions are omitted.

  FIG. 1 is a block diagram of a sensing device 1a of the present invention. The sensing device 1a includes an oscillator 1 and an external unit 3. An oscillation circuit 2 is provided inside the oscillator 1. A power supply (VCC), ground (GND), and oscillator output (OUT) are connected to the oscillation circuit 2 from the outside.

  The oscillation circuit 2 includes a piezoelectric vibrator (not shown) so that oscillation is performed at a predetermined oscillation frequency. A piezoelectric vibrator is a vibrator having a phenomenon in which, when pressure is applied in a specific crystal axis direction of a crystal material typified by quartz, electric charges are generated in the specific axis direction. As the piezoelectric vibrator, it is preferable to use a crystal vibrator, a SAW vibrator, or a vibrator constituted by a microstrip line or micro electro mechanical system technology (MEMS = Micro Electro Mechanical Systems).

  The quartz crystal vibrator is one of the above-described piezoelectric vibrators, in which a quartz piezoelectric element is incorporated in a dedicated container. The SAW vibrator has a structure in which electrodes are alternately arranged on the surface of a piezoelectric body, and the surface vibrates in a wavy manner (surface acoustic wave). The microstrip line is used to connect circuits and components in a unit using microwaves, and one side on the printed circuit board is a ground and the upper side is a signal line. MEMS are electrical and mechanical parts and mechanisms that have been processed using a technology that reduces the size to the micro (micro is 1 / 1,000,000) metric size.

  A case is provided around the piezoelectric vibrator to protect it from being hardly affected by the outside. Thus, by using the piezoelectric vibrator sealed in the case, sensing can be performed while maintaining high stability, and the classification, mass, and physical quantity of chemical substances can be detected with high sensitivity. .

  The oscillation circuit 2 is provided with two outputs from the oscillation loop, and is connected to the external connection terminal 4 of the oscillator 1. The oscillator 1 is connected to the external unit 3 for measuring impedance or admittance (external unit for detection) through the external connection terminal 4.

  FIG. 2 is a conceptual diagram showing the structure of the external unit 3. The external unit 3 is connected to each external connection terminal 4 and is composed of a pair of conductor plates that form a capacitance. The external unit 3 measures the change in frequency due to the impedance or admittance due to the dielectric constant and conductivity of the gas or liquid therein, and detects the type of substance, the mass of the substance, and the physical quantity.

  Since detection is performed by the external unit 3 in this way, there is no need to place the piezoelectric vibrator itself having an oscillation function in the gas or liquid to be measured while it is bare. The stress applied to the child can be reduced and the measurement reliability can be improved. Specifically, the piezoelectric vibrator can be housed in the case with a high degree of sealing, and an external unit made of a metal or the like for impedance measurement is provided. The unit is coupled to an oscillation loop, and the change in impedance is measured as a change in frequency. For this reason, the reliability of the vibrator in measurement can be made very high.

  In addition, the reliability of the sensing apparatus 1a can be improved by configuring the external unit 3 with a highly reliable metal or the like. Further, the external unit 3 can freely select an optimal structure depending on the measurement target. As a result, the measurement object can be expanded as compared with the conventional QCM measurement method, and the measurement can be performed with high accuracy. This can greatly develop the chemical and physical measurement fields in the future.

  FIG. 3 is a block diagram of the sensing device 1b in which one end of the external connection terminal 4 is grounded. The sensing device 1b measures the change in frequency due to the impedance or admittance between the ground and the terminal, and detects the classification of the substance, the mass of the substance, and the physical quantity.

  As an equivalent circuit of the block diagrams of FIGS. 1 and 2, FIG. 4 shows an equivalent circuit of the sensing device.

Equation (4) is a resonance frequency of a circuit including the vibrator series inductance element 7 having the inductance L ₁ and the vibrator series capacitance element 6 having the capacitance C ₁ . Equation (4) shows the oscillation frequency deviation D _L from the series resonance frequency, and equation (5) shows the amount of change dD _L / dC _x per unit capacity.

（５）式のC₀は振動子並列容量要素８の容量、Caは付加容量要素１０の容量、Ccは発振回路容量要素の容量要素9の容量、Cxは外部ユニット３の電極間容量要素５の容量である。

In Equation (5), C ₀ is the capacitance of the resonator parallel capacitive element 8, Ca is the capacitance of the additional capacitive element 10, Cc is the capacitance of the capacitive element 9 of the oscillation circuit capacitive element, and Cx is the capacitive element 5 between the electrodes of the external unit 3. Capacity.

  Figure 5 shows the simulation result of equation (5). From FIG. 5, it can be seen that by decreasing the capacitance of the external unit 3, the frequency change increases and the sensing sensitivity increases.

That is, assuming that the frequency is 26 MHz, the oscillation circuit 2 using the At-Cut resonator: γ capacitance ratio (= 196), C ₀ = 3.15 pF, and the circuit capacitance is Cc = 30 pF, the external unit capacitance is 10 pF. In this case, the device sensitivity = −110 ppm / pF can be obtained with the device sensitivity = −20 ppm / pF and 1 pF.

  Next, when the electrode of the external unit 3 is composed of two metal plates, the capacitance between the electrode plate 5a and the electrode plate 5b is expressed by equation (6).

ここで、ε₀は真空の誘電率、εsは比誘電率、dは極板間距離、Sは極板面積をあらわす。

Here, ε ₀ is the dielectric constant of vacuum, ε s is the relative dielectric constant, d is the distance between the electrode plates, and S is the electrode plate area.

For example, as shown in FIG. 6, the external unit 3 is composed of an electrode plate having a side length W = 0.1 m, an electrode plate area S = W × W = 0.1 × 0.1 = 0.01 m ² , and a distance between electrode plates d = 0.05 m. , Ε ₀ = 8.85 pF / m, the interelectrode capacitance Cx is given by equation (7).

また、比誘電率に対する周波数変化は（5）式及び（7）式より（8）式で示される。

Further, the frequency change with respect to the relative permittivity is expressed by the equation (8) from the equations (5) and (7).

（8）式のシミュレーション結果を図７に示す。

The simulation result of the equation (8) is shown in FIG.

FIG. 8 is a table showing the relative permittivity of main substances. From the relative permittivity table of FIG. 8, in the vicinity of the relative permittivity εs = 1, dD _L / dεs≈130 ppm. That is, when gas is targeted, the amount of change due to gas classification is Δεs≈0.0001, the amount of change is ΔD _L ≈0.013 ppm, and is about 0.3 Hz in terms of frequency. It can be seen that the amount of change in frequency is within the measurable range.

In addition, the relative permittivity of the liquid is larger than 2, and the amount of change due to the classification is about Δεs≈0.1. The amount of change is ΔD _L ≈13 ppm, and the frequency conversion is ≈340 Hz. Therefore, it can be seen that measurement is easy if the amount of change in frequency is this.

  Next, as a method of increasing the element sensitivity to the change of the external unit 3, there is means for inserting the inductor element 11 of the inductor La in parallel with the external connection terminal as shown in FIG.

The frequency deviation is given by equation (9), and the element sensitivity: dD _L / dCx to the capacitance change of the external unit 3 is given by equation (11).

ωaは（10）式で与えられる。また、ω₀は共振角周波数である。

ωa is given by equation (10). Further, ω ₀ is a resonance angular frequency.

また、外部ユニット３内の比誘電率対周波数偏差の関係は（12）式に示される。

Further, the relationship between the relative dielectric constant and the frequency deviation in the external unit 3 is expressed by equation (12).

図11に、（12）式のシミュレーション結果を示す。

FIG. 11 shows the simulation result of the equation (12).

When the inductor La of the inductor element connected to the external connection terminal is 7 μH and the relative dielectric constant is around εs = 1, dD _L / dεs≈50000 ppm, and the element sensitivity can be greatly increased by inserting the inductor element.

  For example, in the case of gas, the amount of change due to gas classification is Δεs≈0.0001, and the amount of change is ΔDL≈5 ppm, and the frequency conversion can be easily measured at about 130 Hz.

  FIG. 12 shows an equivalent circuit of the sensing device in which the additional capacitance element 10 having the capacitance Ca is connected in parallel to the external unit, and the inductor element 11a of the inductor Lc is connected to the circuit.

  Equation (13) shows the oscillation frequency deviation from the series resonance frequency, and Equation (14) shows the amount of change per unit capacity.

図13に、（14）式のシミュレーション結果を示す。外部ユニット３の容量が1pFの場合に、素子感度‐200ppm/pFを得ることができることが示されている。

FIG. 13 shows the simulation result of the equation (14). It is shown that device sensitivity of -200 ppm / pF can be obtained when the capacity of the external unit 3 is 1 pF.

  Further, the relationship between the relative dielectric constant and the frequency deviation in the external unit 3 is expressed by equation (15).

図14に、（15）式のシミュレーション結果を示す。

FIG. 14 shows the simulation result of equation (15).

When the inductor La of the inductor element 11a connected to the external connection terminal 4 is 8 μH and the relative dielectric constant is in the vicinity of εs = 1, dD _L / dεs≈550 ppm, and the element sensitivity can be increased by inserting the inductor element. I understand.

For example, in the case of gas, the amount of change due to gas classification is Δεs≈0.0001, the amount of change is ΔD _L ≈0.055 ppm, and the frequency conversion is about 1.43 Hz, which can be easily measured.

  The external unit 3 in FIG. 1 was replaced with a ceramic capacitor whose interelectrode capacitance value was known in advance, and the oscillation frequency of the crystal resonator accompanying the capacitance change was measured. FIG. 15 is a schematic diagram of an experimental apparatus.

  The measurement procedure is shown below.

  (A) Two electrode plates 19 using metal or the like are made parallel to produce the external unit 3. (B) The electrode plate 19 and the external connection terminal 4 are wired. (C) As shown in FIG. 16, the frequency measuring device 21, the electrode plate 19, and the oscillator 1 are wired. (D) The electrode plate 19 arranged in (a) is inserted into the container 18 containing the liquid 20. (E) The frequency change is measured by the frequency measuring device 21.

  Detailed descriptions of the frequency measuring device 21 and the oscillator 1 will be described. The frequency measuring device 21 is a frequency counter or an impedance analyzer.

  FIG. 16 shows the above measurement results. It can be seen from FIG. 16 that the oscillation frequency increases exponentially as the capacitance decreases. Therefore, if the external unit 3 capable of achieving a state with a smaller electrostatic capacity is produced, measurement with higher resolution and higher sensitivity can be performed.

  Based on these results, it was shown that the type of the liquid 20 can be discriminated using the electrode plate 19 produced by experiment.

  The experimental procedure is shown below.

  Using the experimental system of FIG. 15, the oscillation frequency when the electrode plate 19 is immersed in the liquid 20 is measured using two kinds of liquid 20 such as distilled water and methanol, and whether there is a difference in the oscillation frequency depending on the substance. investigated.

  The experimental results are shown in FIG. FIG. 17 clearly shows that the oscillation frequency varies depending on the liquid 20.

1 is a block diagram of a sensing device according to the present invention. It is a structural diagram of an external unit. 1 is a block diagram of a sensing device according to the present invention. It is an equivalent circuit diagram of the sensing device according to the present invention. It is a figure which shows the simulation result of the equivalent circuit of the sensing apparatus which concerns on this invention. It is a perspective view which shows the structural example of an external unit. It is a figure which shows the simulation result about the relationship between a dielectric constant versus frequency variation. It is a dielectric constant table | surface of each substance. It is an equivalent circuit diagram of the sensing device according to the present invention. It is a figure which shows the simulation result of the equivalent circuit of the sensing apparatus which concerns on this invention. It is a figure which shows the simulation result of the equivalent circuit of the sensing apparatus which concerns on this invention. It is an equivalent circuit diagram of the sensing device according to the present invention. It is a figure which shows the simulation result of the equivalent circuit of the sensing apparatus which concerns on this invention. It is a figure which shows the simulation result of the equivalent circuit of the sensing apparatus which concerns on this invention. It is the schematic of an experimental apparatus. It is a figure which shows the measurement result which measured the frequency with respect to the capacity | capacitance change of an external unit. It is a figure which shows the frequency drop measurement result of methanol and distilled water. It is a block diagram which shows the conventional sensing apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1a, 1b Sensing apparatus 1 Oscillator 2 Oscillation circuit 3 External unit 4 External connection terminal 5 Electrode capacitive element 5a Electrode plate 5b Electrode plate 6 Vibrator series capacitive element 7 Vibrator series inductance element 8 Vibrator parallel capacitive element
9 Oscillating circuit capacitive element 10 Additional capacitive element 11 Inductor element 11a Inductor element 18 Container 19 Electrode plate 20 Liquid 21 Frequency measuring device
C ₁ element series capacitance
Ca additional capacitance element capacitance Cx interelectrode capacitance dD _L / dC _x variation in oscillation frequency deviation per unit capacitance
D _L Oscillation frequency deviation
L ₁ Inductance of series inductance element
La Inductor element inductor connected to external connection terminal
Inductor εs relative permittivity of Lc inductor element

Claims (7)

An oscillation circuit having a piezoelectric vibrator having a specific oscillation frequency and an external connection terminal for forming a part of the oscillation loop outside the circuit, and performing electrical oscillation by the piezoelectric vibrator;
A detection external unit that has a pair of conductor plates and is connected to the oscillation circuit by the external connection terminals and detects a change in capacitance between the conductor plates;
A sensing device characterized in that a change in electrical impedance or admittance of the detection external unit is taken into an oscillation loop and a change in phase or frequency output from the oscillation circuit is measured.   The sensing device according to claim 1, wherein the piezoelectric vibrator is a crystal vibrator.   The sensing device according to claim 1, wherein the piezoelectric vibrator is a SAW vibrator.   The sensing device according to claim 1, wherein the piezoelectric vibrator is a vibrator configured by a microstrip line or a micro electro mechanical system technology.   The sensing device according to any one of claims 1 to 4, further comprising a capacitance element or an inductance element connected in parallel to the detection external unit.   The sensing device according to any one of claims 1 to 5, further comprising a capacitance element or an inductance element connected in series to the detection external unit.   The sensing device according to any one of claims 1 to 6, wherein one of the conductor plates of the external unit for detection is grounded.

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