JP2002357538A - Plasmon sensor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately measure a refractive index with a simple constitution and to realize reductions in size and cost. SOLUTION: A plasmon sensor device 10 comprises a sensor plate 13 connected to an incident optical fiber 11 and an emitting optical fiber 12, and thin films 13A and 13B provided on a pair of opposed both surfaces of the plate 13 to excite a surface plasmon. Thus, a light P for exciting the surface plasmon is incident from the fiber 11 and is irradiated from the fiber 12 through the plate 13. The plate 13 is made of a transparent plate. The fibers 11 and 12 are each a multi-mode optical fiber. The device 10 further comprises a polarizing film 14 provided between the fiber 11 and the plate 13.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a plasmon sensor device as an optical component for measuring the refractive index of a gas or liquid.

[0002]

2. Description of the Related Art Conventionally, as a technique for measuring the refractive index of a substance to be measured (hereinafter referred to as a "sample"), a technique for measuring a critical angle, a technique using surface plasmons (Kretschmann type), and a surface plasmon (optical fiber type) Are known.

A technique for measuring the critical angle is to measure the critical angle at which light is totally reflected at the boundary between the prism and the sample in contact with the prism by using an optical component including a light emitting element, a prism, and a light receiving element. This is for determining the refractive index of the sample.

The technique based on surface plasmon (Kretschmann type) is to obtain a refractive index of a sample by obtaining a resonance angle using an optical component including a light emitting element, a prism and a light receiving element.

[0005] In the technology using surface plasmon (optical fiber type), an optical component in which a core of an optical fiber is exposed and gold is deposited on the core, and a tip of the optical fiber is polished to deposit silver on the tip. In this method, the light entering the optical fiber and the light coming out of the optical fiber are separated by a beam splitter, and the refractive index of the sample is obtained from the spectrum obtained by passing the light coming out of the optical fiber through a spectroscope.

[0006]

However, the above-mentioned prior art has the following problems.

In the technique for measuring the critical angle, the positional relationship between the light-emitting element, the prism, and the light-receiving element is required to have high precision, and a certain size is required in terms of structure. Therefore, it has been difficult to reduce the manufacturing cost and reduce the size.

In the technique using surface plasmons (Kretschmann type), a high precision is required for the positional relationship between the light emitting element, the prism, and the light receiving element, and a certain size is required in terms of structure. Therefore, it has been difficult to reduce the manufacturing cost and reduce the size. In addition, an expensive microcomputer for calculation was required to determine the resonance angle. This is because an inexpensive microcomputer for control does not have sufficient computing power.

In the technology based on surface plasmon (optical fiber type), a certain degree of miniaturization has been achieved by using an optical fiber. However, since the optical fiber must be finely processed, a considerable manufacturing cost is required. In addition to this, a beam splitter, a spectroscope, a microcomputer for calculation, and the like are required, so that it has been extremely expensive.

[0010]

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a plasmon sensor device which can accurately measure a refractive index with a simple structure, thereby realizing miniaturization and low cost.

[0011]

According to a first aspect of the present invention, there is provided a plasmon sensor device, wherein a sensor plate is connected between an input optical fiber and an output optical fiber, and at least a part of the sensor plate is used for exciting surface plasmons. The light for exciting the surface plasmon enters from the input optical fiber, passes through the sensor plate, and exits from the output optical fiber.

The light for exciting the surface plasmon is guided from the optical fiber for incidence, propagates through the sensor plate while repeating total reflection, and emerges from the optical fiber for emission. When light propagates through the sensor plate, it excites compressional waves of electrons called surface plasmons on the thin film, so that the energy of the light is attenuated. The attenuation at this time has a correlation with the refraction rate of the sample in contact with the thin film. Therefore, the refractive index of the sample can be known by measuring the amount of transmitted light. In addition, since fine processing of the optical fiber, a beam splitter, a spectroscope, and a microcomputer for calculation are not required, the refractive index can be accurately measured with a simple configuration.

[0013] The plasmon sensor device according to claim 2 is
A sensor plate is connected between the first and second input optical fibers and the first and second output optical fibers, and a thin film for surface plasmon excitation is provided on at least a part of the sensor plate. One surface plasmon excitation light enters from the first incident optical fiber, passes through the sensor plate and exits from the first exit optical fiber, and the second surface plasmon excitation light enters the second incidence optical fiber. The light enters from the optical fiber, passes through the sensor plate, and exits from the second exiting optical fiber. The first surface plasmon excitation light has such a property that the amount of transmitted light increases in accordance with an increase in the refractive index of the substance to be measured in contact with the thin film. Conversely, the second surface plasmon excitation light has such a property that the amount of transmitted light decreases as the refractive index of the substance to be measured in contact with the thin film increases.

The difference between the transmitted light quantity of the first surface plasmon excitation light and the transmitted light quantity of the second surface plasmon excitation light is different from the respective transmitted light quantities with respect to the change in the refractive index of the substance to be measured. Is big. Therefore, the sensitivity of the refractive index measurement is improved.

Further, the sensor plate may be made of a transparent plate. The input optical fiber and the output optical fiber may be a multi-mode optical fiber. A polarizing film may be provided between the incident optical fiber and the sensor plate (claim 5).

[0016]

FIG. 1 shows a first embodiment of a plasmon sensor device according to the present invention. FIG. 1 [1] is an overall perspective view, FIG. 1 [2] is an exploded perspective view, and FIG. 1 [3]. FIG. 3 is a perspective view of a sensor plate. Hereinafter, description will be made based on this drawing.

The plasmon sensor device 10 of the first embodiment
Are the input optical fiber 11 and the output optical fiber 12
And a pair of opposing surfaces of the sensor plate 13 are provided with thin films 13A and 13B for exciting surface plasmons, and light P for exciting surface plasmons is incident on the optical fiber 11 from the optical fiber 11. 13
Out of the optical fiber 12 through the optical fiber 12. Further, the sensor plate 13 is made of a transparent plate material, the optical fibers 11 and 12 are multi-mode optical fibers, and a polarizing film 14 is provided between the optical fiber 11 and the sensor plate 13.

The sensor plate 13 is made of a transparent glass plate. A thin film 1 of gold (or silver) having a thickness of about 50 [nm]
3A and 13B are formed. At this time, a thin film of Cr having a thickness of about 1 nm may be provided between the glass and the gold thin film in order to increase the adhesion. Optical fiber 1
1, 12, sensor plate 13 and polarizing film 14
Is held by holders 15A and 15B.

The plasmon sensor device 10 is an optical component for measuring a refractive index. The plasmon sensor device 10 causes light P for exciting surface plasmons to be incident on a sensor plate 13 and, based on the amount of transmitted light, a refractive index of a sample in contact with the sensor plate 13. Ask for. Then, the optical fibers 11 and 12, the sensor plate 13 and the polarizing plate filter 14 are attached to the holders 15A and 15A.
B are united.

FIG. 2 is a cross-sectional view taken along the line II-II in FIG. Hereinafter, the operation of the plasmon sensor device 10 will be described with reference to this drawing.

The light P for exciting the surface plasmon is guided from the optical fiber 11, becomes TM mode light by the polarization filter 14, propagates in the sensor plate 13 while repeating total reflection, and is emitted from the optical fiber 12. Light P
When the light propagates through the sensor plate 13, the thin film 13A,
In order to excite a compression wave of electrons called surface plasmon on 13B, the energy of light P is attenuated. The attenuation at this time has a correlation with the refraction rate of the sample in contact with the thin films 13A and 13B. Therefore, by measuring the amount of transmitted light P, the refractive index of the sample can be known.

The light P is totally reflected at the interface between the thin films 13A and 13B made of gold and the sensor plate 13 made of a glass plate. At this time, surface plasmons are excited on the thin films 13A and 13B. Therefore, the refractive index of the glass plate must be larger than the refractive index of the sample. The material of the sensor plate 13 is not limited to glass, but may be a transparent material such as resin, quartz, and sapphire.

FIG. 3 is a cross-sectional view showing an example of a light projecting unit and a light receiving unit used together with the plasmon sensor device of the first embodiment.
FIG. 3B shows a light receiving unit. Hereinafter, FIGS. 2 and 3
It will be described based on.

The light projecting unit 20 includes a light emitting element 21 for outputting light P for exciting surface plasmons, a light receiving element 22 for monitoring the output of the light emitting element 21, a light emitting element 21 and the light receiving element 22. 11 and a holder 23 for connection. The light receiving unit 24 receives the light P
And a holder 26 that accommodates the light receiving element 25 and connects to the optical fiber 12. An LED or a semiconductor laser is used for the light emitting element 21, and photodiodes are suitable for the light receiving elements 22 and 25.

Light P emitted from the light emitting element 21 propagates through the optical fiber 11, is converted into a TM mode by the polarization filter 14, and transmits through the sensor plate 13. The transmitted light propagates through the optical fiber 12 and enters the light receiving element 25 in the light receiving unit 24. The output of the light emitting element 21 is the light receiving element 22
Therefore, by comparing this output with the output of the light receiving element 25 of the light receiving unit 24, the amount of light attenuated by the sensor plate 13 can be obtained.

FIG. 4 is a graph showing the relationship between the refractive index of a sample and the amount of transmitted light in the plasmon sensor device of the first embodiment. Hereinafter, description will be made with reference to FIGS. 2, 3, and 4.

In this measurement example, a synthetic quartz (refractive index: 1.4586) having a thickness of 0.4 [mm] and a length of 30 [mm] is used as the material of the sensor plate 13, and the light emitting element 21 is made of 57 mm.
An LED emitting 4 [nm] light P was used. At this time, it was confirmed that the amount of transmitted light varied with the refractive index of the sample.

FIG. 5A is an overall perspective view showing a second embodiment of the plasmon sensor device according to the present invention. Hereinafter, description will be made based on this drawing.

The plasmon sensor device 30 of the second embodiment
The sensor plate 33 is connected between the optical fibers 31a and 31b for incidence and the optical fibers 32a and 32b for emission, and the thin films 33A and 33B for surface plasmon excitation ( 33B is provided), light Pa for surface plasmon excitation is incident from the optical fiber 31a, exits from the optical fiber 32a through the sensor plate 33, and light Pb for surface plasmon excitation is incident from the optical fiber 31b. Then, the light is emitted from the optical fiber 32b through the sensor plate 33. The light Pa has the property that the amount of transmitted light increases as the refractive index of the sample in contact with the thin films 33A and 33B increases, and the light Pb transmits the amount of transmitted light as the refractive index of the sample contacts the thin films 33A and 33B increases. Has the property of decreasing.

The sensor plate 33 is made of a transparent plate, and the optical fibers 31a, 31b, 32a, and 32b are multimode optical fibers.
A polarizing film (not shown) is provided between 1b and the sensor plate 33.

The sensor plate 33 is made of a transparent glass plate. The thin films 33A and 33B are made of gold (or silver) having a thickness of about 50 [nm]. Optical fibers 31a, 31b, 3
2a, 32b, the sensor plate 33, and the polarizing film (not shown) are held by holders 35A, 35B.

In the second embodiment, light Pa and Pb having two wavelengths are used for exciting surface plasmons. Optical fibers 31a and 31b have different wavelengths of light Pa and Pb, respectively.
A light projecting unit (not shown) that emits light is connected, and separate light receiving units (not shown) are connected to the optical fibers 32a and 32b, respectively. The light Pa and Pb are configured to pass therethrough. That is, a light projecting unit that emits light Pa of the wavelength λ1 is connected to the optical fiber 31a, the light Pa is made incident on the sensor plate 33, and the amount of transmitted light is measured by the optical fiber 3.
The measurement is performed by the light receiving unit connected to 2a. Similarly, a light projecting unit that emits light Pb of wavelength λ2 is
1b, the light Pb is incident on the sensor plate 33, and the amount of transmitted light is measured by a light receiving unit connected to the optical fiber 32b.

FIG. 6 is a graph showing the relationship between the refractive index of a sample and the amount of transmitted light in the plasmon sensor device of the second embodiment. FIG. 6 [1] is a graph showing the relationship between the refractive index of the sample and the amount of transmitted light at different wavelengths, and FIG. 6 [2] is a graph showing the difference between the amounts of transmitted light. Hereinafter, description will be made based on these drawings.

FIG. 6A shows an example of measurement using 574 [nm] as λ1 and 660 [nm] as λ2. The sensor plate at this time is the same as the measurement example in FIG. FIG. 6B illustrates a plot of (the amount of transmitted light of λ1) − (the amount of transmitted light of λ2) + (appropriate offset amount). According to the second embodiment, the amount of change in the amount of transmitted light with respect to the amount of change in the refractive index is larger than in the measurement example of FIG. 4, so that the sensitivity as a sensor can be improved.

FIG. 5B is an overall perspective view showing a third embodiment of the plasmon sensor device according to the present invention. Hereinafter, description will be made based on this drawing. However, the same parts as those in FIG. 5A are denoted by the same reference numerals, and description thereof will be omitted.

The plasmon sensor device 40 of the third embodiment
The sensor plate 33 is connected between the optical fibers 31a and 31b for incidence and the optical fibers 32a and 32b for emission, and the thin films 33A and 33B for surface plasmon excitation ( 33B is provided), surface plasmon excitation light Pa enters from the fiber 31a, exits from the optical fiber 32a through the sensor plate 33, and surface plasmon excitation light Pb enters from the optical fiber 31b. Sensor plate 3
3 and exits from the optical fiber 32b.
The holder 45A, 45B is provided with two opening windows corresponding to the light Pa, Pb, and these opening windows
a, 46b. The light Pa and Pb may have the same wavelength or different wavelengths.

The plasmon sensor device 40 can be used as a biosensor, and the thin film 33A, 33
If an antibody is immobilized on the B surface via a gel thin film, an immunosensor can be obtained. If a plurality of types of antibodies are prepared, two types of antigen concentrations can be known at the same time. That is, the measurement parts 46a, 46b are integrated, and the measurement parts 46a, 46b are integrated.
By immobilizing separate antibodies respectively, two types of antigens can be detected simultaneously. Thus, by integrating a plurality of measurement sites, the sensor plate 33,
A plurality of samples can be measured simultaneously while using only one holder 45A, 45B and one polarizing film.

It is needless to say that the present invention is not limited to the first to third embodiments. For example, the thin film may be provided on only one of the sensor plates, not on both sides. An attachment / detachment mechanism for detachably attaching the optical fiber and the holder may be provided. The polarizing film may be omitted.

An application example of the plasmon sensor device according to the present invention will be described below.

[0040]

[First application example] The cooling water used for the forced circulation type water cooling device of the engine is mixed with an antifreeze liquid to prevent freezing in severe cold. If the antifreeze concentration is high, the freezing temperature will be low, while the cooling capacity will be low. Therefore, it is desirable that the antifreeze concentration be within an appropriate range. In order to monitor the antifreeze concentration, a technique of measuring a specific gravity using a float and a technique of using a reagent are known. However,
The technique using a float is not suitable for use in a vehicle because the float is affected by vibration of an engine or a vehicle body. Further, in the technique using a reagent, cooling water is sampled and reacted in a test tube, so that it is not suitable for in-vehicle use. Therefore, an object of a first application example is to provide a vehicle-mounted antifreeze concentration sensor used in a forced-circulation water cooling device for an engine.

FIG. 7 is a configuration diagram showing a first application example of the plasmon sensor device according to the present invention. Hereinafter, description will be made based on this drawing.

The first application example is an example in which a plasmon sensor device (hereinafter, referred to as "SRP sensor") according to the present invention is used as an antifreeze concentration sensor for a forced circulation type water cooling device for an engine. A water pump 53 for circulating the cooling water W is directly connected to a fan 52 for cooling the radiator 51. The cooling water W is circulated by the water heater pump 53 between the radiator 51 and a flow path called a jacket 54 in the engine. Further, a reserve tank 55 for buffering the volume expansion of the cooling water W is attached. In the reserve tank 55, the SPR sensor 10 and a temperature sensor 57 for measuring the temperature of the cooling water W are attached. In another place, a temperature sensor 58 for measuring the outside air temperature is arranged.

In the SPR sensor 10, as shown in FIG. 1, the optical fiber and the sensor plate are integrated, and the end face of the optical fiber extends to the outside of the reserve tank 55, where the light emitting unit (FIG. 1]) and a light receiving unit (FIG. 3 [2]). An output signal from the light receiving unit is converted into a digital signal by an AD converter, and thereafter, an arithmetic unit (CPU) mounted on an automobile or the like
And a temperature sensor 57 for measuring the cooling water temperature.
And is used to predict the freezing temperature of the cooling water W. On the gold thin film of the SPR sensor 10, a polymer thin film such as alkanethiol is provided to prevent adhesion of suspended particles.

Next, the operation of the SPR sensor 10 will be described with reference to FIGS.

The light P emitted from the light projecting unit propagates through the optical fiber 11, is converted into TM mode light by the polarizing film 14, and propagates in the sensor plate 13 by repeating total reflection. At this time, the light P loses a part of energy by exciting a surface plasmon wave which is a compressional wave of electrons on the thin films 13A and 13B made of gold. Therefore, by measuring the intensity of light incident on the sensor plate 13 and the intensity of light transmitted from the sensor plate 13, it is possible to know the light energy consumed for surface plasmon excitation. Since this excitation condition is affected by the refractive index of the cooling water W in contact with the thin films 13A and 13B, the refractive index of the cooling water W can be known from the amount of light energy consumed by the sensor plate 13 (see FIG. 4).

FIG. 8A is a graph showing the relationship between the antifreeze concentration and the refractive index in the first application example, and FIG. 8B is a graph showing the relationship between the freezing temperature and the refractive index in the first application example. It is. Hereinafter, description will be made based on these drawings.

In the cooling water W, in order to prevent freezing in severe cold,
An antifreeze containing ethylene glycol as a main component is mixed. There is a correlation between the ethylene glycol concentration and the refractive index of the cooling water W (FIG. 8A), and there is also a correlation between the ethylene glycol concentration and the freezing temperature of the cooling water W (FIG. 8).
[2]). Therefore, the freezing temperature of the cooling water W can be predicted by measuring the refractive index of the cooling water W. In the first application example, the refractive index measuring means of the cooling water is SP
An R sensor 10 is used.

As is clear from FIG. 8B, the cooling water W
It can be seen that if the refractive index can be measured in the range of 1.33 to 1.38, the freezing temperature can be predicted up to -30 ° C.
An example in which this range of the refractive index is measured by the SPR sensor 10 is as follows.
As shown in FIG. In this measurement example, a sensor plate made of a material having a refractive index of 1.4586, a thickness of 0.4 [mm] and a length of 15 [mm], and light having a wavelength of 574 [nm] were used. Further, by comparing the predicted freezing temperature of the coolant W with the outside air temperature measured by the temperature sensor 58,
The driver can be notified in advance of the freezing of the coolant W.
This notification of freezing may be displayed on a car navigation device.

According to the first application example, the use of the SRP sensor according to the present invention as an antifreeze concentration sensor for a forced circulation type water cooling device for an engine has the following effects. First, since it is not affected by vibration and electric noise, it is possible to provide an antifreeze concentration sensor suitable for use in vehicles. Second, due to the simplicity of the electrical interface,
Combination with a CPU (computer) can be facilitated.

[0050]

[Second application example] A second application example is an example in which the SRP sensor according to the present invention is used as an antifreeze concentration sensor for a hot water heating apparatus. An antifreeze is mixed into the circulating water (heat medium) of the hot water heater in order to prevent freezing in severe cold and to exchange heat with low-temperature outside air. This antifreeze is injected by a construction company or a maintenance company as needed. However, since there is no sensor that can control the concentration of antifreeze, circulating water may freeze due to too low concentration of antifreeze, or algae and microorganisms may propagate in circulating water due to too high concentration of antifreeze. . Therefore, an object of a second application example is to provide an antifreeze solution concentration sensor for a hot water heating device that has a simple configuration and can accurately measure.

FIG. 9 is a configuration diagram showing a second application example of the SPR sensor according to the present invention. Hereinafter, description will be made based on this drawing.

The circulating pump 61 circulates hot water (circulating water W) in a hot water tank 62 through a heat exchanger 64. The temperature of the circulating water W is measured by the temperature sensor 69. The SPR sensor 10 and the temperature sensor 69 for measuring the water temperature are mounted in the hot water tank 62, and the temperature sensor 60 for measuring the outside air temperature is mounted in another place.

The hot water heater includes an inlet 62a, an overflow 62b, a water level sensor 63, a heating element 65, a temperature sensor 66, a control device 67, a heating switch 67a, and the like.

The SPR sensor 10, as shown in FIG.
The optical fiber and the sensor plate are integrated. The end face of the optical fiber extends out of the hot water tank 62, where it is connected to the light emitting unit (FIG. 3A) and the light receiving unit (FIG. 3B). The output signal from the light receiving unit is converted into a digital signal by an AD converter, and thereafter, is calculated by an arithmetic unit (CPU) and corrected by an output signal of a temperature sensor 69 for measuring a water temperature, thereby obtaining a hot water tank 62. Used to predict the freezing temperature of

The circulating water W used as a heat medium of the hot water heating apparatus is mixed with an antifreeze containing ethylene glycol as a main component to prevent freezing in severe cold. Therefore, the second application example also has the same operation and effect as the first application example, and a detailed description is omitted.

According to the second application example, the use of the SRP sensor according to the present invention as an antifreeze concentration sensor for a hot water heating apparatus has the following effects. Firstly, it is possible to provide an antifreeze concentration sensor for a hot water heating device which has a simple configuration and can accurately measure. Second, since the electrical interface is simple, it can be easily combined with a CPU (computer).

[0057]

[Third application example] A third application example is an example in which the SRP sensor according to the present invention is used as an antifreeze concentration sensor for a heating tower. Even in the circulating water of the heating tower,
Since it is necessary to make the temperature lower than the outside air temperature in order to collect heat from the low temperature outside air, an antifreeze liquid for preventing freezing is used. Therefore, there was a problem similar to that of the conventional hot water heater (second application example). Therefore, an object of a third application example is to provide an antifreeze concentration sensor for a heating tower which has a simple configuration and can accurately measure.

FIG. 10 is a configuration diagram showing a third application example of the SPR sensor according to the present invention. Hereinafter, description will be made based on this drawing.

The heating tower 71 has the same configuration as the open cooling tower. The circulating water W is sprayed from the water spray device 72 toward the filling layer 73, and the outside air passing through the inside of the filling layer 73 and the circulating water W come into direct gas-liquid contact by driving the fan 74. As a result, the low-temperature circulating water W exchanges heat with the outside air, rises to a temperature close to the outside air temperature, and is accumulated in the lower water tank 75. An SPR sensor 10 and a temperature sensor 84 for measuring a water temperature are attached to the watering device 73, and a temperature sensor 85 for measuring the outside air temperature is attached to another location.

In addition to the heating tower 71, a heat pump device 76, a compressor 77, a condenser 78, an expansion valve 79, an evaporator 80, a pump 81, a circulation path 82, a heat exchanger 86 and the like are provided. .

The SPR sensor 10, as shown in FIG.
The optical fiber and the sensor plate are integrated. The end face of the optical fiber extends to the outside of the heating tower 71, where it is connected to a light emitting unit (FIG. 3A) and a light receiving unit (FIG. 3B). An output signal from the light receiving unit is converted into a digital signal by an AD converter, and thereafter, is calculated by an arithmetic unit (CPU) and corrected by an output signal of a temperature sensor 84 for measuring a water temperature, so that a heating tower is obtained. Used to predict the freezing temperature of 71.

The circulating water W used as a heat medium of the heating tower 71 is mixed with an antifreeze containing ethylene glycol as a main component to prevent freezing in severe cold.
Therefore, the third application example has the same operation and effect as the first application example, and thus the detailed description is omitted.

According to the third application example, the following effects can be obtained by using the SRP sensor according to the present invention as the antifreeze concentration sensor for the heating tower. Primarily,
An antifreeze concentration sensor for a heating tower can be provided which has a simple configuration and can accurately measure. Secondly,
Since the electrical interface is simple, the combination with the CPU (computer) can be facilitated.

[0064]

[Fourth Application Example] A fourth application example is an example in which the SRP sensor according to the present invention is used as a fuel type determination sensor for a fuel tank. There are many mistakes in putting fuel, such as putting light oil into a gasoline engine car or putting gasoline into a diesel engine car. When gasoline mixed with light oil is supplied to a gasoline engine vehicle, the output of the engine decreases and the engine stops. Also, when gasoline is supplied to a diesel engine vehicle, the output of the engine decreases, and the fuel injection nozzle needs to be replaced. When refueling a car, a human error is inevitably generated because the worker determines whether the fuel is light oil or gasoline. Even if you make the wrong fuel, if you notice before starting the engine, just replace the fuel and you can avoid the trouble. However, since the conventional fuel tank does not have a function of discriminating the type of fuel, starting the engine without noticing that the fuel is not correctly inserted may cause a trouble. Therefore, an object of a fourth application example is to provide a fuel type determination sensor for a fuel tank, which has a simple configuration and can accurately determine the type of fuel.

FIG. 11 is a configuration diagram showing a fourth application example of the SPR sensor according to the present invention. FIG. 11 [1] is an overall view, and FIG. 11 [2] is a partially enlarged perspective view. Hereinafter, description will be made based on this drawing.

In the fuel tank 91, a float 92 for measuring the liquid level of the fuel F is mounted via a float arm 93. The float 92 moves up and down in accordance with the liquid level of the fuel F. On the lower surface of the float 92, SPR
A sensor 10 is attached.

The SPR sensor 10, as shown in FIG.
The optical fiber and the sensor plate are integrated. The end surface of the optical fiber extends to the outside of the fuel tank 91, where it is connected to a light emitting unit (FIG. 3A) and a light receiving unit (FIG. 3B). The output signal from the light receiving unit is converted into a digital signal by an AD converter, and thereafter, is calculated by a calculation device (CPU), and is used to determine the type of fuel in the fuel tank 91.

FIG. 12 shows the refractive index and S in the fourth applied example.
It is a graph which shows the relationship with PR sensor output. Hereinafter, the operation of the SPR sensor 10 will be described based on FIG. 2, FIG. 11, and FIG.

The light P emitted from the light projecting unit propagates through the optical fiber 11, is converted into TM mode light by the polarizing film 14, and propagates through the sensor plate 13 with repeated total reflection. At this time, the light P loses a part of energy by exciting a surface plasmon wave which is a compressional wave of electrons on the thin films 13A and 13B made of gold. Therefore, by measuring the intensity of light incident on the sensor plate 13 and the intensity of light transmitted from the sensor plate 13, it is possible to know the light energy consumed for surface plasmon excitation. Since the excitation conditions are affected by the refractive index of the fuel F in contact with the thin films 13A and 13B, the refractive index of the fuel F can be known from the amount of light energy consumed by the sensor plate 13.

The fuel F used for the automobile is gasoline and light oil. The refractive index n is as follows.・ Gasoline (regular) ... n = 1.425 (measured at room temperature) ・ Gasoline (high octane) ... n = 1.433 (measured at room temperature) ・ Diesel oil ... n = 1.467 (measured at room temperature) )

Since both gasoline and light oil are a mixture of a plurality of components, their refractive indices differ slightly among fuel manufacturers. However, the difference in the refractive index between gasoline and light oil is clear. That is, if the second decimal place of the refractive index can be distinguished, gasoline and light oil can be sufficiently distinguished.

In the measurement example shown in FIG. 12, the refractive index is 1.517,
A sensor plate made of a material having a thickness of 0.4 [mm] and a length of 15 [mm] and light having a wavelength of 644 [nm] are used. As is clear from FIG. 12, the refractive index of gasoline and the refractive index of gas oil can be clearly distinguished.

According to the fourth application example, by using the SRP sensor according to the present invention as a fuel type discriminating sensor for a fuel tank, it is possible to accurately discriminate the type of fuel while having a simple structure. Can be provided. Therefore, the fuel injection error can be known before starting the engine, so that the trouble caused by the fuel error can be prevented.

Further, by installing the SRP sensor at the bottom of the fuel tank, the entry of water can be detected. The SRP sensor can also detect that the fuel has run out. By providing a temperature sensor for measuring the temperature of the fuel in the fuel tank, the output signal of the SPR sensor may be corrected.

[0075]

According to the plasmon sensor device of the present invention, a sensor plate is connected between an input optical fiber and an output optical fiber, and a thin film for exciting surface plasmons is provided on at least a part of the sensor plate. The light for surface plasmon excitation is provided from the input optical fiber and is output from the output optical fiber through the sensor plate, so that the refractive index can be accurately measured in a simple configuration, so that the size and the size can be reduced. The price can be reduced.

Further, since the length of the optical fiber can be freely selected, for example, the sensor plate can be placed at the bottom of the tank or the like, and the light emitting unit and the light receiving unit can be installed at different places. Furthermore, since the sensor plate and the electric system can be separated, a noisy environment (for example, a factory,
Engine) and the refractive index of flammable liquids such as gasoline. Therefore, a wide range of applications to home appliances and automobiles can be realized.

According to the plasmon sensor device of the second aspect, the first surface plasmon excitation light has the property that the amount of transmitted light increases in accordance with the increase in the refractive index of the substance to be measured in contact with the thin film. Second, the surface plasmon excitation light has the property that the amount of transmitted light decreases as the refractive index of the substance to be measured in contact with the thin film increases.Therefore, by taking the difference between the amounts of transmitted light, the sensitivity of the refractive index measurement can be increased. Can be improved.

According to the plasmon sensor device of the third aspect, since the sensor plate is made of a transparent plate material, metal (Au, Ag, etc.) can be easily deposited, it is cheaper and smaller than a prism, and does not require optical axis alignment. And has the effect of high mass productivity.

According to the plasmon sensor device of the fourth aspect, since the input optical fiber and the output optical fiber are multi-mode optical fibers, the cost can be reduced and the optical axis can be easily aligned.

According to the plasmon sensor device of the fifth aspect, since the polarizing film is provided between the incident optical fiber and the sensor plate, the SN ratio can be improved, so that the resolution can be improved.

[Brief description of the drawings]

1 shows a first embodiment of a plasmon sensor device according to the present invention, wherein FIG. 1 [1] is an overall perspective view, FIG. 1 [2] is an exploded perspective view, and FIG. 1 [3] is a perspective view of a sensor plate. It is.

FIG. 2 is a cross-sectional view taken along the line II-II in FIG. 1 [1].

FIG. 3 is a cross-sectional view illustrating an example of a light emitting unit and a light receiving unit used together with the plasmon sensor device of the first embodiment. FIG. 3 [1] is a light emitting unit, and FIG.
Is a light receiving unit.

FIG. 4 is a graph showing the relationship between the refractive index of a sample and the amount of transmitted light in the plasmon sensor device of the first embodiment.

FIG. 5 [1] is an overall perspective view showing a second embodiment of the plasmon sensor device according to the present invention. Fig. 5 [2]
FIG. 3 is an overall perspective view showing a third embodiment of the plasmon sensor device according to the present invention.

FIG. 6 is a graph showing the relationship between the refractive index of a sample and the amount of transmitted light in the plasmon sensor device of the second embodiment. FIG. 6A is a graph showing the relationship between the refractive index of the sample and the amount of transmitted light at different wavelengths.
[2] is a graph showing the difference between the transmitted light amounts.

FIG. 7 is a configuration diagram showing a first application example of the plasmon sensor device according to the present invention.

FIG. 8 [1] is a graph showing the relationship between the antifreeze concentration and the refractive index in the first application example, and FIG. 8 [2] is the graph showing the relationship between the freezing temperature and the refractive index in the first application example. It is a graph.

FIG. 9 is a configuration diagram showing a second application example of the plasmon sensor device according to the present invention.

FIG. 10 is a configuration diagram showing a third application example of the plasmon sensor device according to the present invention.

FIG. 11 is a configuration diagram showing a fourth application example of the plasmon sensor device according to the present invention.

FIG. 12 is a graph showing a relationship between a refractive index and an output of an SPR sensor in a fourth application example.

[Explanation of symbols]

 10, 30, 40 Plasmon sensor device 11, 31a, 31b Optical fiber for incidence 12, 32a, 32b Optical fiber for emission 13, 33 Sensor plate 13A, 13B, 33A, 33B Thin film 14 Polarizing film

Continued on the front page F term (reference) 2G059 AA02 BB01 BB04 BB12 CC16 EE01 EE02 EE05 EE11 FF07 GG01 GG02 GG04 HH02 HH06 JJ17 JJ19 KK01 MM01 MM09 MM14 PP04

Claims (5)

[Claims] 1. A sensor plate is connected between an input optical fiber and an output optical fiber, a thin film for exciting surface plasmons is provided on at least a part of the sensor plate, and light for exciting surface plasmons is provided. A plasmon sensor device, wherein the plasmon sensor device enters from an input optical fiber, passes through the sensor plate, and exits from the output optical fiber. 2. A sensor plate is connected between the first and second input optical fibers and the first and second output optical fibers, and a thin film for exciting surface plasmons is provided on at least a part of the sensor plate. Is provided, light for exciting the first surface plasmon is incident from the first input optical fiber, exits from the first emitting optical fiber through the sensor plate, and excites the second surface plasmon. Is incident from the second incident optical fiber, exits from the second exit optical fiber through the sensor plate, and the first surface plasmon excitation light is the substance to be measured in contact with the thin film. The second surface plasmon excitation light has a property that the amount of transmitted light decreases with an increase in the refractive index of the substance to be measured. Razumonsensa apparatus. 3. The plasmon sensor device according to claim 1, wherein said sensor plate is made of a transparent plate. 4. The plasmon sensor device according to claim 1, wherein the input optical fiber and the output optical fiber are multimode optical fibers. 5. The plasmon sensor device according to claim 1, wherein a polarizing film is provided between the incident optical fiber and the sensor plate.