JP7533941B2 - Humidity Sensors - Google Patents

Description

The present invention relates to a humidity sensor.

When body temperature rises due to exercise, sweat is secreted from sweat glands. Therefore, by monitoring the humidity of the skin with a humidity sensor, it is possible to measure sweating during exercise. In addition, by detecting the humidity of exhaled breath with a humidity sensor, it is possible to monitor breathing. In order to monitor the humidity of the skin and the humidity of exhaled breath, it is necessary to make the humidity sensor a wearable device.
Polymer capacitance type humidity sensors are also known (see, for example, Japanese Patent Application Laid-Open No. 2003-233634).

JP 2019-007757 A

However, polymer capacitance humidity sensors are vulnerable to noise because they measure capacitance, and this requires shielding the wiring between the humidity sensing section and the signal processing section, which makes the humidity sensor larger. As a result, they are not suitable for wearable devices.
The present invention has been made in view of the above circumstances, and provides a humidity sensor which can be miniaturized and can perform stable measurements even under humidity conditions of 90% RH or higher.

The present invention provides a humidity sensor comprising a sensing unit, the sensing unit including a moisture-sensitive layer and first and second electrodes electrically connected to the moisture-sensitive layer, the moisture-sensitive layer including niobic acid carrying Pd.

The sensing part includes a moisture sensitive layer and first and second electrodes electrically connected to the moisture sensitive layer, and is capable of measuring an electrical resistance of the moisture sensitive layer using the first and second electrodes.
The moisture-sensitive layer contains niobic acid carrying Pd. Therefore, even under high humidity, the electrical resistance of the moisture-sensitive layer changes stably according to the humidity. This fact was made clear by experiments conducted by the inventors of the present application. In addition, the humidity can be calculated from the electrical resistance value of the moisture-sensitive layer measured using the first and second electrodes. Therefore, when the humidity sensor of the present invention is used, the humidity can be measured with high accuracy even under high humidity.
In addition, since the humidity is calculated from the electrical resistance of the moisture-sensitive layer, the humidity sensor of the present invention is less susceptible to the effects of noise, and therefore the humidity sensor can be made smaller.

1 is a schematic plan view of a humidity sensor according to an embodiment of the present invention; 2 is a schematic cross-sectional view of the humidity sensor taken along dashed line AA in FIG. 1. 5A to 5D are explanatory diagrams of a method for manufacturing a humidity sensor. 1 is a graph showing the change in electrical resistance of a moisture-sensitive layer when the relative humidity is alternately changed from 30% to 90%, from 30% to 90%, and back again. 1 is a graph showing the change in electrical resistance of a moisture-sensitive layer when the relative humidity is alternately changed from 30% to 90%, from 30% to 90%, and back again. 1 is a graph showing the change in electrical resistance of the moisture-sensitive layer when the relative humidity is changed from 30% to 90%. 1 is a graph showing the change in electrical resistance of the moisture-sensitive layer when the relative humidity is changed from 30% to 90%. 13 is a graph comparing the measurement results of the fabricated humidity sensor with the measurement results of a commercially available humidity sensor. 1 is a graph showing the measurement results of the pH of a dispersion of unsupported HNb ₃ O ₈ and the pH of a dispersion of Pd-supported HNb ₃ O ₈ . 1 is a graph showing the change in electrical resistance of the humidity-sensitive layer of a 1 wt % Pd HNb ₃ O ₈ humidity sensor with the change in relative humidity. 1 is a graph showing the change in electrical resistance of a moisture-sensitive layer with a change in temperature. 1 is a graph showing the change in electrical resistance of the moisture-sensitive layer when a 1 wt % Pd HNb ₃ O ₈ humidity sensor is deformed. 1 is a graph showing the change in electrical resistance of a LIG electrode and the change in electrical resistance of a silver electrode with change in relative humidity. (a) is a photograph of a humidity sensor attached to a mask, (b) is a graph showing the change in electrical resistance of the moisture-sensitive layer, and (c) and (d) are enlarged views of the graph (b). 13 is a graph showing the change in electrical resistance of the moisture-sensitive layer when a fingertip is brought close to a humidity sensor 15 times. (a) is a photograph of the fabricated humidity sensor, and (b) is a photograph of the humidity sensor attached to a fingertip. 1 is a graph showing the change in electrical resistance of the moisture-sensitive layer when an adult male runs with a 1 wt % Pd HNb ₃ O ₈ humidity sensor attached to his fingertip.

The humidity sensor of the present invention includes a sensing unit, the sensing unit including a moisture-sensitive layer and first and second electrodes electrically connected to the moisture-sensitive layer, and the moisture-sensitive layer includes niobic acid carrying Pd.

The niobic acid is preferably a compound represented by HNb ₃ O ₈ .
The niobic acid preferably contains Nb ⁵⁺ and Nb ⁴⁺ .
The niobic acid carrying Pd is preferably niobic acid carrying 0.001 wt % or more and 3 wt % or less of Pd.
The niobic acid preferably comprises exfoliated nanosheets.

The sensing portion is preferably disposed on a base sheet.
The base sheet is preferably a polyimide film, which allows the humidity sensor to be a flexible sensor that can be attached to the skin or clothing.
The first and second electrodes are preferably carbonized layers on the surface of the polyimide film, which makes it possible to stably measure humidity even when the relative humidity exceeds 90%.

One embodiment of the present invention will be described below with reference to the drawings. The configurations shown in the drawings and the following description are merely examples, and the scope of the present invention is not limited to those shown in the drawings and the following description.

FIG. 1 is a schematic plan view of the humidity sensor of this embodiment, and FIG. 2 is a schematic cross-sectional view of the humidity sensor taken along the dashed dotted line AA in FIG.
The humidity sensor 10 of this embodiment comprises a sensing unit 1, which includes a moisture-sensitive layer 2, and a first electrode 3 and a second electrode 4 electrically connected to the moisture-sensitive layer 2, and the moisture-sensitive layer 2 is characterized in that it contains niobic acid carrying Pd.
The humidity sensor 10 of this embodiment may include a base sheet 5, a waterproof breathable filter 7, or a control unit.

The humidity sensor 10 of this embodiment is a resistive humidity sensor.
The sensing unit 1 is a portion for detecting humidity, and includes a moisture-sensitive layer 2, and a first electrode 3 and a second electrode 4 electrically connected to the moisture-sensitive layer 2. The sensing unit 1 may be disposed on a base sheet 5, or on a substrate. The sensing unit 1 may also have a layered structure in which the first electrode 3, the moisture-sensitive layer 2, and the second electrode 4 are layered in this order.

The humidity sensor 10 may have one sensing unit 1 like the humidity sensor 10 shown in FIG. 1, or may have multiple sensing units 1. When the humidity sensor 10 has multiple sensing units 1, it becomes possible to measure the humidity distribution.

The base sheet 5 can be a flexible sheet. This allows the humidity sensor 10 to be placed on the skin, clothing, a mask, etc., and allows the humidity of the skin, the humidity of the breath, sweating, etc. to be measured. The base sheet 5 can be, for example, a plastic film. The base sheet 5 is, for example, a polyimide film. The thickness of the base sheet 5 can be, for example, 1 μm or more and 500 μm or less.

The first electrode 3 and the second electrode 4 are electrodes electrically connected to the moisture-sensitive layer 2 and are electrodes for measuring the electrical resistance of the moisture-sensitive layer 2. The method for measuring the electrical resistance of the moisture-sensitive layer 2 may be a two-terminal method or a four-terminal method. The first electrode 3 and the second electrode 4 are, for example, a carbon electrode, a graphene electrode, a silver electrode, a gold electrode, a platinum electrode, a copper electrode, an aluminum electrode, etc. The thickness of the first electrode 3 or the second electrode 4 can be, for example, 30 nm or more and 300 μm or less. The interelectrode distance between the first electrode 3 and the second electrode 4 can be, for example, 100 nm or more and 5 mm or less.

When the base sheet 5 is a polyimide film, the first electrode 3 and the second electrode 4 may be a carbonized layer (graphene electrode) on the surface of the polyimide film. This allows the electrical resistance of the moisture-sensitive layer 2 to be stably measured even in a humid environment. In addition, the conductivity of the first electrode 3 and the second electrode 4 can be suppressed from changing due to humidity. The carbonized layer can be formed, for example, by irradiating a polyimide film with laser light. The carbonized layer may be a laser-induced graphene (LIG) layer. The laser used to form the LIG layer is, for example, a _CO2 laser, a fiber laser, a YAG laser, a _YVO4 laser, or the like. In addition, the thickness of the LIG layer and the thickness of the polyimide film left under the LIG layer can be adjusted by adjusting the laser output, scanning speed, etc. In addition, the first electrode 3 and the second electrode 4 may be formed by transferring the LIG layer formed on the polyimide film to the base sheet 5.
In addition, when the first electrode 3 and the second electrode 4 are metal layers or carbon layers, the first electrode 3 and the second electrode 4 can be formed by a printing method, a vapor deposition method, or the like.

The moisture-sensitive layer 2 is a layer whose electrical resistance changes depending on the humidity, and contains niobic acid carrying Pd (palladium). The moisture-sensitive layer 2 may have a porous structure. The thickness of the moisture-sensitive layer 2 may be, for example, 30 nm or more and 100 μm or less, and preferably 1 μm or more and 20 μm or less. The moisture-sensitive layer 2 may be formed by, for example, a coating method or a printing method.

_The niobic acid contained in _the moisture-sensitive layer 2 may be, for example, _{HNb3O8 , HNbO3} , _H4Nb6O17 , or _H4Nb2O7 . The niobic acid contained in the moisture-sensitive layer 2 may be a _layered compound. The niobic acid contained in the moisture-sensitive layer 2 may be a niobic acid nanosheet _formed by peeling off niobic acid, which is a layered compound. The niobic acid contained in the moisture-sensitive layer 2 may be one that has been subjected to ultraviolet irradiation treatment. The niobic acid may be a compound consisting of H (hydrogen), Nb (niobium), and O (oxygen).
The niobic acid contained in the moisture-sensitive layer 2 is preferably a _HNb3O8 nanosheet. It is more preferable that the niobic acid contained in the moisture-sensitive layer 2 is a _{HNb3O8 nanosheet} that has been subjected to ultraviolet irradiation treatment. The valence of _{Nb contained in HNb3O8 is} basically +5, but ^Nb4+ is generated _{in HNb3O8 by} performing ultraviolet irradiation treatment. Therefore, _{the HNb3O8 nanosheet} that has been subjected to ultraviolet irradiation treatment contains ^Nb5+ and Nb4 ⁺ .

Pd is supported on the surface of the niobic acid contained in the moisture-sensitive layer 2. For example, Pd can be supported on the surface of the niobic acid by a photoprecipitation method, an impregnation hydrogen reduction method, or the like.
The niobic acid contained in the moisture-sensitive layer 2 may be niobic acid carrying 0.001 wt % or more and 3 wt % or less of Pd, or niobic acid carrying 0.1 wt % or more and 3 wt % or less of Pd, or niobic acid carrying 0.5 wt % or more and 3 wt % or less of Pd.

The moisture-sensitive layer 2 may be covered with a waterproof breathable filter. By covering the moisture-sensitive layer 2 with a waterproof breathable filter, it is possible to prevent external water (e.g., body fluids such as sweat and urine) from directly contacting the moisture-sensitive layer 2. In addition, water vapor and the like can be supplied to the moisture-sensitive layer 2 through the ventilation holes of the waterproof breathable filter.

The first electrode 3 and the second electrode 4 can be connected to the control unit via wiring, wirelessly, etc. The control unit is, for example, a computer, a microcontroller, an electronic board, a smartphone, etc. The control unit can also include a calculation unit, a memory unit, a display unit, etc. The control unit can also include a power supply unit used to measure the electrical resistance of the moisture-sensitive layer 2. The control unit can, for example, measure the electrical resistance value of the moisture-sensitive layer 2, calculate the humidity from the measured electrical resistance value, and store the calculated humidity in the memory unit. The control unit can also display the calculated humidity on the display unit. The control unit can also wirelessly transmit the measured electrical resistance value of the moisture-sensitive part 2, etc., and the humidity can be calculated by a device (for example, a smartphone) that receives the wireless signal.

Figures 3(a) to (d) are explanatory diagrams of a manufacturing method of the humidity sensor 10 of this embodiment. A base sheet 5 as shown in Figure 3(a) is prepared, and comb-shaped electrodes of the first electrode 3 and the second electrode 4 are formed as shown in Figure 3(b). When the base sheet 5 is a polyimide film and the first electrode 3 and the second electrode 4 are graphene layers, the first electrode 3 and the second electrode 4 can be formed by irradiating the polyimide film with laser light. Also, when the base sheet 5 is not a polyimide film, the first electrode 3 and the second electrode 4 may be formed by transferring a graphene layer formed by irradiating the polyimide film with laser light to the base sheet 5.

Next, a paste containing Pd-supported niobic acid is applied onto the comb-shaped electrode consisting of the first electrode 3 and the second electrode 4, and then dried to form the moisture-sensitive layer 2. Note that since the moisture-sensitive layer 2 is thin, it is not shown in FIG. 3. Thereafter, as shown in FIG. 3(c), wiring 6 is formed to connect the first electrode 3 and the second electrode 4 to the control unit. For example, silver wiring is formed on the base sheet 5. Then, a waterproof breathable filter 7 is attached onto the moisture-sensitive layer 2.
In this manner, the humidity sensor 10 can be fabricated.

Fabrication of humidity sensor Niobium oxide (Nb ₂ O ₅ ) and potassium carbonate (K ₂ CO ₃ ) were mixed in a stoichiometric ratio and the mixed powder was baked at 900°C to synthesize KNb ₃ O ₈ (layered compound). The obtained KNb ₃ O ₈ was added to a 6 mol·L- ¹ nitric acid solution (HNO ₃ ) and stirred for 6 days. This resulted in ion exchange between K ⁺ (potassium ion) and H ⁺ (hydrogen ion), and KNb ₃ O ₈ became HNb ₃ O ₈ (layered compound). The obtained HNb ₃ O ₈ was intercalated using tetrabutylammonium cation (TBAOH) to peel off the layer structure of HNb ₃ O ₈ and obtain nanosheet-like HNb ₃ O ₈ .

Nanosheet-like HNb ₃ O ₈ was dispersed in a mixed solution of distilled water and ethanol (mixing ratio 1:1), and this dispersion was irradiated with ultraviolet light (wavelength: 365 nm) for 30 minutes. As a result, part of the Nb ⁵⁺ contained in HNb ₃ O ₈ was converted to Nb ⁴⁺ . Then, 10 mg mL ^-1 Na ₂ PdCl ₄ aqueous solution was added to this dispersion, and ultraviolet light was irradiated for 1 hour, so that Pd was supported on the nanosheet-like HNb ₃ O ₈ , and Pd-supported HNb ₃ O ₈ nanosheets were obtained. The amount of Pd supported was 1 wt%, 2 wt%, or 3 wt%. In addition, Au-supported HNb ₃ O ₈ nanosheets in which Au was supported on nanosheet-like HNb ₃ O ₈ and Ag-supported HNb ₃ O ₈ nanosheets in which Ag was supported on nanosheet-like HNb ₃ O ₈ were also synthesized.

Using a _CO2 laser system (VLS2.30, UNIVERSAL Laser System), the prepared polyimide film (thickness: 50 μm) was irradiated with a _CO2 laser (wavelength: 10.6 μm, power: 2 W) to cut the polyimide film and form a laser-induced graphene layer (LIG layer). The LIG layer was formed so that the first electrode and the second electrode were opposed to each other to form a comb-shaped electrode, as shown in Figures 1 to 3.
Next, a Pd-loaded _{HNb3O8 nanosheet} aqueous solution (5 mg mL ^-1 ) was applied onto the interdigitated electrode of the LIG layer and dried at 100°C to form a moisture-sensitive layer. Then, silver wiring was formed to connect to the terminal part of the LIG layer so that the electrical resistance of the moisture-sensitive layer could be measured.
In this way, a humidity sensor was formed. In addition, a humidity sensor in which the moisture-sensitive layer was an Au-supported HNb ₃ O ₈ nanosheet layer and a humidity sensor in which the moisture-sensitive layer was an Ag-supported HNb ₃ O ₈ nanosheet layer were also fabricated.

Measurement of the electrical resistance of the moisture-sensitive layer In an environmental tester (Espec, SH-222) capable of controlling temperature and humidity, the following humidity sensors were placed: unsupported HNb ₃ O ₈ humidity sensor (moisture-sensitive layer is HNb ₃ O ₈ nanosheet layer (unsupported)), 1wt% Pd HNb ₃ O ₈ humidity sensor (moisture-sensitive layer is HNb ₃ O ₈ nanosheet layer with 1wt% Pd supported), 2wt% Pd HNb ₃ O ₈ humidity sensor (moisture-sensitive layer is HNb ₃ O ₈ nanosheet layer with 2wt% Pd supported), 3wt% Pd HNb 3 O ₈ humidity sensor (moisture-sensitive layer is HNb ₃ O 8 nanosheet layer with 3wt% Pd supported), 1wt% Au HNb ₃ O 8 humidity sensor (moisture-sensitive layer is HNb ₃ O ₈ nanosheet layer with 1wt% Au supported), 1wt% Ag HNb ₃ O ₈ humidity sensor (moisture-sensitive layer is HNb ₃ O ₈ nanosheet layer with 1wt% Au supported), A _humidity sensor (having a humidity-sensitive layer of 1 wt % Ag-loaded HNb ₃ O ₈ nanosheet layer) was installed, and the electrical resistance of the humidity-sensitive layer was measured.
Figures 4 and 5 show the measurement results when the relative humidity of the environmental tester was repeatedly changed from 30% to 90% to 30% to 90% (temperature was constant at 25°C) (cycle test). Figures 6 and 7 show the measurement results when the relative humidity of the environmental tester was changed from 30% to 90%. Figure 8 is a graph comparing the relative humidity calculated from the electrical resistance of the moisture-sensitive layer with the measurement value of a commercially available humidity sensor.
4 to 7, the vertical axis indicates the resistance change rate ΔR/R ₀ × 100 (R ₀ : the electrical resistance value of the moisture-sensitive layer at the start of the measurement (humidity about 30%), ΔR=R−R ₀ , R: the electrical resistance value of the moisture-sensitive layer corresponding to the horizontal axis). The same is true for the other graphs.

When the relative humidity changed from 30% to 90%, the humidity _- sensitive layer of the unsupported _{HNb3O8 humidity} sensor showed a large resistance change of about 40%, as shown in the graphs in Figures 4 and 6. This is thought to be because the weakly acidic _HNb3O8 nanosheets have a high affinity for water molecules, and further because proton hopping occurs in the physically adsorbed water molecules in the humidity-sensitive layer in a high-humidity environment.
However, in the unsupported HNb ₃ O ₈ humidity sensor, the resistance change rate of the humidity-sensitive layer decreased and the resistance change became unstable when the humidity cycle was repeated. Therefore, it was found that the unsupported HNb ₃ O ₈ humidity sensor has poor reproducibility and stability.

The humidity-sensitive layer of the 1wt%Pd HNb ₃ O ₈ humidity sensor showed a resistance change of about 15% when the relative humidity changed from 30% to 90%, as shown in the graphs of Figures 4 and 6, and showed a stable resistance change even with repeated humidity cycles. Furthermore, even at a relative humidity of around 90%, the humidity-sensitive layer showed a resistance change in response to humidity changes, demonstrating the possibility of humidity measurement.
The humidity change calculated from the resistance change of the humidity-sensitive layer of the 1 wt % Pd HNb ₃ O ₈ humidity sensor was almost the same as the humidity change measured by a commercially available humidity sensor, as shown in the graph of FIG.
The humidity sensitive layers of the 2wt% _{PdHNb3O8 humidity} sensor and _the 3wt% _PdHNb3O8 humidity sensor also showed stable resistance changes during repeated humidity cycles, but the resistance change rate was lower than that of the _1wt % _PdHNb3O8 humidity sensor.
As shown in the graphs of FIG. 5 and FIG. 7, the moisture sensitive layer of the 1 wt % Au HNb ₃ O ₈ humidity sensor and the moisture sensitive layer of the 1 wt % Ag HNb ₃ O ₈ humidity sensor did not show a stable change in resistance even when the relative humidity was changed.

Although it is not clear why a humidity sensor having a Pd-loaded HNb ₃ O ₈ moisture-sensing layer has stable moisture-sensing characteristics, it is believed that this is because proton hopping in physically adsorbed water molecules is adjusted by Pd.
FIG. 9 is a graph showing the results of measuring the pH of the dispersion of unsupported HNb ₃ O ₈ or the dispersion of Pd-supported HNb ₃ O _8. The pH of the unsupported HNb ₃ O ₈ dispersion was about 3.3. This is thought to be because many protons are ionized when unsupported HNb ₃ O ₈ nanosheets are dispersed in water. On the other hand, the pH of the Pd-supported HNb ₃ O ₈ dispersion increased as the amount of Pd supported increased. This is thought to be because the amount of ionized protons decreases when Pd-supported HNb ₃ O ₈ nanosheets are dispersed in water compared to unsupported HNb ₃ O ₈ dispersion. It is thought that such a decrease in the amount of ionized protons contributes to the stabilization of the humidity sensitivity characteristics of the humidity sensor.

FIG. 10 is a graph showing the change in the electrical resistance of the moisture-sensitive layer when a 1wt% Pd HNb ₃ O ₈ humidity sensor is installed in an environmental test machine and the relative humidity is changed from 30% to 43.1% to 30% to 53.9% to 30% to 64.1% to 30% to 73.7% to 30% to 83.8% to 30% to 92.2% to 30% to 99.9% to 30%. As shown in the graph of FIG. 10, the electrical resistance of the moisture-sensitive layer changes according to the relative humidity. Therefore, it was found that the 1wt% Pd HNb ₃ O ₈ humidity sensor can stably detect the relative humidity and can measure the humidity with good sensitivity even when the relative humidity is 90% or more.

FIG. 11 is a graph showing the change in the electrical resistance of the moisture-sensitive layer when a 1wt% Pd HNb ₃ O ₈ humidity sensor is placed in an environmental tester and the temperature is changed from 10°C to 20°C to 30°C to 40°C to 50°C to 40°C to 30°C to 20°C to 10°C. In this measurement, a humidity-blocking film is attached to the humidity sensor to suppress the humidity change caused by the temperature change. As shown in the graph of FIG. 11, the electrical resistance of the moisture-sensitive layer hardly changes even when the temperature changes. Therefore, it was found that the temperature change can be ignored in the humidity measurement with the 1wt% Pd HNb ₃ O ₈ humidity sensor.

Figure 12 is a graph showing the change in the electrical resistance of the moisture-sensitive layer when the 1wt%Pd _{HNb3O8 humidity} sensor is deformed so that the bending radius is 0.8 cm → 1.7 cm → 3 cm → 4.3 cm → 7 cm → flat. As shown in the graph of Figure 12, the electrical resistance of the moisture-sensitive layer hardly changes even when the bending radius is changed. Therefore, it was found that the deformation of the 1wt%Pd _{HNb3O8 humidity} sensor can be ignored in humidity measurement.

In a resistance-type humidity sensor , the first and second electrodes connected to the humidity-sensitive layer must have stable conductive properties regardless of humidity. Therefore, a polyimide film on which a LIG electrode (LIG layer) is formed and a polyimide film on which a silver electrode is formed were placed in an environmental test chamber, and the electrical resistance of the LIG electrode and the electrical resistance of the silver electrode were measured when the relative humidity was changed from 30% to 90% to 30%. The measurement results are shown in FIG. 13. The electrical resistance of the LIG electrode hardly changed even when the relative humidity changed. On the other hand, the electrical resistance of the silver electrode showed an unstable change. Therefore, it was found that by using a LIG electrode as the electrode of a resistance-type humidity sensor, the change in the electrical resistance of the electrode can be ignored in humidity measurement.

Biometric measurements using humidity sensors
A 1wt%Pd HNb ₃ O ₈ humidity sensor was attached to a filtering face mask to measure the humidity change associated with breathing and monitor breathing. The mask was put on and taken off three times during the measurement. A 1wt%Pd HNb ₃ O ₈ humidity sensor was fabricated and used that was large enough to be attached to the mask.
FIG. 14(a) is a photograph of the humidity sensor attached to the mask, FIG. 14(b) is a graph showing the change in electrical resistance of the moisture-sensitive layer, and FIGS. 14(c) and (d) are enlarged views of the graph of FIG. 14(b).
The electrical resistance of the moisture-sensitive layer was 7 MΩ to 7.5 MΩ when the mask was not worn, and 2.6 MΩ to 4.8 MΩ when the mask was worn, and fluctuated with breathing. Therefore, it was confirmed that breathing can be monitored using the 1wt% _{PdHNb3O8 humidity} sensor.

The moisture evaporating from the fingertip was measured using a 1wt% Pd HNb ₃ O ₈ humidity sensor.
FIG. 15 is a graph showing the change in electrical resistance of the humidity-sensitive layer when the fingertip is brought close to the humidity sensor 15 times. The distance between the humidity sensor and the fingertip was 5 mm for the first 5 times, 2.5 mm for the next 5 times, and 1 mm for the last 5 times. As shown in FIG. 15, a decrease in the electrical resistance of the humidity-sensitive layer was measured when the fingertip was brought close to the humidity sensor. In addition, the electrical resistance decreased more significantly as the distance was reduced. Therefore, it was confirmed that the distance to the skin can be monitored using a 1wt%Pd HNb ₃ O ₈ humidity sensor.

Next, a 1wt% _{PdHNb3O8 humidity} sensor was fabricated that was large enough to be attached to a fingertip. In this sensor, a waterproof and breathable filter (TEMISH (registered trademark) manufactured by Nitto Denko Corporation) was attached to the moisture-sensitive layer to prevent sweat from the fingertip from directly contacting the moisture-sensitive layer, and only moisture was supplied to the moisture-sensitive layer. Figure 16(a) is a photograph of the fabricated humidity sensor (before the waterproof and breathable filter was attached), and Figure 16(b) is a photograph of the humidity sensor attached to a fingertip. In addition, the measurement results of the electrical resistance of the moisture-sensitive layer were made so that they could be output to a smartphone via wireless communication.

The electrical resistance of the moisture-sensitive layer was measured when an adult male ran at a speed of 8 km/h with this 1 wt% Pd HNb ₃ O ₈ humidity sensor attached to his fingertip. The measurement results are shown in FIG.
In the measurement, about 2 minutes after the start of the measurement, the plastic sheet placed between the 1wt%Pd HNb ₃ O ₈ humidity sensor and the fingertip was removed, the waterproof breathable filter was placed in contact with the fingertip, and running began about 4 minutes and 20 seconds after the start of the measurement. Then, about 9 minutes and 20 seconds after the start of the measurement, the running was stopped and the subject rested. The adult male had consumed sufficient water before the start of the measurement.
When the plastic sheet was removed, the electrical resistance of the moisture-sensitive layer dropped from about 7.5 MΩ to about 3 MΩ. Then, when he started running, the electrical resistance of the moisture-sensitive layer dropped to about 2.5 MΩ. This is thought to be because the amount of moisture evaporated from the fingertips increased due to exercise. When the adult male started to sweat, the electrical resistance of the moisture-sensitive layer gradually dropped to about 2.1 MΩ. This is thought to be because the humidity of the moisture-sensitive layer became extremely high due to the influence of sweat from the fingertips.
Therefore, it was confirmed that exercise and sweating can be monitored using the 1 wt% Pd HNb ₃ O ₈ humidity sensor.

1: Sensing section 2: Moisture-sensitive layer 3: First electrode 4: Second electrode 5: Base sheet 6: Wiring 7: Waterproof breathable filter 10: Humidity sensor

Claims (7)

A sensing unit is provided.
The sensing unit includes a moisture-sensitive layer and first and second electrodes electrically connected to the moisture-sensitive layer.
The humidity sensor is characterized in that the moisture-sensitive layer contains niobic acid carrying Pd. 2. The humidity sensor according to claim 1, wherein the _niobic acid is a compound represented by _HNb3O8 . 3. The humidity sensor according to claim 1, wherein the niobic acid contains ^Nb5+ and Nb4 ⁺ . The humidity sensor according to any one of claims 1 to 3, wherein the niobic acid carrying Pd is niobic acid carrying 0.001 wt% to 3 wt% Pd. The humidity sensor according to any one of claims 1 to 4, wherein the niobic acid includes exfoliated nanosheets. Further comprising a base sheet,
6. The humidity sensor according to claim 1, wherein the sensing portion is disposed on the base sheet. The base sheet is a polyimide film,
7. The humidity sensor according to claim 6, wherein the first and second electrodes are carbonized layers on the surface of the polyimide film.