Multimodal sensor

Abstract

To provide a multi-modal sensor using a CNT film for measuring a plurality of physical properties only by signal control between a pair of terminals.SOLUTION: A multi-modal sensor for providing measurements of multiple physical properties using a carbon nanotube (CNT) film provided on a flexible substrate. On a substrate, a p-type CNT film and an n-type CNT film are arranged in series along a current path between a pair of output terminals with a p-n junction part provided therebetween, and an element part is included which gives measurements of a temperature change and a shape change from an electromotive force change and a resistance value change measured by giving a current between the pair of output terminals.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to multimodal sensors that use carbon nanotube films to provide measurements of multiple physical properties. [Background technology]

[0002] Multimodal sensors have been proposed that integrate many different sensors on a single chip and provide measurements of multiple physical properties at once.

[0003] For example, Patent Document 1 discloses a sensor sheet that can simultaneously measure temperature and pressure at the same location on a subject. This sensor sheet is configured by overlapping a temperature sensor sheet in which a plurality of temperature sensors, whose electromagnetic characteristics such as resistance change depending on the temperature, are two-dimensionally arranged, and a pressure sensor sheet in which a plurality of pressure sensors, whose electromagnetic characteristics such as resistance change depending on the pressure, are two-dimensionally arranged, so that their respective detection units are positioned at the same location on the subject.

[0004] On the other hand, if it becomes possible to control input and / or output signals using only one element, rather than combining different types of sensors as described above, that is, to measure multiple physical properties by controlling signals between only a pair of terminals, it is expected that smaller and simpler sensing systems will become possible.

[0005] Here, carbon nanotubes (CNTs) are known to be usable for measuring multiple physical properties, such as pressure sensors (e.g., Patent Document 2), temperature sensors (e.g., Patent Document 3), and infrared sensors (e.g., Patent Document 4), and the use of such materials can be considered. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-118552 [Patent Document 2] Japanese Patent Application Laid-Open No. 2019-200189 [Patent Document 3] Japanese Patent Application Laid-Open No. 2012-122864 [Patent Document 4] Japanese Patent Publication No. 2023-85406 Summary of the Invention [Problem to be solved by the invention]

[0007] It has been known that carbon nanotube (CNT) films have a porous structure, high thermoelectric conversion capacity, and ultra-broadband absorption characteristics in the sub-THz to visible light band due to plasmon resonance. The problem is how to provide such a CNT film on a flexible substrate and measure multiple physical properties using only signal control between a pair of terminals, as described above.

[0008] The present invention has been made in consideration of the above-mentioned circumstances, and its purpose is to provide a multimodal sensor that uses a CNT film and can measure multiple physical properties by simply controlling the signal between a pair of terminals. [Means for solving the problem]

[0009] The sensor according to the present invention is a multimodal sensor that measures multiple physical properties using a carbon nanotube (CNT) film provided on a flexible substrate, and is characterized in that a p-type CNT film and an n-type CNT film are arranged in series on the substrate along a current path between a pair of output terminals with a pn junction provided between them, and the sensor includes an element section that provides measurements of temperature change and shape change from changes in electromotive force and resistance value measured when a current is applied between the pair of output terminals.

[0010] According to this feature, it is possible to measure temperature changes and shape changes by controlling signals between a pair of terminals only.

[0011] In the above invention, the pn junction may be provided in plurality along the current path, which makes it possible to measure temperature changes more accurately.

[0012] In the above invention, the element portion may include an extension portion of the current path that amplifies the change in resistance value in response to a change in shape. This feature makes it possible to more accurately measure the change in shape.

[0013] The above-mentioned invention may be characterized in that it includes a light source that irradiates detection light of a predetermined wavelength that has been frequency-modulated, and receives reflected light or transmitted light of the detection light, and provides a physical measurement corresponding to the predetermined wavelength from the electromotive force change corresponding to the frequency modulation. According to this feature, it is possible to provide a physical measurement corresponding to the predetermined wavelength in addition to measuring temperature change and shape change.

[0014] In the above-described invention, a plurality of the element units may be arranged on a flexible substrate, and measurements of physical properties corresponding to positions on the substrate may be provided. According to this feature, measurements of a plurality of physical properties may be provided for each position in a two-dimensional plane.

[0015] In the above invention, The device may be characterized in that a plurality of the element portions are arranged in a matrix on the substrate, and according to this feature, it is possible to measure a plurality of physical properties for each matrix position in a two-dimensional plane. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a plan view showing one embodiment of a multimodal sensor according to the present invention; [Figure 2] This is a photograph showing an example of how the multimodal sensor is used. [Figure 3] FIG. VI shows the results of measuring electromotive force using the multimodal sensor. [Figure 4]FIG. 10A is a diagram showing the relationship between bending and resistance value, and FIG. 10B is a diagram showing the relationship between temperature and electromotive force, both obtained by the multimodal sensor. [Figure 5] FIG. 10 is a plan view of an element portion of a multimodal sensor according to another embodiment. [Figure 6] This is a photo of the appearance of the multimodal sensor. [Figure 7] 10A and 10B are a photograph of the appearance of a multimodal sensor according to still another embodiment, and a plan view of an element portion thereof. [Figure 8] 10A is a photograph showing an example of use of a multimodal sensor according to yet another embodiment, and FIG. 10B is a plan view of the sensor including an element portion. [Figure 9] FIG. 1 is a block diagram of a sensing system using a multimodal sensor. [Figure 10] FIG. 1 is a diagram illustrating the measurement principle of absorbance, temperature, and deformation using a multimodal sensor. [Figure 11] FIG. 2 is a diagram illustrating a light source unit of the sensing system. [Figure 12] 4A and 4B are diagrams illustrating changes in electromotive force generated in a sensor by detection light from first and second light sources. [Figure 13] FIG. 1 is a block diagram showing a method for investigating the physical properties of an object to be measured by detection light. [Figure 14] 1 is a table showing the results of absorbance measurement, the results of absorbance ratio calculation, and the results of identifying materials and thicknesses. [Figure 15] This is a photograph of the appearance of the object to be measured with the measurement area divided. [Figure 16] 10 is a table showing the absorbance and absorbance ratio of the object to be measured. DETAILED DESCRIPTION OF THE INVENTION

[0017] A multimodal sensor according to one embodiment of the present invention will be described below with reference to FIGS.

[0018] [Example 1] 1, the sensor 10 includes an element section 19 formed by a substrate 11 and a current path made of a carbon nanotube (CNT) film provided thereon. In the element section 19, a p-type CNT film 13 and an n-type CNT film 14 are arranged in series along the current path with a pn junction 15 provided therebetween. A pair of output terminals 16a and 16b are provided at both ends of the current path.

[0019] The current path near the pn junction 15 can function as a temperature measurement unit that can measure temperature changes as electromotive force changes from the output terminals 16a and 16b using the Seebeck effect. Furthermore, the narrow portion 12 of the substrate 11, which is narrower than the surrounding area, is the portion that deforms and bends preferentially when force is applied to the substrate 11. Therefore, the portion of the current path provided on the narrow portion 12 primarily expands or compresses in response to the deformation of the substrate 11 and functions as a deformation measurement unit that changes the resistance between the output terminals 16a and 16b. In other words, the deformation measurement unit can measure the deformation of the substrate 11 as a change in the resistance between the output terminals 16a and 16b. In this way, the sensor 10 is a multimodal sensor that provides measurements of temperature changes and shape changes.

[0020] In particular, to increase sensitivity to deformation, the deformation measurement unit is preferably formed of a current path extension 17 that extends the current path. The current path extension 17 extends the current path in a direction that causes tension or compression when the substrate 11 is bent at the narrow width portion 12, while folding back to straddle the narrow width portion 12 multiple times. For example, it has been confirmed that when the number of times that the narrow width portion 12 is straddled is increased to 11 times compared to when the number of times is increased to one, the ratio of the resistance value between the output terminals 16a and 16b before and after deformation is 10 times or more. In other words, the provision of the current path extension 17 increases the change in resistance value with respect to bending, enabling more accurate measurement of shape changes.

[0021] Figure 2 shows sensor 10 in the form of a nail attached to a person's finger. The tip of sensor 10 protrudes from the tip of the finger, and when the object to be measured is touched by pinching it with the fingertips, the protruding part of sensor 10 comes into contact with the object to be measured. By placing sensor 10 on the fingertip in this way, it is possible to measure temperature and shape changes of sensor 10 when the finger is moved to touch the object to be measured. In other words, it is possible to measure multiple physical properties of the object to be measured.

[0022] 3 and 4(b), the sensor 10 can measure a temperature change (ΔT) as a change in electromotive force (ΔV) when a current is applied between the output terminals 16a and 16b. In other words, the Seebeck effect can be obtained by the pn junction 15, and the electromotive force between the electromotive force output terminals 16a and 16b can be changed by a temperature change and can be measured.

[0023] 4(a), when a current is applied between output terminals 16a and 16b, sensor 10 can measure the change in shape as a change in resistance. The change in resistance appears as a change in the slope of the line that accompanies a change in current on the VI diagram (FIG. 3).

[0024] On the VI diagram, the electromotive force changes in response to changes in resistance, but when the current value is changed, the resistance value can be measured from the slope of the VI diagram. Therefore, the change in electromotive force due to changes in resistance can be measured. As a result, the change in electromotive force due to changes in temperature can be measured separately. In other words, by changing the current value and measuring the voltage, the change in electromotive force due to temperature change and the change in resistance due to shape change can be measured simultaneously and individually, allowing the temperature change and shape change to be measured simultaneously.

[0025] [Example 2] 5 and 6 show an element section 29 consisting of a current path of a sensor 20 having another structure as a multimodal sensor, and photographs of the sensor 20, respectively. The sensor 20 has, as the element section 29, a plurality of pn junctions 25 along the current path. Specifically, in the element section 29, the current path is rectangular overall, with portions extending from each side of the rectangle toward the center and folding back, and further extending from one side toward the periphery with output terminals 26a and 26b. Near the portion extending toward the center and folding back, an inner-periphery pn junction 25a is provided, and near each corner of the rectangle, an outer-periphery pn junction 25b is provided. That is, on each side, a p-type CNT film 23 is disposed from the corner to the central folding back portion, an n-type CNT film 24 is disposed with the inner-periphery pn junction 25a sandwiched between them, and the current path is formed so that it continues to the next side with the outer-periphery pn junction 25b sandwiched between them.

[0026] In this case, for example, if the temperature changes in the central portion 22 where the folded portions are concentrated, the temperatures of the four inner pn junctions 25a will also change. If the temperatures of the outer pn junction 25b and the output terminals 26a and 26b are constant, the electromotive forces due to the Seebeck effect in the serially connected current paths will be superimposed and measured at the four inner pn junctions 25a. As a result, temperature changes can be measured more accurately.

[0027] On the other hand, suppose the current path of the element section 29 is deformed together with the substrate 21 by moving the central section 22 toward the front or back of the paper. This causes bending to occur mainly in the current path extensions 27 at eight locations that connect the rectangular sides to the central section 22. The current path extensions 27 are deformed in either a compressed or expanded manner in relation to the substrate 21, changing their resistance value. By applying deformation (compressed or expanded) in the same direction at eight locations of the current path extensions 27, the change in resistance value with respect to bending is increased, thereby increasing the sensitivity to shape changes.

[0028] In the sensor 20, by applying and varying a current, it is possible to measure the change in electromotive force and the change in resistance between the output terminals 26a and 26b, and thus to simultaneously measure the change in temperature and the change in shape from these.

[0029] [Example 3] 7 shows a multimodal sensor 30 with yet another structure. In the sensor 30, a plurality of element units 39 each consisting of a current path are arranged on a flexible sheet-like substrate 31. Here, the element units 39 are arranged in a matrix.

[0030] 1(b), the element section 39 has a current path that is approximately square overall, with the p-type CNT film 33 arranged to extend from the output terminal 36a on the lower left side of the page along two sides (left and top sides) that sandwich a corner of the square, and the n-type CNT film 34 arranged to return along those two sides, sandwiching the p-n junction 35a. Furthermore, the p-type CNT film 33 is arranged to extend along the other two sides (bottom and right sides), sandwiching the p-n junction 35b, and the n-type CNT film 34 is arranged to return along those two sides, sandwiching the p-n junction 35c, and the output terminal 36b is arranged on the lower left side.

[0031] In this case, for example, if the temperature changes in the upper right portion adjacent to pn junctions 35a and 35c, and the temperature of other portions, including lower left pn junction 35b, remains constant, the electromotive forces due to the Seebeck effect will be superimposed and measured at two points, pn junctions 35a and 35c, in the current path connected in series. Furthermore, such a current path is prone to deformation, for example, bending the upper left and lower right corners with the upper right pn junctions 35a and 35b as free ends. This deformation can be measured as a change in resistance.

[0032] That is, by applying and changing a unidirectional current to the element portion 39, it is possible to measure the change in electromotive force between the output terminals 36a and 36b and the change in resistance value, and from these, it is possible to simultaneously measure the temperature change and the shape change. In the sensor 30 in which the element portions 39 are arranged side by side, it is possible to measure the physical properties of the surroundings that cause the temperature change or the shape change in the element portion 39 corresponding to the position on the substrate 31 where the element portion 39 is arranged.

[0033] [Example 4] FIG. 8 shows an example of a multimodal sensor 40 attached to a robot arm 48. The sensor 40 includes a flexible, substantially rectangular substrate 41 and an element unit 49 provided on the substrate 41. The element unit 49 includes a plurality of straight-shaped p-type CNT films 43 and n-type CNT films 44 as current paths, which are arranged alternately with their longitudinal ends aligned, and the vicinity of the longitudinal ends is alternately joined to form p-n junctions 45a and 45b, which are connected in series. The p-n junction 45a is located near the longitudinal end of the substrate 41 (on the left side of the drawing). On the other hand, the p-n junction 45b is located approximately in the longitudinal center of the substrate 41. Of the alternatingly arranged p-type CNT films 43, the end opposite the pn junction 45a was used as an output terminal 46a, and the end opposite the pn junction 45a of the outermost n-type CNT film 44 was used as an output terminal 46b.

[0034] The sensor 40 is attached to the robot arm 48 so that the end of the sensor 40 including the p-n junction 45a protrudes from the tip of the finger-like portion of the robot arm 48. When the robot arm 48 moves the tip of the sensor 40 to contact the object under test, the tip of the sensor 40 including the p-n junction 45a abuts against the object under test. The sensor 40 bends between the tip end including the p-n junction 45a and the central portion including the p-n junction 45b, and is affected by the temperature of the object under test against which the tip abuts. The change in shape due to bending can be measured by measuring the change in resistance between the output terminals 46a and 46b, and the temperature change can be measured by measuring the change in electromotive force between the output terminals 46a and 46b. This allows, for example, the robot arm to detect contact with the object under test and obtain information about the object's temperature.

[0035] [Example 5] 9 shows a multimodal sensing system using the above-described sensors 10, 20, 30, 40, etc. As shown in the figure, the system 50 includes a control processing unit 51, a sensor unit 52 including sensors similar to the above-described sensors 10, 20, 30, 40, and a light source unit 53. The sensor unit 52 and the light source unit 53 are each connected to the control processing unit 51. The light source unit 53 will be described in detail later.

[0036] The control processing unit 51 is connected to a pair of output terminals of the sensor in the sensor unit 52, and can apply a current to the sensor and control the current to be changed. Furthermore, the control processing unit 51 can measure the voltage between the output terminals of the sensor and can calculate the resistance between the output terminals from the applied current and the measured voltage. This allows the system 50 to measure temperature changes and shape changes simultaneously. A lock-in amplifier, for example, can be suitably used as the control processing unit 51.

[0037] As described above, the sensor included in the sensor unit 52 has a current path formed by a CNT film. The CNT film has ultra-broadband absorption characteristics in the sub-THz to visible light band due to plasmon resonance, and can generate an electromotive force due to the photothermoelectric effect generated by absorbing light. Therefore, for example, by irradiating the object to be measured with light of a predetermined wavelength within the above-mentioned band as detection light and measuring the transmitted or reflected light of the detection light with the sensor unit 52, a physical measurement such as absorbance corresponding to the light of the predetermined wavelength of the object to be measured can be obtained. In other words, the sensor described above measures the electromotive force due to the photothermoelectric effect of the transmitted or reflected light, and measures the absorbance, and thereby other physical quantities.

[0038] For example, as shown in FIG. 10, the sensor unit 52 can measure light (absorbance of the detection light), temperature, and deformation (pressure). As described above, temperature and deformation can be measured from changes in electromotive force and resistance value. Here, when the control processing unit 51 modulates light with frequency f and irradiates it from the light source unit 53 as detection light, the transmitted light or reflected light from the object to be measured is also modulated with frequency f. As a result, the electromotive force obtained by the sensor unit 52 from the transmitted light or reflected light also oscillates with frequency f. This makes it possible to measure the electromotive force due to temperature and the electromotive force due to light absorption separately, allowing temperature change and absorbance to be measured simultaneously.

[0039] Furthermore, as shown in Fig. 11, each of the multiple light sources emits a test light having a different frequency (or wavelength) and modulated differently. This allows the absorbance of the test light having each frequency (or wavelength) to be measured. For example, the first light source can emit light with a frequency of 1.4 THz, and the second light source can emit light with a frequency of 361 THz. The first light source outputs a test light modulated with a square wave of f = 4 Hz, and the second light source outputs a test light modulated with a square wave of f = 1 Hz. The test light from each light source is then simultaneously irradiated onto the object under test.

[0040] As shown in Figure 12, when the sensor unit 52 receives transmitted or reflected light from the object to be measured, the electromotive force response due to these lights is modulated at 4 Hz (middle waveform) and 1 Hz (bottom waveform), respectively. In reality, the lights are irradiated simultaneously, so the electromotive force response is a waveform obtained by combining these lights. Since this combined waveform is a combination of known different modulation frequencies, it can be easily separated using a band-pass filter or the like, and the absorbance of the detection light corresponding to each modulation frequency can be measured. Note that instead of irradiating the detection lights with different wavelengths simultaneously, they may be irradiated at different times. By synchronizing the measurements with different times, it is possible to measure each individual detection light.

[0041] Since it is possible to measure the absorbance of light of multiple different frequencies, we will explain the results of using this to investigate the properties of multiple substances.

[0042] As shown in FIG. 13, the light source unit 53 includes three light sources A to C. Light source A emits light with a wavelength of 375 nm (frequency: approximately 800 THz, ultraviolet light), light source B emits light with a wavelength of 532 nm (frequency: approximately 564 THz, visible light), and light source C emits light with a frequency of 218 GHz (wavelength: approximately 1.38 mm, GHz light). The ultraviolet light, visible light, and GHz light are each modulated differently and irradiated onto the object under test, and the transmitted light is measured by the sensor unit 52. Five types of objects were used: 1 mm-thick plates made of PS (polystyrene), PET (polyethylene terephthalate), PP (polypropylene), and PC (polycarbonate), and a 2 mm-thick plate made of PS. The absorbance of the transmitted light was measured for each of the five objects under test, designated as samples A to E, with the material and thickness unknown.

[0043] Figure 14 shows the absorbance of samples A to E measured with ultraviolet and visible light. Because the absorption spectrum differs depending on the material, we wanted to identify the material by matching its characteristics, but because the thickness is unknown, we could not identify the material by simply checking the absorbance of the two types of light. Therefore, we calculated the absorbance ratio from the absorbance of ultraviolet light / absorbance of visible light. By calculating the absorbance ratio, we were able to identify the absorption spectrum of the material, which in turn allowed us to identify the material. Furthermore, by identifying the material, we were able to determine the thickness of the sample from the relationship between the absorbance and thickness.

[0044] Furthermore, the surface of the PS plate was divided into two areas, and the absorbance of ultraviolet light, visible light, and GHz light was measured, as shown in Figure 15. One specimen had friction marks in measurement area b, as shown in Figure 15(a), and the other specimen had measurement area b soaked in water, as shown in Figure 15(b), and the absorbance measurement results for each measurement area were compared.

[0045] As shown in Figure 16, for a 1 mm thick PS plate, the absorbance ratio, obtained by dividing the absorbance of visible light by the absorbance of GHz light, is higher in measurement area b compared to measurement area a. This result was obtained because the friction marks in measurement area b scatter visible light but not GHz light. In other words, the presence or absence of friction marks could be distinguished by the absorbance ratio.

[0046] Furthermore, in a 2mm thick PS plate, the same absorbance ratio was found to be lower in measurement area b compared to measurement area a. This result was obtained because visible light passes through water, but GHz light is absorbed by water. In other words, the presence or absence of water impregnation could be distinguished by the absorbance ratio.

[0047] In this way, the multimodal sensor described above can provide physical measurements according to a predetermined wavelength in addition to measuring temperature changes and shape changes.

[0048] Although the embodiments of the present invention and modifications based thereon have been described above, the present invention is not necessarily limited to these examples. Furthermore, those skilled in the art will be able to find various alternative embodiments and modifications without departing from the spirit of the present invention or the scope of the appended claims. [Explanation of symbols]

[0049] 10 sensors 11 Circuit Board 13 p-type CNT film 14 n-type CNT film 15 pn junction 16a, 16b output terminals 17 Current path extension 19 Element section

Claims

1. 1. A multimodal sensor that provides measurements of multiple physical properties using a carbon nanotube (CNT) film provided on a flexible substrate, comprising: A multimodal sensor comprising: a p-type CNT film and an n-type CNT film arranged in series on the substrate along a current path between a pair of output terminals with a pn junction provided therebetween; and an element section that provides measurements of temperature change and shape change from electromotive force change and resistance change measured by applying a current between the pair of output terminals.

2. 2. The multimodal sensor according to claim 1, wherein the pn junction is provided in plural along the current path.

3. 3. The multimodal sensor according to claim 2, wherein the element portion includes an extension of the current path that amplifies the change in resistance value in response to a change in shape.

4. 2. The multimodal sensor according to claim 1, further comprising a light source that irradiates detection light of a predetermined wavelength that has been frequency-modulated, and receives reflected light or transmitted light of the detection light, and provides a physical measurement corresponding to the predetermined wavelength from a change in the electromotive force corresponding to the frequency modulation.

5. 5. The multimodal sensor according to claim 1, wherein a plurality of the element portions are arranged on a flexible substrate, and measurements of physical properties corresponding to positions on the substrate are provided.

6. 6. The multimodal sensor according to claim 5, wherein a plurality of the element portions are arranged in a matrix on the substrate.

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