Patent Publication Number: US-2023157903-A1

Title: Sensor, detection system, and detection method

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority benefits of Japanese application no. 2021-190475, filed on Nov. 24, 2021. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification. 
     BACKGROUND 
     Technical Field 
     The present invention relates to a sensor, a detection system, and a detection method. 
     Description of Related Art 
     Patent Literature 1 (Japanese Patent Laid-Open No. 2019-166040) discloses that the size of the non-contact range with a liquid in an electrode in an absorbing member is detected by utilizing the amount of parasitic resistance which changes according to the size of the non-contact range with the liquid in the electrode. 
     SUMMARY 
     The inventors have found that it is effective to vary the sensitivity of a sensor depending on the positions, for example, when the sensor is used on diapers or the like which have a position for intensively detecting the presence of a liquid and a position for preliminarily detecting the presence of a liquid. One of the objects of the present disclosure is to provide a sensor having different sensitivities depending on the positions, a detection system using the sensor, and a detection method. 
     In accordance with an embodiment of the present invention, a sensor is provided for detecting presence of a liquid, and the sensor includes a first electrode and a second electrode. The first electrode and the second electrode each have a thread-like or band-like structure, and are arranged side by side in a direction intersecting a longitudinal direction for detecting the liquid existing between the electrodes. At least one of the first electrode and the second electrode includes a first portion having a first surface area at a first position in the longitudinal direction, and includes a second portion having a second surface area larger than the first surface area at a second position in the longitudinal direction different from the first position. 
     In accordance with an embodiment of the present invention, a detection system is provided for detecting presence of a liquid in an object to be detected, and the detection system includes a sensor having a first electrode and a second electrode and mounted on the object to be detected; a communication device connected to the sensor and outputting a sensing result of the sensor by wireless communication; and a receiver receiving the sensing result. The first electrode and the second electrode each have a thread-like or band-like structure, and are arranged side by side in a direction intersecting a longitudinal direction. At least one of the first electrode and the second electrode includes a first portion having a first surface area at a first position in the longitudinal direction, and includes a second portion having a second surface area larger than the first surface area at a second position in the longitudinal direction different from the first position. 
     In accordance with an embodiment of the present invention, a detection method is provided for detecting presence of a liquid. A first electrode and a second electrode each having a thread-like or band-like structure are arranged side by side in a direction intersecting a longitudinal direction. The first electrode and the second electrode are made of different materials, and generated power is generated between the electrodes when the liquid is present between the electrodes as the electrodes come into contact with the liquid existing between the electrodes. At least one of the first electrode and the second electrode includes a first portion having a first surface area at a first position in a longitudinal direction, and includes a second portion having a second surface area larger than the first surface area at a second position in the longitudinal direction different from the first position. The fact that a predetermined amount of the liquid is present is detected by detecting that an amount of the generated power exceeds a threshold value. The threshold value is a value larger than a maximum value of an amount of generated power of the first portion and smaller than a maximum value of an amount of generated power of the second portion. 
     Further details will be described as embodiments provided below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a schematic view of the detection system  100  according to an embodiment. 
         FIG.  2    is a cross-sectional view of the absorbing member body taken along the line M-M of  FIG.  1   . 
         FIG.  3    is a schematic view illustrating the configuration of the detection device. 
         FIG.  4    is a diagram illustrating the measurement results of the generated current of the sensor obtained by the inventors. 
         FIG.  5    is a diagram illustrating the measurement results of the change over time of the charge voltage of the capacitor obtained by the inventors. 
         FIG.  6    is a diagram illustrating the measurement results of the radio signal, obtained in an experiment of detecting the replacement time of the absorbing member body by the detection system, obtained by the inventors. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     &lt;1. Overview of the Sensor, the Detection System, and the Detection Method&gt; 
     (1) The sensor according to an embodiment is a sensor for detecting the presence of a liquid, and includes a first electrode and a second electrode. The first electrode and the second electrode each have a thread-like or band-like structure, and are arranged side by side in a direction intersecting a longitudinal direction. At least one of the first electrode and the second electrode includes a first portion having a first surface area at a first position in the longitudinal direction, and includes a second portion having a second surface area larger than the first surface area at a second position in the longitudinal direction different from the first position. 
     By setting the second surface area of the second portion to be larger than the first surface area of the first portion, the second portion has a larger area in contact with the liquid than the first portion. Therefore, when the same amount of liquid is present between the first portion and the second portion between the electrodes, the detection sensitivity of the presence of the liquid between the electrodes of the second portion is improved, compared to the detection sensitivity between the electrodes of the first portion. That is, the sensitivity can be made different depending on the positions in the longitudinal direction of the sensor. 
     (2) According to an embodiment, the first electrode and the second electrode are made of different materials, and generated power is generated between electrodes in response to the liquid being present between the electrodes, and second generated power generated by the second portion is larger than first generated power generated by the first portion. Since the second generated power is larger than the first generated power, the sensitivity of the sensor which detects the presence of the liquid by using the generated power can be made different in the longitudinal direction. 
     (3) According to an embodiment, the sensor further includes an output part which outputs a detection signal indicating detection of the liquid, and the output part is connected to the first electrode and the second electrode. Thus, the sensor can output a detection signal according to the generated power. 
     (4) According to an embodiment, the first electrode and the second electrode are provided so as to be in contact with an absorbent of a worn article having the absorbent which receives excrement, and the first position is located in front of the second position in the case of a wearer wears the worn article. The worn article having the absorbent which receives excrement is, for example, a diaper. 
     By providing the first electrode and the second electrode to be in contact with the absorbent of the worn article having the absorbent which receives excrement, the sensor can detect whether there is excrement on the worn article by the liquid contained in the excrement. By providing the first electrode and the second electrode to put the first position in front of the second position when the wearer wears the worn article, the rear sensitivity can be made higher than the front sensitivity. When excrement comes from the front of the worn article and the wearer is in a supine position, the liquid absorbed by the absorbent proceeds rearward, and the entire absorbent absorbs the liquid. By making the rear sensitivity higher than the front sensitivity, it is possible to detect the state where the entire absorbent absorbs the liquid, that is, the timing of replacement in the case of a diaper. 
     (5) According to an embodiment, at least one of the first electrode and the second electrode is sewn on a fabric. Thus, the surface area can be easily made different between the first portion and the second portion. 
     (6) According to an embodiment, the first portion and the second portion have different sewing structures of the electrodes with respect to the fabric. The sewing structure refers to a structure which the electrode forms with respect to the fabric as the electrode is sewn on the fabric. Since the electrode has a thread-like or band-like structure, the surface area can be easily made different between the first portion and the second portion by changing the sewing structure. 
     (7) According to an embodiment, the sewing structure of the second portion has a higher density of electrode with respect to the fabric per unit than the sewing structure of the first portion. Thus, the second surface area which can be in contact with the liquid can be made larger than the first surface area. 
     (8) According to an embodiment, the first electrode and the second electrode are in contact with each other via a water absorbent, at least one of the first electrode and the second electrode is sewn with the water absorbent as the fabric, and the sewing structure of the second portion has a shorter sewing pitch than the sewing structure of the first portion. Thus, the second surface area which can be in contact with the liquid can be made larger than the first surface area. 
     (9) According to an embodiment, the sewing structure of the second portion has a larger area of electrode appearing on a surface of the fabric in contact with the liquid than the sewing structure of the first portion. Thus, when the surface of the fabric is in contact with the absorbent, the second surface area which can be in contact with the liquid can be made larger than the first surface area. 
     (10) According to an embodiment, the sewing structure of the second portion has an overlap with respect to a sewing direction of the electrode. Thus, the second surface area which can be in contact with the liquid can be made larger than the first surface area. 
     (11) The detection system according to an embodiment is a system for detecting the presence of a liquid in an object to be detected, and includes a sensor having a first electrode and a second electrode and mounted on the object to be detected; a communication device connected to the sensor and outputting a sensing result of the sensor by wireless communication; and a receiver receiving the sensing result. The first electrode and the second electrode each have a thread-like or band-like structure, and are arranged side by side in a direction intersecting a longitudinal direction, and at least one of the first electrode and the second electrode includes a first portion having a first surface area at a first position in the longitudinal direction, and includes a second portion having a second surface area larger than the first surface area at a second position in the longitudinal direction different from the first position. 
     By making the second surface area of the second portion larger than the first surface area of the first portion, the sensitivity can be made different depending on the positions in the longitudinal direction of the sensor. By mounting this sensor on the object to be detected, when the object to be detected has a position for intensively detecting the presence of the liquid and a position for preliminarily detecting the presence of the liquid, such as a diaper, the presence of the liquid can be detected depending on the positions. By providing the communication device which outputs the sensing result of the sensor by wireless communication and the receiver which receives the sensing result, the sensing result can be obtained from the signal received by the receiver. Therefore, it is possible to obtain the sensing result remotely, or obtain the sensing result without touching the object to be detected. 
     (12) The detection method according to an embodiment is a method for detecting the presence of a liquid, in which a first electrode and a second electrode each having a thread-like or band-like structure are arranged side by side in a direction intersecting a longitudinal direction; the first electrode and the second electrode are made of different materials, and generated power is generated between electrodes in response to the liquid being present between the electrodes; at least one of the first electrode and the second electrode includes a first portion having a first surface area at a first position in a longitudinal direction, and includes a second portion having a second surface area larger than the first surface area at a second position in the longitudinal direction different from the first position; and the fact that a predetermined amount of the liquid is present is detected by detecting that an amount of the generated power exceeds a threshold value. The threshold value is a value larger than a maximum value of an amount of generated power of the first portion and smaller than a maximum value of an amount of generated power of the second portion. 
     By using the sensor in which the second surface area of the second portion is larger than the first surface area of the first portion, the presence of the liquid can be detected with different sensitivities in the longitudinal direction of the sensor. By mounting this sensor on the object to be detected, when the object to be detected has a position for intensively detecting the presence of the liquid and a position for preliminarily detecting the presence of the liquid, such as a diaper, the presence of the liquid in the second portion can be detected by comparing the threshold value and the amount of power generated in the second portion. 
     &lt;2. Examples of the Sensor, the Detection System, and the Detection Method&gt; 
       FIG.  1    is a schematic view of the detection system  100  according to the present embodiment. The detection system  100  is a system for detecting the presence of a liquid in an object to be detected. In the present embodiment, the object to be detected is an absorbing member body  5 . The detection system  100  detects the liquid which exists in the absorbing member body  5  by a sensor  1  installed in the absorbing member body  5 .  FIG.  2    is a cross-sectional view of the absorbing member body  5  taken along the line M-M of  FIG.  1   . 
     In the present embodiment, the absorbing member body  5  has a basic configuration as a diaper. That is, the absorbing member body  5  includes a front sheet  51 , a back sheet  52 , and an absorbent  53 . The absorbent  53  is arranged between the front sheet  51  and the back sheet  52 . The absorbing member body  5  has a front side  54  located on the front side of a wearer and a rear side  55  located on the back side of the wearer when worn on the wearer. The wearer&#39;s excrement is given to the absorbent  53  from the side of the front sheet  51 . The absorbing member body  5  has a substantially rectangular shape in a plan view in a deployed state. 
     The front sheet  51  is a substantially rectangular liquid permeable sheet. The front sheet  51  is made of, for example, a non-woven fabric or a woven fabric. The front sheet  51  comes into contact with the wearer&#39;s skin when worn on the wearer. The front sheet  51  is configured to improve the permeability of the liquid so that the permeating liquid does not easily return to the wearer side. Thus, the urine excreted from the wearer can rapidly permeate into the absorbent  53 . Thus, even if the wearer urinates, the front sheet  51  does not substantially retain urine and is in a substantially dry state as long as the absorbent  53  has a surplus capacity for water absorption. As a result, contact between urine and the wearer&#39;s skin is suppressed. 
     The back sheet  52  is a substantially rectangular non-liquid permeable sheet. The back sheet  52  is made of a waterproof material having a waterproof film or the like. The back sheet  52  prevents the urine absorbed by the absorbent  53  from leaking to the outside. 
     The absorbent  53  is composed of an absorbent fiber such as pulp and a highly absorbent polymer. The highly absorbent polymer allows many liquids to be retained in the absorbent  53 . The absorbent  53  is a substantially rectangular mat body which is long in the front-rear direction. The absorbent  53  is arranged across the front side  54  and the rear side  55  of the absorbing member body  5  with the longitudinal direction substantially coinciding with the front-rear direction of the absorbing member body  5 . Therefore, the absorbent  53  can absorb the urine excreted on the front side  54  and absorb the urine exceeding the absorption amount of the front side  54  on the rear side  55 . 
     The sensor  1  is arranged between the absorbent  53  and the back sheet  52 . That is, the sensor  1  is arranged on the side of the back sheet  52  of the absorbent  53 . The sensor  1  functions as a urine power generation battery. The sensor  1  has a pair of electrodes  11  and  12 . The electrodes  11  and  12  each have a thread-like or band-like structure. The sensor  1  is arranged so that the pair of electrodes  11  and  12  are in contact with the absorbent  53  at an interval in the width direction intersecting the longitudinal direction. The pair of electrodes  11  and  12  are arranged so as to extend in the front-rear direction along the absorbent  53  which is long in the front-rear direction. That is, the electrodes  11  and  12  are arranged with the longitudinal direction substantially coinciding with the longitudinal direction of the absorbent  53 . 
     The electrodes  11  and  12  function as a positive electrode and a negative electrode, respectively. The electrodes  11  and  12  generate power by coming into contact with the liquid existing between the electrodes. The sensor  1  detects that the liquid is present between the electrodes  11  and  12  by the generated power of the electrodes  11  and  12 . 
     At least one of the electrodes  11  and  12  is sewn on a fabric  13 . In this example, both the electrodes  11  and  12  have a conductive thread-like structure and are sewn to the fabric  13 . The electrode  11  which functions as the positive electrode is made of a silver thread as an example. The electrode  12  which functions as the negative electrode is made of an aluminum thread as an example. The fabric  13  is cloth and, for example, is made of cloth of a cotton material. The fabric  13  is arranged in contact with the absorbent  53  on the side of the back sheet  52 . Thus, the electrodes  11  and  12  made of the threads sewn on the fabric  13  come into contact with the absorbent  53  on the side of the back sheet  52 . 
     As at least one of the electrodes  11  and  12 , the electrode  11  includes a first portion  111  having a first surface area S 1  at a position (first position in the longitudinal direction) corresponding to the front side  54  of the absorbing member body  5 , and has a second portion  112  having a second surface area S 2  at a position (second position in the longitudinal direction) corresponding to the rear side  55  of the absorbing member body  5 . The second surface area S 2  is larger than the first surface area S 1  (S 2 &gt;S 1 ). The surface area refers to the area in contact with the absorbent  53 , and refers to the surface area of the portion of the electrodes  11  and  12  made of threads sewn on the fabric  13  exposed to at least the surface of the fabric  13  on the side of the absorbent  53 . 
     The first portion  111  and the second portion  112  of the electrode  11  have different thread sewing structures for the fabric  13 . The sewing structure refers to a structure which the thread forms with respect to the fabric as the thread is sewn on the fabric  13 . The difference in the sewing structure between the first portion  111  and the second portion  112  is, for example, that the sewing method of the thread forming the electrode  11  is different between the first portion  111  and the second portion  112 . Specifically, the second portion  112  is sewn by a sewing method having a higher density with respect to the fabric  13  per unit than the first portion  111 . 
     As an example, the sewing method having a high density with respect to the fabric  13  per unit is a sewing method in which a large area of the thread forming the electrode  11  appears on the surface of the fabric  13  on the side of the absorbent  53 . For example, the first portion  111  is sewn to the fabric  13  by wave stitching, and the second portion  112  is sewn to the fabric  13  by back stitching. The back stitching refers to lock stitching or half back stitching. 
     As another example, as illustrated in  FIG.  1   , the second portion  112  is sewn with a sewing length longer than the first portion  111 . In the example of  FIG.  1   , the first portion  111  is sewn once by wave stitching, whereas the second portion  112  is sewn by a sewing method having an overlap with respect to the sewing direction of the thread. 
     The fabric  13  is made of cloth, and may function as a part of the absorbent  53 . In this case, the electrodes  11  and  12  sewn on the fabric  13  are arranged with a water absorbent in between. 
     The sewing method having a high density with respect to the fabric  13  per unit in this case is, for example, a sewing method in which the thread forming the electrode  11  is sewn to the fabric  13  at a short pitch. Specifically, the first portion  111  is sewn to the fabric  13  by wave stitching with a long pitch, and the second portion  112  is sewn to the fabric  13  by wave stitching with a short pitch. 
     Thus, the thread forming the electrode  11  is exposed to the surface of the fabric  13  on the side of the absorbent  53  more in the second portion  112  than in the first portion  111 . Therefore, the electrode  11  is in contact with the absorbent  53  more in the second portion  112  than in the first portion  111 . 
     The above example illustrates a case where both the electrodes  11  and  12  have a conductive thread-like structure, but one of the electrodes  11  and  12  may have a conductive band-like structure. 
     Since the electrodes  11  and  12  are arranged in contact with the absorbent  53 , the absorbent  53  which has absorbed the liquid serves as a current generation path between the electrodes  11  and  12 . Therefore, a current is generated at the electrodes  11  and  12  as the electrodes  11  and  12  are in contact with the liquid absorbed by the absorbent  53 . Since the electrodes  11  and  12  generate power by the liquid absorbed by the absorbent  53 , the sensor  1  is used for detecting the liquid absorption to the absorbent  53 . 
     The sensor  1  is connected to a detection device  3 . The detection device  3  is connected to the ends of the electrodes  11  and  12  on the front side  54 . Thus, the detection device  3  is prevented from pressing the body when the wearer wearing the absorbing member body  5  is in a supine position. 
       FIG.  3    is a schematic view illustrating the configuration of the detection device  3 . With reference to  FIG.  3   , the detection device  3  includes a capacitor  31 . The capacitor  31  is connected to the sensor  1  and stores the power generated by the electrodes  11  and  12 . 
     The detection device  3  includes an intermittent power conversion circuit  32 . The capacitor  31  is connected to the power supply terminal of the intermittent power conversion circuit  32 . The intermittent power conversion circuit  32  operates using the capacitor  31  as an operating power supply. The intermittent power conversion circuit  32  monitors the charge voltage of the capacitor  31 . 
     A wireless transmitter  33  is connected to the intermittent power conversion circuit  32 . The wireless transmitter  33  performs wireless communication with a receiver  7 . The wireless communication is, for example, Bluetooth®, Bluetooth Low Energy® or the like. 
     When the intermittent power conversion circuit  32  detects that the charge voltage of the capacitor  31  reaches a set voltage Vt set as the driving condition of the wireless transmitter  33 , the intermittent power conversion circuit  32  supplies the power charged in the capacitor  31  to the wireless transmitter  33 . Thus, a radio signal SG is output from the wireless transmitter  33 . 
     When the power of the capacitor  31  is consumed by supplying power from the intermittent power conversion circuit  32  to the wireless transmitter  33 , the potential of the capacitor  31  drops, and the intermittent power conversion circuit  32  stops operating. Thus, the supply of power to the wireless transmitter  33  is stopped. If the electrodes  11  and  12  are generating power, the capacitor  31  is charged again. 
     If the electrodes  11  and  12  are generating power, the capacitor  31  repeats charging and discharging. Along with this, the output of the radio signal SG from the wireless transmitter  33  becomes intermittent. Therefore, the radio signal SG output from the wireless transmitter  33  is a detection signal indicating the detection of the liquid existing between the electrodes  11  and  12 . 
     The interval H of the output of the radio signal SG from the wireless transmitter  33  depends on the charging speed to the capacitor  31 . The charging speed increases as the amount of power generation increases. Therefore, the interval H of the output of the radio signal SG from the wireless transmitter  33  becomes shorter as the amount of power generation of the electrodes  11  and  12  increases, and becomes longer as the amount of power generation decreases. 
     The amount of power generation increases as there is more contact between the electrodes  11  and  12  and the liquid. That is, since the electrodes  11  and  12  are arranged in contact with the absorbent  53  with the longitudinal direction substantially coinciding with the longitudinal direction of the absorbent  53 , the amount of power generation increases as the amount of liquid absorbed by the absorbent  53  increases. Therefore, the interval H of the output of the radio signal SG from the wireless transmitter  33  represents the amount of liquid absorbed by the absorbent  53 . 
     The radio signal SG transmitted from a transmitter  95  is received by the receiver  7 . The receiver  7  is connected to a management device  9  and gives the received radio signal SG to the management device  9 . The management device  9  is a computer having a processor  91  and a memory  92 , and is, for example, a terminal device such as a smartphone. 
     The processor  91  can perform processing related to the degree of water absorption of the absorbent  53  of the absorbing member body  5  by executing a program stored in the memory  92 . The processing related to the degree of water absorption of the absorbent  53  of the absorbing member body  5  is, for example, processing of determining the necessity of replacing the diaper. When the liquid reaches the rear side  55  of the absorbent  53 , it is taken as the replacement time of the absorbing member body  5 . When it is determined necessary to replace the diaper, an output device  93  of the management device  9  outputs that it is necessary to replace the diaper. 
     The inventors arranged the sensor  1  having the electrode  11  made of a silver thread and the electrode  12  made of an aluminum thread on the absorbing member body  5 , and measured the generated current of the sensor  1  while injecting a liquid into the absorbing member body  5  to obtain and the generated current characteristic of  FIG.  4   . In the measurement, the liquid was injected from the front side  54  of the absorbing member body  5 , and the generated current of the sensor  1  was measured with the passage of time. The passage of time is represented in  FIG.  4    by the length of the absorbent  53  absorbing the liquid in the longitudinal direction from the end of the front side  54 , that is, the length of the electrode in contact with the liquid (wet length). The horizontal axis of  FIG.  4    represents the wet length, and the vertical axis represents the amount of the generated current. 
     The measurement result L 11  of  FIG.  4    represents the measurement result of the generated current in the sensor  1  in which the electrode  12  was formed by wave stitching an aluminum thread to the fabric  13  of a cotton material, and the electrode  11  was formed by overlapping wave stitching in the first portion  111  and lock stitching in the second portion  112  five times in the sewing direction. The measurement result L 21  of  FIG.  4    is the measurement result as a comparative example, and represents the result obtained by measuring the generated current, under the same conditions as the sensor  1 , in a sensor in which the electrode  11  was formed by wave stitching a silver thread without overlapping in the sewing direction. The length of the electrodes  11  and  12  of the sensor  1  used in the longitudinal direction was 520 mm, the first portion  111  of the electrode  11  was 440 mm, and the second portion  112  was 80 mm. 
     The value A represents the measured value of the measurement result L 11  when the wet length was about 310 mm. The position P 1  about 310 mm from the end of the front side  54  of the absorbing member body  5  is a point included in the first portion  111 . Therefore, the value A is the measured value in a state where the liquid was absorbed by the absorbent  53  up to the position P 1  and the liquid was not absorbed in the second portion  112 . 
     The value B represents the measured value of the measurement result L 11  when the wet length was about 450 mm. The value C represents the measured value of the measurement result L 21  when the wet length was about 440 mm. The position P 2  about 440 mm from the end of the front side  54  of the absorbing member body  5  and the position P 3  about 450 mm from the end of the front side  54  of the absorbing member body  5  are points included in the second portion  112 . Therefore, both the values B and C are the measured values in a state where the liquid was absorbed up to the second portion  112 . 
     With reference to  FIG.  4   , it was confirmed in both the measurement results L 11  and L 21  that the generated current tends to increase as the wet length of the electrode becomes longer. The generated current characteristic was obtained that when the wet length becomes larger than 440 mm, which is the first portion  111 , the rate of increase of the measured value in the measurement result L 11  becomes sharply larger than the rate of increase of the measured value in the measurement result L 21 , and the value B is 150 μA or more larger than the value C. 
     From the generated current characteristic of  FIG.  4   , it was verified that by setting the second surface area S 2  of the second portion  112  of the electrode  11  larger than the first surface area S 1  of the first portion  111 , the amount of power generation when the liquid reaches the second portion  112  can be made much larger than the amount of power generation when the liquid is absorbed up to the first portion  111 , compared to the case where the surface area is not changed. That is, it was verified that the amounts of power generation of the sensor  1  before and after the liquid reaches the second portion  112  of the absorbent  53  can be made significantly different. 
     In the sensor  1 , the amount of power generation when the liquid reaches the second portion  112  is made much larger than the amount of power generation when the liquid is absorbed up to the first portion  111 , which can increase the difference between the charging speeds to the capacitor  31  when the liquid is absorbed up to the first portion  111  and when the liquid reaches the second portion  112 . 
     When detecting water supply to the second portion  112 , it is conceivable to provide the electrode  11  or  12  in only the second portion  112 , that is, only the rear side  55 . However, by arranging the electrode  11  up to the first portion  111 , the sensor  1  can generate power in the entire longitudinal direction, and increase the amount of power generation. 
     The inventors connected the detection device  3  to the sensor  1  used for the measurement of  FIG.  4    and the sensor according to the comparative example, and measured the change over time of the charge voltage of the capacitor  31  to obtain the charging characteristic of  FIG.  5   . The generated power of the sensor  1  and the sensor according to the comparative example, in a state where the liquid was absorbed by the absorbent  53  up to the points P 2  and P 3  at which the values B and C in  FIG.  4    were obtained, was used for charging the capacitor  31 . An aluminum electrolytic capacitor having a load capacity of 4.4 mF was used as the capacitor  31 . The horizontal axis of  FIG.  5    represents the time elapsed from the start of charging, and the vertical axis represents the charge voltage. 
     The measurement result L 12  of  FIG.  5    represents the measurement result of the charge voltage when the sensor  1  was used, and the measurement result L 22  represents the measurement result of the charge voltage when the sensor according to the comparative example was used. In both the measurement results L 12  and L 22 , the charge voltage rose sharply at time T 1  which was about 10 seconds after the start of charging, and then gradually rose. 
     In  FIG.  5   , in the measurement result L 12 , the charge voltage exceeded 0.6 V at time T 1 , whereas in the measurement result L 22 , the charge voltage at time T 1  rose only to about 0.5 V. In the measurement result L 22 , it took 150 seconds from the start of charging for the charge voltage to reach 0.6 V due to the gradual rise after time T 1 . 
     From this result, it was found that by setting the second surface area S 2  of the second portion  112  larger than the first surface area Si of the first portion  111 , the capacitor  31  can be charged quickly, compared to the case where the second surface area S 2  is not larger. In other words, it was verified that the charging speeds of the capacitor  31  before and after the liquid reaches the second portion  112  of the absorbent  53  can be made significantly different. 
     Based on these verifications, the set voltage Vt of the intermittent power conversion circuit  32  of the detection device  3  is set lower than the charge voltage of the capacitor  31  when the sensor  1  is used at time T 1  and higher than the charge voltage when the sensor according to the comparative example is used. In other words, it is a value larger than the maximum value of the amount of power generation in the first portion  111  and smaller than the maximum value of the amount of power generation in the second portion  112 . In the case of the sensor  1  used in the verifications of  FIG.  4    and  FIG.  5   , the set voltage Vt is set to 0.6 V or more (Vt≤0.6 V) as an example. Preferably, the set voltage Vt is 0.6 V (Vt=0.6 V). 
     Thus, the wireless transmitter  33  is not activated in a state where the liquid is absorbed by the absorbent  53  to a position corresponding to the first portion  111  and does not reach a position corresponding to the second portion  112 . As a result, the radio signal SG is not output in this state. When the liquid reaches the second portion  112 , the wireless transmitter  33  is activated. As a result, the radio signal SG is output. Therefore, by receiving the radio signal SG at the receiver  7 , that is, by making the surface areas different in the longitudinal direction in this way, the accuracy of detecting the liquid in the longitudinal direction of the sensor  1  can be made different. The management device  9  can determine that the liquid has been sufficiently absorbed by the absorbent  53 , that is, the key to the effect of a diaper. 
     The inventors constructed the detection system  100  by mounting the sensor  1  used for the measurements of  FIG.  4    and  FIG.  5    on the absorbing member body  5  (diaper), and carried out an experiment of detecting the replacement time of the absorbing member body  5  with the detection system  100 . The absorbing member body  5  used was injected with water from the front side  54 , so that the water absorption of the absorbent  53  proceeded from the front side  54  to the rear side  55 . The absorbent  53  was in a state of absorbing water up to the rear side  55  with injection of about 600 ml of water in total. The liquid used was physiological saline. 
     In the experiment, the amount of liquid injected was one injection, and the second injection was performed after 600 seconds or more had elapsed from the first injection, and a total of 600 ml of liquid was injected into the absorbing member body  5 . Whether the radio signal SG was received by the receiver  7  from the start of injection was measured, and the measurement result of  FIG.  6    was obtained. The horizontal axis of  FIG.  6    represents the time elapsed from the start of injection, and the vertical axis represents whether the radio signal SG was received. The value “0” indicates no reception, and the value “1” indicates reception. 
     From the result of  FIG.  6   , the radio signal SG was received once in the period T 2  after the first injection and before the second injection after 71 seconds. In the period T 3  after the second injection, the radio signal SG was received once 22 seconds after the injection and then four times. During the period T 3 , the radio signal SG was received 5 times in 600 seconds. 
     From this result, it can be seen that the amount of power generation of the sensor  1  increased more rapidly in the period T 3  than in the period T 2 . In other words, it can be seen that in the first injection, the first portion  111  was in contact with the liquid and the second portion  112  was not in contact with the liquid, whereas in the second injection, the second portion  112  was in contact with the liquid. Therefore, by using the detection system  100 , it was verified that when the reception interval H of the radio signal SG is smaller than a threshold value and the radio signal SG is received more than a predetermined number of times, it is determined in the management device  9  that it is time to replace the diaper. 
     In the management device  9 , the threshold value of the reception interval H of the radio signal SG is set to a value shorter than the reception interval at the maximum power generation amount of the first portion  111  and longer than the reception interval at the maximum power generation amount of the second portion  112 . Thus, the threshold value of the amount of generated power can be set to a value larger than the maximum value of the amount of generated power of the first portion  111  and smaller than the maximum value of the amount of generated power of the second portion  112 , and exceeding this threshold value can be detected by the reception interval being shorter than the threshold value of the reception interval. That is, this detection system  100  can reliably detect that the liquid has come into contact with the second portion  112 , and can reliably determine the time to replace the diaper. 
     &lt;3. Addendum&gt; The present invention is not limited to the above embodiment, and various modifications are possible.