Patent Publication Number: US-2021172789-A1

Title: Wire sensing apparatus

Description:
TECHNICAL FIELD 
     The present invention relates to a wire sensing apparatus, and more particularly to a wire sensing apparatus capable of detecting the state of an object using the resonant frequency of a wire and the principle of static electricity. 
     BACKGROUND ART 
     In general, the electrostatic power generation principle includes 1) contact and separation, 2) separation, 3) single electrode and 4) free standing. Energy harvesting, to which such electrostatic power generation principle is applied, uses the phenomenon that a positively charged substance and a negatively charged substance are charged due to static electricity, to produce electric energy. Here, when a positively charged substance and a negatively charged substance collide with each other and then are separated from each other, electrons in the positively charged substance move to the negatively charged substance. Again, when the positively charged substance and the negatively charged substance collide with each other, electrons move from the negatively charged substance to the positively charged substance. Such electron flow forms the flow of current, which is called electrostatic power generation. 
     Recently, research into detecting structural defects such as cracks has been continuously conducted. In particular, research into simply detecting the state of an object at low cost regardless of conditions such as object types and application environments is being conducted. 
     DISCLOSURE 
     Technical Problem 
     Therefore, the present invention has been made in view of the above problems, and it is one object of the present invention to provide a wire sensing apparatus capable of detecting the state of an object using the resonant frequency of a wire and the principle of static electricity. 
     Technical Solution 
     In accordance with an aspect of the present invention, the above and other objects can be accomplished by the provision of a wire sensing apparatus, including: a vibrable wire part; a generator configured to generate electrostatic force through interference with the wire part to generate electric energy; and a sensor part connected to at least one of the wire part and the generator and configured to measure a resonance frequency of the wire part to detect a state of an object. 
     According to an aspect, the wire part may be provided with any one of a wire made of a metal material charged by a positively or negatively charged substance and a wire made of a non-metal material including a polymer, and the generator may include a charged layer provided to face the wire part and charged with a negatively or positively charged substance; and an electrode layer on which the charged layer is laminated. 
     According to an aspect, the charged layer may include Teflon, and the electrode layer may be made of a conductive material including at least one of aluminum (Al), ITO and graphene. 
     According to an aspect, the generator may generate the electric energy in any one of a single electrode mode and a freestanding triboelectric mode. 
     According to an aspect, the sensor part may calculate a resonance frequency of the wire part according to the following equation, 
     
       
         
           
             f 
             = 
             
               
                 n 
                 
                   2 
                    
                   
                       
                   
                    
                   L 
                 
               
                
               
                 
                   T 
                   μ 
                 
               
             
           
         
       
     
     wherein f denotes a resonance frequency of the wire part, n denotes the degree of freedom, L denotes a length of the wire part, T denotes tension, and μ denotes linear density. 
     According to an aspect, the wire part may be formed of a metal material or a non-metal material, and the sensor part may be connected to the electrode layer to calculate resonance frequencies in real time through Ardoino Coding. 
     In accordance with another aspect of the present invention, there is provided a wire sensing apparatus, including: a vibrable wire part; a generator configured to generate Triboelectric Energy Harvesting (TENG) through interference with the wire part; and a sensor part connected to any one of the wire part and the generator and configured to measure a resonance frequency of the wire part to detect a state of an object. 
     According to an aspect, the wire part may be made of a metal material charged with a positively charged substance or a non-metal material including a polymer, the generator may include a charged layer provided to face the wire part and made of a non-metal material charged with a negatively or positively charged substance; and an electrode layer which is made of a conductive material and on which the charged layer is laminated, and the wire part may approach or recede from the charged layer through vibration due to flicking to generate AC voltage and, accordingly, sense frequencies. 
     According to an aspect, the charged layer may include Teflon. 
     According to an aspect, the sensor part may calculate a resonance frequency of the wire part according to the following equation, 
     
       
         
           
             f 
             = 
             
               
                 n 
                 
                   2 
                    
                   
                       
                   
                    
                   L 
                 
               
                
               
                 
                   T 
                   μ 
                 
               
             
           
         
       
     
     wherein f denotes a resonance frequency of the wire part, n denotes the degree of freedom, L denotes a length of the wire part, T denotes tension, and μ denotes linear density. 
     According to an aspect, the wire part may be made of a manually or automatically flickable metal material, and the sensor part may be connected to the wire part and configured to sense resonance frequencies in real time through Ardoino Coding. 
     Advantageous Effects 
     In accordance with the present invention having the configuration, first, electric energy is generated due to interference by vibration of a wire so that the state of an object can be detected according to the measurement of a resonance frequency. Accordingly, a sensor capable of corresponding to various conditions can be provided at low cost. 
     Second, triboelectric energy harvesting is possible, which contributes to efficiency improvement using own power. 
     Third, a sensor can be set to have desired conditions by adjusting the linear density and tension of a wire. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  schematically illustrates a sectional view of a wire sensing apparatus according to a preferred embodiment of the present invention. 
         FIG. 2  schematically illustrates TENG operations due to the wire sensing apparatus according to the embodiment shown in  FIG. 1 . 
         FIG. 3A  to  FIG. 3F  schematically compare output changes dependent upon the linear density of a wire part according to the embodiment shown in  FIG. 1 . 
         FIG. 4A  to  FIG. 4D  schematically compare output changes dependent upon the tension of a wire part according to the embodiment shown in  FIG. 1 . 
         FIG. 5  schematically illustrates an embodiment of a suspension bridge to which the wire sensing apparatus according to the embodiment shown in  FIG. 1  is applied. 
     
    
    
     BEST MODE 
     Hereinafter, the present invention will be described in detail by explaining particular embodiments of the invention with reference to the attached drawings. However, it should be understood that the spirit and scope of the present disclosure are not limited to the embodiments and can be modified by addition, modification, or deletion of elements constituting the embodiments and such additions, modifications, and deletions are also within the spirit and scope of the present disclosure. 
     Referring to  FIG. 1 , a wire sensing apparatus  1  according to a preferred embodiment of the present invention includes a wire part  10 , a generator  20  and a sensor part  30 . 
     The wire part  10  includes a wire that vibrates when flicked. The wire part  10  of the present embodiment includes a wire, such as a guitar string, made of a metal material and charged with a positively or negatively charged substance, and is exemplified as being charged with a positively charged substance. In addition, the wire part  10  may be manually flicked by an operator or may be automatically flicked due to interference by an object (not shown). 
     Meanwhile, the wire part  10  may be made of a non-metal material, such as a polymer material formed of a polymer compound, as well as a metal material. In addition, tension may be adjusted depending upon the thickness of the wire part  10 . It is natural that the thickness of the wire part  10  is not limited to the illustrated embodiment. 
     The generator  20  generates electric energy when charged by electrostatic force through interference with the wire part  10 . Here, the generator  20  is not in direct contact with the wire part  10 , and a single electrode mode wherein electric energy is generated through approaching or receding operations is applied thereto. 
     In addition, the generator  20  includes a charged layer  21  that is provided to correspond to and face the positively charged wire part  10  made of a metal material and is charged with a negatively charged substance; and an electrode layer  22  on which the charged layer  21  is laminated. That is, the generator  20  has a multilayer structure wherein the charged layer  21  is laminated on the electrode layer  22 , and the charged layer  21  faces the wire part  10  to be interfered by the wire part  10 . Here, the charged layer  21  is exemplified as being formed of a Teflon material, and the electrode layer  22  is formed of a conductive material including at least one of aluminum (Al), ITO and graphene and is connected to ground G. 
     For reference, when the wire part  10  includes a wire made of a non-metal material such as a polymer material, not a metal material, or is charged with a negatively charged substance, the charged layer  21  may be charged with a positively charged substance, not a negatively charged substance. That is, the charged layer  21  facing the wire part  10  may be charged with any one of a negatively charged substance and a positively charged substance. 
     Hereinafter, an electric energy generation operation of the generator  20  is described with reference to  FIG. 2 . 
     As in (a) of  FIG. 2 , when force is applied to the wire part  10 , i.e., a positively charged substance, the wire part  10  vibrates in a specific frequency band (hereinafter referred to as “resonance frequency”) depending upon the own characteristics of the wire part  10 , i.e., tension, length and linear density. The wire part  10  repeatedly approaches or recedes from the charged layer  21  due to the vibration of the wire part  10 , so that electric charge moves and, accordingly, AC voltage is generated. 
     More particularly, when a positively charged substance of the wire part  10  recedes from a negatively charged substance of the charged layer  21  due to vibration, electrons attached to the negatively charged substance move to the ground G to achieve electrical balance, as in (b) of  FIG. 2 . Here, when the wire part  10  approaches the charged layer  21  again, the electrons that have been moved to the ground G move to the electrode layer  22  again, thereby generating electric energy. Triboelectric Energy Harvesting (TENG) occurs through such interference between the wire part  10  and the generator  20 . 
     For reference, TENG, which is electric energy generated in the generator  20 , may be used as power of the wire sensing apparatus  1  described in the present embodiment. 
     The sensor part  30  is connected to at least one of the wire part  10  and the generator  20  and serves to sense a resonance frequency according to generation of AC voltage in the wire part  10 , thereby detecting the state of an object (not shown). In the present embodiment, it is exemplified that the sensor part  30  is connected to the wire part  10  made of a metal material to receive electrical signals. However, the present invention is not limited to the embodiment, and it is natural that, when the wire part  10  is made of a non-metal material and the generator  20  is charged with a positively charged substance, the sensor part  30  may be connected to the electrode layer  22  of the generator  20 . 
     Meanwhile, with regard to the sensor part  30 , a resonance frequency of the wire part  10  may be calculated according to the following Equation 1. 
     
       
         
           
             
               
                 
                   f 
                   = 
                   
                     
                       n 
                       
                         2 
                          
                         
                             
                         
                          
                         L 
                       
                     
                      
                     
                       
                         T 
                         μ 
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                      
                     
                         
                     
                      
                     1 
                   
                   ] 
                 
               
             
           
         
       
     
     wherein f denotes the resonance frequency of the wire part, n denotes the degree of freedom, L denotes the length of the wire part, T denotes tension, and μ denotes linear density. 
     It can be confirmed from the graphs of  FIGS. 3A and 4D  that, when the degree of freedom (n) is constantly limited to 0.5, the resonance frequency of the wire part  10  is adjusted according to the tension and linear density of the wire part  10 . 
     Referring to  FIGS. 3A to 3F , the freedom degree (n) of the wire part  10  was fixed to 0.5, the tension (T) of the wire part  10  was fixed to 4 kgf, and the length of the wire part  10  was fixed to 30 cm. Under these conditions, linear density-dependent changes were measured and compared through graphs. The linear density of the wire part  10  used in the experiments increases with increasing thickness of the wire part  10 . A resonance frequency of the wire part  10  dependent upon such a linear density is calculated according to Equation 1. For reference, with regard to the thickness of the wire part  10 , the thickness gradually increases from the 1 st  wire of  FIG. 3A  to the 6 th  wire of  FIG. 3F . 
     As in  FIGS. 3A to 3F , resonance frequency decreases with increasing linear density. Such a tendency tends to decrease similar to the number of actual TENG peaks per unit time. In addition, when the number of TENG peaks during one second was measured and compared to a theoretical value, the number of TENG peaks was almost similar to the theoretical value, in consideration of a maximum error of 0.045%, as shown in Table 1 below. 
     
       
         
           
               
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                   
                   
                 Tuning 
                   
                   
               
               
                 Wire 
                 Linear 
                 Theoretical 
                 App 
                 TENG 
                 Percent 
               
               
                 Number 
                 Density 
                 Value 
                 Value 
                 Value 
                 Error 
               
               
                   
               
             
            
               
                 1 st  Wire 
                 0.000548 kg/m 
                 446 Hz 
                 452 Hz 
                 451 Hz 
                 0.011% 
               
               
                 2 nd  Wire 
                 0.000967 kg/m 
                 336 Hz 
                 339 Hz 
                 340 Hz 
                 0.012% 
               
               
                 3 rd  Wire 
                 0.002050 kg/m 
                 230 Hz 
                 235 Hz 
                 236 Hz 
                 0.026% 
               
               
                 4 th  Wire 
                 0.003052 kg/m 
                 189 Hz 
                 194 Hz 
                 194 Hz 
                 0.027% 
               
               
                 5 th  Wire 
                 0.005081 kg/m 
                 146 Hz 
                 153 Hz 
                 153 Hz 
                 0.045% 
               
               
                 6 th  Wire 
                 0.008282 kg/m 
                 115 Hz 
                 118 Hz 
                 116 Hz 
                 0.011% 
               
               
                   
               
            
           
         
       
     
     As described above, the resonance frequency of the wire part  10  decreases with increasing linear density of the wire part  10 , whereby a voltage output value increases. In addition, it can be confirmed that a surface area to be approached increases with increasing thickness of the wire part  10 , whereby a voltage output value also increases. 
       FIGS. 4A to 4D  illustrate comparison results of resonance frequency changes in the wire part  10  which are dependent upon tension applied to the wire part  10 .  FIGS. 4A to 4D  illustrate resonance frequency comparison results when the tension (T) values of the wire parts  10  are 4 kgf, 8 kgf, 12 kgf and 16 kgf, respectively. As shown in the graphs of  FIGS. 4A to 4D , it can be confirmed that the resonance frequency increases with increasing tension of the wire part  10 . In addition, it can be confirmed that accurate resonance frequency measurement is possible because a theoretical value and an error are a maximum of 0.028% as shown in Table 2. 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                   
                   
                 Tuning 
                   
                   
               
               
                   
                 Theoretical 
                 App 
                 TENG 
                 Percent 
               
               
                 Tension 
                 Value 
                 Value 
                 Value 
                 Error 
               
               
                   
               
             
            
               
                  4N 
                 115 Hz 
                 118 Hz 
                 116 Hz 
                 0.011% 
               
               
                  8N 
                 162 Hz 
                 164 Hz 
                 165 Hz 
                 0.017% 
               
               
                 12N 
                 199 Hz 
                 197 Hz 
                 196 Hz 
                 0.013% 
               
               
                 16N 
                 229 Hz 
                 223 Hz 
                 223 Hz 
                 0.028% 
               
               
                   
               
            
           
         
       
     
     For reference, the sensor part  30  configured to calculate a resonance frequency according to Equation 1 may calculate resonance frequencies of the wire part  10  in real time through Ardoino Coding. In addition, the output of electric energy generated from the generator  20  may be adjusted by changing a surface material of the charged layer  21  as a negatively charged substance, conditions, or the like, so that the generated electric energy may be used as a power supply source for a sensing operation. That is, the wire sensing apparatus  1  according to the present embodiment is capable of self-charging and may detect the state of various objects in real time. 
       FIG. 5  illustrates an embodiment of the wire sensing apparatus  1  applied to a suspension bridge. As shown in  FIG. 5 , when the wire sensing apparatus  1  according to an embodiment of the present invention is applied to a portion of a suspension material of the suspension bridge, the sensor part  30  is capable of detecting electric energy generated between the generator  20  and the wire part  10  due to flicking of the wire part  10 , thereby detecting resonance frequencies in real time. Accordingly, the wire sensing apparatus  1  may detect changes in resonance frequencies calculated in real time, thereby being capable of easily detecting sagging of the suspension bridge over time or the presence or absence of abnormality in the suspension material and a main cable during safety inspection. 
     In addition, the wire sensing apparatus  1  according to the present invention may be applied to overload vehicle inspection to determine the allowable weight of a vehicle based on TENG generated by flicking of the wire part  10 , although not shown in detail. Further, the wire sensing apparatus  1  may be applied to structures to detect structural defects therein, such as cracks, by flicking the wire part  10 . 
     While the present invention has been described referring to the preferred embodiments, those skilled in the art will appreciate that many modifications and changes can be made to the present invention without departing from the spirit and essential characteristics of the present invention.