Patent Publication Number: US-10788933-B2

Title: Tactile presentation panel, tactile presentation device and electronic equipment

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This Nonprovisional application claims priority under 35 U.S.C. § 119(a) on Patent Application No. 2016-125802 filed in Japan on Jun. 24, 2016, the entire contents of which are hereby incorporated by reference. 
     FIELD 
     The present application relates to a tactile presentation panel, a tactile presentation device and electronic equipment. 
     BACKGROUND 
     Recently, there are a number of information devices mounted with a touch panel. A touch panel may directly detect a position of operation by a human body (e.g., finger) to use the position for input, and is effective for improvement in the usability of the user. Currently, such a touch panel is present that employs the technology of presenting a sense of tactile perception, pressure or vibration (hereinafter referred to as “tactile sense”). To present the feel of texture of an object surface as the tactile sense, for example, electrostatic force generated on a panel surface is used. The electrostatic force here is generated through the capacitive coupling formed between a human body and an electrode that are opposed to each other across an insulating film. 
     An example of such technology includes a tactile presentation device described in the publication of United States Patent Application No. 2014/0266648. The tactile presentation device has a configuration where a conductor to which signal voltage is directly applied, an insulating layer, a semiconductor layer and a surface insulating layer are layered in the order from the lower layer side to the upper layer side touching a human body, to make the user perceive the tactile sense through the capacitive coupling formed between the semiconductor layer and the human body. 
     It is however possible that the surface of the panel used for the presentation of tactile sense may be damaged during the use, resulting in a scar which may grow in the depth direction to reach the electrodes. 
     Moreover, a conductive foreign substance such as water may intrude into the scar, for example. In the example described in the publication of United States Patent Application No. 2014/0266648, a conductive foreign substance may possibly intrude into the scar which extends from the surface of the surface insulating layer to the semiconductor layer. 
     It is however difficult to recognize the depth and internal state of the scar by visual contact from the surface side. Thus, the user may continue using the panel with an advanced scar. In the case where the panel in such a state is used, charge accumulated in the electrodes may leak out to the human body through the foreign substance when the user touches the portion with the scar. The charge flowing here is referred to as “leakage current” in the description below. 
     Even if the leakage current flows, the human body will not be affected if the magnitude thereof is sufficiently low. However, the tactile presentation device described in the publication of United States Patent Application No. 2014/0266648 does not suggest the necessity or mechanism of reducing such current. For example, charge proportional to the magnitude of the electrostatic capacitance of the capacitor formed between the conductor and the semiconductor layer is accumulated in the semiconductor layer, while the magnitude of the electrostatic capacitance is proportional to the area of the semiconductor layer. 
     Meanwhile, the area of the semiconductor layer used in the tactile presentation device described in the publication of United States Patent Application No. 2014/0266648 is substantially the same as the size of the operation region used for operation by the user. Thus, the magnitude of the electrostatic capacitance of the capacitor formed between the semiconductor layer and the conductor necessarily takes a large value, making it difficult to suppress the magnitude of the leakage current. 
     SUMMARY 
     According to one aspect, a tactile presentation panel includes a support substrate, a drive electrode located on the support substrate, a first insulating film located on the support substrate and covering the drive electrode, a plurality of floating electrodes independent from one another disposed on the first insulating film, and a second insulating film covering the plurality of floating electrodes. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of this disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a section view illustrating the schematic configuration of a tactile presentation device according to Embodiment 1 (corresponding to the position along I-I in  FIG. 2 ); 
         FIG. 2  is a plan view of an example where the floating electrodes are arrayed, seen from the side of the insulating film on the surface side; 
         FIG. 3  schematically illustrates the use in the state where a conductive foreign substance intrudes into a scar reaching the floating electrodes; 
         FIG. 4  illustrates a positional relationship in the case where a foreign substance is in contact with the largest number of floating electrodes; 
         FIG. 5A  illustrates the sectional structure of Comparative Example 1 used for simulation; 
         FIG. 5B  illustrates the sectional structure of Embodiment 1 used for simulation; 
         FIG. 6  is a transparent perspective view illustrating a contact model between a human body and floating electrodes according to Embodiment 1; 
         FIG. 7A  is a graph illustrating simulation results obtained for different states of the human body; 
         FIG. 7B  is a graph illustrating simulation results obtained in the case where the human body has a dry finger; 
         FIG. 8  is a section view illustrating the schematic configuration of a tactile presentation device according to Embodiment 2 (corresponding to the position along VIII-VIII in  FIG. 9 ); 
         FIG. 9  is a plan view of the configuration example of a drive electrode according to Embodiment 2 seen from the side of the insulating film on the surface side; 
         FIG. 10  is an enlarged view of a portion of the drive electrode indicated by a reference code X in  FIG. 9 ; 
         FIG. 11  is a transparent perspective view illustrating the association between diamond electrodes and floating electrodes according to Embodiment 2; 
         FIG. 12  schematically illustrates the use in the state where a conductive foreign substance intrudes into a scar reaching the floating electrodes; 
         FIG. 13  illustrates a positional relationship in the case where a foreign substance is in contact with the largest number of floating electrodes; 
         FIG. 14A  illustrates the sectional structure of Comparative Example 2 used for simulation; 
         FIG. 14B  illustrates the sectional structure of Embodiment 2 used for simulation; 
         FIG. 15A  is a graph illustrating simulation results obtained for different states of a human body; 
         FIG. 15B  is a graph illustrating simulation results obtained in the case where the human body has a dry finger; 
         FIG. 16  is a section view illustrating the schematic configuration of a drive electrode according to Embodiment 3; 
         FIG. 17  is a section view illustrating the schematic configuration of a drive electrode according to Embodiment 4; and 
         FIG. 18  illustrates an example of the outer appearance of electronic equipment mounted with a tactile presentation device. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Embodiments of the present invention will now be described with reference to the drawings. It is understood that the embodiments described below are mere examples pertaining to the scope of the invention. 
     Embodiment 1 
       FIG. 1  illustrates the schematic configuration of a tactile presentation device  1  according to Embodiment 1. The tactile presentation device  1  is configured with a tactile presentation panel  2  and a signal power supply  3 . The tactile presentation panel  2  is driven by a drive signal applied from the signal power supply  3 , e.g., by a voltage signal, to allow the user who uses the panel surface as an operation region to perceive the tactile sense. It is assumed in the present embodiment that the signal power supply  3  is externally connected to the tactile presentation panel  2 . However, the signal power supply  3  may also be integral with the tactile presentation panel  2 . 
     The tactile presentation panel  2  is constituted by a support substrate  11 , a drive electrode  12 , a first insulating film  13 , floating electrodes  14  and a second insulating film  15 . On the upper surface of the support substrate  11 , the drive electrode  12 , the first insulating film  13 , the floating electrodes  14  and the second insulating film  15  are layered in the described order from the lower layer side to the upper layer side touching the human body. For the respective members, known materials are used, which will be described later. It is noted that each of the members constituting the tactile presentation panel  2  is desirably made of transparent material in the case where characters, images, video and other information need to be visually recognized by seeing through the tactile presentation device  1 . If it is unnecessary to visually recognize information by seeing through the tactile presentation device  1 , each of the members constituting the tactile presentation panel  2  may be made of non-transparent material. 
     The drive electrode  12  is a single electrode having substantially the same area as the support substrate  11 . The first insulating film  13  is formed on the upper surface of the support substrate  11 , and is disposed to cover the entire surface of the drive electrode  12 . According to the present embodiment, acrylic resin is used for the first insulating film  13 . According to the present embodiment, the first insulating film  13  has a film thickness D 1  of 5 μm. It is understood that this numeric value is a mere example. 
       FIG. 2  is a plan view of the floating electrodes  14  seen from the side of the second insulating film  15 . Multiple floating electrodes  14  that are electrically independent from one another are disposed on the upper surface of the first insulating film  13 . According to the present embodiment, the floating electrodes  14  are disposed in a two-dimensional array, as illustrated in  FIG. 2 . It is understood that the array of the floating electrodes  14  illustrated in  FIG. 2  is a mere example. As illustrated in  FIG. 1 , each of the floating electrodes  14  forms a capacitor with the drive electrode  12  opposed thereto, and induces voltage by capacitive coupling with the drive electrode  12 . The electrostatic capacitance of the capacitor formed by each floating electrode  14  and the drive electrode  12  is determined by the area of the floating electrode  14 . 
     According to the present embodiment, as illustrated in  FIG. 2 , the multiple floating electrodes  14  all have the same shape and the same area. It is, however, possible for the floating electrodes  14  to have different shapes and different areas. According to the present embodiment, it is assumed that the shape of a scar generated at the second insulating film  15  has a substantially cylindrical shape with a diameter of 3 mm. 
     Here, the minimum shape of the floating electrode  14  accommodating the scar corresponds to a square with one side measuring 3 mm. In the present embodiment, therefore, the floating electrode  14  is configured to have a square shape with each side measuring 3 mm. Here, the area of the floating electrode  14  is 9 mm 2 . It is understood that the shape or area of each floating electrode  14  is a mere example, and may be determined in accordance with the shape or dimension of an assumed scar. According to the present embodiment, adjacent floating electrodes  14  are arrayed in a plane with a gap of 0.5 mm between each other. 
     As illustrated in  FIG. 1 , on the upper surface of the multiple floating electrodes  14 , the second insulating film  15  covering these electrodes  14  are disposed. The second insulating film  15  also serves as an operation surface directly touched by the user, preventing the human body  4  from making contact with the floating electrodes  14 . According to the present embodiment, for example, acrylic resin is used for the second insulating film  15 . Moreover, the second insulating film  15  has a film thickness D 2  of 5 μm. It is understood that this numeric value is a mere example. According to the present embodiment, the film thickness D 1  of the first insulating film  13  is the same as the film thickness D 2  of the second insulating film  15 . However, the film thickness D 2  of the second insulating film  15  is not necessarily the same as the film thickness D 1  of the first insulating film  13 . 
     Subsequently, an example will be described where the tactile presentation device  1  according to the present embodiment is used. In the case where the second insulating film  15  has no scar, or a scar, if any, has not yet reached the floating electrode  14 , when a part of the human body  4  touches the second insulating film  15 , a capacitor is formed between the human body  4  and one or more floating electrodes  14  opposed to the human body  4  across the second insulating film  15  with respect to the position of contact, which causes electrostatic force according to the magnitude of the voltage induced by the floating electrodes  14  to act on the human body  4 . 
     According to the present embodiment, 100 Hz is applied to the drive electrode  12  as signal frequency. The signal frequency satisfies the range (5-500 Hz) in which the user may perceive the tactile sense (see Japanese Patent Application Laid-Open No. 2015-97076). Accordingly, the user may perceive the change in the electrostatic force as the tactile sense. 
       FIG. 3  illustrates the state where a scar reaching the floating electrodes  14  is generated in the second insulating film  15 , and a conductive foreign substance  20  such as water enters inside the scar. As described earlier, the present embodiment assumes that a scar having a substantially cylindrical shape with the diameter of 3 mm is formed. In such a case, the foreign substance  20  is in electrically contact with four floating electrodes  14  at most, as illustrated in  FIG. 4 . In  FIG. 4 , each of a and b represents the length of each side of the floating electrode  14 , while c represents the diameter of the foreign substance  20 . In the present embodiment, a, b and c each corresponds to 3 mm. Here, when the human body  4  touches the foreign substance  20 , charge accumulated in the capacitor corresponding to the total area (36 mm 2 ) of the four floating electrodes  14  flows in the human body  4  as leakage current I. However, the leakage current I is equal to the amount of charge accumulated in an electrode having the area corresponding to 36 mm 2 , and is significantly smaller than that in the tactile presentation device not provided with any measures for the leakage current I. 
     A result of simulation for the difference in magnitude between the leakage current possibly flowing in the tactile presentation device  1  according to the present embodiment and the leakage current possibly flowing in the tactile presentation device without any measures will be described below. First,  FIGS. 5A and 5B  illustrate structural examples of models used for simulation.  FIG. 5A  illustrates a cross-sectional structure of Comparative Example 1 where no measures are taken for leakage current.  FIG. 5B  illustrates a cross-sectional structure of the present embodiment. It is noted that the cross-sectional structure illustrated in  FIG. 5B  corresponds to the structure illustrated in  FIG. 6 .  FIG. 6  illustrates a transparent view of the tactile presentation device  1  seen from the diagonally upper side. 
     In  FIGS. 5A and 5B , the thickness D 1  of the first insulating film  13  and the thickness D 2  of the second insulating film  15  are both 5 μm. It is assumed here that a scar has a cylindrical shape with a diameter of 3 mm, and a foreign substance  20  enters therein. The impedance of the human body  4  is represented by Z. The permittivity of vacuum ε 0  may be calculated by 8.85×10 −12  F/m, while the relative permittivity ε of each insulating film is assumed as 3.0. In the case of  FIG. 5A , the drive signal of 150 V/100 Hz is applied to the drive electrode  12 . In the case of  FIG. 5B , on the other hand, the drive signal of 184 V/100 Hz is applied to the drive electrode  12 . 
     The floating electrode  14  in the present embodiment has the shape of a square with each side measuring 3 mm, as described earlier. Thus, according to the present embodiment illustrated in  FIG. 5B , the foreign substance  20  is in contact with four floating electrodes  14  at most, as illustrated in  FIG. 6 . Therefore, the maximum area of the electrodes being in contact with the human body  4  through the foreign substance  20  is 36 mm 2 . In Comparative Example 1 illustrated in  FIG. 5A , on the other hand, the area being in contact with a finger through the foreign substance  20  corresponds to the total area of the drive electrode  12 . 
     The thickness of the insulating film is different between the present embodiment and Comparative Example 1. Because of this, if the devices in the present embodiment and Comparative Example 1 are driven by the signal voltage of the same magnitude, a difference occurs in the intensity of the tactile sense perceivable on the panel surface. In the simulation, therefore, the signal voltage of 184 V is applied in the present embodiment, to comply with the intensity of the tactile sense perceived on the panel surface in Comparative Example 1. 
       FIGS. 7A and 7B  illustrate the results of simulation.  FIG. 7B  is an enlarged view of a part of  FIG. 7A . The present simulation was carried out for three patterns including [1] the case where a part of the human body  4  being in contact with the panel surface is dry and is not in contact with GND, [2] the case where a part of the human body  4  is dry and is in contact with GND, and [3] the case where a whole of the human body  4  is wet with water and is in contact with GND. In the drawings, the outlined bars indicate the magnitude of the leakage current I 1  for the tactile presentation panel (Comparative Example 1) not provided with the measures for reducing leakage current, whereas the hatched bars indicate the magnitude of the leakage current I 2  for the tactile presentation panel (Embodiment 1) provided with the measures for reducing leakage current. Note that the current value perceptible by a human being is referred to as “minimum perception current.” The minimum perception current is generally regarded as 1 mA as illustrated by the broken line in  FIG. 7A  (“Basic Facts about Electric Shocks and Fatal Accident Statistics for the Last 30 Years” National Institute of Occupational Safety and Health, 2009, p14, 1.2.1). 
     In the case of [2] where a part of the human body which is in contact with the panel surface is dry and is in contact with GND, the magnitude of the leakage current I 1  is 2.53 mA in Comparative Example 1 provided with no measures for reducing the leakage current, whereas the magnitude of the leakage current I 2  is reduced to 22.1 μA in the present embodiment provided with measures for reducing the leakage current, as illustrated in  FIG. 7A . Also in the case of [3] where the whole body is wet with water and is in contact with GND, the magnitude of the leakage current I 1  is 300 mA in Comparative Example 1, whereas the magnitude of the leakage current I 2  is reduced to 22.1 μA in the present embodiment. In the case of the dry finger, the magnitude of the leakage current I 1  is 9.42 μA in Comparative Example 1, whereas the magnitude of the leakage current I 2  is reduced to 7.60 μA in the present embodiment, as illustrated in the enlarged view of  FIG. 7B . 
     As can be clearly seen from  FIGS. 7A and 7B , in any case of [1] to [3], the leakage current I 2  in the tactile presentation device  1  according to the present embodiment is smaller compared to the leakage current I 1  in Comparative Example 1. Moreover, the magnitude of the leakage current I 2  is significantly smaller than the minimum perception current. Specifically, in the case of [2] and [3], the leakage current I 1  corresponding to Comparative Example 1 exceeds the minimum perception current, whereas the leakage current I 2  corresponding to the present embodiment is significantly reduced to below the minimum perception current. According to the simulation results, the use of the tactile presentation device  1  employing the structure proposed in the present embodiment may reduce the leakage current to a safe level even if a scar is made on the second insulating film  15  and a conductive foreign substance  20  enters therein, preventing the user from perceiving the leakage current. 
     Embodiment 2 
       FIG. 8  illustrates the schematic configuration of a tactile presentation device  101  according to Embodiment 2. In  FIG. 8 , parts corresponding to those in  FIG. 1  will be denoted by the same reference codes.  FIG. 8  illustrates the cross-sectional structure at the position taken along VIII-VIII in  FIG. 9  which will be described later. The tactile presentation device  101  has a basic structure similar to that of the tactile presentation device  1  according to Embodiment 1. A difference exists in that a drive electrode  112  constituting a tactile presentation panel  102  is divided into multiple electrodes. 
       FIG. 9  illustrates a planar view of the structure of the drive electrode  112  employed in the present embodiment. The drive electrode  112  is constituted by multiple X electrodes  112 A extending in the first direction (X direction) on a support substrate  11  and multiple Y electrodes  112 B extending in the second direction (Y direction) on the support substrate  11  as well. The multiple X electrodes  112 A are connected to an X-electrode driving circuit (not shown) while the multiple Y electrodes  112 B are connected to a Y-electrode driving circuit (not shown). 
       FIG. 10  is an enlarged view of a portion indicated by the reference code X in  FIG. 9 . One X electrode  112 A has a shape obtained by connecting multiple diamond-shaped electrodes  114 A together in a beaded manner through respective connection parts  113 . On the other hand, one Y electrode  112 B has a shape obtained by connecting multiple diamond-shaped electrodes  114 B together in a beaded manner through respective connection parts  113 . According to the present embodiment, a dimension d of the diamond electrode  114 A in the Y direction is 1668 μm, whereas a dimension e thereof in the X direction is 1692 μm. Same applies to the diamond electrode  114 B. 
     The X electrode  112 A overlaps with the Y electrode  112 B only at the corresponding connection part  113 , while the diamond electrode  114 A is adjacent to the diamond electrode  114 B on the same plane with a gap between them. That is, there is no area where the diamond electrode  114 A overlaps with the diamond electrode  114 B. The X electrode  112 A and the Y electrode  112 B cross each other at the corresponding connection part  113  with an insulating film placed between them so as to maintain electrical insulation from each other. 
     In the tactile presentation device  101  according to the present embodiment, the X-electrode driving circuit drives the X electrode  112 A with 150 V/1000 Hz, whereas the Y-electrode driving circuit drives the Y electrode  112 B at 150 V/1240 Hz. The reason for applying signal voltage of different signal frequencies respectively to the X electrode  112 A and the Y electrode  112 B is to present a tactile sense by making use of beat phenomenon. It is thus necessary for both the electrostatic force caused by the diamond electrode  114 A and the electrostatic force caused by the diamond electrode  114 B to act between each floating electrode  14  and the human body  4 . 
     In the present embodiment, therefore, the area of the contact part  113  which is a portion where the X electrode  112 A overlaps with the Y electrode  112 B in planar view is made as small as possible. This can reduce the load capacitance in the case where AC voltage signals are applied to the X electrode  112 A and the Y electrode  112 B. As a result, increase in the size of the tactile presentation device  101  as well as enhancement in the spatial resolution are made possible, thereby suppressing the induction of unnecessary voltage which may be generated by capacitive coupling between electrodes. 
     The floating electrode  14  according to the present embodiment has the same shape as each of the diamond electrodes  114 A and  114 B in planar view. Moreover, as illustrated in  FIG. 11 , the floating electrodes  14  in the upper layer are opposed to the diamond electrodes  114 A and  114 B in the lower layer in one-to-one correspondence to form capacitors. That is, the floating electrodes  14  are disposed directly above the respective diamond electrodes  114 A and  114 B. Furthermore, each of the diamond electrodes  114 A and  114 B are preferably aligned with each of the floating electrodes  14  in planar view. 
     The one-to-one correspondence between the diamond electrodes  114 A or  114 B and each of the floating electrodes  14  allows the electrostatic force caused by both voltage signals applied to the X electrode  112 A and the Y electrode  112 B to act between each floating electrode  14  and the human body  4  without waste. Furthermore, the positions of the diamond electrodes  114 A and  114 B to which drive signals for presenting the tactile sense are applied may be aligned with positions on the panel surface where the tactile sense is presented. This prevents lowering in the resolution of the tactile sense. Misalignment is however recognized in the positional relationship between the diamond electrode  114 A or  114 B and each of the floating electrodes  14  within the permissible range in manufacturing. It is understood that the floating electrodes  14  are electrically isolated from each other in the present embodiment. 
     Subsequently, an example will be described where the tactile presentation device  101  according to the present embodiment is used. In the case where the second insulating film  15  has no scar, or a scar, if any, has not yet reached the floating electrode  14 , when a part of the human body  4  touches the second insulating film  15 , a capacitor is formed between the human body  4  and one or more floating electrodes  14  opposed to the human body  4  across the second insulating film  15  with respect to the position of contact, which causes the electrostatic force according to the magnitude of the voltage induced by the floating electrodes  14  to act on the human body  4 . 
     As described earlier, the signal frequency applied to the X electrode  112 A and the signal frequency applied to the Y electrode  112 B are both 500 Hz or higher, while the absolute value of the difference between two signal frequencies is 240 Hz. The driving condition satisfies a condition for the user to perceive the feel of texture (each of two signal frequencies is 500 Hz or higher and the absolute value of the difference between two signal frequencies is higher than 10 Hz and lower than 1000 Hz) (see Japanese Patent Application Laid-Open No. 2015-97076). Accordingly, the user may perceive the change in the electrostatic force as the feel of texture. 
       FIG. 12  illustrates the state where a scar reaching the floating electrodes  14  is generated in the second insulating film  15 , and a conductive foreign substance  20  such as water enters inside the scar. Here, it is also assumed that a scar having a substantially cylindrical shape with the diameter of 3 mm is formed. According to the present embodiment, the foreign substance  20  is in electrically contact with fourteen floating electrodes  14  at most.  FIG. 13  illustrates the contacting floating electrodes  14  by hatching. It is understood that the number of floating electrodes  14  is smaller depending on the position of contact. 
     When the human body  4  touches the foreign substance  20 , charge accumulated in the capacitor corresponding to the total area (19.7 mm 2 ) of the fourteen floating electrodes  14  flows in the human body  4  as leakage current I. However, the magnitude of the leakage current I is substantially equal to the amount of charge accumulated in the electrodes having the area corresponding to 19.7 mm 2 , and is significantly smaller than that in the tactile presentation device not provided with any measures for leakage current. 
     A result of simulation for the difference in magnitude between the leakage current possibly flowing in the tactile presentation device  101  according to the present embodiment and the leakage current possibly flowing in the tactile presentation device without any measures will be described below.  FIGS. 14A and 14B  illustrate structural examples of models used for simulation.  FIG. 14A  illustrates a cross-sectional structure of Comparative Example 2 where no measures are taken for leakage current.  FIG. 14B  illustrates a cross-sectional structure of the present embodiment. 
     In  FIGS. 14A and 14B , the thickness D 1  of the first insulating film  13  and the thickness D 2  of the second insulating film  15  are both 5 μm. It is assumed here that the scar has a cylindrical shape with a diameter of 3 mm, and the foreign substance  20  enters therein. The impedance of the human body is represented by Z. The permittivity of vacuum co may be calculated by 8.85×10 −12  F/m, while the relative permittivity c of the insulating film is assumed as 3.0. In the case of  FIG. 14A , the drive signal of 150 V/1240 Hz is applied to the drive electrode  112 . In the case of  FIG. 14B , the drive signal of 184 V/1240 Hz is applied to the drive electrode  112 . 
     Moreover, the floating electrode  14  according the present embodiment has a diamond shape with the dimension in the Y direction of 1668 μm and the dimension in the X direction of 1692 μm. Since the thickness of the insulating film is different between the present embodiment and Comparative Example 2, if they are driven by the signal voltage of the same magnitude, a difference occurs in the intensity of the tactile sense perceivable on the panel surface. In the simulation, therefore, the signal voltage of 184 V is applied in the present embodiment, to comply with the intensity of the tactile sense perceived on the panel surface in Comparison Example 2. Since frequency is increased while the impedance Z is lowered, the leakage current I 2  is easier to flow. Thus, in the present simulation, between 1000 Hz used for driving the X electrode  112 A and 1240 Hz used for driving the Y electrode  112 B, the higher frequency of 1240 Hz is employed. This is because, if it is safe with 1240 Hz, the safety is ensured even when driven with 1000 Hz which is more difficult for current to flow. 
       FIGS. 15A and 15B  illustrate the results of simulation.  FIG. 15B  is an enlarged view of a part of  FIG. 15A . Similarly to the case in  FIG. 7A , the present simulation was also carried out for three patterns including [1] the case where a part of the human body  4  being in contact with the panel surface is dry and is not in contact with GND, [2] the case where a part of the human body  4  is dry and is in contact with GND, and [3] the case where a whole of the human body  4  is wet with water and is in contact with GND. In the drawings, the outlined bars indicate the magnitude of the leakage current I 1  for the tactile presentation panel (Comparative Example 2) not provided with the measures for reducing leakage current, whereas the hatched bars indicate the magnitude of the leakage current I 2  for the tactile presentation panel (Embodiment 2) provided with the measures for reducing leakage current. 
     The minimum perception current is regarded as 1 mA as illustrated by the broken line in  FIG. 15A . In the case of [2] where a part of the human body which is in contact with the panel surface is dry and is in contact with GND, the magnitude of the leakage current I 1  is 6.36 mA in Comparative Example 2 provided with no measures for reducing the leakage current, whereas the magnitude of the leakage current I 2  is reduced to 148 μA in the present embodiment provided with measures for reducing the leakage current. Also in the case of [3] where the whole body is wet with water and is in contact with GND, the magnitude of the leakage current I 1  is 300 mA in Comparative Example 2, whereas the magnitude of the leakage current I 2  is reduced to 150 μA in the present embodiment. In the case of the dry finger, the magnitude of the leakage current I 1  is 117 μA in Comparative Example 2, whereas the magnitude of the leakage current I 2  is reduced to 73.4 μA in the present embodiment, as illustrated in the enlarged view of  FIG. 15B . 
     As can be clearly seen from  FIGS. 15A and 15B , in any cases of [1] to [3], the leakage current I 2  in the tactile presentation device  1  according to the present embodiment is smaller compared to the leakage current I 1  in Comparative Example 2. Moreover, the magnitude of the leakage current I 2  is significantly smaller than the minimum perception current. Specifically, in the case of [2] and [3], the leakage current I 1  corresponding to Comparative Example 2 exceeds the minimum perception current, whereas the leakage current I 2  corresponding to the present embodiment is significantly reduced to below the minimum perception current. According to the simulation results, the use of the tactile presentation device  101  employing the structure proposed in the present embodiment may reduce the leakage current to a safe level even if a scar is made on the second insulating film  15  and a conductive foreign substance  20  enters therein, preventing the user from sensing the leakage current. 
     Embodiment 3 
       FIG. 16  illustrates the schematic configuration of a tactile presentation device  201  according to Embodiment 3. In  FIG. 16 , parts corresponding to those in  FIG. 8  will be denoted by the same reference codes. The tactile presentation device  201  has a basic structure similar to that of the tactile presentation device  101  according to Embodiment 2. A difference exists in that the drive electrode  212  and the first insulating film  213  constituting the tactile presentation panel  202  have structures as follows. 
     (a) Drive Electrode  212   
     The area of the diamond electrodes  114 A and  114 B constituting the drive electrode  212  is one-fifth the area of the diamond electrodes  114 A and  114 B according to Embodiment 2. 
     (b) First Insulating Film  213   
     The film thickness D 11  of the first insulating film  213  is one-fifth the film thickness D 1  of the first insulating film  13  according to Embodiment 2. That is, D 11  corresponds to D 1 / 5 . 
     As such, the electrostatic capacitance of the capacitor formed between the floating electrode  14  and the corresponding diamond electrode  114 A or  114 B is represented by the following formula. 
     
       
         
           
             
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                   1 
                 
               
             
           
         
       
     
     Here, C 201  is the electrostatic capacitance of the capacitor formed between the floating electrode  14  and the corresponding diamond electrode  114 A or  114 B. S 201  represents the area of the diamond electrodes  114 A and  114 B in the present embodiment, whereas S 101  represents the area of the diamond electrodes  114 A and  114 B in Embodiment 2. 
     With reference to the second representation on the right-hand side, the numerator and denominator both include a constant, i.e., ⅕. Here, if the constant is removed, the value after the removal will be the same value as the electrostatic capacitance of the capacitor formed between the floating electrode  14  and the corresponding diamond electrode  114 A or  114 B in Embodiment 2. That is, the electrostatic capacitance of the capacitor formed between the floating electrode  14  and the corresponding diamond electrode  114 A or  114 B takes the same value as that in Embodiment 2. Accordingly, the impedance for the signal frequency applied to the X electrode  112 A and the Y electrode  112 B also takes the same value as that in Embodiment 2. 
     Thus, even if a scar reaching the floating electrode  14  is generated in the second insulating film  15  of the tactile presentation device  201  and leakage current I 2  flows in the human body  4  through the conductive foreign substance  20  intruded into the scar, the same effect of reducing such leakage current I 2  as that in Embodiment 2 may be obtained. Also, the dimension of the floating electrode  14  in the present embodiment is equal to that in Embodiment 2, so that the area where the human body  4  is opposed to the floating electrode  14  as well as the potential difference between the human body  4  and the floating electrode  14  are also the same. The tactile presentation device  201  may therefore provide the user with the same tactile sense as that in the case where the tactile presentation device  101  according to Embodiment 2 is used. In addition, according to the present embodiment, the first insulating film  213  may be made thinner, which can reduce the entire thickness of the tactile presentation device  201 . 
     Embodiment 4 
       FIG. 17  illustrates the schematic configuration of a tactile presentation device  301  according to Embodiment 4. In  FIG. 17 , parts corresponding to those in  FIG. 8  will be denoted by the same reference codes. The tactile presentation device  301  has a basic structure similar to that of the tactile presentation device  101  according to Embodiment 2. A difference exists in that a tactile presentation panel  302  formed by layering an anti-glare layer  316  on the upper surface of the first insulating film  13  is employed in place of the floating electrodes  14  and the second insulating film  15 . 
     The anti-glare layer  316  is a so-called reflection protecting layer. The anti-glare layer  316  according to the present embodiment is formed with conductive particles  314  serving as floating electrodes and an insulating coat layer  315  serving as the second insulating film. The anti-glare layer  316  is formed by, for example, applying material used for the insulating coat layer  315  that evenly contains conductive particles  314  onto the surface of the first insulating film  13 . The anti-glare layer  316  has a film thickness D 12  of, for example, 5 μm. It is understood that this numeric value is a mere example. 
     The conductive particles  314  are present while being electrically insulated from each other inside the coat layer  315 . Thus, the conductive particles  314  function similarly to the floating electrodes  14  in Embodiment 2. The particles  314  inside the coat layer  315  preferably have the total area of 19.7 mm 2  or smaller that is in contact with the human body  4  in the case where a cylindrical scar with the diameter of 3 mm is formed in the coat layer  315 . 
     The anti-glare layer  316  according to the present embodiment may be applied not only to the tactile presentation panel  102  according to Embodiment 2 as described earlier, but also to the tactile presentation panel  2  according to Embodiment 1 or the tactile presentation panel  202  according to Embodiment 3. In any of the described cases, the manufacturing procedure for the floating electrode  14  and the second insulating film  15  may be simplified. 
     Other Structural Examples 
     (a) While acrylic resin is exemplified as the material for the first insulating film  13  in the embodiments described earlier, transparent material such as SiO 2 , SiN or diamond-like carbon which has higher strength may also be used. In such a case, the drive electrodes  12 ,  112  and the floating electrodes  14  are formed as transparent electrodes. Of course, non-transparent material stronger than acrylic resin may alternatively be used if it is unnecessary to visibly recognize characters, images, video and other information by seeing through the tactile presentation device. The use of stronger material prevents a crack from occurring in the first insulating film  13 . Moreover, even if a crack is generated in the second insulating film  15  and the coat layer  315 , the crack is unlikely to expand to the first insulating film  13 . As a result, the first insulating film  13  may be made thinner. The thinning of the first insulating film  13  may also be applied to the first insulating film  213  (see  FIG. 16 ) in Embodiment 3. Due to the reduced film thickness, it is also possible to employ insulating material which requires a long time for deposition. 
     (b) While acrylic resin is illustrated as an example of material for the second insulating film  15  in the embodiments described earlier, transparent material such as SiO 2 , SiN or diamond-like carbon which has higher strength may also be used. In such a case, the drive electrodes  12 ,  112  and the floating electrodes  14  are configured as transparent electrodes. Of course, non-transparent material stronger than acrylic resin may alternatively be used if it is unnecessary to visibly recognize characters, images, video and other information by seeing through the tactile presentation device. The use of stronger material prevents a crack from occurring in the second insulating film  15 , and also lowers the growth risk of a crack. Since the second insulating film  15  may be made thinner, it is also possible to employ insulating material which requires a long time for deposition. It is noted that the material of the second insulating film  15  may be the same as that of the first insulating film  13 . 
     Applied Example 
       FIG. 18  illustrates an example of the outer appearance of electronic equipment  400  which is an application of the tactile presentation device  1 ,  101 ,  201  or  301  according to each of the embodiments described earlier. The electronic equipment  400  is, in particular, a smartphone, a tablet electronic book reader, a notebook personal computer or the like. 
     The electronic equipment  400  includes a touch panel display device  401  and a tactile presentation device  402 . The tactile presentation device  402  is a tactile presentation device according to any one of the embodiments described earlier, and is disposed on the display screen side or the rear side of the touch panel display device  401 . As for the input scheme of the touch panel display device  401 , an input scheme other than the electrostatic capacitive type which is the current mainstream (e.g., optical or resistance film type) is used. This is because the tactile presentation device  402  according to each embodiment described earlier and the touch panel display device  401  of the electrostatic capacitive type both utilize the capacitive coupling with a human body, and thus cannot be compatible in terms of their functions. 
     The electronic device  400  has a processor  403  built therein, and the processing result is displayed on the touch panel display device  401 . The user inputs data for the content displayed on the display screen of the touch panel display device  401  through touching operation to multiple operation keys  404  and the like. Alternatively, the electronic equipment  400  may display the processing result of an external device (such as a desktop personal computer, for example) externally connected thereto through a cable or wireless communication, and return the operation input back to the external device. 
     While several embodiments of the present invention have been described with reference to the drawings, the present invention is not limited to the embodiments described above. The present invention may also have a configuration employing a known optional structure as long as the effect of reducing leakage current flowing through a human body is obtained. 
     According to the present disclosure, even if leakage current flows in a human body through a scar formed on an operation surface, the magnitude thereof may be suppressed. 
     As this invention may be embodied in several forms without departing from the spirit of essential characteristics thereof, the present embodiment is therefore illustrative and not restrictive, since the scope of the invention is defined by the appended claims rather than by the description preceding them, and all changes that fall within metes and bounds of the claims, or equivalence of such metes and bounds thereof are therefore intended to be embraced by the claims.