Patent Publication Number: US-9413272-B2

Title: Power generation device having a dielectric body and an electret

Description:
This application is based on Japanese Patent Application No. 2011-190391 filed Sep. 1, 2011, the contents of which are hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a power generation device that generates energy (converting energy from kinetic energy (energy of vibration) to electrical energy) by varying the distance between a dielectric body and an electret; and in particular to a capacitive power generation device of vibratory drive design, manufactured employing a micro electromechanical system (MEMS) technique. 
     2. Description of Related Art 
       FIG. 33  is a schematic diagram showing a prior art example of a vibratory power generation device. In  FIG. 33 , reference numeral  101  designates an upper substrate, reference numeral  102  designates a lower substrate, reference numeral  103  designates an electret, reference numeral  104  designates an opposite electrode, reference numeral  105  designates a base electrode, and reference numeral designates  106  a spring. The upper substrate  101  is a moveable body that is elastically supported so as to be displaceable in two axial planar directions (an X direction and a Y direction) with respect to the lower substrate  102 . 
     The basic principle of operation of a vibratory power generation device having the aforementioned configuration is a system whereby the surface area of overlap of the electret  103  and the opposite electrode  104  is varied through vibration in two axial planar directions (the X direction and the Y direction) while maintaining a predetermined gap distance, to extract, in the form of electrical current, changes in electric charge induced in the opposite electrode  104  (a so-called electrostatic induction system). 
     As techniques related to vibratory power generation devices manufactured employing MEMS techniques, there may be cited Patent Document 1 (Japanese Laid-Open Patent Application 2007-312551); Non-patent Document 1 (Y. Naruse, N. Matsubara, K. Mabuchi, M. Izumi, K. Honma, “ELECTROSTATIC MICRO POWER GENERATOR FROM LOW FREQUENCY VIBRATION SUCH AS HUMAN MOTION”, Proceedings of PowerMEMS 2008+, Sendai, Japan, Nov. 9-12, (2008); and Non-patent Document 2 (M. Edamoto, Y. Suzuki, N. Kasagi, K. Kashiwagi, Y. Morizawa, T. Yokoyama, T. Seki, and M. Oba, “LOW-RESONANT-FREQUENCY MICRO ELECTRET GENERATOR FOR ENERGY HARVESTING APPLICATION”, Proc. IEEE Int. Conf. MEMS 2009, Sorrento, (2009), pp. 1059-1062. 
     However, in the aforementioned vibratory power generation device of the prior art, the generated power is at most on a microwatt scale, and applications for it were limited. 
     Moreover, the aforementioned vibratory power generation device of the prior art has a structure in which the electret  103  and the opposite electrode  104  are facing one another, and when the gap distance between the electret  103  and the opposite electrode  104  is designed too small, electrostatic attraction acting between the electret  103  and the opposite electrode  104  poses a risk of the two coming into contact, or of the charge introduced from the electret  103  being discharged. For this reason, the gap distance between the electret  103  and the opposite electrode  104  must be designed to be somewhat large, but having thusly expanded the gap distance, it now becomes necessary to design the electret  103  and the opposite electrode  104  to have large surface areas, in order for vibration-induced change in capacity to be large, giving rise as a result to a negative cycle whereby the gap distance must be expanded even further. Due to this sort of negative cycle, in the aforementioned vibratory power generation device of the prior art, it has been difficult to miniaturize the device and/or reduce the gap size, while boosting the generated power. 
     SUMMARY OF THE INVENTION 
     With the foregoing in view, it is an object of the present invention to offer a compact, high-output power generation device. 
     In order to achieve the aforementioned object, the power generation device according to the present invention has a dielectric body and an electret, the distance between the dielectric body and the electret being varied, whereby power is generated. 
     These and other characteristics, elements, steps, advantages, and features of the present invention will be apparent from the following detailed description of the preferred embodiments and the appended drawings relating thereto. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram showing a first configuration example of a power generation device; 
         FIG. 2  is an equivalent circuit diagram of a power generation device; 
         FIG. 3  is a simplified diagram of a measurement system; 
         FIG. 4  is a descriptive diagram of a corona discharge device; 
         FIG. 5  is a table showing the relationship among variable resistance, output voltage, and generated power; 
         FIG. 6  is a graph showing the relationship between variable resistance and output voltage; 
         FIG. 7  is a graph showing the relationship between variable resistance and generated power; 
         FIG. 8A  is an oscilloscope waveform chart at maximum power output; 
         FIG. 8B  is a simulation waveform of output voltage Vm versus gap distance G; 
         FIG. 9  is a comparison diagram of generating capacity according to the state of electrical connection at the back surface of a dielectric body; 
         FIG. 10  is a schematic diagram showing a second configuration example of a power generation device; 
         FIG. 11  is a schematic diagram showing a third configuration example of a power generation device; 
         FIG. 12  is a schematic diagram showing a first packaging example of a power generation device; 
         FIG. 13  is a schematic diagram showing a second packaging example of a power generation device; 
         FIG. 14  is a schematic diagram showing a third packaging example of a power generation device; 
         FIG. 15  is a schematic diagram showing a fourth packaging example of a power generation device; 
         FIG. 16  is a schematic diagram showing a fifth packaging example of a power generation device; 
         FIG. 17  is a schematic diagram showing a sixth packaging example of a power generation device; 
         FIG. 18  is a schematic diagram showing a seventh packaging example of a power generation device; 
         FIG. 19  is a schematic diagram showing an eighth packaging example of a power generation device; 
         FIG. 20  is a schematic diagram showing a first guide example of a dielectric body; 
         FIG. 21  is a schematic diagram showing a second guide example of a dielectric body; 
         FIG. 22  is a schematic diagram showing a first implementation example of a ground ring; 
         FIG. 23  is a schematic diagram showing a second implementation example of a ground ring; 
         FIG. 24  is a schematic diagram showing an example of a combination of dielectric body shape and lower electrode shape; 
         FIG. 25  is a schematic diagram showing a first example of lower electrode shape; 
         FIG. 26  is a schematic diagram showing a second example of lower electrode shape; 
         FIG. 27  is a schematic diagram showing a third example of lower electrode shape; 
         FIG. 28  is a schematic diagram showing a first structure for realizing triaxial capability; 
         FIG. 29  is a schematic diagram showing a second structure for realizing triaxial capability; 
         FIG. 30  is a schematic diagram showing a third structure for realizing triaxial capability; 
         FIG. 31  is a schematic diagram showing a fourth structure for realizing triaxial capability; 
         FIG. 32  is a graph showing the relationship between generating capacity and relative permittivity of a dielectric body; and 
         FIG. 33  is a schematic diagram showing a prior art example of a vibratory power generation device. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     (First Configuration Example) 
       FIG. 1  is a schematic diagram showing a first configuration example of a power generation device (a sectional view seen in a lateral direction). The power generation device  10  of the first configuration example has a dielectric body  11 , an electret  12 , a lower electrode  13 , a resistor  14 , an upper electrode  15 , a substrate  16 , and a gap layer  17 . At the top in  FIG. 1 , the power generation device  10  is depicted in a first state (a state in which the dielectric body  11  and the electret  12  are spaced apart), while at the bottom in  FIG. 1 , the power generation device  10  is depicted in a second state (a state in which the dielectric body  11  and the electret  12  are close together). 
     Herein, for the sake of convenience in description, where not specified otherwise, the upper edge side of the page is defined as the vertically upward direction, and the description is premised on a configuration in which the dielectric body  11  vibrates in the up-and-down direction (vertical direction); however, the direction of vibration of the dielectric body  11  is not limited thereto; it also being possible, for example, to configure the dielectric body to vibrate in the left-and-right direction (horizontal direction) through 90-degree rotation of the page. 
     The dielectric body  11  is a moveable body, the relative position of which varies with respect to the electret  12  due to vibration imparted to the power generation device  10 . The bottom face of the dielectric body  11  faces the top face of the electret  12  with the gap layer  17  therebetween. Lead zirconate titanate (PZT), barium titanate (BTO), or the like can be employed as the dielectric body  11 . This will be discussed below. The dielectric body  11  may be formed to a plate shape or to a film shape. For example, the substrate itself may be formed by a dielectric body; a dielectric body film may formed over the substrate by a thin-film printing technique; or a dielectric body of plate shape formed by a separate process may be adhered onto the substrate. 
     The electret  12  is a member that retains a quasi-permanent electric charge. As the electret  12 , there may be employed an organic electret that retains an electric charge in a polymer compound, such as CYTOP™; or an inorganic electret that retains an electric charge in a substrate of silicon oxide (SiO 2 ), silicon nitride (SiN), or the like. The electret  12  is formed so as to cover the entire surface of the lower electrode  13 . By adopting such a configuration whereby the lower electrode  13  is not exposed, outflow of charge to the exposed lower electrode  13  when a charge is introduced to the electret  12  can be prevented, and therefore it is possible to increase the efficiency at which charge is introduced to the electret  12 . 
     The lower electrode  13  corresponds to a first electrode which is connected to the bottom face side of the electret  12  (the side not facing toward the dielectric body  11 ). The lower electrode  13  is connected to a grounding terminal via the resistor  14 . An aluminum electrode or the like can be employed as the lower electrode  13 . 
     The resistor  14  is a load for drawing, in the form of a voltage, electrical current flowing between the lower electrode  13  and the grounding terminal due to vibration of the power generation device  10 . 
     The upper electrode  15  corresponds to a second electrode which is connected to the top face of the dielectric body  11  (the side not facing toward the electret  12 ). The upper electrode  15  is directly connected to the grounding terminal. An aluminum electrode or the like can be employed as the upper electrode  15 . 
     The substrate  16  is a plate-shaped member for supporting the electret  12  and the lower electrode  13 . A quartz substrate, a silicon wafer having an oxide film, or the like can be employed as the substrate  16 . However, from the standpoint of minimizing parasitic capacitance, it is more preferable to employ a quartz substrate or the like, than a silicon wafer having an oxide film. 
     The gap layer  17  is a gap present between the dielectric body  11  and the electret  12 . The thickness of the gap layer  17  (the gap distance separating the dielectric body  11  and the electret  12 ) varies due to displacement of the dielectric body  11  in association with vibration. The gap layer  17  may be placed in a low vacuum state (a state that is neither a high vacuum state nor an ultrahigh vacuum state), or filled with air, with an inert gas (N 2  or the like), with a gas having discharge-preventive effect (for example, a gas containing SF 6  as the principal component), or the like. In a case in which the gap layer  17  is placed in a low vacuum state, a degassing step may be employed, or a phenomenon whereby gas is removed from the gap layer  17  during some high-temperature process, creating a low vacuum state naturally, may be utilized. The reason it is undesirable to place the gap layer  17  in a high vacuum state or an ultrahigh vacuum state is so as to avoid discharge of the electret  12 . Herein, a “low vacuum state” refers to a state of atmospheric pressure to 10 −1  Pa; a “high vacuum state” refers to a state of 10 −1 -10 −5  Pa, and an “ultrahigh vacuum state” refers to a state of 10 −5  Pa or below. When moisture is contained in the gap layer  17 , water molecules tend to settle on the surface of the electret  12  and remove charge, and it is therefore preferable to sufficient eliminate moisture contained in the gap layer  17  and bring about a low humidity state. 
     In the aforementioned manner, the power generation device  10  of the first configuration example has at least one dielectric body  11 /electret  12  pair, and is configured to generate power by varying the gap distance between the dielectric body  11  and the electret  12 . The basic principle of power generation is described below. 
     With the power generation device  10  in the first state (a state in which the dielectric body  11  and the electret  12  are spaced apart) as shown at the top in  FIG. 1 , attracted by negative fixed charges (in  FIG. 1 , portrayed as symbols of white squares with minus signs) held by the electret  12 , intrametallic positive charges (in  FIG. 1 , portrayed as symbols of white circles with plus signs) are induced on the surface of the lower electrode  13  (the interface with the electret  12 ). These intrametallic positive charges assume the character of positive charges that arise as a result of free electrons being expelled from sites within the lower electrode  13  (metal), creating potential difference from surrounding free electrons. Consequently, with regard to the aforementioned physical phenomenon, it is more correct to say free electrons within the lower electrode  13  are pushed out, rather than that positive charges within the lower electrode  13  are attracted by negative fixed charges held by the electret  12 . The intrametallic positive charges within the lower electrode  13  are supplied from the grounding terminal (the free electrons within the lower electrode  13  move to the grounding terminal), and therefore the potential of the lower electrode  13  remains at 0 V. 
     On the other hand, upon transition of the power generation device  10  from the first state to the second state (a state in which the dielectric body  11  and the electret  12  are close together) as shown at the bottom in  FIG. 1 , the interior of the dielectric body  11  becomes polarized due to the negative fixed charges held by the electret  12 , and positive polarized charges (in  FIG. 1 , portrayed as symbols of black circles with plus signs) become localized at the bottom surface of the dielectric body  11 . At this time, (a portion of) the correspondence relationships between the positive charges within the lower electrode  13  and the negative charges within the electret  12  which arose in the first state are now dissolved. Due to this phenomenon, a transitory surplus of positive charges arises within the lower electrode  13 . However, because the lower electrode  13  is connected to the grounding terminal via the resistor  14 , movement of the surplus positive charges (electrical current) from the lower electrode  13  to the grounding terminal arises, until the transitory rise in potential of the lower electrode  13  returns to 0 V. The bottom of  FIG. 1  shows a state subsequent to movement of a portion of the positive charges from the lower electrode  13 . The remaining charges that have not flowed out from the lower electrode  13  are denoted by Q 1 . 
     When, in the opposite of the above process, the power generation device  10  has transitioned from the second state to the first state, movement of positive charges (i.e., electrical current) from the grounding terminal to the lower electrode  13  arises, and therefore this electrical current can be drawn out as electrical energy. 
     In the second state of the power generation device  10 , negative polarized charges (in  FIG. 1 , portrayed as symbols of black circles with minus signs) become localized at the top surface of the dielectric body  11 , due to internal polarization of the dielectric body  11 . Consequently, at the top surface of the upper electrode  15  (the interface with the dielectric body  11 ), intrametallic positive charges are induced through attraction to the aforementioned negative polarized charges. However, because the intrametallic positive charges within the upper electrode  15  are supplied from the grounding terminal, the potential of the upper electrode  15  remains at 0 V. 
     Viewed in electromagnetic terms, the second state of the power generation device  10  is a state of lower electrostatic potential energy than the first state (a stable state in which distances between positive charges and negative charges are closer together than in the first state). Consequently, when the power generation device  10  is transitioned between the first state and the second state by imparting kinetic energy (vibration) from the outside, it is possible for kinetic energy to be converted to electrical energy. 
     In particular, the power generation device  10  of the first configuration example is configured to be furnished with the upper electrode  15  on the top face of the dielectric body  11 , with this upper electrode  15  connected to the grounding terminal. Because of this configuration, in the second state of the power generation device  10 , no potential difference arises in the interior of the upper electrode  15 , and therefore it is possible to drag down the potential energy of the second state, and increase the generation efficiency. 
     (Equivalent Circuit Diagram) 
       FIG. 2  is an equivalent circuit diagram of the power generation device  10 . Sign C 1  shows electrostatic capacitance (fixed value) of the electret  12 , sign C 2  shows electrostatic capacitance (fixed value) of the dielectric body  11 , sign C 3  shows electrostatic capacitance (variable value) of the gap layer, and sign C 4  shows serial composition of capacitance of the dielectric body  11  and the gap layer  17  (C 4 =C 2 ×C 3 /(C 2 +C 3 ). Sign R shows the resistance value (fixed value) of the resistor  14 . 
     The most notable point in this equivalent circuit diagram is that the electret  12 , which fulfills the role of the power supply, should be called a “constant charge supply” that retains a constant charge Q. 
     When the power generation device  10  is transitioned from the first state (top in  FIG. 2 ) to the second state (bottom in  FIG. 1 ), charge is distributed to the dielectric body  11  side as well. As the electrostatic capacitance of a capacitor distributed to a constant charge increases, the potential of the capacitor decreases. In terms of a phenomenon, this is equivalent to a case in which a capacitor is charged with a charge, then disconnected from the power supply and connected to another capacitor. 
     At this time, where Q 1  denotes charge remaining in the capacitor between the electret  12  and the lower electrode  13 , Q 2  denotes charge paired with induced charge in the dielectric body  11 , and V denotes potential difference between contacts A-A′, the following Equation (1) and Equation (2) apply.
 
 Q=Q 1 +Q 2  (1)
 
 V=Q 1 /C 1 =Q 2 /C 4  (2)
 
     From the aforementioned Equation (1) and Equation (2), the charge Q 1  is represented by the following Equation (3):
 
 Q 1 =Q 1 ×C 1/( C 1 +C 4)  (3)
 
     In Equation (3), the electrostatic capacitance C 1  and the charge Q of the electret  12  are fixed values, whereas the serial composition of capacitance C 4  of the dielectric body  11  and the gap layer  17  is a variable value that varies depending on the thickness of the gap layer  17  (and, hence, on the electrostatic capacitance C 3  of the gap layer  17 ). Consequently, as the serial composition of capacitance C 4  varies in response to displacement of the dielectric body  11  in association with vibration, the ratio of charge Q 2  and charge Q 1  will vary. In the power generation device  10 , the redistribution of charge associated with this change in capacitance is drawn out as electrical current. 
     Generating capacity is formulated as follows. The electrical current i flowing through a circuit at given time t is given by the time derivative of the charge Q 1 . Where the time derivative of a given function f is denoted by f′, the electrical current i is represented by the following Equation (4), based on the aforementioned Equation (3): 
     
       
         
           
             
               
                 
                   
                     
                       
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     Moreover, the serial composition of capacitance C 4  of the gap layer  17  is represented by the following Equation (5), employing the electrostatic capacitance C 2  of the dielectric body  11  and the electrostatic capacitance C 3  of the gap layer  17 :
 
 C 4=( C 2 −1   +C 3 −1 ) −1   (5)
 
     From the aforementioned Equation (5), the time derivative C 4 ′ of the serial composition of capacitance C 4  is represented by the following Equation (6): 
     
       
         
           
             
               
                 
                   
                     
                       
                         
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     As the gap distance between the dielectric body  11  and the electret  12  varies time-wise, the electrostatic capacitance C 3  of the gap layer  17  simultaneously varies as well. Here, in a case in which the gap distance of the dielectric body  11  and the electret  12  in the initial state is denoted as X 0 , and additionally the dielectric body  11  is experiencing simple harmonic motion at an amplitude A and an angular velocity ω, the capacitance C 3  of the gap layer  17  and the time derivative C 3 ′ thereof are represented by Equation (7) and Equation (8). The sign ∈ 0  in the equations is the dielectric constant of a vacuum (8.85×10 −12  F/m).
 
 C 3=∈0 ×∈r×S×{X 0 +A ×sin(ω× t )} −1   (7)
 
 C 3′=−∈0 ×∈r×S×A ×ω×cos(ω× t )×{ X 0 +A ×sin(ω× t )} −2   (8)
 
     The voltage V 2  output from both terminals of the resistor  14  furnished to the power generation device  10 , due to the flow of electrical current i, is represented by Equation (9), employing the resistance value R of the resistor  14 :
 
 V 2 =i×R   (9)
 
     The power P drawn from the resistor  14  is represented by Equation (10), employing the average value I of the electrical current i and the resistance value R of the resistor  14 . The sign T in the equation is the vibration period of the dielectric body  11 , and is given by T=2×π/ω.
 
 P=I   2   ×R=T   −1 ×∫ 0   Ti   2   dt×R   (10)
 
     Simulation values of output voltage waveforms based on the aforementioned Equation (9) are shown in  FIG. 8B . An output waveform based on this formulation is not a sine wave, but rather a waveform theoretically distorted from a sine wave (discussed in detail below). 
     Here, the gap layer  17  present between the dielectric body  11  and the electret  12  plays a useful role. The greater the electrostatic capacitance C 3  of the gap layer  17  is, specifically, the smaller the thickness (gap distance) of the gap layer  17  is, the greater is the amount of polarized charge in the dielectric body  11 , and the generating capacity increases in accordance therewith. 
     As stated previously, the power generation device  10  of the first configuration example differs from the prior art configuration in which the electret and the opposite electrode face one another (see  FIG. 33 ), in that the dielectric body  11  and the electret  12  face one another, and therefore even if the dielectric body  11  and the electret  12  are close (or touching), discharge of the electret  12  basically does not arise. 
     Consequently, with the power generation device  10  of the first configuration example, when generating power in response to changes in the gap distance separating the dielectric body  11  and the electret  12 , the dielectric body  11  and the electret  12  can be brought closer together until the gap distance reaches its minimum of zero, whereby it is possible to obtain extremely large generating capacity (on a milliwatt scale). 
     (Power Generation Test) 
     (Measurement System) 
       FIG. 3  is a simplified diagram of a measurement system employed in a power generation test. The measurement system X employed in this power generation test includes a dielectric body X 1 , an aluminum panel X 2 , an electromagnetic type vibration exciter X 3 , a test sample X 4 , an aluminum panel X 5 , a three-axis stage X 6 , a base X 7 , a coaxial cable X 8 , a coaxial cable X 9 , a shield case X 10 , a coaxial cable X 11 , a low-pass filter X 12 , a coaxial cable X 13 , and an oscilloscope X 14 . 
     The dielectric body X 1  (which corresponds to the dielectric body  11  of  FIG. 1 ) is arranged with the top face facing towards the bottom surface of the test sample X 4 , and the bottom surface is connected to the aluminum panel X 2 . Lead zirconate titanate (PZT) is employed as the dielectric body X 1  (the dielectric constant of the PZT used in the test is 2,600). 
     The aluminum panel X 2  (which corresponds to the upper electrode  15  of  FIG. 1 ) is connected at the top surface thereof to the dielectric body X 1 . The aluminum panel X 2  is directly connected to the grounding terminal of the measurement system X. 
     The electromagnetic type vibration exciter X 3  imparts vibration (of 40 Hz frequency) in the up-and-down direction to the dielectric body X 1  which is connected to the top surface of the aluminum panel X 2 . 
     The test sample X 4  (which corresponds to the electret  12 , the lower electrode  13 , and the substrate  16  of  FIG. 1 ) is connected at a quartz substrate at the upper surface side thereof (thickness: 1.0 mm) to the aluminum panel X 5 , while an electret at the lower surface side thereof (thickness: 5.6 μm) faces towards the dielectric body X 1 . CYTOP™ is employed as the electret. No patterning has been carried out on the electret. Meanwhile, patterning to pectinate array shape (width: 30 μm, pitch: 60 μm) has been carried out on the lower electrode, which is covered by the electret. The lower electrode is connected to a first terminal of the coaxial cable X 8 . 
     The aluminum panel X 5  provides support to the test sample X 4 . 
     The test sample X 4  supported on the aluminum panel X 5  is moved in three axial directions by the three-axis stage X 6 . 
     The base X 7  provides support to the three-axis stage X 6 . 
     The coaxial cable X 8  is connected at a first terminal thereof to the lower electrode of the test sample X 4 , and at a second terminal thereof to a first terminal of the coaxial cable X 9 . 
     The coaxial cable X 9  is connected at a first terminal thereof to a second terminal of the coaxial cable X 8 , and at a second terminal thereof to a first connector X 10   a  of the shield case X 10 . 
     The shield case X 10  houses load resistances Rv, R (the resistor  14  of  FIG. 1  corresponds to the serial composition of resistance of Rv and R). The main body of the shield case X 10  is connected to the grounding terminal of the measurement system X. The first connector X 10   a  of the shield case X 10  is connected to the grounding terminal of the measurement system X via the load resistances Rv, R. In this way, in the measurement system X, the test sample X 4  and the load resistances Rv, R are connected by a coaxial wire, not by a lead wire. The connection node of the load resistances Rv, R connects to a second connector X 10   b  of the shield case X 10  as the measurement node for output voltage Vm. The ground line of the second connector X 10   b  is connected to the grounding terminal of the measurement system X. Of the load resistances Rv, R, the resistance Rv that is connected between the first connector X 10   a  and the second connector X 10   b  (the resistance for which voltage at either terminal is not measured) is a variable resistance (a potentiometer), whereas the resistance R that is connected between the second connector X 10   b  and the grounding terminal (the resistance for which voltage at either terminal is measured as the output voltage Vm) is a fixed resistance (100 kΩ). 
     The coaxial cable X 11  connects the second connector X 10   b  of the shield case X 10  and the input terminal of the low-pass filter X 12 . 
     The low-pass filter X 12  eliminates noise that overlaps the output voltage Vm. The cutoff frequency fc of the low-pass filter X 12  is set to 200 Hz. 
     The coaxial cable X 13  connects the output terminal of the low-pass filter X 12  and the input terminal of the oscilloscope X 14 . 
     The oscilloscope X 14  displays the waveform of the output voltage Vm (temporal variation of the electrical signal) in the form of a graph. In the graph displayed by the oscilloscope X 14 , the vertical axis is output voltage, and the horizontal axis is time. The ground terminal of the oscilloscope X 14  is connected to the grounding terminal of the measurement system X. 
     (Test Procedure) 
     The test procedure employing the measurement system X is as follows. In Step S 1 , a corona discharge device Y shown in  FIG. 4  is employed under predetermined conditions (corona discharge voltage: 10 kV, 0.1 mA; grid voltage: 1.5 kV) to introduce a charge into the electret of the test sample X 4 . In  FIG. 4 , signs X 41 , X 42 , and X 43  respectively show the constituent elements (the electret, the lower electrode, and the substrate) that form the test sample X. Signs Y 1  to Y 4  respectively show the constituent elements (a grid, a discharge electrode needle, a grid power supply, a DC high voltage power supply) forming the corona discharge device Y. In Step S 2 , the surface potential of the test sample X 4  is measured. In Step S 3 , the test sample X 4  is connected to the measurement system X. In Step S 4 , the dielectric body X 1  is vibrated by the electromagnetic type vibration exciter X 3 . In Step S 5 , the waveform of the output voltage Vm arising in response to the dielectric body X 1  and the test sample X 4  moving closer together/apart is observed with the oscilloscope. In Step S 6 , Step S 4  to Step S 6  are repeated while varying the resistance value of the variable resistance Rv. In Step S 7 , the output power P of the power generation device  10  is calculated based on the output voltage Vm thusly obtained. 
     Firstly, the average value Vms of the output voltage Vm is calculated from (11), following:
 
 Vms=T   −1 ×∫ 0   T   Vmdt   (11)
 
     However, in a case in which the waveform of the output voltage Vm approximates a sine wave, by measuring the maximum amplitude Vpp (the peak-to-peak value) of the output voltage Vm, it is possible to derive an estimate value of the average value Vms, from the equation Vms≈0.354×Vpp. 
     Next, the voltage VL at which the load resistance (R+Rv) is generated is calculated by the following Equation (12).
 
 VL=Vms ×( R+Rv )/ R   (12)
 
     Then, employing the following Equation (13), the generated power P can be calculated from the voltage VL.
 
 P=VL   2 /( R+Rv )  (13)
 
     (Test Results) 
     First, the results of measuring surface potential of the test sample X 4  are described. Subsequent to the introduction of charge in Step S 1 , the average potential at the test sample X 4  surface was approximately −525 V. 
     Next, the results of vibratory power generation test carried out while varying the resistance value of the variable resistance Rv are described.  FIG. 5  is a table showing the relationship among variable resistance Rv (Me), maximum amplitude Vpp of the output voltage Vm (V), and generated power Pm (μW).  FIG. 6  is a graph showing the relationship between variable resistance Rv (MΩ) and maximum amplitude Vpp of the output voltage Vm (V).  FIG. 7  is a graph showing the relationship between variable resistance Rv (MΩ) and generated power Pm (μW). It was confirmed that the generated power Pm reaches maximum (975 μW=0.97 mW) when the variable resistance Rv is 10 MΩ. In this way, in the vibratory power generation test employing the measurement system X, exceedingly large generating capacity (on a milliwatt scale) can be obtained. 
       FIG. 8A  is an oscilloscope waveform chart at maximum power output. The driving waveform of a vibration simulator is shown at top in  FIG. 8A . It will be appreciated that, since the drive signal is a sine wave, the dielectric body X 4  provided to the electromagnetic type vibration exciter X 3  experiences simple harmonic motion. On the other hand, the output waveform of the output voltage Vm is depicted at bottom in  FIG. 8A . The output waveform of the output voltage Vm is a shape that differs from a sine wave. However, this waveform is a theoretically correct waveform, not a sine wave distorted by disturbance elements such as noise. This will be described in the next section. 
       FIG. 8B  is a simulation waveform of the output voltage Vm versus the gap distance G. The gap distance of the test sample X 1  and the dielectric body X 4  is depicted at the top in  FIG. 8B , and the output voltage Vm of the measurement system X theoretically calculated employing the previously cited Equation (3) to Equation (9) is depicted at the bottom in  FIG. 8B . As the parameters used in the computations, numerical values identical to the parameters belonging to the test sample X 1 , the dielectric body X 4 , and the resistances R and Rv employed in the measurement system X used in the actual power generation test were input. However, for the initial value of the gap distance G of the test sample X 1  and the dielectric body X 4  (specifically, X 0  in Equation (7)), and for the amplitude of vibration imparted to the dielectric body X 4  by the electromagnetic type vibration exciter X 3  (specifically, A in Equation (7)), correct numerical values could not be measured. Accordingly, mathematical operations were performed on the hypothesis that gap distance G of the test sample X 1  and the dielectric body X 4  varies in the manner shown by the waveform depicted at the top in  FIG. 8B . The waveforms of  FIG. 8A  and  FIG. 8B  match extremely well, and it can considered proven that measured output voltage Vm is outputted as the result of power generation based on the proposed basic principle. 
     Next, the relationship between the generating capacity and the electrical connection of the aluminum plate X 2  at the back surface of the dielectric body X 1  will be described. A vibratory power generation test analogous to that above was performed in a state in which the aluminum plate X 2  was disconnected from the grounding terminal.  FIG. 9  is a comparison diagram of generating capacity according to the state of electrical connection at the back surface of the dielectric body X 1 . As shown in  FIG. 9 , it was verified that, between the case in which the aluminum plate X 2  is connected to the grounding terminal (the black bar graph) in the measurement system X versus the case in which it is not connected (the hatched bar graph), differences arise both in the maximum amplitude Vpp of the output voltage Vm and in the generated power Pm. This phenomenon will be discussed in detail while citing the following second configuration example and third configuration example. 
     (Second Configuration Example) 
       FIG. 10  is a schematic diagram showing a second configuration example of a power generation device. The power generation device  10  of the second configuration example is substantially analogous in configuration to that of the first configuration example, but has the feature that the upper electrode  15  that was furnished on the top surface side of the dielectric body  11  has been removed. Specifically, the power generation device  10  of the second configuration example can be considered to have a configuration in which the dielectric body  11  is unconnected to any electrode. Viewed another way, the power generation device  10  of the second configuration example can be considered to have a configuration in which the entire movable section, including the dielectric body  11 , is in an electrically floating state (a state of being unconnected to any potential point). The entire movable section, including the dielectric body  11 , may be retained by, for example, an insulator (an insulating spring or the like). 
     The power generation device  10  of the second configuration example differs from the preceding first configuration example in that, in the second state in which the dielectric body  11  and the electret  12  are brought close together (at bottom in  FIG. 10 ), it assumes a state of high electrostatic potential energy (an unstable state), and therefore the generating capacity drops in comparison with the first configuration example. However, the power generation device  10  of the second configuration example does not require wiring to be connected to the vibrating dielectric body  11 , and therefore it is more advantageous than the first configuration example in terms of the ease of device fabrication and the stability of the power generation operation. 
     (Third Configuration Example) 
       FIG. 11  is a schematic diagram showing a third configuration example of a power generation device. The power generation device  10  of the third configuration example is substantially analogous in configuration to that of the first configuration example, but has the feature that a metal body  18  in an electrically floating state is formed on the top surface side of the dielectric body  11 . The metal body  18  is a member made of metal, and differs from the upper electrode  15  which was intended to be connected to some potential point (grounding terminal), in that it is in an electrically floating state. Consequently, the power generation device  10  of the third configuration example has in common with the preceding second configuration example a configuration whereby the entire moveable section that includes the dielectric body  11  is in an electrically floating state. The metal body  18  may be plate-shaped or film shaped. 
     In the power generation device  10  of the third configuration example, in a second state in which the dielectric body  11  and the electret  12  are brought close together (at bottom in  FIG. 11 ), negative polarized charges become localized at the top surface of the dielectric body  11  due to internal polarization of the dielectric body  11 . Consequently, at the bottom face of the metal body  18  (the interface with the dielectric body  11 ), intrametallic positive charges are induced through attraction to the aforementioned negative polarized charges. 
     The power generation device  10  of the third configuration example differs from the previously discussed first configuration example in that, because the metal body  18  is not connected to a grounding terminal, positive charges cannot be attracted to the metal body  18  from the grounding terminal. However, because multiple free electrons (in  FIG. 11 , depicted as symbols having white circles with minus signs) are present in the metal body  18 , these free electrons move away from the interface of the metal body  18  and the dielectric body  11 , whereby an effect analogous to that when positive charges are attracted the metal body  18  from the grounding terminal is obtained. 
     Due to the aforementioned effect, it is possible with the power generation device  10  of the third configuration example to obtain higher generating capacity than with the second configuration example from which the upper electrode  15  has been completely eliminated. In the power generation device  10  of the third configuration example, however, the aforementioned effect is hindered by bias (potential difference) of the charges arising in the interior of the metal body  18 . Consequently, in the power generation device  10  of the third configuration example, the generating capacity declines in comparison to the first configuration example in which the upper electrode  15  is connected to a grounding terminal. However, in the same way as the second configuration example discussed previously, in the power generation device  10  of the third configuration example, there is no need to connect wiring to the vibrating dielectric body  11 , and it is therefore more advantageous than the first configuration example in terms of the ease of device fabrication and the stability of the power generation operation. 
     In this way, viewed in relation to generating capacity, the first configuration example is superior to the third configuration example, which is in turn superior to the second configuration. Viewed in terms of the ease of device fabrication and the stability of the power generation operation, the second configuration example is equal to the third configuration example, and these are superior to the first configuration example. Consequently, with regard to the configuration of the power generation device  10 , no one configuration can be considered to be always the best, and it is preferable to adopt any of the first to third configurations according to a particular application or required characteristics. 
     (Packaging) 
       FIG. 12  is a schematic diagram showing a first packaging example of a power generation device (a cross sectional view taken from a lateral direction). The power generation device  20  of the first packaging example has a substrate  21 , a lower electrode  22 , an electret  23 , a dielectric body  24  (in which a dielectric body, electrodes, and a weight are unified), a package  25 , an adhesive  26 , and a wire  27 . In the description below, it makes no difference whether there is an upper electrode connected to the dielectric body  24 . 
     The lower electrode  22  is formed on the top surface of the substrate  21 . The electret  23  is formed so as to cover the lower electrode  22 . One terminal of the lower electrode  22  is exposed from the electret  23 , extends out to a terminal section of the substrate  21 , and is connected to the wire  27  in the terminal section. The wire  27  is connected to a grounding terminal via a resistor, not shown. The package  25  is a cover member (a hollow cylinder, a hollow post, a half sphere, or the like) furnished at one surface with an opening, and the opening is bonded by the adhesive  26  to the substrate  21 , with the electret  23  and the dielectric body  24  housed in the interior thereof. The package  25  may be made of a plastic such as a resin or acrylic. 
     In the power generation device  20  of the first packaging example, the dielectric body  24  is unsupported in any way, but rather is housed displaceably (moveably up and down) along the inner wall of the package  25 . When the power generation device  20  is in a stationary state, the dielectric body  24  is close to the electret  23  due to electrostatic attraction (this corresponds to the second state at bottom in  FIG. 1 ). Consequently, by imparting kinetic energy (vibration) from the outside in order to move the dielectric body  24  away from the electret  23 , it is possible to convert kinetic energy to electrical energy. 
       FIG. 13  is a schematic diagram showing a second packaging example of a power generation device. The configuration of the second packaging example is substantially analogous to that of the first packaging example, but has the feature of having an elastic member  31  that pendently supports the dielectric body  24  in the interior of the package  25 . A coil spring or an accordion spring (meander configuration) may be employed as the elastic member  31 . By adopting this kind of configuration, the kinetic energy for moving the dielectric body  24  away from the electret  23  can be dragged down, thereby making it possible to perform power generation with smaller vibration. It is also possible to prevent contact of roof surface of the package  25  and the dielectric body  24 . 
       FIG. 14  is a schematic diagram showing a third packaging example of a power generation device. The configuration of the third packaging example is substantially analogous to that of the first packaging example, but has the feature of having elastic members  32  that support both terminals of the dielectric body  24  in the interior of the package  25 . Coil springs or accordion springs (meander configuration) may be employed as the elastic members  32 . By adopting this kind of configuration, it is possible to prevent contact of the dielectric body  24  and the inside surfaces of the package  25 , without hampering up-and-down motion of the dielectric body  24 . 
       FIG. 15  is a schematic diagram showing a fourth packaging example of a power generation device. The configuration of the fourth packaging example is substantially analogous to that of the first packaging example, but has the feature of having an elastic member  33  whereby the dielectric body  24  is repulsed from the roof surface of the package  25 . A plate spring may be used as the elastic member  33 . By adopting this kind of configuration, it is possible to prevent contact of the dielectric body  24  and the top surfaces of the package  25 , without hampering up-and-down motion of the dielectric body  24 . 
       FIG. 16  is a schematic diagram showing a fifth packaging example of a power generation device (a cross sectional view in a direction from the top). The configuration of the fifth packaging example is substantially analogous to that of the first packaging example, but has the feature of having elastic members  34  that support up-and-down motion of the dielectric body  24  while minimizing horizontal movement thereof in the interior of the package  25 . In the vibration device  20  of the fifth packaging example, the dielectric body  24  and the package  25  are formed to a cross section of rectangular shape in plan view. As the elastic members  34 , it is possible to employ a combination of four plate springs (in a spring arrangement shaped as an equilateral cross with four arms bent at right angles) providing cantilever support of the four side surfaces of the dielectric body  24  from respectively orthogonal support surfaces (inside surfaces of the package  25 ). By adopting this kind of configuration, it is possible to prevent contact of the dielectric body  24  and the top surfaces of the package  25 , without hampering up-and-down motion of the dielectric body  24 . 
       FIG. 17  is a schematic diagram showing a sixth packaging example of a power generation device. The configuration of the sixth packaging example is substantially analogous to that of the first packaging example, but has the feature of having magnets  35   a  and  35   b  (a magnetic force spring) for repulsing the dielectric body  24  and the package  25  from one another. By adopting this kind of configuration, it is possible to prevent contact of the dielectric body  24  and the top surfaces of the package  25 , without hampering up-and-down motion of the dielectric body  24 . 
       FIG. 18  is a schematic diagram showing a seventh packaging example of a power generation device. The configuration of the seventh packaging example is substantially analogous to that of the first packaging example, but has the feature of having magnets  36   a  and  36   b  (a magnetic force spring) for repulsing the dielectric body  24  and the electret  23  from one another. By adopting this kind of configuration, the kinetic energy for moving the dielectric body  24  away from the electret  23  can be dragged down, thereby making it possible to perform power generation with smaller vibration. It is also possible to prevent contact of electret  23  and the dielectric body  24 . 
       FIG. 19  is a schematic diagram showing an eighth packaging example of a power generation device. The configuration of the eighth packaging example is substantially analogous to that of the first packaging example, but has the feature of having a stopper  37  protruding from the surface of the electret  23 . The stopper  37  may be furnished on the surface of the dielectric body  24  as well. By adopting this kind of configuration, the kinetic energy for moving the dielectric body  24  away from the electret  23  can be dragged down, thereby making it possible to perform power generation with smaller vibration. It is also possible to prevent contact of electret  23  and the dielectric body  24 . 
     Any combination of the configurations described individually in the aforementioned first to eighth packaging examples is possible as well. For a configuration furnished with a spring or springs, it is preferable to design the spring constant such that the inherent resonance frequency of the spring matches the frequency of the vibration imparted to the power generation device  20 . On the other hand, in a case in which the frequency of the vibration imparted to the power generation device  20  is unstable, it is preferable to adopt a configuration not furnished with a spring, or to employ a soft spring (a spring with a low spring constant). 
     (Dielectric Body Guide Configuration) 
       FIG. 20  is a schematic diagram showing a first guide example of a dielectric body (a top view, and a cross sectional view from a lateral direction). In the power generation device  20  of the first guide example, the dielectric body  24  and the package  25  are formed such that their respective outside edges and inside edges are circular, when the power generation device  20  is seen in plan view. The dielectric body  24  is housed in an arrangement in which ball members  38  (steel spheres) are wedged between it and the inner wall of the package  25 . The ball members  38  are respectively furnished at four equidistant positions along the outer rim of the dielectric body  24  (the inner rim of the package  25 ) when the power generation device  20  is seen in plan view. Rail slots  24   a  are respectively formed in the up-and-down direction in the dielectric body  24 , at the positions of abutment with the ball members  38 . Meanwhile, recessed sphere-receiving sections  25   a  are respectively formed on the inner wall of the package  25 , at the positions of abutment with the ball members  38 . By adopting this kind of configuration, it is possible to prevent contact of the dielectric body  24  and the inside surfaces of the package  25 , without hampering up-and-down motion of the dielectric body  24 . 
       FIG. 21  is a schematic diagram showing a second guide example of a dielectric body (a top view, and a cross sectional view from a lateral direction). The power generation device  20  of the second guide example is analogous to the first guide example in that the dielectric body  24  and the package  25  are formed such that their respective outside edges and inside edges are circular, when the power generation device  20  is seen in plan view. The dielectric body  24  is housed by an arrangement in which rail members  39  abut the inner wall of the package  25 . The rail members  39  are respectively furnished at four equidistant positions along the outer rim of the dielectric body  24  (the inner rim of the package  25 ) when the power generation device  20  is seen in plan view. Rail slots  25   b  are respectively formed in the up-and-down direction on the wall of the package  25 , at the positions of abutment with the rail members  39 . By adopting this kind of configuration, it is possible to prevent contact of the dielectric body  24  and the inside surfaces of the package  25 , without hampering up-and-down motion of the dielectric body  24 . The rail members  39  may be integrally formed by machining of the dielectric body  24 , or formed separately from a material different from the dielectric body  24  and having good slide properties (a fluoroplastic or the like). 
     (Ground Ring) 
     Next, a ground ring that may be of service when a configuration not furnished with an electrode on the dielectric body side (see the second configuration example of  FIG. 10 ) is adopted will be described.  FIG. 22  is a schematic diagram showing a first implementation example of a ground ring (a cross sectional view from a lateral direction). The arrows in the drawing show lines of electric force. The power generation device  40  of the first implementation example has a dielectric body  41 , an electret  42 , a lower electrode  43 , a resistor  44 , and a ground ring  45 . The ground ring  45  is a conductive member (for example, aluminum) formed so as to encircle the perimeter of the electret  42  and the lower electrode  43 , at a predetermined distance away therefrom. The ground ring  45  is directly connected to a grounding terminal. 
     In the power generation device  40 , as the dielectric body  41  and the electret  42  are brought closer together, negative polarized charges become localized on the top surface of the dielectric body  41  due to internal polarization of the dielectric body  41 . According to the power generation device  40  of the first implementation example, lines of electric force can escape from the negative charges of the dielectric body  41  towards the positive charges of the ground ring  45 , and therefore it is possible to minimize repulsion between the negative charges of the dielectric body  41  and the negative charges of the electret  42 , and hence it is possible to increase generation efficiency. 
       FIG. 23  is a schematic diagram showing a second implementation example of a ground ring (a cross sectional view from a lateral direction). The arrows in  FIG. 23  show lines of electric force. As shown in the drawing, it is not essential for the ground ring  45  to be formed so as to encircle the perimeter of the electret  42  and the lower electrode  43 ; the ground ring  45  and the electret  42  may instead be disposed alternately in mutually adjacent fashion. According to this sort of configuration, when polarization in a horizontal direction arises in the interior of the dielectric body  41 , lines of electric force can escape from the negative charges of the dielectric body  41  towards the positive charges of the ground ring  45 , and therefore it is possible to minimize repulsion between the negative charges of the dielectric body  45  and the negative charges of the electret  42 , and hence it is possible to increase generation efficiency. 
     (Shape of Dielectric Body and Lower Electrode) 
       FIG. 24  is a schematic diagram showing an example of a combination of dielectric body shape and lower electrode shape. The power generation device  50  of the present example has a dielectric body  51 , an electret  52 , a lower electrode  53 , and a substrate  54 . 
     The dielectric body  51  may have a configuration in which the bottom surface that faces the electret  52  has been planarized (see the left side in  FIG. 24 ), or a configuration in which the bottom surface has been patterned (see the right side in  FIG. 24 ). With the former configuration, the gap distance of the dielectric body  51  and the electret  52  can be made uniform. With the latter configuration, lines of electric force easily concentrate at sites that have been sharpened through patterning, and improved generation efficiency through optimization of patterning can be anticipated. 
     The lower electrode  53  may be formed to a planar shape, without patterning being performed ( FIG. 25 ); or patterning may be carried out to form a pectinate shape ( FIG. 26 ) or spiral shape ( FIG. 27 ). However, from the standpoint of generation efficiency, it is preferable to adopt the former configuration. 
     The combination of the shape of the dielectric body  51  (patterned or non-patterned) and the shape of the lower electrode (patterned or non-patterned) is arbitrary. 
     (Triaxial Capability) 
       FIG. 28  is a schematic diagram showing a first structure for realizing triaxial capability. The power generation device  60  of the first structure has a dielectric body  61 , electrets  62 , and a lower electrode  63 . A plurality of protruding portions  61   a  are formed on the dielectric body  61 , and a plurality of recessed portions  62   a  adapted to mate with the protruding portions  61   a  are formed at predetermined intervals on the electrets  62 . While not depicted in  FIG. 28 , the power generation device  60  has an analogous structure in the depthwise direction of the page as well. By adopting such a structure, the gap distance of the dielectric body  61  and the electrets  62  may be made to vary in cases in which the dielectric body  61  vibrates in the up-and-down direction of the page, in cases in which the dielectric body  61  vibrates in the left-and-right direction of the page, and in cases in which the dielectric body  61  vibrates in the depthwise direction of the page, whereby it becomes possible to generate power efficiently. 
     In the power generation device  60  of the first structure, the electrets  62  are respectively disposed to either side of the dielectric body  61 . Through such a configuration, it is possible to further increase generation efficiency. While not depicted in  FIG. 28 , through a configuration in which the dielectric bodies  61  are stacked in multiple layers with the electrets  62  disposed to either side of each, further improvement in generation efficiency can be anticipated. It is of course possible to implement such a multilayer structure in the basic structure discussed previously (in  FIG. 1 , etc.), that lacks the protruding portions  61   a  and the recessed portions  62   a.    
       FIG. 29  is a schematic diagram showing a second structure for realizing triaxial capability. In the power generation device  70  of the second structure, an electret  72  is formed on the inner wall of a hermetic container, and particles of a dielectric body  71  are sealed inside the hermetic container. A lower electrode  73  is formed so as to encircle the outside peripheral side of the electret  72 , and is connected to a grounding terminal via a resistor  74 . By adopting such a structure, in cases in which vibration in any direction is imparted to the power generation device  70 , the gap distance of the dielectric body  71  and the electret  72  will vary, and it is therefore possible to generate power efficiently. 
       FIG. 30  is a schematic diagram showing a third structure for realizing triaxial capability. In the power generation device  80  of the third structure, an electret  82  is formed on the inner wall of a hermetic spherical body, and a spherical dielectric body  81  is sealed inside the hermetic spherical body. A lower electrode  83  is formed so as to encircle the outside peripheral side of the electret  82 , and is connected to a grounding terminal via a resistor  84 . By adopting such a structure, in cases in which vibration in any direction is imparted to the power generation device  80 , the gap distance of the dielectric body  81  and the electret  82  will vary, and it is therefore possible to generate power efficiently. 
       FIG. 31  is a schematic diagram showing a fourth structure for realizing triaxial capability. In the power generation device  90  of the fourth structure, a dielectric body  91  is given a spherical shape, and a plurality of electrets  92  are formed so as to encircle the dielectric body  91 . A lower electrode  93  is formed on each of the plurality of electrets  92 , and is connected to a grounding terminal via a resistor  84 . By adopting such a structure, in cases in which vibration in any direction is imparted to the power generation device  90 , the gap distance of the dielectric body  91  and the electret  92  will vary, and it is therefore possible to generate power efficiently. 
     (Relative Permittivity and Generating Capacity of Dielectric Body) 
       FIG. 32  is a graph showing the relationship between generating capacity and relative permittivity of a dielectric body. The horizontal axis of  FIG. 32  shows the relative permittivity Er of a dielectric body, and the vertical axis of  FIG. 32  shows the generating capacity P (%) (normalized using the generating capacity in a case in which the relative permittivity ∈r is infinite). The present graph shows computation results obtained by the previously cited Equations (3) to (9), under hypothetical conditions of an electret relative permittivity of 2, an electret film thickness of 5 μm, a dielectric body vibration amplitude of 20 μm, and a gap layer (an air layer) thickness (gap distance) of 1 μm, when the dielectric body and the electret are closest. However, the generated power outputs in the drawing have been normalized using a generating capacity of 100% in a case in which the relative permittivity ∈r of the dielectric body is infinite. The circle symbols, square symbols, and diamond symbols in  FIG. 32  respectively show computation results when the thickness of the dielectric body was 0.01 mm, 0.1 mm, and 1 mm. 
     As will be appreciated from  FIG. 32 , the computation results vary according to the thickness of the dielectric body. When the thickness of the dielectric body is 0.01 mm, maximum generating capacity of 90% is obtained when the relative permittivity ∈r is approximately 30. On the other hand, when the thickness of the dielectric body is 1 mm, relative permittivity ∈r of approximately 3,000 is necessary to obtain maximum generating capacity of 90%. Consequently, in order to increase the generating capacity, it is preferable for the dielectric body to be as thin as possible. 
     However, when the dielectric body is too thin, there is a risk that charges within the electret will be discharged upon contact with the electret. Consequently, from the standpoint of both increasing the generating capacity and preventing discharge, it would conceivably be appropriate to use a dielectric body having thickness of 0.1 mm and relative permittivity Er of 300 or above, for example. However, the values for thickness and relative permittivity given here are merely one example, and other values are acceptable. Considered from an overall standpoint of charge retention characteristics, generating capacity, device size, production costs, and the like, as a design range for practical purposes, the dielectric body may suitably employ a material having a thickness of 0.01 to 1.0 mm (preferably 0.01 to 0.1 mm), and from which maximum generating capacity of 80% or more can be obtained. 
     As the method for fabricating the dielectric body, it is possible to adopt any of various methods, depending on the thickness of the dielectric body. For example, dielectric bodies of a thickness of one micron or less to several microns can be fabricated by a sputtering process or electron beam deposition process. Dielectric bodies of a thickness of one micron or less to several tens of microns can be fabricated by a hydrothermal synthesis process including a sol-gel process, accompanied by spin coating and firing. Dielectric bodies of a thickness of several tens of microns or more can be fabricated by firing of a powder, pressure molding or another molding process, and thickness adjustment by slicing, cutting, polishing, or the like. 
     (Material of Dielectric Body) 
     The most desirable material is barium titanate (BaTiO 3 , BTO). The relative permittivity at service temperatures (expected to be 0 to 100° C.) is approximately 1,000, which meets the aforementioned condition. The material is relatively cheap, and has minimal environmental impact by virtue of being lead-free, and is therefore advantageous for commercial purposes as well. In environments of 120° C. and above, the relative permittivity drops. Moreover, the relative permittivity drops in cases in which the operating frequency is 100 kHz or above. However, as the expected operating frequency is from 1 to several hundred Hz, the aforementioned characteristics are not a drawback for the present device. The only problem is that, by virtue of being a ferroelectric body, there is hysteresis in the dielectric characteristics. 
     The next most desirable material is lead zirconate titanate (PZT). Because of the extremely high relative permittivity (2,000 to 3,000), the material is effective in cases in which it is desired to make the generating capacity as great as possible. However, drawbacks are relatively high cost, and high environmental impact by virtue of containing lead. Moreover, like barium titanate, it is a ferroelectric body, and it is necessary to be aware of hysteresis in the characteristics. 
     Further, it is desirable to add to alkaline earth metals such as potassium (K), calcium (Ca), strontium (Sr) or the like, or rare earth metals such as yttrium (Yt), neodymium (Nd), or the like, to barium titanate. Typically, the addition of these produces a drop in the relative permittivity of barium titanate, and effects such as the following may be anticipated. 
     A first effect is to depress the Curie temperature. A ferroelectric body has a unique temperature, known as the Curie temperature, in proximity to which temperature the maximum permittivity is observed. Consequently, by setting the Curie temperature of a dielectric body to closely approximate the service temperature of the power generation device, the permittivity at operating temperature can be increased to a level greater than that of pure barium titanate. However, permittivity varies considerably with temperature variations, and destabilized generation efficiency is a drawback. 
     A second effect is that as the added amount is increased, the nature of the material varies from a ferroelectric body to a paraelectric body. A paraelectric body exhibits minimal variation of permittivity due to temperature variations, and lacks hysteresis, and therefore stable power generation can be anticipated. Due to permittivity that is high among paraelectric bodies, a modicum of generating capacity can be assured. 
     Next, strontium titanate may be cited. Strontium titanate is the result of substituting strontium for barium in barium titanate. The material is a ferroelectric body, with permittivity of approximately 300, and has the advantage of meeting the aforementioned condition. However, the permittivity is low in comparison with barium titanate. Another drawback is that strontium is a rare metal, and is costly. 
     Next, as examples of lead-free piezoelectric high-k dielectric bodies, there may be cited lanthanum iron oxide (LaFeO 3 ), potassium niobate (KNbO 3 ), lanthanum titanate (LaTiO 3 ), magnesium silicate (MgSiO 3 ), and barium titanate zirconate (Ba(Ti, Zr)O 3 ). 
     A characteristic of lanthanum iron oxide (LaFeO 3 ) is that the relative permittivity of a monocrystal layer is 1,000 or above, with the relative permittivity reaching several tens of thousands or more at high temperatures. The addition of a trace amount of lanthanum iron oxide (LaFeO 3 ) to potassium niobate (KNbO 3 ) has the effect of pulling up the permittivity. For example, addition of 0.2% lanthanum iron oxide (LaFeO 3 ) boosts the relative permittivity of potassium niobate (KNbO 3 ) at room temperature from 500 to 1,250. 
     The crystalline structure of potassium niobate (KNbO 3 ) is a perovskite structure. At −10° C. or below it is rhombohedral, but at normal temperature it becomes orthorhombic, at 225 to 435° C. it becomes tetragonal, and at 435° C. (the Curie temperature) and above it becomes cubic. As advantages of this there may be cited: (1) the material is a ferroelectric body and shows high piezoelectricity; (2) the material is a ferroelectric body having a bismuth layer structure, as well as being a lead-free piezoelectric ceramic; (3) the material is easily polarized (polarization at 5 to 6 kV/mm or less at 150° C. is possible); (4) the material has relative permittivity (800 to 1,000) comparable to that of lead zirconate titanate (PZT); and (5) the material has a relatively flat relative permittivity curve from room temperature up to about 200° C. Conversely, as drawbacks there may be cited: (1) difficulty in sintering, by virtue of being a ceramic; (2) remaining unreacted potassium oxide adversely affects moisture resistance due to its deliquescent nature; and (3) the principal component niobium is a rare metal, and is costly. 
     The Curie temperature of barium titanate zirconate (Ba(Ti, Zr)O 3 ) can be brought to below 120° C. Where Ti:Zr=8:2, the Curie temperature is 40° C., and relative permittivity is 4,000. 
     Next, as polymer-based ferroelectric bodies, there may be cited polylactic acid and polyureic acid. Polymer-based ferroelectric bodies are pliable and have relatively high permittivity, and therefore applications such as protective films for contact surfaces and the like may be anticipated. The relative permittivity of polylactic acid is approximately 22. Polyureic acid is an organic piezoelectric material with relative permittivity of 3.6 to 11.8. 
     Next, relaxor ferroelectric bodies may be cited. As characteristics common to relaxor ferroelectric bodies, there may be cited: (1) large piezoelectric effects; (2) extremely large permittivity and low temperature variation thereof; (3) anomalously large relative permittivity reaching into the several tens of thousands; (4) having a broad permittivity peak and frequency distribution; and (5) having spontaneous polarization characteristics that show slow variation up to high temperatures. 
     Most relaxor ferroelectric bodies have a compound structure of the complex perovskite type (A(B′,B″)O 3 ) in which divalent ions are present at the A sites, and two different types of ions having on average tetravalent charge are present at the B sites. These may be broadly classified into a type containing ions of +2 valence and +5 valence in a 1:2 ratio (A(B′ 1/3 B″ 2/3 )O 3 ), and types containing ions of +3 valence and +5 valence or ions of +2 valence and +6 valence in a 1:1 ratio (A(B′ 1/2 B″ 1/2 )O 3 ). Most relaxor ferroelectric bodies form mixed crystals with the ferroelectric body PbTiO 3 , and give rise to interesting phenomena. 
     As examples of relaxor ferroelectric bodies there may be cited (1−x)Pb(Mg 1/3 Nb 2/3 )O 3 .xPbTiO 3 , (1−x)Pb(Zn 1/3 Nb 2/3 )O 3 .xPbTiO 3 , and (1−x)Pb(In 1/2 Nb 1/2 )O 3 .xPbTiO 3 . 
     As characteristics of solid solutions (PZN/xPT) of Pb(Zn 1/3 Nb 2/3 )O 3  and PbTiO 3  there may be cited: (1) they are ferroelectric bodies and piezoelectric bodies; and (2) in the case of PZN/9PT, the piezoelectric constant d 33  is approximately 2,500 pC/N. The compositional ratio of PZN and PT is in a range termed the morphotropic phase boundary (commonly known as the MPB) that exactly divides trigonal from tetragonal, and various experimental techniques are being employed to search for the cause of the high piezoelectric effect, from the standpoint of the drop in symmetry observed at the MPB. 
     As a characteristic of (Ba, La) (Ti, Cr)O 3 , it may be cited that the material is a lead-free relaxor ferroelectric body. The correct composition is (Ba 1-x La x )(Ti 1-x Cr x )O 3  (where 0≦x&lt;1). When x=0.035, relative permittivity is 2,000, and stable permittivity is shown at close to room temperature. 
     (Applications) 
     By implementing the aforementioned power generation devices as a power supply for sensors of various kinds or wireless devices (for example, ZigBee 300 MHz band-specific low-power wireless devices), there can be built a ubiquitous environment of wireless sensors and a wireless sensor network. Specifically, because the need for power supply wiring for the various sensors and the wireless devices is obviated, it is possible for individual devices to be disposed in dispersed fashion, and to realize information linkages within the network. 
     Besides application in tire pressure monitoring systems (TPMS), some of which are already in use, as service scenarios for ubiquitous environments employing the aforementioned power generation devices, there may be cited, for example, the medical and health fields (health management and safety confirmation), monitoring of structures (monitoring for wire disconnects or loose bolts), monitoring plants (monitoring for equipment faults), and logistics management (monitoring logistics and product quality). Moreover, because motors and other such electrical machinery vibrate at the power supply frequency (50 Hz or 60 Hz), where the resonance condition of a spring system incorporated into a power generation device is matched to the aforementioned power supply frequency, even larger generating capacity can be anticipated, and therefore use of the generated power output as a power supply of a data processing device or the like is conceivable. Further, applications in which the aforementioned power generation devices are attached to the body to generate power, or applications in which the aforementioned power generation devices are installed in a mobile device such as a mobile telephone, may be envisioned as well. 
     EFFECT OF THE INVENTION 
     According to the present invention, power is generated from Z-axis component vibration of a vibrator, thereby obviating the need for fine patterning of the electret and the electrodes; and because the dielectric body and the electret do not discharge even if in contact, there is no need to avoid contact of the dielectric body and the electret as well, whereby it is possible to offer a compact, high-output power generation device, and hence possible to relieve the user of any concern about battery life. 
     INDUSTRIAL APPLICABILITY 
     The power generation device according to the present invention is a technique suitably applicable as a power supply employed by various types of sensors and wireless devices (wireless sensor networks, health monitoring, and the like). 
     Additional Alternative Examples 
     The configuration of the present invention is not limited to the aforementioned embodiments and alternative examples, and various additional modifications are possible without departing from the spirit of the invention. Specifically, the aforementioned embodiments are in all respects merely exemplary, and should not be construed as limiting, the technical scope of the present invention being shown by the scope of the claims rather than the description of the aforementioned embodiments, and being understood to include all modifications equivalent in meaning to and falling within the scope of the claims. 
     LIST OF REFERENCE NUMERALS 
     
         
           10  Power generation device 
           11  Dielectric body 
           12  Electret 
           13  Lower electrode 
           14  Resistor 
           15  Upper electrode 
           16  Substrate 
           17  Gap layer 
           18  Metal body 
           20  Power generation device 
           21  Substrate 
           22  Lower electrode 
           23  Electret 
           24  Dielectric body (unified dielectric body, electrodes, and weight) 
           24   a  Rail slots 
           25  Package 
           25   a  Sphere-receiving sections 
           25   b  Rail slots 
           26  Adhesive 
           27  Wire 
           31 - 34  Elastic members 
           35   a ,  35   b ,  36   a ,  36   b  Magnets 
           37  Stopper 
           38  Ball member 
           39  Rail member 
           40  Power generation device 
           41  Dielectric body 
           42  Electret 
           43  Lower electrode 
           44  Resistor 
           45  Ground ring 
           50  Power generation device 
           51  Dielectric body 
           52  Electret 
           43  Lower electrode 
           54  Substrate 
           60  Power generation device 
           61  Dielectric body 
           61   a  Protruding portions 
           62  Electret 
           62   a  Recessed portions 
           63  Lower electrode 
           70 ,  80 ,  90  Power generation device 
           71 ,  81 ,  91  Dielectric body 
           72 ,  72 ,  92  Electret 
           73 ,  83 ,  93  Lower electrode 
           74 ,  84 ,  94  Resistor 
         X 1  Dielectric body 
         X 2  Aluminum plate 
         X 3  Electromagnetic type vibration exciter 
         X 4  Test sample 
         X 41  Electret 
         X 42  Lower electrode 
         X 43  Substrate 
         X 5  Aluminum plate 
         X 6  Three-axis stage 
         X 7  Base 
         X 8  Coaxial cable 
         X 9  Coaxial cable 
         X 10  Shield case 
         X 10   a  First connector 
         X 10   b  Second connector 
         X 11  Coaxial cable 
         X 12  Low-pass filter 
         X 13  Coaxial cable 
         X 14  Oscilloscope 
         Rv, R Load resistance 
         Y Corona discharge device 
         Y 1  Grid 
         Y 2  Discharge electrode needle 
         Y 3  Grid power supply 
         Y 4  DC high voltage power supply