Abstract: A capacitive electro-mechanical transducer includes a plurality of cavities, a communicating portion for connecting the cavities to each other, and two electrodes sandwiching each of the cavities. The cavities are sealed from outside, and at least a portion of the communicating portion is closed to interrupt the communication between the cavities through the communicating portion.

Abstract: A MEMS piezoresistive resonator (8, 78) is driven at a higher order eigenmode (32) than the fundamental eigenmode (31). The route of flow of a sense current (22) is arranged in relation to a characteristic of the higher order eigenmode (32), for example by being at a point of maximum displacement (50) or at a point of maximum rate of change with respect to distance (x) of displacement of the higher order eigenmode (32). The route of flow of the sense current (22) may be arranged by fabricating the MEMS piezoresistive resonator (8, 78) with a trench (15) formed between two beams (11, 12) of the MEMS piezoresistive resonator (8, 78), the end of the trench being located at the above mentioned position.

Abstract: A bimorphic structure responsive to changes in an environmental condition, sensor structures incorporating one or more of such bimorphic structures, and a method of forming such bimorphic structures. The sensor structure has an electrically-conductive first contact on a substrate, and a bimorph beam anchored to the substrate so that a portion thereof is suspended above the first contact. The bimorph beam has a multilayer structure that includes first and second layers, with the second layer between the first layer and the substrate. A portion of the first layer projects through an opening in the second layer toward the first contact so as to define an electrically-conductive second contact located on the beam so as to be spaced apart and aligned with the first contact for contact with the first contact when the beam sufficiently deflects toward the substrate.

Abstract: An electrostatic comb drive actuator for a MEMS device includes a flexure spring assembly and first and second comb drive assemblies, each coupled to the flexure spring assembly on opposing sides thereof. Each of the first and second comb assemblies includes fixed comb drive fingers and moveable comb drive fingers coupled to the flexure spring assembly and extending towards the fixed comb drive fingers. The comb drive fingers are divided equally between the first and second comb drive assemblies and placed symmetrically about a symmetry axis of the flexure spring assembly. When electrically energized, the moveable comb drive fingers of both the first and second comb drive assemblies simultaneously move towards the fixed comb drive fingers of the first and second comb drive assemblies.

Abstract: The invention concerns a novel magnetic actuator mechanism suitable for use on untethered microrobots. It relies on the interaction of magnetic bodies in an external magnetic field. By an oscillating field, the bodies are driven to oscillatory motion, and the energy stored in the oscillation is harnessed. The untethered wireless microactuator according to the invention comprises a mechanical system with at least two magnetic bodies resiliently connected to one another, wherein the mechanical system is capable of being oscillated, in particular driven to resonance, by an oscillating external magnetic field. The actuation system according to the invention comprises such a microrobot as well as a magnetic field generator with adjustable field direction and oscillation frequency. The actuation method comprises exciting two or more magnetic bodies with an oscillating magnetic field such that they perform mechanical oscillations, and harnessing this energy for propulsion of the device or to fulfill other tasks.

Abstract: When the initial displacement greatly varies among cells in an element, there is a need to reduce a bias voltage to be applied between electrodes. This decreases the sensitivity. An electromechanical transducer of the present invention includes an element having a plurality of cells. Each of the cells includes a first electrode and a second electrode that are provided with a cavity being disposed therebetween. A groove is provided at a position at a predetermined distance from the cavity of the cell on the outermost periphery of the element.

Abstract: Asymmetric membrane capacitive micromachined ultrasonic transducer (“cMUT”) devices and fabrication methods are provided. In a preferred embodiment, a cMUT device according to the present invention generally comprises a membrane having asymmetric properties. The membrane can have a varied width across its length so that its ends have different widths. The asymmetric membrane can have varied flex characteristics due to its varied width dimensions. In another preferred embodiment, a cMUT device according to the present invention generally comprises an electrode element having asymmetric properties. The electrode element can have a varied width across its length so that its ends have different widths. The asymmetric electrode element can have different reception and transmission characteristics due to its varied width dimensions. In another preferred embodiment, a mass load positioned along the membrane can alter the mass distribution of the membrane. Other embodiments are also claimed and described.

Abstract: When an actuator is driven, a stationary element continuously generates a pressing force for spreading in a radial direction such that the stationary element is relatively retracted into movable elements positioned at both ends of the stationary element. As a result, a distance between the movable elements adjacent to each other is reduced, and a contracting operation is performed. When the actuator is not driven, only a relatively low frictional force is generated between the moving elements and the stationary element. Hence, the movable elements and the stationary element can change relative position by small external force.

Abstract: An acoustic transducer has a first transducer which transmits an acoustic primary wave having two frequency components, and a second transducer which, in order to receive a reflected wave of an acoustic secondary wave generated with propagation of the acoustic primary wave, is disposed so that a region for receiving the reflected wave is superimposed on the first transducer as seen along the direction of transmission of the acoustic primary wave.

Abstract: A micro-image acquisition and transmission system is provided. In a preferred embodiment, the system is comprised of an image acquisition chip comprising an electronic imager, control electronics and a micro powered rotary stage comprising a transceiver array that acts as a hub to optically link a group of distributed image acquisition chips. A preferred embodiment is further comprised of a transceiver array chip comprising one or more micro-powered rotary stages having a transceiver array assembly disposed thereon. The micro-powered rotary stage is supported by a micro-brush bearing.

Abstract: A magnetostrictive actuator comprises an assembly of at least two GMM rods (8, 9) spaced apart from each other on the same longitudinal axis, each rod being surrounded by a respective energising electromagnetic coil (10,11) 5 and being mounted between respective biasing permanent magnets (12, 13, 14), the assembly being mounted between mechanical pre-stressing means (20, 21) and a foot (3) adapted to couple the forces produced by the actuator into a surface.

Abstract: Implementations of a capacitive micromachined ultra-sonic transducer (CMUT) include a feedback component connected in series with the CMUT. The feedback component applies a feedback on a voltage applied on the CMUT for affecting the voltage applied on the CMUT as a capacitance of the CMUT changes during actuation of the CMUT.

Abstract: An electrostatic actuator comprising: first and second comb arrays of electrodes arranged on a base, the electrodes of the first and second comb arrays being interleaved; a third comb array of electrodes spring mounted over the first and second comb arrays, the electrodes of the third comb array being aligned with the electrodes of the second comb array; and, means for applying a first voltage to the third comb array and a second voltage to the first and second comb arrays to generate an attractive force acting on the third comb array to move the third comb array toward the second comb array; wherein: the electrodes of the third comb array each have a thickness tj and a width a such that a?tf, the electrodes of the second comb array each have a width b such that a?b?10a; the electrodes of the first and second comb arrays are separated by a distance d such that 0.5Z><d?4b; and, the electrodes of the first comb array each have a width c such that 0.5b<c?5b.

Abstract: A flywheel system has an approximately toroidal flywheel rotor having an outer radius, the flywheel rotor positioned around and bound to a hub by stringers, the stringers each of a radius slightly smaller than the outer radius of the flywheel rotor. The hub is suspended from a motor-generator by a flexible shaft or rigid shaft with flexible joint, the flywheel rotor having a mass, substantially all of the mass of the flywheel rotor comprising fibers, the fibers in large part movable relative to each other. The motor-generator is suspended from a damped gimbal, and the flywheel rotor and motor-generator are within a chamber evacuatable to vacuum. An electrostatic motor/generator can also be within the same vacuum as the flywheel.

Abstract: Provided is an ultrasonic probe for simultaneously achieving improvement of both of a generatable sound pressure and a gain. An upper electrode 3 is provided as a separate element from a diaphragm 6, is fixed to a part of the diaphragm through a binding site 8, and thus is arranged between the diaphragm 6 and a lower electrode 2.

Abstract: A micro oscillating element includes a frame and an oscillation section connected to the frame via a torsional joining section. The oscillation section includes a movable functional section, an arm section and a first comb-tooth electrode. The arm section extends from the functional section. The first comb-tooth electrode includes first electrode teeth extending from the arm section in a direction intersecting the arm section. The micro oscillating element further includes a second comb-tooth electrode to cooperate with the first comb-tooth electrode for causing the oscillation section to oscillate about an oscillation axis defined by the torsional joining section. The second comb-tooth, electrode includes second electrode teeth extending from the frame in a direction intersecting the arm section.

Abstract: A drive element is provided having a substrate, a seismic mass, a drive electrode and a counter-electrode, one of the two electrodes being connected to the substrate and the other of the two electrodes being connected to the seismic mass; and the drive electrode and the counter-electrodes being provided for the excitation of motion of the seismic mass in a main direction of motion; and in addition, the drive electrode includes a first and a second partial electrode, which are switchable separately from each other.

Abstract: The present invention relates to volume and/or shape memory systems for which the volume and/or shape can be adjusted by controlling one or more variables such as applied voltage and temperature. In one embodiment, the volume and/or shape memory systems of the present invention are controlled and/or adjusted by way of a temperature mechanism. In another embodiment, the volume and/or shape memory systems of the present invention are controlled and/or adjusted by way of a voltage mechanism. In still another embodiment, the present invention provides a device that contains, in part, a smart volume and/or shape memory material that exhibits high energy densities, and can provide large displacements over broad temperature and/or voltage ranges.

Abstract: Low temperature wafer bonding (temperature of 450° C. or less) is employed to fabricate CMUTs on a wafer that already includes active electrical devices. The resulting structures are CMUT arrays integrated with active electronics by a low-temperature wafer bonding process. The use of a low-temperature process preserves the electronics during CMUT fabrication. With this approach, it is not necessary to make compromises in the CMUT or electronics designs, as is typical of the sacrificial release fabrication approach. Various disadvantages of sacrificial release, such as low process control, poor design flexibility, low reproducibility, and reduced performance are avoided with the present approach. With this approach, a CMUT array can be provided with per-cell electrodes connected to the substrate integrated circuitry. This enables complete flexibility in electronically assigning the CMUT cells to CMUT array elements.

Abstract: The invention encompasses a method for production of electric power from a system of contacts of nanostructured conductive surfaces with a thin water-containing layer, and a hydroelectric generator for carrying out the method. The basis of the invention is a discovery, confirmed by experiments, that the contacts of the conductive surfaces, having nano-dimensional structural and/or parametrical heterogeneities, with the water-containing layer, having a thickness from several nanometers to a fraction of a millimeter, under certain conditions, described in the present disclosure, generate electromotive force in an external electrical load. The invention utilizes new principles for building power systems, which can find further wide application in various areas of science and technology.

Abstract: An electrostatic drive MEMS (Micro Electro Mechanical Systems) element includes a substrate; a fixed electrode disposed on the substrate; a movable electrode arranged to face the fixed electrode in a vertical direction and be movable toward the fixed electrode through an electrostatic force generated between the fixed electrode and the movable electrode; and an insulation film disposed on one of an upper surface of the fixed electrode and a lower surface of the movable electrode and formed of an insulation member containing a conductive fine particle.

Abstract: In an electromechanical transducer which includes a vibration membrane provided with an upper electrode, a substrate provided with a lower electrode, and a support member adapted to support the vibration membrane in such a manner that a gap is formed between the vibration membrane and the substrate with these electrodes being arranged in opposition to each other, it is constructed such that a part of the vibration membrane and a region of the substrate are kept in contact with each other without application of an external force, and a remaining region of the vibration membrane other than its region in which the contact state is kept is able to vibrate.

Abstract: Methods are provided for production of pre-collapsed capacitive micro-machined ultrasonic transducers (cMUTs). Methods disclosed generally include the steps of obtaining a nearly completed traditional cMUT structure prior to etching and sealing the membrane, defining holes through the membrane of the cMUT structure for each electrode ring fixed relative to the top face of the membrane, applying a bias voltage across the membrane and substrate of the cMUT structure so as to collapse the areas of the membrane proximate to the holes to or toward the substrate, fixing and sealing the collapsed areas of the membrane to the substrate by applying an encasing layer, and discontinuing or reducing the bias voltage. CMUT assemblies are provided, including packaged assemblies, integrated assemblies with an integrated circuit/chip (e.g., a beam-steering chip) and a cMUT/lens assembly. Advantageous cMUT-based applications utilizing the disclosed pre-collapsed cMUTs are also provided, e.g.

Abstract: A vibrating element includes: a vibrating body having frequency temperature dependency; and a temperature characteristic correcting part provided on a surface of the vibrating body. The temperature characteristic correcting part has a temperature characteristic of at least one of a Young's modulus and a thermal expansion coefficient and is expressed by a temperature characteristic curve which has at least one of an inflection point and an extremal value. In the vibrating element, a temperature of at least one of the inflection point and the extremal value is within an operating temperature range of the vibrating body.

Abstract: An electrostatic drive having at least three intermediate frames, each two adjacent intermediate frames being connected to one another via at least one intermediate spring whose longitudinal directions lie on a first axis of rotation, and intermediate electrode fingers being situated on frame girders oriented parallel to the first axis of rotation of the intermediate frames, and having an outer frame that surrounds the intermediate frames and that is connected to the outermost intermediate frame via at least one outer spring whose longitudinal direction lies on a second axis of rotation that is oriented non-parallel to the first axis of rotation, and outer electrode fingers being situated on frame girders oriented parallel to the second axis of rotation of the outer frame and of the outermost intermediate frame of the at least three intermediate frames.

Abstract: A micro-electro mechanical device includes a first structure, a second structure offset from the first structure by a gap. The first structure is configured to be electrostatically actuated to deflect relative to second structure. A pulse generator is configured to combine at least two different pulses to electrostatically drive at least one of the first structure and the second structure between an initial position and a final position.

Abstract: A capacitive generator has a generator circuit (G) and a charge priming circuit (P) consisting of variable capacitors (1, 2, 101, 102) all coupled to a mechanical transmission which acts to vary the capacitance of the capacitors and to actuate an array of switches (K). A small residual charge on the priming circuit (P) can thus be amplified and conveyed to the generating circuit (G) where it is used to generate an alternating current between the variable capacitors (1, 2) of the generating circuit. The capacitance of the generating capacitors (1, 2) is varied in antiphase in response to the movement of the transmission. An electrical energy extraction device (8) in circuit with the generator capacitors (1, 2) extracts electrical energy from the circuit in reaction to the alternating current which can then be used to power or recharge a small portable device.

Abstract: A micro movable device suitable for suppressing deterioration of driving characteristics, and a micro movable device array including such a micro movable device are provided. The micro movable device (X1) of the present invention includes a movable portion including a first driving electrode, a second driving electrode for generating electrostatic attraction between the first driving electrode and the second driving electrode, a first conductor portion (22c) electrically connected to the first driving electrode, a second conductor portion (22b) electrically connected to the second driving electrode, and a third conductor portion (21a) which is not electrically connected to the first and the second driving electrodes and which is bonded to the first conductor portion (22c) via an insulating film (23) and bonded to the second conductor portion (22b) via the insulating film (23).

Abstract: A component has a substrate and a compensation layer. A lower face of the substrate is mechanically firmly connected to the compensation layer. The lower face of the substrate and the upper face of the compensation layer have a topography.

Abstract: Cantilever beam electrostatic actuators are disclosed. A cantilever beam electrostatic actuator in accordance with the present invention comprises an actuator beam having a first width at a support anchor point and a second width at a distal end of the actuator, wherein the first width is narrower than the second width. Another actuator in accordance with the present invention comprises an actuator region, having a first width, a beam, having a second width, coupled between an edge of the actuator region and a pivot point, the beam being approximately centered on the actuator region, wherein the second width is narrower than the first width, and at least one auxiliary actuator flap, coupled to the actuator region, the at least one auxiliary actuator flap coupled to the actuator region along the edge of the actuator region, the at least one auxiliary actuator flap being farther away from a centerline of the actuator than the beam.

Abstract: Methods of fabricating a microelectromechanical systems (MEMS) device with spacers between plates and MEMS devices formed by the same are disclosed. In one embodiment, a MEMS device is fabricated by laminating a front substrate and a carrier, each of which has components preformed thereon. The front substrate is provided with stationary electrodes formed thereover. A carrier including movable electrodes formed thereover is attached to the front substrate. The carrier of some embodiments is released after transferring the movable electrodes to the front substrate. In other embodiments, the carrier stays over the front substrate, and serves as a backplate for the MEMS device. Features are formed by deposition and patterning, by embossing, or by patterning and etching. Spacers are provided between the front substrate and the backplate to maintain a gap therebetween. The methods not only reduce the manufacturing costs, but also provide a higher yield.

Abstract: Provided is an electrostatic motor, in which a disc-shaped stator (S) and a disc-shaped rotor (R) are opposed to each other in a vacuum container (11). In the stator (S), first electrodes (34A) and second electrodes (34B), which are attached to electrode supports (31, 32), respectively, and which are electrically insulated from each other by an insulator (33), are arranged alternately in the circumferential direction. In the rotor (R), first electrodes (44A) and second electrodes (44B), which are attached to electrode supports (41, 42), respectively, and which are electrically insulated from each other by an insulator (43), are arranged alternately in the circumferential direction. The first electrodes (34A) and the second electrodes (34B) on the side of the stator (S) are arranged at a spacing of two or more rows at a predetermined distance from the center of a rotating shaft (1).

Abstract: A gap-closing actuator includes a stator having one or more first electrodes, a mover having one or more second electrodes interposed among the first electrodes, and a biasing mechanism for applying a non-capacitive bias to the mover for urging the mover to move in a desired direction with respect to the stator. The non-capacitive bias is different from a capacitive force generated between the first and second electrodes when the gap-closing actuator is in operation.

Abstract: An integrated MEMS and IC system (MEMSIC), as well as related methods, are described herein. According to some embodiments, a mechanical resonating structure is coupled to an electrical circuit (e.g., field-effect transistor). For example, the mechanical resonating structure may be coupled to a gate of a transistor. In some cases, the mechanical resonating structure and electrical circuit may be fabricated on the same substrate (e.g., Silicon (Si) and/or Silicon-on-Insulator (SOW and may be proximate to one another.

Abstract: A driver (100f) comprises a base section (110), a movable stage section (130) for mounting a driven article (12), a resilient section (12) for connecting the base section and the stage section and exhibiting resiliency for moving the stage section along one direction (Y axis), and a section (161, 162, 22) which applies a shaking force to the resilient section in order to move the stage section to oscillate alone the one direction at a resonance frequency determined by the stage section and the resilient section.

Abstract: A driving apparatus (100j) is provided with: a base portion (110); a stage portion (130) on which a driven object (12) is mounted and which can be displaced; an elastic portion (120) which connects the base portion and the stage portion and which has elasticity to displace the stage portion in one direction (Y axis); a first applying device (161, 162, 22) for applying an excitation force for displacing the stage portion such that the stage portion is resonated in the one direction at a resonance frequency determined by the stage portion and the elastic portion; and a frequency adjusting device (170) for dynamically adjusting the resonance frequency.

Abstract: To provide an electret whose surface potential is improved and an electrostatic induction conversion device comprising the same, an electret is formed by spin-coating a fluorine-containing polymer composition for coating which contains a fluorine-containing polymer having a ring structure in its main chain, a silane coupling agent, an aprotic fluorine-containing solvent, and a fluorine-containing alcohol as a protic fluorine-containing solvent on a copper substrate and baking it.

Abstract: A micro-electromechanical resonator includes a resonator body having a semiconductor region therein doped with boron to a level greater than about 1×1018 cm?3 and even greater than about 1×1019 cm?3, in order to obtain reductions in the temperature coefficient of frequency (TCF) of the resonator over a relatively large temperature range. Still further improvements in TCF can be achieved by degenerately doping the resonator body with boron and/or by boron-assisted aluminum doping of the resonator body.

Abstract: An electromechanical transducer of the present invention includes a first electrode, a vibrating membrane formed above the first electrode through a gap, a second electrode formed on the vibrating membrane, and an insulating protective layer formed on a surface of the second electrode side. A region where the protective layer is not formed is present on at least part of a surface of the vibrating membrane.

Abstract: An antenna device includes an oscillating body capable of oscillating at a predetermined natural frequency, and being displaceable by external magnetic field, and a converter for converting motion of the oscillating body to an electrical signal. When a radio wave signal of a frequency band at which the oscillating body resonates comes, the oscillating body resonates with a magnetic field component of the radio wave signal, and the converter converts the motion to the electrical signal, whereby an electrical signal corresponding to the radio wave signal is outputted.

Abstract: Apparatus and method for harnessing heat energy uses at least one thermally conductive material in communication with a heat collecting material in order to conduct heat from a first region of the heat collecting material to a second region of the heat collecting material. The thermally conductive material can be interspersed within the heat collecting material and/or applied externally to the heat collecting material. Heat drawn from the second portion can be stored and/or converted into another form of energy for providing power to a structure or vehicle. Conversion can use the differential between the temperature of the second region and the temperature of a cold sink. Additional heat can be added to the heat collecting material.

Abstract: An electrostatic acting device in which leakage of charge from an electret film is suppressed. The electrostatic acting device comprises a movable electrode section (20) having a movable electrode (22), a fixed electrode section (10) having an electret film (12) opposed to the movable section (20) at a predetermined distance and capable of storing charge and a conductive layer (14) formed on a predetermined region on the upper surface of the electret film (12), and an insulating film (13) interposed between the electret film (12) and the conductive layer (14).

Abstract: A driving apparatus (100t) is provided with: stage portion (130) which can be displaced; a first elastic portion (120-1) whose one end is connected to the stage portion and which has elasticity to displace the stage portion in one direction; a driving source device (180), to which other end of the first elastic portion is connected, comprising: a first applying device (181) for applying an excitation force for displacing the stage portion such that the stage portion is resonated in the one direction at a resonance frequency determined by the stage portion and the first elastic portion; and a second applying device (182) for applying a driving force for displacing, in a stepwise manner or in a continuous manner, the stage portion in other direction; a second elastic portion (120-2) whose one end is connected to the driving source device and which has elasticity to displace the stage portion in the one direction; a third elastic portion (120-3) whose one end is connected to other end of the second elastic porti

Abstract: A resonator includes a translator, a stator, and a control circuit. The control circuit is configured to provide first and second translator voltages and first through third stator voltages, wherein the translator is configured to move with respect to the stator at a resonant frequency of the resonator in response to the control circuit.

Abstract: A driving apparatus is provided with: a first base portion; a first stage portion; a first elastic portion which has elasticity to displace the first stage portion in one direction (X axis); a second stage portion which is disposed on the first stage portion and on which a driven object is mounted; a second elastic portion which has elasticity to displace the second stage portion in other direction (Y axis); a first applying device for applying an excitation force for displacing the second stage portion such that the second stage portion is resonated in the other direction at a resonance frequency determined by the second stage portion and the second elastic portion; and a second applying device for applying a driving force for displacing, in a stepwise manner or in a continuous manner, the first stage portion in the one direction.

Abstract: To provide a polymer actuator which is light in weight and capable of linear expansion and contraction with a low voltage. The polymer actuator 1 is composed of a plurality of gel/electrode complexes arranged in an electrolytic aqueous solution 6, said gel/electrode complex being composed of a polymer gel (2a, 2b) containing at least either of acidic or basic functional groups and electrodes (3a, 3b) placed in the polymer gel, said electrodes being made of a material capable of occluding and releasing hydrogen electrochemically, such that the polymer gel (2a, 2b) in the gel/electrode complex changes in pH upon application of voltage across the electrodes (3a, 3b) of the gel/electrode complexes (4a, 4b) and each of the gel/complexes changes in volume in response to the pH change.

Abstract: The present invention relates to a static pressure slider including a stationary member 2, and a movable member 3 configured to be movable relative to the stationary member 2 under a condition that a static pressure fluid layer is provided between the stationary member 2 and the movable member 3. The static pressure slider further includes a first conductive layer 25 (26-28), and a second conductive layer 31A (32A-34A) with a distance at least in a portion relative to the first conductive layer 25 (26-28) configured to be changeable by an electrostatic force imposed between the first and second conductive layers 25 (26-28) and 31A (32A-34A). The present invention further relates to a transferring device and a processing device both provided with the static pressure slider.

Abstract: A micro movable device includes: a micro movable substrate in which a micro movable unit is formed, the micro movable unit including a frame, a movable part, and a coupling part for coupling the frame and the movable part to define an axial center of rotation of the movable part; a supporting substrate; and a reinforced fixed part provided between the frame and the supporting substrate, and including a first spacer that joins the frame to the supporting substrate and an adhesive part that covers the first spacer and joins the frame to the supporting substrate, wherein the frame includes a first area facing the movable part in a direction of extent of the axial center, and a second area different from the first area, and the reinforced fixed part is bonded to the second area of the frame.

Abstract: A resonator for an angular parameter sensor, the resonator comprising a bell of electrically-insulating material provided with a central stem and an electrically-conductive layer, the conductive layer comprising branches extending from a central portion of the bell to a peripheral edge of the bell, the number of said branches being a prime number not less than seven.

Abstract: This electrostatic actuator includes an electret film and a conductor layer formed on the electret film, and the conductor layer is so formed as to have a sectional shape reduced in width upward from the side closer to the electret film.