An electret includes a composite oxide having an ABO.sub.3 type perovskite structure containing two different metal elements A and B. The composite oxide is in a polarized state, at least a part of one of the metal elements A and B is substituted with a dopant element having a lower valence than the one of the metal elements A and B, and the composite oxide has a bandgap energy of 4 eV or more.

An electret includes a composite oxide having an ABO.sub.3 type perovskite structure containing two different metal elements A and B. The composite oxide is in a polarized state, at least a part of one of the metal elements A and B is substituted with a dopant element having a lower valence than the one of the metal elements A and B, and the composite oxide has a bandgap energy of 4 eV or more.

The present invention provides an electret sheet that exhibits excellent piezoelectricity even by light stress. The electret sheet of the invention is characterized by including a charged porous sheet, in which the electret sheet has a compressive elastic modulus of 80 to 300 MPa when compressively deformed at 25° C. and a 50% compression stress of 120 to 300 kPa at 25° C., and thus has the excellent piezoelectricity for light stress and exhibits the excellent piezoelectricity even by light stress (0.5 N or less) caused by a pulse wave or a breathing.

The present invention provides an electret sheet that exhibits excellent piezoelectricity even by light stress. The electret sheet of the invention is characterized by including a charged porous sheet, in which the electret sheet has a compressive elastic modulus of 80 to 300 MPa when compressively deformed at 25° C. and a 50% compression stress of 120 to 300 kPa at 25° C., and thus has the excellent piezoelectricity for light stress and exhibits the excellent piezoelectricity even by light stress (0.5 N or less) caused by a pulse wave or a breathing.

A vibration sensor having a moveable mass adapted to move in response to vibrations or accelerations. The sensor includes a damping arrangement that includes a damping fluid or gel. The moveable mass is arranged to interact directly or indirectly with the damping fluid or gel in order to reduce a mechanical resonance peak of the vibration sensor. The damping fluid or gel has a viscosity between 1000 cP and 100000 Cp and damping properties that are substantially stable over time.

Ultrasonic transducers that include membrane films and perforated baseplates. An ultrasonic transducer includes a baseplate having a conductive surface with a plurality of apertures, openings, or perforations formed thereon or therethrough, and a membrane film having a conductive surface. The membrane film is positioned adjacent to the apertures, openings, or perforations formed on or through the baseplate. By applying a voltage between the conductive surface of the membrane film and the conductive surface of the baseplate, an electrical force of attraction can be created between the membrane film and the baseplate. Varying this applied voltage can cause the membrane film to undergo vibrational motion. The dimensions corresponding to the size and/or shape of the apertures, openings, or perforations formed on or through the baseplate can be varied so that different regions of the baseplate produce different frequency responses, allowing the net bandwidth of the ultrasonic transducer to be increased.

Provided is a wireless earphone capable of suppressing an influence on the sound quality of an electroacoustic transducer due to the arrangement of electrical parts such as a battery and a circuit board while reducing the size of a casing. The wireless earphone includes an electroacoustic transducer 14 that outputs a sound wave corresponding to a sound signal from a sound source S, a reception circuit 151 that receives the sound signal from the sound source S via a wireless communication line, a circuit board 15 to which the reception circuit 151 is attached, and a casing 11 that accommodates the circuit board 15 and the electroacoustic transducer 14. The casing 11 includes a first casing 11A that accommodates the electroacoustic transducer 14, and a second casing 11B that accommodates the circuit board 15.

A device, including an implantable microphone, including a transducer, and a chamber in which a gas is located such that vibrations originating external to the microphone based on sound are effectively transmitted therethrough, wherein the transducer is in effective vibration communication with the gas, wherein the transducer is configured to convert the vibrations traveling via the gas to an electrical signal, the chamber and the transducer correspond to a microphone system, wherein the chamber corresponds to a front volume of the microphone system, and the transducer includes a back volume corresponding to the back volume of the microphone system, and the implantable microphone is configured to enable pressure adjustment of the front and/or back volume in real time.

An actuator is provided, including a plurality of conducting layers and a plurality of electret layers. The electret layers are respectively sandwiched between the conducting layers, and form gaps between the conducting layers. Directions of preset electric fields of the adjacent electret layers are opposite, and the adjacent conducting layers are respectively electrically connected to a first voltage end and a second voltage end to receive a driving voltage.

A micro-electromechanical transducer including one or more moveable members, and a viscoelastic substance having a predetermined viscoelasticity, the viscoelastic substance being adapted to influence the response of the transducer in a predetermined manner. The micro-electromechanical transducer of the present invention may include a MEMS transducer, such as a MEMS microphone, a MEMS vibration sensor, a MEMS acceleration sensor, a MEMS receiver.