Abstract: An electret capacitor microphone is constituted by a surface conductive diaphragm, a fixed electrode provided opposite to the diaphragm at a regular interval and a solid state device for converting, into an electric signal, a voice given to the diaphragm with a change in an electrostatic capacity between the diaphragm and the fixed electrode. The microphone comprises a dielectric casing having a bottomed hollow portion for accommodating the diaphragm, the fixed electrode and the solid state device. Since the casing itself is dielectric, it does not deed to accommodate a special dielectric or a board for the solid state device but can be directly provided in the hollow portion. Therefore, the microphone can be very small-sized and thinned. The hollow portion of the casing has a stepped portion and the diaphragm or the fixed electrode is fixed onto the stepped portion.

Abstract: Dyed inorganic composite particles having a mean particle diameter of 0.1 to 10.0 micrometers and a particle dispersibility value of at least 80%, each of said particles consisting of at least three layers comprising a core, a dyed layer on the surface of the core and a coated layer on the dyed layer, the core being composed of an inorganic compound, the dyed layer being composed of a dye or a mixture of a dye and an inorganic compound, and the coated layer being water-insoluble and light-pervious and composed of an inorganic compound or a mixture of it with a dye. The particles are useful as a carrier for preparing an immunological diagonostic reagent by binding an immunologically active substance (an antigen and an antibody) to them, particularly an immunological diagnostic reagent for use in a microtiter method, or as a hydrophilic pigment.