Abstract: A probe microphone comprising an acoustic transducer with a cavity, to which a probe tube and a matching tube are connected. The matching tube is divided into several small tubes of a total internal transverse cross sectional area substantially corresponding to the internal transverse cross sectional area of the probe tube. The small matching tubes improve the frequency response because of their acoustic loss. Moreover, a further improvement is achieved when the matching tubes are of different lengths, the already reflected signals thereby outbalancing each other. As a result, a probe microphone with a more uniform frequency response than previously known is achieved.

Abstract: The present invention provides a substantially gauss-shaped sound field by means of an ultrasonic transducer, the potential on one side of the transducer being varied continuously by means of a thick-film electrode applied in a uniform or varying thickness. The thick-film can be a resistance paste or a conductive paste applicable in different thicknesses onto selected portions of the surface in question. The resistance paste can for instance be trimmed to different resistance values on selected portions of the surface. Such a technique makes it possible to alter the distribution of the potential so as to vary the distribution of the pressure in the sound field in such a manner that for instance a substantially gauss-shaped sound field is obtained.

Abstract: Pressure gradient microphone comprising a membrane (2) and a back electrode (4), the latter being provided with a film (6) of an electret material divided into semicircular sections, one of them being provided with a permanent electrostatic charge. The back electrode is supplied with an inverse potential by means of an external, adjustable voltage source. As a result the pressure gradient microphone is able to subtract two almost equal values from each other so as to indicate the pressure difference and consequently the pressure gradient with greater accuracy than previously known.

Abstract: A photoacoustic gas analyzer comprising a measuring chamber, a modulated light source, and at least one microphone in connection with the measuring chamber and measuring the changes of pressure caused by the absorption of the light in the chamber. The measuring chamber comprises an inner surface with a reflecting coating. The measuring signal is thereby proportional to the gas concentration and is not provided as the difference between two almost equal values. As a result it is possible to measure small gas concentrations provided the light intensity within the measuring chamber suffices.