Ultrasonic converter

Details Ultrasonic converter Ultrasonic converter

1994-05-13

1995-10-10

Budd, Mark O.

Electrical generator or motor structure

Non-dynamoelectric

Piezoelectric elements and devices

310334, H01L 4108

Patent

active

054573521

DESCRIPTION:

BRIEF SUMMARY
DESCRIPTION

The invention relates to an ultrasonic converter having a housing and a cylindrical ceramic oscillator of slight thickness at whose front faces metal electrodes are arranged and at one front face of which, facing the medium to be irradiated, an adaptation layer of a synthetic material is arranged which is in a form-fitting and operating connection with the membrane formed by the floor of the housing and whose remaining housing interior is filled with a damping layer of a synthetic material.
Due to the physical behavior of the ultrasonic converters acting as transmitting and receiving converters, these have the disadvantage that the measurement of the path between the membrane and the reflection plane is possible only up to a minimum distance. This means that a portion of the storage capacity of a container or of a storage area or the flow volume of the sluice can partially not be utilized because a monitoring of the fill and flow height within the minimum distance between the membrane and the reflection plane is not possible.
This minimum distance is determined in that in the case of converters operating with sonic pulses, the oscillations of the membrane at the end of the transmission pulse do not suddenly stop, but the membrane continues to oscillate for a little while longer. During the continuing oscillation time, however, no arriving echo pulses can be received or at least cannot be recognized. The timespan in which a reception or the evaluation of the echo pulse is not possible, is generally described as a blocking distance.
In the German Patent No. 3,301,848, for the reduction of the blocking distance, it is proposed to provide the entire ultrasonic converter with a foam casing made of a polyurethane foam except for the side of the synthetic adaptation layer facing the sound-emitting medium. Such a foam filler is to solve the task of influencing the oscillating behavior of the converter by damping the mechanical oscillation and thus to shorten the blocking distance. This takes place in that through the penetration of the sound wave into the polyurethane foam, a portion of the oscillation energy is lost and thus the oscillation behavior of the ceramic oscillator is reduced. However, the solution proposed in DE-PS 3,301,848 has the disadvantage that due to the varying density of ceramic material and polyurethane foam, only a very poor transition of the acoustic impedance of the ceramic oscillator to the foam casing is given. In particular, a disadvantage lies in that polyurethane foam is not temperature-resistant and for this reason, a usable reduction of the blocking distance can take place only during ideal constant temperatures, which rarely occur in practice.
According to further developments in the state of the art, as also described in DE-PS 3,301,848, the synthetic layer, which is for the adaptation of the acoustic impedance of the ceramic material to the acoustic impedance of the medium provided between the ceramic oscillator and the membrane in which the sound pulse is to be irradiated, consists of a polystyrene lacquer with embedded hollow spheres made of silicon dioxide. However, also epoxy resins and, as shown in column 1, line 36 of DE-PS 3,301,848, silicone elastomers have become known for this task. For example, Selastic E by the Dow Corning Co. represents a readily used material.
An additional disadvantage of the proposed damping of the ceramic oscillator with a polyurethane foam is that the material of the adaptation layer cannot bond with the material of the damping material and that, especially at high temperatures, quite frequently a detachment of the layers occurs.
For this reason, in the instructions proposed in DE-PS 3,301,848, the interior housings of this type of ultrasonic converter are frequently filled with a silicone elastomer, except for the side of the adaptation layer facing the irradiating medium. Such silicone elastomers, such as Eccosil 5952 of Grace Electronic Materials Co., have the advantage that the damping layer has a base which is chemically simila

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patent: 4616152 (1986-10-01), Saito et al.
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patent: 5274296 (1993-12-01), Hiki et al.

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