Coupling element, ultrasonic transducer and ultrasonic flow meter

1. An ultrasonic transducer, comprising:

a coupling element;

a piezo-electric element, and

a support disk,

said coupling element comprises a first recess

with said piezoelectric element arranged in said first recess, said first recess comprises a terminal base surface, on which an ultrasound signal that is generated by said piezoelectric element can be introduced into said coupling element, wherein:

in said first recess, said support disk is arranged, on whose upper side that is directed away from said coupling element, said piezoelectric element is arranged;

said support disk and said base surface delimit a space in which an adaptation layer is arranged; and

said support disk is provided for reducing thermal stresses on said piezoelectric element,

wherein within said first recess, the coupling element comprises one or a plurality of stops, each having at least one stop surface, which extends along a plane; and said plane runs parallel to said base surface of said first recess and a space is defined between said plane and said base surface for accommodating material for an acoustic adaptation layer,

wherein said plurality of stops is formed as a single stop as at least one bar, which peripherally protrudes into said first recess, or wherein said plurality of stops are formed as a plurality of bars, which peripherally protrude into said first recess and whose stop surfaces are in the plane.

2. The ultrasonic transducer according to claim 1 , wherein:

said adaptation layer is a λ/4 adaptation layer (±25% of this value).

3. The ultrasonic transducer according to claim 1 , wherein:

said coupling element comprises a second recess which is connected with said first recess via an overflow channel.

4. The ultrasonic transducer according to claim 1 , wherein:

said plurality of stops has a stop formed as one or more spacer(s), which protrude from said base surface of said first recess.

5. The ultrasonic transducer according to claim 1 , wherein:

said stop(s) is/are an integral part of said coupling element.

6. The ultrasonic transducer according to claim 1 , wherein:

said bar(s) have an undercut.

7. The ultrasonic transducer according to claim 1 , wherein:

the ultrasonic transducer has the following impedance ratios in the direction of propagation of the ultrasound signal:

Z Piezoelectric element >Z Support disk >Z Adaptation layer >Z Coupling element

wherein Z stands for the impedance (in Rayl) of said piezoelectric element, said support disk, said adaptation layer and said coupling element.

8. The ultrasonic transducer according to claim 1 , wherein:

the ultrasonic transducer has a gradient of the thermal coefficient of expansion (ppm/K) in the direction of propagation of the ultrasound signal:

Coefficient of expansion Piezoelectric element <Coefficient of expansion Support disk <Coefficient of expansion Adaptation layer <Coefficient of expansion Coupling element .

9. The ultrasonic transducer according to claim 1 , wherein:

said adaptation layer consists of a polymerized synthetic material, which is polymerized under the influence of heat and shows a higher shrinkage during the polymerization than the temperature-related shrinkage of said coupling element and shows less shrinkage after polymerization than the temperature-related shrinkage of said coupling element.

10. The ultrasonic transducer according to claim 1 , wherein:

said adaptation layer consists of a permanently elastic material with a Shore hardness of 30-60°±5° at 25° C. according to DIN 53505.

11. The ultrasonic flow meter for determining the flow velocity or the volumetric flow rate of a measurement medium with a measuring tube and at least two ultrasonic transducers according to claim 1 , arranged along the measuring tube, wherein each one of said ultrasonic transducers comprises a coupling body with a contact surface, at which a generated ultrasound signal can be transmitted or received in the measuring tube or in the measurement medium.