GB2486561A

GB2486561A - Piezoelectric sound transducer

Info

Publication number: GB2486561A
Application number: GB1121445.9A
Authority: GB
Inventors: Martin Abele; Karl Bendel; Andre Gerlach; Marko Liebler
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2010-12-14
Filing date: 2011-12-13
Publication date: 2012-06-20
Anticipated expiration: 2031-12-13
Also published as: DE102010062990A1; GB201121445D0; FR2968838A1; FR2968838B1; GB2486561B

Abstract

The sound transducer comprises at least one piezoelectric element 10 connected to a carrying element 12. The carrying element 12 has a sound-active surface 13 that may be raised and differently-shaped (fig 2). The carrying element 12 has at least one fixing element 20 so that the carrying element 12 can be arranged at a distance above or spaced from a fixing plane 30. The piezoelectric element 10 may be attached to various parts of the carrying element 12 (figs 3, 4 & 5) and the transducer may be used as part of an array of similar transducers (fig 6). A transducer of this form is said to be more suitable for use in an external environment, e.g. on a vehicle.

Description

Description Title

Sound transducer with at least one piezo element

Description

The invention concerns a sound transducer with at least one piezo element, the piezo element being connected to a carrying element, according to the pre-characterizing clause of Claim 1.

Prior art

From published specification EP 1 791 192 Bi, a sound transducer with at least one bending actuator element in the form of a strip or plate is known. It is coated on one side with a piezoelectric body, and has a piezoelectrically inactive multilayer base body. The base body is in the form of a carrying element for a piezoelectric body which is attached to one side of it. Both the carrying element and the base body can have one or multiple layers. However, it has been shown to be disadvantageous that a sound transducer with such a structure is not very robust against humidity, dust, spray, ice, snow or mechanical effects, since the piezoelectric body is connected directly to the base body. Thus fitting the sound transducer externally, e.g. for motor vehicles or robots with direct exposure to environmental effects, is unsuitable for lasting, reliable functioning.

Disclosure of the invention

It is thus the object of the invention to create an S improved sound transducer which because of its construction ensures lasting, secure and high operational reliability when it is used externally, e.g. attached to the exterior of a motor vehicle.

To achieve this object, a sound transducer according to the features of Claim 1, in particular with the features of the characterizing part, is proposed. In the dependent claims, preferred further developments of the invention are explained.

According to the invention, it is provided that the carrying element has a surface, the surface being in sound-active form, and the carrying element having at least one fixing element, so that the carrying element can be arranged at a distance from a fixing plane. The sound transducer according to the invention can act as both sound transmitter and sound receiver. The piezo element converts electrical voltages into mechanical deformations, and vice versa. The sound transducer on the one hand outputs, and on the other hand receives, these mechanical deformations as sound waves.

The core of the invention is that the piezo element is not connected directly to the fixing plane. Thus the piezo element, with the carrying element, which has a sound-active surface, forms one unit, the oscillation behaviour of which is not determined by the fixing plane. Because of this structure, the piezo element can be protected effectively from mechanical stresses and/or external environmental influences, e.g. humidity, dust, ice, snow or similar. This structure also provides the advantage that at S least two sound transducers can be arranged so that the distance between them is less than half the wavelength of sound in air. This is then called an array arrangement, which can provide extended possibilities in signal processing. For an ultrasound frequency of, for example, 50 KHz, the wavelength of sound in air is about 7 mm. This means that the sound transducers can be about 3.5 mm at maximum from each other. This maximum distance limits the size of the sound transducers, which can be produced by the structure according to the invention. Because of the size limitation for array transducers, today mainly MEMS (micro-electro-mechanical system) elements are used for air ultrasound arrays. However, such MEMS elements are not very suitable in the case of humidity, dust, spray, ice, snow or mechanical effects, as already described.

It is specially advantageous that the surface has a plane sound-active elevation. In this case various geometrical shapes such as triangular, rectangular or circular surfaces can be used. Thus depending on the shape of the surface, different emission behaviour of the sound transducer can be made possible. Surfaces which are roughened or provided with a profile are also conceivable, so that the sound emission characteristic of the sound transducer is also changeable. The height of the elevation can also be variable, so that the sound-active surface can be deducted geometrically from the carrying element. The advantage of this is that a protective screen which has an opening, which is in the shape of the sound-active surface, can be used, so that the sound-active surface can be guided. In this way, it is possible to decouple the piezo element from the sound-active surface, so that interfering environmental influences come into contact with the sound-active surface only directly.

It is also advantageous that the fixing element and the carrying element can be produced from uniform or different materials. Thus different oscillation behaviours can be made pcssible by different use of different materials. If the fixing element and the carrying element are made of uniform materials, inexpensive, simple production is possible. By making the fixing element and the carrying element of different materials, the oscillation behaviour of the sound transducer can be influenced in a simple, defined manner by the selection of materials. It is also conceivable that the. fixing element is executed in one piece with the carrying elements. The carrying element can then be attached to the fixing element by an adhesive or welding method. It is also conceivable that the carrying element, the fixing element and the fixing plane are executed in one piece and of uniform material. Various materials can be used. It is advantageous that the fixing element and/or the carrying element contain materials such as metal, in particular light metal such as aluminium, ceramic or plastic. In this way, the oscillation behaviour of the sound-active surface can be changed corresponding to the requirements.

It has also been proved to be advantageous that the fixing element can be arranged at a right angle to the carrying element. In this way, the whole structure can be simplified. Use of a U-shaped fixing element is also conceivable. The fixing element can be attached to the fixing plane by an adhesive or welding method. A screwed connection which fixes the fixing element to the fixing plane is also conceivable. Because of the U-shaped form, the piezo element can be attached on the inside of the U-shaped form, so that the piezo element can be protected by the fixing element. Other shapes are also conceivable, it being possible to form two or more U-shaped fixing elements into one fixing element as one unit.

It is advantageous that the plane sound-active elevation and the carrying element are formed of uniform materials.

In this way, simplified production of both elements, the plane sound-active elevation and the carrying element, can be made possible. This structure can significantly reduce the production costs of the whole structure. Also, in this way the oscillation behaviour can be influenced depending on the material.

It is also advantageous that the piezo element can be attached to the fixing element. The result is several possibilities for varying the oscillation behaviour. In the case of a U-shaped fixing element, the piezo element can also be attached to the lateral surface. If multiple sound transducers next to each other are used, so that a linear array can result, it is advantageous that the width of the piezo element is not greater than that of the fixing element. In this way, the ultrasound transducers can be connected directly to each other, so that implementations the dimension of which can be less than or equal to half the wavelength of sound in air are possible. Limiting the sound-active surface in a second dimension makes it possible to use linear arrays or linear arrays with additional elements. The fixing elements can be attached to a fixing plane which is made to be resistant to bending.

The dimension of the fixing plane can correspond to the surface which can be used to fix the fixing element to the fixing plane.

A further preferred embodiment consists of an array arrangement with at least two sound transducers according to the invention, the distance between the sound transducers being less than half the wavelength of sound in air which can be imitated via the plane sound-active elevation, so that a dynamically changed ultrasound beam can be generated. In this way, in transmission operation, a large sound pressure level pan be generated. In reception operation, a high sensitivity to sound is thus ensured.

Thus resonantly working air sound transducers with a working frequency in the range of 48 K1-Iz can be provided, and are suitable for an array and also specially robust against external environmental influences. The working frequency of 48 KHz is specially suitable for ultrasound-based environment sensing, since the frequency position is above typical interfering sound sources, the air absorption is not yet too great, and animals are hardly disturbed.

The sound transducer according to the invention can be produced from metals, ceramic or plastic, together with one, two or more piezo elements. Because of the chosen materials and the minimum dimensions, with which it is possible to comply, these transducer elements are robust against mechanical and other environmental effects. Two piezo elements can be combined in such a way that the sound transducer, compared with sound transducers with only one piezo element, obtains special additional properties, which can be used singly or in combination. These are characterized by increased effectiveness of the sound emission and/or increased sensitivity in the case of sound reception. Fast switching between transmission operation and reception operation is also made possible. Self-diagnosis of the oscillation-mechanical properties is also possible.

Further actions and advantages of the invention are given in the claims, the following description and the drawings.

In the drawings, the invention is shown in several embodiments. The features which are mentioned in the claims and the description can be essential to the invention individually or in any combination.

Fig. 1 shows a schematic view of a sound transducer in U-shaped form, Fig. 2 shows a schematic view of a sound transducer with a sound-active plane elevation, Fig. 3 shows a schematic view of a sound transducer with a piezo element, which is attached laterally to a fixing element, Fig. 4 shows a schematic view of a sound transducer, multiple piezo elements being arranged on the fixing elements and carrying element, Fig. 5 shows a schematic view of a sound transducer, an asymmetrical form of the fixing element and carrying element having been chosen, and Fig. 6 shows a schematic view of an array arrangement of two sound transducers.

In Fig. 1, a schematic view of a sound transducer 1 according to the invention is shown. The carrying element 12 with its two fixing elements 20 is in U-shaped form. The carrying element 12 has a sound-active surface 13, the whole surface of the carrying element 12 functioning as a sound-active surface 13. The width 16 of the carrying element 12 corresponds exactly to the width 22 of the fixing element 20. A piezo element 10 is undetachably attached on the opposite side of the sound-active surface 13, below the carrying element 12. The fixing elements 20 are connected mechanically and/or substance-to-substance to a fixing plane 30. the piezo element 10 can be glued or welded to the carrying element 12. The same applies to the fixings of the carrying elements 20 to the fixing plane 30, it being also possible here to use a screwing method, in which the fixing elements 20 can be screwed to the fixing plane 30. In Fig. 1, the carrying element 12 is in a form which is of uniform material and in one part with the two fixing elements 20.

In Fig. 2, a further sound transducer 1 is shown schematically, the carrying element 12 having a plane elevation 14, which acts as the sound-active surface 13.

This plane elevation 14 can be executed in various geometrical forms, in particular a circular, triangular or rectangular shape, and be of uniform material with the carrying element 12. Otherwise, the sound transducer 1 from Fig. 2 has no technical differences from the previously described sound transducer 1 from Fig. 1. In this case too, the width 22 of the two fixing elements 20 equals the width 16 of the carrying element 12, the fixing elements 20 each being connected to the fixing plane 30, and the sound transducer 1 as a whole being U-shaped.

In Fig. 3, a further sound transducer 1 with only one piezo element 10 is shown schematically, this sound transducer 1 being constructed essentially cuboidally, apart from the projecting plane elevation 14, which acts as the sound-active surface 13. This plane elevation 14 too can be executed in various geometrical forms, in particular a circular, triangular or rectangular shape. In the cuboidal sound transducer 1, an also essentially cuboidal recess 24 is provided. To fix the sound transducer 1, the essentially U-shaped fixing element 20, which is connected to the fixing plane 30 over a large area and over the whole width 22 and length of the sound transducer I by its bottom crossbar of the "U", is used. The two vertical legs of the U-shaped fixing element 20 are of the same geometrical form, and at their top ends hold the horizontally running beam-like carrying element 12. The piezo element 10, which generates the oscillation, is arranged externally on one side on one leg of the U-shaped fixing element 20. The horizontally running beam-like carrying element 12 is itself built flat (height of the beam-like carrying element 12), to improve the oscillation behaviour. The height of the beam-like carrying element 12 corresponds approximately -10 -to half the width 22 of the fixing element 20, or half the width 16 of the carrying element 12. The carrying element 12, because of the U-shaped fixing element 20, is arranged significantly above and at a distance from the fixing plane 30, the corresponding distance between the fixing plane 30 and the carrying element 12 corresponding approximately to the length of the carrying element 12. Consequently, the shape of the outer periphery of a lengthways section through the sound transducer 1 is also square.

In Fig. 4, a sound transducer 1 is shown schematically (similarly to Fig. 1), multiple piezo elements 10 being arranged on the fixing elements 20 and the carrying element 12. One piezo element 10 is arranged on the outsides of the legs of the U-shaped fixing element 20, and a third piezo element 10 can optionally be attached below the carrying element 12 on the opposite surface to the rectangular elevation 14 in the recess 24. The rectangular elevation 14 is provided centrally on the top of the carrying element 12. The width 16 of the carrying element 12 equals the width 22 of the fixing element 20.

In Fig. 5, a schematic, asymmetrical version of a sound transducer 1 is shown. It is also in cuboidal form (as in Figs. 3 and 4), but the corresponding cuboidal recess 24 is arranged asymmetrically in height and length to the basic shape. The cuboidal elevation 14 on top of the carrying element 12 is arranged centrally over the cuboidal recess 24. The two legs of the U-shaped fixing element 20 have different thicknesses. The thinner leg of the fixing element 20 has two piezo elements 10, which are each attached laterally on the leg of the fixing element 20, on -11 -an inner side in the cuboidal recess 24 and on an opposite outer side. The width of the piezo elements 10 corresponds to the width 16 of the carrying element 12. The length of the piezo elements 10 corresponds essentially to the length or height of the inside of the leg of the fixing element 20. Use of multiple piezo elements 10 makes it possible to fix a predefined oscillation switching characteristic. In this case too, the width 16 of the carrying element 12 equals the width 22 of the fixing element 20.

In Fig. 6, an array arrangement 2 with two sound transducers 1, which are fixed parallel to each other on a fixing plane 30 (not shown), is shown schematically.

Between two adjacent sound transducers I of the array arrangement 2, an (air) gap is provided, so that a mutual influence of the two corresponding sound transducers 1 is as small as possible. It goes without saying that the array arrangement 2 can be extended in both length and width by further adjacent sound transducers 1, each of which can be controlled individually. The two sound transducers 1 shown as examples have a sound-active elevation 14 on their carrying elements 12, and correspond essentially to the sound transducer 4 shown in Fig. 4, the third piezo element on the inside of the carrying element 13 being omitted.

On both outer sides of the legs of the fixing element 20, a piezo element 10 is arranged. This array arrangement 2 can generate a dynamically changeable ultrasound beam. This array arrangement 2 can of course also be formed by the already disclosed sound transducer 1. A mixed arrangement of sound transducers 1 in different forms in an array arrangement 2 is also conceivable.

Claims

-12 -Claims 1. Sound transducer (1) with at least one piezo element (10), the piezo element (10) being connected to a carrying element (12), characterized in that the carrying element (12) has a surface (13), the surface (13) being in sound-active form, and the carrying element (12) having at least one fixing element (20), so that the carrying element (12) can be arranged at a distance from a fixing plane (30).
2. Sound transducer (1) according to Claim 1, characterized in that the surface (13) has a sound-active plane elevation (14).
3. Sound transducer (1) according to Claim 1 or 2, characterized in that the fixing element (20) and the carrying element (12) are formed of uniform or different materials.
4. Sound transducer (1) according to Claim 1 to 3, characterized in that the fixing element (20) and/or the carrying element (12) are of metal, ceramic or plastic.
5. Sound transducer (1) according to any one of the preceding claims, characterized in that -13 -the fixing element (20) can be arranged at a right angle to the carrying element (12).
6. Sound transducer (1) according to any one of the preceding claims, characterized in that the fixing plane (20) can be in u-shaped form.
7. Sound transducer (1) according to any one of the preceding claims, characterized in that the plane sound-active elevation (14) and the carrying element (12) are formed of uniform materials.
8. Sound transducer (1) according to any one of the preceding claims, characterized in that the sound-active surface is in triangular, rectangular or circular form.
9. Sound transducer (1) according to any one of the preceding claims, characterized in that the piezo element (10) can be attached to the fixing element (20)
10. Sound transducer (1) according to any one of the preceding claims, characterized in that the width (22) of the fixing element (20) is at maximum the width (16) of the carrying element (12) -14 -
11. Array arrangement (2) with at least two sound transducers (1) according to any one of Claims 1 to characterized in that the distance between the sound transducers (1) is less than half the wavelength of sound in air which can be emitted via the plane sound-active elevation (14), so that a dynamically changeable ultrasound beam can be generated.
12. A sound transducer substantially as herein described with reference to the accompanying drawings.
13. An array arrangement substantially as herein described with reference to the accompanying drawings.