DD211439A1 - RADIAL RESONANCE SWITCH WITH ADDITIONAL MASS FOR FREQUENCY TRANSFORMATION - Google Patents

Abstract

Radial oscillators with additional masses for frequency transformation are used as sound transducers, e.g. in electroacoustic systems. The object of the invention is to expand the application possibilities of the piezoelectric material and to create new constructional possibilities. The object of the invention is to provide a method by which the resonant frequency of piezoelectric disks can be changed continuously. This object is achieved in that the additional masses are mounted on the lateral surface or the lateral surfaces of a piezoelectric disk or a piezoelectric cylinder.

Description

Radial resonance oscillator with additional masses for frequency transduction

Application of the invention

The invention can be used where mechanical vibrations are used for the manufacture of sound transducers.

Characteristic of the known technical solutions

High power slept acoustic acoustic transducers are operated at one of their resonant frequencies, which depend on the length considerations of the transducers. The change in the resonance frequency by the attachment of Susatzmassen on the top surfaces piezoce-. tric discs is common in thick vibrations and is known by the term "dumbbell or sandwich transducer" (Laiigevin, P. Franz. Patent Hr. 502913; 505703; 575435).

It has been shown that the use of different vibration modes is suitable for sound radiation. In particular, piezoelectric disks can be used to emit high acoustic powers in terms of thickness when the disks are operated in radial resonance (DD / '</ P 2313821). The radial resonance frequency of piezoelectric disks depends on the dimensions and materials standardized by the manufacturer, thus only such radial frequencies are available which correspond to the mentioned graduations. So far it is not known that

the radial resonance frequencies of piezoelectric disks through. the attachment of additional masses have been continuously changed.

Object of the invention

The aim of the invention is to expand the possible uses of the piezoelectric material and to create new design possibilities.

Explanation of the essence of the invention

The object of the invention is to provide a method with which the radial resonance frequency of piezoelectric disks can be changed continuously. The radial resonance frequency of disks is dependent on the existing boundary conditions on the lateral surfaces. · If swing or these lateral surfaces free adjacent to a medium with a much lower acoustic impedance than that of the disk material, the boundary conditions by the absence of mechanical normal stresses (zeros of pressure) are given the lateral surfaces, as shown schematically in Fig. 1. This state is only possible at very specific frequencies, the natural or resonant frequencies (Pig. 1, Pig. 2).

According to the invention will now be a lateral surface (or more lateral surfaces) with a concentric ring, d. H. an additional mass connected, whereby the distance between the zeros of the radial voltage increases and thus the radial resonance frequency is reduced.

Purely thin X-ring discs can calculate the required for a desired reduction of the resonance frequency Breii; e of the ring. The radial displacement amplitude y of the oscillation satisfies the differential equation

if

In this mean:

y: displacement (amplitude) γ-: length coordinate in the radial direction CO i angular frequency

Cy : speed of sound in the radial direction

The radial normal stress <S " _r is

The boundary conditions on the free lateral surfaces are therefore

Where:

ψ ': Poisson number f : density

On the interfaces between the piezoelectric material and the additional ring the physically necessary continuity conditions \ i _A " Hz apply , ie the equality of the displacements and <3τ% "<S"r ₂ the equality of the normal stresses on both sides of the boundaries.

By suitable combinations of materials with the piezoelectric material, the radial stresses can be lowered and thus increase the load capacity of the vibrator. In addition, the vibration amplitude can be increased on the outer surface, which is advantageous in the case of an intended sound radiation in the radial direction.

Ausführung'sbeispiel

Also known as the base body is a piezolan L piezoelectric ring disk of the type 1576.3-6622.94 from the production of Keramische Werke Hernisdorf. The dimensions are:

Thickness' = 6 mm Bore = 15 mm Disc diameter = i 50 mm AL ring diameter = 70 mm

The radial resonance frequency of the simple piezoelectric disk 1 is 110 kHz. On the outer jacket is a concentric aluminum ring-2 of the. same height (6 mm) and fixed by 10 rome width. The aluminum ring reduces the radial resonance frequency of the combined vibrator (piezoelectric disk with additional ring) to 90 kHz.

Die.kraftschlüssige connection between the materials is made by bonding with epoxy resin to avoid an electrical short circuit of the silver electrodes 3 on the Aluminiumriig, the piezoelectric disc 1 facing Kanten.des aluminum ring are broken. In addition, the squeezed out during assembly surplus of the adhesive in the generated by edge refraction groove 4 ensure sufficient galvanic separation of the silver coatings from the aluminum ring. The obtained frequency response of 110 kHz to kHz has been determined experimentally by wobbling the electrical impedance of the piezoelectric disk with and without aluminum ring. The laughter can also be achieved by the numerical treatment of equations (1) to (3) with the mentioned continuity conditions.

In Pig. 4, the calculated normal voltages and the resulting positions of the zeros thereof are shown. In Fig. 5, the calculated radial deflections between the inner and outer disc shells are shown. It can be seen that the deflection on the outer jacket is increased by the presence of the aluminum ring.

If one wanted a piezoelectric ring disk (with the same inside diameter and the same thickness) with a radial resonance frequency, of 90 kHz, d. H. instead of 17.5 mm, it would have to be 22.2 mm (FIG. 5). & on-off Pig. 5, that the fast amplitude at the outer edge of both variants behave like 6.6 / 4.9. '

That means: . ,

The radial energy radiation due to the aluminum ring is. by the ratio (6.6 / 4.9) = 1.8 greater than in a simple piezoelectric disc with a ring width of 22.2 Γαία, which have the same resonant frequency of 90 kHz for d e.

Claims (4)

Brfindungsansprüche 1. Radial resonance oscillator with additional masses for frequency transformation characterized in that they'auf the lateral surface or the lateral surfaces of a piezoelectric disc or a piezoelectric cylinder are mounted. 2. Radial resonance oscillator with additional masses for frequency transformation according to item 1 characterized in that they are arranged on one or more lateral surfaces of an annular piezoelectric disc or piezoelectric hollow cylinder with any cross-sectional contour. 3. Radial resonance oscillator with additional masses for frequency transformation according to item 1 and 2, characterized in that the additional masses are non-positively connected to the piezoelectric material by a pourable and hardenable material on the entire contact surface. .4. Radial resonance oscillator with additional masses for frequency transformation according to point 3, characterized in that the plastic adhesive ensures a galvanic separation of the electrodes of the piezoelectric material of metallic Susatzmassen. For this purpose, see drawing