FI58849B - ELECTROMECHANICAL FILTER - Google Patents

Description

ΓΒ1 «« AD PUBLICATION ς Q Q ϋ Q

lBJ (11) utläggningsskmft 58849 C Patent granted on 10 April 1981

Patent meddelat (51) K ».ik.1Ma1 h 03 H 9/02 SUOMI — FINLAND (21) r ***** ™» »- 2725/71 (22) H» k * ml * pthrt —An * ökitfnpd «| 29.09.71 (23) Alkupllvft — GIMfhafsdag 29.09.71 (41) TuHttt | utklMkil - Victims offantlig 31.03.72 huntti- |> rtkiattrihallltn. ηΜΜ *, .. | * · Μ Μ.η ..

PMMitOch reglrtarstyrslMn 'Anriftan uthgd och uti ^ krifun pubitMnd 31.12.80 (32) (33) (31) found • Tuoikeo * —S ^ ird prtorit · * 30.09.70

Federal Republic of Germany-Förbundsrepubliken Tyskland (DE) P 20U8162.3 (71) Siemens Aktiengesellschaft, Berlin / Munchen, EE; Wittelsbacherplatz 2, 8 Munchen 2, Federal Republic of Germany-Förbundsrepubliken Tyskland (DE) (72) Karl Traub, Olching, Federal Republic of Germany-Förbundsrepubliken Tyskland (DE) (7 * 0 Berggren Oy Ab (5 ^) Electromechanical filter - Elektromekan

The invention relates to an electromechanical filter consisting of a plurality of mechanically coupled mechanical bending oscillators arranged in a housing.

Mechanical filters consist, as is known, of a plurality of mechanically connected mechanical oscillators, in which the filter characteristic curve is determined by the oscillation event of the oscillator and the switches. Among the many possible forms of oscillation of oscillators and coupling elements, the use of a bending oscillation for oscillators and the use of a longitudinal oscillation for coupling elements are advantageous in particular. To protect against external influences, the filter is usually fitted in a housing. The air surrounding the mechanical filter is also subjected to vibrations from the movements of the various vibrators. Due to the low vibration goodness of the air, the attenuation of the vibrators then occurs.

5 8849

This attenuation becomes particularly large and sometimes leads to a decrease in frequency if - depending on the internal dimensions of the housing - air spaces are formed which are resonant at the operating frequency of the filter. Distortions in the filter attenuation curve at the eigenfrequencies of this airspace are then the result.

U.S. Pat. No. 2,905,909 already discloses a mechanical filter provided with longitudinal, transverse oscillating oscillators, which cover them with a resilient, such as rubber or foam-like, plastic material. This covering is the other side of the filter body for holding and on the other side of the vibrator to suppress unwanted own taivutusvärähtelyjä. Thus, a certain filling pressure is required for the oscillators.

The object of the invention is to suppress interfering air resonances inside the housing in a mechanical filter formed by mechanical bending vibrators without at the same time adversely affecting the vibration of the bending vibrators.

The invention relates in particular to a type of filtered, in which the oscillators are connected to one another by means of a coupling element which performs longitudinal oscillations, in which the space bounded by the outer surface set out in the appended claim 1.

The invention is based on the finding that the same oscillator quantities have bending oscillators, compared to oscillators which perform other forms of oscillation, generally with relatively large surfaces which are exposed to air resistance in the bending oscillation. For this reason, bending oscillators in filters have an interfering effect of air resonances on the damping effect of the filter, especially when the housing dimensions are unfavorable. In these filters, in the opposite phase oscillation of two adjacent oscillators, the air space between them will alternately increase and decrease. For this reason, perpendicular to the direction of oscillation of the bending oscillators, air waves are excited, which are reflected against the walls of the shell and can form standing waves. These air resonances have a disturbing effect on the filter characteristic curve in that, in part, considerable attenuation distortions occur. However, it is possible to change the lengths of the co-oscillating air columns by appropriately selecting the internal dimensions of the housing so that no air resonances and thus no damping distortions can occur. However, due to the high temperature dependence of the speed of sound in air, a sufficiently good result can be achieved only in a relatively small temperature range.

3,58849

In addition, the maximum allowable housing dimensions and their tolerances have a limiting effect on the use of this method.

The invention is described in more detail below with reference to the accompanying drawing.

The figure shows a filter formed by a plurality of mechanical bending oscillators 1, which are connected together by a through-going coupling element which performs longitudinal oscillations. The end vibrators are provided with electromechanical transducers 2 and 2 'for the transition from electrical vibrations to mechanical vibrations, respectively, for the transition from mechanical vibrations to electrical vibrations. Initially, the oscillators with a circular cross-section are flattened on one side, against which the oscillation nodes are fitted with holder elements 4, which in turn are anchored to the base plate 5. The oscillators are shown with their ends facing the viewer and the coupling element 3 is required. the middle part. In fact, transducers are located in the same plane and subjected to flexural so as to perform the double arrow 6 flexural direction, ie., One parallel with the bottom plate 5. As a result, also performs the switching element 3 pituusvärähtelyjä direction of the double arrow 6. The kucdat is surrounded on all sides by a housing 7 to keep external influences at bay. Between the filter body and the housing there is an intermediate layer 8 made of a sound-absorbing material, which dampens the air resonances occurring perpendicular to the direction of vibration 6. In the example of the lining, a plastic, namely polyester cardboard gauze with a thickness of 0.3 mm, is used as the material of the intermediate layer 8. It has been found that with this device, in the entire temperature range in question, i.e. 0-55 ° C, no attenuation distortions caused by air resonance can be detected.

In the exemplary embodiment, the intermediate layer is arranged directly on the oscillators and more specifically on the opposite side of the coupling element 3. The intermediate layer is thus parallel to the oscillation direction 6 of the oscillators and can, if necessary, extend over the entire length of the oscillator.

It has been tried with a much thinner cardboard gauze with a thickness of about 0.1 mm or with a plastic with a hard inner surface .: jagged, but they have not produced sufficient improvement. This indicates that the effect of the 0.5 mm thick karst gauze depends mainly on the absorption of sound waves and only to a lesser extent on the reflection from the rough surface of the interlayer.

^ 58849

Moreover, it has proved to be particularly advantageous from the manufacturing point of view that the intermediate layer 8 does not have to be fixedly attached to the housing, but can rest against the vibrators 1 without interfering with the damping effect. All you have to do is make sure that the distance between the housing and each vibrator is so large that they are not affected by any pressure during the vibration. for bone materials such as felt or foam, the polyester cardboard gauze used proves to be superior in terms of both resistance and moisture resistance.

Claims (6)

5,58849 An electromechanical filter arranged in a housing with a plurality of mechanical bending oscillators connected to each other by a coupling element performing longitudinal oscillations, in which a space bounded by (8) is a sound-absorbing material and is arranged parallel to the oscillation direction (6) of the bending vibrators (1) so that during vibration the vibrators (1) are not subjected to any appreciable pressure, and the thickness of the intermediate layer (8) is selected to achieve almost complete sound absorption. Electromechanical filter according to Claim 1, characterized in that the intermediate layer (8) is made of plastic, in particular polyester carded gauze. Electromechanical filter according to Claim 1 or 2, characterized in that the intermediate layer (8) extends over the entire length of the vibrators. Electromechanical filter according to one of the preceding claims, characterized in that the oscillators are connected via a through-coupling element (3) and that the intermediate layer (8) is arranged on the side opposite the coupling element (3) of the oscillators (1). 1. A high pressure electromechanical filter with a flotation mechanical resonator, a spark plug and a mechanical coupling through and above the open circuit of the coupling element, a flush filter and a rotary shield with a negative voltage at the resonator the resonator ligands, the absorption absorbers of the reflectors, on the other side of the resonator (8) are used in combination with the reflectors (6) of the resonators (1) (1), and with the aid of the breast (8) valts sä, att en näranog fullständigt ljudabsorption upp- 'r, kommer.