FI74183B - PIEZOELEKTRISK OMVANDLARE. - Google Patents

Description

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SUOMI FINLAND

(Fl) (21) Patent application - Patentansökning 802943 (22) Application date - Ansökningsdag 18.09.80

National Board of Patents and Registration (23) Start date - Giltighetsdag 18.09.80

Patent-och registerstyrelsen (41 j Published public - Biivit offentMg 20.03.81 (44) Date of publication and of publication - o ^ 08 87

Ansökan utlagd och utl.skriften publicerad J '(86) Kv. application - Int. ansökan (32) (33) (31) Privilege claimed - Begärd priority 19 * 09-79

Germany 1i i ttotasava1ta-Förbunds Repub 1i ken Tyskland (DE) P 2937922.4 (71) Siemens Aktiengesellschaft, Berlin and Munich, Wi ttel sbacherplatz 2,

Munich, Federal Republic of Germany-Förbundsrepubliken Tyskland (DE) (72) Klaus Baier, Munich, Erwin Martin, Munich, Federal Republic of Germany-Förbundsrepublen Germany (DE) (74) Berggren Oy Ab (54) Piezoelectric transducer - Piezoelectric converter

The invention relates to a piezoelectric transducer for a ringing sound radiation source, which transducer is provided with a transducer plate with a piezoelectric layer attached between the support members, in particular for telephone equipment.

A piezoelectric transducer of the above-mentioned quality is known from DE patent publication 61 61 217. Such transducers are in principle used as sound-producing devices or sound receivers.

If these transducers are used as sounding devices, especially as signaling devices for speech centrifuges, then it is necessary to perform certain measures in order to achieve a high volume.

In high quality transducers, steps are taken to set the resonant frequencies largely outside the frequency range involved in telephone traffic, so that the characteristics of the mechanical deviation of the sound field and the transducer plate in the participating 2 74183 frequency range are largely frequency independent. In order to achieve the highest possible efficiency, in electro-acoustic transducers used in telephones, it is generally not possible to dispense with the transducer plate mounting being chosen so that one or more resonant frequencies are within or in the vicinity of the participating frequency range. However, in order to keep the frequency dependence of the electroacoustic transmission coefficient within a certain orange pattern, such transducers are connected to correspondingly adjusted resonators to compensate for the resonance h u i p u t.

If such transducers are used as signaling devices in telephone equipment, then no requirements are placed on a flat frequency curve, but can be used to improve the sound transmitted at the resonant points.

The object of the invention is to tune the transducers and the ringing oscillators acting as a control part with respect to each other so that a penetrating, audible call of the signaling device can be achieved.

According to the invention, the task is solved by controlling the ringing oscillator 11a, which produces two alternating signals, the frequencies of which are tuned to the two resonant frequencies of the converter.

With the aid of the two variable signals of the ringing oscillator tuned to the resonant frequency of the converter, the desired call strength can be achieved relatively without any problems.

It is expedient when the second resonant frequency is formed by means of the plate resonance determined by the transducer plate.

The resonance of the transducer plate is determined by the strength of the transducer plate itself and, moreover, to a decisive extent by its attachment. The resonance can become maximal when the transducer plate is fixed in its peripheral region as damped as possible, such as this I.

3 74183 can advantageously be obtained by attaching a transducer plate to two elastic support pads.

The second resonant frequency can preferably be determined by means of a Helmholtz resonator arranged in front of the sound-emitting side of the transducer plate.

Furthermore, it may be expedient for the resonant frequency of the Hi m h o 1tz resonator to be higher than the resonant frequency of the novel plate. This resonant frequency is used to determine the maximum volume of the signaling device. In this case, a slight dispersion of the frequency and the sound level is advantageous.

In the following, the invention will be explained in more detail with the aid of two figures, of which Fig. 1 shows the basic structure of a piezoelectric signaling device in a sectional view, and Fig. 2 is a circuit breaker of the device according to Fig. 1.

The signaling device shown in Fig. 1 consists of a housing 1, in the inner part of which a transducer plate 3 provided with a piezoelectric layer 2 is arranged between two elastic support pieces 4 and 5. By means of the arrangement of the transducer plate, the transducer is divided into two different volumes, namely a rear space 6 with a volume V and a flexibility C 1, and a front space 7 with a volume V 1 and a flexibility Co. Arranged outwards is a cylindrical opening «3, which forms an opening of the Heimholtz resonator n with a mass m, a friction resistor r and an area A. The transducer plate 3 has a mass m, flexibility and frictional resistance r ^. Outwardly, the transducer is connected with an acoustic impedance Z

ak Using the names shown, a substitute circuit diagram is shown in Figure 2, which is divided into the following areas: A for the generator ΰ for the transducer C for the Heimholtz resonator and D for the acoustic terminal Z.

ak 74183 4

A piezoelectric voice call converter for transmitting a voice call, the transducer comprising a piezoelectric layer (2) with a peripheral layer (2) fixed between the flexible support body (4, 5) and controlled by a ringing oscillator 11a, which produces two alternating signals, in particular that the frequencies of the signals are tuned to two resonant frequencies of the transducer, the second resonant frequency being formed by the plate resonance n determined by the transducer plate (3) and the second resonant frequency determined by the Heimholtz resonator (7, 8; C) arranged in the transducer plate in front of the audio page.

Piezoelectric transducer according to Claim 1, characterized in that the resonant frequency of the Heimholtz resonator is higher than the resonant frequency of the transducer plate.