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Electroacoustic Transducer

IP.com Disclosure Number: IPCOM000079291D
Original Publication Date: 1973-Jun-01
Included in the Prior Art Database: 2005-Feb-26
Document File: 4 page(s) / 48K

Publishing Venue

IBM

Related People

Baechtold, W: AUTHOR [+2]

Abstract

Described herein is an electroacoustic transducer for decoding of coded signals and converting them to sound flux, and a method of operating this transducer. In Fig. 1 a piezoelectric transducer is depicted schematically, which is controlled by coded electrical signals and directly converts them to sound waves. The essential component of this transducer is a piezoelectric bender plate; one end is solidly fixed, and the other end moves freely and is connected by a thin rod to a diaphragm. The piezoelectric bender plate consists of two layers of ceramic properties. A metal coating is located between these two layers as a counter electrode.

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Electroacoustic Transducer

Described herein is an electroacoustic transducer for decoding of coded signals and converting them to sound flux, and a method of operating this transducer. In Fig. 1 a piezoelectric transducer is depicted schematically, which is controlled by coded electrical signals and directly converts them to sound waves. The essential component of this transducer is a piezoelectric bender plate; one end is solidly fixed, and the other end moves freely and is connected by a thin rod to a diaphragm. The piezoelectric bender plate consists of two layers of ceramic properties. A metal coating is located between these two layers as a counter electrode.

On the upper surface of the piezoelectric bender plate six rectangular bit electrodes, with different area dimensions, are mounted in one row side-by-side as driving electrodes. Each of these bit electrodes is connected to a separate electric line.

When a given voltage is applied between one of these bit electrodes and the common counter electrode, the end of the bender plate and with it the diaphragm are deflected by a given amount. The electrodes are so dimensioned and are distributed on the bender plate in such a way that the deflections caused by the bit electrodes, when energized with equal signals, have the same ratio as the position weights in a binary code, i.e., 1: 2: 4: 8: 16: 32. The rightmost bit electrode No. 6 causes the smallest deflection (one unit), and the leftmost bit electrode No. 1 close to the mixture causes the largest deflection (32 units). If several bit electrodes are energized simultaneously, the deflections are added together. If the bit electrodes are controlled directly by the bit signals of a 6-bit code (or through six switches which are connected to a common voltage or current source), decoding or digital-to-analog conversion will be achieved. Simultaneously, a conversion to mechanical motion and the generation of corresponding sound pressure are effected. Thus, decoder and electroacoustic transducer are integrated in one unit.

The pure binary code was merely chosen as an example. Linear codes with any other position weights can also be used, if the electrodes are suitably dimensioned.

Instead of ceramic piezoelectric layers, monocrystalline layers can be used. With these, improved accuracy and sensitivity can be achieved because of the material's homogeneity. The crystal, however, must be protected from humidity and is more sensitive to temperature.

Calculation of the deflection caused by a single bit electrode on a long, narrow piezoelectric bender plate, as depicted in Fig. 1, is described in connection with Fig. 2.

The selected electrode F extends from position X(i) to position X(2). For small deflections, angle d phi over the element dx is proportional to dx. If the membrane force is neglected, the following relations hold:

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Equations (1) to (3) are valid for frequencies below the lowest resonance frequenc...