RU1840790C - Cylindrical piezoelectric receiver - Google Patents

Abstract

FIELD: measurement equipment.

SUBSTANCE: invention is related to the field of acoustic measurement equipment. Metal disk is arranged as a whole with axis passing trough its centre, and is adhered to ends of piezoelectric cylinders.

EFFECT: improved vibration stability achieved by the fact that device is made of two identical piezoelectric cylinders, metal disk and axis.

5 dwg

Description

1. Introduction

Electro-acoustic receivers very often work in conditions when they are affected by an acoustic field and vibration. To weaken the effect of vibrations on the receivers, they tend to untie them from the source of vibrations with the help of shock-absorbing devices. However, when switching to low sound and infrasound frequencies, it becomes very difficult to achieve good quality depreciation in a wide frequency range.

An increase in the vibration resistance of the receiver in this case can be achieved without the use of shock absorbing devices by using the principle of mutual compensation of electrical signals that occur under the action of vibrations in various parts of the sensitive element of the receiver.

This application proposes the design of a cylindrical piezoelectric receiver, in which such compensation is achieved through a special method of mounting the sensitive element. As a result, the sensitivity to vibrations turns out to be theoretically equal to zero, but practically significantly less than that of conventional receivers of this type.

The scope of the receiver of the proposed design is antennas for low-frequency direction finding and devices for studying low-frequency noise fields.

2. Description of receiver design

The proposed design in two versions is schematically represented in figure 1. The receiver consists of identical piezoceramic cylinders (1), rigidly fastened (glued) with a metal disk (2). For the disk, the receiver is rigidly fixed to other structural elements using the axis (3) passing through its center (figa), or a concentric perforated cylinder (5), as shown in figb.

In all cases, the outer surface of the piezoelectric cylinder is in contact with the working medium, and the inner volume is sealed (for example, with a rubber layer (4)).

, и вращательное с угловым ускорением

(фиг.2). Будем считать оба вектора приложенными к центру диска.Under the action of forces applied to the axis, the disk generally makes a complex motion, which can be represented as a backward movement, which we will characterize by the acceleration vector

, and rotational with angular acceleration

(figure 2). We assume that both vectors are applied to the center of the disk.

может быть разложен на две составляющие: в направлении оси цилиндра (

) и в плоскости, перпендикулярной оси (

). При ускорении

возникает продольно растяжение и сжатие цилиндров, причем имеет место распределение механических напряжений по длине чувствительного элемента, показанное на фиг.2. Везде далее считаем, что вибрации происходят на частотах, значительно ниже резонансной частоты цилиндрического приемника. При этом можно считать, что все точки механической системы движутся с одной скоростью, а напряжения в ней определяются только силами инерции, возникающей при этом движении).Acceleration vector

can be decomposed into two components: in the direction of the axis of the cylinder (

) and in the plane perpendicular to the axis (

) Under acceleration

longitudinally tensile and compression of the cylinders occurs, and there is a distribution of mechanical stresses along the length of the sensing element, shown in figure 2. Everywhere further, we believe that vibrations occur at frequencies well below the resonant frequency of a cylindrical receiver. Moreover, we can assume that all points of the mechanical system move at the same speed, and the stresses in it are determined only by the inertia forces arising from this movement).

Mechanical stresses of different signs, equal in magnitude, cause, under the condition of a uniform piezoelectric element, the appearance of equal charges, differing in signs, which, when the electrodes are connected in parallel, completely compensate each other.

происходит изгиб цилиндра в плоскости, проходящей через ось цилиндра и вектор

. При этом, вследствие симметрии, механические напряжения, возникающие в точках цилиндра, симметричных относительно плоскости, перпендикулярной вектору

(XOZ), равны по величине и противоположны по знаку. Поэтому сумма зарядов, образующихся в каждом сечении, перпендикулярном оси цилиндра, равна нулю.Under acceleration

the cylinder bends in a plane passing through the axis of the cylinder and the vector

. Moreover, due to symmetry, mechanical stresses arising at points of the cylinder that are symmetrical with respect to a plane perpendicular to the vector

(XOZ) are equal in magnitude and opposite in sign. Therefore, the sum of the charges formed in each section perpendicular to the axis of the cylinder is zero.

, и при этом виде изгиба происходит взаимная компенсация зарядов, возникающих в соответствующих частях чувствительного элемента.The rotational movement of the disk can also be decomposed into two components: rotation around the axis of the cylinder with angular acceleration ϖ _x and rotation with angular acceleration ϖ _r (Fig.2). During rotation around the axis, the cylinder is twisted, as a result of which shear stresses arise in it. Shear stresses with the used direction of polarization do not cause the appearance of electric charges on the electrodes. With acceleration ϖ _r , bending of the cylinders occurs. Similar to what happened during acceleration

, and with this type of bending, mutual compensation of charges arising in the corresponding parts of the sensitive element occurs.

Thus, if the piezoelectric cylinder is homogeneous, with the proposed method of fastening it should be insensitive to vibrations of any direction. It can be shown that with other methods of fixing the cylinder, the receiver does not have the property of vibration resistance in full and responds to certain types of vibrations.

3. Experimental data

To verify the conclusions made, a receiver model of the proposed design and a model of a cylindrical receiver, the fastening of which was made at the end face, was made and tested on a vibrostand, which corresponds to the most common type of fastening at present.

As the sensitive elements were used cylinders (1), glued from two piezoceramic rings with radial polarization with an outer diameter of 48 mm, a thickness of 3 mm and a height of 32 mm (Fig. 3). Two such cylinders are rigidly glued together with an epoxy mass with a central steel disk (2) 6 mm thick, made as a unit with the axis (3). The cylinder is sealed with flanges (5) and a rubber layer (4). The conclusions from the cylinders were made separately, so that it was possible to check the effect of compensating the charges arising on the two halves of the receiver by comparing the voltage at the output of the parallel connection of the cylinders with the voltage on one of them.

The results of the experiment are summarized in a table in which the values of the sensitivity of the receiver to vibration, expressed in values of mV / g, are given under various conditions of fixing and switching on the sensitive element.

Table Vibration Sensitivity (mv / g) The nature of the fastening and inclusion of the elements of the receiver Vibration direction Along the axis Perpendicular to the axis Cylindrical receiver fixed to the end 38 32 The receiver is mounted on the central disk. One cylinder is on 10 0.33 The receiver is fixed to the central disk. Cylinder Parallel 0.45 0.33

The frequency characteristics of the sensitivity of the receiver mockups to vibration are linear in the range of 10 Hz ÷ 100 Hz, as a result of which the sensitivity can be characterized by a single value. The proposed design option corresponds to the last row of the table. As you can see, the sensitivity to vibration in this case is much less than with other methods of fixing and turning on the elements.

Claims (1)

A cylindrical piezoceramic receiver, characterized in that, in order to increase vibration resistance, it is made of two identical piezoceramic cylinders glued to the ends with a hard (e.g., metal) disk, by means of which the active element is fixed to the supporting structure.

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