DE1616505C - Piezoelectric transmission element - Google Patents

Description

3 4

define on its two sides opposite to each other in such a way that corresponding to polarize the electrodes. The ring electrode can catch the shape of the resonance body, all lateral vibrations also be arranged at the edge of the disk-shaped resonance modes to form a single circumferential expansion body, in order to merge the complete radial vibration, to facilitate its ~ resonance frequency pre-polarization, and with over the 5 through the planar dimensions of the resonance disk gripping parts be provided to a body is given. "'- ■' -. ■" · - ^:: -o- ■ · ■ ^: - / ^ - · ι - ^; -k - ^ - A- ·. ./■:. To prevent extinguishing effect. The radial direction of oscillation, which is necessary for resonator

Finally, by adding one body according to the invention, it is essential that there is further concentric to the circular electrode as an isolated waveform neither in quartz; still and outside of it arranged ring electrode io itself in single crystals of a ferroelectric measure on each side of the material polarized in the radial direction. ^ ■■: · ■■■ '■ ■■' ■ >: -ν ί _; =: _£ ; ·; Resonance body possible, an impedance conversion A characteristic of the pre-polarized ferroelec-: and voltage increase. Irish ceramics is the "aging" of electrical

In the following, the invention is based on the mechanical coupling and the slow change

Figures described. 15 other properties, e.g. the dielectric

Fig. 1 is a plan view of a piezoelectric constant and the frequency constant with time

Transfer element according to the invention; and / or the temperature. As receptivity

Fig. 2 is a section along line 2-2 of the for. the aging and temperature dependence of

F i g. 1; Properties is different, will be more stable

F i g. 3 is the resonator element of FIG. 1 to 20 materials such as lead titanium zirconate preferred.

and test circuit including 2; The disc 12 as well as all the others in the

t) F i g. 4 is one of the F i g. 2 similar section through figures shown resonating bodies are strong

another embodiment; shown enlarged compared to their true size.

F i g. 5, 6 and 7 correspond to FIGS. 1, 2 and 3 - their size depends on the desired work spokesperson Representations of a different execution frequency from, i. i.e. the pane is dimensioned in such a way example; that the resonance of the radial waveform at 'jf i g. 8 shows the distribution of the radial and tangentials of a preselected frequency. When the disc tial tension in a radial direction with, for example, as a filter for intermediate frequencies (such as: the fundamental and the first upper frequency oscillating 455 to 465 kHz) is designed and at their basic transmitter element; 30 resonance is to be operated, then it is very small

F i g. 9 shows the transmission characteristic of a and has a diameter of about 4.7 mm. When

Filters according to the invention. . making the slice thin compared to hers

The F i g. 1 and 2 show a piezoelectric diameter power, then the resonance frequency

Transmitter element 10 according to the invention with frequency as in the case of an infinitely thin disc

a disc-shaped or plate-shaped reso 35 as. Function of the diameter considered alone

nanzkörper 12 (which will be called a disc in the following. However, it is not a small extension

is drawn) from a ferroelectric poly- the only point of view then it is cheaper that

crystalline ceramic material with electrodes disc for operation in the first or second

is provided, which are to be dimensioned here by a central electrical transverse oscillation, so that larger '

trode 14, 16 small diameter and one 4 ° discs each are possible. Has a thin slice

concentric ring electrode 18, 20 on each side with a fundamental frequency of about 180 kHz a first

of the disc. Harmonics in the intermediate frequency range (approx

The material from which the disc 12 or the 455 kHz) then has a diameter of other, further below shown sound box approximately 12.5 mm. A disk that exists at a top may be a ferroelectric poly crystalline vibration of low order (1st or 2nd) ceramic composition. Examples of drifting has, in addition to the convenient size, suitable substances are barium titanate, lead zirconate - in the intermediate frequency range, further advantages, the titanate or their modifications. ;: ;;; * rL: General be explained comprise .:: ^ _y. ,:.
the ferroelectric ceramics considered here. B. polarize by pressing, extrusion or stretch casting and thereby piezoelectric initially brought to an oversize and then obtained according to properties that are retained after the removal of the firing by grinding and polishing finished field. Such ceramics are made. The raw disc can, however, also be cut off from the usual perovskite crystal structure and a cylindrical piece of fired ceramic are piezoelectrically more effective than most natural ones. . ., -; '
borrowed piezoelectric crystals. With a suitable forward at the g in the 'F i Auspolarisation shown) 1 and 2 are in particular in the Bleititanzirko- guide for the Scheibe.12 is in the fields of naten remanent electromechanical coupling of between the opposite electrodes 14, 16 to 50 ° / ₀ or more in the plane or radial oscillation 60 and 18, 20 in the axial direction, pre-polarized , which direction of movement is not unusual. Furthermore, arrows -30 are indicated in by the double-headed ^v . Unlike most piezoelectric crystals. B. on the following. Type can be achieved: all ferroelectric ceramic materials in one to the First, the electrodes 14, 16 and 18, 20, polarization axis or direction perpendicular to the plane made of burned-on or air-dried silver are isotropic. Sound box made of such a kera- 65 or the like. Can be applied. Afterwards who mix substance therefore have axial or thickness and the leads 22, 24, 26 and 28 soldered or radial or circumferential expansion oscillation forms somehow differently attached to each one electrode, and on. The circumferential expansion vibration can then be the feeds on the one

5 6

Side of the disk 12 with the one pole of a high of the circuit according to FIG. 3 using the following

DC voltage source (not shown) and the resistance values determined.

Feeds on the other side of the disc with

the other pole of this source "connected. The field resistance 33. '. 1000 ohms

strength; the duration and other conditions are 5 · Resistance 35 1000 Ohm

the special kerä resistance 37 ... '. '.. ·. 5000 ohms. -

mix material adapted. ;: s ": /;; v; '":,' / '; - "."'., ^:

In Figs. 1 and 2, the middle elec- The mode of operation of the transmitter element 10 is correct trode 14 and the concentric ring electrode 18 on as follows: If the disc 12 for basic and upper ones Side of the disc 12 in their position and in ίο resonance in a radial oscillation form in the their area with the corresponding elec- Center frequency of the pass band or at a Trodes 16 and 20 on the other side match and are close to the same frequency. face them directly. The. Area and the. sioned, then call alternating voltage signals Position of the electrodes is important. Because such outside of the pass band no or only one Correlations for different execution cases -15 little effect in the disc 12 emerge and become However, games can be summarized in general and therefore weakened. Frequencies within the pass with the way in which the resonator body works, however, the exit area puts the disk 12 in a strong position , are linked, further details are only given further radial vibrations at their natural frequency (basic below. . 'or harmonic frequency). For applications in the interim.

It should be noted at this point that the output frequency range provides the broad separation of the sum pressure "Concentric ring electrode" on the general and differential frequencies so that the overlying position of the electrode 18 should indicate. This support element only applies to the desired harmonic electrode however, it does not have to be continuous and stimulated.

the middle electrode 14 completely surround, 'but the radial oscillation of the disc 12 generates a it is sufficient if the electrode 18 has approximately the shape of a piezoelectric alternating voltage at the center

C. This makes the feasibility of the frequency or one close to it

Invention not affected. '_ .. "" frequencies. This alternating voltage appears

ReSofiator body according to the ". Invention can the central electrodes 14, 16. By suitable

individually or in groups and alone or in a configuration and dimensioning of the electrodes Connection with the usual electrical switching elements 30 can be a favorable impedance conversion 'and

can be used in the known circuits. Since this increases the voltage of the continuous

the special switching technology does not reach frequencies for the invention. ^;

hears a special circuit and its operation The disc 12 has matching electrodes

described on the basis of a test circuit, which one pairs 14, 16 and 18, 20 and is only between the polarized electrode pairs for measuring the characteristics of the resonators 35. Similar results

can use (Fig. 3). "but you can also use a modified elec-

In FIG. 3, a generator 32 leads the electrode arrangement to be achieved, as shown on the basis of the

nator 10 an input signal of any frequency transmitter element 10 a of FIG. 4 is shown.

to. In a real application this could be The transmitter element 10a includes a disk 12a Input signal z. B. in a mixing stage or in a 40 made of ferroelectric ceramic, which over their

Intermediate frequency amplifier stage of an intermediate frequency polarized whole cross section in the axial direction

quenzempfänger arise. . . is. It only has three electrodes: a middle one

As the F i g. 3 shows, a voltmeter V _{{is used} for electrode 14 and a concentric ring electrode 18 is used to display the input on a resistor 33 on one side of the disk, the corresponding output voltage and a voltmeter V ₀ to display 45 numbered electrodes of the Ausder described first The output example shown on a resistor 35 is the same, and an electrode 16a, voltage. One endpoint of generator 32 and both covering all of the other side of the disc or electrodes (e.g. 16 and 20) on one side of at least most of it. The discs are grounded. The other end point of the polarization can be reached by both generator 32 is completely covered over the resistor 37 with the 50 sides of the disc 12 a with electrodes concentric electrode 18 on the other side. Then either the polarization of the disk and the counter-electrodes in series are removed and new electrodes are placed, 37 and 33 would be connected to earth. The electrode or polarization electrodes are connected to ground via resistor 35. Correct areas removed to obtain the desired "Abs of Fig. 3 it can be seen that the input 55 shape of the operating electrodes. The surface voltage between the concentric electrodes 18 _ of the electrode 16 a should be at least equal to the sum and 20 des The resonator body 10 is applied, while that of the surfaces of the electrodes 14 and 18 are directly opposite the output signal from the central electrodes 14 and electrodes 14 and 18. The and 16 are removed 32 generated signal 60 increase stray capacitance, but otherwise the operations over a range which includes the pass frequency of the characteristics are substantially the same as for the resonator 10, the pass characteristics resonator 10.

ristics of the resonator from the ratio V ₀ / Vt- Another embodiment of the invention is to be averaged. A graphic representation of V ₀ ) Vi the transmitter element 10c according to FIGS. 6 and 7 over the frequency of the input signal for execution 65 It has an example according to the invention arranged on the edge of the disk is shown in FIG. 9 ring or circumferential electrode 34, two middle ones shown and will be explained below. Electrodes 14 and 16 and two concentric rings - The values recorded in Fig. 9 are measured with electrodes 18 and 20 which are numbered accordingly

Electrodes correspond to the embodiments described above. As indicated by the arrows 30, the disk 12c of FIG. 6 is completely pre-polarized in the radial direction by connecting the leads 22 and 24 of the central electrodes 14 and 16 both to one pole of the polarization voltage source and the leads 26 and 28 of the two concentric ring electrodes 18 and 20 connects to the other pole. This leads to a radial polarization between the central and concentric ring electrodes. Then the ring electrodes 18 and 20 are connected together to that pole of the voltage source that was originally connected to the central electrodes, while the lead 38 of the ring electrode 34 arranged on the edge of the disk is connected to the other pole in order to ensure the radial polarization in the; Complete the area between the ring electrodes and the circumference of the disc. A uniform polarity of the polarization field is thus maintained. - - · ..-.

The test circuit of the transmitter element 10c is shown in FIG. 5 shown. On the basis of FIG. 1 to 7 are exemplary embodiments of the invention described, which contain examples of two main features, namely 1. for the direction or directions of the fore ' »Polarization of the ceramic disc and 2. for the electrodes, their number and their shape. It is shown that the disk is axially pre-polarized over its entire cross-section or only between the electrodes or that it can be completely radially pre-polarized. Also can be three, four or five Electrodes are used. Three electrodes, the at least one middle electrode and one concentric one Include electrode are at least required.

The factors which influence the number, area and position of the electrodes are made up the following mathematical treatment of the mode of operation of the resonators according to the invention.

The expressions that are used in the arithmetical consideration are defined as follows:

T _e = tangential or circumferential stress, Tr = radial stress,

Tz = axial stress,

Er = radial field,

Ez = axial field,

g _3l == coefficient of the piezoelectric output voltage with mechanical stress perpendicular to the polarization direction, .g ₃₃ = coefficient of the piezoelectric output voltage ._ with mechanical stress parallel to the polarization direction,

for barium titanate g ₃₁ = -y ^ g ^,
r = disk radius.

In FIG. 8, the functions of the radial and tangential stresses of a thin ceramic disk, which vibrates in the radial direction at the fundamental frequency and the first harmonic frequency, are approximately represented by the curves Tr and Τ _θ . The axial stress Tz, which is caused by the Poisson effect, is very small for thin disks and is therefore shown in FIG. 8 omitted. The solid curves apply to basic resonance. They show that the radial stress Tr is 0 at the edge of the disk and that it is greatest in the middle, where Tr = T _e. The tangential stress Τ _θ at the edge of the disk has a smallest value greater than 0. The stresses T _B and T _R , which are assumed to be positive, are in phase and opposite in phase: to the voltage T _z , which is therefore negative :, . _i: ., Li-. ■ -: ■;,; w'Av:;, ^ ,

In the following, a computational example is given for the case where a disk which vibrates in the radial direction at its fundamental frequency is only prepolarized in its axial direction. This embodiment is shown in FIGS. 1 to 4 shown. The strain curves are the same as the solid curves in F i g. 8, but in this case the axial field is represented by:

= g _3i (Te '+ Tr) + g ₃₃ Tz.

Since gag and T ₂ are phase shifted by 180 ° with respect to g _n , T _e and Tr , no erasing effect occurs, which can occur if the electrode 34 does not have any protruding edges. 3. J-.

By suitable selection of the area and the position of the electrodes, the elimination of the quenching effect and an impedance conversion with an increase in voltage are achieved. The transformer elements described here therefore serve as impedance converters and as electrical wave filters. - ' ^: V

The same applies to transmission elements that are used in work of a harmonic / Fig. 8 shows dashed lines a voltage curve for such a transmitter element. This consists of a disc that in the radial direction in its first harmonic with about 2.5 times the frequency of the fundamental resonance frequency swings. According to the figure, the following states of tension prevail:

1. In the center of the disk with radius r:

(b) Τ _θ Tr are positive maxima,

(c) Tz is negative.

2. For the middle area (πα ² ) of the disc, where

a = 0.4 R,

(a) ΣΤ _Θ and Σ Tr are positive,

(b) Σ Te> Σ Tr,

(c) Tz is negative.

3. At the circumference (2πα) of the middle part of the disk:

(a) Te is positive,

(b) Tr is 0,

(c) Tz is negative ..,

4. For ^ as outer, ', area jr (/ · * -c ^a ) of the disc:

(a) Σ Te is negative ^ - >'

(b) Σ Tr is negative, -

(c) Σ Tr is more negative than ΣΤ _Θ .

Wenrfaiio the disc in the F i g. l or 4 has a central electrode 14 with a radius α of approximately 0.4 times the disk radius r, the ring electrode 20, apart from a narrow gap, covers the remaining surface of the disk, and the disk oscillates in the radial direction in its first harmonic, the axial field is given by

'; Ez = £ 31 (Te + fs) + g _m T _z . . (5)

309 622/215

9 \ 10

Since all the links for the middle part of the disc can be said in summary that the " are positive, there is no quenching effect, and the described transmission elements can be a voltage association achieve very favorable impedance conversion. Strengthening deliver that through an impedance conversion

The above calculation was based on the assumption that is received. The impedance conversion depends on the fact that the disks are thin (e.g. disks with an area and therefore on the capacitance ratio of the diameter from about 5 to 10 times the thickness). Primary and secondary electrodes and from the position in such disks are the axial tensions of the electrodes, which lead to the elimination of the small and therefore mostly negligible fields, the resonance frequency of thin disks is almost negligible. Γ.: ..- '.-,; .- ^ ^ -.-. ^' V. <'..: ■ - ■■ - ^. ^; ^ - ^: - "■■
solely a function of the diameter. The transmission characteristic of a typical transfer element according to the invention can of course also be used in larger thickness disks in FIG. 9; in this case, however, affects the thickness shown. FIG. 9 has been determined with a transmitter element, the resonance frequency and the axial stresses according to FIG. 4, which are not small in its. In particular, when the thickness of the fundamental frequency F ₀ (solid curve) and the disc with its diameter in such a loading -is first harmonic F ₁ (dashed line) is on the relationship that the radial and axial resonance * circuit according to the F i g. 3 works. The radius of the coincident, then also axial stresses occur in the center electrode is 0.4 times the radius of the disc 12a, which are of the same order of magnitude as that and the ring electrode 18 covers the remainder of the radial and tangential stresses. Disc surface except for a narrow gap between

In all axially pre-polarized disks the ao you and the electrode 14 can be seen from the curves

axial field reproduced by that transfer elements according to the invention,

ρ - "(r 4-T \ ν T used as a filter, sharp pass bands, high f \

^ ftiUsTJüMsä ^ · Voltage gain and a high signal-to-noise ratio

A fairly thick resonator disk shows a substantial proportion. According to the four-pole theory, axial stresses Tz can be used and therefore the 95 finally uses several transformer elements to produce filter heights ^ 33 coefficients. '■> networks are united.

1 sheet of drawings

Claims (8)

1 2 - Claims · The invention relates to piezoelectric transfer elements. 1. Piezoelectric transmitter element, whose It is known piezoelectric transmitter elements Sound box made of a pre-polarized kera- with a sound box in the form of a flat one mix material, such as barium titanate or lead 5 to use disk with electrodes to add titanium zirconate in the form of a flat disk for the input voltage and for the decrease, which is covered with electrodes for supplying the input and output voltage. The output voltage and to decrease the output resonance body from plates, which consist of a quartz voltage is occupied, thereby marked crystal at a certain angle to the show that the ceramic body (12, 12a, ao crystal axis has been cut out. 12 c) for a radial waveform .vorpolari- It is also known to use piezoelectric resonance is siert and-dimensioned that it is also in itself body made of a piezoelectric ceramic, i. as is known, either two of the feeder made of a pre-polarized ceramic material or the decrease in electrical vibrations to produce barium titanate and lead titanium zirconate, Serving electrode pairs (14, 16; 18, 20; 26, 28) 15 The known resonance bodies can have longitudinal, or three electrodes (14, 16a, 18; 14, 16, 34) showing bending, shearing or torsional vibrations, one or more of which lead constituent. In the case of the anisotropic quartz crystals, both the input and the output, however, a radial or circumferential expansion oscillation circle are, and that ultimately these electrodes do not stimulate or take advantage of the supply mode. For this are arranged so that on one side 20 are, however, the isotropic ceramic resonance des disc-shaped resonance body which enables the body (see Annals of Physics, Circular electronics covering the central area. 5. Series, Vol. 15, No. 8, pp. 881 to 902). It goes further trode (14) of small diameter and from the French patent 1 117 325 out, concentrically to this, an outer ring electrode to connect piezoelectric transducers made of barium titanate (18, 34), while the other side of the body 25 manufacture its oscillating body as a circular ring is formed either with electrodes (16, 20) from the same plate, but is known in this case education is proven. or only with such a device only to an oscillation in the transverse direction ge-Elekfrbde (16c). . thought. The invention is based on the knowledge 2. Transmitter element according to claim 1, characterized in that when the prepolarized kerage is used, that the ceramic resonance 3 ° mix isotropic material radial or circumferential body (12, 12a) pre-polarized in the axial direction, generate expansion vibrations and allow them to be exploited, is. The invention is based on the object 3. Transmitter element according to claim 1 or 2, the piezoelectric transmitter element described characterized in that the ceramic type with a resonance body made of ceramic Specify resonance body (12c) in the radial direction before 35 material that polarizes small, handy ones is. · Measurements and simple structure in the radial 4. Transfer element according to claim 2, characterized in the vibration mode or as a circumferential expansion vibration, that the resonance body only works ger and a sharply defined frequency between the pass band on both sides, high voltage gain and a opposing electrodes (14, 16; 18, 20) 40 has a high signal-to-noise ratio ″, is polarized. According to the invention is the transmitter element 5. Transmitter element according to claim 1, characterized in that the ceramic body for characterized in that the ring electrode (34 is prepolarized into a radial waveform and be-F i g. 5 and 6) is measured at the edge of the disc, that it is also in a manner known per se föimigen resonance body (12c) is located. 45 either two of the supply or the removal 6. Transmitter element according to claim 1, electrode pairs used for characteristic electrical vibrations characterized by the addition of a further or three electrodes, one of which or concentric to the circular electrode (14 several components of both the input and or 16) and outside of it are the output circle, and that finally this Ring electrode (18, 20 in Fig. 6) on each side 50 electrodes are arranged so that on one of the resonance side polarized in the radial direction of the disk-shaped resonance body one the body. Circular electrode covering central area 7. Transfer element according to claim 1 and 4, small diameter and concentric characterized in that the surface of the circular for this purpose has an outer ring electrode, while the other shaped electrode (14) and the surface and 55 side of the body either with electrodes same Position of the ring electrode (18 or 34) in the training is occupied or only with such relationship to the distribution and phase of the plane electrode. ■ - · '■: · Vibration voltages in the resonance body Such a transmitter element is an electrical one is chosen in such a way that the compensation of opposing wave filters or fields that can be used as an impedance converter is kept to a minimum. ...-. 60 and can be used as a bandpass filter in the intermediate frequency 8. Transfer element according to claim 1, characterized in that the area is formed; it can be used for the most diverse characterized in that the circular electrode forms operating conditions and is characterized (14) a radius of about 0.4 times the radius due to low and relatively high transmission losses of the resonance body and that the ring selectivity is off. electrode (18) essentially the entire remaining 65. The ceramic resonance body can be in Covered area on the same side of the disc. pre-polarized in the axial direction or also in the radial direction being. Another option is to use the sound box only between the