US2451967A - Vibrational energy transmitter or receiver - Google Patents

Description

Oct. 19, 1948. A SA 2,451,961

VIBRATIONAL ENERGY TRANSMITTER OR RECEIVER- Original Filed June 2, 1944 v 1 I c l 'o l INVENTOR.

FRANK M A FIG. 6

BY 75A ATTO Patented et. 19, 1948 VIBRATIONAL ENERGY TRANSMITTER R RECEIVER Frank Massa, Cleveland Heights, Ohio, assignor to The Brush Development Company, Cleveland, Ohio, a corporation of Ohio Originalapplication June 2, 1944, .Serial No.

538,469, now Patent No. 2,427,062, dated September 9, 1947.

Divided and this application July 28, 1947, Serial No. 764,099

tion Serial No. 538,469, filed June 2, 1944, now Patent No. 2,427,062, granted September 9, 1947,

for Vibrational energy transmitter or receiver.

An object of the invention is to provide a transducer for radiating and/or receiving vibrational energy which has a directional pattern comprised of a main and minor lobes in which the ratio of the vibrational energy in the main lobe to the vibrational energy in the minor lobes is maximum.

Another object of the invention is to provide new and novel piezoelectric transducers.

It is also an object 01 this invention to provid a new method of manufacturing piezoelectric transducers.

It is also an object of the invention to provide a transducer whose directional patternmay be easily changed.

A further object of the invention is to provide a transducer of simple, practical construction yet which closely approximates certain optimum conditions which are obtainable only with more complicated and expensive construction.

Other objects and a fuller understanding of the invention may be had by referring to the specification, claims and to the. single sheet oi drawing.-

In accordance with this invention there is provided, in a transducer, a substantially circular piston surrounded by a first and by a second annular piston section. The circular piston is adapted to vibrate wtih an amplitude A1, the first annular piston vibrates in phase with the circular piston but with an amplitude A2, and the second annular piston vibrates in phase with the circular piston but with an amplitude A3. The ratio oi thet radii R1, R2 and R: of the circular, first annular and second annular pistons, respectively, is as follows: R1 to R2=6.'76, R1 to Ra=.476; and the ratio of A1 to A: is 1.9, while the ratio of A1 to A: is 5.8. This causes the ratio of the main lobe energy radiated normal to the plane of the pistons to the secondary lobe energy to be a maximum.

In the single sheet of drawing, Fig. 1- diagrammatically represents a circular vibrating piston;

Fig. 2 diagrammatically represents a composite piston comprised of a circular piston surrounded by an annular piston; Fig. 3 represents by a solid line the directional pattern of the vibrating piston of Fig.1, and by a dotted line the directional pattern of the vibrating-composite piston of Fig. 2; Fig. 4 diagrammatically"represents a vibrating piston comprised of a circular piston and two concentric annular pistons surrounding the circular piston; Fig. 5 is a circuit diagram showing one form of my invention, and Fig. 6 is a'circuit diagram showing another form of my invention.

In the past it has been general practice to design transducers for receiving and/or transmitting vibrational energy in the form of a circular piston which vibrates with substantially the same amplitude and phase throughout its area. Such a piston is diagrammatically illustrated by Fig. 1 and it has a directional response pattern which is illustrated by the solid lines in Fig. 3 and comprised oi a main lobe Ill, a secondarylobe H and a tertiary lobe l2. Other minor lobes may be present but for the purpose of illustrating my invention showing them in the figures might only lead to confusion.

In order to obtain a better response pattern than is obtainable from a single vibrating piston (Fig. 1),, the effect ofa composite piston comprised of a central circular piston with an annular piston surrounding it should be obtained, and certain relationships should exist between the radii and amplitudes of vibration of the several parts of the'composite piston. This eifect may be obtained by utilizing separate piston surfaces, or a single piston surface may be driven with a plurality of amplitudes.

When a certain ratio of amplitudes of motion oi the circular and annular pistons exists and when a certain ratio of radii of the circular and annular pistons exists, it is possible to obtain a maximum in the ratio of vibrational energy in the main lobe compared to the vibrational energy in the minor lobes.

In Fig. 2 there is shown a circular vibrating piston l3 of radius R1 and. an annular vibrating piston it having an inner radius R1 and an outer radius R2. If the annular piston It vibrates through an amplitude A: which is less than the amplitude A1 of vibration of the circular piston I3 and the main lobe of the polar distribution pattern will be somewhat broadened as is shown by the dotted line Ill in Fig. '3, and at the same time the secondary lobes as illustrated by the reference characters II and I2 will be mate-- rially reduced in sensitivity. The optimum detained.

sign for a transducer having a composite vibratins surface comprised of the'circular piston 03 and one annular piston it is as iollows: The ratio of the amplitude or movement A; of the circular piston 58 to the amplitude of movement A: of the annular piston it should be about 2.4. The ratio of the radius R1 of the circular piston to the radius R: of the annularpiston it should be about .607. When these two ratios exist the vibrational energy in the main lobe iii of the directional pattern of the transducer compared to the vibrational energy in the minor lobes ii. 62 of the directional pattern is a maximum. For example, if the directional pattern Ml, ii, it has an 18 db. reduction between its main lobe it and its secondary lobe ii, the directional pattern it,

i, 82' obtained from a transducer having the optimum design ratios will have approximately 32 db. reduction between'the peak of its main lobe ill and the peak of its secondary lobe ii.

The three-section piston surface diagrammatically illustrated by Fla. 4 should have the following ratios of radii and amplitude of movement in order to obtain the best directional pattern. The ratio between the amplitude A1 of movement of the circular piston I3 and the amplitude A2 of movement of the first annular piston It should be about 1.9, and the ratio of the amplitude A1 of movement of the circular piston is to the amplitude A: of movement of the second annular piston I B should be about 5.8. The ratio of the radius R1 oi the circular piston to the radius R: of the first annular piston should be about .676, and the ratio of the radius R1 to the radius R3 of the second annular piston is should be about .476. When these ratios exist there will be approximately 38 db. reduction in signal intensity between the peak of the main lobe and the peak of the secondary lobes.

It'is also possible to design transducers having more than two annular piston portions and a slightly better directional pattern will be ob- However, the improvement over the three-section composite piston surface is not such as to warrant the added manufacturing cost of such a unit unless special results are desired.

The improvement arises from the main lobes of the response patterns of the circular and annular pistons reinforcing each other while the secondary lobe of the response pattern of the circular piston and the tertiary lobe of the response pattern of the annular piston tend to cancel each other as they are out of phase. Thus, in order to obtain the maximum improvement the magnitudes of the secondary lobe of the response pattern of the circular piston should be the some as the magnitude of the tertiary lobe of the response pattern of the annular piston. The secondary lobe of the response pattern of the annular piston is reduced in magnitude to a point below the peak of the secondary lobe of the response pattern of the composite piston as the main lobe of the response pattern of the circular piston is out of phase with the secondary lobe of the response pattern of the annular piston and partially cancels it.

The optimum ratios for a two and a threesection composite piston are given and there is illustrated by mathematics the method of designing a two-section composite piston. A person skilled in the art will then be able to design 'a composite piston having more than two sections.

The amplitude of a sound wave at a. point P distant from a sound source making an angle 0 with the normal to the plane of the circular piston may be expressed by the following well-known equation:

i J1UW'1 sin Amplitude at P-Ai r, and the amplitude of a sound wave at the point P distant from the sound source making the angle a with the normal to the plane of the annular piston may be expressed by the following welllmown equation:

Where A the amplitude of movement of the circular piston r =the radius of the circular piston A3=th8 am litude of movement of the annular piston r =the ra ius of the annular piston J Bessel function k 2w 21f c where f=frequency c=velocity of sound in the medium The amplitude of the sound wave at point P due to the composite piston therefore is: Eq. (1)

has maxima for z=o; 1.6381; 2.6661; 3.694,; The flrst term in Eq. (2) will have its secondary maxima at 1.6381 101' The second term in Eq. (2) will have its tertiary maximum at kn sin 0=1.638w or sin 0= To reduce the secondary maximum of the response pattern of the composite piston source as much as possible the secondary maximum of the response pattern of the circular piston is made to coincide in space with the tertiary maximum of the outer annulus which is out of phase with the secondary maximum. This means that the angles are made to coincide or, expressed mathematically:

Another condition which must be satisfied is that the ratio of the combined amplitudes of the Bessel functions at angle zero to the combined amplitudes at the angle at which the secondary and tertiary maxima coincide shall be a maximum.

From Bessel tables we and:

Substituting in Eq. (2)

schematically shown in Fig. 2, is to connect all of the crystal elements 25 comprising the circular piston portion of the transducer in parallel to a voltage source V1, and to connect all of the crystal elements 26 comprising an" annular piston to a voltage source V2. The crystal elements 25 are equivalent to the crystal elements 28 in size and thickness, but V1 is greater than V2 in accordance with the desired amplitude ratio A1 to A2; 1. e. for a two-section piston V1=2.4V2. and for a three-section piston having three banks of crystals V1=1.9V2=5.8Vs.

Fig. 6 illustrates another method for obtaining different amplitudes of vibration. The expander crystal elements 28 comprising the center portion of the diaphragm are longer than the expander crystal elements 21 comprising an annular portion of the diaphragm by an amount determined by the desired amplitude ratio, and all are-connected in parallel to a single source of voltage. Thus, the longer crystals 28 will. vibrate with greater amplitude than the shorter crystals 29, in accordance with the ratio of their lengths.

Other methods such as varying the thickness of the crystals and various combinations of the which specifically claims the two-section composite transducer.

While the invention has been described with a certain degree of particularity, it is to be understood that the illustrated means are by way of I example, and that changes may be made in the construction and arrangement of parts without departing from the spirit and scope of the invention.

I claim as my invention:

In a transducer for radiating and/or receiving vibrational energy and having mainand secondary directional lobes, a substantially circular piston of radius R1, a first substantially annular piston 01' inner radius R1 and outer radius R: surrounding and lying in the same plane as said circular piston, a second substantially annular piston of inner radius R: and outer radius R: surrounding and also lying in the same plane as said circular piston, said circular piston being adapted to vibrate at a given frequency with an amplitude A1, said first annular piston being adapted to vibrate in phase with said circular piston with an amplitude A2, and said second annular piston being adapted to vibrate in phase with said circular piston with an amplitude As, the ratio of R1 to R2 being substantially .676, the ratio of R1 to R3 being substantially .476, the

, ratio of A1 to A: being substantially 1.9, and the ratio of A1 to A: being substantially 5.8, whereby the ratio of the main lobe energy radiated substantially normal to the plane of the said pistons to the secondary lobe energy is maximum.

FRANK mesa. REFERENCES vcrrm) The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,407,329 Turner Sept. 10, 1946 FOREIGN PATENTS Number Country Date 279,878 Great Britain Mar. 8, 1928

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