U.S. patent number 3,707,131 [Application Number 05/081,842] was granted by the patent office on 1972-12-26 for electroacoustic transducers of the bilaminar flexural vibrating type.
This patent grant is currently assigned to Massa Division Dynamics Corporation of America. Invention is credited to Frank Massa.
United States Patent |
3,707,131 |
Massa |
December 26, 1972 |
ELECTROACOUSTIC TRANSDUCERS OF THE BILAMINAR FLEXURAL VIBRATING
TYPE
Abstract
A sound opaque mask, contained within a spider-like frame
structure, is assembled in accurate alignment with a piezoelectric
transducer element. The mask is positioned so that only those
portions of the vibrating bilaminar elements, which vibrate in
phase, are exposed to the medium. The piezoelectric elements and
the mating plate portions of the frame structure cooperate to form
a bilaminar flexural vibrating element having combined dimensions
which determine the resonant frequencies.
Inventors: |
Massa; Frank (Cohasset,
MA) |
Assignee: |
Massa Division Dynamics Corporation
of America (Hingham, MA)
|
Family
ID: |
22166742 |
Appl.
No.: |
05/081,842 |
Filed: |
October 19, 1970 |
Current U.S.
Class: |
310/324;
381/173 |
Current CPC
Class: |
H04R
17/10 (20130101) |
Current International
Class: |
H04R
17/10 (20060101); H04r 017/10 () |
Field of
Search: |
;179/11A,179
;310/8.2,9.4 ;340/8L,8FT,10,15 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Claffy; Kathleen H.
Assistant Examiner: Klundert; Thomas L.
Claims
I claim:
1. An electroacoustic transducer of the flexural vibrating type
comprising a single spider-like frame member including a peripheral
rim portion and a central vibratile plate portion connected to said
peripheral rim portion by a plurality of spoke-like members, two
plates of piezoelectric material, one of said piezoelectric plates
being bonded to each opposite surface of said central vibratile
plate portion, a first housing member comprising a perforated lid
portion surrounded by a peripheral rim portion, said perforated lid
portion including a central plate portion and a plurality of
spoke-like members connecting said central plate portion to said
peripheral rim portion, a second and closed housing member
including a peripheral rim portion, means for mounting and
capturing said single spider-like frame member between said
peripheral rim portions of said first and second housing members,
and means for securing together said two housing members and said
single frame member into a unitary structure.
2. The invention in claim 1 wherein said central vibratile plate
portion of said spider-like frame member is square.
3. The invention in claim 2 wherein said central plate portion of
said first housing member is square, and the area of said central
plate portion of said first housing member is less than the area of
said central vibratile plate portion of said spider-like frame
member.
4. The invention in claim 3 wherein said central square plate
portions of said frame member and said first housing member are
spaced parallel to one another with their centers located on a
common axis and one of said square plate portions is oriented with
its sides rotated 45.degree. with respect to the corresponding
sides of the other of said square plate portion.
5. The invention in claim 4 further characterized in that the area
of said central plate portion of said housing member is
approximately one-half the area of said central vibratile plate
portion of said spider-like frame member.
6. The invention in claim 5 further characterized in that the
spoke-like connecting members of said spider-like frame member are
attached to the centers of each side of said central vibratile
square plate portion.
7. The invention in claim 6 further characterized in that the
spoke-like connecting members of said first housing member are
attached to the corners of said central square plate portion
contained within the perforated lid portion of said first housing
member.
8. An electroacoustic transducer of the flexural vibratile type
comprising a spider-like frame member including a peripheral rim
portion and a plurality of central vibratile plate portions
connected to said peripheral rim portion by a plurality of
spoke-like members, means comprising piezoelectric transducer
material bonded to each of said central vibratile plate portions
for generating sonic energy, a first housing member comprising a
lid portion having open spaces surrounded by a peripheral rim
portion, said lid portion including a plurality of central plate
portions and a plurality of spoke-like members connecting said
central plate portions to the said peripheral rim portion, a second
housing member comprising a structure with a peripheral rim portion
which mates with the peripheral rim portion of said first housing
member, means for mounting said spider-like frame member between
said first and said second housing members with said plurality of
said central plate portions in said lid portion of said first
housing member being located in axial alignment with said plurality
of said central vibratile plate portions in said spider-like frame
member.
9. The invention in claim 8 characterized in that said plurality of
said central vibratile plate portions contained within said
spider-like frame members are substantially square.
10. The invention in claim 9 further characterized in that said
plurality of said central plate portions contained within said lid
portion of said first housing member are substantially square and
still further characterized in that the area of each of said
central plate portions in said lid portion are less than the
respective areas of the vibratile plate portions in said
spider-like frame member.
11. The invention in claim 10 further characterized in that said
central vibratile plate portions in said frame member are spaced
parallel to the central plate portions in said lid portion of said
first housing member and further characterized in that the sides of
the plates portions contained within said lid portion of said
housing member are rotated 45.degree. with respect to the
corresponding sides of the vibratile plate portions in said
spider-like frame member.
12. The invention in claim 11 further characterized in that the
area of each of said plate portions in the lid portion of said
housing member is approximately one-half the area of the
corresponding aligned vibratile plate portions contained within
said spider-like frame member.
13. The invention in claim 12 further characterized in that the
spoke-like connecting members in said spider-like frame member are
attached to the centers of the sides of the said vibratile plate
portions.
14. The invention in claim 13 characterized in that the spoke-like
connecting members in said lid portion of said housing member are
attached to the corners of said plate portions contained within
said lid portion of said housing member.
15. An electroacoustic transducer of the flexural vibrating type
comprising a first spider-like frame member including a peripheral
rim portion and a plurality of central vibratile plate portions
connected to said peripheral rim portion by a plurality of
spoke-like members, a second spider-like frame member including a
peripheral rim portion and a plurality of central plate portions
connected to said peripheral rim portion by a plurality of
spoke-like members, and means for holding said first and said
second frame members in fixed spaced parallel alignment with the
center of each plate portion in said second frame member aligned
with the center of each corresponding vibratile plate member in
said first frame member.
16. The invention in claim 15 characterized in that said plate
members in both of said frame members are substantially square.
17. The invention in claim 16 further characterized in that the
area of each of said plate members within said second frame member
is approximately one-half the area of the vibratile plate member
within said first frame member.
18. The invention in claim 17 characterized in that the sides of
the plates in said first frame member are rotated 45.degree. with
respect to the sides of the plates in the said second frame
member.
19. The invention in claim 18 characterized in that the spoke-like
members in said first frame member are attached to the centers of
the sides of said vibratile plate member.
20. The invention in claim 19 further characterized in that the
spoke-like members in said second frame member are attached to the
corners of said plate members.
Description
This invention relates to electroacoustic transducers employing a
bilaminar resonant plate operating at its fundamental flexural mode
of vibration, and more particularly, to simplified structures
having reduced cost.
Reference may be made to a co-pending application Ser. No. 17,430,
filed Mar. 9, 1970 by Frank Massa and Gilbert C. Barrow, entitled
"ELECTROACOUSTIC TRANSDUCERS," and assigned to the assignee of this
invention. The principal effort of the present invention is to
achieve all of the advantages of the earlier invention at a reduced
cost and with a simplified structural configuration.
Accordingly, an object of this invention is to design new and more
efficient, low-cost electroacoustic transducers utilizing a
bilaminar plate operating at a fundamental free resonant mode.
Another object of this invention is to combine a plurality of
bilaminar plate, flexural mode transducer elements, within a very
simple spider-like frame structure. Here, an object is to assemble
the elements within a common housing having a plurality of flexural
vibrating plate transducer elements, each operating in a different
frequency region.
A still further object of this invention is to accurately position
the bilaminar plates within a spider-like frame structure having
plate sections, which form parts of the bilaminar resonant
structures.
A further object of this invention is to provide an inexpensive
housing structure which includes sound opaque masking elements that
cover portions of the vibrating bilaminar resonating elements.
Other objects, features, and advantages will become more apparent
from the following description when taken in conjunction with the
accompanying drawings in which:
FIG. 1 is a plan view of one embodiment of the inventive transducer
construction;
FIG. 2 is a cross-sectional view taken along the line 2--2 of FIG.
1;
FIG. 3 is a plan view of a flat spider-like frame member containing
a square center plate portion for supporting a piezoelectric
transducer;
FIG. 4 is a plan view of another embodiment of the inventive
transducer including a unitary spider-like frame member containing
two independent flexural transducer elements, operating at
different resonant frequencies;
FIG. 5 is a cross-sectional view taken along the line 5--5 of FIG.
4; and
FIG. 6 is a plan view of the flat spider-like frame member
containing two independent square vibratile plate portions of
different sizes, held together by thin connecting spoke-like
members.
In FIGS. 1, 2 and 3, the reference character 10 identifies a
portion of a housing structure which might be fabricated from a
molded plastic material, for example. In the center of the flat
surface of the housing member 10, a square or somewhat
diamond-shaped portion 12 is connected, at its four corners, by
spoke-like members 13 extending to the main peripheral rim portion
of the structure. A second, mating, cup-shaped portion of the
housing structure 14 contains electrical terminals 15 and 16 which
extend through its base, as illustrated in FIG. 2.
A vibratile transducer element is contained within a spider-like
frame member 17 which may be punched from a thin metallic sheet,
for example. A square center plate portion 18 is connected by four
spoke-like members 19 to the peripheral rim portion of the
structure. Four holes are located in the periphery of the member 17
to enable an assembly of the housing portions 10 and 14.
A first, thin square polarized piezoelectric ceramic plate 21 is
rigidly bonded to one side of the central square plate portion 18
(FIG. 3). A second ceramic plate 22 is bonded to the opposite side
of plate portion 18 (FIG. 2). Electrode surfaces 23 and 24 are
formed on the outside surfaces of the ceramic plates 21 and 22.
Electrical conductors 25 and 26 are connected between these
electrodes and the terminals 15 and 16. The other electrode
surfaces on the piezoelectric ceramics 21 and 22 (not seen in FIG.
2) are in common electrical contact with the metallic plate member
18. The polarization of the ceramic plates is such that a
conventional series electrical circuit is achieved by means of the
wiring arrangement shown in FIG. 2.
The complete transducer assembly is achieved by placing the
assembled ceramic and frame member 17 between the housing portions
10 and 14 and securing the structure together by means of four
rivets 27. The assembly just described results in a very low
manufacturing cost for a transducer having the same general
characteristics as the transducer described in the co-pending
parent application Ser. No. 17,430.
As explained in the parent application, the sound mask portion 12
covers those portions of the ceramic 21, 23 which are vibrating
out-of-phase with respect to the vibrations of the uncovered
portions of the ceramic. Thus, the uncovered portions of the
ceramic cause a transmission of in-phase sonic energy. If the mask
12 were not present, much of the transducer energy would be
dissipated by mutual cancellation of the out-of-phase
vibrations.
A second embodiment of the transducer construction is illustrated
in FIGS. 4, 5 and 6. In this design, the housing portion 31 (which
may be molded plastic) contains two separate square or somewhat
diamond-shaped mask portions 32 and 33. These masks are
interconnected by thin spoke-like members extending to the
peripheral rim portion of the housing structure 31 (FIG. 4). A
second cup-shaped housing portion 34 contains electrical terminals
35, 36 and 37, which extend through its bottom surface (FIG.
5).
The vibratile transducer element assembly comprises a spider-like
frame member 38 (FIG. 6) which contains two central square plate
portions 39 and 40, connected by thin spoke-like members to the
outer rim portion of the frame member. One face of the square plate
portion 39 has a large polarized piezoelectric ceramic plate 41
bonded thereto. The face of the square plate member 40 has a small
ceramic plate 42 bonded thereto (FIG. 5).
Split electrodes 43 and 44 are attached to the exposed surface of
the large ceramic plate 41. Similar split electrodes 45 and 46 are
attached to the exposed surface of the small ceramic plate 42. Each
of the ceramic plates has another electrode (not shown) located on
the face of the ceramic plate which is bonded to the metallic
center plate portions 39 and 40. This electrode arrangement is one
of several that might be used and is not necessarily a required
part of this invention. A more complete description of the split
electrode shown may be found in U.S. Pat. No. 3,128,532.
Electrical conductors 47, 48, 49 and 50 connect the various
electrode surfaces of the ceramic plates to the terminal pins 35,
36 and 37 (FIG. 5). For the electrical connection illustrated,
electrodes 43 and 46 are connected to the common terminal 36. It
is, of course, obvious that the electrodes could be connected to
separate terminals if a four terminal arrangement were desired.
Lining the inside bottom surface of the housing member 34 is a
layer of soft sound absorbing material 53 which prevents standing
waves from occurring during operation of the transducer.
In the transducer structure, just described, there is an assembly
of two separate flexural vibrating elements mounted within a common
low-cost housing structure. The resonant frequency of each of the
vibratile transducer elements is determined by the width and
thickness dimensions of the plate members 39 and 40 and the
attached ceramic elements 41 and 42. The resonant frequencies of
the two elements may be widely separated, if desired. Or, the two
resonant frequencies may be adjusted to lie close to one another in
order to achieve a broad band performance by overlapping the
response characteristic of both units.
The final assembly of the transducer (FIGS. 4, 5 and 6) is
completed in the same manner as described above for the embodiment
of FIG. 1. The housing portions 31 and 34 are assembled with the
frame member 38 located with the holes 51 lined up to receive the
rivets 52.
The described construction effectively achieves the mounting of a
resonant square vibratile plate at its nodal points. These point
appear at the centers of the sides of the square bilaminar
elements. The thin spoke-like strips offer negligible restraint to
the vibrating freedom of the transducer element assembly since they
are attached to the nodal points of the square resonating bilaminar
structure.
During the operation of the vibrating plates at the flexural
fundamental resonant frequency, the four corners of the square
bilaminar elements vibrate together and in the same phase. The
amplitudes of the four corners are in phase opposition to the
center portion of the bilaminar square plate.
Therefore, to improve the radiation efficiency of the vibratile
transducer elements, the square or somewhat diamond-shaped masks
12, 32 and 33 follow the shape of the nodal lines on the surface of
the vibratile plates. Thus, by the arrangement of these simple
component parts, only the four corners of the vibratile resonant
bilaminar elements are exposed to the medium. The diamond-shaped
opaque portions of the housing structures 10 and 31 prevent the
out-of-phase radiation from the center areas of the vibratile
transducer elements from neutralizing the radiation from the four
corners of the vibratile plates.
Thus, an inexpensive transducer design is achieved by the
illustrative construction. This construction enables the mass
production of an efficient electroacoustic transducer at very low
cost. Although, only two vibratile elements have been shown in the
dual frequency transducer construction, it is obvious that more
than two vibratile elements may be used. There is no exact limit to
the frequency range over which the described design may be
utilized. However, the design lends itself extremely well for
operational frequencies within the upper audible region or within
the ultrasonic region ranging from approximately 5 kHz to 100
kHz.
While several specific embodiments of the present invention have
been shown and described, it should be understood that
modifications and alternative constructions may be made. Therefore,
the appended claims are intended to cover all equivalents falling
within their true spirit and scope.
* * * * *