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Патент USA US2138036

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Nov. 29, 1938.
Filed Sept. 9, 1933
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FIG. 3'
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wi/ly ffunze
Patented Nov. 29, 1938
Willy Kunze, Bremen, Germany, assignor to Sub
marine Signal Company, Boston, Mass., acor
poration of Maine
Application September 9, 1933, Serial No. 688,770
In Germany December 24, 1932
3 Claims. (Cl. 177-386)
The vpresent invention relates to underwater They are consequently very well adapted for
sound receivers and transmitters and more particularly to such instruments employing piezoelectric crystals.
In the past the piezo-electric properties of
quartz have been employed for sending and re-
noise reception. If they are to be used for sig
ceiving sound waves in water. However, quartz
instruments have had a number of disadvantages
which were particularly noticeable when used for
10 receiving. On the one hand, the piezo-electric
effect of quartz is comparatively weak so that
great ampli?cation had to be resorted to in order to obtain the necessary results. On the other hand, quartz is a comparatively expensive ma15 terial which usually can be obtained in only rel-
with the signal frequency.
Rochelle-salt crystals are soluble in water. It
is for this reason necessary to place them in a
watertight housing. The crystals are preferably 10
cut to provide two surfaces which are perpendic
ular to an electrical axis and to permit the com
pressional wave vibrations to act upon the sur—
faces. The receivers can be so built that only
one surface is acted upon by the pressure waves 15
atively small crystals which, therefore, must be
while the other surface of the crystal is rigidly
assembled by special means in a mosaic fashion
fastened to a fixed mass in the housing, or al
to produce senders or receivers of reasonable
size. Practical results can only be obtained with
20 quartz if the natural resonance of the crystals is
made use of.
It has been known that substantially better
nal reception, then care must be taken by suit
ably dimensioning the crystal with respect to the
cooperating metal elements that oscillatory sys- 5
tems result whose natural frequency coincides
piezo-electric operation can be obtained with
certain other crystals, for example, of such salts
as sodium potassium tartrate which are also
known as Rochelle-salt crystals. Experiments
have shown that the use of Rochelle-salt crystalsv is particularly advantageous for receiving
sound in water.
One object of ‘the present invention is to provide for submarine sound senders and receivers
a means for utilizing the piezo-electric effect of
Rochelle-salt crystals for the transformation of
compressional vibrations into electric vibrations,
and vice versa. Rochelle-salt crystals can readily be produced in comparatively large sizes and
are relatively cheap. Theirs special value lies,
however, in the fact that as compared with the
piezo-electric materials which have been used
in the past Rochelle-salt crystals produce especially energetic effects.
The conditions attending sound transmission
under water are not accompanied by compara-
tively large amplitudes of the medium with rel45 atively small pressure changes as is the case in
air, but vice versa with'large pressure changes
and small amplitudes. For this reason a Rochelle-salt crystal is particularly advantageous
since it responds well to pressure variations, and
50 it is especially good for underwater sound receivers. Since these crystals have no natural
frequency in the audio frequency range, it is possible by means of these crystals to build submarine sound receivers which can receive over the
ternatively both surfaces may be arranged to
be acted upon by the pressure waves in the wa
Further features of the invention will be ap
parent from the description of the arrangement
shown in the drawing in which Fig. 1 shows a
double diaphragm transmitter or receiver and
Fig. 2 shows a plan view looking at Fig. 1 from
the bottom; Fig. 3 shows in vertical section a
modi?cation of the device shown in Fig. 1; and
Fig 4 is a horizontal section of the modi?cation
shown in Fig. 3; Fig. 5 shows a further modi?ca
tion in which a single thin rubber diaphragm is
used to conduct the vibrations to and from the
crystals and the water.
A simple construction of a Rochelle-salt sender
or receiver is shown in Fig. 5 in which the radiat
ing surface of the crystal is covered with a thin
rubber diaphragm which protects the crystal
chamber from the water. A rather massive pot
shaped metallic housing I contains the crystal
2 which is mounted so that one surface 3 is rig
idly held against the back wall of the housing
which is in the form of a rigid mass. The other
surface 4 projects slightly from the opening of
the housing. The surface 4 is covered by a dia
phragm 5, for example, of rubber whose outer
edge is tightly clamped to the housing by a 45
clamping ring 6. Care is taken that there is
substantially no space between the crystal and
the walls of the housing in which a pressure re—
lease could take place. Two metal plates 1, for
example, in the form of leaf springs, press light- 50
ly against the crystal and act as electrodes. They
are fastened to the housing by means of insulat
ingmembers 8. Two conductors 9 and I0 lead
out of the housing and connect with cable ll.
55 entire audible frequency range without distortion. ,
Sound waves in water striking the rubber dia- 55
phragm 5 are transferred to the crystal 2 and
by virtue of the piezo-electric e?ect produce cor
responding electrical potential variations at the
electrodes 7, which are conducted to an amplifier
and made audible in this manner.
If the two conductors are connected to the
terminals of an alternating current source, thev
receiver may be used as a sender.
To increase
the piezo~electric effect while receiving it may
be desirable to apply to the electrodes a polariz
ing potential. It should be noted, however, that
the diaphragm 5 produces in itself a de?nite
constant initial pressure upon the crystal, there
by giving it a pressure polarization.
If the surface covered by the crystal is suf
?ciently large, one obtains a sharp directional
effect, that is to say, when the wave length of
the sound is small with respect to the dimensions
of the diaphragm.
A double~diaphragm instrument is shown in
Figs. 1 and 2. In these ?gures I is a rigid hous
ing closed at one end by a piston diaphragm 2
forming part of the housing and closed at the
other end by a cover II which also forms the
piston diaphragm 3. Between the piston dia
phragms is mounted the Rochelle-salt crystal 5.
6 and ‘I are electrodes, for example, thin metal
foil mounted on the crystal by suitable adhesive
and connected to the conductors 8 and 9 which
serve to conduct electric energy to and from the
crystals. The inner surfaces of the piston dia
phragms 2 and 3 are separated from the crystal
by insulating layers I 0 and are pressed tightly
against the crystal by the tension of the dia
It will be noted that the areas of the dia
phragms are large compared with the areas of
the active surfaces of the crystal. This has the
effect of greatly increasing the sensitivity of the
device when used as a receiver.
‘The increased sensitivity by virtue of the
larger radiating surface can also be obtained by
means of the modi?cation shown in Figs. 3 and 4.
In this case the radiating surfaces are semi
cylindrical in form. In Figs. 3 and 4 the
Rochelle~salt crystal 5 is mounted between two
semi-cylindrical‘rigid bodies II. On the other
hand, the members II may be made of insulating
material. The members are held together by a
shell I2 which may be of rubber and designed
to press the members II tightly against the sur
faces of the crystal 5. I3 and III are two metal
plates which serve as holding members for the
shell I2 which is clamped to them by means of
55 the rings I‘! and I8 which press the shell I2
into grooves I5 and IS in the members I3 and I4.
The whole arrangement is in this manner made
It will be observed that the curved surfaces
30 of the members II serve as radiating surfaces
while the internal surfaces of the members II
are made ?at and are pressed against the crys
In order that the members II may each
vibrate as nearly as possible as a whole and
transfer the pressure with best e?lciency to the
crystal 5, they are separated by a small air space.
However, the use of the shell I2, as shown in
Figs. 3 and 4, is thought to be preferable and
avoids the necessity of ?lling the spaces between
the members II, so that they can vibrate freely.
In the devices according to the present inven
tion care should be taken to avoid any looseness
between the diaphragm and the crystal or be
tween the crystal and the back plate in order that
the pressure variations may be e?iciently trans
ferred to the crystal. To this end the crystal
may be mounted on the housing or the diaphragm
by a suitable adhesive or by other suitable means.
It has been found that with the described de
vices distortionless reception with sumcient sen
sitivity may be obtained up to 20,000 cycles per .
second. The devices are therefore particularly
useful for the receipt of frequencies in the
vicinity of or above the audible range. They
are also useful for noise reception on account 10
of their large frequency range. Whenever it is
necessary that the received sound vibrations be
transformed into electrical vibrations with as
nearly the same phase relations as possible as is,
for example, the case with group of the so-called
multispot listening arrangements, the receivers 15
according to ‘the present invention are partic
ularly advantageous.
Also when used in a device towed by a moving
vessel, for example, in which a plurality of re 20
ceivers are arranged in a straight line at equal
distances from one another, the receiver accord
ing to the present invention is of particular ad
vantage on account of its freedom from disturb
ing noises. In this case the individual receivers 25
are preferably enclosed within a common shell
as, for example, a rubber housing which protects
the receivers from the water and holds them at
the proper distances from one another.
It will be understood that the present inven
tion may be used for producing sound waves in
water by applying a potential to the electrodes.
Having now described my invention, I claim:
1. A compressional wave submarine sender or
receiver comprising a. housing closed at one end 35
by a heavy mass and having an opening at the
other end, a Rochelle-salt piezo-electric crystal,
having electric and compressional axes, mounted
therein in contact with said mass and with its
compressional axis perpendicular to the plane of
said opening, a yielding rubber-like diaphragm 40
in contact with said crystal and covering said
opening, said diaphragm having a thin portion
between the place of contact of the crystal and
the edge of the opening, and means for conduct
ing electric energy to or from the electric axes 45
of said crystal.
2. A compressional wave submarine sender or‘
receiver comprising a. housing closed at one end
by a heavy mass and open at the other end, a
Rochelle-salt piezo-electric crystal having elec
tric and compressional axes mounted so that one
compressional surface abuts said end mass and
its opposite surface projects slightly through said
opening, a rubber sheet, means for stretching 55
said sheet over said opening and said projecting
crystal surface, whereby the crystal is pressed
?rmly against the end mass of the housing, and
means for conducting electric energy to and from
said crystal.
3. A compressional wave submarine sender or
receiver comprising a casing having a heavy back
wall and heavy sides and open at one end, a
Rochelle-salt piezoelectric crystal substantially
?lling the interior of the casing and supported
against the back thereof, said crystal having its
compressional axes normal to the casing and
extending substantially to‘ the end surfaces of
the sides thereof, a thin yielding diaphragm
covering the open end of said casing and means 70.
clamping said diaphragm in position, said clamp
ing means extending substantially to the edges
of the inner wall of said opening.
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