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Патент USA US2263902

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Patented Nov. 25, 1941
ST? .S
William- Spencer Percival, Ealing, London, England, assignor to Electric &, Musical Industries
Limited, Hayes, Middlesex, Engi‘and‘, a company
of GreatBritain.
Application February 2, 1939,.Serial.No'..254>,l_71
In Great-Britain February 8, 1-938
5 Claims. ((31; 178-44)
mission of high; frequency signals and according
This inventionv relates to delay devices and
to the‘ invention an. electric time delay device
is of general application: in obtaining delay in
the transmission of electric oscillations repre
senting signal or controlling voltages.
High frequency signalling transmitting and
receiving systems sometimes include delay net
works which are required for example when the
comprises a: quartz crystal. for generating super
sonic waves in aliquid through which saidwaves
are transmitted and then' detected‘ by another
quartz crystal, the delay in transmissionv being
determined by the. distance. through the. liquid
between the crystals. Water or kerosene have
been found to be suitable liquids for‘ the. purpose
of the invention. The crystalsshould; have the
same or substantially. the: same resonant fre
quency and provision may‘ be made. to» ensure
order that the transmission times of the separate
an‘ unimpeded path through the liquid. between
channels shall be equal, a delay network is placed
the‘ crystals in order to-reduce or avoid. reflec
‘in the channel having the shorter transmission
15 tion of the supersonic waves.
Again, in the interference.- suppression system
The liquid container may be tubular: in shape
described in the speci?cation of British Patent
or narrow in one dimension and wide in another
signals are passed through separate channels,
the outputs of which are subsequently com
bined and the time of transmission through one
channel is different from that in the other. In
#468,994, for “Improvements in. and relating. to
or wide in both dimensions. The effective length
of’ the liquid container will, of‘ course, depend
transmission systems,” accepted July- 8, 1937, an 20 upon the amount of‘ delay required. If any of
auxiliary channel supplied with interfering sig
the dimensions other than those of the length
nals provides a controling voltage which serves
are notv small compared with the length it‘ is
to switch off the main signal channel and in
desirable- to take steps to reduce re?ection of
order that the controlling voltage shall be ap
the waves passing through the-liquid. Such re
the reduction of interference in electrical signal
plied to the main channel at the desired in? 25 ?ection can be reduced» or- eliminated by cov
stant, the delay in the auxiliary‘ channel due
ering the walls of'the liquid container with a
to the selective and voltage generating circuits,
suitable absorbent material such as wool or' cork
is compensated in the main channel by the pro
or alternatively the inside- of’ the‘ liquid‘ container
vision of a delay network capable of passing a
may‘ have a number of narrow" slots or holes
30 formed therein- so that the- waves passing into
band of signal frequencies.
In low frequency volume compression or ex
the slots or holes are rapidly absorbed;
pansion systems, it is necessary to generate a
a number of sheets of" absorbent material may
controlling voltage proportional to the compres
be hung in the liquid so as to leave clear a
sion effect introduced and in such systems delay
line between the quartz crystals.
in the auxiliary circuits provided, again has to be 35
to obtain a large delay in a com
paratively small volume of liquid the container
In the speci?cation of U. S. Patent application
may be divided into a number of compartments,
Serial No. 223,911, ?led Sept. 8, 1938, for “Sig
space being left alternatively at each end of
naling system,” by William S. Percival, now U. S.
Pat. #2219936, patented Oct. 29, 1949, there 40 the container so as to provide re?ecting surfaces
is described a wave ?lter system in which pro
vision is made for selecting from a range of
signal frequencies a frequency band of given
width and subsequently including said selected
for the supersonic waves which are thus re?ected
into the adjacent compartments. Such a con
struction is shown diagrammatically in the ac
companying drawing in which I represents a
band within said range, the output from a ?lter 45 liquid container, 2 a tortuous space in the con
employed to elfect the selection of the smaller
band being subtracted from said range. The
whole of the frequencies in the range are in cer
tain cases delayed before the subtraction is ef
tainer in which kerosene or water is placed,
quartz crystals 3 and 5 being arranged at 0p
posite ends of the space 2. The approximate
path of travel of the supersonic waves gener
fected by a period equal to the time delay of the
ated by the quartz crystal 3 to the crystal 4 is
shown by the dotted line 5.
Assuming a velocity of the supersonic waves
of 105 ems/sec. a distance through the liquid of
10 cms. will give a delay of 100 micro seconds.
The delay may, of course, be varied by adjusting
The delay networks employed may con
sist of ?lter sections including inductance and
capacity in known combinations.
The object of the present invention is to pro
vide apparatus for producing delay in the trans- .
the position of one or other of the quartz crystals
3 and 4 along the length of the path 2.
2. The method of obtaining a large time delay
in the transmission of electric oscillations cover
The delay obtained by the use of the device
described can be advantageously utilised for most
purposes by employing a carrier wave of, for eX
transmitting said oscillations through a liquid
ample, 10 megacycles per second which carrier
wave can be modulated by the signal it is desired
to delay.
The use of a modulated carrier wave
is desirable owing to the relatively rapid change
of attenuation with frequency and owing to the
resonant character of the quartz crystals. If a
wider frequency band is desired than can be
obtained by means of the natural damping of
the quartz crystals by the liquid then the natural
frequency of the two crystals can be “staggered”
ing a wide band of frequencies which consists in
indirect path between a transmitting and a re
ceiving quartz crystal source, the ?uid volume
of said path being small as compared with the
length of the time delay path which is determ
ined by the distance through the liquid between
the transmitting source and the receiving source.
3. An electric time delay device comprising a
casing member, a liquid within said casing, a
pair of quartz crystals located within said casing
member, one of said crystals arranged for gen
erating supersonic waves in said liquid through
to obtain a relatively ?at response over a wide
which said waves are transmitted and subse
pass-band. The device described enables delays
quently detected by the other quartz crystal, a
labyrinth having slanting side walls creating a
to be obtained of the order of several hundred
micro seconds with a pass-band of one mega
cycle or more.
A particular application of the invention lies
in the system described in the speci?cation of
co-pending U. S. Patent application Serial No.
228,911, now Patent No. 2,235,018, March 18,
1941, the device taking the place of the delay net- works consisting of ?lter sections including in
ductance and capacity as indicated in that speci
?cation. The device can, however, replace any
delay network when a long time delay covering a
wide pass-band is required. In such cases it will
generally be desirable to include either a modu
lating and demodulating device respectively be
fore and after the delay in order to change the
frequency band to within a region of the order
of, for example, 10 magacycles. Alternatively, '
an oscillator may be used to heterodyne the
signal to be delayed to the required frequency.
' I claim:
1. An electric time delay device comprising a
?rst piezo-electric crystal for generating super- sonic Waves in a liquid, a second piezo-electric
crystal for detecting said waves, a structure for
increasing the length of time delay path, a liquid
within said structure through which said waves
are transmitted, said ?rst crystal located at one
end of said delay path, said second crystal 10
liquid relatively long indirect path of varying
volume and located within said casing, the time
delay in transmission being determined by the
distance through said liquid path, labyrinth and
between the crystals.
4. An electric time delay device comprising a
casing member, a liquid within said casing, a
labyrinth having slanting side walls creating a
liquid relatively long path of varying volume and
located within said casing, a pair of quartz
crystals located within said casing, said crystals
having substantially the same resonant fre
quency as the waves which are to be transmitted,
one of said crystals arranged for generating the
frequency to be transmitted through said liquid
path contained Within said labyrinth, the other
crystal being arranged to receive said waves, the
time delay being determined by the distance
through said liquid path within the labyrinth and
between the crystals.
5. An electric time delay device comprising a
?rst piezo-electric crystal for generating Waves
in a liquid, a second piezo-electric crystal for
detecting said Waves, a casing member, a plu
rality of partitions within said casing which form
a tortuous space to provide a relatively long in
direct liquid path, the opposed surfaces of said
partitions being shaped to act as re?ectors to
ensure unimpeded re?ection of the transmitted
waves from said ?rst and second piezo-electric
cated at the other end of said delay path, a plu
rality of partitions and re?ecting surfaces with
in said structure to form an indirect time delay
path, and means within the Walls of said struc 50
ture for absorbing undesired re?ection of said
waves passing through said liquid.
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