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Патент USA US2406360

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A118» 27» 1946'
w. B. ELLwooD
Filed oct. 4, 1944
Patented Aug. 27, v1946
2,406,3to »
Walterß. Ellwood,r New York, N. Y.,
assîgnor - to
Bell Telephone Laboratories, Incorporated, New
York, N. Y., a corporation of New York
Application October 4, 1944,`Serial No. 557,194
8 Claims.
(ci. 17a-t2)
This invention relates to communication sys
tems and more particularly communication sys
ber 1928, vol. 7, pp, 762-796. See also “Magnetic
hysteresis at low flux densities? by Ellwood, pub
lished in Physics for July 19,35, vol. 6, pp. 215-226,
and “Study of magnetic losses at low flux densi
ties in permalloy sheets” byEllwood and Legg,
tems employing low frequency electromagnetic
An object of this invention is to provide an
improved communication system employing low
published in the Journal of Applied Physics for
or audio frequency alternating magnetic fields.
` May 1937, V01. 8, DD. 313-358.
In accordance with the present invention an
» One possible explanation for theimproved re
improved receiving device is provided capable of
obtained at low ñelds isY that the Bark
responding to extremely Weak alternating cur 10
f hausen steps are much smaller at low iields than
rent electromagnetic fields in the audio Vfrequency
at high ñelds. Consequently, the lmaterial re
range and giving an amplified output. I
to smaller changes‘in' the applied field.
In accordance> with an exemplary embodiment
Furthermore, since the steps are smaller the am
plitude of the noise dueto this-effect is smaller. `
of the present invention an elongated core o-f
magnetic material is placed in the electromag
suitable magnetic material which is provided
When-a magnetic >device >in accordance with
this invention is operated in this region it be
with windings for producing voltages in accord
ance with the electromagneticfñeld. In order to
produces a ,considerablyÁ greater »voltage output
netic field.
The core has a center section of
comes extremely sensitive‘to small applied fields, l
improve the sensitivity of the device ,a source of 20 for said small iields, and produces less noise than
is produced by the magnetic devices of the prior
alternating current is applied to certain of the
windings and the output voltage derived from
other of the windings.
l '
.I-Ioweven since it is necessary to operate the
material at extremely low values- ofapplied field
Magnetic detectors and` amplifiers provided
and flux, it is necessary to accurately. control '
with somewhat similar cores and windings have
the bias or operating point on the magnetization
been employed in the past to detect and produce
curve and to balance out >'the core flux from
amplified voltages in response to electromagnetic
sources other than thesourcefrom which it is
fields. In the devices employed for thispurpose
desired to receive signals. ‘Devices of this-type
in the past, the alternating current or the, alter
:are capable of responding to electromagnetic
nating current field has been sufficient to, or ex 30 iields considerably weakerthan the earth’s mag
ceeded, that required for saturation of the mag
netic field. Consequently, it is also necessary to
netic material. However; the devices of the lprior
balance out the ñux of the earth’s magnetic field
art are not suitable rfor detecting weak fields;
from the core or cores of the present device. In
first, because they are not sensitive to weak ñelds;
to provide the necessary balancing cur
and second, because they generate. appreciable i
rents or voltages, the output of the device is ram
noise which tends to mask or interfere with the
pliiied and the amplified components of ythe out
received signals.
having frequencies below the signaling»y fre
In accordance with the present invention .the
quency, including direct current, are employed
alternating current supplied to the. device does
to neutralize the earth’s field and other stray low
not tend to saturate the magnetic material of -'
frequency fields having frequencies belowf the
the cores employed. Instead the magnitude of
signaling `frequency. .
the alternating current is maintained suñiciently
small so. that the ilux in the material does not
saturate the material or even approachthe so
The foregoing objects and features and other
objects and features of the present invention may
be more fullyunderstood from the following de
called ‘knee” of the magnetization curve. 'I'hel 45
scription of an exemplary embodimentvthereof
magnetic material is operated exclusively in the
low iiux density region where the magnetization
-curve or the hysteresis loop is approximately
defined by Rayleigh’s law. >The manners and
_modes of operation-.of magnetic material'` inthe
lo‘w'- flux reg-ion is described >in greater detail in
La paper kry E.v Peterson entitled “HarmonicPro
yductiomin ferromagnetic materials at` low-fre
quencies an'd low yflux densities”'and published
«inthe Bell' System Technical* Journal for Octo 55
when said description is read‘with referenceïto
Y the drawing-which shows in schematic form the
various elements' which cooperate to -provide an
improved receiving‘device for receiving -audio fre
quency electromagnetic waves. The following de
scription is not in anyway intended to limit or
increase the scope of ‘the claims appended hereto
.which` speciiicallv` point out the novel features
of this invention.
l -
Referring now to the drawing l and 2 repre
to a paper published in Journal of Applied Physics
for May 1937, vol. 8, pp. 313-358 by Ellwood and
Legg entitled “Study of magnetic losses at low
flux densities in permalloy sheets.”
Output terminals 23and 24 areconnected to» '
¿band-pass filter II. The bandfpass filter II may
be of any suitable type and as shown in Fig. 1 is
frequency or frequency range but may be em
designed to pass a frequency lrange of from 940
cycles to 1060 cycles. This band-pass filter is em
ployed to prevent the higher harmonics and ex
ployed'in magnetic fields of any suitable fre
quency. Inasmuch as such low frequency fields,Y
are frequently employedl in communication be
“Magnetic hysteresis at low flux densities” and
sent an elongated core of magnetic material.
This core is placed in the region where the mag-1
netic field is to be detected. For the purpose of
illustration, it is assumed that it is desired to
receive an electromagnetic field of 25 cycles. It
will be apparent to persons skilled in the art that
the invention is not limited to any particular`
traneous noisekfrom affecting the operation of
the remainder of the system. Band-pass filter I I
may be of any suitable type typical examples of
15 whichr are described in detail in United States
>-Patents 1,227,113 and 1,227,114 granted to Camp
tween ships the core will be madeY relatively long> y
and mounted aboard ship preferably above- deck
and away from the major portionV of the magnetic
material and structure of the ship, as -for example,
10 to 15 feet above the Ideck of the ship.' When
desired this coreand coil structure vmaybe made '
in the form of a cable and towed by the ship.
It may be necessary to float the device inquiet
water if extreme range is desired.
bell onMay 22, 1917, or any ,suitable modiñcation
of such filters. The output of the filter I I is con
nected to an amplifier I2 which is capable of am
The core- is'composed ofv a plurality-of sections
'I,v 2.' and 3, as lshowni'n Fig. 1; ï These core sections
maybe made of ‘any suitable magnetic material
as, for example; any of the various iron-nickel
-alloys-which have a high'permeability at low 25
Imagnetic ñelds.
The core sections I and 2 are separated by cen
ter section 3 comprising a magnetic core having at
least two legs 4 and 5.l The center section 3 is 30
made of magnetic material which possesses eitherl
a'high hysteresis coeñicient or a high rate of
plifying the frequency-band passed'by filter II.
Such amplifiers are well'known and operate in
their usual-manner when> employed in combina
tionwith the other elements of the present in- v
vention. The output of ampliñer I2 is connected f
to thein'put »circuit of a mixer or modulating ‘de
-vice I3. A source of alternating current I0, which
may be 1000 cycles in the specific embodiment
shown in thedrawing, is also connected to the
mixer I3 through a suitable attenuator I4. The
-attenuator I4 may be of any suitable type and
usually comprises a ‘resistance network, certain
elements of which are lusually variable.
Mixer I3 combines the output of amplifier
- change of permeability'witn field at low values of
' applied field or flux or both. A particularly Suit
and the output of the-attenuator I4 Iso as to ob
able type >of core material is' describedin-detail
tain an output which is a product of the input
in the United States Patent 1,768,443 granted toY V35 from theampliñer I2 and the attenuator I4. The
-Elmen June 24, 1930, which -patent is hereby made
mixer or modulator I3V may be of any suitable
part of the present application by reference as
type which are well known as mixers or first de
. if fully' included herein. Howevenit can be shown
tectors in the so-called “heterodyne” or “super
that-'the device is most effective when the per
heterodyne” radio receivers. Receivers of these
.meabilities of sections I, 2 and 3 are high and 40 types are described in greater detail in “Prin
approximately equal while the material of the
ciples of Radio» Communication” by Morecroft,
third edition, 1933, on pages 1035 through 1040,
also pages 634 through' 646 Vand 765 through 774.
.center section 3should have either as high a hys
teresis coeiiicient orf as high .a rate of changeV
of permeability with ñeld as possible or both.
Each of the legs 4 and 540i the center section
Vof the core is provided with two windings, 6 and 8,
“and 1 and 9, respectively. Windings 6 and 1 Vare
vconnected to a source of alternating current .I0
having a frequency which is high compared to the
For more modern mixer circuits reference is made
45 ’to
chapter 15, pages 99 through 114 of “The
ture comprising sections I, 2 and 3„no voltage
if fully included herein. The high-pa'ssïiilter I5
Radiotron Designer’s Handbook,” third edition,
by F. L. Smith.
The output of mixer I3 is connected to two
»ters I5 and I6. Filter I5 is a high-pass ñlter while
~ highest signaling'frequency or vcomponent there V50
fil/ter I6 is a low-pass filter. These two filters
of 'to be transmitted while windings 8 an‘d 9 are
be designed and connected together in any
connected to the receiving system as will-bel de
suitable manner, as for1 example, as described in .
scribed hereinafter.'
greater vdetail in United States Patent 2,076,248
The windings B, 1, 8 and 9 are so connected
granted April 6, 1937 , to Norton which patent' is
relative to each other that when no external maghereby
made a part of the present disclosure a-s
l netic ñeld is applied to the composite core struc
rappears across the output vterminals 23 and v24
of coils 8 and 9 even when the windings 6 and 'I
However, when an 60
. are connected to source I0.
external field is applied tothe core structure com
» prising elements I, Zand 3.a voltage is produced
is connected to an output amplifier I'I which is in
turn connected to anysuitabledetector or receiv
ing :device I8 responsive to the low frequency sig
nallingcurrent.- In the exemplary embodiment
of the. invention described herein this'low fre
quency current may be either a `25 or 50-cycle
current or both depending upon the bias or op
material or due tothe change in the permeability 65 erating point vof the core..y Device I8 may include
any suitable receiver'such as a headset,-sounder,
of the core material orY >both as described in the
-between terminals 23` and 24. This output voltage
maybe due to either theY hysteresis of the core
above-identified publication by Peterson. All. of
the above-identified publications are hereby made
recorder, or printer, as for example,»a printer of
the type shown Lin' United States Patent 1,904,164
V,granted to S. Morton et al. on Aprí1 18, 1933.
70V . Low-pass'iilter I6 is designed to pass all fre
quencies below some cri-ticalY frequencyA which ,
For amore detailed description of the response
a part of ythis application as ifA fully included
of ferromagnetic material in weak magnetic fields
and the application of Rayleigh’s law, reference
is made'to a paper published in Physics for July
.1935, vol.- 6,_ pp.' 215-226k by Ellwood, _entitled
critical frequency is below the desired signalling
lfrequency. Assume’for purpose> of illustration
*thatV filter I6 passes all' frequencies below Y10
cycles. In view of .theifact that the" interfer
ence usually encountered in systemsof this type
Vis ofalow~ frequency; hfghand low-pass `filters to.' separate the. signals< and in.
.terferencac In case high frequency interference
-is alsol encountered a `band-pass flltermay be; em.
.ployed for filter I5 and a band elimination ñlter
for filter I6 as will be readily understood by per
Sonslskilled in the art.
.The output of filter I6 is connected through a
a voltage relatedto the valueof the applied field
is obtained from the _output of «mixerA I3. yThe
high frequencyory signalling component of this
vvoltage passes through the highfpass I5 andam
Aplifier I'I to thereceiver I8 while the lowjfre
yquency component passes- through iilter„|6,`am
`plifier I9, manually controlledpower supply`24,
phase control apparatus 20,> the kmanuallycon
vdirect lcurrent "supply circuit 2| to Wind
manually .controlled directcurrent power supply 10 -trolled
and 21, where* these currents tend to bal
.device 24 to amplifier I9 which. amplifier is a so
ance ,out the steady and low frequency compo
.called direct. current amplifier because itv will i nentsof the applied field.> In this manner.` cores
>amplify. continuous aswell as alternating Acurrent
4 and 5 are in effect subjected to only the signal
.voltages and produce a continuous as well as an
field orV fields having frequencies of the desired
¿alternating current voltagelor vcurrentï- output. 15 signalling
frequency band. In~ this manner itis
output of amplifier. I9 is connected to a
possible to maintain the total fiux through the `
phase control circuit 20 which >is provided to
cores 4 and 5 to an extremely low value and thus
properly control the phase of the current to be
'provide the maximum 'sensitivity for the device.
.fed back t0 the windings 25 and 26 on the core
In case it is desirable to apply a small biaspto
sections I and 2 respectively so the entire detect 20 the core structure lit will be` necessary Ito accu
ing> arrangement will be stable. For a morecom
rately control' the magnitude of the biasso that
plete description of a phase control equipmentv 20
the total net or effective >field applied tothe >core
and the requirements thereof, reference is made
.Will not extend beyond the desired region. Fur
to an article entitled “Relation between attenua
it is necessary toacCurately :control
tion and phase in feedbackv amplifier design,” by 25 thermore,
the operating point to increase the stability and
H. yW. Bode, inv the Bell .System Technical Jour
reliability‘ofv -operation of the device. '
na1,'vol. 19, July 1940, beginning on page 421,
l Inorder to apply a bias to the core source 2|
which article is hereby made a part of the pres
or more usuallyk `24 will bef-adjusted to supply -a
ent application as if fully included herein.
small voltage which will either add to orzoppose
Y As shown in the drawing, the output of the 30 the. earth’s field. , 'I'he veffect. of this vvoltage'will
phasecontrol apparatus 2i)v is connected to a
bereducedl due to the operation of the feedback
manually .controlled> direct current power sup
circuit. However, a small fraction of this volt
ply. In the exemplary embodiment of this inven
age will still be `effective and act as a small bias
tion shown in thel drawing, themanually con
trolled power supply comprisesy two batteries 22
or other suitable source» of direct current and a
manually controlled potentiometer 23.
for the core structure.> , Under these circum
stances the operation. of the. remainder of the‘cir‘
cuits and apparatus rwill be as described above.
Due to the degenerative action of the feedback
arrangement the effect of. small changes in the
manually l.controlled power supplies 2| and> 24
may be employed Ito control the. bias or operating
magnitude of sources 2I vand 24 lare reduced so .
point: of the core ofthe device.. The manually 40 that the bias~ is accurately maintained atpthe
controlled supply 2| may also be used to relieve
desired level and at the. same time the effects. of
the amplifier I9 and the.- remainder of thewsys
tem'> ofv alarge part of the. burden cfproviding the
yvery low frequency and direct current necessary
.to counter-balance the. earth’s field. Usually
supply 2|; will be employed to reduce the output
required froml amplifiery while supply 24 will be
Y ,used to accurately control. the bias or operating
stray fields. and currents, including the earth’s
field, is largely balanced out of the core soits
sensitivity to the desired field or signals will be
In the foregoing description reference has been
made tospecific types of equipment suitablefor
use in combination with the other elements »of
point of thefmagnetic materiall of the core struc
the present invention. Persons skilled'in the art,>
ture of the entire device. If' the device isy located 50 however, will readily appreciate that many otherA
aboard. ship and supply 2| is used to reduce the
types of equipment andA apparatus aresuitable
burden on. amplifier I9 it will be necessary to pro
for the various components of the present» inven
vide a. chart or table or both, showing the posi
, tion and may be employed therein without mate
tion of thee ship.V asv well as its bearing and indi
rial modification. 'I'his invention‘is accordingly
cate the proper setting of the manually con 55 not limited toany‘ of the specific devices specif
trolled power supply system.
ically referred to above.
_f As: -will@ be readily understood »by persons
What is claimed is:
-SkillerlA in' the art, the manually controlled sup
1. In a.> communication system a receiving> de
ply 2l maybe completely eliminated by providing
viceÍ comprising an elongated core of ferromag
properly designed amplifier, ters, and phase 60 netic material, a. center portion thereof having a
control circuitsV if it is so desired.
- high rate of change of permeability with low val
The output of the phase control and manual
.ues ofA field; intensity,V meansV for applying a low
' supply system is connected to' coils 25 and 26
amplitude. high frequency field to said core,A a re
surrounding .the coresections I and 2. respectively
ceiving amplifier, windings'- on said core connect
amt-aire> so.v connected as' to produce a flux which 65 ed to said amplifier, and~ `feed-back;windings also
is in- opposition'r to and neutralizes the flux pro
duced by the4 external magnetic field applied to
thecore structure I, 2 and 3*.,
VAupon. saidcore connected> to said amplifier for
neutralizing the. effects upon. said core of »all
fields applied thereto. except a field having the
>In operation, the core structure I,> 2 and 3 is
same frequency as the signalling frequency of said '
>mountedfin- apositionso as to be subjected to the 70 system and except said high frequency ñe'ld.
-electromagnetic field which itis desired to receive
`2. A receiving device responsive to electromag
from., When.- an external field is applied to this
netic waves. comprising a core' of ferromagnetic
cores structurel voltages will be> induced in leads
material, means for providing a plurality of mag
23 and 24 which voltages are amplified by ampli
neticlpaths through a portion of" said core, apf
ñerlî Iì2î and their dëmodulated by mixer 23 so that 75 'vpar'atusî for applying a low intensity high> fre'
quencyA field tof'each ofsaîd paths in different' di
rections orïphases, loutput -windings interlinking
ingìthe> plurality of said pathsand connected.A so
' that nov output 'potential differenceîis'developed
saidîmagnetic pathsî and. connected in* Vsuch va
manner: that no output voltage is wdeveloped. across
across. the output terminals: thereof. ,whenïn'oï ex
yternall'field is applied tojsaid core; an amplifier
connected to' saidoutput terminal, ya _mixing or
»said windings when no external 'field is applied cn modulating device; connected to 'the .output .of _said
` Vto saidcore, an amplifierconnected to said out-`
amplifier and to said high„f'requencyr :source -for
put windings, 'feedback windings. also interlink?,
developing a voltage having afrequencyiwhich’is
difference between' the 'frequency 1of.- saidzout'saidA amplifier andsaid' feedback windings“ for
put’voltagefand the frequency of said high-fre.
»neutralizing the effects of all external fields upon
»quency current, filter equipment connected to the
lsaid core and; means rendering said=neutralizing` Y output of- said mixing equipment for` selectingthe
windings' ineffective. at the signalling .frequency
signal frequency- 5 thereof, :feedback windings<„also
interlinking said core, connected'equipmentffor
>3. In a telegraph system .9, Vreceiving device
comprising a long core V.of ferromagnetic -mate-`
' connecting said feedbackV winding tosaid feed
` ’ rial, acenter portion thereof having a, plurality
of magnetic paths and composed of ferromagnetic
alloy having a high rate of'change of permeabil
ity atlow values of field intensity, a source of
relatively high. frequency alternating ' current, 20
windings'interlinking said plurality of paths'con-`
nected to said source of high frequency current
-forvapplying to said magnetic paths an alternat-`
fing. current, field of low intensity’ in the; region
`wherethe hysteresis loop of said material is de
fined by Rayleigh’s law, output windings inter
linking said magnetic paths, a receiving ampli-`
back equipment so as to `feedbackall frequencies
exceptlsaid signalV frequency and Íthe, frequency
.of said source, and'phase. control equipment for
causing the phase’of. all l,of thefeedbackcurrents
to substantially'neutralize all _the externalfields
applied to rsaid core exceptÍ the.I signaling-:fre
6. A Vmagnetic-,device responsive to A.magnetic
fields comprising acore'structure-of laminated
ferromagnetic material, a source-.of«¿high .fre
quency alternating currentpower supplyïforlsaid
device, power windings connectedto saidsource
and >interlinking said core, voutput windings also
interlinking’ said core and connected '.to'output
connected to said filter networks, and feedback 3.0 terminals for developing a voltage betweenfthe
output terminals which is'a function of the exter
fierîconnected to said'windings, .filter networks
-connected to( said amplifienia receivingî device
windings interlinking said lcore also- connected Vto `
nal field applied to said core, a mixer or ,demodu- '
said network for maintainingy the total field with
in said magnetic material in Yal1 except lthe sig
nallin'g frequency range and the frequency of
said source within thelregionv wherein the hys 35
and to Vsaid sourceofhigh frequency „alternating
teresis loss is defined by >lìtayleigh’s law.
' 4; In a telegraph system a receiving device
the applied'external magnetic ñeld.
lator connected Vto said outputwinding 'terminals
current for deriving an output havingV a wave
form substantially the samev as the wave' form .of
' "
7..,Asignal receiving device,..comprising a.core
of ferromagnetic material, alternating current
magnetic paths and .composed of ferro-magnetic ,40 power supply windings interlinking said core, 'out'
put windings interlinkingv said core Aand connected
Vallow having 'a high hysteresis coeñicientlfat low
to` develop an output which isfjointly afunction
values of field intensity,l a source of vrelatively
of said’power supply alternating current and all
high frequency alternating current, windings in
other magnetic ñelds to ,which saidcore is "sub
terlinking said plurality- of paths connected to
comprising a long core of ferromagnetic material,
a> centerV portion thereto having a plurality of
said source of high frequency current. for apply
ing'to said magnetic paths Van alternatingcur
-rent field of vlow intensity in the regionk where the
hysteresisY -loop' of said material is defined by
jected, a mixer or demodulator .connected to said
output windings and provided with a power input
terminal for deriving an output having a'wave
form substantially the same* as the .wave »form'of f
the magnetic field to whichsaid core is subjected
1Rayleigh’s law, output windings interlinking said
V`magnetic paths, a receiving amplifier connected 50 vexclusive of the field created by said power sup'
ply windings, feedback windings 'interlinking `said
to said windings, filter networks connected to said
core, filter and phase control networks‘connected
_ampliñen a receiving 'device connected to ’said
>between said mixer andY said feedback windings
filter networks, feedback windings 4«interlinking
Vfor re'ducingfthe field to which said core is sub'
said- core also connected :to said networks for
maintaining the total fieldiwithin said> magnetic 55 jected except for specified> frequencies or fre‘
material in all except the signalling frequency -and
the frequency of said source range within the
' region wherein the hysteresis loss is defined by
quency ranges.
8.- A magnetic device responsive- to external
» magnetic fields comprising a >core of ferromafg- f
vnetic material, a source of Valternating current
of direct current connected in said feedback wind 60 having a frequency which is high compared tothe
frequencies of said external vfield'torwhich said
ings for neutralizing the effect of the constant
,device is responsive, .power windings interlink-v Y
portion of earth’s magnetic field upon said core.
ingv said core, outputrwi'ndings also'interlinking
5. Apparatus responsiveV to electromagnetic
-said core for developing ayoltage which is- a func'
fields comprising a core structure including end
sections and a center.section,'a plurality of mag 65 tion` of the external >field rappliedrto. saidî core,
Rayleigh’s law, and amanually controlled source
feedback windings also interlinking's'aid"core,` a
Yfeedback circu'itsextendingv from'said output tei"
minals- and including said feedbackïwindings'to
current power supply windings interlinking said
supply current to said feedback‘windingsV t‘o »neu
paths through said center section, a source of rel
atively high frequency alternating current', in 7,0 tralize- a portionof the effect of the externalfield
applied. to, Vsaid'c‘ore, a -directA current., source' of
terconnections betweenv said ysource and said
'potentialïconnected in said feedback-circuitîï'to
windings for supplying alrelatively high fre--v
rapplyya bias 'to' saidY core through said feedback
quency alternating current field vof low intensity
to each of said plurality of paths ina different
netic paths extending between each of ' said end
' Ysections through said center section, alternating
,phase> relation, outputj windings „also interlink;
75 ¿l
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