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Патент USA US2407202

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Sew 3, 1945-
‘ VAL VACQUIER
2,407,202
APPARATUS FOR RESPONDI-NG 'I'O MAGNETIC FIELDS
Original Filed July 21, 1941
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ATTORNEY
Patented Sept. 3, 1946
- 2,407,202
UNITED STATES. “PATENT oFFicE
2,407,202 1
A APPARATUS FOR RESPONDING T0
‘
MAGNETIC FIELDS
Victor V. Vacquier, Garden City, N. Y., assignor to
,
Gulf Research & Development Company, Pitts
burgh, Pa., a corporation of Delaware
Original application July 21, 1941, Serial No.
403,455. Divided and this application July 17,
1945, Serial No. 605,550
6 Claims.
1
I
-
2
_
This invention relates to improvements in ap
paratus ‘for responding to magnetic fields and in
particular it concerns improved apparatus which
responds to» and measures the space gradient of
a magnetic ?eld.
4
(01. 1714-380) -
-
The instant application is a division of my co
pears in the output circuit. Such a system prop- '
erly modi?ed has been used to measure mag]
netic gradient, but this apparatus is in practice
seriously lacking in sensitivity. ,
5
Among the objects achieved in this invention
are the provision of an apparatus adapted to re- .0
spond to the gradient of a magnetic ?eld, char
acterized by an extraordinarily high sensitivity,
which, however, is accompanied by reliability and
magnetic ?elds.
'
In many arts it is desired to'produce an elec 10 insensitivity to mechanical shocks and vibrations;
theprovision of such an apparatus the output of
trical signal or impulse in accordance with rela~
which is independent of acceleration; the provi
tively small changes inmagnetic ?elds. For ex
sion of such a device adapted for accurate quan
ample, in detecting submarines from ships or air
titative measurement of magnetic ?eld gradient;
planes, a device is desired which will produce a
pending application, Ser. No. 403,455, ?led July
21, 1941, entitled Apparatus for responding to
usable electric signal on the rather small change 15 and thev provision of such an apparatus involving
use of magnetically susceptible transformer cores
in local magnetic ?eld due to the relatively dis
in which error due to residual magnetism in the
tant iron mass of the submarine, and a similar
cores is avoided.
need arises in military mines intended to set off
The present invention makes special applica
explosives on approach of a vehicle or ship within
a predetermined distance. Inaut‘omatic ship or 20 tion of the knowledge that a core of material or
high permeability and low energy requirement for
aircraft piloting apparatus it is desired to pro
vide a device responsive to the earth’s magnetic a saturation (Hypernik, Mu-metal or Permalloy,
for example) exhibits a hysteresis loop of peculiar
form; and upon the discovery that the unique
direction in such ?eld. Similar problems arise 25 ?ux-?eld relation can be taken advantage of, by
suitable expedient§§~ to a?ord a magnetically re
in magnetometry, involving investigation of the
sponsive circuit of extraordinary sensitivity; a
magnetic fields of metallic or non-metallic speci
?eld and capable of producing an electric signal
on a small deviation from some predetermined
mens, or of the earth's ?eld as in prospecting " ‘ sensitivity of the order of 10 to 100 times that
attainable with the most highly perfected ap
work. In measurements of magnetic gradient an
instrument sensitive to differences of magnetic 30 paratus of the prior art known to me.
In detail, oscillographic studies show that on
field is required. ‘
periodically magnetically energizing a small, thin
Magnetic ?eld responsive apparatus of various
core of high permeability alloy, to saturation, the
types have been proposed. Most apparatus here
hysteresis loop exhibits a sharp knee at'the sat
tofore known has su?ered from a lack of sum
uration point. The magnetic flux changes very
cient magnetic sensitivity, or has been unduly
35 rapidly with applied ?eld and then suddenly be
sensitive to mechanical shocks and vibrations, or
vis dependent, as regards its output, on accelera
comes constant at saturation.
In my invention, in its best embodiment, two
tion.
,
.
One magnetically responsive system of the prior
cores are provided, of minimal cross-sectional
area (for reasons explained below), carrying
art. which is promising on its face but is rather
disappointing in results, makes use of a pair of 40 windings energized by a periodic current source of
matched transformers having cores of high-per
su?lcient amplitude to energize the cores periodi
meability material, the primaries of which are
cally beyond saturation, and other windings care
arranged for periodic energization and the sec
fully balanced on each core for taking off an ,
ondaries of which are connected in opposed rela 45 induced voltage. By virtue of the described break
tion to each other and are connected to a trans
in the hysteresis loop, the voltage induced in‘ each
ducing device of a type which responds to any
output winding is a wave of extremely distorted
and all electrical signals applied to it. With such
shape, which rises more or less gradually and
a circuit, in'the absence of an ambient magnetic
then drops suddenly to a low value or zero, at
?eld, the voltages induced in the secondaries are
instants in time corresponding to the arrival, in
equal and opposite and no signal appears. In the 50 each core, of the ?ux at said knee in the hys
presence of a magnetic ?eld, in each magnetiza
teresis loop. The output windings are connected
tion cycle of the transformers, the ?eld and flux
in
opposition, the cores and their windings being
developed in one of the cores is increased by a
‘ balanced, so that in the absence of any space
certain amount and that in the other core re
duced by the same amount, so that energy‘ ap 65 variation of the applied magnetic ?eld the net
3
2,407,809
output is zero. Now, it the ambient magnetic
?eld is diiferent at the locations occupied by the
two cores, the ?eld and ?ux developed in one
core during each energization cycle is correspond
ingly different ‘from that in the other. The pulse
in one secondary terminates abruptly, and slight
ly before the pulse in the other secondary termi
nates.
By virtue of the opposed connection of Y
the
secondaries
this phase lshifttgivesh‘risett'gi a
v
sharpvoltage pulseint eou putc cui , .e.
aepyulse of short‘ duration but higlrintensity. The
amount of energy in the pulse depends upon the
degree of phaseshift and in turn on the gra
dient of the applied ?eld.
4
The theory underlying the operation of my
apparatus has been described in detail in my co
pending application Ser. No. 403,455 for purposes
of measuring magnetic ?eld strength rather than
gradient of magneticfleld. For the former pur
pose parallel cores 2n and 2| are placed in close
proximity to each other, primary windings 22
and 23 are oppositely wound with respect to each
other, and secondary windings 24 and 25 are also
oppositely wound with respect to each other.
The present invention, being a division of the
aforesaid application, contemplates measurement
of the space gradient of the magnetic ?eld. For
this purpose cores 20 and 2| are still maintained
To take advantage of this pulse (which while 15 parallel, but spatially separated by a known dis
non-oscillatory per se can be considered as a
summation of vibratory components of high fre
' tance X so as to detect such gradient of mag
netic intensity. Primary windings 22 and 22 are
now similarly-wound with respect to each other,
and. secondary windings 24 and 25 are also simi
copending application Ser. No. 403,455), the am-. 20 larly-wound with respect to each other and con
pli?er or~other transducing device is made'to
nected in series opposition. If now the compo- be selective to sharp pulses, by biasing it so that
nent of ‘the magnetic ?eld parallel to the length
applied potentials below a predetermined value
of cores 20 and 2| has a‘ gradient in the spatial
do not affect it, and ‘by careful selection of the
direction X of separation of cores 20 and 2 I, each
quencies) and to distinguish it from other en
ergy pulses or waves (of origin explained in my
several circuit constants as described in detail 25 core will experience a, di?erent degree of mag
below.
'
netization due to the difference in the ambient
While the transformer primariescan be en
?eld at the two cores, and there will be di?er
ergized .with almost any kind of periodically vary
ent signals induced in the secondary windings.
ing voltage, including pure sinusoidal alternat
These signals will be qualitatively similar in
ing energy, there are advantages in employing a 30 shape, but one will lead the other slightly in time;
saw-tooth wave or pulse series for the periodi
that is, there will be a, phase shift or displace
cally applied energy. These considerations are
ment between the signals from the two second
aries. As these voltage signals are opposed, the
described in detail in. my aforementioned copend
ing application.
net signal is obtained by subtracting one wave
The manner in which the apparatus of my 35 form from the other. This manner of operation
invention accomplishes its objects will become
is similar to that described in more detail in my
apparent in the following speci?cation of which
copending application Ser. No. 403,455 previously
the accompanying drawing forms a part. _In the
referred to. The unbalanced pulses in the sec
drawing,
.
ondary circuit are fed by leads 32 into the pri
Fig. 1 is a circuit diagram of one embodiment 40 mary of step-up transformer 33 and are subse
of the invention, and
V
Fig. 2 is another embodiment of the inven
tion employing a simpli?ed electrical circuit.
quently ampli?ed and ?nally exhibited by unit 35.
The signal in leads 32 has for each energizing
cycle a very high peak and a number of smaller
peaks. These sharp peaks change in amplitude
Refen'ing to the drawing and in particular
Fig. 1, a spatially separated pair of parallel trans 45 very rapidly as the ambient ?eld is changed.
Due to the very steep wave front of the magnetiz
former cores,.20 and 2|, is provided, these cores
taking the form of very thin strips or ribbons of _
a magnetic material which has a high permea
ing pulses, the core material is magnetized in a
very small part of one cycle ‘so that the angular
phase shifts produced by the ambient ?eld are
very small, and by reason of the abrupt change
at saturation the differential E. M. F. appearing
at the output of circuit is a very sharp pulse
Permalloy. Absolute and relative dimensions of
of short duration. Accordingly, the secondary
the cores are important, as explained, and for
windings are designed to have a su?iciently low
highest sensitivity, the cores and their windings
65 distributed capacity to permit the very high fre
should be very carefully matched.
quency components to appear at the terminals.
_ The cores are provided with similarly-wound
bility and a low energy requirement for satura
tion. Among suitable materials for the cores are
the alloys known- as Hypernik, Mu-metal and
primary windings 22 and 23, and similarly-wound
secondary windings 24 and 25. The primaries
Likewise, associated ampli?er equipment is de
signed to_handle the essentially unidirectional,
are connected in parallel as shown and are pe
high frequency pulse appearing at the output ter
riodically energized by an oscillator making use 60
minals.
'
Since the voltage induced in the secondaries
is dependent upon the rate of change of magnetic
battery 21, resistor 28 and condenser 29, to supply
?ux, the more rapidly the magnetization cycle
energy pulses through a connection 30 to the pri
is traversed the higher will be the output voltage
maries. Screen voltage is secured by a voltage
65 for a given ambient ?eld. However, due to the
divider 3| across the plate circuit, by means of
effects of distributed capacity and time-constant
which amplitude and frequency of the oscilla
limitations in associated ampli?er equipment the
tions can be adjusted.
optimum rate at which'the magnetization cycle
The secondaries are connected to each other
should be traversed is a, compromise between
in series opposition through'a circuit including
these opposing e?'ects. Rates of 60 to 1000 cycles
leads 32 and the primary of a step-up transform 70 are the most useful.
er 33, as shown, at the input of an ampli?er,
Considering now the ampli?er circuit of Fig. l,
described in detail below, constructed and ar
which as stated is devised to accentuate the '
ranged to be selective to the high frequency pulses
sharp pulses produced as described: the ampli
appearing at the transformer.
75 ?er, the output of which is delivered to an exhib
of a hot cathode gas triode 26, in circuit with a
‘ 9,407,902
iting device 88, includes two ampli?er stages 88
and 81 and a vacuum tube recti?er 38, arranged
in a circuit. the constants of which-are selected to
emphasize high frequencies and rapid ?uctua
tions. Thus, input transformer 88 and inter
6
- u. a man frequency choke n is maintained in
the battery circuit in order to keep signals from
the energizing oscillator ‘28 out of the battery cir
cuit. Current from the battery circuit, misbe
tires both cores in the same direction, ordinarily
that direction which opposes the ambient ?eld.
stage transformers 88 and II 'are of_a low in- .
Fig. 2 shows a simpli?ed embodiment of the
' invention. The two cores in and u with-their
ductance type capable of passing ‘frequencies
015'20900. cycles or more. Certain small audio,
frequency transformers are available for this
respective primaries “and 28 are periodically
energized by a circuit comprising a battery 21, a
resistor "and a condenser 29, connected to a
purpose. A bias battery ll, self-biasing resis
tors I! of abnormally high values and bypass
gas-?lled cold cathode tube 228 in circuit with
primaries 22 and 28 as shown. The battery
condensers‘ 48 of low values are provided, in oil'
cuit as shown, so that the tubes are biased nearly
charges the condenser and > when the J charge
to their cut-off points and only positive pulses
operate the tubes. Such‘ circuit degenerates low 15 reaches a certain potential the tube breaks down
and discharges a pulse of current through the
frequencies, and the net result‘is a high degree
primaries. Pulses occur at regular intervals, de
of discrimination against pulses of low ampli
termined by the battery voltage, the values se
tude‘, pulses of low frequency andpulses of un
,lected for the elements 28 and 28, and the break
desired polarity. The transformers are all
phased to make the highly sensitive sharp pulses 20 down voltage of tube 226.‘ The sensitivity of the
apparatus is not affected by the rate of impulse
received through leads 82 result in positive pulses
generation. A‘hot cathode tube may be substi
at the grids of the three tubes. Transformer 88
tuted for the tube 228 if desired.
‘
advantageously has a high, step-up ratio. ‘By
The direction of winding and connection of the
having its primary inductance ‘low, it favors the
primary coils 22 and 28 is such that the right
more rapid changes of the signal ‘and tends to
short circuit the slow changes.
hand end of each core 28 and 2! is energized
‘
Tube 88 is a recti?er ‘of the grid leak type.
Each pulse peak drives its grid momentarily
positive, causing a grid current to ?ow. This
current charges the condenser 44 to a voltage 30
nearly equal to the peak value. - Resistor 45 is
large enough so that condenser M is but par-v
tially discharged between peaks. Hence the grid
with thesame polarity. Secondary coils I4 and
28 are wound and connectedtso that their induced
pulse voltages are opposed when there is no ?eld
gradient in the direction X. The secondaries It
and 28 are connected to primary of transformer
33 whose secondary 46 is connected to a. vacuum
tube voltmeter indicated generally by 88 and
which may include one or more stages of ampli
remains negative over most of the cycle by an
?cation. Thus. when wound cores 28 and II are
placed in near proximity to each other so that
their separation X is practically zero, no indica
tion is obtained on meter 88. when the wound
proportion to the signal strength. A buck-out
cores 28 and 2| are separated a distance X, the
battery 58 and adjustable resistor 5i may be used
with a sensitive meter if high sensitivity is de 40 meter 88 will exhibit a de?ection proportional to
amount varying with the strength‘ of the signal. _
The plate current as exhibited at meter 85 thus
decreases from. its normal maximum value in
sired.
'
the appropriate magnetic gradient.
I
,
Each of the wound cores 20 and Il may be en
closed by a concentric solenoid or coil 88. This
coll may be connected in a simple series circuit,
In the operation of Fig. 1, for making meas
urements of the space gradient of a magnetic
?eld, the two wound cores 28 and 2| are ?rst
placed near to each other so that X is essentially 45 together with reversing switch 8!, variable resis
tor 88, meter 81 and battery 84. Solenoid 83
zero and meter 35 is set to zero by adjusting vari
may be energized so as to oppose the greater part
able resistor 8!. The wound cores 20 and 2| are
of the ambient ?eld thereby making the device
then separated a known distance X in the direc
more sensitive to the gradient of such ?eld.
tion of the gradient to be determined and oriented
I have illustrated in Figures 1 and 2 my device
so that their long dimension is in the direction 50
set up to measure two types‘ of partial gradients,
of the ?eld component whose gradient is to be
but the apparatus may be used for determining
determined. If such a gradient exists, meter 85
any type of space gradient according to the' geo
will no longer read zero, and its readingmay be
metrical arrangement of cores'2ll and 2| with re
calibrated in terms of ?eld strength di?erence
over the known distance X. Because of the 55 spect to the direction X. Thus, in Figure 1 the
component of magnetic ?eld being observed is
shown normal to the direction of separation X,
this arrangement may measure the quantities
aforementioned manner of operation of recti?er
88, only response in one sense may have adequate
sensitivity; should meter 8! become relatively in
sensitive, lt may be desirable to reverse the polar
ity of the pulses in transformer 33 by reversing
the primary connections 32 or by changing’ the
60
relative output of the detector coils with biasing
8:
versing the positions of units 28 and II may be
.
.
"
6x
as
magnets or the equivalent. In some cases, re
all that is necessary.
as
65.
The sensitivity to gradient may be increased in '
where Hy and H: are respectively the components
of the total ?eld H in the 11 and 2 directions re
cases of relatively high ambient ?elds by the ap
spectively. In Figure 2 the component of mag
plication of a compensating current to the pri
mary coils. Thus, in the initial adjustment of
netic ?eld being observed is shown parallel to the \
direction of separation X. this arrangement will
the device as above described, switch 8| may be 70 measure the quantity
closed in the proper direction so that a current
@
_ from battery 41 may iiow through the coils 22
B:
and 28 to compensate for the greater part of the
where
H:
is
the
component
or the total ?eld in
ambient ?eld, the amount of such compensating
current being controlled by adjustable resistance 75 the x direction. Similarly, by appropriately ori
2,407,202
.‘
7
eating the wound cores other partial or total
energizing cycle which is shifted by changes in
the ambient ?eld at said core, windings adjacent
components of the gradient may be measured.
The cores may also be placed at an angle to each
said cores connected in opposition to deliver the
other in order to measure angular components
difference between voltages induced by said cores, '
of gradient in cylindrical or other coordinate sys
tems used to describe the ?eld.
1
5 whereby said phase shifts cause production of
sharp voltage pulses which vary in magnitude
In all embodiments of the invention, the ap
with a change in ?eld at either one of the cores,
and transducing means selective to said pulses
paratus sensitivity is very high, yet is accom
plished by a high degree of inertness to mechani
cal shocks and disturbances. Except where de
in. energy-receiving relation to said windings, and
10 means for subjecting the cores to a?eld approxi
liberately provided for otherwise, the predeter
“mately equal and opposite to the ambient ?eld.
4. An apparatus responsive to space gradient
of magnetic ?eld comprising a pair of slender
mined intensity level at which it gives a signal is
independent of acceleration, that is to say the
rate of change of speed at which the apparatus '
cones separated a distance such that the gradient
approaches, or is approached by, the foreign 15 may establish 2, difference in ?eld at their respec
magnetic body. This ‘makes possible ‘?ne meas
tive locations, said cores being of high permeabil
urements of magnetic intensity and gradient from
ity material not exceeding approximately 0.02
a moving conveyance as a destroyer or airplane.
inch in thickness and characterized in that the
hysteresis loop thereof‘exhibits' a sharp knee
1. An apparatus responsive to space gradient 20 where saturation is reached, windings by which
What I claim is:
.
.
of magnetic ?eld comprising a pair of slender
the cores may be energized to saturation in the
cores of minimal cross-sectional area and of ma
same sense, means for cyclically energizing said
terial of high permeability and characterized in
that the hysteresis loop thereof exhibits a sharp
. windings in a. manner whereby the cores abruptly
reach saturation at phases of the energizing cycle
25 which are shifted by changes in the ambient ?eld
ranged parallel to each other and with a spacing
at said cores, a secondary circuit having means
between them such that the gradient may estab
4 therein linked with said cores to deliver the differ
lish a difference in ?eld at their respective loca
ence between the voltages induced by said cores,‘
whereby said phase shifts cause production of
tions, means forcyclically energizing said cores to '
saturation in the same sense whereby each core 30 sharp voltage pulses which vary in magnitude with
a change in ?eld at either of the cores, and
abruptly reaches saturation at a phase of the
transducing means selective to said pulses in
energizing cycle which is shifted by changes in
knee where saturation is reached, said cores ar
energy-receiving relationship to said secondary
the ambient ?eld at said core, windings adjacent
circuit.
said cores connected in opposition to deliver the
differences between voltages induced by said cores, 3-),. ' 5. An apparatus responsive to space gradient
of magnetic ?eld comprising a pair of cores
whereby said phase shifts cause production of
spatially separated a distance such that the
sharp voltage pulses which vary in magnitude
gradient may establish a difference in ?eld at
with a change in ?eld at either one of the cores,
their respective locations and of material of high
and transducing means selective to said pulses in
40 permeability and characterized in that the hys
energy-receiving relation to said windings.
2. An apparatus responsive ‘to space gradient _
teresis loop thereof exhibits a sharp knee where
saturation is reached, means for cyclically ener
of magnetic ?eld comprising a pair of parallel
gizing said cores to saturation in the same sense
cores spatially separated a distance such that the
in a manner whereby each core reaches saturation
gradient may establish a difference in ?eld at
their respective locations and of material of high 45 at a phase of the energizing cycle which is shifted
by changes in the ambient ?eld at said core, a
permeability and characterized in that the hys-'
secondary circuit having means therein linked
teresis loop thereof exhibits a sharp knee where
with said cores to deliver the difference between
saturation is reached, similarly phased primary
the voltages induced in said means by said cores,
windings on the cores, means connected-to said
primary windings for periodically energizing said {H' whereby said phase shifts cause production of
cores to saturation in the same sense whereby each '
core abruptly attains saturation at a phase of the
energizing cycle which is shifted by changes in
the ambient ?eld at said core, secondary windings
sharpvoltasepulseswhichvaryinmagmtude with
a change in ?eld at either of the cores, and am
pli?er means in energy-receiving relation to said
means biased to a level such as to respond to
on the cores connected in opposition to deliver ;_I_‘ said sharp pulses while not responding to rela
the difference between the voltages induced by
said cores, whereby said phase shifts cause pro
duction of sharp voltage pulses which vary in
magnitude with difference in ?eld between said
spatially separated cores, and amplifying .means
arranged to receive said sharp voltage pulses and
to amplify them selectively while discrlminating
against low amplitude voltage pulsations.
‘
3. An apparatus responsive to space gradient
' ‘
tively low voltage ?uctuations.
6. An apparatus responsive to space gradient of
magnetic ?eld comprising cores of material of
(NI
high permeability and characterized in that. the
hysteresis loop thereof exhibits a sharp knee
where saturation is reached, said cores being
spatially separated a distance such that the
gradient may establish a difference in ?eld at
their respective locations, means for cyclically en
ergizing said cores to saturation in the same sense
of magnetic ?eld comprising a pair of slender
cores of minimal cross-sectional area spatially 65 in a manner whereby each core reaches satura
tion at a phase of the energizing cycle which is
separated a distance such that the gradient may
shifted by changes in its ambient ?eld, a second
establish a difference in ?eld at their respective
ary circuit having means therein linked with said
locations and of material of high permeability and
characterized in that the hysteresis loop thereof 7" cores to deliver the difference between the voltages
induced in said means by said cores and trans
exhibits a sharp knee where saturation is reached,
ducing means in energy-receiving relationship
means for cyclically energizing said cores to sat
uration in the same sense whereby each core
abruptly reaches saturation at a phase of the
to said secondary circuit.
VICTOR v. VACQU'IER.
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