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Патент USA US2406139

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Aug. 20, A1946. ì
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.‘ C, G, FlNK ¿TAL
2,406,139
PHOTQGELL' FOR MEASURING LONG WAVE RADIATIONS
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Filed Feb.. 27,» 1941
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@193.
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BY
_,
ATTORNEY
2,406,139
Patented Aug. 20, 1946
UNITED STATES PATEN T oFElcE "
2,406,139
PHoToCELL Fon MEASURING LONG WAVE
RADIATIoNs
Colin l(B‘r. Fink, New -York, N. Y., andJohnstone S.,
Mackay, Prospect Park, Pa.
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Application YFebruary 27, 1941, Serial No..380,868
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(C1. 13e-89')
7 Claims.
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1
This invention relates to photoelectric cells,
and more particularly to such for measuring long
transmitted from a distance and concentrated
on acell, embodying our invention, for increas
ing the sensitivity thereof..
Referring to, the drawing in detail, and first
considering the embodiment of our invention
Wave or infrared radiations.
The principal object of our invention, generally
considered, is the production of a photocell com
prising a solid photo-element, bismuth sulfide,
bismuth selenide, or equivalent, which is adapted
to efficiently measure infrared rays including
those of relatively long wave lengths.
Another object of our invention is the produc--
illustrated in Figures l and 2, our cell I I con
sist-s essentially of a soft metal backing I2, de`
sirably of tin, covered with a layer I3 of a bis
muth compound,_such as the sulfide, (BizSs),
and the selenide (BizSes‘), which is in turn‘coated
with a thin translucent film I4 of a conductor
such as copper, silver, cadmium, carbon, bis
tion of a photocell employing an element which
has a large proportion or nearly all of this activ
ity due to infrared radiations. `
v muth, lead, tin, 'combination of tWo or more `of
the metals mentioned, or equivalent material. '
A further object of our invention is Ito develop
a photocell which efficiently responds to infrared 1
radiation, as by developing as much as five mi
croamperes per lumen, or the equivalent in mi
crowatts, of energy received.
.
A still further object of our invention i-s the
employment of bismuth sulfide for measuring ini
. frared radiations to 70,000 Angstrom units, With
« only a small response to visible radiations and
Bismuth sulfide A(or equivalent) of such a `cell
is a solid photo-element corresponding to the
cuprous ‘oxide or selenium of the rectifier type
of photocell. Such a cell generates its oWn power
under the inñuence of radiations, Without `the
external application of electromo-tive force. ` Both
the direction of response and the efficiency of
such a photocell, are dependent on the char
those of shorter Wave length.
_
acteristics of the photosensitive material which
Other objects and advantages of the inven
might be described as asemi-conductor.
Y
tion, relating to the particular arrangement and 25 The distinguishing feature of our cell, is that
construction of the various parts, will become
it is sensitivelto energy in the infrared outto a
apparent as the description proceeds.
'
threshold wave length of 70,000 Angstrom units.
Referring tothe drawing illustrating our in- `
By comparison, the selenium cell is sensitive to
energy out to 8,000 Angstrom units, caesium to
vention:
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Figure 1 is a transverse sectional view of a 30 15,000 Angstrom units, and cuprous oxide to
simple form .of photoeleotric cellpembodying our
14,000 Angstrom units.
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Figure 2 is a face View of `the cell looking from
Although it is possible to detect infrared radi
ations having wave lengths of 15,000 Angstrom
Figure 3 is a view of a cell, such as shown in
units by means of a thermopile, which is a very
expensive and delicate instrument, our inven
tion makes direct reading of Ithe long Wave length
invention.
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the left in Figure 1.
Figure 2, `embodying a grid for increasing the
conductivity of the photosensitive layer.
Figure 4 is a View of a cell, such as shown in
Figure 1, .the photosensitive portion 'of which is,
however, duplicated on" ltheback so that it is
adapted to receive radiations> from both sides.
infrared radiations cheap and practical.
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The bismuth sulfide layer I3 may be about".005
inch in thickness, .although thi-cker films have'
40 been used.
It is applied to the tin backing I2
under high pressure, such as about ñfty tons
Figure 5 is a face View of a cell, such as shown
per square inch. Other metals besides tin-may
in Figure 2, except that it is of the null reading
be employed if desired, but tin has been'found
or compensating type.
satisfactory. We prefer to make the bismuth
.FigureV 6 is a view showing how a cell, such as- 45 »sulfide by chemical precipitation With hydrogen
illustrated in Figure 1, may be adjustably
mounted in position and associated with a'ñlter.
Figure 7 is an elevational view of the com-`
sulfide from acid solution, avoiding an excess of
bismuth or sulfur. Such procedure is Well known
to all chemists. An acid treatment after prepa
bination of a cell, embodying our `invention,with
ration has been found desirable. We have, how
'50 ever, tried other methods of preparationybu-t the
-Figure 8 is a vertical sectional view on `«they line
one mentioned has given goodresults.
Ä _
VlIlI--VVIII- of Figure 7 in the direction of they
When the bismuth sulfide is firmly pressedinto
a directional shield.
La_rrOWS-
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Figure? is" agdiagrammatic View, showing how. `
and onto the tin or. other soft'metal backing plate
, .I 2,"5- the f outer surface Vof l:the f »phot'olayerï Vis cov
radiations from an infrared source may be '5 ered with a thin layer of infrared transmittingV
2,406,139
3
conducting strap 28,'extending from a binding
l electrical‘conducting material, and forms what
` post 29. A set screw 30, holds the cell tight and
, has often been called the “translucent” layerA I4.
` This coating is desirably done by electrolytic de-~ `
position from an acid sulfate rof copper bath or ‘
provides an electrical connection with the metal
base |29. >Leads I‘Ie and I8e extend, respectively,
from- the binding post 29 and screw 30, to the
millîammeter or other measuring instrument, not
by sputtering the material selected from the list
previously given. As an alternative, it has been
i found satisfactory to rub a conducting very thin
shown.
1 with a micrometer, and has been found to trans
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units, or hard rubber which is a good transmitter
In order to connect a cell produced, as shown 1
of heat rays.
i in >Figure 2, with a measuring instrument ¿such
.
It is also desirable, inrmany cases, to enclose
the cell in .order to protect it fromY fumes, dust
or other deteriorating action, in which case any
Í asa milliammeter i5, a ring Iâ of metal or-other l
1 conducting material is .desirably applied, as
g, shown, in engagement with the translucent
layer I4, in order to make good contact there-K->`
with, and the instrument I5 connectedbetween
infrared transmitting substance may be used over
the front face, such as one of the ñlters given
above, and hermetically 'sealed to the box.
Asfit is desired to avoid heat from extraneous
sources, which might vitiaterthe results, 'the box
, i saidring I6 and the soft'metal base, as by leads
I'I and I8.'
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which will pass infrared up to about 18,000
.Angstrom units, heat transmitting glass which
transmits rays between 8,000 and 40,000 Angstrom
mit about 20% of the radiation from an incan- `
Í descent tungsten ñlament lamp, as mea'sureclby .
‘._a selenium cell.
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The filter 25, shown covering .the cell face in
order to- limit the range :of infrared radiations
to be detected, may be formed of “Pyrex”l glass,
layer of graphite on the surfaceaof the photo
l layerV I3. Such a 'coating is'too ïthinfto measure
v
The electrical resistances of cells, produced in
21% enclosing the cell is desirably formed-»of heat
j accordance ywith our invention, have been Vfound `
to vary considerably. That is, they may be as lc'iv
asï'75 ohms and ashigh as 15,600 Ohms, depend`
insul-ating material, such a's Celotex.
Isa, like the ringv I6 of 'Figures land A2, as shown 1
in Figure 3.
.6, if desired.-
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In infrared signalling, a highly udirectional ef
fect is often desired. vlin such a case, afshield .3i
ing on the thickness of bismuth 'sulñde the
of insulating and heat absorbing `>material may
method of preparaticn,and thekind of contacts
be used with a bc-X 24F holding-a bismuth suliide
made to it.
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.In order to marke g-ocd contact, a metallic layer l 30 `cell Hf, as shown in Figures ’7 .and-»8. ln this
case the iront contact 22.“ is provided by; the »box
may besputtered or electrically deposited, as in,
itself, and >the backcontact bythe setscrewZi-ílf
dicated at Iâ in Figure rl, land'inorder to »cut
down the cell resistance, lmultiple contacts may
which
box v2¢ifengages
may be the
provided
metalwith
backing
a-pocket
plate25f
f lilf.for the
be made with the translucent layer Ill by a grid
reception
rof
ia
iilter,
like
the
lilter
25
of Figure
like structure Iâ connected to a 4peripheral ring 35
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IAsan example of how’directional »effects Ímay '
Figure ‘l illustrates a further'ernbodiment of` ' be obtained, which also amplifyV the readings of
a cell embodying our invention, Figure 9, shows
our invention in whichvthemetal backing plate
; I2"b is inthe center,:.and'both surfaces-are coat-f` 40 a _50111138.32 of infrared radiations, such -as a
Nernst .glowe'n a heated platinumball, ora llow'
` y ed with layers 93h of .bismutnrsulñde Vthe outer
temperature projection' lamp, mounted at .the
1 V‘surfaces of -which layers vare then, in .turnfeacl-.r
i'ocus ofthe sending device> 33, which'is `shown
, 4coated with atranslucent"cenductinfßnlm isb; -
' _ in the form of a parabolicreiiector.
. The films arethen- desirablylconnécted in parai-= '
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-A ybismuth.‘sulfide« cell vi ig, constructed in-ac
cordancewith ourinvention, is mounted~=at~the
lel, as by means of .conductorâh through con- Y
necting> rings lâh. and themilliamnieter Íor other
focus of a receiving device .34, which is alsoshown '
indicating Yinstrument may be connected to
duplex cell. by leads >I'i’b and Ißb> from one ,of the .
inthe form of> a parabolic reilector, the `sensitive
rìngs"`I6b and the metal plate lâh;as„illustrated.`
surface >facing inward' or toward the ¿reflecting '
surface ofthe device 35i. 'in this way theuenergy
*Forf convenience in measuring, anull rea
. is transmitted Afrom 'the sending deviceito the
or compensated cell may be constructed, as `shox -
‘receiving device without much loss, and-focused
in Figure 5, that is, two equivalent photoelectr
on the cell Which is then ina position to efliciently
a
mountedzon a suitable base'fäü, `and 'balanced
record the radiations.
_against one another through a resistance izan-:l . :
i . milliammeter or other sensitive measuring Tin»
strumentv 23.
After theyhave beenY both
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Tests of bismuthsulñde cells, constructed in
accordance with our invention, rshow that y-they
have good stability, small fatigue, -slow response,
and a lconductivity, which is only yslightly asym
f metric. The current producedis roughly-pro
>posed to the same vamount and kind ofradiation,
and balanced against one another, then’the con-1
nections may be changed 'toA make them act to
portional to the area exposed, vinversely propor
tional tothe squareof the-distance iromrthe
gether, the output from one cell 'being'then 'de-l
¿ termined as ,one-half that of both, then the out-`
.light source, and both current and voltage; are
kdirectly proportional to the wattage» of the ¿light
i A' putgfromone of Athe cells may be balanced by a
known v electromot'ive‘ force, asis usual with _'_su'ch`
source.Y
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The degree of sensitivity. ,and` stabiiitylîyahes "
vFigure 6 illustrates a'forin' of cell I i¿ijconstruct-`> Y _agreat _deal from cell tc cell, largely due to »varia
"ed as shownin'Figures 'l and?, ‘and "adiustably` ‘ [tions bound ,to occur .in construction-andïmore
`mounted§in al box“ 214; where it 'may be employed Y Aor ."lessV accidentalV characteristics. :The ,silver
".electroplatedï,bismuthfsulñde*cell'which ,had a`
Wf'transmitting electricalV conducting'jlayer" isc;
poor response, showed a relatively »highiunïipolar
conductivity. The ratio ofßthe...conductivity'in
Aopposite ï‘directions was te'nÍ toi-one. -In‘A thea-cases
of the' higher sensitivity cellsfit lwas'around> two
1‘ ’ Contact is 'rríadej‘withfjthe Vlatter, #through a
` . .graphite 4.front contact 21, mountedY otra;resilient,y
is; the 'resistance 'staifted’oiit ‘about this_¿same l as
`’Io
metal ba'seî‘I‘Ze; ai photosenis'it'ive" layer’ ' of’ bismuth '
f .v ßlllfide fsezfah'dà translucent lol'ltl’l'irlfíñfl'àred
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to one, although this was not instantanefóusgùthat
2,406,139
A
for other cells, but would then drift down if the
current Was in one direction and up if it were in
,
1. A photovoltaic cell having about 80% of its
photoactivity in the infrared region and compris
the other.
The bismuth sulfide cell in Which the outer
conducting or translucent layer was formed by
ing a conducting base, a layer of material selected
from the group consisting of bismuth sulñde and
bismuth selenide thereover, and a thin trans
evaporating Wood’s metal thereon, showed good
asymmetric conductance and the only near
instantaneous current response observed for any
of such cells.
6
We claim:
lucent electrically conducting iilm over said layer.
2. A photovoltaic cell sensitive t0 infrared
radiations shorter than 70,000 Angstrom units
and comprising a conductive base, a layer of
material selected from the group consisting of
bismuth sulfide and bismuth selenide thereover,
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The experimental bismuth sulñde cells We made
Were not so photosensitive as the seleniumcell
for radiations from an incandescent tungsten
lamp or from the sun. Also, they were not so
good as a sensitive thermopile for infrared radia
and a thin translucent electrically conductive ñlm
over said layer.
tions. They are much cheaper, however, than a
thermopile. A cell produced in accordance with
our invention can, for example, be used to in
dicate the amounts of energy radiated from black.
bodies at low temperatures. Thus radiations from
3. A photovoltaic cell having about 80% of its
photoactivity in the infrared region and compris
ing a tin base, a layer of bismuth sulñde there
over, and a thin translucent l layer of metal
selected from the group consisting of copper,
a flat iron heated to about 450° -C. gave ñfty 20l silver, cadmium, bismuth, lead, tin and combina
microamperes when the iron was disposed 5 cm.
tions of two or more of 'such metals deposited
from the cell.
thereon.
Photovoltaic cells produced in accordance with
4. A photovoltaic cell having 80% of its photo
our invention should find numerous practical ap
activity in the infrared region of the spectrum
plications in controlling furnaces,l detecting sig 25 and comprising a conducting base, a layer of bis
nals in fog, burglar alarms, automatic ñre sig
nals, sprinkler systems, chemicalreaction con
trol device, and in any place Where it is desired
to control relatively low temperatures. Although
.muth sulñde, and a thin translucent electrically
conducting film over said layer.
5. A photovoltaic cell having about 80% of its
photoactivity in the infrared region and compris
the cells which We,Í have experimented with have 30 ing a conducting base, a layer of bismuth sulfide
had areas of about 1.2 square inches, it is possible
thereover, a' thin translucent electrically conduct
to produce cells of almost any desired surface
ing ñlm deposited on said layer, and a contact
area. The thickness of the backing metal is not
ring engaging said layer.
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critical, but should be great enough to stand
6. A photovoltaic cell having about 80% of its
having the sensitive coating pressed thereinto 35 photoactivity in the infrared region and compris
and properly rigidify the cell. The great advan
ing a conducting base, a layer of bismuth sulfide
tage of our cells, over other means for detecting
thereover, an electrically conductive translucent
infrared radiations, is that they may be con..
structed at small expense, While the total photo
ñlm on said layer, and an electrical conductive
grid engaging said film for increasing the con
electric sensitivity compares favorably with that 40 ductance of said layer.
of the vacuum tube photoelectric cells, being
much greater than that of the sodium, and about
7. A photovoltaic cell comprising a conducting
base, a layer of bismuth suliide pressed into each>
face of said base, and a translucent iilm of elec
the same as that of the caesium cell.
Although preferred embodiments of our inven
trically conducting material disposed over each
tion have been disclosed, it will be understood 45 layer.
that modifications may be made'within the spirit
and scope of the appended claims which are not
all limited to bismuth sulfide, as another com
pound of bismuth, such as the selenide, may be
substituted.
50
COLIN G. FINK.
J OHNSTONE S. MACKAY.
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