Note: Descriptions are shown in the official language in which they were submitted.
70577-71
~ t~ 7~y~
CIRCUI~ ARRAMGEMENT FOR SUPERCONDUCTIVE QUANTUM
INTERFERENCE DETECTORS (SQUIDs)
SPECIFICATION
Field of the Invention ..
My present invention relates to a circuit arrangement -
for superconductive quantum interference detectors (SQUIDs)
with the electronic circuitry for generating outputs therefrom
and, more particularly/ to improved magnetic sensors utilizing
superconductive detectors, especiallv for low frequency
operation, for example, to detect biomagnetic signals such as
heart and brain activity. .
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18004
~C~ 0U~ th$~c~~
Wi h the develop~rlt o~ hlgh temperature
~uperconductore ( see High-~e~p~rature Superaonduator~ On
th~ Road to Applic~at~on~, Chan~i¢~l and Englnesring Newo,
27 November lg89, page~ 9~E~), lt h~ become posf;lble to
pr~id superconductive quantum inter~er0n e d~t~ctor~
~SRUIl)~) with op~rating temperature~ ln the, temparatur~3
range of ~he boilin51 point o~ llquid nitrogen and higher
temperature~.
Such sQuIn& are provlded in various embodiment~ and
con~i~aurations, including ~ingla-hole 8QVIDs or two-hole
SQUID~ in gradiom2tsr6, both in ~a~8ive bodies or by thin
teahr~ ues. ~hen the ~nh~rent nois~ o~ ~uch ~sansors
at ~requencie~ abov~ about 100 Hz has attraatively low
~15 valua~, the ~SQUID can be u~0d at low-r ~ignal treclu~3n~::ies .
: :~ in: tha ranye oP ~oYeral HZ and le~ Por avaluating
bio~agnQtic ~ignals ~uch as blomagn~t~c ~gnal~ o~ th~
haart~ or brain activlty. Wi~h ~u~h applications it ha~
be~n ~oundf however, that decr~a~in~ *requ~3n¢i~ ar~
ao ~ as-oc1ated with inareasing levell6 of~ ~xtxin~i~ noi~e.
b~0~t~
~: ; It i~ herqfore , an ob~ ect oP the ir~vention to :: :
prov1de a aircuit arrangement which ~xpands th~ Pield of
appllcation o~ ~nagn~t:l:a detectora ae descrlbed ln th~ .
25 ~ ~bove-idonti~ied ;application.
An~equal.1y important ob~e~t i~ to prov:lde a magn~ic
sor ~yet~3m uti11s~ g 8QUID~ and whioh i~ oharacterized
.
by a reduced 1e~Y~1 0~ noi~e, i . a. has an output wh1ch 19
:~ ~: not mat~ria11y e~Qc:t~3d by noi~
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18004 ~ i 7 I'J
It i~ still anoth~r ob~ect o~ the lnvention tc)
provlde a circuit arr2~rlgem0nt :eor SQUIl)~ which reduc~s the
e~ct o~ noi~ on ~ny output ~ignal~ produced therQby.
~1~ .
The~e ob~ect~ are attained, in ~cc~rdance with the
invention by prc~Yidin~ two SQUID detel::tors, e . g . ~n~ore oi~
the typ~ described in the above~ nti~i~d ¢opending
application irl parall~31 with one another i~nd providing the ;~
~3lectcric airouiit:ry with whi~h the~e deteators ~re
¢r~rln~cted, with a aorrelation c:lrcuit having th~ e~Pe¢t o~
removlrlg nonaorrQ~ated sxtrin~ noise ~rom thQ nutput
~ignal~. ~ta~ed oth~ e the aorrelation ¢ixcult i6 able ; ~ .
~o d~t~ extrinsl~: noi~ o~ the ~wo detector~; which cannot . -
be cbrrelat~d arl~C thu~ re~ove~ thi~ noncorralated extrln~
:
~ noi~ o thalt ths re~naining ~ignal-to-tloiss r~tio can be
co~paratively high.
or~ p~rticularly, the ~agn~tic ~en~or SQUID ~y~tem
o~ the lnvent:lor~ can ¢omprl~a
two superconducting qtuantum inter~er~noe detectors ~ .
:~ 20 ¢onra@ct~ad. in parallel and having re/lpective output ~ignalF3
~; inaluding measurement ~ignals, inharant nol~ and, upo~
: ~ operation at cartain ~re~encie~, f3xtxin~;1a noiset and
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18004 ~ 3~ ~
circuit mea~ inoluding a correl~tion electronic
circuit connected to ~oth o~ tha l~uperconducting quantum
interferenc~ d~tector~ ~orm~ng an output ~or o~tput ~ignal~
Pro~ the measureme~t signal~ o~ t]he parall~l ~onnected
~uperconducting quantu~ ~nter~erence detector~ for
eli~nating ~r~m the output, ~lgnal~ reipre~énting
uncorrQlated noi~e ~ignal~ ~rom tbe ~uperoo~ducting quantum
intar~erence deteotor~.
Th~ principlQ~ o~ correlation el~ctronlc~ and ~::
~iorr~latlon analy i~ ar~ wall known tse~ Engineering ,: .
AppIlcations o~ Correlation and 8p~atral Analy~
Jullu~ S. Bendat and Allan G. Piarsol, John Wiloy and So~
Naw YorkO 1980). Utiliz~ing theso prinaiplee ~nd ~uoh
circuitry, I am abl~ to extract the uncorrelated n~i~e
~5 whil~ leaving the u~eSul compsn~nt o~ the output signal .
lntaot. Thli~ prinolpl~ oan b~ ~ployed in variou~i ways in
accordanc~ wlth oorr~lation analy~l~, e.g~ ~y a time-based ~ -
; extraction o~ the nonoorrolated noise utiliiæing ;~.
utocorrQlation and crosis corr~lation principles, or ~y
20~ ;~ ensemble an~lysis in a multi-channel system. The latter :
meth~d i5 0~ greàte~t advan~age wh~n th~ time con~itant ~or
,
th~ analy~ ust be i~all ~y ao~parl~on with the ~ignal
tim~ constant ~r ln the aa~e o~ nonpsriodia ~ignal~.
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For high t~n~paratllr~ ~up~rconductor~3 the sen~itivity
can be e~pecially increa~ed by thla ~ e of th~ correla~cion
proc~:~s c)f the invention. The higher operatlng
temp~3r~ture~3 o HTSC S5~UID~3 (hiyh temp~ratur~
6up~rconduct~ng SQUIl)a~ are~ a~sooiated with higher th3rmal
inh~rent noi6e and, when correlation analysit3 i6 u~d as
descrlbed to reduce th~ e~fsc:t Qf th~ noiF~6~ on the output
lgnal and h~nc~ to inaxea6~ the ~ignal ~o no:Lsel ratio,
~uch H~SC ~QUID~ aan be employed everl ~or tha detection of
brain ~ignal~ to which the high th~rmal noise lev~l has
bsen a barrier heretofore.
The use o~ the c:orrel~tis:~n technlqu~ o~ the
invention al~o represent~ a ~igni~icarlt improvement for
æQUID~ of t3~ more cla~sical ~uperconductor~, being
. .
a8~30aiated wlth an improve~ent in 8en ivlty to leval~
which could not be attainable hereto~ore.
Pre~erably the SQUID~3 whic:h are uF.13d are thos~e
: ~ ~ de~;cribed in t~ above-iderlt:l~Eied application and (;erman
Patent Document 39 31 441. q!he~;a SQUID-type ~3en~0r~
provide uperconductlns~ rlng~ in a tank airauit which can
include a Jo~3ph~30n junotlon or element.
The tank c~irc::uit C~ aompri~s a strip reso3~ator in
the ~orm oP a ~uperc:onducting ~tr~p havinçl an opanlng which
~OrmB the superco~duclting rlng in which th~ Jo~eph~on
~5 ~ elem~nt i~ incorporated. ~ore ~peai~ically, the SQUID
oo~npri~ a ~up~rcorlduativl3 ring having a Jo~3eph~0n
:~ ~l6smenl~ or a p:Lurality oi~ Jo~eph90n ~unction~ ~orming a
Jo~3eph~on QleT~er~t incorps~rated th~rein and which i~ coupled
l~o an electric o~ atory or tz~n~C circuit.
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Advantag~ou~sly, ac:cording to thç~ invention the
electr~ c o~cillatory circu~t cDmp;ri~e~ a p:Lece o~ a etrlp
conduGtor ~orming a re~orla'cor ~or s~anding elec:tr~ cal waves
on an appropriate aubatrat~ and w~hich iR ~orlD~d with an
opening traver6ed by lthe magnetlc ~lux to be measur~d, the
opening being bounded by z~t lea~t one Josephson elemerlt ~30
that the~ relulting ~uper¢ollduotiv~ ring ~ ~or~ed around thi~
opening ansl inoludin5~ the Joseph;0r3 21ement~ i~ integrated
in th~ strip r880n21tOr ~ormed by that condu¢tor. The
~02~ephson ~lQm~nl: i8 ori~nted ~30 lthat it exterld~3 als:~ng an
axl~ oP th~ ~trip re~onator, na~ely, lt~ cent~r l ine or
middla axis or a ls~ngltudinal axis thereo~ and th~ couplirlg
o~ th~ ~trip resonator to th~ evaluatia~g electronic
ciroll~try, i~e. tha o~cillation da~ping or voltage drop
: 15 ~ d~t~tor i.8 capacig~ve and ~ e~fect~d through a further
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piec~ D~E a etrip conductor lying along th~ ~trip re~onator.
~dvantag~aouE~ly to the invQntion, there~ore, the
~ nl3or has it~ fiuperconductlve ring and tank circuit ~ormad
a~ a ~3lngle ~tructural unit and con~t ~ tuted by the ~trip
20~ re~o3~ator E~O that the 6trip re~onator itsE31~ ~orm9 a tank
clrcuit and it~ boundary arouncl th~a operling c:on~titutes the . ~
uperconductiv~ rirlg in whlch the Jo ekh~-:>n ~1l3men~ iE~ ..
incorporated. : :.
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Since the Josephson element lies on a longitudinal
a~i~3 of the ~strip re~30nator, ~ l3u~eZiciently hlgh ~reguency
current can b~ fed thereto to 2nsur~ that tl~er~ will flow
in tha Joseph~on ~uns:tion th~ requislte current ~or the
measurement of the magnetis: flux.
For operation o~ tho Gen~Or, o~ cour~, it i6
nec:essary to ~:upply the ~trip re60nator with a resorl~nt
~reguency which can genarate E~tanding wave~; in the ~trip
re~30n2ltor. For a given length of ths strlp reson~tor, this
~0 can be ea~3ily done by ad~u~;ting the applied r2~;0nant
~requerlay until ~tanding wave~3 d~3velop in the ~trip
re80nator, utillzlng, ~or exampl~, a variable ~requency
~ourca ~
However, it is also po~sibla 'co operat~ with a fisc~d
frequency ~ource and to ad~ust the ~ engt~ oP the strip
re~;onator 50 that ~ita slectrical length 1 wiLll correspond -;.
to an odcl number multiple o~ th~ halP wavelength s:~f th~
oporating ~requenay .
To in~orporat~ the Josephson ~unotion ira the
20 ~ ~uperconductiv~ ring E;O it will be maximally e~ctive, it
i~ po~3itloned in the ~;trip resonator at a locatlon c~f
maxi~num current ~low in the strip x ssonator .
It ha~3 bl~en Pound to bs de~irable, ~or good coupling
or th3 ~trip re~onator to the ~lsctronia circuitry ror
deteating damplng and henc:e outputtlng th~ me~ur~ment of
magn~tio i~lux and which operate8 at xoom temperatur~,
~r-inaglk~r re~rred to a~ the room tempe:ratur~ eleotrs>nia
alrc:ultry, to utlllze ~or thi~ coupling the ic'urthl3r pi~ce
Or ~tr~p oondllcltor and to loca~e ik in a r~ion c: ~ ~he
strip re~;onator at which a ~tanding wav-3 antinode i8 ::
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A nu~ber o~ piece~ o~ the strip conduator ~erving
~or coupling purpoee~ oan be ~pplled to th0 strip r~sonator
at ~ ~ultipliaity o~ 8uch ~tanding w~va antinode~.
The ~en~or ~y~t~m o~ the invention, by comparl~on
with sarll~r seneor~ utllizing a rlng ~nd a JosQph~on
~unotion or ~le~snt incorpor~t~d therein, ha~ hlgh~r :~
sen~itivity to ~easurem~nt~ o~ chang~ in the magnetic
~lux. As a rule, th~ mea~urem~nt i~ ~ot a meaaure~Qnt o~
absolute values o~ magnetic flux.
Io More ~pecifically, eaah d~teotor o~ the pre~e~t
By~t~ can comprl~es
a ~trip ~upercon~ctor having a longitudinal axis .
and for~ing a strip re~onator ~or standlng electriaal wavss
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:~ ~ at;an operatlng fr~uency, thc ~trip r~sonator ~eing formed
~wlth an openlng and being ~ravar~able by the magnetic ~lux
nd~bounded ~y ~ supsroonductive ring o~ the ~trip -~
up-roondu~tor having a Jo~eph~oD ele~nt incorporat~d .
tha~e~in and ~t a boundary o~ the opening BO thàt the ring
~ 1ntegrated in the ~trip resonator, th2 JQ6ephson ~lement
:~ ~20 lying along the axl~ oP s~rip r~onator, and at least on~
further ~trlp conductor ly~ng Gn tha ~trlp re~onator and
; ~ aapaoitively coupl~d therete ~or oonnecting the re~pective
detaQ~or to the clrauit mean~. .
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U~;ually ~en~ors of this type ars use~ul only for
determining c:hange~ $n the magnetlc ~lux by moving th~3
~en~or along a body or ~y6tem along which th~ magnetic
~ield varie~ or by leaving the s~nsor in placa in a cas~
whlsre magn~atic variability r88ult~ ~rola the mag~3'cic Xleld
source. In the mea~ur~3ment rang~, therePore, a homogeneous
magnetic f ~ eld can ba detected by a lack o~ relative change
o~ the magnetic Plux by ~he ~ea~urQment.
When a nonhomoqeneou~ magnet1G ~Eluac i~ to be
detec:t~d, i.e. evaluated by mea~uring it, and it 18 .
de~irable to ~liminata the e~f~t o~ a ~uperimposed
hf:>mogeneous magnetic ~lux, ~or exampl~, in the region o~ a
60urce o~ ~lux dl~turbance, I can u~e a versi4n o~ the
sen~or of the invent~an in which along the center line or
lS ~ long~tudinal axi~ o~ th~ ~triE; re onator ther~3 are form~d a
plurality oP openlnstfi~ or holes in ~uac2s~3ion and bstwe~3n
wh~ch th~ Jo~ph~on element or el~ments can be prc~vid~d.
~he ~trllp re~onatl:>r in the region Qi~ the opening as well as
with re~poat to thl3 openlng and with r~paat to lts canter
.
lirle or lon~itudinal aacis ~hould than b3 ~ormed
a~ymmetricall~f .
Tbe asymmatry o~ the 0trip re,sollator in the region
o~ ~he opening~ a~3rVe# to gen~rate a hlgh ~requency current
in the Jo~3eph~0n ~lem~3nt. The asymmetry can be realiz~3d by
~ providlng the l rlp re~onator at one o~ tha openirigs with a
lateral outout or re~ o l:h~k a oon~trict~on i~ ~ormed
~ at thiE~ loaation. The aurrent i~low ln this aonstrlction o:e
, . .
lthe ~trip res~nator, ther~Pore, i~ erenk ~rom th~
curr~3nt ~low at th2 corre~ponding location in th~ viainity
o~ tha other opening, i . e. lthe current di~trlbution along
th~ two o~enlng~ diPPers~ Thls ensure~ a resultant current
through the ~ro~eph~on ~unation.
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18004
It 1~ al~o po~;iblQ to detect or to ~ea~iure an
~nhomoqeneou~ maqnetic 1ux in the region o~ both openingF: : :
or a di~erently changlrlg magnetic ~lux irl thi~ meaJ3uring
rang~3 with re~renc~ to th~ two op~nlngEi, ~or example, in
the ca~ of changing braln ourrent~
~ccording to this a~p~at ,ie the inv~nt~on, gurthar,
the opening~ can be arrangeid ~y~metrically o~ the ceinter ::
linei or longitudinal axi~ o~ tha 6trlp. A~ ntioned ;
above, moroOvQr~ t;he~ lungth 1 o~ tbe f~trip re~sonator can be
an odd number ~ultiple o~ th~ hal~ wavelength o~ ths
opera~ing Prequency, thl3 Josephsoll element c~n be di~3po~ad
at a ~axi~u~ curr~nt~ ~low loc~ on oP th~ ~trip re~onator :
and th~ strip condua~or ~or capacitive coupl ing o~ the
trip ro30nat~r can ~bei di~po~ed in a regiosl O:e a curren1: ;:
~ ant:inode of the standin~ wav~
Nor~ ~peoi~i~ally, one or both o~ the detactors can ~ ;
aompri~e a strip ~uperoonduc~or having a longitudinal axis
and~f~ormlng a ~tr~p resonator ~or ~itanding el~ctrical waves
at:~an operating ~requency, the ~trip re~onator being ~ormed
: with two eguial ~z~d opening~ ~ormed in ~iucce~ion in the
strip re~on~bor along thei axi~ and h~ving a ~o~eph~on
elam-nt p~ovidedl thsr~betw0en BO th~t tha openin~ de~ine :
uparsondu~tive rlngs~ int~grated in ths ~trip resonator
; with the Joseph~on ~ ment lylng generally along the axl~, ;
: 25 ~ th- strip r~sonator in ~he region o~ the openings and with
r~p~at:to the axi~ being ~ormed ~ym~etrically, and a ;:
urth~r :~trip aondua~or lying on the Btrip resonator and
; capacitively coupled thareto ~or oonnectlng the respective
detec~or to khe c~rcui~ m~ans.
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Accordlng to a Purther ~eature Or the invention, ~he
Jo~3phson ~lem~nt 1~ ~orm6~d a~3 ~ ~icrobridg~ and the part
o~ the oubstra~e b~n~aath th~ Jo~3eph~0n el~3ment 1
~on~tltuted o~ tarlal h~3vln~ th~ lle~t po~l3ible
th~rmal conduGtivity, l.e~ a low thelrmal c:onductiYlty alnd a
thermal conductivlty that iEI l ~awer tharl that o~ the strip
condu¢tor~3. In th1s manner, the he~t g~nerated in the
Jo~eph~on elem~nt by ~ ;ipation at th~ r:ritic:al c:urrent o~
th~ ~oseph~;on ~lement can be r~duc~d in ~ particularly
l3~Pectiva mann~r wh~n the period dl ration of th~ operatinr3
fre~uency of th~ ~;en~or i~ 6mall by s;:o~nparilsorl witb th~ -
tl~ ov~r whis::h th~ h~at arisin5~ ~n th~ Jc~6eph~n ele~nent
: mu~;t be carri~d away by thea~mal conductiv1ty .
15 ~ ~Q ahove and~other ob~ect~ eature nd advantagss
~: ,
o~ my inv~ntio3l will becoma more r~adily apparent ~ro~ the
rollowirlg de~cription, re~erence beirlg made ~o ~he
ac¢ompanying highly diagrammatio drawing in which:
FIG. 1a i8 a platl viaw o~ one ver~3ion o~ ~ d~tector
20 ~ ~ wh~ah can ~ u~ed in aa¢ordan~e with the invention having a
n~le operling in th~ superaonduct~v~ ~trip xesonator and
showing~ th~ Purt:her ~trip conductor a~ ~lightly og~sst fro
: th0 ~trip re~orleltor ~lthough it normally will be ~o t::lo8ely
uxtapo~ed ther~wl~ll a~ to b~ aapaaitlYely coupleà
2 ~ ~ ~h~3r~to ~
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70577-71
FIG. lb is a section taken gene ~ ~y along the line
A B of FIG. la, i.e. is a longitudinal section through the
strip resonator thereof;
FIG. 2a is a view similar to FIG. la but in a version
wherein the strip resonator has two holes or openings;
FIG. 2b is a section along the line A'-B' of the
strip resonator of FIG. 2a;
FIG~ 2aa is a view similar to FIG. 2a but showing a
slightly modified version;
FIG. 2bb is a section along line A"-B" of the strip
resonator of FIG. 2aa;
FIG. 3 is a view similar to FIG. la but showing the
meahanical support for the sensor and its electrical connections;
FIG. 4 is a block circuit diagram for the circuit
;means associated with each detector or sensor;
FIG. 5 is a block diagram of the o~erall circuitry ~ ~
of the SQUID of the invention; and ;~ ;
FIG. 6 is a block diagram of the correlation circuit.
Specific Description
~ In accordance with the principles set out in the
:, . -
above-ldenti~ied United States application, the sensor shown in
a~slmpllfied form in FIG. la comprises a strip resonator 1
having an opening or hole 2 integrated therein and ~orming
~around that opening a superconducting ring. The resonant
current paths are represented at R, Rl in FIG. la. The closed-
,,
path~low traverses a Josephson element 3 disposed along alongitudinal a~is LA which is parallel to the centerline CL of
the strip resonator 1. What is important, of course, is that
the~portion ll of t:he strip resonator opposite the Josephson
elemen~ 3 is wlder than the Josephson element.
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The ring and the Jo~3~ph~0rl ~lemsn~ 3 ~or~ a tank
¢irauit in which an o~cillation i.E~ genor~ted with thl3
oscillat10n aurrent R, R~L A maglnet~c ~lux through the
hole 3 or even ad~acent th~: seneor will aau~3i3 damping o~
tha o~oiLllation a~ desaribed abov~ and this e~ect, coupled
to the E~t:andir;lg wav~ in the ~trlp 3:e8011atOX', ::an be :
capacitiv~3ly detecl:ed in another ~3trip conduotor 4 arranged
parallel to the strip resonator 1 and ~;erving ~or the
oapacltive coupling o~ the ~;triLp resonator to the circuit
means repre~erlted in FIGS. 4 and 5.
StrIp re~onator and the ~urlth~r ~trip conductor ~
are applied to a substrate 6 which~ ~n turr~ ; aarried by
a ~ub~trate holder 7 th~ length 1 o~ the 6trip resonator i~ ~
~o dl~ 3n~iDned 'chat it c:c7rrespond~ to an odd ~ultiple o;
. . ~
th~ hal~ wavelength of th~ operating ~r~quency ~. ~he
Jos~ph~on ele2a~rlt i~ loc~t~d at A raglon oie ~axl~nur~ curra~t
flow of tha Ætrip resonator.
FIC;. 1~ ~how~3 the ~en~or o~ FIG. 1 in longitudinal
ction.
.
In thlE; ~IGUP~ the ~;ubstrate holder 7 is shown in
qreater d01:ail and can be bo h highly e1Q~triCa11Y ~nd
hlghly th~rmally ~onductlv~3, i . e~ compc~sed olE a mat~3rial
copper. q'~Q 0ub~3trate ~ i~ a T~atf~rial alP the ~malle~t
pos3sibl~3 diç~lec:trio lo~ type a~nd oan be compo~;e::l, Por
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example, of A12O3 (1 mm thick~. The strip resonator 1 is
composed of a superconductive material, for example Nb 100 nm
in thickness and is formed with the opening 2. Note that other
superconductor~ such as the high~temperature superconductors
described in the aforementioned publications can be employed
and that the device is intended to operate at cryogenic
temperatures, below the critical temperature Tc oE the niobium
or other superconductor.
The version of the sensor illustrated in FIGS. 2a and
2b also makes use of a strip resonator 1 in which, however, two
openings 2a and 2b are provided with the Josephson element 3
disposed between these openings. The other strip conductor 4
providing the capacitive pickup, has also been illustrated.
In the region of the gradiometer opening 2_, the
strip resonator 1 is formed with a cutout or recess 5.
Alternatively, as indicated in FIG~ ~aa r the strip resonator
is formed with a cutout or recess 5 in the region of opening 2a
as well as 2b so that the strip resonator is only point
symmetrical with respect to a point formed b~ the Josephson
element 3. As has been developed above, this version of the
sensor is particularly efective for the measurement of non-
homogeneous magnetic fluxes.
FIG. 3 illustrates the mechanical support and the ;
electrlc~al connection to the sensox.
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on tha ~ubstrata holder 7, a Purther !3ubE~trate 6~, $~;
provld~d And ç~rrle~ urth~r pil~G~ ~ Or ea ~trip condu~ or
(5 ohm~) whiah ia c:e~entad to the ~ub~trat~ The 13trip
condus::tor piec~ 4 i~ rlc:ally c:onneoted wl'sh the ~3trip
S aonduatQr 8 by ~hort ~1l uminum wire~ 9 ~nd the sheath oP ~
coaxial oabl~s 10 i~ aold~red to th~ holder 7 while the ¢ore
wire o~ the coaxial cabl~3 iB ~oldered to the Btr:lp
conduotor 8 . The aahle 10 run~ to th~ ~lec:troni ::
evaluation circuitry.
Io FIG. 4 lllu~tr~ts~ thia clrcuitry in the c:ontext o~
thla lnvent ~on.
For the operation O~e th-3 l3en~30r ot t21~ inYention ~ a
high ~ ~r~quency curren~ 1~ g~3n~rated, e.g. a a ~ruquency o~
3 . 5 GHz. For thl~ puxpof3e a hlgh ~requency generator ~o i~
;- 15 : ~ p~ovided~ It~ a~plitude ia controlled by a variable
a~ttanuator PIN to ~t t:h~ optl~ur~ lavel ~or the re~p~Sative
nsor.
: Thl~ current 1~ ~up~rimpo~ed upon tha Btrip
;re30nator via a directional coupl~r DC. ~h~ voltage acros~ -
; 20 ~ ~tbo~ r~sonator i~ 1ni~1ally ampl~led ln a preampl~er ~MP
and ~ubj~atad to a~plitude demodulation at SA.
: : ::, : :
~: ~ rh~ r~ulting low frequency voltage whioh aontains
tha lnrormation a~ to ~hang~ in tha magnetic ~lux .~ ~
travqr~ing~tha:sensor aan be d~playad on an o~CillosCopQ :,
25 ~ whioh;c~n~b~ optloDal ~ reprasented ~y th~ dot-dash 1ines
whon~th oorre1atio~ ctronice oP the lnventio~ aro
employe~ In that C~5~ t~ output o~ the aorr~lation
leatronlo~ can~b~ connected to the SQUID di~play, e.g. an ~;~
oso1110scope or~any other analysi~ or display d~vic~. ;
,
.: .
1800~
Th~ en~o~ pr~erably oparat~d in a ~lux-lock~d
loop sylatam and ~or that purpo~o a low Pre~ ncy generator
11 hav~ ng an output of approximal;ç~ly 2 kHz 1~ connect~d to
a coil 12 dl~pQsed i~ th~ regioll o~ the ~en~or to provide a
magn~ti¢ alternating ielux feedbac~ with a ~req[uency ot' 2
k~Z c ,,.
Vla th~ loak in ampli~ler LKI and integrator INT, -~
th~ n~agnetic flux ~uperimpo~ed on the ~en~or oan be
malntained con~tant. A switch 13 in E;Qries with a resi~ter
~L4 aan cut in th~ ~lux locked loop c:~ rcuitry.
Fl~;. S ~hov~ the interconnectlon o~ two ~y~te~s o~
the lty~?e illuo r~t~d i3~ ~IGS. 3 and 4 to ~orm a SQUID with
~orralation alectronic~ XE ~or al imillating uncorrelated
noi~a sl~nalc.
15: Th~ two block~ S ~ A sh~wn in FTG~ 5 each c:orraspond
to th~ ~n~or 8 oP ~I&. 4 plu~ the ra6peCtivQ oircuitry A : :
`
f~or valuating the sen~or output . Thi a circuitry has a
lte~inal: ~ which 1~ oonneated to a r~pective input o~ the
corralat~cn cirou~ltry KE. AB ind$cat~d prllaviou~ly, that
. ~: 2 o :~: c:irc:uitry can utilize autocorr~alation oircuitry (sea
chapt~er 25, pag~ e and 15 ~ o~ P~adar Handbook, Merrlll
: I . Bkolnilc, HcGraw-Hill Book Company~ ~ew Yorlc, 1970 or : :
ahapter 20 page~ 21 ~ th~reo~ 86~e al~o c:hapter 20 pages 3
fe~ ~ cros~3 oorrelation circultry o~ c:ol3ventional design or :
~5 : ~n~mble proo0e~ g clrouitry. The output Q can b~ ::
applled to a aG~putar ~valu~tlng the output o~ th~ S52UID
and aontrolling th~ display on an oaaillo~cope or other C:RT
yater~ of the blomas3 netis:~ brain or heart ~;ignal s or the
.
l ike .
1 6 -
.
,,
'
18 004
For ~ensor~ oP 1:21e type ~hown in FIGS. la ~nd 1l3 the
~ollowing parameters c:an be u~ed~
The ~3ub~r~te 6 can consi~t o~ ~apphire with
dlmen~lon~ o~ 25 x 5 x 1 mm3 (widlth x length x
thicknes~3. The niobiu~ appli~d ln a thick7le~s o~
100 n~ by cathodia sputtering, util~zing a ma~k or the like
to 3tructure~ lts ~11~ and ~orm th~ opaning ~ th~r~in. Th2
~trip conductor re~onator 1 can have a length cP 2 0 ~n and
a width of 1 ~. Tha op~ning 2 o~ tho ~en6~0r ~a~
dl~ensions o~ 40 x 40 ~icrs:~Meter~. Th~ Jo eph~on ele~e3~t 3
18 tormed a~ a aicrobridg~ with ~ wldth oP 150 ~icrometer8
ansl ~ lerlgth o~ 3 m~cromatarsO It al~o ¢aE~ c:on3i;t o~ a
Jo~eph~c~n tunnel ~unction. Tha ~ub~trata hold~r 7 wa~ a
copp~3r blcsak. The appl ~ ~d high ~ra~uenoy ourr~nt had a
15: ~ fregu~ncy o~ 3.5 GHz with a pow-r o~ 40 d~. The
PluY-d~pendont voltag~3 chang~ d~tect~d by the tank clrcui1:
carl aD~ount to ~aver~l hundred 2~lcrovolt~ pe~k-to- peak. q`ha
measurements were carried out at a temperatur~ o~ tha
sen~or o~ 4 . 2k.
~ ~ ~irl~ilar paraD~ter~ . can b-3 u~ed wlth th~ sansor o~
FIG6. ~3a and ~
ln ~IG/ 6 I h~e ~how~ a corr~lation airauit I~E
:
wl~ich ma~ bo u~ad a~ the correla'clon oirau~'cry ~or
ellmlriatin5f unoorr01ated noise ~rom tha output and which
~S : ba~ically i~ ~ xoot ~nean equara d~vica whosQ amplî~ier~ 20
nd ~1 ar~ aonnec:t~d to th~ two SQUID ~3en~0rs and
.
~ : ..
18004 ~ i 7 .~ ~
......... .. . .
'':'
respectively ~eed a ~ultiplier 22 ~ollowed by ~rl av~rager
23 ~nd a root-taking unit 24, all o~ which ara Or
conventional s:ircult de~ign. Whil~ the E~ensor e,y8'Cerrl oP
the~ lnventlon ha~3 been ~hown with only two SS2UID~, it will
be under~tood that additional air~ of SQllIDs ~ay al~o be
used ~30 that th~ sy8tem can operate with ~our or eix SQUIDs
working into the correlation c ircuitryO
i: : : ~ :
::: : : :
. ,. . ......... ... ., . , ". ,, . ,~ , . . .. .. .
