Note: Descriptions are shown in the official language in which they were submitted.
1:~8
m e present invention relates to apparatus for locating
non-linear junctions between metallic materials and/or semicon-
ductive materialsO It is becoming more essential every day to be
able to detect and locate devices containing metallic materials
or semiconductive materials having non-linear junctions there~
between. Diodes, transistors, semiconductive devices, and corroded
joints between the electrical conductors represent some of the
non-linear junctions. Such ~unctions occur in a great variety of
electronic and electrical devices and in particular occur in
electronic bugs and radio-controlled mechanisms. m e detection
of these devices using readily available close proximity sensors,
which relay on the magnetic and dielectric properties o~ materials
is virtually impossible in buildings and structures. Non-linear
~unctions which exhibit a ~uare law respon~e with respec~ to
voltage and current across the junction when illuminated by
electromagnètic signal~ re-radiate ha~monics rela~ed to the
frequency o~ the illum~nating electromagnetic signals. m ese
~unctions act as multipliers so that a signal, which may be
represented by ~ sin ~lt, when multiplied by itsel~ in a square
law junction, gives the standard square law response o~ equation 1.
(~ æ~n Wlt)2 = E12 (1 - cos 2 ~lt) (1)
The El cos 2 ~lt term gives the second harmonic term.
Higher harmoniG terms are produced b~ a successive ~
sel~ multiplication process. ~.
~4 ~ ~
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These signals have been a problem in th~ l~w frequency
communications bands where power output and ~ransmitter density
are high and in the microwave bands where the ~unctions are most
efficlent. The above radiated signals are known as inter modulation
interference and the prior art ha~ concentrated on locating the~e
signal sources using the principal that theæe re-radiated or
return ~ignals are harmonics o~ a sin~le frequency. The prior art
thereore has concentrated on detectlng the second and third
harmonic return signals. One o~ the~e apparati which overcomes
some of the difficulties a~sociated with magnetic and dielectric
detection provide~ a transmitter for transmitting a single signal
of requency o and two receivers which are tuned to receive the
second and third h~rmonics, 2fo and 3fO respectively o~ the trans-
mitted signal. A pure signal o~ ~requency ~O 1B empLoyed to
illuminate an ~rea suspected o containing non-linear ~unctions.
If the suspected area does not contain non-linear ~unctions, the
area will re1ect only a signal of original frequency o, which
signal is ignored, If the suspected area does contain non-linear
junctions~ the re-radiated ~ignal will not only contain original
frequency fO~ but will al50 contain harmonics of frequency fO.
These harmonics will be detected by multiple receivers tuned to
these harmonic frequencies. Th~ d~tector contains a transmitter
~hat generate~ and radiates a pure signal of frequency fO. This
tranæmitter is carefully shielded and iltered so as to prevent
the leakage of harmonicæ from the transmitter. The detector al50
contains two receivers, on~ tuned to the seco~d harmonic 2o of
the transmitted frequency~ The local o~cillators of both of these
receivers are derived from the transmitted frequency.
However, this apparatus ha~ ~ot been entirely satis-
~actory since the sens~tivity o~ the apparatus is limited due tothe problem of having to decouple transmitter harmonics ~rom the
receiver channel as well as to avoid harmonic response in the
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receiver to the fundamental transmitter frequency~ The latter
sources of spurious re~ponse ~eriously limit the sensitivity of
the apparatus. It becomeæ increasingly costly ~o attempt to
improve the sensitiv~ty o the device by improYin~ the decoupling
o the transmitter harmonic~ from the receiver channel and/or
eliminztion of harmonics from the transmitted frequency.
~hs applicant has provided a novel apparatus providing
improved sensiti~it~ without the a~tendant complexity and expense
of prior art apparatus. In a pre~erred em~odiment, the apparatus
la comprises means for radiating a firæt signal having a frequency fl,
means for radiating a second signal having a frequency f2 different
rom said first signal, and mean~ for detecting the presence of a
predetermined frequency in a return signal, said predetermined
frequency being glvan by nlfl~n2f2 where nl and n~ are inta~ers~
The apparatus will be de~cribed in greater d~tail with
reference to the dr~wings in which:
Figure 1 i~ a block diagram of the apparatus.
Fig~, 2 and 3 are block dlagrams of other embodiments of
the apparatus.
Fig. 4 show~ an embodiment of the sonic transponder.
In the pre~ent i~vention9 the applicant provides as
shown in Figure 1 in bl~ock form, signal generators 1 and 2, w*~h
output carrier freque~cies of fl and f2 respectively, ~nteDna~ 3
and 4 for radiating the carrier signals fl and f2, an antenna 5
which receives signalsg returned by a device 8 to be located, to
provide an input to a receiver 6, and a display unit 7 which
presents the receiver output in a sultable ~orm.
Although i~em~ 3, 4 and 5 are shown as separate elements
in the figures, it is to be understood that they may be combined
into a single unit, such as by the use o~ a multiplexer.
V~rious other changes and improvements such as providing
frequencies fl and f2 from a singl~ oscillator as well as the
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local oscillator signal for the tuned rece~ver are co~templated.
The principal o operatio~ of the appl~cants novel
app~ratus will now be more ully de~cribed with the aid o~ the
following equa~ionæ.
The expansion of the product o two slgnals represented
by Elsin CJ lt and E~sin ~ 2t is giv~n by equation 2.
(Elsin ~ lt ~ E2sin ~ 2t) ~ E1sin ~ lt ~ 2 ElE2sin ~ 1t.sln ~ 2t
E2S~n2 ~ 2t (2)
The squared terms may be expanded to produce
El coæ 2 ~ lt and E2 cos 2 ~ 2t (3)
2 2
and the product term may be expanded to produce
, . . _
1 2 1 ~J 2)t - ElE2 cos ( ~
Higher order harmonic terms ~nd terms with frequencies
given by nl ~ 1 * n2 C~ 2 (where nl and n2 are integers) are pro-
duced in addition to those indicated by equations 3 and 4 by a
succes~ive sel~ multiplication process.
The applicants apparatus by providing two transmitter
frequencies, i~ able to cause the non-linear ~unction to re-
radiate frequenc~es which are not only harmon~cs or squared term
product~ as given in eq~ation 3, and as is the case in prior art
apparatus, ~ut frequencies whlch are the sum and diference of
the transmitted requencies or product term ~reguenci~ given by
equation 4. This allows the applicant~ apparatus to have
unexpectedly higher discrimination and selectivity than prior art
apparatus of the same complexity.
It is to be understood that where the ~erm non-linear
~unctions ~s used, it is meant to comprise semiconductive ~unctions
such as occur in de~ices made ~rom semiconductin~ material ~or
example, transistors, integrated circuit~ and related devices,
semiconductive ~unctions formed by oxidatlon products of metals
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and related phenomena~
The above apparatus may be adapted ~or use in location
of radio oontrolled apparatus, unlicensed or unauthorized equip-
ment, airport surveillance9 detection of stolen goods~ detection
and location of electronic bugging devices and remote sensors
placed for intelligence purposes.
A second embodiment a~ shown in Figure 2 i8 similar to
that shown in Figure 1, except that it ~how~ modulation signals 9
and 10 superimpo~ed on the carrler signals to provide increased
~ensitivity, in detection and identification by providing improved
discrimination and diferention between desired and spurious
signals. With increased power and the increase of sensi-tivlty and
discrimination available through the u~e o ~odulated carrier
si~nals, the apparatus may be adapted ~or the det~ction oE aircra~t,
either foreign or cr~shed, detection and location o~ ships over
the horlzon, and sub~arines.
The present invention al80 contemplates the use of
carr~er modulation scheme~ to obtain additional in~ormation such
as range and bearlng of the d~vice to be located as well as
providing range and be~rlng selectivity. With range and bearlng
capability, the above apparatus could be used for the provision
o~ channel markers as an aid to navigation at night and in bad
weather9 collision avoidance, search and re~cue operations, pro-
vi~ion o passive markers for surveying purposes~ and automatic
focusing of movle and television cameras on moving ob~ects or on
fixed ob~ects when the camera is moving.
It is also contemplated that devices containing non-
linear elements could be placed at ~obile or ~ixed locations or
various re~ote sensing, interrogating control and communication
purposes~ The above apparatus could then be used for remote
sensor interrogation, motion detectorfi, proximity indicators and
uses, and securing communications by having a sender modulate the
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mlxing efficiency of a diode connected to an ante~na which is
illumlnated by two signals at fre~uencies ~upplied by the intended
receiver.
In another embodiment o~ the invent~on, it is conte~plated
that the present inventlon may act a8 a sonic transponder. The
sonic transponder consists of a ~ound e~ergy to electrical energy
converter or transducer 11 a6 shown in Figure 4. The electrical
output of the transducer i9 fed to a non-linear element 12 which
produces currents having requencies equal to the Sums and differ-
ences between harmonic~ of the frequencies of the ~ound waves 13incident on the tran~ducer. The transducer co~verts these currents
into sound waves 14 which eminate there~rom in such a manner that
the sonic transponder behaves like a ~onic rectifier.
In Figure 37 which is ~imilar to Figure 2, the transmitter
2 o~' frequency ~2 i8 modulated by a 8ignal 9 with a requency ~3.
The output o the tuned receiver i8 fed to ~ phase detector 15
which compares the pha~e o~ the 8ignal 9 with the demodulated
output 16 from the tuned receiver. The element 5 may be an antenna
or a suitable recep~ion transponder, The elements 11 a~d 12 form
the sonic rectifier or transponder. The outputs 17 and 18 are
respectively output~ to a range indicator and a direction indlcator.
The sonic transponder ~ay be used as a sonlc position
; 1ndicator. The distance between a reference marker containing the
sonic transpo~der a~d the transmit-receive assembly ie obtained
from the phase di~ference between the modulation signal f3 at the
transmitter and its demodulated version at the receiver. The
direction of the reference marker is obtained by rotating the
direction~l transmit-receive array consisting of elements 3, 4 and
5 to maximize the de~odulated receiver output. If the difference
requency 1 - f2 is an audio-~requency, it could also be used or
direction indlng. It can thus be seen that the prasent invention
is capable of operation in air, liquid, gas or solid and may be
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used to detect man-made devices a~d natural m~ter~al~ exhibiting
sonic rect~fication,
In summary, the applicant has pro~ided in a preferred
embodiment, a first slgnal generator means providin~ a firæt
carrler signal having a frequency fl~ a ~econd ~ignal ~enerator
means providing a second carr~er æignal having a frequency f2,
first and ~econd ~ntennas or radiating the carri~r signals, a
third antenna, and a receiver connected to the third antenna and~
tuned to detect 8ign~18 radiatlng from any non-linear element,
which signals have requencies given by the sum and difference
of the products of nl times the fir~t carrier signal and n2 time~
the 6econd carrier signal where nl and n2 are integers.
