Proximity detecting apparatus

Apparatus and method for detecting changes in capacitance of an antenna due to intrusion into the antenna field by a body of different dielectric constant, in the presence of induced AC voltages on the antenna from electromagnetic radiation. The apparatus includes four operational amplifiers connected in a circuit for processing the production of voltage pulses. The first amplifier operates to rectify the AC voltages from the antenna to a DC fluctuating voltage, which voltages are averaged to produce a constant voltage above ground potential so long as there is no intrusion of the field. During this period no signal voltage is transmitted to the second amplifier. Intrusion will result in a decreased voltage level which causes the second amplifier output to swing from quiescent level to a lower level whereupon a negative going square wave voltage pulse appears at the output of the second amplifier and, through a capacitor, is applied to the inverting input of the third amplifier having its noninverting input terminal grounded. Normally, the third amplifier has zero output voltage and a negative going square wave voltage pulse from the second amplifier will produce a positive going square wave voltage pulse from the third amplifier, which feeds through a combined diode and R/C circuit and accumulator which has its output connected to the non-inverting input terminal of the fourth amplifier whose output is a positive going square wave voltage pulse applied to a transistor for triggering an alarm after a predetermined number of pulses have been accumulated.

BACKGROUND OF INVENTION 
Heretofore, proximity detecting apparatus have been composed of active 
elements that require a continuous supply of energy. 
One such apparatus has a continuously operating oscillator connected to a 
sensing element. When the capacitance on the sensing element changed due 
to the presence of an intruder in the field of the sensing element, the 
capacitance reactance would disturb the tuning of the oscillator circuit 
and it would cease oscillating to produce an increased current flow in the 
oscillator to activate a relay in an alarm circuit. 
Another apparatus has more than one oscillator, one tuned to operate at a 
constant frequency and another operable at a frequency determined by the 
charge and voltage on the sensing element. When there is a change in the 
charge and thus the voltage at the sensing element a beat frequency would 
be produced which would be detected to cause an alarm to be activated. 
Still another type of apparatus utilizes a metal oxide silicon field effect 
transistor instead of a vacuum-tube oscillator and the usual gas-type 
relay tube has been replaced with an npn bipolar transistor. When 
energized the oscillator will oscillate if there is no intrusion of the 
sensing element field. When intrusion occurs the oscillation ceases and 
there will be an increase in current in the transistor. This energizes the 
npn that is in the circuit of a relay that controls the alarm circuit. 
There are several drawbacks to such apparatus. The first is that they all 
use oscillators which must be kept oscillating during the quiescent period 
between intrusions and this represents a constant expenditure of 
electrical energy. This in turn makes it necessary to utilize the power 
lines as a source of energy with the attending drawbacks of power lines 
for power failure, providing easy access to circuits that might be cut and 
the attending transient peak voltages that often trigger false alarms. 
With the advent of the microelectronics and integrated circuit chips it is 
now possible to procure the extreme sensitivity, lower power drain and 
greater reliability. It is possible to provide circuits that have 
practically zero current drain during the quiescent periods thus making it 
possible to utilize batteries as a source of power and which now can serve 
for long periods of time without replacement. It is now possible to 
produce detecting apparatus smaller in size, with a minimum of complexity, 
less costly to produce and operate and easy to use. With these 
possibilities in mind it is the intent to provide a much improved 
proximity detector apparatus that may be used with simple and complex 
security systems. 
OBJECTS OF THE INVENTION 
It is an object of the invention to provide an extremely sensitive and 
reliable detecting apparatus. 
Another object of the invention is to provide a proximity detecting 
apparatus that is capable of operating with a minimum power drain and 
which can be powered with a battery. 
Another object of the invention is to provide a proximity detector that is 
affordable to the small operator, home owners and small offices 
establishments. 
Yet another object of the invention is to provide a detecting apparatus 
that is more selective in its response whereby greater reliability may be 
achieved. 
Other objects of the invention will become obvious as the disclosure 
proceeds.

DESCRIPTION OF THE APATUS 
The apparatus includes a sensing element such as an antenna and the 
detecting apparatus, each subjected to separate treatment necessary for 
the results that are to be produced. For the purpose of disclosure of the 
invention and particularly the antenna and detecting apparatus as a means 
for contributing to those results, they are disclosed together. The 
antenna in the present disclosure is one that is suitable to be placed 
under a rug or carpet along a path that would have to be followed by an 
intruder. It is also designed to frame a window and door and other means 
of access to the secure area. By using an antenna with a very restricted 
field its ability to pick up radiation will be restricted, and the noise 
voltages therein reduced. By placing the antenna along the path the 
intruder would have to follow it is assured that there will be an 
intrusion of the field of the antenna. Other types of antenna may be used 
and the disclosure of this particular one is not intended to be limiting 
the use of the invention thereto. 
An antenna cannot, unless shielded, be completely isolated from the 
radiation surrounding it and there will be alternating current voltages 
induced in the antenna though greatly reduced. By use of restricted 
lengths the antenna is made more responsive to higher frequencies which 
are of less intensity. However, the dominant radiation to which the 
antenna is subjected, is the sixty cycle radiation from electrical wiring 
of the building and power lines in the vicinity. In the present invention 
the voltage so induced in the antenna from the sixty cycle radiation is 
put to use in the establishment of a constant voltage whose level will be 
altered when an intruder enters the field of the antenna. The apparatus 
responds only to negative going changes in the level of the constant 
voltage which is produced by an increase in capacitance of the antenna 
when the intruder enters the field of the antenna. As the capacitance is 
increased by the intruder entering the field of the antenna, the voltage 
at the output of the antenna will decrease as will be seen from the 
equation 
EQU E=Q/C 
where E is the voltage in volts, Q is the charge on the antenna in columbs 
and C is the capacitance in farads. 
The antenna is shown as a conductor 8 which with conductor 9 serving as a 
ground is a twin conductor cable adapted to be laid under a rug and on the 
framing of a door or window. The antenna conductor 8 is connected through 
the input resistor 3 to the non-inverting input terminal of the first 
amplifier of the detecting apparatus. The amplifier is what is known as an 
operational amplifier of the type disclosed in FIG. 3 of the drawing. The 
non-inverting input terminal in FIG. 3 is terminal 78 connected to the 
transistor 46 of the operational amplifier. The ground conductor 9 is 
connected to the ground buss 2. The inverting input terminal of the 
amplifier is connected between the resistors 6 and 7 of a voltage divider 
that is connected between the voltage buss 1 and the ground buss 2 shown 
in FIG. 1. Amplifier 11 has a feedback circuit comprising a resistor 4 and 
variable capacitor 5 in parallel connected from the output terminal of 
amplifier 11 and the non-inverting input terminal of the amplifier 11. 
The ratio of the resistance of the resistor 4 to the resistance of resistor 
3 determines the amplification factor of the amplifier 11. The variable 
capacitor, being adjustable can adjust for differences in distributed 
capacitances between the conductor 8 and 9 and is for nulling out the 
capacitance. 
The sixty cycle radiation, if present on the antenna, will provide a sixty 
cycle alternating voltage on the antenna about the potential of ground. 
When applied to the non-inverting input terminal of amplifier 11, with the 
inverting input terminal biased at a voltage of V/2 from the voltage 
divider, there will be a sixty cycle direct current fluctuating voltage at 
the output of amplifier 11. The fluctuation will be about the V/2 voltage 
level. This output is transmitted through a diode 10 connected to the 
output and a filter circuit. 
The filter circuit comprises a capacitor 12 in parallel with a resistor 13 
connected to the ground buss 2. The output of the filter is through a 
capacitor 14. The alternating voltages from amplifier 11 are ironed out in 
the filter circuit to produce a constant voltage which will be at a level 
of V/2. This is applied to the capacitor but it will not be transmitted. 
The capacitor transmits only changes in voltage. Thus it will seen that 
until and only if there is a change in the level of the contant voltage in 
the filter circuit there will be no signal voltage transmitted beyond the 
capacitor 14. The constant voltage state of the filter circuit is during 
the quiescent periods between the intrusions of the antenna field. 
When there is an intrusion of the antenna field there is an increase in 
capacitance on the antenna. The increase in capacitance results in a 
negative going square wave voltage pulse being produced on the capacitor 
14. This square wave voltage pulse produces two spike voltage changes at 
the output of capacitor 14. The leading one having a negative going step 
voltage change followed by an exponential positive going decaying voltage 
as the charge on capacitor 14 changes, and a positive going spike voltage 
change having a positive going step voltage change followed by an 
exponential decaying voltage change at the conclusion of the negative 
going square wave voltage pulse. 
The output of the capacitor 14 is connected to the non-inverting input 
terminal of the second amplifier 15. The inverting input terminal of 
amplifier 15 is connected to the voltage divider between resistors 6 and 
7, whereby it is biased at a voltage of V/2. The output of amplifier 15 is 
connected through a feedback resistor 16 to the non-inverting input 
terminal of amplifier 15. 
As previously stated, the non-inverting input of amplifier 15 is normally 
substantially constant. When a negative going square wave voltage pulse 
with the negative going spike voltage change occurs, there is enough input 
to cause the output voltage to swing towards the negative value, where it 
remains until the positive going spike voltage change occurs at the end of 
the square wave voltage pulse, which causes the output to swing back to 
the initial level of V/2, where it remains until another square wave 
voltage pulse occurs. 
Thus, there is produced at the output terminal of the amplifier 15 a 
negative going square wave voltage pulse from a negative going square wave 
voltage pulse at its input. 
If a positive going square wave voltage pulse is produced in the filter 
circuit, as may well happen, there would be at the non-inverting input 
terminal of amplifier 15 a positive going spike voltage change followed by 
a negative going spike voltage change. This would cause the output of 
amplifier 15 to swing between the V/2 voltage level and the V voltage 
level and back to the V/2 voltage level to produce a positive going square 
wave voltage pulse at the output of amplifier 15. It should be noted that 
the voltage swings at the output of amplifier 15 are of equal amplitude 
and the amplitudes are constant and amplified over the input voltage 
changes. 
The output of the amplifier 15 is connected through capacitor 17 to the 
inverting input terminal of the third amplifier 19. The inverting input 
terminal is also biased from the voltage buss 1 through resistor 18 and 
the non-inverting input terminal of the amplifier 19 is connected directly 
to the ground buss 2. Amplifier 19 is also an operational amplifier of the 
structure shown in FIG. 3 to be described later. The non-inverting input 
terminal is connected to the gate of transistor 46 of the amplifier 19. 
Thus transistor 46 is the same as an open circuit. During the quiescent 
period the inverting input terminal has a V/2 voltage applied thereto 
causing a voltage drop across the capacitor 17. This produces a V/2 
voltage on the gate of transistor 42 (FIG. 3) causing it to have a current 
therein. The current flowing through transistor 42 produces a voltage drop 
across the resistor 40 and transistor 41 which is connected to the output 
terminal of amplifier 19, making it at a low voltage. 
Now when there is a negative going square wave voltage pulse transmitted to 
capacitor 17, this produces a negative step voltage change on the 
capacitor 17 followed by a positive going step voltage change at the 
conclusion of the square wave voltage pulse. A negative going step voltage 
change on the capacitor results in a greater voltage drop across capacitor 
17 and the voltage on the inverting input terminal will be decreased to 
zero. This produces a decrease in current in transistor 42 of amplifier 19 
and through resistor 40 and transistor 41 and thus an increase in the 
voltage at the output of amplifier 19. When the following positive going 
step voltage change is transmitted to the inverting input terminal the 
voltage at the output of amplifier 19 will increase to V/2 and the current 
in transistor 42, transistor 41 and resistor 40 will increase to produce a 
decrease in voltage at the output of amplifier 19. Thus there is the 
production of a positive going square wave voltage pulse from the 
amplifier 19 when there is a negative going square wave voltage pulse at 
its input terminal. 
Instead of a negative going square wave voltage pulse, let it be a positive 
going square wave voltage pulse produced at the output of amplifier 15. 
Again we start with a V/2 voltage level at the output of amplifier 19. 
Now if there is a positive going square wave voltage pulse, the positive 
going step voltage change would cause a decrease in the voltage across 
capacitor 17. This would result in an increase in voltage on the inverting 
input terminal of amplifier 19 and an increase in current in transistor 
42. This in turn produces a decrease in voltage at the output of amplifier 
19. But, this cannot happen because of the output from amplifier 19 is 
already at the zero level. Thus, the amplifier 19 does not respond to 
positive going square wave voltage pulses. This accounts for the 
selectivity of response of the apparatus for negative going square wave 
voltage pulses, which enhances the reliability of the apparatus. 
The output of amplifier 19 is connected through a resistor 20, shunted by a 
switch 21 and through a diode 22 to a parallel circuit having resistor 23 
and capacitor 24 connected to the ground buss 2. The circuit is connected 
from a point between the diode 22 and the parallel circuit to the 
non-inverting input terminal of the fourth amplifier 25. The inverting 
input terminal of amplifier 25 is connected to a voltage divider between 
resistors 26 and 27 which is connected between the voltage buss and the 
ground buss 2. The output of amplifier 25 is connected to the base of 
transistor 29 through resistor 28, which is in a circuit with a relay coil 
of relay 30, connected between the voltage buss and the ground buss 2. 
The coupling between the third and fourth amplifier 25 operates to select 
between one pulse response and a predetermined number of pulses. When the 
switch 21 is closed the fourth amplifier responds to single pulses from 
the third amplifier 19. When the switch is open, the fourth amplifier 
responds to a predetermined number of voltage pulses after the 
predetermined number of pulses raises the voltage on capacitor 24 so the 
the fourth amplifier is triggered. The output from amplifier 25 is coupled 
through resistor 28 which limits the current in the base emitter circuit 
of transistor 29. When transistor 29 becomes conductive, the relay is 
activated to close the contacts which are in an alarm circuit and the 
alarm is activated. 
FIG. 2 shows the same type of detector apparatus which is adapted for use 
of a single conductor antenna. An earth ground connection such as to water 
pipe, a ground rod driven in the ground is to be connected to the ground 
buss 2. The single wire antenna is connected through a diode 80 and 
resistor 3 to the non-inverting input terminal of the first amplifier. 
Otherewise the second version of the invention is the same as the first. 
The purpose of the diode 80 is to produce rectification of the input from 
the antenna to the non-inverting input terminal. 
FIG. 3 discloses the structure of the amplifiers in the chip which are four 
in number. They are operational amplifiers using metal oxide silicon field 
effect transistor structure, wherein the input is to gates made of a thin 
layer metal forming a capacitor input. The only difference between the 
amplifiers in the circuit of FIG. 1 is in the nature of the external 
connections and components that are connected to the amplifiers. 
As shown in FIG. 3. the amplifier is composed of three sections, namely the 
input section, the setting section and the output section. The input 
section is composed of a first and second circuit connected in parallel 
and in series with a constant current transistor 43. 
The first circuit comprises a resistor 40, transistor 41 which serves as a 
resistor and transistor 42. The gate of transistor 42 is connected to the 
inverting input terminal 77, made so by the connection 74 between the 
input and output sections connected between the transistors 41 and 42. 
The second parallel circuit of the input stage or section is composed of 
resistor 45 and transistors 45 and 46. Transistor 45 also serves as a 
resistor. The gates of transistors 41 and 45 are connected together and to 
the second parallel circuit between the transistors 45 and 46. The gate of 
transistor 46 is connected to the non-inverting input terminal 78. The 
conductivity of transistors 41 and 45 is decreased and increased as the 
current through transistor 46 is increased and decreased. The gate of 
transistor 43 is connected to the constant voltage buss 50 and the voltage 
is determined by the setting section. 
The setting section consists of two parallel circuits, one comprising of 
resistors 47, 48, transistor 49 connected to the constant voltage buss 50. 
The resistor 47 is shunted by the source-drain channel of transistor 55, 
which has its gate connected to the movable contactor of a three position 
switch 56. One position is connected to the voltage buss 1, another is 
connected to the conductor 70 leading to an exterior terminal 75 and the 
third of which is unconnected. 
The constant voltage buss 50 is connected to the gates of transistors 
43,51, 52, 58, and 63, and to the source-drain channels of the transistors 
51, 56, and 53. Transistors 52 and 53 have their drains connected together 
and through the source-drain channel of transistor 54 to the ground buss 
2. The gate of transistor 54 is connected to the movable contactor of a 
three position switch 59. One position is connected to the ground buss 2, 
another is connected to the circuit 79 and the third is unconnected. The 
circuit 79 has a connection 60 which will join the circuit 79 to the 
exterior terminal 75. 
The second of the parallel circuits of the setting section comprises a 
transistor 57 in series with transistor 58 between the voltage and ground 
buss 2. The gates of transistors 49 and 57 are connected together and to 
the second parallel circuit of the setting section at a point between the 
transistors 57 and 58. The second of the parallel circuits of the setting 
section serves as a voltage divider to control the bias on the gates of 
transistors 49 and 57. 
The output section is comprises of three parallel circuits connected 
between the voltage and ground busses 1 and 2. The first of said three 
circuits comprise of transistors 61 and 62 in series with transistor 63. 
Transistors 61 and 62 are in parallel with each other. The gate of 
transistor 61 is connected to the conductor 74 that connects the input and 
out put sections together. The first parallel circuit serves only to 
provide the bias on the gates of transistors 62 and 64. The second 
parallel circuit of the output section is comprised of transistors 64 and 
65 in series between the voltage and ground busses 1 and 2. The gates of 
transistors 65 and 76 are connected together and to the second parallel 
circuit of the output section. The second section serves only to 
determined the bias on the transistors 65 and 76. The third parallel 
circuit of the output section comprise of the transistors 67 and 76 in 
series between the voltage and ground busses 1 and 2. The gate of 
transistor 67 is connected to the conductor 74. The conductor 74 is also 
connected to the third parallel circit between the transistors 67 and 76 
through a capacitor 68 and a portion of conductor 71. The output terminal 
69 is connected to the same point on the third parallel circuit. 
A zener diode 66 is connected between the ground buss and the gates of the 
transistors 65 and 76. A zener diode 73 is connected between the conductor 
74 and the voltage buss 1. The output of the amplifier is determined by 
the voltage applied to the gate of transistor 67. The conductivity of the 
transistor 76 is held constant. The conductor 71 is connectable through 
the contacts 72 to the external terminal 75. 
Amplifiers 11, 15 and 25 have their non-inverting inputs connected to the 
terminal 78. Amplifier 19 has its input connected to terminal 77. 
Amplifiers 11 and 15 have their terminal 77 connected to the voltage 
divider. Amplifier 25 has its inverting input terminal connected to the 
second voltage divider between resistors 26 and 27. Amplifier 19 has its 
inverting input terminal connected to terminal 77 and its non-inverting 
input terminal connected directly to the ground buss 2. 
The mode of operation has already been made clear through the disclosure of 
the various sections of the apparatus. 
The most distinguishing features about the present invention is that the 
voltages derived from the radiation is utilized to provide a constant 
voltage at one level which is decreased in level when there is an 
intrusion of the field of the antenna. The apparatus selectively is 
responsive to negative going square wave voltage pulses and not to 
positive going voltage pulses, thus eliminates many of the causes of false 
alarms. The apparatus is extremely sensitive by utilizing all the 
capabilities of the amplifiers. Its current drain during quiescent period 
is so low that a battery can be used to power the apparatus, thus 
eliminating the need for use of power lines with all their attending 
drawbacks. 
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List of components and values 
Resistors Capacitors 
______________________________________ 
3 10 m 5 variable 
4 100 m 12 1 mf 
6 10 m 14 .1 mf 
7 10 m 17 .1 mf 
13 1 m 24 .1 mf 
16 100 m 
28 10 k 
20 560K 
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It will be apparent that various changes and modifications can be made in 
the details of the structure and use without departure from the spirit of 
the invention especially as defined in the following claims.