Method and system for detecting intrusions into a particular region

• US 6,271,754 B1
• Filed: 07/01/1999
• Issued: 08/07/2001
• Est. Priority Date: 07/01/1999
• Status: Expired due to Term

• Current Assignee: Microlynx Systems, Ltd.
• Original Assignee: Microlynx Systems, Ltd.
• Inventors: Durtler, Willem
• Primary Examiner(s): TONG, NINA C
• Application Number:
  US09/345,858
• Time in Patent Office: 768 Days
• Field of Search: 340/552, 340/565, 340/540, 340/541, 340/545.3, 340/567, 342/27, 342/28
• US Class Current: 340/552
• CPC Class Codes: B61L 23/041 Obstacle detection
• CPC Class Codes: G01S 13/04 Systems determining presence of a target based on relative movement of target G01S13/56
• CPC Class Codes: G08B 13/2491 Intrusion detection systems, i.e. where the body of an intruder causes the interference with the electromagnetic field
• CPC Class Codes: G08B 13/26 by proximity of an intruder causing variation in capacitance or inductance of a circuit

Abstract

An intrusion detection system for detecting objects entering a particular region is comprised of a transmitter, receiver and cable assembly, wherein the transmitter and receiver are connected at opposite ends of the cable assembly. In a first embodiment, the cable assembly is comprised of a transmit and receive cable pair that are aligned at each end and positioned at a constant distance from each other along the length. The transmitter is connected to the transmit cable at one end of the cable assembly, and the receiver is connected to the receive cable at the opposite end of the assembly, with a uniform electromagnetic field established between the cables. An intrusion perturbs the field, which causes a change in the magnitude and/or phase of the received signal. In a second embodiment, the cable assembly is comprised of a single detection cable with the transmitter and receiver connected to opposite ends. An electromagnetic field of propagation extends beyond the unshielded, or partially shielded detection cable and an intrusion causes a change in the effective dielectric constant of the cable. The change in the dielectric constant causes either a positive or negative phase shift depending on whether the intruding object is entering or departing the electromagnetic field. In either embodiment, the phase, or magnitude or both of the received signal are detected to produce a comparison signal which may be filtered to remove environmental effects. A response signal monotonically related to the magnitude of the changes may be produced and then compared to one or more thresholds. An alarm is indicated when the response signal exceeds a threshold.

Claims

1. A method for detecting the intrusion of objects into a region comprising the steps of:

A. generating a continuous wave (CW) radio frequency (RF) signal,

B. transmitting the CW RF signal into a first end of a cable assembly that includes one or more non-graded cables,

C. receiving the transmitted CW RF signal at a second end of the cable assembly,

D. detecting the phase or magnitude or both of the received CW RF signal,

F. comparing the phase or magnitude or both of the received CW RF signal to a CW RF reference to produce a comparison signal, and

G. generating an alarm when the phase or magnitude or both of the received CW RF signal differs from the phase or magnitude or both of the reference signal by more than a predetermined amount;

wherein said method further comprises;

a. filtering the comparison signal to remove slowly varying changes occurring in the comparison signal due to background environmental effects,

b. calculating a response signal monotonically related to the magnitude of the comparison signal, and

c. in the step of generating an alarm, generating the alarm when the response signal exceeds a predetermined threshold.

2. The method of claim 1, wherein the cable assembly includes a transmit cable and a receive cable of approximately equal length that are disposed at an approximately constant distance from each other, said transmit cable having a first end, a second end and a characteristic impedance, said receive cable having a first end, a second end and a characteristic impedance, said first end of the transmit cable aligned with said first end of the receive cable to correspond to said first end of the cable assembly, said second end of the transmit cable aligned with said second end of the reception cable, and further wherein:

in the transmitting step, said transmitter transmits the CW RF signal into the first end of the transmit cable, and

in the receiving step, said receiver receives the transmitted CW RF signal at the second end of the receive cable.

3. The method of claim 2 wherein

i. the transmitting step further includes terminating the transmit cable with an impedance equal to the characteristic impedance of the transmit cable;

and

ii. the receiving step further includes terminating with an impedance equal to the receive cable characteristic impedance.

4. The method of claim 2, wherein the transmit and receive cables are unshielded balanced cables.

5. The method of claim 2, wherein the transmit and receive cables are slotted coaxial cables.

6. The method of claim 2, wherein one of the transmit cable or the receive cable is a slotted coaxial cable and the other cable is a balanced, unshielded cable.

7. The method of claim 1, wherein the cable assembly is comprised of a single detection cable having a first end corresponding to said first end of the cable assembly and a second end corresponding to said second end of the cable assembly, and further wherein:

in the transmitting step, said transmitter transmits the CW RF signal into the first end of the detection cable; and

in the receiving step, said receiver receives the transmitted CW RF signal at the second end of the detection cable.

8. The method of claim 7, wherein the detection cable is a balanced cable.

9. The method of claim 7, wherein the detection cable is a slotted coaxial cable.

10. An intrusion detection system comprised of:

A. a local oscillator for generating a continuous wave (CW) radio frequency (RF) signal,

B. a cable assembly that includes one or more non-graded cables, the cable assembly having a first end and a second end;

C. a transmitter connected to the first end of the cable assembly for transmitting the CW RF signal,

D. a receiver connected to the second end of the cable assembly for receiving and detecting the phase of the transmitted CW RF signal,

E. means for comparing the phase of the received CW RF signal to the phase of a reference CW RF signal to produce a comparison signal, and

F. an alarm circuit for generating an alarm when the phase of the received signal differs from the phase of reference signal by more than a predetermined amount;

wherein said intrusion detection system further comprises;

a. a filter for filtering the comparison signal to remove slowly varying changes occurring in the comparison signal due to background environmental effects,

b. a circuit for calculating a response signal monotonically related to the magnitude of the comparison signal, and

c. the alarm circuit generates the alarm when the response signal exceeds a predetermined threshold.

11. The system of claim 10, wherein the cable assembly is comprised of a transmit cable and a receive cable of essentially equal length and disposed at a constant distance from each other, and wherein:

said transmit cable has a first end, a second end and a characteristic impedance, said first end of the transmit cable connected to the transmitter,

said receive cable has a first end, a second end and a characteristic impedance, said second end of the receive cable connected to the receiver, and further wherein;

said first end of the transmit cable is aligned with said first end of the receive cable to correspond to said first end of the cable assembly, and said second end of the transmit cable is aligned with said second end of the receive cable to correspond to said second end of the cable assembly.

12. The system of claim 11 further including

a means for comparing the magnitude of the received CWRF signal to the magnitude of a reference CWRF signal;

and

the alarm circuit generating an alarm when the magnitude of the received signal differs from the magnitude of the reference signal by more than a predetermined amount.

13. The system of claim 11 wherein:

a. said second end of the transmit cable terminated in the characteristic impedance of the transmit cable, and

b. said first end of the receive cable terminated in the characteristic impedance of the receive cable.

14. The system of claim 11, wherein the transmit and receive cables are unshielded balanced cables.

15. The system of claim 11, wherein the transmit and receive cables are slotted coaxial cables.

16. The system of claim 10, wherein the cable assembly is comprised of a single detection cable having a first end corresponding to said first end of the cable assembly and connected to said transmitter, and a second end corresponding to said second end of the cable assembly and connected to said receiver.

17. The system of claim 16, wherein the detection cable is a balanced cable.

18. The system of claim 16, wherein the detection cable is a slotted coaxial cable.

19. A system for detecting the intrusion of objects into a region adjacent to a railroad track, the system including:

A. a local oscillator for generating a continuous wave (CW) radio frequency (RF) signal,

B. a cable assembly having a first end and a second end, the cable assembly being situated adjacent to a length of the railroad track;

C. a transmitter connected to the first end of the cable assembly for transmitting the CW RF signal,

D. a receiver connected to the second end of the cable assembly for receiving and detecting the phase of the transmitted CW RF signal,

E. means for comparing the phase of the received CW RF signal to the phase of a reference CW RF signal to produce a comparison signal, and

F. an alarm circuit for generating an intrusion alarm when the phase of the received signal differs from the phase of the reference signal by more than a predetermined amount;

wherein said system further comprises;

a. a filter for filtering the comparison signal to remove slowly varying changes occurring in the comparison signal due to background environmental effects,

b. a circuit for calculating a response signal monotonically related to the magnitude of the comparison signal, and

c. the alarm circuit generates the alarm when the response signal exceeds a predetermined threshold.

20. The system of claim 19, wherein the cable assembly is comprised of a transmit cable and a receive cable of essentially equal length and disposed at a constant distance from each other, and wherein:

said transmit cable has a first end, a second end and a characteristic impedance that produces, when the CW RF signal is present on the cable, an associated electromagnetic force that attenuates along the length of the cable based on the distance from the first end of the cable, said first end of the transmit cable being connected to the transmitter,

said receive cable has a first end, a second end and a characteristic impedance that produces, when the CW RF signal is present on the cable, an associated electromagnetic force that attenuates along the length of the cable based on the distance from the second end of the cable, said second end of the receive cable being connected to the receiver, and further wherein;

said first end of the transmit cable being further aligned with said first end of the receive cable to correspond to said first end of the cable assembly, and said second end of the transmit cable being aligned with said second end of the receive cable to correspond to said second end of the cable assembly.

21. The system of claim 20 further including

a means for comparing the magnitude of the received CW RF signal to the magnitude of a reference CW RF signal;

and

the alarm circuit generating an alarm when the magnitude of the received signal differs from the magnitude of the reference signal by more than a predetermined amount.

22. The system of claim 20 wherein:

a. said second end of the transmit cable is terminated in the characteristic impedance of the transmit cable, and

b. said first end of the receive cable is terminated in the characteristic impedance of the receive cable.

23. The system of claim 20, wherein the transmit and receive cables are unshielded balanced cables.

24. The system of claim 20, wherein the transmit and receive cables are slotted coaxial cables.

25. The system of claim 19, wherein the cable assembly is comprised of a single detection cable having a first end corresponding to said first end of the cable assembly and connected to said transmitter, and a second end corresponding to said second end of the cable assembly and connected to said receiver, wherein an intrusion into the region adjacent to the railroad track results in a change in a dielectric constant associated with the cable and produces in the received CW RF signal an associated change in the phase, magnitude or both.

26. The system of claim 25, wherein the detection cable is a balanced cable.

27. The system of claim 25, wherein the detection cable is a slotted coaxial cable.