WO2012087386A1

WO2012087386A1 - Single-wire earth return electric fence with instruction location ability

Info

Publication number: WO2012087386A1
Application number: PCT/US2011/047894
Authority: WO
Inventors: Jin Hao; Xuekang Shan
Original assignee: Jin Hao; Xuekang Shan
Priority date: 2010-12-22
Filing date: 2011-08-16
Publication date: 2012-06-28
Also published as: KR20120071305A

Abstract

An electric fence is described for perimeter security. The electric fence has a metal wire that surrounds the area to be protected, a signal generator and a receiver. The signal generator's output connects to the metal wire and ground, forming a single ended system. The receiver is also connected between the wire and ground via a transmit/receive switch. The signal generator launches the signal into the wire/ground loop. Preferably, the signal is a single or multiple short electric pulses or coded pulse train. At the end of the wire, part of the signal energy is returned towards the receiver. When an intruder touches the wire at a point, a shorter return path is established, and the receiver receives this returned signal earlier than without an intrusion. The distance of the intrusion point to the terminal can be calculated by the time difference when the signal is launched and when the returned signal is received, since the signal propagation speed is 300m per micro second.

Description

Single- wire Earth Return Electric Fence with Intrusion

Location Ability

Background of the invention

Electric fences are widely used for a variety of applications, mainly being animal control and border security. These electric fences generally consist of bare metal wires mounted on poles via insulators. The metal wires are electrically coupled to a charging device to have a high electric potential relative to ground. The wires will send an electric shock to the intruder or animal when touched.

In some situations, especially in security applications, accurate location of intrusion is essential, since the security personnel needs to quickly determine the type of the intrusion and take corresponding counter measures.

However, most of the present day electric fences do not have this location ability. A recently filed patent (application number 12954704) described a transmission line based electric fence with intrusion location ability. It consists of a transmission line (a metal wire pair), a pulse transmitter, and a receiver. The transmitter launches a short electric pulse into the transmission line, which than propagates down the line. When the intruder touches the line, the line will see an impedance change at the point of intrusion, and a portion of the launched energy will be reflected back towards the receiver. From the time interval between launching the pulse and receiving the reflected pulse, the intrusion can be located. In this transmission line based electric fence, a metal wire pair is needed. This metal pair needs to have low loss, to be weather resistant, to be rust free, and needs to be installed properly so as to have a uniform

characteristic impedance throughout. As a result, the cost of the wires and their installation becomes a considerable part of the system total cost.

Therefore, if a single wire electric fence could provide similar

functionality, it would be highly desirable.

Summary of the Invention

The present invention is a system for locating an intrusion alone an electric fence. It consists of a single metal wire, a signal generator, and a receiver. The metal wire is mounted on fence poles via insulators. The signal generator's output is applied between one end of the wire and the earth. The receiver is connected to the same end of the wire via a transmit/receive switch and a band-pass filter, and the earth. The other end of the wire is connected the earth directly or via a resistor. These components form a single-ended system between the wire and the earth. The signal generator launches signal into this system. When there is no intrusion, the receiver will only see the returned signal from the end of the system. When an intruder touches the wire at a point, a new and shorter earth path is established. The receiver will see an earlier returned signal than without the intruder touching the wire. The distance of intrusion can be calculated from the time interval from the time the signal is launched to the time the returned signal is received, since the pulse propagation speed is 300m per micro second.

Brief Description of the Drawings Fig.l shows a preferred embodiment of the present invention;

Fig.2 shows an experimental result without noise reduction;

A single 33 nano second pulse was launched, and a returned signal was detected with a 480 nano second interval. The distance was calculated as 72 meters. Since there was no noise reduction, one can see a curved baseline, indicating unwanted background noise in the system;

Fig.3 shows a predicted result with noise reduction. One can see a straight baseline, showing the unwanted background noise is removed.

Detailed description of the embodiment Fig.l shows the details of the present invention. The electric fence 9 includes signal generator 12, metal wire 10, electric receiver 13, transmit/receive switch 15, and signal processor 14. Metal wire 10 is supported by insulators which are mounted on a wall or normal fence. Signal generator 12 launches signal (preferably a single or multiple pulses or coded pulse train) into metal wire 10 with a given time interval. The other end of metal wire 10 is connected to earth directly or via resistor 16. When there is no intrusion, the signal generated by electric signal generator 12 propagate along transmission line 10 till its end and then return towards the receiver. Signal processor 14 records this signal as reference signal. When intruder 17 touches the metal wire at point 18, a shorter return path is established, and therefore the receiver sees an earlier return signal. Signal processor 14 records this signal and

compares it with the reference signal recorded earlier. This comparison determines that there has been an intrusion.

Compared to the transmission line based electric fence which employs a wire pair, this single wire earth return electric fence is more susceptible to electro-magnetic interference, as is shown in Fig, 3. One can see a curved base line in the received signal, which is background noise. In order to improve the received signal quality, one or more of the

following methods can be applied to reduce background noise: Band-pass filtering. Since the launched signal and the returned signal have the same electric frequency band, band-pass filter 19 may be inserted between the signal generator/receiver and the metal wire/ground, as is shown in Fig. 1.

Averaging. Since noise is random and the signal is repetitive within a certain time scale, averaging may be used to enhance the signal to noise ratio SNR. For example, the transmitter can launch pulses 1000 times a second. Assume the intruder touches the wire for at least 50 milliseconds. A moving average of 30 -50 pulse periods may improve the SNR.

Using coded pulse train. As is well known in communications theory and sensor technology, sending a coded pulse train can considerably enhance received signal to noise ratio.

Claims

Claims:

1. An electric fence that comprises an electric signal generator for generating short single or multiple electric pulses or coded electric pulsed train, a single wire earth return system for said electric pulses to propagate and return to receiver, a receiver for receiving said returned electric pulses when said single wire earth return system is touched by an intruder.

2. The electric fence as in Claim 1 , wherein said electric signal

generator is an electric pulse transmitter and said generated signal is a single or multiple electric pulses or coded pulse train.

3. The electric fence as in Claim 1, wherein said single wire earth return system comprises a single metal wire that is connected to said electric signal generator and said receiver at one end, and is connected to the earth directly or via a resistor at the other end.

4. The electric fence as in Claim 1, wherein said signal processor calculates the location of intrusion by measuring the time required by the returned electric pulses traveling from the point of intrusion.

5. The electric fence as in Claim 1, wherein band-pass filtering, averaging, and use of coded pulse train can be employed to reduce background noise, so as to achieve better performance.