WO2011075778A1 - Low frequency electric field sensor - Google Patents
Low frequency electric field sensor Download PDFInfo
- Publication number
- WO2011075778A1 WO2011075778A1 PCT/AU2010/001723 AU2010001723W WO2011075778A1 WO 2011075778 A1 WO2011075778 A1 WO 2011075778A1 AU 2010001723 W AU2010001723 W AU 2010001723W WO 2011075778 A1 WO2011075778 A1 WO 2011075778A1
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- sensor
- voltage
- amplifier
- electric field
- plates
- Prior art date
Links
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
- G01V3/00—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation
- G01V3/08—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation operating with magnetic or electric fields produced or modified by objects or geological structures or by detecting devices
- G01V3/088—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation operating with magnetic or electric fields produced or modified by objects or geological structures or by detecting devices operating with electric fields
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
- H03F3/45—Differential amplifiers
- H03F3/45071—Differential amplifiers with semiconductor devices only
- H03F3/45076—Differential amplifiers with semiconductor devices only characterised by the way of implementation of the active amplifying circuit in the differential amplifier
- H03F3/45475—Differential amplifiers with semiconductor devices only characterised by the way of implementation of the active amplifying circuit in the differential amplifier using IC blocks as the active amplifying circuit
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F2200/00—Indexing scheme relating to amplifiers
- H03F2200/261—Amplifier which being suitable for instrumentation applications
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F2203/00—Indexing scheme relating to amplifiers with only discharge tubes or only semiconductor devices as amplifying elements covered by H03F3/00
- H03F2203/45—Indexing scheme relating to differential amplifiers
- H03F2203/45544—Indexing scheme relating to differential amplifiers the IC comprising one or more capacitors, e.g. coupling capacitors
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F2203/00—Indexing scheme relating to amplifiers with only discharge tubes or only semiconductor devices as amplifying elements covered by H03F3/00
- H03F2203/45—Indexing scheme relating to differential amplifiers
- H03F2203/45548—Indexing scheme relating to differential amplifiers the IC comprising one or more capacitors as shunts to earth or as short circuit between inputs
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F2203/00—Indexing scheme relating to amplifiers with only discharge tubes or only semiconductor devices as amplifying elements covered by H03F3/00
- H03F2203/45—Indexing scheme relating to differential amplifiers
- H03F2203/45594—Indexing scheme relating to differential amplifiers the IC comprising one or more resistors, which are not biasing resistor
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F2203/00—Indexing scheme relating to amplifiers with only discharge tubes or only semiconductor devices as amplifying elements covered by H03F3/00
- H03F2203/45—Indexing scheme relating to differential amplifiers
- H03F2203/45604—Indexing scheme relating to differential amplifiers the IC comprising a input shunting resistor
Definitions
- This invention relates to electric field sensors for geophysical use either on the ground or in the air and also in marine, borehole and space applications.
- USA patent 6373253 discloses a method of measuring high frequency electric fields.
- USA patent 6686800 discloses a low noise electric field sensor which uses an ultra high impedance amplifier and a guard. The noise levels are unacceptably high.
- USA patent application 2004/0070446 discloses a system for measuring a free space electric field in which the signal is amplified using an ultra high impedance amplifier stabilized using a guard that has the same input potential as the input to the amplifier which is made up of the input signal and a bias current generated by the amplifier.
- USA patent 2005/0073302 discloses capacitive sensors in combination with magnetic sensors. The use of charge amplifiers is not suggested and the noise levels are too high.
- USA patent 7002349 discloses an airborne geophysical sensor system using electric field sensors and magnetometers and an angular motion detector connected to the electric field sensors to compensate for errors caused by the angular motion of the aircraft. This also appears to be too noisy to be useful.
- USA patent 7183777 discloses a capacitive sensor for geophysical applications in which an oscillator is coupled to the capacitive array. This requires ground galvanic contacts which may corrode.
- Attepting to directly measure the voltage between two plates that are capacitively coupled to their environment is difficult or even impossible at low frequencies as a correct measurement is dependent on the input impedance R of the measurement device greatly exceeding the impedance of the sensors, given by inverse of the product of angular frequency and capacitance between the sensor plates and their environment. At low frequencies the required input impedance becomes
- This invention provides a low frequency electric field sensor in which the two plates of the capacitive sensor are each connected to a charge amplifier causing an identical voltage to form across an output of low impedance.
- the amplifier and detector circuitry is enclosed between the plates to minimise noise.
- the voltage from the charge amplifier preferably a differential charge amplifier, is amplified and the data is either digitised and recorded or may be modulated and transmitted at a high frequency to an external receiver where it is digitised and stored.
- the use of wireless transmission avoids the noise created by using cables to connect to the external device. Noise from the voltage amplifier is minimised by optimising the physical separation of the charge and voltage amplifiers within the box bounding sensor.
- the transmitter preferably operating at high frequency outside the bandwidth of interest (for example an FM modulated VHF band), is also enclosed within the sensor bounds using sufficient frequency to escape but not affect the voltage measurement at low frequencies.
- this invention does not require galvanic contacts which introduce electric noise due the chemical reactions (corrosion) induced by the physical contact between the electrode and the ground.
- This lack of galvanic contacts means the device of this invention can be used in the atmosphere or in space because guarding is not essential.
- Figure 1 is a schematic illustration of the sensor system of this invention
- Figure 2 is an illustration of a second embodiment dfthe invention
- Figure 3 is a schematic illustration of the function of the embodiment of figure 2;
- Figure 4 is the circuit for one differential amplifier pair
- Figure 5 is a schematic of an experimental apparatus
- Figure 6 illustrates E field data from a first experiment using the system
- Figure 7 illustrates E field data from a second experiment using the system.
- the system illustrated in figure 1 consists of a pair of conductive sensor plates 1 inside or outside the electrically resistive container 2.
- the plates 1 are connected to the inputs of a differential charge amplifier 3 which is enclosed between the plates 1.
- the signal from the differential charge amplifier 3 is voltage amplified by the amplifier 4 and then digitised and stored in the storage media 5.
- the amplified signal may be FM modulated and transmitted at a higher frequency 6 in, for example , the VHF band.
- the transmitted data is remotely demodulated by receiver 7 and digitised and stored.in the storage media 8.
- the conductive sensors may be arranged on the six sides of a box so that each pair of opposing plates provide 3 orthogonal measurements. No electric contact is allowed between conductive plates at/the edges of the cube.
- Figure 4 shows the circuit for each differential amplifier pair.
- DV is a floating buffer which is referenced to a "big object" main ground via a large potential difference.
- the high pass 3 dB frequency is 160Hz.
- Figure 2 illustrates an octagon showing the layout of differential amplifiers
- Output voltages Va to Vh are combined in different combinations to measure voltage differences in three orthogonal directions.
- Figure 3 shows the voltage drop in each x,y,z, direction by using the average voltage difference across opposite halves of an octagon.
- Vz (Vb+Vb+Vc+Vd) - (Va+Vf+Vg+Vh)
- Vx (Vd+Vd+Vh+Vg) - (Va+Vb+Ve+Vf)
- Vy (Va+Vb+Vc+Vh) - (Vd+Ve+Vf+Vg)
- This system can be adapted to any shape or perimeter of a volume and connect one or more sensors on roughly opposite sides ' to produce up to 3 independent component measurements of varying sensitivity tailored to expected signals.
- These sensors could be arrayed on the sides of an airship or balloon with each plate differentially amplified and the output voltages summed/differenced in groups so as to form composite electrodes.
- the sensor of this invention has been tested in motion in two field experiments. As shown in figure 5 the sensor was suspended below the middle of two long plastic rods, whose electrical resistivity is similar to that of dry air. The rods were are long as possible while still being able to lift the sensor. The ends of the rods were then carried by field crew, with the Electric field data transmitted by radio to a nearby computer data acquisition system. Because the plastic rods and the crew members were aligned in the plane of the sensor plates, essentially aligned as far as possible along the central plane of the sensor system, their effect on the measured signal was minimised. The crew walk in direction A , perpendicular to the component B of the electric fields sensed by the system.
- the sensor collected E field data along a road extending over the Heathcote fault zone in Victoria, and through use of a nearby reference was able to detect the known contrast between resistive and conductive rocks, and provide a conductivity- depth section to a depth exceeding 500 m. The results are shown in figure 6. The system also detected the electrical short over a known near-surface conductor. It should be noted that the background E Field is non uniform at the surface but should be quite uniform at a height above the surface.
- Figure 7 showsjhe sensor collected E field data on profile extending away from a CARIS transmitter loop operating at 4920 Hz.
- the total field measured showed the expected amplitude decay in primary field together with secondary responses. This measurement was made in rough terrain and anomalies are to be expected due to severe topography and buried targets.
- the sensors of this invention may be combined with magnetic sensors attached to or in the vicinity of the electric sensors to measure magnetic or the time rate of change of magnetic fields.
- the frequency band may be other than F modulated VHF and may be selected from FM odulated VHF, UHF S and C bands.
- a preferred transmitter - receiver pair uses 4.8 GHz.
Landscapes
- Engineering & Computer Science (AREA)
- Physics & Mathematics (AREA)
- Remote Sensing (AREA)
- Life Sciences & Earth Sciences (AREA)
- Electromagnetism (AREA)
- Environmental & Geological Engineering (AREA)
- Geology (AREA)
- General Life Sciences & Earth Sciences (AREA)
- General Physics & Mathematics (AREA)
- Geophysics (AREA)
- Power Engineering (AREA)
- Geophysics And Detection Of Objects (AREA)
Abstract
A low frequency electric field sensor in which the two plates of the capacitive sensor are each connected to a charge amplifier causing an identical voltage to form across an output of low impedance. The amplifier and detector circuitry is enclosed between the plates to minimise noise. The voltage from the differential charge amplifier, is amplified and the data is either digitised and recorded or may be modulated and transmitted at a high frequency to an external receiver where it is digitised and stored. The use of wireless transmission avoids the noise created by using cables to the external device. Noise from the voltage amplifier is minimised by optimising the physical separation of the charge and voltage amplifiers within the box bounding sensor. The transmitter, for example, an FM modulated VHF band, is also enclosed within the sensor bounds using sufficient frequency to escape but not affect the voltage measurement at low frequencies.
Description
LOW FREQUENCY ELECTRIC FIELD SENSOR
This invention relates to electric field sensors for geophysical use either on the ground or in the air and also in marine, borehole and space applications.
Background to the Invention
Electric field sensors for geophysical surveying have been proposed.
USA patent 6373253 discloses a method of measuring high frequency electric fields.
USA patent 6686800 discloses a low noise electric field sensor which uses an ultra high impedance amplifier and a guard. The noise levels are unacceptably high. USA patent application 2004/0070446 discloses a system for measuring a free space electric field in which the signal is amplified using an ultra high impedance amplifier stabilized using a guard that has the same input potential as the input to the amplifier which is made up of the input signal and a bias current generated by the amplifier.
USA patent 2005/0073302 discloses capacitive sensors in combination with magnetic sensors. The use of charge amplifiers is not suggested and the noise levels are too high.
USA patent 7002349 discloses an airborne geophysical sensor system using electric field sensors and magnetometers and an angular motion detector connected to the electric field sensors to compensate for errors caused by the angular motion of the aircraft. This also appears to be too noisy to be useful.
USA patent 7183777 discloses a capacitive sensor for geophysical applications in which an oscillator is coupled to the capacitive array. This requires ground galvanic contacts which may corrode.
Attepting to directly measure the voltage between two plates that are capacitively coupled to their environment is difficult or even impossible at low frequencies as a correct measurement is dependent on the input impedance R of the measurement device greatly exceeding the impedance of the sensors, given by inverse of the product of angular frequency and capacitance between the sensor plates and their environment. At low frequencies the required input impedance becomes
prohibitively high and the measurement excessively noisy.
It is an object of this invention to provide an electric field sensor that is useful at low frequencies and also ameliorates some of the shortcomings of the prior art.
Brief Description of the invention
This invention provides a low frequency electric field sensor in which the two plates of the capacitive sensor are each connected to a charge amplifier causing an identical voltage to form across an output of low impedance. Preferably the amplifier and detector circuitry is enclosed between the plates to minimise noise. The voltage from the charge amplifier preferably a differential charge amplifier, is amplified and the data is either digitised and recorded or may be modulated and transmitted at a high frequency to an external receiver where it is digitised and stored. The use of wireless transmission avoids the noise created by using cables to connect to the external device. Noise from the voltage amplifier is minimised by optimising the physical separation of the charge and voltage amplifiers within the box bounding sensor. The transmitter, preferably operating at high frequency outside the bandwidth of interest ( for example an FM modulated VHF band), is also enclosed within the sensor bounds using sufficient frequency to escape but not affect the voltage measurement at low frequencies.
Unlike prior art low frequency sensors this invention does not require galvanic contacts which introduce electric noise due the chemical reactions (corrosion) induced by the physical contact between the electrode and the ground. This lack of galvanic contacts means the device of this invention can be used in the atmosphere or in space because guarding is not essential.
Detailed description of the invention
Preferred embodiments of the invention will now be described with reference to the drawings in which:
Figure 1 is a schematic illustration of the sensor system of this invention;
Figure 2 is an illustration of a second embodiment dfthe invention;
Figure 3 is a schematic illustration of the function of the embodiment of figure 2;
Figure 4 is the circuit for one differential amplifier pair;
Figure 5 is a schematic of an experimental apparatus;
Figure 6 illustrates E field data from a first experiment using the system;
Figure 7 illustrates E field data from a second experiment using the system.
The system illustrated in figure 1 consists of a pair of conductive sensor plates 1 inside or outside the electrically resistive container 2. The plates 1are connected to the inputs of a differential charge amplifier 3 which is enclosed between the plates 1. The signal from the differential charge amplifier 3 is voltage amplified by the amplifier 4 and then digitised and stored in the storage media 5. Alternatively the amplified signal may be FM modulated and transmitted at a higher frequency 6 in, for example , the VHF band. The transmitted data is remotely demodulated by receiver 7 and digitised and stored.in the storage media 8.
The conductive sensors may be arranged on the six sides of a box so that each pair of opposing plates provide 3 orthogonal measurements. No electric contact is allowed between conductive plates at/the edges of the cube.
Figure 4 shows the circuit for each differential amplifier pair. DV is a floating buffer which is referenced to a "big object" main ground via a large potential difference. . The high pass 3 dB frequency is 160Hz.
Figure 2 illustrates an octagon showing the layout of differential amplifiers
connected to each of discrete conductive sheets a to h. Output voltages Va to Vh are combined in different combinations to measure voltage differences in three orthogonal directions.
Figure 3 shows the voltage drop in each x,y,z, direction by using the average voltage difference across opposite halves of an octagon. By using discrete sensors on 8 sides of the octagon with 8 differential charge amplifiers connected each plate with components being calculated from summing and differencing voltages 4 at a time.
Vz= (Vb+Vb+Vc+Vd) - (Va+Vf+Vg+Vh)
Vx= (Vd+Vd+Vh+Vg) - (Va+Vb+Ve+Vf)
Vy= (Va+Vb+Vc+Vh) - (Vd+Ve+Vf+Vg)
This system can be adapted to any shape or perimeter of a volume and connect one or more sensors on roughly opposite sides' to produce up to 3 independent component measurements of varying sensitivity tailored to expected signals.
These sensors could be arrayed on the sides of an airship or balloon with each plate differentially amplified and the output voltages summed/differenced in groups so as to form composite electrodes.
The sensor of this invention has been tested in motion in two field experiments. As shown in figure 5 the sensor was suspended below the middle of two long plastic rods, whose electrical resistivity is similar to that of dry air. The rods were are long as possible while still being able to lift the sensor. The ends of the rods were then carried by field crew, with the Electric field data transmitted by radio to a nearby computer data acquisition system. Because the plastic rods and the crew members were aligned in the plane of the sensor plates, essentially aligned as far as possible along the central plane of the sensor system, their effect on the measured signal was minimised. The crew walk in direction A , perpendicular to the component B of the electric fields sensed by the system.
Experiment 1 :
The sensor collected E field data along a road extending over the Heathcote fault zone in Victoria, and through use of a nearby reference was able to detect the known contrast between resistive and conductive rocks, and provide a conductivity- depth section to a depth exceeding 500 m. The results are shown in figure 6. The system also detected the electrical short over a known near-surface conductor. It should be noted that the background E Field is non uniform at the surface but should be quite uniform at a height above the surface.
Experiment 2:
Figure 7 showsjhe sensor collected E field data on profile extending away from a CARIS transmitter loop operating at 4920 Hz. The total field measured showed the expected amplitude decay in primary field together with secondary responses. This measurement was made in rough terrain and anomalies are to be expected due to severe topography and buried targets.
The sensors of this invention may be combined with magnetic sensors attached to or in the vicinity of the electric sensors to measure magnetic or the time rate of change of magnetic fields.
The frequency band may be other than F modulated VHF and may be selected from FM odulated VHF, UHF S and C bands. A preferred transmitter - receiver pair uses 4.8 GHz.
Those skilled in the art will realise that this invention provides a significant advance in detecting low frequency electric fields in a variety of environments. Those skilled in the art will also realise that this invention may be implemented in embodiments other than those disclosed.
Claims
1. A low frequency geophysical electric field sensor in which the two plates of the capacitive sensor are each connected to a charge amplifier causing an identical voltage to form across an output of low impedance.
2. A geophysical sensor as claimed in claim 1 in which the amplifier and
detector circuitry is enclosed between the plates to minimise noise.
3. A geophysical sensor as claimed in claim 1 or 2 in which the voltage from the charge amplifier , is amplified and the data is either digitised and recorded or is modulated and transmitted at a high frequency to an external receiver where it is digitised and stored.
4. A geophysical sensor as claimed in claim 1 in which the charge amplifier is a differential charge amplifier.
5. An array of geophysical sensors as claimed in any one of claims 1 to 4
connected in pairs and arranged on the surface of a volume to provide up to 3 orthogonal electric field measurements.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| AU2010336021A AU2010336021A1 (en) | 2009-12-24 | 2010-12-23 | Low frequency electric field sensor |
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| AU2009906283A AU2009906283A0 (en) | 2009-12-24 | Low Frequency Electric Field Sensor | |
| AU2009906283 | 2009-12-24 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| WO2011075778A1 true WO2011075778A1 (en) | 2011-06-30 |
Family
ID=44194824
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| PCT/AU2010/001723 WO2011075778A1 (en) | 2009-12-24 | 2010-12-23 | Low frequency electric field sensor |
Country Status (2)
| Country | Link |
|---|---|
| AU (1) | AU2010336021A1 (en) |
| WO (1) | WO2011075778A1 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| RU2691165C1 (en) * | 2018-05-22 | 2019-06-11 | Федеральное государственное бюджетное учреждение науки Институт радиотехники и электроники им. В.А. Котельникова Российской академии наук | Device for receiving electromagnetic field in sea |
Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3641427A (en) * | 1969-09-24 | 1972-02-08 | Us Navy | Electric field sensor |
| US4686475A (en) * | 1984-07-12 | 1987-08-11 | Denver Mineral Exploration Corp. | Passive geophysical prospection system based upon the detection of the vertical electric field component of telluric currents and method therefor |
| US5396166A (en) * | 1992-08-27 | 1995-03-07 | The United States Of America As Represented By The Secretary Of The Navy | Fiber optic interferometric electric field and voltage sensor utilizing an electrostrictive transducer |
| US20020109545A1 (en) * | 2001-02-13 | 2002-08-15 | Krupka Michael Andrew | Low noise, electric field sensor |
-
2010
- 2010-12-23 WO PCT/AU2010/001723 patent/WO2011075778A1/en active Application Filing
- 2010-12-23 AU AU2010336021A patent/AU2010336021A1/en not_active Abandoned
Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3641427A (en) * | 1969-09-24 | 1972-02-08 | Us Navy | Electric field sensor |
| US4686475A (en) * | 1984-07-12 | 1987-08-11 | Denver Mineral Exploration Corp. | Passive geophysical prospection system based upon the detection of the vertical electric field component of telluric currents and method therefor |
| US5396166A (en) * | 1992-08-27 | 1995-03-07 | The United States Of America As Represented By The Secretary Of The Navy | Fiber optic interferometric electric field and voltage sensor utilizing an electrostrictive transducer |
| US20020109545A1 (en) * | 2001-02-13 | 2002-08-15 | Krupka Michael Andrew | Low noise, electric field sensor |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| RU2691165C1 (en) * | 2018-05-22 | 2019-06-11 | Федеральное государственное бюджетное учреждение науки Институт радиотехники и электроники им. В.А. Котельникова Российской академии наук | Device for receiving electromagnetic field in sea |
Also Published As
| Publication number | Publication date |
|---|---|
| AU2010336021A1 (en) | 2012-05-31 |
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