AMR Magnetometer Data on Moving Military Vehicles 

at Aberdeen Proving Ground 

by Jonathan E. Fine, Alan S. Edelstein, and David M. Hull 

ARL-TR-4267 September 2007 

Approved for public release; distribution unlimited. 
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Army Research Laboratory 

Adelphi, MD 20783-1197 

ARL-TR-4267 September 2007 

AMR Magnetometer Data on Moving Military Vehicles 

at Aberdeen Proving Ground 

Jonathan E. Fine, Alan S. Edelstein, 

and David M. Hull 

Sensors and Electron Devices Directorate, ARL 

Approved for public release; distribution unlimited. 
ii

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September 1999 

5a. CONTRACT NUMBER 

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AMR Magnetometer Data on Moving Military Vehicles at Aberdeen Proving 

Ground 

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6. AUTHOR(S) 

Jonathan E. Fine, Alan S. Edelstein, and David M. Hull 

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U.S. Army Research Laboratory 

ATTN: AMSRD-ARL-SE-SE 

2800 Powder Mill Road 

Adelphi, MD 20783-1197

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Approved for public release; distribution unlimited. 

13. SUPPLEMENTARY NOTES 

14. ABSTRACT 

We have collected magnetic signature data on three vehicles of military interest at Aberdeen Proving Ground, MD, in 

September 1999 using low cost, commercial anisotropic magnetoresistance sensors. Vehicles were driven passed sensors that 

were located at 12 ft and 36 ft from the center of the track. The magnetic signatures that were obtained were different for the 

three different vehicles investigated, although some details of the signal were lost at the larger distance. The total field from the 

tank varied as 1/r3

 where r is the distance between the sensor and the vehicle. The different magnetic signals generated from a 

tank moving backward and forward, rotating the tank’s turret, and raising and lowering the tank’s gun were clearly 

distinguishable. The signals from the tank had nearly the same values at the 12 ft and 36 ft distances, when their values were

normalized by the peak values, and time axis was normalized by time interval between half-maximum amplitude points.

15. SUBJECT TERMS

AMR magnetometers, vehicle detection, magnetic signatures 

16. Security Classification of: 

19a. NAME OF RESPONSIBLE PERSON

Jonathan E. Fine 

a. REPORT 

Unclassified 

b. ABSTRACT 

Unclassified 

c. THIS PAGE 

Unclassified 

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OF 

ABSTRACT 

SAR 

18. NUMBER 

OF PAGES 

32 19b. TELEPHONE NUMBER (Include area code) 

(301) 394-2357 

Standard Form 298 (Rev. 8/98) 

Prescribed by ANSI Std. Z39.18 
Contents 

List of Figures iv

List of Tables v

1. Introduction 1

2. Magnetometers Used In Test 2

3. Test Instrumentation 3

4. Field Test Arrangement and Test Procedures 4

5. Test Results 5

6. Conclusions 19

Distribution List 21 

iii
List of Figures 

Figure 1. Networked microsensor concept showing the deployment of multiple sensors and 

the rf communication links between the sensors as they detect objects of military 

significance. ...............................................................................................................................1 

Figure 2. AMR magnetometer (HMC 2003-T) used in field test with and without its cover. .......2 

Figure 3. Diagram of instrumentation used in field test showing sensors, junction box, 

cables, compute,r and printer.....................................................................................................3 

Figure 4. Layout of test field showing locations of sensor array and instrumentation van. ...........4 

Figure 5. Arrangement of magnetometer array beside track. .........................................................5 

Figure 6. The x-axis signatures of a light wheeled vehicle (Vehicle A), tank (Vehicle B), and 

2.5-ton truck (Vehicle C) as the vehicles passed by a sensor near the track (12 ft from 

center of track). ..........................................................................................................................6 

Figure 7. The x-axis signatures of all three vehicles as recorded from the magnetometer near 

the track (12 ft from center of track)..........................................................................................7 

Figure 8. The y-axis signatures of all three vehicles as recorded from the magnetometer near 

the track (12 ft from center of track)..........................................................................................8 

Figure 9. The z-axis signatures of all three vehicles as recorded from the magnetometer near 

the track (12 ft from center of track)..........................................................................................9 

Figure 10. Vehicle A magnetic field components detected by two three-axis magnetometers: 

the nearer one 12 ft from the center of the track, and the farther one 36 ft from the center 

of the track. ..............................................................................................................................10 

Figure 11. Magnetic field components of Vehicle B (tank) detected by two three-axis 

magnetometers: the nearer one 12 ft from the center of the track, and the farther one 36 ft 

from the center of the track......................................................................................................11 

Figure 12. Magnetic field components of Vehicle C (truck) detected by two three-axis 

magnetometers: the nearer one 12 ft from the center of the track, and the farther one 36 ft 

from the center of the track......................................................................................................12 

Figure 13. Comparison of Total Field of each of three vehicles for sensors near (12 ft from 

center of track) and far (36 ft from center of the track)...........................................................13 

Figure 14. Total field signal from sensor near the track for Vehicle B (tank) showing the 

definition of signal width as the time difference between the two half-maximum 

amplitude (nT) signal points. ...................................................................................................14 

Figure 15. Similarity of total field signal shapes of Vehicle B from near and far sensors 

when fields are normalized with peak amplitude, and time is given in units of signal 

width. .......................................................................................................................................15 

Figure 16. Comparison of x-, y-, and z-anomaly fields for tank (Vehicle B) moving 

backwards and then forwards on track.....................................................................................16 

iv
Figure 17. Comparison of x-, y-, and z-anomaly fields for tank (Vehicle B) rotating its turret 

as seen by sensors near (12 ft from center of track) and far (36 ft from center of the 

track). .......................................................................................................................................17 

Figure 18. Comparison of x-, y-, and z-anomaly fields for stopped tank (Vehicle B) raising 

and lowering its gun twice as seen by sensor 12 ft from the track. These signals have 

been averaged over every 10 data points to smooth out the bit noise which is 7 nT...............18 

List of Tables 

Table 1. Total field signal amplitude and width for three vehicles as seen by sensor near 

track and far from track............................................................................................................14 

v
vi

INTENTIONALLY LEFT BLANK
1. Introduction 

The Signal and Image Processing Division of the Army Research Laboratory is seeking to 

develop technology using small, low-power, low-cost sensors to detect magnetic fields in the 

battlefield generated by the presence and/or movement of armed troops, tracked and wheeled 

vehicles, and/or mines. The magnetic sensors will be part of an array of microsensors of various 

technologies that also include other sensor modalities such as acoustics, seismic, infrared, radio 

frequency (RF), and extremely low frequency electric field sensors. These sensor systems are to 

be deployed as unattended ground sensors (UGS) with remote activation/data acquisition as 

depicted in figure 1. We anticipate that multi-modal data fusion will provide enhanced detection 

and/or discrimination capability. We prefer sensors that can be fabricated by microelectronic/ 

thin film techniques that use the existing industrial base to lower cost. 

Figure 1. Networked microsensor concept showing the deployment of 

multiple sensors and the rf communication links between the 

sensors as they detect objects of military significance. 

Networked Microsensors Concept

Here we report the results of an earlier test using anisotropic magnetoresistance (AMR) sensors 

conducted at Spesutie Island, Aberdeen Proving Ground, MD. The purpose of this testing 

program was to determine what useful information on vehicles of military interest could be 

obtained using low cost anisotropic AMR vector magnetometers. Such magnetometers may be 

one of the sensors employed in UGS networks. Three kinds of vehicles were investigated: a 

light wheeled vehicle (Vehicle A), a tank (Vehicle B), and 2 1⁄2 ton truck (Vehicle C). We 

measured the difference in the signal when the tank was going forward and when it was going 

backward. We also investigated the signal generated by rotating the gun turret and raising and 

lowering the gun. 

1
2

2. Magnetometers Used In Test

We used for these tests an array of four Honeywell HMR-2300, 3-axis anisotropic AMR 

magnetometers. The sensing element of an AMR magnetometer is a permalloy (nickel-iron 

alloy) thin film layer deposited on a silicon substrate.1 The resistance due to the application of a 

magnetic field is about 4 percent. The material is used in a Wheatstone bridge configuration in 

which an applied field creates a voltage imbalance between two arms of the bridge: one being 

exposed to the field to be detected, and the other shielded from the field.2 These sensor elements 

are manufactured on wafers and assembled with other circuit components using microelectronic 

fabrication techniques. We chose these magnetometers even though they have a sensitivity of 

only 7 nT because they are made commercially, represent the present industrial capability, and 

are available for about $500.00 each. As seen in figure 2 the sensor is quite small. 

AMR 3-Axis Magnetometer

Used in Test

Figure 2. AMR magnetometer (HMC 2003-T) used in field 

test with and without its cover. 

 1Caruso, Bratland, Smith and Schneider. A New Perspective on Magnetic Field Sensing. Proceedings of Sensor Expo San 

Jose (Halmers Publishing Co.) Peterborough, New Hampshire 1998, pp 351-370. 

2

Lenz, James; Edlestein, Alan S. Magnetic Sensors and Their Applications. IEEE Sensors Journal 2006, 6 (3), 635-637. 
The magnetometer consists of three sensor elements positioned with their sense directions 

orthogonal to each other to measure the three rectangular components of an external magnetic 

field. Each of the sensor elements is packaged in a bridge configuration and each output is 

connected to a 16-Bit A/D converter. A computer records the digital outputs for storage and 

analysis.3 

3. Test Instrumentation 

The instrumentation block diagram that includes the four sensors used in the test is shown in 

figure 3. The magnetometer connects to the serial port of the computer with an RS-485 four-port 

isolated interface card, which allows simultaneous monitoring of the four magnetometers at 

distances up to 4,000 ft. The software interface to the computer is a National Instruments 

LabVIEW program. The program is compiled, and enables data collected at 20 samples per 

second, to be stored in a data file, and enables one of the magnetometer’s outputs to be displayed 

graphically on the monitor as the data is being collected. The LabVIEW program attaches a 

time-stamp from the computer’s clock to the data as it is being stored. The data Baud rate is 

19,200 sec–1. 

Junction

Box

Magnetometers

Magnetometers

RS-485 Interface Board

Monitor Computer

Printer

Instrumentation Used in

Field Test

Figure 3. Diagram of instrumentation used in field test showing sensors, 

junction box, cables, computer, and printer. 

Each HMC 2003-T magnetometer has a DB9-pin connector. Four of the pins were used: two 

signal leads, and two power leads. A special junction box contains 8 D-cells to provide voltage to 

all four magnetometers and has suitable interconnections for sending data from all four sensors 

back to the computer on a single 8-wire cable. This allows the power to be supplied in the 

vicinity (within about 30 feet) of the magnetometers, but does not require power to be 

 3

Honeywell, HMR-2300 Smart Digital Magnetometer Manual. 

3
transmitted the several hundred feet from the computer. The junction box contains four 

connectors wired for the magnetometers, and two connectors wired for data signals to the 

computer. This method allows the computer to be located in a van about 300 to 400 ft from the 

magnetometers. The junction box is 30 ft from the magnetometers. 

4. Field Test Arrangement and Test Procedures 

The test field shown in figure 4 consists of a test track, which was a dirt and gravel track about 

14 ft wide and about one mile in circumference. The long direction of the track ran due north 

and south, and the van was located at the southern end about 100 feet from an electrical power 

pole. The four magnetometers were arranged in a square array as shown in figure 5. Two 

magnetometers were about 24 ft apart along the track and 12 ft from the center of the track. Two 

additional sensors were 24 ft further from the first two sensors, or 36 ft from the center of the 

track. There was about a 2 ft uncertainty in the position of the vehicles relative to the center of 

the track. The orientation of the magnetometers inadvertently was not recorded. The test 

procedure was to initiate recording when the vehicle started at the far end of the track and to stop 

when the vehicle passed out of range of the sensors. 

Van with computer and

data recording equipment

Sensor

Array

Track North

Layout of Field Showing Magnetometer Array

Van with computer and

data recording equipment

Sensor

Array

Track North

Layout of Field Showing Magnetometer Array

Figure 4. Layout of test field showing locations of sensor array 

and instrumentation van. 

4
14 ft

7ft 7 ft

12 ft

12 ft

24 ft

24 ft

24 ft

N X

Y Z

Magnetometer

Orientation

Sensor Array

Magnetometer 3

Magnetometer 0

Magnetometer 2

Magnetometer 1

Track

Figure 5. Arrangement of magnetometer array beside track. 

5. Test Results 

Distinguishing Different Vehicles 

Figure 6 shows the signatures of three vehicles described earlier as they passed in succession by 

the magnetometer located 12 ft from the center of the track. Figures 7, 8, and 9 compare the x-, 

y-, and z-anomalies for the three vehicles as seen by the sensor 12 ft from the center of the track. 

Each vehicle has a distinct signature as compared with the other vehicles. One sees that for each 

axis, all three anomalies are distinct, with the tank, vehicle B, having the largest amplitude. 

5
A 

B 

C 

Figure 6. The x-axis signatures of a light wheeled vehicle (Vehicle A), tank (Vehicle B), 

and 2.5-ton truck (Vehicle C) as the vehicles passed by a sensor near the track 

(12 ft from center of track). 

6
 

 Vehicle A 

 

 Vehicle B 

 Vehicle C 

-2,000

-1,000

0

1,000

2,000

3,000

7 8 9 10 11 12 13

Time (sec)

-15,000

-10,000

-5,000

0

5,000

10,000

15,000

29 30 31 32 33

Time (sec)

-6,000

-4,000

-2,000

0

2,000

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41 42 43 44 45 46 47

Time (sec)

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0

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Time (sec)

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-10,000

-5,000

0

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10,000

15,000

29 30 31 32 33

Time (sec)

-6,000

-4,000

-2,000

0

2,000

4,000

41 42 43 44 45 46 47

Time (sec)

Figure 7. The x-axis signatures of all three vehicles as recorded from the magnetometer near the 

track (12 ft from center of track). 

7
-2,000

-1,000

0

1,000

2,000

3,000

4,000

5,000

8 9 10 11 12 13

Time (sec)

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0

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29 29.5 30 30.5 31 31.5 32 32.5 33

Time (sec)

-6,000

-4,000

-2,000

0

2,000

4,000

6,000

41 42 43 44 45 46 47

Time (sec)

Vehicle C 

Vehicle B 

Vehicle A 

Figure 8. The y-axis signatures of all three vehicles as recorded from the magnetometer near 

the track (12 ft from center of track). 

8
Vehicle A 

Vehicle B 

 

 

Vehicle C 

-1,000

0

1,000

2,000

3,000

4,000

5,000

6,000

41 42 43 44 45 46 47

Time (sec)

-2,000

0

2,000

4,000

6,000

8,000

10,000

12,000

29 29.5 30 30.5 31 31.5 32 32.5 33

Time (sec)

-200

0

200

400

600

800

1,000

7 8 9 10 11 12 13

Time (sec)

Figure 9. The z-axis signatures of all three vehicles as recorded from the 

magnetometer near the track (12 ft from center of track). 

These distinctions disappear in the sensor 36 ft from the center of the track. This is evident in 

figures 10, 11, and 12 for Vehicles A, B and C, respectively. The left side of each figure shows 

the x-, y-, and z-axis anomaly signals for the sensor near the track, and the right side shows the 

corresponding signals from the sensor farther from the track. For every vehicle each axis signal 

from the near sensor, which is 12 ft from the center of the track, is distinct. The right side shows 

the same vehicle as seen by the sensor far from the track, which is 36 ft from the center of the 

track. (The signals from the farther sensor have been averaged over 10 data points to smooth out 

the bit noise, which is about 7 nT.) Note that the signal for each axis also is distinct. However, 

9
the details detected by the close sensor cannot be seen in the data taken using the far sensor. The 

signals detected by the far sensor are more like a magnetic dipole. 

 Sensor near track Sensor far from track

-2,000

-1,000

0

1,000

2,000

3,000

7 8 9 10 11 12 13

Time (sec)

-100

-50

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0 5 10 15 20

Time sec

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400

600

800

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7 8 9 10 11 12 13

Time (sec)

-20

0

20

40

60

80

0 5 10 15 20

Time (sec)

Figure 10. Vehicle A magnetic field components detected by two three-axis magnetometers: the nearer one 12 ft 

from the center of the track, and the farther one 36 ft from the center of the track. 

10
 Sensor near track Sensor far from track 

-15,000

-10,000

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0

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Time (sec)

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Time (sec)

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Time (sec)

-50

0

50

100

150

200

250

300

350

26 28 30 32 34

Time (sec)

Figure 11. Magnetic field components of Vehicle B (tank) detected by two three-axis magnetometers: the nearer 

one 12 ft from the center of the track, and the farther one 36 ft from the center of the track. 

11
 Sensor near track Sensor far from track 

 

-6,000

-4,000

-2,000

0

2,000

4,000

41 42 43 44 45 46 47

Time (sec)

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-150

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0

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38 40 42 44 46 48 50

Time (sec)

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Time (sec)

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Time (sec)

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0

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5,000

6,000

41 42 43 44 45 46 47

Time (sec)

-50

0

50

100

150

200

38 40 42 44 46 48 50

Time (sec)

Figure 12. Magnetic field components of Vehicle C (truck) detected by two three-axis magnetometers: the nearer 

one 12 ft from the center of the track, and the farther one 36 ft from the center of the track. 

A comparison of the right hand side of figures 11 and 12 shows that, at the far sensor, the tank 

and the truck are indistinguishable from each other in terms of anomaly shape, but that the tank 

signal has a much greater amplitude. 

The significance of these results is that this UGS-appropriate technology, when comparing the 

vector component signals, can discriminate gross feature differences between vehicles. The 

component amplitudes indicate the relative magnetic size of vehicles that pass at the same 

distance from the sensor. 

12
Total Field Anomaly For Sensors Near and Far From Track 

The total field signal is a useful tool in obtaining information about the vehicles. The total field 

at each time data point is calculated as the square root of the sums of squares of the component 

values. The total field signals are shown in figure 13 for all three vehicles. The signals from the 

near sensor are on the left, and the corresponding signals from the far sensor are on the right side. 

The total field signal for each vehicle lacks the distinguishing shape features of the component 

signals and the amplitude decreases with distance from the sensor. 

-5,000

0

5,000

10,000

15,000

20,000

25,000

0 10 20 30 40 50

Time (sec)

Vehicle A

Vehicle B

Vehicle C

-100

0.00

100

200

300

400

500

600

700

0 10 20 30 40 50

Time (sec)

Vehicle A

Vehicle B

Vehicle C

Sensor near 

road.

Sensor far

From road.

Figure 13. Comparison of Total Field of each of three vehicles for sensors near (12 ft from center of track) and far 

(36 ft from center of the track). 

We now examine the dependence of the amplitude and signal width on distance of the sensor 

from the vehicle. Figure 14 shows a typical total field signal, and demonstrates the relationship 

between the amplitude and signal width—defined as the time difference between the two halfmaximum amplitude (nT) signal points. 

13
-5,000

0

5,000

10,000

15,000

20,000

25,000

28 29 30 31 32 33 34

Time (sec)

Vehicle B

Maximum = 22,661 nT

Half-maximum = 11,330 nT

Width at half-maximum 

amplitude = 0.6 sec

Figure 14. Total field signal from sensor near the track for Vehicle B 

(tank) showing the definition of signal width as the time 

difference between the two half-maximum amplitude (nT) 

signal points. 

Table 1 lists the total field signal amplitude and width for all three vehicles for the sensor 12 ft 

from the center of the track and 36 ft from the center of the track. It also lists the cube root of the 

12 ft to 36 ft amplitude ratios. The field created by a dipole at two different distances varies as 

the inverse cube of the sensor distance ratio. Because, in our test, the ratio of the far sensor 

distance to the near sensor distance is three, the cube root of the total field amplitude ratios 

should be three. This ratio for the three vehicles is about 3. Table 1 also shows that the signal 

widths are larger, and the amplitudes are smaller for the further sensor. As expected the widths 

are larger for the more distant sensor. 

Table 1. Total field signal amplitude and width for three vehicles as seen by sensor near track and far from track. 

Maximum Signal 

Amplitude (nT) 

Signal Width at 

Half-Maximum 

Amplitude (sec) 

(Ampl near/Ampl far)1/3 

Sensor near track 

Vehicle A 3,942 1.34 2.8 

 Vehicle B 22,661 0.6 3.3 

Vehicle C 6,949 1.16 2.8 

Average 3.0 

Sensor far from track 

Vehicle A 187 2.7 n/a 

Vehicle B 626 2.0 n/a 

Vehicle C 319 2.1 n/a 

14
Figure 15 shows the total field data for the tank, Vehicle B, adjusted in three ways. First, we 

adjusted the time axis so that the peaks occur at the same time. Second, we normalized the 

amplitudes of each signal to be unity at the peak. Third, we scaled the time by the time interval 

between the signal half-maximum amplitude points defined earlier. The two curves nearly 

coincide when the data is plotted in this way. At this point we are considering a dipole-like 

signal. In this case, the total field signal shape, when treated in this way, is independent of the 

separation between the target and the sensor, and may prove useful in location and tracking 

algorithms.4

The significance of these results is that the total field signal amplitude indicates the relative 

magnetic size of vehicles passing at the same distance of closest approach (PCA) to the sensor. 

The normalized and scaled total field signals are independent of sensor-target distance. These 

features may be helpful when the signals are used in location and tracking algorithms. 

0.0

0.2

0.5

0.7

1.0

1.2

10 12 14 16 18 20

Time/T(half-max ampl)

Sensor near road. 

Sensor far from road.

Figure 15. Similarity of total field signal shapes of Vehicle B from near and far sensors 

when fields are normalized with peak amplitude, and time is given in units of 

signal width. 

 4

Edelstein. US Patent No. 6,675,123, “Magnetic Tracking Methods and Systems,” June 6 2004. 

15
Distinguishing Direction of Motion of Tank 

The magnetometer near the track distinguished between the tank moving backward and forward 

on the track, as shown in figure 16. This figure compares the x-, y-, and z-anomalies for the tank 

moving backward (left column) and forward (right column). It is clear that each anomaly for 

backing up is the mirror image of the corresponding anomaly for going forward. The traces for 

moving forward are greater in amplitude and more compressed in time, probably as a result of 

the tank going forward faster than backing up. The differences in amplitude going forward may 

be due to the tank’s path being slightly closer to the sensor. 

 Tank moving backwards Tank moving forwards 

-10,000

-5,000

0

5,000

10,000

130 140 150 160 170 180

Time (sec)

-10,000

-5,000

0

5,000

10,000

15,000

215 220 225 230 235 240 245

Time (sec)

-5,000

0

5,000

10,000

15,000

20,000

130 140 150 160 170 180

Time (sec)

-5,000

0

5,000

10,000

15,000

20,000

25,000

30,000

220 225 230 235 240

Time (sec)

-1,500

-1,000

-500

0

500

1,000

1,500

130 140 150 160 170 180

Time (sec)

-8,000

-6,000

-4,000

-2,000

0

2,000

220 225 230 235 240

Time (sec)

 

Figure 16. Comparison of x-, y-, and z-anomaly fields for tank (Vehicle B) moving backwards and then 

forwards on track. 

16
Stationary Tank Rotates Turret 

Figure 17 compares the anomalies for the sensor 12 ft from the track with the sensor 36 ft from 

the track when the stationary tank rotated its turret once. The far sensor (right side of figure 17) 

clearly loses details that are detected by the near sensor. 

 Sensor near track Sensor far from track 

-3,000

-2,000

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0

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4,000

0 20 40 60 80 100

Time (sec)

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0

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5,000

0 20 40 60 80 100

Time (sec)

-6,000

-4,000

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0

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4,000

0 20 40 60 80 100

Time (sec)

-150

-100

-50

0

50

100

150

200

0 20 40 60 80 100

Time (sec)

-300

-200

-100

0

100

200

0 20 40 60 80 100

Time (sec)

-200

-150

-100

-50

0

50

100

150

0 20 40 60 80 100

Time (sec)

Figure 17. Comparison of x-, y-, and z-anomaly fields for tank (Vehicle B) rotating its turret as seen by sensors 

near (12 ft from center of track) and far (36 ft from center of the track). 

Tank Raising and Lowering Gun 

Figure 18 contains the x-, y-, and z-anomalies detected by the sensor 12 ft from the track when 

the tank is stationary and the gun is raised and lowered twice. All three traces exhibit the same 

oscillatory motion. The y-anomaly has the largest amplitude, about 950 nT, compared to 170 nT 

17
for the x-anomaly and 70 nT for the z-anomaly. These results show that vector magnetometers 

using UGS-appropriate AMR technology can distinguish different activities of a tank. 

-150

-100

-50

0

50

100

0 20 40 60 80 100 120

Time (sec)

-600

-400

-200

0

200

400

600

0 20 40 60 80 100 120

Time (sec)

-40

-20

0

20

40

60

0 20 40 60 80 100 120

Time (sec)

Figure 18. Comparison of x-, y-, and z-anomaly fields for stopped tank 

(Vehicle B) raising and lowering its gun twice as seen by sensor 

12 ft from the track. These signals have been averaged over 

every 10 data points to smooth out the bit noise which is 7 nT. 

18
6. Conclusions 

We have presented magnetic sensor data taken with four AMR magnetoresistance sensors of 

three vehicles. In the case where the sensors were 12 ft from the center of the track, the vector 

component signals were quite different for the light wheeled vehicle, a tank, and a 2 1⁄2 ton truck. 

The signals measured at 36 ft from the center of the road were approximately that of magnetic 

dipoles. However, the orientation of the dipole for the light wheeled vehicle was different from 

the orientation of the dipole of the tank and the truck. The time between when the signal was at 

half its maximum values was larger for the more distant sensors. One can detect when the tank’s 

gun turret was rotated with both the sensors at 12 and 36 ft from the tank. The signal from 

raising and lowering the gun was smaller than the signal from rotating the gun turret and could 

only be detected by the sensor that was 12 ft from the tank. The signals detected at 12 ft and 36 

ft from the tank had the same shape when the amplitudes and times were scaled. For all vehicles 

tested, the ratio of the cube root of the signal of the sensor near the track to that of the sensor far 

from the track approximately equals 3, as expected for the dipole model. When the total field 

signal is normalized by the maximum detected field, and the times are expressed in terms of the 

signal width at half-maximum field, the detected total field signal shape is independent of the 

distance between the sensor and the target. 

When the total field signals from each sensor are normalized by the maximum detected field, and 

the times are expressed in terms of the signal width at half-maximum field, the detected total 

field signal shape is identical for a sensor near the target and a sensor further away. The signal 

shape when modified in this manner is positive, has a clearly-defined peak, and is independent of 

the target speed, shape or distance from the sensor. This modified total field signal (normalized 

field amplitude versus scaled time) when considered in conjunction with the usual signal (field 

amplitude versus time) may be useful in target location and detection algorithms. The results 

reported on here indicate that low cost AMR magnetic sensors appropriate for use in UGS 

networks can provide information useful in classifying target vehicles, distinguishing some 

vehicle activities, and estimating vehicle magnetic size. 

19
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