## 2 System Design  
The experimental system consists of a sensor array and instrumentation circuit (SA and IC), an analogue to digital converter (ADC), a three axis motion control system (TAMCS), data acquisition and main control systems (DAQ and MCS), and a graphical user interface unit (GUIU). In the Figures 1 and 2, the basic diagram and the appearance of the BED system are shown, respectively. A fluxgate sensor named TE100 (Figure 3) is preferred for magnetic field measurements in SA and IC system design. The TE100 fluxgate sensor contains appropriate parameters for measuring the earth's natural magnetic field strength. The natural magnetic field strength anywhere on the earth is between 25 and 65 micro Tesla (\(\upmu\)T), and the measurement range of TE100 is \(\pm\)100 \(\upmu\)T. It generates differential voltage from 1.5 V to 3.5 V depending on the magnitude of applied magnetic field. This voltage range is ideal for working with microcontrollers or microprocessors. TE100 also has specifications of \(\%\)\(\pm\)0.3 \(\upmu\)T accuracy, \(<\)2 nT/K zero shift, and 0 to 1 kHz (\(-\)3 dB) bandwidth. It is possible to change the differential voltage of the TE100 output (\(+\)) and output (\(-\)) pins in two ways. (i) Changing the magnetic field strength and field line angles around a fixed positioned TE100. (ii) Moving the TE100 at different angles according to constant magnetic field lines. If it is assumed that the designed passive measurement system is moved on a land surface, so it is understood that it will not be possible to keep the direction of TE100s constant, and therefore output voltages of the sensors will change continuously depending on their direction. It is difficult to  
Figure 1: Basic diagram of buried explosive detection (BED) system. determine whether these changes are due to a buried object-dependent anomaly or a change in the position. Therefore, these changes, which are a function of the TE100 position, and which have noise characteristics must be removed or minimized. In this study, a measuring circuit was developed to minimize the noise caused by TE100's position and to detect magnetic anomalies that only the buried object generates. Figure 4 and Figure 5 show the basic diagram and the circuit schematic of the instrumentation circuit we designed, respectively. It is known that the vectoral sum of the magnitudes of two magnetic fields in the same axis but in different directions is zero. With this information, an aim was to produce 0 V in total for two TE100s placed in the same axis but in different directions. Using the circuit in Figure 5 for each sensor, a sensor array consisting 33 pieces of TE100 was formed as shown in Figure 4. Thus, using this sensor array, the BED system, shown in Figure 1, was designed. All these sensors are in the same measurement axis, but only one TE100, to be used for reference sensor (Sref), is in the opposite direction. In the absence of magnetic anomalies, the output of all TE100 channels is equal to 0 V. In the case of magnetic anomalies, the output voltages of TE100 channels change according to the magnitude and intensity of the anomalies. Deviations in the voltages of the channels are due to the MA and contain data about the buried object. Two magnetic field sensors were placed in the same line with opposite directions in order to produce voltages equal in magnitude but opposite in sign. As shown in Figure 5, the output signal of the reference sensor is common for the 32 channel sensor array. In order to distribute this signal to all channels without attenuation and noise, buffer amplifiers with a gain of 1 were preferred at the channel inputs. Voltages of the buffer amplifier output and the OUT (+) output of the channel sensor are added with each other by the resistors R1 and R2. The resistance values of R1 and R2 are equal. Thus, a signal which is the half of the signal obtained by adding the OUT (+) outputs of the reference and channel sensor arrives at the (+) input of the instrumentation amplifier.