applied sciences  
A Magnetic Field Camera for Real-Time Subsurface Imaging Applications  
[PERSON] 1,*\({}^{\text{c}}\), [PERSON] 1,*, [PERSON] 2, [PERSON] 2 and [PERSON] 3  
School of Electrical Engineering and Informatics, Institut Teknologi Bandung, Bandung 40132, Indonesia School of Electrical Engineering, Teknom University, Bandung 40257, Indonesia; [EMAIL_ADDRESS] (A.D.S.); [EMAIL_ADDRESS] (D.R.) Faculty of Advanced Technology and Multidiscipline, Universitas Airlangsa, Surabaya 60115, Indonesia; [EMAIL_ADDRESS] Correspondence: [EMAIL_ADDRESS] (A.B.S.); [EMAIL_ADDRESS] (D.D.)  
Footnote 1  
In [1], we constructed a magnetic field imaging system utilizing the built-in magnetometer of a smartphone. To obtain an image that represents the distribution of the magnetic flux density caused by an ambient magnetic field, such as the Earth's magnetic field [2], one has to scan an imaging area and then execute a reconstruction algorithm to obtain all field values of the area. Therefore, this device is categorized as a scanner, which is referred to as a B-Scanner, where \"B\" refers to the notation of magnetic flux density, which is normally denoted by \(\vec{B}\). Magnetic field scanners have also been employed in geomagnetic surveys [3] and industrial testing [4]. Micro-circuitry faults of an IC (integrated circuit) can also be detected by a magnetic field scanner [5]. A close relative to magnetic imaging is eddy-current imaging, which has also been investigated actively by researchers [6; 7; 8; 9; 10]. In the biomedical area, extremely sensitive SQUID (superconducting quantum interference device)-based magnetometers have been used to detect and image brain activities in magnetoencephalography research [11; 12].  
In magnetic field surveys, one typically uses a highly sensitive sensor solely designed for research purposes [3]. Magnetic field sensors are currently easily found at low prices. These sensors make use of giant magneto-resistance (GMR) [13; 14; 15] or anisotropic magneto-resistance (AMR) phenomena, which refer to the change in resistance of a material due to the impact of a magnetic field. In contrast to conventional sensors such as proton magnetometers, GMR/AMR-based devices can be implemented as compact and low-cost IC sensors. Most mobile phones today include a built-in GMR/AMR magnetometer as one of their standard features.  
This paper describes the design and realization of a magnetic field camera, or the B-Camera. The proposed B-Camera has the capability to capture and display the magnetic field distribution of a region instantly thanks to an array of magnetometers that simultaneously measures the field values on a regular grid of the area. Then, a reconstruction algorithm interpolates all of the values within the observed area and displays the result on a screen. We use a similar reconstruction and display subsystems as in the B-Scanner; i.e., data collected by the sensor-array are send to a PDU (processing and display unit), which can be implemented on smartphones, tablets or computers through a USB or a Bluetooth port.  
The rest of the paper is organized as follows. In Section 2, we briefly describe the principle of the proposed B-Camera. The following Section 3 describes the experiments, including the arrangement, reconstruction of images and analysis of the results. Section 4 summarizes and concludes the paper.