This paper develops an active magnetic near field probe (H-field probe) by using a fourlayer printed circuit board (PCB) technique. Two-turn detection structure and a low noise amplifier are used to improve probe's frequency response. The two-turn detection structure can maximize the use of PCB stack resources, and a 14.5 dB gain amplifier can increase signal output capability. The probe can then be used for electromagnetic compatibility (EMC) test from 150 kHz to 3 GHz. Compared with traditional active shielded-loop H-field probe (TAHP) with loop area of 500 𝜇m 2 , the frequency response of the proposed probe can improve 20 dB at 0.5 GHz. Different from the method of comparing the sensitivity of the probe only through the frequency response, this paper measures and analyzes the real sensitivity of the probing device composed of the proposed probe. Under the condition of the same receiver parameter setting, the sensitivity at 0.5 GHz is increased by 11.7 dB compared with commercial passive probing device and 20.2 dB at 0.5 GHz compared with the probing device with TAHP device. It reaches −32.4 dB µA. In addition, the proposed probe has acceptable spatial resolution of 1.28 mm at 1 GHz, which is more suitable for printed circuit board level EMI analysis.

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A wideband circularly polarized (CP) cross-dipole antenna with folded ground plane is presented. The antenna consists of an L-shaped stepped patch as driven elements and four rotated L-shaped metallic ground strips as parasitic elements. A sequential phase feeding structure is used to provide 90°phase difference, which is composed of a pair of vacant-quarter printed rings. It is noticed that the four rotated parasitic L-shaped metallic ground strips and ground plane are directly connected to form a folded ground plane instead of the traditional disconnection between parasitic elements and ground plane. By using these elements, multiple CP resonances can be excited to meet the requirement for the wideband CP radiation. The presented antenna shows outstanding CP feature with a broad axial-ratio bandwidth (ARBW) of 85.7% (1.3-3.25 GHz) and a wide impedance bandwidth (IBW) of 100% (0.95-2.85 GHz). This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

A magnetic near-field probe (H-field probe) with dual output has been developed using a four-layer printed circuit board (PCB) technique. To achieve the improvement of detection sensitivity, the symmetrical double-loop is adopted to double the detection signal while suppressing the electric field coupling, which is also illustrated in a circuit model. The calibration factor (defined as the ratio of the external magnetic field to the induced response voltage of the probe) of the proposed H-field probe reaches 37.74 [dB (A/m)/V] at 0.5 GHz with the loop area of 0.8 mm 2 , resulting in a better sensitivity than the single-loop probe. For the suppression of unwanted electric field a floating shield is added to the bottom of the probe, leading to an excellent common electric field suppression ratio of 29 dB in the frequency range up to 10 GHz. The probe is also characterised by parameters such as high differential electric field suppression, spatial resolution and probe influence on the device under test. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Coal fractography is a powerful tool for interpreting coal fracture behaviors, which is significant for dealing with failure issues encountered in deep coal mining. However, the accuracy of coal fractography highly depends on the method of quantitatively characterizing coal fracture surfaces. In this study, coal fractography under dynamic impact loading was investigated based on a multifractal method, the multifractal spectrum parameters were proposed to quantitatively describe the coal fracture surfaces. The width of the multifractal spectrum [Formula: see text] characterizes the uniformity of the surface asperity distribution, and the spectrum parameter [Formula: see text]–[Formula: see text] characterizes the proportion of dominant asperities on fracture surface. The coal fractography results indicate that larger loading rate leads to more asperities on the coal fracture surfaces, i.e. rougher fracture surfaces, and the fracture surfaces are dominated by small asperities induced by dynamic impact loading. In addition, significant anisotropy effect was found on the fracture surfaces under dynamic impact loading by the spatial distributions of multifractal spectrum parameter [Formula: see text]. The parameter [Formula: see text] was further utilized to determine the macrocrack direction and microfracture markings on the coal fracture surfaces, the results transpire that the multifractal method is feasible for coal fractographic analysis under dynamic loading conditions.