Design and Characterization of a Multi-Processed Differential Magnetic Field Probe by Using Asymmetric Calibration Method

In order to improve the spatial resolution of a magnetic near field probe, the design method combining multiple ports with multiple production processes has been proven effective. However, the asymmetry of transmission structure introduced by the junction between two different processes is a key problem that limits the performance of these probes. In this paper, a differential magnetic near field probe (diff-H-probe) combining flexible printed circuit (FPC) process with print circuit board (PCB) process has been manufactured to achieve high spatial resolution. The measurement results show that this probe can recognize a serpentine line with $100~\mu \text{m}$ -width of trace and $100~\mu \text{m}$ -space between traces. Meanwhile, an asymmetric calibration method (ACM) has been applied to significantly improve the performance of the diff-H-probe. Some key parameters of the probe with and without using the ACM are compared by using an air-dielectric microstrip line. The compared results show that the detection frequency range of the proposed probe is broaden to 12 GHz. Moreover, the results also demonstrate that the ACM can improve the differential electric field suppression up to 4.1 dB and improve the common mode electric field suppression to 20 dB at the frequency below 12 GHz.

I. Introduction

Magnetic near field measurement technique has been paid more attention in recent years [1]–[6]. Many techniques can be used to realize magnetic field measurement, such as fluxgate (FG) sensors [7], [8], optical pumping (OP) sensors [9], [10], superconducting quantum interference device (SQUID) sensors [11], diamond nitrogen-vacancy center (DNVC) sensors [3], [12], and near field probe [2], [4], [13]. They are widely used for shielding effectiveness analysis [14], [15], fault detection of device [1], [16], high sensitivity magnetic field measurement [11], nondestructive inspection of suspicious areas on cryptographic large-scale integration chips [17], electromagnetic interference prediction [18] and electromagnetic emission analysis of integrated circuits in IEC 61967 [19], [20]. In general, FG and OP sensors are more suitable for high sensitivity magnetic field measurement with frequency range below several hundreds kHz. The SQUID sensor based on the principle of low temperature superconductivity is more suitable for high sensitivity magnetic field measurement, its frequency range usually below several hundreds MHz and the spatial resolution is usually several (such as Magma EFI HiRes). The DNVC sensor is usually suitable for high spatial resolution magnetic field measurement, its spatial resolution can reach several tens nm (such as QSM system of Qzabre). Compared with these sensors mentioned above, near field probes in IEC61967 [19], [20] have the advantages of low production cost, simple application configuration and wide detection frequency band. It is mainly used in near field scanning analysis, such as radiation emission evaluation and coupling path analysis of electronic products.