Shudong Lin

Magnetocardiography (MCG) offers a contactless and noninvasive approach to evaluating cardiac electrophysiological activity by measuring its associated magnetic fields. Recent advances in optically pumped magnetometers (OPMs) with femtotesla-level sensitivity have enabled the development of compact, high-density MCG systems suitable for clinical applications. In this work, we present a 64-channel integrated OPM-MCG system based on self-developed miniaturized single-beam magnetometers (3.8 cm³ volume, average sensitivity better than 10 fT/√Hz, and best sensitivity of 6 fT/√Hz in the 2–30 Hz band). A micro–nanofabricated planar lightwave circuit splitter distributes a single laser source into 64 stable, low-loss optical paths, achieving substantial reductions in system size and cost compared with conventional MCG/MEG platforms. The modular design allows for straightforward expansion to higher channel counts and sensor densities. Comprehensive evaluations of sensitivity, bandwidth, and measurement accuracy confirm the system’s high performance. In a magnetically shielded environment, the system successfully captured high-quality adult MCG signals, enabling detailed time-frequency analysis and precise cardiac magnetic field mapping. These results demonstrate the feasibility of large-scale OPM-based MCG for noninvasive cardiac functional assessment and underscore its potential as a platform for future cardiac diagnostic studies.

The dual-axis magnetic field measurement using atomic magnetometers is significant in scenarios with an uncertain magnetic field direction. The π-pulse resonance is a pulse parametric resonance that can realize a dual-axis measurement by periodically flipping the electron spin. It is difficult to determine, especially in uncertain or fluctuating external magnetic fields, which seriously limits its scope of application. This study demonstrates an experimental observation of the π-pulse resonance in spin-exchange relaxation-free (SERF) magnetometers. The π-pulse parameters are studied in detail, guiding the resonance determination and the dual-axis measurement optimization. We propose herein a method of introducing a weak off-resonance to reduce the interaxial coupling, which can be significantly reduced at a certain response cost. We also implement a closed-loop control of the resonance or minimum coupling point that is effective when the external magnetic field along the pumping axis is unstable, extending the potential application scenarios of the π-pulse dual-axis magnetometers to the conditions of the semi-open magnetic shield environment and unshielded geomagnetic environment.

The weak-value-amplification (WVA) effect, which is also called weak measurement, has been developed extensively in various sensing systems. Here, we report the actual realization of the WVA effect in spin-exchange relaxation-free atomic magnetometer system, wherein the slight separation of transverse momentum of the probe light is amplified by introducing orthogonal pre- and post-selection states. A differential detector is used to obtain the transverse position of the probe light accurately in real time. The weak coupling of the magneto-optical interaction with atoms will be reflected in the differential signal. The WVA effect is observed and demonstrated directly and a high sensitivity of 8 fT/Hz is achieved. Also, we obtain the stable and distinct simulated magnetocardiography signal through our system. The present successful implementation of this probe method paves the way for further technical noise suppression and sensitivity improvement of quantum sensors.

In this paper, a series of four novel microstrip antenna array designs based on different annular-microstrip feeding lines at 60-GHz millimeter wave (mmW) band are proposed, aiming at the potential usage of the mmW coverage antenna with multi-directional property. As the feeding network, the annular contour microstrip lines are employed to connect the patch units so as to form a more compact array. Our first design is to use an outer contour annular microstrip line to connect four-direction linear arrays composed of 1 × 3 rectangular patches, thus the gain of 8.4 dBi and bandwidth of over 300 MHz are obtained. Our second design is to apply the two-direction pitchfork-shaped array each made up of two same linear arrays as the above, therefore the gain of 9.65 dBi and bandwidth of around 250 MHz are achieved. Our third design is to employ dual (inner and outer contour) annular-microstrip feeding lines to interconnect the above four-direction linear arrays, while our fourth design is to bring bridged annular-microstrip feeding lines, both of which can realize the goal of multi-directional radiation characteristic and higher gain of over 10 dBi.