Atomic magnetometers are widely acknowledged as one of the most sensitive devices for magnetic field measurement. Our study presents a novel method that enables bandwidth expansion of single-beam magnetometers in the spin-exchange relaxation-free regime. This method bases on increasing the modulation amplitude of magnetic field combining with negative feedback with proportional gain. Through our method, the magnetometer’s total relaxation rate is moderately increased by elevating modulation amplitude and frequency, and correspondingly, the detection bandwidth experiences dramatic improvement from 230 Hz to 1380 Hz. The application of negative feedback with proportional gain further increases this bandwidth to higher than 4 kHz, which is over 17 times of its original value. The sensitivity of the magnetometer under this condition is measured as 25 fT/ $\text {Hz}^{\text {1/2}}$ for open-loop scheme and 35 fT/ $\text {Hz}^{\text {1/2}}$ for closed-loop scheme. Comparatively, the sensitivity measured on conventional conditions in our experiment is 12 fT/ $\text {Hz}^{\text {1/2}}$ . This approach offers a profitable trade-off that extraordinary expansion of detection bandwidth can be acquired with the price of a little sensitivity loss. Our method is advantageous for miniaturization of atomic magnetometers as no extra hardware is added, which is of special interest for applications including biomagnetic measurement where large detection bandwidth is sometimes in need.

The increasing switching frequency of inverters in new electric power technology causes leakage currents at tens or even hundreds of kHz, exceeding the measurement frequency range of conventional AC residual current sensors. In addition, the cost of residual current sensors developed specifically for DC is high, limiting further application promotion. Hence, this paper focuses on designing a wideband closed-loop residual current sensor based on self-excited oscillation fluxgate, which outperforms ordinary measurement methods. The sensor is developed through the optimization of demodulation circuits, and the increase of AC windings and the construction of excitation voltage regulating circuits. The DC residual current measurement accuracy of the sensor is better than 0.2%. The standard deviation of zero-point change is 0.0046 mA. The introduction of this innovative sensor not only enables precise and stable measurement of residual currents but also facilitates current monitoring in high-frequency applications. It can be fully applied in the field of power technology and will promote the development of efficient and reliable power systems.

Three-axis atomic magnetometers have an excellent advantage for determining the complete vector information of a magnetic field to be measured. However, the crosstalk effect, which leads to an error output on one axis owing to a magnetic field on the other axes, can reduce the measurement accuracy. In this study, we propose an effective suppression method for the crosstalk effect in a three-axis atomic magnetometer. First, we investigated and analyzed the main factors that introduce the effect. Based on this, the modulation parameters were optimized to improve the scale factors, which obtained a coupling coefficient of less than 6% for the atomic magnetometer. Subsequently, the associated transfer matrix was corrected to further suppress the crosstalk effect. After correction, all the coupling coefficients were decreased to less than 3%, with the majority being lower than 1%.

In technology and industrial production, many applications require wide-bandwidth current measurements. In this paper, a signal fusion scheme for a current sensor comprising tunneling magnetoresistance and a current transformer is proposed, achieving a flat frequency response in the DC to MHz range. The measurement principles in different cases of the scheme are introduced, and the total transfer function of the entire scheme is derived by analyzing each section separately. Furthermore, the feasibility and selected parameters of the scheme are verified through a systematic simulation utilizing the MATLAB software. Based on the proposed scheme, a group of principal prototypes are built to experimentally evaluate the bandwidth, amplitude and phase flatness, accuracy, sensitivity, and impulse response. The relative amplitude variation in the passband of the fusion sensor is less than 4%, and the estimated bandwidth of the fusion sensor is close to 17 MHz. The accuracy is better than 0.6%, even when measuring the current at 1 MHz, and the relative standard deviation is 5% when measuring the impulse signal. The sensors developed using this scheme, with a low financial cost, have advantages in many wide-bandwidth current measuring scenarios.

Zero-field optically pumped magnetometers operating in the spin-exchange relaxation-free (SERF) regime have been extensively studied, and usually depend on zeroth-order parametric resonance to measure the magnetic field. However, the studies conducted on this topic lack thorough analyses and in-depth discussion of nonzero-order magnetic resonances in single-beam SERF magnetometers. In this paper, we analyzed the nonzero-order resonance, especially the first-order resonance, based on a single-beam SERF magnetometer, and discussed its various applications. A comprehensive theoretical analysis and experiments were conducted with respect to multiple functions, including nonzero finite magnetic field measurements, spin polarization measurement, and in situ coil constant calibration. The results showed that first-order resonance can be utilized for nonzerofinite magnetic field measurements, and the spin polarization of alkali-metal atoms can be determined by measuring the slowing-down factor using the resonance condition. Furthermore, acquiring the first-order resonance point at an equivalent zero pump light power through fitting offers an approach for quick and precise in situ coil constant calibration. This study contributes to the applications of SERF magnetometers in nonzero finite magnetic fields.

A novel fluxgate current sensor scheme based on a dual-core configuration is proposed in this study. By integrating a direct current (DC) zero-flux detector, an alternating current (AC) zero-flux detector, and a secondary compensation coil module, a unified design of multi-coil and multi-signal processing circuits is achieved. Compared with conventional three-core fluxgate designs, the proposed approach offers a simplified structure while maintaining high bandwidth and high-accuracy measurement capabilities. A prototype was developed based on the proposed principles, which was subsequently evaluated through experiments. The results demonstrate that the sensor achieves a -3dB bandwidth exceeding 1.6 MHz. Within the frequency range of 10 Hz to 100 kHz, the amplitude response variation remains below 2%, and the phase deviation is within 2°. When benchmarked against a precision shunt resistor, the measurement error of 100 kHz AC current is maintained within 3%. The sensor also exhibits a step-response rise time of approximately 300 ns. These findings indicate that the proposed dual-core fluxgate sensor is well-suited for wideband current measurement applications demanding high dynamic performance and accuracy.