A compact and closed-loop spin-exchange relaxation-free atomic magnetometer for wearable magnetoencephalography

Atomic magnetometers operated in the spin-exchange relaxation-free(SERF)regime are the promising sensor to replace superconducting quantum interference devices(SQUIDs)in the biomagnetism field.The SERF magnetometer with compact size and good performance is crucial to the new generation of wearable magnetoencephalography(MEG)system.In this paper,we developed a compact and closed-loop SERF magnetometer with the dimensions of 15.0×22.0×30.0 mm^(3)based on a single-beam configuration.The bandwidth of the magnetometer was extended to 675 Hz while the sensitivity was maintained at 22 f T/Hz^(1/2).A nearly 3-fold enhancement of the bandwidth was obtained in comparison with the open-loop control.The implementation of the closed-loop control also greatly improved the dynamic range,enabling the magnetometer to be robust against the disturbance of the ambient field.Moreover,the magnetometer was successfully applied for the detection of humanα-rhythm and auditory evoked fields(AEFs),which demonstrated the potential to be extended to multi-channel MEG measurements for future neuroscience studies.

Dependence of α-phase size on flow stress during dynamic recrystallization steady state in Ti60 alloy

The dependence of α-phase size on flow stress was characterized by a proposed kinetic model during dynamic recrystallization （DRX） steady state in Ti60 alloy. Accord- ing to the isothermal compression tests, the influence of deformation parameters on the steady-state flow stress was analyzed and the constitutive equation was established to predict the steady-state flow stress under different defor- mation temperatures and strain rates. A power-law rela- tionship between the DRX average grain size and steady- state flow stress with an exponent of -2 is obtained from the dynamic balance during DRX steady state. The effect of deformation parameters on at-phase size was observed through the microstructure after deformation, and the applicability of the model for Ti60 alloy was verified by the comparison between predicted and experimental data.

Hot deformation behavior and processing parameter optimization of BT25y alloy with an initial equiaxed microstructure using processing map

The high-temperature plastic deformation behavior of BT25y alloy with an initial equiaxed microstructure was investigated by hot compression tests. Processing maps were established to evaluate the power dissipation efficiency （η） and identify the flow instability regions. When the strain reaches steady state, the optimum processing window is distributed in the area covering most of the studied deformation temperatures and strain rates of 1 × 10-2 to 1× 10-1 s-1. True strain has great effects on the power dissipation efficiency under the condition of 880 ℃/1× 10-3 s-1, but the efficiency values remain approximately constant （η= 0.40） at conditions of 900-940 ℃/1× 10-2 to 1 × 10-1 S-1 and 980-1000 ℃/ 1× 10-1 s- 1. Besides, the instability regions are distributed in high strain rate areas no matter how many of the strains. Based on the processing map and microstructural observa- tion, it can be concluded that the deformation mechanisms related to Region I with small strain rate and lower temper- ature in α＋β phase field, Region II with medium strain rate and higher temperature inα＋β phase field, Region III with medium strain rate and high temperature in βphase field are superplasticity and strain-induced transformation, dynamicrecrystallization （DRX） and phase transformation, β phase dynamic recovery and local DRX, respectively.