Compact atomic magnetometer (AM) has potential applications in biomedical devices to measure magnetic signals fromhuman organs, e.g. magnetocardiography and magnetoencephalography. Reducing the size of Helmholtz coils is anessential step for a design of compact AM, which also leads to lower cost in manufacturing processes. However, thehomogeneity and magnitude of the magnetic fields and the size of a rubidium vapor cell must be considered for thedecrease of the coil size. Here, we report a design of compact AM with square Helmholtz coils of 24×24×24 cm3housing a rubidium vapor cell of 7.5 cm in length. The coils were calculated to induce a constant magnetic field of 0.5gauss covering the length of 10 cm along the axis of symmetry of the coils. The field gradient was measured to be lessthan 4% of the magnitude over the distance of 6 cm. For zero-field condition, the field gradient was no more than 1mgauss in all axes. Further developments of square Helmholtz coils for improving the field gradients are still neededbefore implementing in the compact AM.
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