Injection-locking benefits for weak AC magnetic field detection in Coupled-Core Fluxgate Magnetometers

Recent theoretical and experimental efforts have shown that spontaneous oscillations can be induced by unidirectionally coupling overdamped nonlinear systems, subject to the appropriate system conditions; these oscillations are triggered by a control parameter, the coupling strength, exceeding a threshold value. These concepts have been exploited in the practical realization of a Coupled Core Fluxgate Magnetometer (CCFG) wherein an odd number of wound ferromagnetic cores are coupled in a ring oscillator configuration (cyclic boundary conditions). This scheme yields better signal detection performance, compared to its single-core counterpart, when one uses the CCFG to detect weak dc target magnetic fields. In this paper, we consider the effects of injection-locking by an externally applied time-sinusoidal magnetic field. Injection locking is the locking of the oscillator frequency to the reference source (the "locking signal") with a concomitant lowering of the noise floor. We present, here, simulations and experiments that confirm the benefits of injection locking in the CCFG for weak ac target magnetic fields, in line with earlier theoretical predictions