This paper has made a comprehensive investigation of the contribution of inertial measurement unit (IMU) signal denoising in terms of navigation accuracy, through theoretical analysis, simulations and real tests. Analysis shows that the integral step in the inertial navigation system (INS) algorithm is essentially equivalent to a super low-pass filter (LPF), whose filtering strength is related to the integral time of the INS. Therefore the contribution of the IMU denoising filter is almost completely overshadowed by the effect of the integral step for normal navigation cases. The theoretical analysis result was further verified by the simulations with an example of inertial angle estimation and by real tests of INS and GPS/INS systems. Results showed that the IMU signal denoising cannot bring observable improvement to INS or GPS/INS systems. This conclusion is strictly valid in the condition that the equivalent cut-off frequency of the integral step (which equals the reciprocal of the INS working alone time) is lower than the cut-off frequency of the denoising filter, which is the usual case for INS applications (except for some static data processing such as the stationary alignment of INS).

In this study, the AC magnetic permeability of polycrystalline Fe81Ga19 alloy (Galfenol), without crystal orientation under both the bias applied fields and frequencies, was investigated by the method of measuring inductance of ring specimens. The results showed that the AC permeability of the alloy can reach more than 160 Gs/Oe under the conditions of low frequencies or quasi-static state. The permeability decreased with the increase of frequency. When the frequency was higher than 6 kHz, the permeability decreased slowly, and gradually stabilized with the increase of frequency. When applying a little of parallel bias magnetic field, the permeability decreases obviously with the increase of frequency. But applying a perpendicular bias magnetic fields, the permeability of the only initial point of the measuring frequency decreases a little compared to the permeability without bias field.