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Urban road near‐surface anomalous structures are buried at shallow depths (≦20 m) and small scale. Current geophysical methods, such as the transient electromagnetic, ground‐penetrating radar and shallow seismic methods with reflection wave, refraction wave and Rayleigh surface wave, do not provide sufficient detection accuracy for near‐surface anomalous structures. Although the back‐scattered method is promising in this task, it still needs improvement. This paper proposes an efficient near‐surface seismic back‐scattered method to realize the rapid lateral imaging of urban road anomalous structures. The proposed method uses a principal component analysis algorithm to directly extract the anomalous structure information. It does not require the knowledge of parameters such as velocity or the seismic wavelet so that the solutions are not affected by these parameters. Moreover, the proposed method retains the high transverse resolution of the back‐scattered wavefield and does not lose the wavefield information. Simulation and experimental operation show that the proposed method is very efficient. Combined with the hardware equipment provided by the towed seismograph, the proposed method can realize rapid detection and data imaging, which has a high engineering application value. [ABSTRACT FROM AUTHOR]

A type of differential resonant magnetic field sensor is developed by employing the composite elements of FeGa plates, piezoelectric quartz crystal double-ended tuning forks (DETFs) and bias permanent magnets. The model and analysis show that the differential design brings the benefits of doubled sensitivity, increased linearity and low temperature drift. Importantly, a small and compact magnetic circuit containing a pair of permanent magnets and dual FeGa plates ensures the generation of differential actuation, which not only reduces the leakage flux but also improve the field-sensitivity and resolution. The magnetic circuit model based on the “lumped parameters” method is established. As an important aid, the distribution of magnetic flux density along the longitudinal direction of the FeGa alloy is simulated by finite element analysis software. In order to avoid the prediction error caused by parameter errors, simulations in different conditions are carried out for comparative analysis. This method ensures the magnetic circuit provides qualified magnetic field. The experimental results show that the differential resonant magnetic field sensor with frequency readout has the characteristics of high sensitivity of 4.4 Hz/Oe, high resolution of ${< }3.04\times 10^{-4}$ Oe, low temperature drift and excellent linear (non-linearity error of 1.3%FS) and low hysteresis (1.5%FS) over its measurement full scale (FS) of ±100Oe. [ABSTRACT FROM AUTHOR]

In order to overcome the low efficiency and poor resolution of single‐frequency transmitters for electromagnetic sounding and wireless power transfer (WPT), a well‐organized multifrequency resonant network is proposed to generate a synthetized current with two or more frequencies. The complete design and realization of the hybrid‐frequency current source is presented. The characteristic equation method is applied to extract the resonance frequencies from the given network. On the other hand, the nonlinear equation system about the passive elements is built and solved by the trust–region algorithm based on the expected frequencies. The multifrequency sinusoidal pulse width modulation method is first proposed to create the barcode driving signals for a full‐bridge inverter. The asynchronous modulation is recommended to reduce the harmonic components beyond the resonance frequencies, and the modulation ratios for the driving signals are adjusted at any resonance frequency so that the energy can be distributed evenly at different resonance points. The simulation results prove that almost all energy is concentrated at the resonance frequencies, and the frequency leakage is hardly seen. The resonant network and its control method is very useful to create a hybrid‐frequency current source for high‐efficiency and high‐resolution electromagnetic sounding and WPT. © 2019 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [ABSTRACT FROM AUTHOR]