Gradient coils are essential for the performance of the MR imaging system. Usually, coils are designed assuming thin wire tracks. Here, we design an MR gradient coil set using a more general approach considering the exact track width using the discrete wire approach. The effect of track width on the DC current density distribution and resultant magnetic fields using both loop and Golay coils are first demonstrated. Both, self-shielded X and Z gradient coils of definite width/thickness are designed and optimized. The resistance and inductance of the coils are calculated using the stream functions approach. Track current distribution was used to compute the magnetic fields over the desired volume, and at the cryostat. The linearity of the magnetic field over the volume, the figure of power , and the shielding ratio of the coil are used as parameters in the optimization process. The DC characteristics of the designed coils with definite (small) track width and thickness were compared for verification to that of the corresponding thin wire design where they were found to have approximately similar characteristics. Using our design methodology, the coils' frequency-dependent resistances and inductances were directly/efficiently calculated. The harmonic and transient eddy current interactions between the longitudinal and transverse gradient coils were computed where track slitting was employed to reduce such interactions. This work stresses the importance of considering coil track width in the design process particularly for wide tracks as well as computing the coil's figure of merit, harmonic and transient coil characteristics/interactions.

Wireless power transmission (WPT) is commonly used today in many important daily applications, such as electric vehicles, mobile phones, and implanted medical devices. The transmitter and receiver coils are essential elements in the WPT system, and the coupling coefficient between these coils plays an important role in increasing the power transfer efficiency. In this work, we introduce a new approach to optimizing the coupling coefficient between the transmitter and the receiver coils by changing the geometries and locations of the coil turns. In the optimization process, the geometry of the turns varies from a rhombus to a circular and then a rectangular shape according to a quasi-elliptical parameter value. The Neuman formula is used to calculate the self-inductance, mutual inductance, and coupling coefficient for each specific geometry and turn location. The configuration with the highest coupling coefficient is then selected at the end of the optimization process. The final WPT coils are tested and verified using Ansys software through electromagnetic and AC analysis simulations. The results show that the new approach could achieve smooth and easily manufacturable coils with higher coupling coefficients, thereby increasing the power transfer efficiency of WPT.

Gradient coils are essential for MRI where fast and large electrical current pulses are typically applied to conventional, single-channel gradient coils, particularly for high-performance gradient applications. However, these pulses result in significant power losses and heating of the coil. We investigate the design of power-efficient multi-channel Z-gradient coils operating in the conventional mode comparing them to conventional single-channel coils designed using similar dimensions and alike DC performance characteristics. The power-efficiencies of thirteen different two-channel configurations having various section lengths for two different dimensions are analyzed. The current density of each section is approximated by Fourier series expansion where a linear equation relating the desired target field and current density is formulated and then solved. A stream function is derived from the obtained current density and then used to extract the final winding patterns of each section using a particular track width and a specific number of turns. The design process involves optimizing the current driving each channel, the distribution of coil windings, and the section size. Similarly, the performance of three-channel coils is also investigated. Results show that a power dissipation reduction of 17-28% and ∼23% can be achieved using two-and three-channel coils, respectively. Moreover, we showed that multi-channel coils may have a slightly better shielding efficiency compared to conventional coils. A new methodology for designing two-and three-channel coils is presented where an advantage in terms of power efficiency can be gained depending on design parameters, coil's dimensions, number of turns, and other metrics.INDEX TERMS Gradient coil array, MRI, power dissipation, stream function, and target-field method.

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