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This paper presents an investigation of methods for improving homogeneity inside various dielectric phantoms situated in a 10.5 T human-sized MRI. The transmit B 1 (B 1 +) field is excited with a quadrature fed circular patch-probe and a 12 element capacitively-loaded microstrip array. Both simulations and measurements show improved homogeneity in a cylindrical water phantom, an inhomogeneous phantom (pineapple), and a NIST standard phantom. The simulations are performed using a full-wave finite-difference time-domain solver (Sim4Life) in order to find the B 1 + field distribution and compared to the gradient recalled echo image and efficiency result. For additional field uniformity, the wall electromagnetic boundary conditions are modified with a passive quadrifilar helix. Finally, these methods are applied in simulation to head imaging of an anatomically correct human body model (Duke, IT'IS Virtual Population) showing improved homogeneity and specific absorption rate for various excitations.

Additive manufacturing has emerged as a promising approach for fabricating graded refractive index structures that control the electromagnetic response of radio frequency (RF) devices. However, current 3D printing methods cannot produce continuous gradients from multiple materials. Here, low‐loss graded dielectrics via active mixing of nanocomposite inks composed of block copolymers and oxide nanoparticles are designed and printed. By simultaneously tailoring their rheological, printing, and their local filler particle‐to‐polymer ratio using an active mixing printhead, a conductive microstrip‐graded substrate matching network with a gradually changing dielectric response, is created. In these printed devices, the impedance of the RF signal is controlled by the graded substrate rather than by varying the conductive microstrip geometry, enabling the fabrication of smaller RF devices. This approach enables the rapid design and fabrication of high‐performance RF devices with locally tunable dielectric properties.

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