UCLA

The millimeter wave band, which corresponds to frequencies between 30 and 300 GHz, is heavily used in radar and satellite communications. For these applications, transmit-and-receive (T/R) modules are used to boost output power of the transmitted signal and establish noise figure, which is the degradation in the signal-to-noise ratio, of the system for receiving. Inside these modules, magnetic components such as circulators and isolators are critical to direct the flow of signals and allow both simultaneous transmission and reception using a single antenna. However, the inherently incompatible crystal structures of the ferrite-based magnetic components and their semiconductor-based electrical counterparts make integration of the two using conventional manufacturing methods difficult.

Additive manufacturing has emerged as a method of fabricating structures with complicated shapes. Recent efforts have begun incorporating magnetic materials with the method. One application for additive manufacturing of magnetic materials is miniaturization and integration of circulators. Using circulators in the 40-50 GHz range as a motivating application, requirements arise for the printed films, namely immunity to eddy currents, sufficient magnetization to act as a self-biasing field, and out-of-plane orientation of the self-biasing field. Based on these required properties, hexaferrite particles are selected for their strong magnetocrystalline anisotropy and low conductance. Due to their large internal anisotropy field, the particles of these materials tend to rotate to the field direction instead of changing magnetization direction under application of an external magnetic field, which is less than the anisotropy field. Methods of fabricating composites of hexaferrite particles and liquid polymer, SU8 were developed. Rotation of hexaferrite particles in polymer matrix and thus magnetic anisotropy has been demonstrated in the composite, which is subsequently cured to hold the physical position and orientation of the particles. The anisotropy of the self-biasing field provided by the films has been experimentally characterized via techniques like vibrating sample magnetometer and magnetic force microscopy, and a ferromagnetic resonance (FMR) frequency ~48 GHz has been observed via short waveguide method. We have also characterized the viscosity of the particle-laden polymer at different particle concentrations. 3D printing of this composite with poling will make direct printing of magnetic components that require out-of-plane and in-plane anisotropic magnetization possible.