The Effect of 2-Directional Magnetic Biasing Used for Tuning of a Ferrite-Loaded Re-entrant Cavity

Abstract

SummaryCavities that are partially filled with ferrite material provide a tunable resonance frequency by making use of the changing µ-characteristics of ferrites when exposed to an external magnetic bias field. The concept of using either parallel or perpendicular magnetic biasing to reach a certain resonance frequency of a cavity has been known for many years. However, a cavity based on superposition of perpendicular and parallel magnetic fields to obtain improved ferrite characteristics was suggested in W. R. Smythe "Reducing ferrite tuner power loss by bias field rotation," IEEE Trans. Nucl. Sci., vol. 30, no. 4, pp. 273-275, 1983, but to our knowledge was neither tested nor built. Such a 2-directional biasing is expected to provide a reduction in RF losses for an identical tuning range as compared with the classical 1-directional magnetic bias. We have successfully tested this theory with a measurement set-up consisting of a ferrite-filled cavity, exposed to external biases that allow the clear separation of the two orientations of superposed magnetic bias fields. The outcome is an enlargement of tuning range with high cavity Ԛ and the possibility of fast tuning. In this paper, we describe the measurement set-up and present the tuning ranges that we attained by applying different bias schemes. Abstract-Cavities that are partially filled with ferrite material provide a tunable resonance frequency by making use of the changing -characteristics of ferrites when exposed to an external magnetic bias field. The concept of using either parallel or perpendicular magnetic biasing to reach a certain resonance frequency of a cavity has been known for many years. However, a cavity based on superposition of perpendicular and parallel magnetic fields to obtain improved ferrite characteristics was suggested in W. R. Smythe "Reducing ferrite tuner power loss by bias field rotation," IEEE Trans. Nucl. Sci., vol. 30, no. 4, pp. 273-275, 1983, but to our knowledge was neither tested nor built. Such a 2-directional biasing is expected to provide a reduction in RF losses for an identical tuning range as compared with the classical 1-directional magnetic bias. We have successfully tested this theory with a measurement set-up consisting of a ferrite-filled cavity, exposed to external biases that allow the clear separation of the two orientations of superposed magnetic bias fields. The outcome is an enlargement of tuning range with high cavity and the possibility of fast tuning. In this paper, we describe the measurement set-up and present the tuning ranges that we attained by applying different bias schemes.

Computation of Complex Eigenmodes for Resonators Filled With Gyrotropic Materials

“…Yet, the quality factor strongly depends on both field components. Consequently, this model is compliant with the experimental finding that a 2-directional bias scheme is beneficial [39]. The results for the resonance frequency and quality factor are summarized in figure 4.9.…”

“…As expected from theory [102], such bias schemes might lead to a higher quality factor while sustaining the same tuning range. This fact has been successfully confirmed in recent experiments [39]. A numerical analysis of a 2-directional bias scheme requires the knowledge of all components of the permeability tensor (2.22) for all magnetization states.…”

“…Besides, a high phase stability was observed. The basic principle of the introduced methods are thus similar to approaches known from literature, namely for instance [34][35][36][37] for the reflection measurement and [38,39] for the transmission measurement.…”

Nano-Magnetodielectric Composite Based Substrate for Use in Microwave Planar Devices in X-Band

“…Miniaturization can also be achieved by increasing the other parameter μ r (such as by using ferrite based materials). But, reports suggests that bulk ferrites generally have high saturation magnetization and dispersive magnetic losses [4][5][6] and needs strong external dc-bias fields to alter its permeability property [7], making it unsuitable for compact applications requiring higher efficiency. Further, shift of operational frequency of resonant devices on ferrite substrates due to application of external bias [8,9] causes difficulty in integrating it with other systems.…”

Ferrite Characterization for the Design of an Accelerating Cavity With Perpendicular Biasing

“…The garnet G-510 from Trans-Tech, Inc. [7] was evaluated to be most suitable for perpendicular biasing within a frequency range of 18 to 40 MHz with regards to the available range in relative permeability and related magnetic losses. In [8] and [9] a possible resonance sweep was investigated by using G-510 toroidal samples in a re-entrant measurement cavity. It was shown that superposition of a magnetic bias with both perpendicular and parallel components with respect to the RF magnetic field can be advantageous in terms of frequency tuning range and quality factor.…”