The development and current status of microwave ferrite technology is reviewed in this paper. An introduction to the physics and fundamentals of key ferrite devices is provided, followed by a historical account of the development of ferrimagnetic spinel and garnet (YIG) materials. Key ferrite components, i.e., circulators and isolators, phase shifters, tunable filters, and nonlinear devices are also discussed separately.

Since the early 1980s, a number of electrical imaging techniques based on capacitance, resistance, or inductance measurement at low frequencies have been developed for the monitoring of industrial processes, such as oil- and gas-multiphase flows. In principle, microwave tomography would produce higher resolution images than these low-frequency techniques. But it has mainly been studied for medical applications over the past two decades and is less developed for industrial applications. In this paper, the development of an experimental microwave-tomography system intended for oil- and gas-flow measurements is described, which includes the hardware for data acquisition and the numerical algorithm for image reconstruction. The investigation of the system for the imaging of static–dielectric phantoms modelling oil- and gas-flow distributions is reported together with the images obtained at two different microwave frequencies: 2.5 GHz and 4 GHz. It has been demonstrated that images of the dielectric phantoms can be reconstructed using the system, with the images obtained at 4 GHz having better quality and higher resolution.

Optical cavities and waveguides are essential building blocks of many modern optical devices. They rely upon photonic bandgaps, or total internal reflections, to achieve field confinement. Here a new phenomenon is reported of wave localization that is attributable to neither of the above light guiding mechanisms. It is found that what is known as the Dirac point within a photonic band structure can play the role of a photonic bandgap with the establishment of field confinement. The new localized mode occurs at a Dirac frequency that is beyond any complete photonic bandgap, and exhibits a unique algebraic profile. The features of this new wave localization will add new capabilities and more flexibility to the design techniques of novel photonic components and photonic chip architectures.

Based on the application requirements of the suspended microstrip circuit, a novel broadband microstrip line-suspended microstrip line transition circuit is designed in this paper. The transition structure uses "V-grooved" ground structure to realize the transition from microstrip line to suspended microstrip line in the direction of electric field, and uses gradient signal line for impedance matching to expand the bandwidth. The final simulation results show that the echo loss of the structure is better than 15 dB and the insertion loss is less than 0.165 dB in the frequency range of 0-40 GHz, and the sensitivity of circuit performance to circuit size is low. This design combines the ultra-low loss suspension line with the most commonly used microstrip line circuit, and has the advantages of broadband, low insertion loss, easy processing and compact structure. It improves the application scope of the suspension microstrip circuit and can be better integrated with other circuits or systems.

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