B. M. Yao

Rapid microwave phase detection based on a solid state spintronic device

A technique for rapidly detecting microwave magnitude and phase has been developed using a spintronic device as a microwave sensor, which allows a lock-in amplifier to perform real-time microwave measurement. To demonstrate the feasibility and reliability of the proposed approach, the resonance including the amplitude and phase in a complementary electric inductive-capacitive resonator has been characterized. The results are in agreement with measurement preformed by a vector network. This sensor approach is not limited for use only with spintronic devices, but can also be used with semiconductor devices and hence offers a useful alternative to existing microwave imaging and characterization technologies.A technique for rapidly detecting microwave phase has been developed which uses a spintronic device that can directly rectify microwave fields into a dc voltage signal. Use of a voltage-controlled phase shifter enables the development of a spintronic device that can simultaneously ”read” the magnitude and phase of incident continuous-wave (CW) microwaves when combined with a lock-in amplifier. As an example of many possible practical applications of this device, the resonance phase in a complementary electric inductive-capacitive (CELC) resonator has been characterized using a spintronic sensor based on a magnetic tunnel junction (MTJ). This sensor device is not limited for use only with spintronic devices such as MTJs, but can also be used with semiconductor devices such as microwave detectors, and hence offers a useful alternative to existing microwave imaging and characterization technologies.

Quantifying the complex permittivity and permeability of magnetic nanoparticles

The complex permittivity and permeability of superparamagnetic iron-oxide nanoparticles has been quantified using a circular waveguide assembly with a static magnetic field to align the nanoparticles magnetization. The high sensitivity of the measurement provides the precise resonant feature of nanoparticles. The complex permeability in the vicinity of ferromagnetic resonance (FMR) is in agreement with the nanoparticles measured magnetization via conventional magnetometry. A rigorous and self-consistent measure of complex permittivities and permeabilities of nanoparticles is crucial to ascertain accurately the dielectric behaviour as well as the frequency response of nanoparticle magnetization, necessary ingredients when designing and optimizing magnetic nanoparticles for biomedical applications.

Life signal detection using an on-chip split-ring based solid state microwave sensor

A technique for measuring the amplitude and frequency of breathing and heartbeat has been developed using an on-chip solid state sensor integrating a semiconductor microwave sensor and a split ring operating at a resonance frequency of 4.2 GHz. This technique allows the lock-in amplifier to make real-time measurements, analogous to measurements taken by a vector network analyser through an antenna, but with the advantage of being portable and having a user friendly DC output. The effectiveness of this approach is shown by performing several experiments to determine the breathing and heartbeat frequency with and without the presence of an obstacle between the test subject and the microwave sensor and transducer. The experimental results demonstrate the high sensitivity and large dynamic range over which the proposed system can be used for practical applications.

Voltage control of cavity magnon polariton

We have experimentally investigated the microwave transmission of the cavity-magnon-polariton (CMP) generated by integrating a low damping magnetic insulator onto a 2D microwave cavity. The high tunability of our planar cavity allows the cavity resonance frequency to be precisely controlled using a DC voltage. By appropriately tuning the voltage and magnetic bias, we can observe the cavity photon magnon coupling and the magnetic coupling between a magnetostatic mode and the generated CMP. The dispersion of the generated CMP was measured by either tuning the magnetic field or the applied voltage. This electrical control of CMP may open up avenues for designing advanced on-chip microwave devices that utilize light-matter interaction.

Cooperative polariton dynamics in feedback-coupled cavities

The emerging field of cavity spintronics utilizes the cavity magnon polariton (CMP) induced by magnon Rabi oscillations. In contrast to a single-spin quantum system, such a cooperative spin dynamics in the linear regime is governed by the classical physics of harmonic oscillators. It makes the magnon Rabi frequency independent of the photon Fock state occupation, and thereby restricts the quantum application of CMP. Here we show that a feedback cavity architecture breaks the harmonic-oscillator restriction. By increasing the feedback photon number, we observe an increase in the Rabi frequency, accompanied with the evolution of CMP to a cavity magnon triplet and a cavity magnon quintuplet. We present a theory that explains these features. Our results reveal the physics of cooperative polariton dynamics in feedback-coupled cavities, and open up new avenues for exploiting the light–matter interactions.Rabi oscillations of magnons typically do not have few photon control of single spin quantum systems. Here, the authors use a feedback cavity architecture to increase magnon-photon cooperativity, enabling increased control of light-matter interactions in magnonic systems via cooperative polariton dynamics.

Ground penetrating detection using miniaturized radar system based on solid state microwave sensor

We propose a solid-state-sensor-based miniaturized microwave radar technique, which allows a rapid microwave phase detection for continuous wave operation using a lock-in amplifier rather than using expensive and complicated instruments such as vector network analyzers. To demonstrate the capability of this sensor-based imaging technique, the miniaturized system has been used to detect embedded targets in sand by measuring the reflection for broadband microwaves. Using the reconstruction algorithm, the imaging of the embedded target with a diameter less than 5 cm buried in the sands with a depth of 5 cm or greater is clearly detected. Therefore, the sensor-based approach emerges as an innovative and cost-effective way for ground penetrating detection.

On-chip artificial magnon-polariton device for voltage control of electromagnetically induced transparency

We demonstrate an on-chip device utilizing the concept of artificial cavity magnon-polariton (CMP) coupling between the microwave cavity mode and the dynamics of the artificial magnetism in a split ring resonator. This on-chip device allows the easy tuning of the artificial CMP gap by using a DC voltage signal, which enables tuneable electrodynamically induced transparency. The high tunability of the artificial magnon-polariton system not only enables the study of the characteristic phenomena associated with distinct coupling regimes, but also may open up avenues for designing novel microwave devices and ultra-sensitive sensors.

Experimental realization of negative refraction using one metasurface

A designed one metasurface metamaterial that can provide both negative permittivity and negative permeability and therefore a negative refractive index is experimentally realized in this work. Effective parameters are retrieved from the measured S parameters and are in good agreement with the numerical simulation data. Over our working frequency range, negative refractive index, index near zero, and positive index are all observed, which is confirmed by the two-dimensional wave propagation behaviour. This result can help simplify the design for negative refraction application and can further be used to fabricate negative index materials at optical wavelengths as well as three-dimensional metamaterials.