Xinzhi Shi

Effects of coil shapes on wireless power transfer via magnetic resonance coupling

The wireless system with four coil resonators is a popular configuration for mid-range wireless power transfer (WPT) via magnetic resonance coupling. The design parameters of four coils have strong impact on efficiency, bandwidth, and transfer distance of the WPT system. In this work, a comprehensive study on effects of coil shapes is conducted. In particular, helix coils, planar spiral coils, and square helix coils are studied. It is shown that the helix coils offer the best performance (e.g. the highest efficiency, the widest bandwidth, and the longest transfer distance) under optimal load whereas the planar spiral coils exhibit the worst performance among these three types of coils. Nevertheless, the performance of the WPT system with helix coils degrades more rapidly than these with other two types of coils when the distance between the transmitting and receiving coils increases.

Rate-equation-based VCSEL model and simulation

Vertical-Cavity Surface-Emitting Lasers (VCSELs) are a new generation of semiconductor lasers that have many advantages. In this paper, we present a comprehensive circuit-level VCSEL model that addresses the basic spatial and thermal behavior of VCSELs based on the rate equations without sacrificing the numerical efficiency demanded by the circuit-level simulation of optoelectronic systems. The model is implemented into SPICE-like simulators, and the simulated results exhibit a good agreements with references.

Thermal circuit model of MQW VCSEL laser

A thermal circuit model of multiquantum-well (MQW) Vertical-Cavity Surface-Emitting Lasers (VCSEL) based on a modified rate equation is presented. This model accounts for the thermal and static and dynamic behavior of the MQW VCSEL. A three level scheme for the rate equations has been chosen in order to model carrier transport effects. The introduction of quasi-two-dimensional (quasi-2-D) gateway states between unbound and confined states has been used to calculate, for each well independently, carrier density and gain. This model has been implemented on a SPICE circuit emulator. Numerical examples are introduced to replicate the multi-quantum well VCSELs typical dc, Small-signal and transient operation, including temperature-dependent light-current (LI) curves, modulation responses, and diffusive turn-off transients.

Thickness-dependent strain effect on the deformation of the graphene-encapsulated Au nanoparticles

The strain effect on graphene-encapsulated Au nanoparticles is investigated. A finite-element calculation is performed to simulate the strain distribution and morphology of the monolayer and multilayer graphene-encapsulated Au nanoparticles, respectively. It can be found that the inhomogeneous strain and deformation are enhanced with the increasing shrinkage of the graphene shell. Moreover, the strain distribution and deformation are very sensitive to the layer number of the graphene shell. Especially, the inhomogeneous strain at the interface between the graphene shell and encapsulated Au nanoparticles is strongly tuned by the graphene thickness. For the mono- and bilayer graphene-encapsulated Au nanoparticles, the dramatic shape transformation can be observed. However, with increasing the graphene thickness further, there is hardly deformation for the encapsulated Au nanoparticles. These simulated results indicate that the strain and deformation can be designed by the graphene layer thickness, which provides an opportunity to engineer the structure and morphology of the graphene-encapsulated nanoparticles.

A CMOS LC-VCO with enhanced PSR based on common-mode replica compensation

A novel 1.575GHz CMOS common-mode replica compensated LC voltage-controlled oscillator with enhanced power supply rejection (PSR) is introduced for global position system (GPS) system-on chip application. In order to improve the PSR and reduce the power consumption, additional regulating circuit with feed forward and feedback amplifiers are implemented using transconductance stages with common-mode replica compensation which has little impact to oscillator phase noise performance. The simulation results under mixed-signal 0.18µm 1P6M process show that this novel oscillator achieves −68.5dB PSR at low frequency. The proposed system exhibits phase noise of −123.3dBc/Hz at a 600 KHz offset from a 1.575GHz carrier, 21% tuning range while only consuming 3.63mA in 1.8V power supply.

Multimode rate-equation-based VCSEL thermal and spatial model of circuit level

In recent years, the characteristics of VCSELs have improved enormously that they have attracted more considerable interest. The corresponding developments of circuit-level VCSEL models are required for use in the design and simulation of optoelectronic applications. Unfortunately, existing models lack either the computational efficiency or the comprehensiveness warranted. In this paper, we present a VCSEL model that addresses the spatial dependent and thermal behavior of VCSELs based on multimode rate equations without sacrificing the numerical efficiency demanded by the circuit-level simulation of optoelectronic systems. Moreover, the thermal behavior is modeled by a laser diode based on Tuckers model with the parameters extracted directly by method of Gao and temperature dependent parasitic resistor and reverse saturation current are also considered. The equivalent circuit of the model is given and it is implemented into SPICE-like simulators to simulate the dc, ac and transient features of a 863nm bottom-emitting AlGaAs VCSEL. The simulated results exhibit good agreements with references.

Effects of receiver parameters on the wireless power transfer system via magnetic resonance coupling

ABSTRACT The wireless system with four-coil resonators is a popular configuration for mid-range wireless power transfer via magnetic resonance coupling. It has broad range of applications. But it is difficult to make the parameters of receiver (including receiving coil and load coil) to be consistent with the parameters of transmitter (including driving coil and transmitting coil) in different application environments. The parameters of receiving coil and load coil have strong impacts on efficiency of the wireless power transfer system. In this work, a comprehensive study on effects of receiver (including receiving coil and load coil) parameters, such as coils radius, wire radius, number of turns and length of coil, is conducted. Some important observations on the effects of the receiver parameters are drawn based on theoretical studies and PSPICE simulation, which are also verified by experiments. It is shown that the radius of receiver has more significant impacts on the power transfer efficiency than other parameters.

A study on effects of coil locations in wireless power transfer

A study on effects of coil locations in the wireless system with four coils is presented by full-wave electromagnetic simulation. Three operational regions can be defined in terms of the distances between neighboring coils: over coupling, strong coupling and under coupling. It is shown that the distance between the receiving and load coils has significant impact on the power transfer efficiency in the strong coupling regime. Design guidelines for optimal coil locations are also presented.

Frequency effects of coil locations on wireless power transfer via magnetic resonance coupling

The wireless system with four coil resonators is a popular configuration for mid-range wireless power transfer via magnetic resonance coupling. The locations of four coils have strong impact on efficiency, resonant frequency and bandwidth of the wireless power transfer system. In this work, a comprehensive study on frequency effects of coil location parameters, such as the distances between neighboring coils, is conducted by virtue of full-wave electromagnetic solution. It is shown that the distance between the driving and transmitting coils may merely affect the bandwidth and the resonant frequency in the strong coupling regime. The distance between the transmitting and receiving coils can have strong impact on both the bandwidth and the resonant frequency. The research will provide design guidelines for optimal coil locations of the wireless power transfer system.

Circuit model of quantum cascade lasers for simulation of influence of doping density

In this paper, a new equivalent circuit-level model of QCLs is introduced to overcome drawbacks of the previous models. The photon gain coefficient and injection current efficiency both depend on the injector doping density in the model. A revised three-level rate equations that permit a compact and computationally efficient implementation. The electron scattering time, relaxation time and escape time between the corresponding levels are obtained by employing a fully non-equilibrium self-consistent Schrödinger-Poisson analysis of the scattering rate and energy balance equations. A general diode sub-circuit is adopted to model the current-voltage relationship. This new circuit-level model can be readily incorporated into a standard circuit simulation environment such as SPICE, which enables electronic integrated circuit designers to simultaneously evaluate the performance of both QCL and electronic devices.