Minh Quoc Nguyen

Field Distribution Models of Spiral Coil for Misalignment Analysis in Wireless Power Transfer Systems

This paper presents design and optimization methods for spiral coils utilized for wireless power transfer in wireless medical implant applications. A theoretical model was examined for near-field distributions of spiral-type transmitter antennas in both orthogonal components. Finite-element simulations were performed to verify the theoretical radiation patterns. Receiver antenna voltages were measured at planes of interest as a means to map field distributions. Theoretical, simulation, and experimental results were conducted in free space and they agreed well. Understanding the orthogonal field components and their distributions in various distances between the worn transmitter coil outside the body and the receiver coil of implant that has a much smaller size provides a means to find the optimal location and angle to harvest maximum energy. The analysis method for near-field wireless power transmission can be utilized to determine design strategies of the transmitter spiral coil with considerations also in the amplifier circuit and physical constraints in practical scenarios to obtain maximum power and link efficiency for the implant devices. The method can be extended to investigate field distributions affected by human tissues, which construct a much more complex environment, and will be conducted in future works.

Investigation of wireless power transfer in through-wall applications

In this work, we proposed a through-wall wireless power transfer system and investigated effects of various wall materials. The power transfer system was based on inductive coupling of metal coils at 1.3-MHz resonance. Softwood lumber, concrete brick and drywall with insulation filling were tested at two different thicknesses. Two sets of coils, each set consisting of two coils with identical dimensions, having radii of 5 and 15 cm were utilized. Each experiment was conducted with sequential tuning in receiver circuit, operating frequency and in transmitter circuit to reach maximum output power or maximum power transfer efficiency. The output power and transfer efficiency as well as their changes were obtained before and after tuning for different media and thicknesses. It is concluded that the power attenuation with spacing distance dominates the output power and transfer efficiency, while tuning could counteract the parasitic effects in the material and recover the power lost in deviation from resonance. The power attenuation with distance requires design considerations in coil dimensions. With larger coils, more power can be collected through thicker walls and the system tolerates more variation in wall thickness. Tests on randomly chosen walls in our laboratory building were conducted to validate the system performance.

Wireless power transfer by inductive coupling for implantable batteryless stimulators

This study investigated wireless power transfer with inductive coupling at a distance addressing the power requirement for chronic gastrostimulator implants. The energy harvesting system was designed to collect 3 to 20 mW power to operate an implantable stimulator to deliver 1 to 6 mA electric current into stomach tissues. The power transfer system efficiencies were investigated with different dimensions and turn numbers in coil antennas, distances between the two antennas, and variable loads. Clinical practicality and patient comforts were considered for implanting in the stomach through endoscopic procedures. Thus, the antenna size of the transmitter was configured to be between 4 and 6 cm in diameter, to increase portability while the implant coil was fixed at 10×35 mm2. The distance between the two antennas varied from 4 to 10 cm in air. The system efficiency measured as the ratio of output power to input power included tuning a class-E amplifier in the transmitter at 1.3 MHz carrier frequency. A maximum efficiency was achieved at 9.59%. At all distances measured, the delivered power to the implant was more than 3 mW which was the minimal requirement for the operation of the implant.

Multiple-Inputs and Multiple-Outputs Wireless Power Combining and Delivering Systems

In this paper, we investigated the effect of power combining and delivering in multiinput and multioutput wireless energy transmission systems, which consist of more than one transmitter antennas as sources and more than one receiver antennas as loads and repeaters. Theoretical expressions were developed to model the system operation that can be in a large-scale wireless energy network architecture. System characteristics, such as power transfer between antennas, power losses induced in each antenna, wireless efficiency, coil misalignment, and power fluctuation due to the loss of frequency synchronization were examined by theory and verified with experiments. Measurement results matched well with the theory demonstrating the feasibility of combining and delivering power with high efficiencies in large-scale wireless energy transmission systems.

A multi-input and multi-output wireless energy transfer system

In this work, we present for the first time a multi-input and multi-output (MIMO) wireless power transmission system in which there are more than one source (transmitter antenna) and more than one load (receiver antenna). Theoretical expressions are developed to analyze the power transfer between antennas, power loss induced in each antenna and system efficiency of wireless power transfer. The theoretical model is verified with measurements in a prototype system consisting of two transmitter, two receiver and one repeater coils. Experimental results match well with theory demonstrating wireless power combining and delivering in the MIMO system.

Wireless sensor nodes for environmental monitoring in Internet of Things

Wireless networking sensor nodes for environment monitoring in Internet of Things (IOT) are reported in this work. The IOT network includes individual self-sustaining nodes wirelessly transmitting sensor signals to hubs that can be shared in the Internet Cloud. Each node consists of an optimized energy harvesting module, a System-on-Chip (SoC) integrated low-power Bluetooth Smart transceiver, and multi-functional sensor array to monitor environmental parameters. The energy harvesting module is able to adapt and collect energy from solar power, ambient radio waves, and direct wireless power transmission (WPT). The sensor arrays include pH sensor, temperature sensor, photo-detector, electromagnetic wave detector and acoustic noise detector. The SoC processes data and transmits compressed information about environmental conditions to the hub. This platform demonstrated the concepts of combining power harvesting techniques and low-power sensors for the IoT applications.

Position and angular misalignment analysis for a wirelessly powered stimulator

This study investigated the effects in inductive coupling of wireless power due to the contribution of both positional and angular misalignment between the transmitter and implanted stimulator antennas. The implant antenna radius was limited to 1.5 cm for endoscopic implantation while the transmitter coil radius was kept at 21 cm in order to transfer sufficient power for tissue stimulation. The power transfer distances between the two antennas examined were 5, 7 and 10 cm, typical for stimulator implant applications. Theoretical radiation patterns were examined with magnetic field distribution and compared with measured output voltages. Experimental results agreed well with the theoretical models. The optimal location for maximal output power in the receiver was identified with respect to different angular misalignments and distances. The method can guide the re-adjustment strategy of the transmitter coil worn by the patient after implantation and during therapy.

Wireless Power Transfer for Autonomous Wearable Neurotransmitter Sensors

In this paper, we report a power management system for autonomous and real-time monitoring of the neurotransmitter L-glutamate (L-Glu). A low-power, low-noise, and high-gain recording module was designed to acquire signal from an implantable flexible L-Glu sensor fabricated by micro-electro-mechanical system (MEMS)-based processes. The wearable recording module was wirelessly powered through inductive coupling transmitter antennas. Lateral and angular misalignments of the receiver antennas were resolved by using a multi-transmitter antenna configuration. The effective coverage, over which the recording module functioned properly, was improved with the use of in-phase transmitter antennas. Experimental results showed that the recording system was capable of operating continuously at distances of 4 cm, 7 cm and 10 cm. The wireless power management system reduced the weight of the recording module, eliminated human intervention and enabled animal experimentation for extended durations.

Wimpy or brawny cores: A throughput perspective

In this paper, we conduct a coarse-granular comparative analysis of wimpy (i.e., simple) fine-grain multicore processors against brawny (i.e., complex) simultaneous multithreaded (SMT) multicore processors for server applications with strong request-level parallelism. We explore a large design space along multiple dimensions, including the number of cores, the number of threads, and a wide range of workloads. For strong CPU-bound workload, a 2R-core wimpy-multicore processor is found to be on par with an R-core brawny-multicore processor in terms of throughput performance. For strong memory-bound workload, core-level multithreading is largely ineffective for both wimpy-multicore and brawny-multicore processors, except for the case of low core and thread counts per memory/disk interface. For both wimpy-multicore and brawny-multicore, there is an optimal core number at which the highest throughput performance is achieved, which reduces, as the workload becomes deeper memory-bound. Moreover, there is a threshold core number for a wimpy-multicore, beyond which it is outperformed by its brawny-multicore counterpart. These behaviors indicate that brawny-multicores are better choices than wimpy-multicores in terms of throughput performance.

ForkTail: a black-box fork-join tail latency prediction model for user-facing datacenter workloads

The workflows of the predominant user-facing datacenter services, including web searching and social networking, are underlaid by various Fork-Join structures. Due to the lack of understanding the performance of Fork-Join structures in general, todays datacenters often resort to resource overprovisioning, operating under low resource utilization, to meet stringent tail-latency service level objectives (SLOs) for such services. Hence, to achieve high resource utilization, while meeting stringent tail-latency SLOs, it is of paramount importance to be able to accurately predict the tail latency for a broad range of Fork-Join structures of practical interests. In this paper, we propose ForkTail, a black-box Fork-Join tail latency prediction model that covers a wide range of Fork-Join structures. In ForkTail, all Fork nodes are treated as black boxes, admitting both homogeneous and inhomogeneous cases, and different requests in the request flow are allowed to spawn different numbers of tasks forked to different numbers of Fork nodes. On the basis of the central limit theorem for queuing models under heavy load, we are able to arrive at a highly computational effective, empirical expression for the tail latency as a function of the means and variances of the task response times. Since this expression can be applied to request sub-flows at any granularities, it can be used for tail-latency prediction for services in a consolidated environment, where different services and applications may share the same datacenter cluster resources. Our extensive testing results based on model-based and trace-driven simulations, as well as a real-world case study in a cloud environment demonstrate that the expression can consistently predict the tail latency within 20% and 15% prediction errors at 80% and 90% load levels, respectively. Moreover, our sensitivity analysis demonstrates that such errors can be well compensated for with no more than 5% and 3% resource overprovisioning at these two load levels, respectively. This, together with its extremely low computational complexity, makes ForkTail a viable tool for both offline and online job scheduling and resource provisioning for user-facing datacenter applications.