Power Management ICs for Internet of Things, Energy Harvesting and Biomedical Devices

This dissertation focuses on the power management unit (PMU) and integrated circuits (ICs) for the internet of things (IoT), energy harvesting and biomedical devices. Three monolithic power harvesting methods are studied for different challenges of smart nodes of IoT networks. Firstly, we propose that an impedance tuning approach is implemented with a capacitor value modulation to eliminate the quiescent power consumption. Secondly, we develop a hill-climbing MPPT mechanism that reuses and processes the information of the hysteresis controller in the time-domain and is free of power hungry analog circuits. Furthermore, the typical power-performance tradeoff of the hysteresis controller is solved by a self-triggered one-shot mechanism. Thus, the output regulation achieves high-performance and yet low-power operations as low as 12 µW. Thirdly, we introduce a reconfigurable charge pump to provide the hybrid conversion ratios (CRs) as 1⅓× up to 8× for minimizing the charge redistribution loss. The reconfigurable feature also dynamically tunes to maximum power point tracking (MPPT) with the frequency modulation, resulting in a two-dimensional MPPT. Therefore, the voltage conversion efficiency (VCE) and the power conversion efficiency (PCE) are enhanced and flattened across a wide harvesting range as 0.45 to 3 V. In a conclusion, we successfully develop an energy harvesting method for the IoT smart nodes with lower cost, smaller size, higher conversion efficiency, and better applicability. For the biomedical devices, this dissertation presents a novel cost-effective automatic resonance tracking method with maximum power transfer (MPT) for piezoelectric transducers (PT). The proposed tracking method is based on a band-pass filter (BPF) oscillator, exploiting the PT’s intrinsic resonance point through a sensing bridge. It guarantees automatic resonance tracking and maximum electrical power converted into mechanical motion regardless of process variations and environmental interferences. Thus, the proposed BPF oscillator-based scheme was designed for an ultrasonic vessel sealing and dissecting (UVSD) system. The sealing and dissecting functions were verified experimentally in chicken tissue and glycerin. Furthermore, a combined sensing scheme circuit allows multiple surgical tissue debulking, vessel sealer and dissector (VSD) technologies to operate from the same sensing scheme board. Its advantage is that a single driver controller could be used for both systems simplifying the complexity and design cost. In a conclusion, we successfully develop an ultrasonic scalpel to replace the other electrosurgical counterparts and the conventional scalpels with lower cost and better functionality

A novel fast resonance frequency tracking method based on the admittance circle for ultrasonic transducers

For ultrasonic systems, the resonance frequency tracking (RFT) is the most critical step. The rapid development in advanced material processing and microelectronics package has increased the demand of high speed RFT. Therefore, this paper proposes a fast RFT (FRFT) method according to the characteristics of piezoelectric transducers' (PT) admittance circle. In the proposed method, the PT is driven at two different frequencies, and the PT's admittance is collected and calibrated. Then, the PT's mechanical resonance frequency is derived using the admittance information after calibration. The proposed method is not affected by the parallel capacitor and the matching circuit. Additionally, the optimal initial values of the involved parameters are determined in order to improve the accuracy of the proposed method. Furthermore, an improved method based on multiple tracking is also provided. Simulations and experiments demonstrate that using the proposed FRFT method, the ultrasonic system can track the resonance frequency in a short time with high accuracy

A high-tolerance matching method against load fluctuation for ultrasonic transducers

Fluctuation of acoustic load significantly weakens the performance of ultrasonic system. To address this problem in a simple way, we consider the main input and output variables related to the ultrasonic transducer's performance and propose a detailed mathematical model based on the simplest LC matching network containing only one capacitor and one inductor. In this model, a new resonance frequency f0 brought by matching components was found and defined. The optimum analysis method is used to solve the model, and a high-tolerance matching method against load fluctuation is obtained. Analysis indicates that when activated at the mechanical resonance frequency, the impedance and apparent power of the PT matched by the proposed method are constant no matter how the load changes, and thereby can significantly increase the stability and robustness of ultrasonic systems. For its simple structure and high performance, the proposed matching method can be widely applied in most ultrasonic systems. The tolerance of the proposed method against other environmental factors and high-order LC matching networks were also discussed. In addition, the feasibility and advantage of the proposed matching method are also verified by experiments

Improved performance of motor-drive systems by SAW shaft torque feedback

The paper describes the application of a non-contact, high bandwidth, low cost, SAW-based torque measuring system for improving the dynamic performance of industrial process motor-drive systems. Background to the SAW technology and its motor integration is discussed and a resonance ratio control (RRC) technique for the coordinated motion control of multi-inertia mechanical systems, based on the measurement of shaft torque via a SAW-based torque sensor is proposed. Furthermore, a new controller structure, RRC plus disturbance feedback is proposed, which enables the controller to be designed to independently satisfy tracking and regulation performance. A tuning method for the RRC structure is given based on the ITAE index, normalized as a function of the mechanical parameters enabling a direct performance comparison between a basic proportional and integral (PI) controller. The use of a reduced-order state observer is presented to provide a dynamic estimate of the load-side disturbance torque for a multi-inertia mechanical system, with an appraisal of the composite closed-loop dynamics. The control structures are experimentally validated and demonstrate significant improvement in dynamic tracking performance, whilst additionally rejecting periodic load side disturbances, a feature previously unrealisable except by other, high-gain control schemes that impose small stability margins

Development of techniques for detection and dissolution enhancement of mineral deposits in petroleum pipelines using ultrasound.

Scale formation in petroleum pipelines causes progressive flow reductions, leading to large production losses and operating costs. The composition and thickness of the scale deposits vary widely, but with present technology they cannot be accurately quantified or monitored. Remedial treatments such as chemical de-scaling etc. are therefore largely based on guesswork, which can lead to expensive chemical wastage and production shutdowns. This project is intended to address some of the above problems using ultrasonic techniques. Work presented in this thesis branches out into two main areas of interest, namely: (a) developments concerning location of deposits from both top-side and down-hole locations; and (b) developments relating to enhancement of scale removal, using ultrasound. With regard to top-side scale detection, the major challenge in this work was to develop a technique by which acoustic signatures are synthetically generated, which can be used with the techniques previously developed for pipeline inspection. This required the determination of a suitable type of transducer and the study of its radiation characteristics in developing comprehensive mathematical models for artificially generating reference echoes. The model allowed the first three multiple echoes (in steel objects) to be computed for given test parameters. Close agreement of the synthesised echoes with practical measurements was demonstrated with good repeatability. An essential requirement for the detection of deposits in down-hole is the accurate alignment of the test probes with respect to the pipe-wall. In this regard, a novel technique for remote alignment of the transducers was successfully formulated. It is based on identifying symmetrical properties of the signals received from the test probe itself when scanned around the correct angular position with respect to the target. However, through extensive practical measurements, it was found that an important requirement for applying this technique is to know in advance whether a particular combination of probe, target diameter and separation distance would give satisfactory angular resolution. Extensive practical examination of these factors showed that no general conclusion can easily be drawn with respect to this requirement. Therefore a mathematical model was successfully developed, which would predict the suitability of given probe/target parameters. It has been reported in previous studies that ultrasonic irradiation could greatly enhance the chemical dissolution of localised deposits during de-scaling operations. In this regard, a major challenge was to improve the efficiency of power transducers radiating into confined spaces at elevated temperatures. That required the study of radiation characteristics of ultrasonic power transducers and compensation techniques to regain loss of efficiency at elevated temperatures. Alternative types of transducers - based on flexural-horn designs - were also investigated and their relative merits presented. Significant findings related to the performance variations of ultrasonic transducers and transmission cables at elevated temperatures have been made. After examining the transducer efficiency drop with temperature, a closed-loop compensation strategy was proposed for maintaining optimal performance. The matching requirements of the cables transmitting power from top-side to down-hole power transducers were also investigated as part of optimisation of ultrasonic power output. From this study it was found that, within the temperature range of interest, the cable in itself does not require changes to the matching requirements as the environmental temperature fluctuates. However, it was noted that the transducer impedance changes rapidly with temperature and therefore a unified compensation strategy incorporating both cable and transducer impedances was proposed as a better solution. Overall, the main objectives of the project concerning pipeline scale detection were well achieved, namely: (a) modelling of a suitable type of ultrasonic transducer to synthesise the reference multiple echoes to aid top-side scale detection; and (b) development of a remote sensing technique for ultrasonic probe alignment in downhole pipes. With regard to dissolution enhancement, techniques for enhancing power output of ultrasonic transducers to aid dissolution enhancement of scale deposits have been determined. Further work includes the improvements to software algorithms developed and hardware integration to achieve the expected performance of the techniques presented

Fiber-optic three axis magnetometer prototype development

The goal of this research program was to develop a high sensitivity, fiber optic, interferometric, three-axis magnetometer for interplanetary spacecraft applications. Dynamics Technology, Inc. (DTI) has successfully integrated a low noise, high bandwidth interferometer with high sensitivity metallic glass transducers. Also, DTI has developed sophisticated signal processing electronics and complete data acquisition, filtering, and display software. The sensor was packaged in a compact, low power and weight unit which facilitates deployment. The magnetic field sensor had subgamma sensitivity and a dynamic range of 10(exp 5) gamma in a 10 Hz bandwidth. Furthermore, the vector instrument exhibited the lowest noise level when only one axis was in operation. A system noise level of 1 gamma rms was observed in a 1 Hz bandwidth. However, with the other two channels operating, the noise level increased by about one order of magnitude. Higher system noise was attributed to cross-channel interference among the dither fields

Closed-Loop Control of a Piezo-Fluidic Amplifier

Fluidic valves based on the Coand\u{a} effect are increasingly being considered for use in aerodynamic flow control applications. A limiting factor is their variation in switching time, which often precludes their use. The purpose of this paper is to demonstrate the closed-loop control of a recently developed, novel piezo-fluidic valve that reduces response time uncertainty at the expense of operating bandwidth. Use is made of the fact that a fluidic jet responds to a piezo tone by deflecting away from its steady state position. A control signal used to vary this deflection is amplitude modulated onto the piezo tone. Using only a pressure measurement from one of the device output channels, an output-based LQG regulator was designed to follow a desired reference deflection, achieving control of a 90 m/s jet. Finally, the controller's performance in terms of disturbance rejection and response time predictability is demonstrated.Comment: 31 pages, 23 figures. Published in AIAA Journal, 4th May 202

Research on the propagation efficiency of ultrasonic guided waves in the rail

Ultrasonic guided waves (UGW) technique has the advantages of low detection frequency, long detection distance, strong anti-electromagnetic interference ability, and large coverage. Hence it has potential advantages in real-time detection of breakages in the rail. Based on the research background of UGW-based broken rail detection, this paper focuses on the characteristics optimization of piezoelectric ultrasonic transducers (PUTs) to improve the propagation efficiency of UGW in the rail. Due to the influence of energy attenuation, multimodal, dispersion, and on-site noise when the UGW propagates in the rail, the amplitude of the received UGW signal is low and the signal-to-noise ratio is poor. Therefore, this thesis mainly systematically studies the characteristics optimization of PUTs from the aspects of impedance matching, driving circuit optimization, and excitation signal optimization. The main work is as follows: 1. To deeply study of the electromechanical characteristics of longitudinal vibration sandwich piezoelectric ultrasonic transducer (referred to as PUTs), the PSpice equivalent circuit models of a piezoelectric ultrasonic transducer and the PSpice equivalent circuit model of a pitch-catch setup are established based on one-dimensional wave and transmission line theory. The PSpice model of the PUT and the PSpice model of the pitch-catch setup are analyzed from the time and frequency domains, respectively, and the accuracy of the built PSpice models is verified through some experiments. It is shown that the PSpice model of a PUT established above is highly scalable and can be combined with amplifiers, driving circuits, diodes. 2. With the aim of solving the problem of impedance mismatch between the piezoelectric ultrasonic transducer and the driving circuit and the rail surface, the effect of the impedance matching on the electromechanical properties of the piezoelectric ultrasonic transducer was studied from the electrical and acoustic ends, respectively. From the electrical side, the effects of different electrical impedance matching networks on the electromechanical characteristics of PUTs are studied in both time and frequency domains. It is shown that in the two LC impedance matching networks, the matching network formed by the series inductance and parallel capacitance is better. From the acoustic side, an experimental method is used to study the effect of acoustic impedance matching on the transient characteristics of PUTs. It is concluded that when the epoxy resin is doped with 10% tungsten powder and the coating thickness is 8 mm, the acoustic impedance matching effect is better. 3. To overcome the problems of the existing driving circuits that the excitation voltage is not high enough, the extra high voltage DC voltage is required and the impedance matching is not considered, this thesis proposed a high voltage pulse driving circuit based on the full-bridge topology. The driving circuit takes into account the suppression of overshoot and oscillation when the power MOSFET is turned off, and at the same time conducts the impedance matching and tailing absorption of the excitation signal for PUTs. The suppression of overshoot and oscillation adopts the RC snubber circuit, and the tailing absorption is accomplished by a bleeder resistor and a bidirectional thyristor. The correctness and effectiveness of the proposed high-voltage pulse driving circuit are verified through experiments. It was also found that the combined use of electrical impedance matching and absorption circuits can effectively improve the energy conversion efficiency of PUTs. 4. To obtain the optimal performance of PUTs, the excitation signal of PUTs is optimized in terms of excitation signal frequency and excitation coding. First of all, to solve the problem of PUTs with having a resonance frequency shift after loading, this thesis proposes an optimal excitation frequency tracking method based on a digital band-pass tracking filtering. Then its correctness and stability are verified through some field experiments. Secondly, to improve the signal-to-noise ratio of the UGW signal, it is proposed to apply the Barker code excitation method to the broken rail detection, and use the pulse compression technique at the receiving end to realize the rapid recognition of the signal characteristics. Finally, for the case where the pulse-compressed signal produces undesirable peak sidelobes due to the effects of bandwidth, multipath, and noise, an adaptive peak detection algorithm based on the Hilbert transform combined with a digital bandpass tracking filter and a triangle filter. The accuracy and effectiveness of the above-mentioned Barker code excitation method and the adaptive peak detection algorithm are verified through experiments. The study in this thesis presents a feasible solution for improving the propagation efficiency of UGW in the rails and at the same time provides theoretical guidance for the large-scale application of the real-time broken rail detection system based on UGW

Acoustic power distribution techniques for wireless sensor networks

Recent advancements in wireless power transfer technologies can solve several residual problems concerning the maintenance of wireless sensor networks. Among these, air-based acoustic systems are still less exploited, with considerable potential for powering sensor nodes. This thesis aims to understand the significant parameters for acoustic power transfer in air, comprehend the losses, and quantify the limitations in terms of distance, alignment, frequency, and power transfer efficiency. This research outlines the basic concepts and equations overlooking sound wave propagation, system losses, and safety regulations to understand the prospects and limitations of acoustic power transfer. First, a theoretical model was established to define the diffraction and attenuation losses in the system. Different off-the-shelf transducers were experimentally investigated, showing that the FUS-40E transducer is most appropriate for this work. Subsequently, different load-matching techniques are analysed to identify the optimum method to deliver power. The analytical results were experimentally validated, and complex impedance matching increased the bandwidth from 1.5 to 4 and the power transfer efficiency from 0.02% to 0.43%. Subsequently, a detailed 3D profiling of the acoustic system in the far-field region was provided, analysing the receiver sensitivity to disturbances in separation distance, receiver orientation and alignment. The measured effects of misalignment between the transducers are provided as a design graph, correlating the output power as a function of separation distance, offset, loading methods and operating frequency. Finally, a two-stage wireless power network is designed, where energy packets are inductively delivered to a cluster of nodes by a recharge vehicle and later acoustically distributed to devices within the cluster. A novel dynamic recharge scheduling algorithm that combines weighted genetic clustering with nearest neighbour search is developed to jointly minimise vehicle travel distance and power transfer losses. The efficacy and performance of the algorithm are evaluated in simulation using experimentally derived traces that presented 90% throughput for large, dense networks.Open Acces