Stability and instability of a random multiple access model with adaptive energy harvesting

We introduce a model for the classical synchronised multiple access system with a single transmission channel and a randomised transmission protocol (ALOHA). We assume in addition that there is an energy harvesting mechanism, and any message transmission requires a unit of energy. Units of energy arrive randomly and independently of anything else. We analyse stability and instability conditions for this model

Spatial Analysis: Development of Descriptive and Normative Methods with Applications to Economic-Ecological Modelling

This paper adapts Turing analysis and applies it to dynamic bioeconomic problems where the interaction of coupled economic and ecological dynamics over space endogenously creates (or destroys) spatial heterogeneity. It also extends Turing analysis to standard recursive optimal control frameworks in economic analysis and applies it to dynamic bioeconomic problems where the interaction of coupled economic and ecological dynamics under optimal control over space creates a challenge to analytical tractability. We show how an appropriate formulation of the problem reduces analysis to a tractable extension of linearization methods applied to the spatial analog of the well known costate/state dynamics. We illustrate the usefulness of our methods on bioeconomic applications, but the methods have more general economic applications where spatial considerations are important. We believe that the extension of Turing analysis and the theory associated with dispersion relationship to recursive infinite horizon optimal control settings is new.Spatial analysis, Economic-ecological modelling

Very-Large-Scale-Integration Circuit Techniques in Internet-of-Things Applications

Heading towards the era of Internet-of-things (IoT) means both opportunity and challenge for the circuit-design community. In a system where billions of devices are equipped with the ability to sense, compute, communicate with each other and perform tasks in a coordinated manner, security and power management are among the most critical challenges. Physically unclonable function (PUF) emerges as an important security primitive in hardware-security applications; it provides an object-specific physical identifier hidden within the intrinsic device variations, which is hard to expose and reproduce by adversaries. Yet, designing a compact PUF robust to noise, temperature and voltage remains a challenge. This thesis presents a novel PUF design approach based on a pair of ultra-compact analog circuits whose output is proportional to absolute temperature. The proposed approach is demonstrated through two works: (1) an ultra-compact and robust PUF based on voltage-compensated proportional-to-absolute-temperature voltage generators that occupies 8.3× less area than the previous work with the similar robustness and twice the robustness of the previously most compact PUF design and (2) a technique to transform a 6T-SRAM array into a robust analog PUF with minimal overhead. In this work, similar circuit topology is used to transform a preexisting on-chip SRAM into a PUF, which further reduces the area in (1) with no robustness penalty. In this thesis, we also explore techniques for power management circuit design. Energy harvesting is an essential functionality in an IoT sensor node, where battery replacement is cost-prohibitive or impractical. Yet, existing energy-harvesting power management units (EH PMU) suffer from efficiency loss in the two-step voltage conversion: harvester-to-battery and battery-to-load. We propose an EH PMU architecture with hybrid energy storage, where a capacitor is introduced in addition to the battery to serve as an intermediate energy buffer to minimize the battery involvement in the system energy flow. Test-case measurements show as much as a 2.2× improvement in the end-to-end energy efficiency. In contrast, with the drastically reduced power consumption of IoT nodes that operates in the sub-threshold regime, adaptive dynamic voltage scaling (DVS) for supply-voltage margin removal, fully on-chip integration and high power conversion efficiency (PCE) are required in PMU designs. We present a PMU–load co-design based on a fully integrated switched-capacitor DC-DC converter (SC-DC) and hybrid error/replica-based regulation for a fully digital PMU control. The PMU is integrated with a neural spike processor (NSP) that achieves a record-low power consumption of 0.61 µW for 96 channels. A tunable replica circuit is added to assist the error regulation and prevent loss of regulation. With automatic energy-robustness co-optimization, the PMU can set the SC-DC’s optimal conversion ratio and switching frequency. The PMU achieves a PCE of 77.7% (72.2%) at VIN = 0.6 V (1 V) and at the NSP’s margin-free operating point

Parametric Instabilities for Vibratory Energy Harvesting under Harmonic, Time-Varying Frequency, and Random Excitations

This effort investigates and evaluates the prospect of using parametric instabilities for vibratory energy harvesting. To that end, we consider a parametrically-excited piezoelectric cantilever beam and study its performance as an energy harvester under i) fixed-frequency harmonic excitations, ii) time-varying frequency excitations, and iii) band-limited Gaussian noise. In the case of fixed-frequency excitations, we use the Method of Multiple Scales to obtain approximate analytical expressions for the steady-state response amplitude and instantaneous output power in the vicinity of the first principle parametric resonance. We show that the electromechanical coupling and load resistance play an important role in determining the output power and characterizing the bandwidth of the harvester. Specifically, we demonstrate that the region of parametric instability wherein energy can be harvested shrinks as the coupling coefficient increases, and that there exists a coupling coefficient beyond which the peak power decreases. We also show that there is a critical excitation level below which no energy can be harvested. The magnitude of this critical excitation increases with the coupling coefficient and is maximized for a given electric load resistance. Theoretical findings were compared to experimental data showing good agreement and reflecting the general physical trends. In the case of time-varying frequency excitations, we consider two beams of different nonlinear behaviors: one exhibiting a softening response while the other exhibiting hardening characteristics. We show that, for both beams, the bandwidth of the harvester decreases with increasing frequency sweep rate and that the instantaneous peak power during a sweep cycle decreases and shifts in the direction of the sweep. Furthermore, experimental findings illustrate that the average output power of the iii harvester is significantly higher when the sweep is in the direction in which the steady-state principle parametric resonance curves of the beams bend. Also, as the frequency sweep rate increases, the average output power decreases until beyond a threshold sweep rate where no power can be harvested. Based on the preceding conclusions, we introduce the new concept of a Softening- Hardening Hysteretic Harvester (SHHH), which is designed to scavenge energy effi- ciently from an excitation source whose frequency varies with time around a center frequency. Introductory experimental investigation on the SHHH illustrated that this concept produces more power than either a softening or a hardening beam alone. Finally, in an effort to duplicate real-world scenarios under which energy harvesting occurs, both the hardening and the softening beam were subjected to parametric, band-limited, random Gaussian excitations and their performance in scavenging energy under different excitation bandwidths was evaluated. We observed that, under narrow bandwidth excitations (on the order of the harvester\u27s steady-state bandwidth) and regardless of the beam\u27s nonlinear characteristics, the parametric instability was activated for the length of the experiment. However, the average output power was very low (on the order of micro-Watts under excitations having a variance of 1.5 g). The power decreased even further as the bandwidth of the excitation was increased

Synchronising energy harvesting and data packets in a wireless sensor

We consider a wireless sensor node that gathers energy through harvesting and reaps data through sensing. The node has a wireless transmitter that sends out a data packet whenever there is at least one “energy packet” and one “data packet”, where an energy packet represents the amount of accumulated energy at the node that can allow the transmission of a data packet. We show that such a system is unstable when both the energy storage space and the data backlog buffer approach infinity, and we obtain the stable stationary solution when both buffers are finite. We then show that if a single energy packet is not sufficient to transmit a data packet, there are conditions under which the system is stable, and we provide the explicit expression for the joint probability distribution of the number of energy and data packets in the system. Since the two flows of energy and data can be viewed as flows that are instantaneously synchronised, this paper also provides a mathematical analysis of a fundamental problem in computer science related to the stability of the “join” synchronisation primitive

A critical analysis of research potential, challenges and future directives in industrial wireless sensor networks

In recent years, Industrial Wireless Sensor Networks (IWSNs) have emerged as an important research theme with applications spanning a wide range of industries including automation, monitoring, process control, feedback systems and automotive. Wide scope of IWSNs applications ranging from small production units, large oil and gas industries to nuclear fission control, enables a fast-paced research in this field. Though IWSNs offer advantages of low cost, flexibility, scalability, self-healing, easy deployment and reformation, yet they pose certain limitations on available potential and introduce challenges on multiple fronts due to their susceptibility to highly complex and uncertain industrial environments. In this paper a detailed discussion on design objectives, challenges and solutions, for IWSNs, are presented. A careful evaluation of industrial systems, deadlines and possible hazards in industrial atmosphere are discussed. The paper also presents a thorough review of the existing standards and industrial protocols and gives a critical evaluation of potential of these standards and protocols along with a detailed discussion on available hardware platforms, specific industrial energy harvesting techniques and their capabilities. The paper lists main service providers for IWSNs solutions and gives insight of future trends and research gaps in the field of IWSNs