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The proposed circuit intends for an electromagnetic generator to harvest kinetic energy. A synchronous split-capacitor boost converter operating in boundary conduction mode (BCM) is proposed to efficiently convert the AC input to a DC output. BCM operation is uniquely achieved through zero current detection (ZCD) control of an AC input enabling impedance matching. The ZCD control offers simplicity over previously reported methodologies. To reduce power consumption and increase efficiency, the proposed circuit topology combines the rectifier and power stage while dynamically controlling the power stage. The proposed circuit is designed and laid out in 0.13 μm BiCMOS technology. Post layout simulations verify the operation of the proposed circuit. 

As continuous health monitoring and treatment outside of the traditional clinical environment has become of interest to healthcare providers and governments, the manufacturers of miniaturized wireless biomedical devices have sought to facilitate this idea. Much research has been devoted to smart-and-connected health technologies of various form factors including injectables, implantables, ingestibles, and wearables. Such devices are constrained in physical size, power-consumption budget, storage capacity, and computing power. Yet, they handle sensitive, private information and require trust as they directly affect the health of the patient by means of stimulation and/or drug delivery. In this work, we discuss the role of security as a fundamental component of these devices. We propose a generic layered model to support lightweight and cost-effective implementation of data security and protection mechanisms against possible attacks. 

The proposed circuit aims to harvest energy from body heat, in which the thermal gradient is only a few degrees. The boost converter operating in a burst mode offers a high conversion ratio while minimizing power loss. Maximum power point tracking based on the fractional open circuit voltage method ensures that the proposed circuit can be applied for a variety of thermoelectric generators (TEGs) and TEG setups. The proposed circuit is designed and laid out in CMOS 0.25 μm technology. Post layout simulation results indicate the converter is able to boost input voltages as low as 50 mV to the regulated output of 3 V, while achieving peak efficiency of 81%. 

Intermittent computing applications in the IoT space, such as long-term monitoring of the structural integrity of infrastructures, rely on battery-less computing systems powered through scavenged energy. For such systems, power-loss is a fact of life, and there is a need for a secure power transition mechanism to convert the active system state into a protected nonvolatile form and back. We evaluate the architectural needs to secure these power transitions and to adapt computations based on the scavenged energy. Our objective is to enforce confidentiality, integrity, freshness, and authenticity over the system state across power loss. We observe that secure power transitions are delicate and complex. We need secure checkpoints which are expensive to compute, and which may require hardware-accelerated cryptography and isolated secure non-volatile storage. Next, we observe that in intermittent systems, the energy subsystem does not adapt to the needs of the application. Rather, the application must adjust its computing pattern to the available energy. We define an energy-harvester subsystem interface to optimize the run-time activity of the intermittent system. The interface drives the optimized execution of a secure communication protocol (covering key-exchange and bulk encryption), such that wasted energy is eliminated and that run-time performance is improved. We report results from several prototyping experiments. 

Recent advancements in energy-harvesting techniques provide an alternative to batteries for resource constrained IoT devices and lead to a new computing paradigm, the intermittent computing model. In this model, a software module continues its execution from where it left off when an energy shortage occurred. Enforcing security of an intermittent software module is challenging because its power-off state has to be protected from a malicious adversary in addition to its power-on state, while the security mechanisms put in place must have a low overhead on the performance, resource consumption, and cost of a device. In this paper, we propose SIA (Secure Intermittent Architecture), a security architecture for resource-constrained IoT devices. SIA leverages low-cost security features available in commercial off-the-shelf microcontrollers to protect both the power-on and power-off state of an intermittent software module. Therefore, SIA enables a host of secure intermittent computing applications such as self-attestation, remote attestation, and secure communication. Moreover, our architecture provides confidentiality and integrity guarantees to an intermittent computing module at no cost compared to previous approaches in the literature that impose significant overheads. The salient characteristic of SIA is that it does not require any hardware modifications, and hence, it can be directly applied to existing IoT devices. We implemented and evaluated SIA on a resource-constrained IoT device based on an MSP430 processor. Besides being secure, SIA is simple and efficient. We confirm the feasibility of SIA for resource-constrained IoT devices with experimental results of several intermittent computing applications. Our prototype implementation outperforms by two to three orders of magnitude the secure intermittent computing solution of Suslowicz et al. presented at IGSC 2018.