Exponential growth in computing, wireless communication, and energy storage efficiency is key to allowing smaller and scalable IoT solutions. These advancements have made it possible to power devices from energy harvesters (EH) and explore other energy storage solutions that can increase the lifetime and robustness of IoT devices. We summarize current trends and limits for the current paradigm as the basis of our forecast. The trend shows that conventional ceramic capacitors are sufficient for energy storage for today’s EH powered wireless IoT devices and that in the future, IoT devices can either perform more advanced tasks with their current volume or be shrunk in size.

Advancements in semiconductor technology have reached the point at which ambient energy in the surrounding environment can power sensors and microprocessors. This capability enables new strategies for energy management, which are necessary to continue the sensorization of our environment. With the vast amount of interconnected devices and the rate at which the number of such devices is increasing, there is a need to power resource-constrained devices through means other than disposable batteries. Harvesting ambient energy from the surroundings of the device is one solution to this challenge. 

It has been estimated that the global demand for bearings will reach 104.5 billion dollars in 2018 with an annual increase of 7.3%. Bearings are mechanical parts that are essential for rotating machinery and that have the potential to measure and monitor vital parts of a machine. A scenario in which bearings contain embedded electronics to monitor process and health parameters that can be analyzed on site and collected from remote locations is a crucial motivator for this thesis. 

The investigated technologies should be applicable in dirty and encapsulated industrial environments; therefore, vibrational and rotational kinetic energies are considered in this thesis. For each energy source, both the physics and the associated electronics are modeled and to some extent experimentally verified. Vibration harvesters are investigated and modeled in SPICE to verify performance gains using a novel circuit for nonlinear power extraction for piezoelectric materials. The simulations revealed that a weak coupling from the electrical system to the mechanical system would greatly benefit nonlinear extraction techniques. Such a weakly coupled system can be created in a bearing. Mechanical load and rotation generate cyclic strain in the bearing's raceway; the cyclic strain can be utilized by applying piezoelectric patches to the raceway to power embedded systems, and sensory information from the piezoelectric patch can also be used to monitor the bearing. Finally, trends and limits for the energy costs of computing, communication and data acquisition are investigated to determine suitable energy storage technologies to combine with the advancements in energy harvesting for machine elements such as rolling element bearings. 

The results indicate that high integration between the mechanical and electrical parts is desired, which, in combination with capacitive energy storage, appears to be the long-term direction for real-world implementations.

This paper proposes a passive Barkhausen noise sensor design suitable for low power applications. The sensor uses a permanent magnet and the relative motion between itself and a measured specimen instead of the conventional method that uses a fixed sensor and an alternating magnetic field. Since this novel design is passive, the sensor is well suited for low power applications and could potentially be used in e.g. A condition monitoring system integrated into a rolling element bearing. Proof of concept testing has been performed showing that the proposed sensor produces similar results as conventional Barkhausen noise sensors when applied to specimens being cyclically loaded until failure in a rotating bending rig. The results imply that material fatigue detection using the Barkhausen noise can be performed with the proposed sensor at a fraction of the energy cost compared to a conventional sensor. This warrants future research into the development of the proposed sensor, its advantages, disadvantages, and functionality

The circuit presented in this paper provides increased transfer efficiency for the electric charge generated by a piezoelectric element to the storage device, it also enables a simplified active control circuitry required for switched harvesting solutions as the control transistors are referenced to ground. This is achieved by inverting the voltage potential across the piezoelectric element and thereby maintaining a higher voltage while extracting energy. The increased potential allows vibration harvesters to operate over a broader frequency range. For weakly coupled piezoelectric harvesters, the increased potential allows the electrical power output to be increased. In this paper, the circuit is simulated in SPICE using existing models of discrete components in conjunction with a model of a piezoelectric vibration harvester. The power output and mechanical behavior of the harvester using the presented circuit are compared to two existing technologies: Synchronous Switch Harvesting on Inductor (SSHI) and a full-wave rectifying bridge. The comparison demonstrates that the novel Interleaved Switch Harvesting on Inductor (ISHI) circuit outperforms state-of-the-art active harvesting solutions, e.g., SSHI, as a result of the decreased energy losses from diodes. In addition, the ISHI circuit requires fewer components than does the SSHI circuit and solves the floating transistor source issue that arises in SSHI implementations. To achieve the maximum power conversion efficiency, impedance matching is required, which can be achieved by controlling the voltage of the storage device

The generation of electricity from vibrations has attracted considerable attention over the past decade. For this purpose, a piezoelectric-type harvester tuned to resonate at a specific frequency is typically used. This paper proposes a SPICE model capable of modeling piezoelectric energy harvesters. The model is parametrized enabling simple introduction of relevant physical parameters. Underlying theory based on Euler-Bernoulli beam theory is presented and modeling simplifications are justified. The SPICE model is verified by comparison to examples for which analytical and experimental solutions has been published. The SPICE model is valid close to the analyzed mode center frequency and delivers results within 1% compared to experimental and analytical data. Furthermore, we also show that the harvester can be electrically tuned to match the excitation frequency. This makes it possible to maximize the power output for both linear and non-linear loads. The here presented model enables efficient analysis of harvester design and changes of harvesting conditions

With the number of interconnected devices, many of which being wireless, exceeding the human population, there is a need to power resource-constrained devices through means other than disposable batteries. Harvesting ambient energy from the vicinity of the device is one solution.SKF, a producer of rolling element bearings, produces approximately one billion bearings per year. If parts of the produced bearings could be self-sucient devices powered through ambient energy, the smart integration of electronics in mechanical systems could be achieved. A scenario in which rolling element bearings are embedded with electronics is presented, through which the development of new services, data collection, data transfer and data interpretation can be realized. This scenario is the key motivation for thisthesis.This thesis presents some of the most common sources of energy used for harvesting energy in rotating environments and discusses how dierent transduction methods can convert ambient energy into electrical energy. Finding a general, robust and cost-eectivetechnology that can be applied to or in the vicinity of a rotating system is one of the main focuses of this thesis. The investigated technologies should be applicable to a dirty and encapsulated industrial environment; therefore, certain energy sources, e.g., sun light and radio frequencies, are not investigated. Advancements in vibrational energy harvesting are also presented in the form of a parameterized SPICE model of a piezoelectric vibrationharvester that can be simulated in conjunction with non-ideal and non-linear circuit models. The SPICE model is used to verify the performance of a novel energy harvesting circuit that actively extracts energy from a piezoelectric transducer. The harvesting circuit enables the enforcement of greater electrical damping on the mechanical system, thereby enabling more electrical energy to be extracted. For weak electromechanically coupled piezoelectric harvesters, the circuit can increase the power output by more than 300% compared to a full-wave rectifying bridge. The simulation results with the modeledharvester under the dened operating conditions in conjunction with the active harvesting circuit indicate that an average of more than 1 mW of power can be extracted, which is assumed to be sucient for powering a resource-constrained embedded device.

Using sensors to measure parameters of interest in rotating environments and communicating the measurements in real-time over wireless links, requires a reliable power source. In this paper, we have investigated the possibility to generate electric power locally by evaluating six different energy-harvesting technologies. The applicability of the technology is evaluated by several parameters that are important to the functionality in an industrial environment. All technologies are individually presented and evaluated, a concluding table is also summarizing the technologies strengths and weaknesses. To support the technology evaluation on a more theoretical level, simulations has been performed to strengthen our claims. Among the evaluated and simulated technologies, we found that the variable reluctancebased harvesting technology is the strongest candidate for further technology development for the considered use-case.

Lightweight Real-Time Operating Systems have gained widespread use in implementing embedded software on lightweight nodes. However, bare metal solutions are chosen, e.g., when the reactive (interrupt-driven) paradigm better matches the programmer’s intent, when the OS features are not needed, or when the OS overhead is deemed too large. Moreover, other approaches are used when real-time guarantees are required. Establishing real-time and resource guarantees typically requires expert knowledge in the field, as no turn-key solutions are available to the masses.In this paper we set out to bridge the gap between bare metal solutions and traditional Real-Time OS paradigms. Our goal is to meet the intuition of the programmer and at the same time provide a resource-efficient (w.r.t. CPU and memory) implementation with established properties, such as bounded memory usage and guaranteed response times. We outline a roadmap for Real-Time For the Masses (RTFM) and report on the first step: an intuitive, platform-independent programming API backed by an efficient Stack Resource Policy-based scheduler and a tool for kernel configuration and basic resource and timing analysis.

This paper presents how strain in rolling element bearings can be utilized to power embedded systems. Mechanical strain can be converted to the electrical domain by using piezoelectric materials; here, we present how piezoelectric patches should be dimensioned and mounted to optimize power output. Previous work has not addressed how repetitive strain in bearings can be used to harvest energy. Simulation data from the SKFtool BEAST are analyzed together with linear piezoelectricity to extract the power output. In the simulated case, results show that piezoelectric patches can be used to power embedded systems and that sensory data can be extracted to monitor the bearings.