Energy harvesting has grown from long-established concepts into devices for powering ubiquitously deployed sensor networks and mobile electronics. Systems can scavenge power from human activity or derive limited energy from ambient heat, light, radio, or vibrations. Ongoing power management developments enable battery-powered electronics to live longer. Such advances include dynamic optimization of voltage and clock rate, hybrid analog-digital designs, and clever wake-up procedures that keep the electronics mostly inactive. Exploiting renewable energy resources in the device's environment, however, offers a power source limited by the device's physical survival rather than an adjunct energy store. Energy harvesting's true legacy dates to the water wheel and windmill, and credible approaches that scavenge energy from waste heat or vibration have been around for many decades. Nonetheless, the field has encountered renewed interest as low-power electronics, wireless standards, and miniaturization conspire to populate the world with sensor networks and mobile devices. This article presents a whirlwind survey through energy harvesting, spanning historic and current developments.

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Energy scavenging for mobile and wireless electronics

Singular Integral Equations. By N.I. Muskhelishvili. Translated fromthe 2nd Russian edition by J.R.M. Radok. Pp. 447. F1. 28.50. 1953. (Noordhoff, Groningen)

It is well known that the trapezoidal rule converges geometrically when applied to analytic functions on periodic intervals or the real line. The mathematics and history of this phenomenon are reviewed, and it is shown that far from being a curiosity, it is linked with computational methods all across scientific computing, including algorithms related to inverse Laplace transforms, special functions, complex analysis, rational approximation, integral equations, and the computation of functions and eigenvalues of matrices and operators.

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The Exponentially Convergent Trapezoidal Rule

In recent years, thermoelectric (TE) devices have emerged as promising alternative environmental friendly applications for heat pumps and power generators since the environmental issues such as the global warming and the limitations of energy resources gradually drew worldwide attentions. Due to the green feature and distinct advantages, the thermoelectric technology have been applied to different areas in an effort of designing simple, compact and environmental friendly systems. The applied areas are extended from the earliest application on kerosene lamp to aerospace applications, transportation tools, industrial utilities, medical services, electronic devices and temperature detecting and measuring facilities. The application potentials of TE in directly conversing thermal energy into electrical power have been identified, especially for where the cost of thermal energy input need not to be considered, such as waste heat utilization, in the light of the present low efficiency of thermoelectric conversion. The capability of TE in producing thermal energy (in terms of cooling or heating) with the use of electrical power is also well identified. This paper reviews the status of the material development and thermoelectric applications in different areas and discusses the difficulties in terms of the commercialisations of advanced materials. Other than this, the main purpose of this paper is to present the great potential of achieving both environmental and economic benefits by exclusively utilizing thermoelectric applications in different areas. It also comes to the conclusion that the thermoelectric applications with the current conversion efficiency are economically and technically practical for micro/small applications. However, it would be transformed to a more significant green energy solution for improving the current environment and energy issues by using medium/large scale thermoelectric applications when the thermoelectric materials with a figure-of-merit over 2 come into commercial practice.

A review of thermoelectrics research – Recent developments and potentials for sustainable and renewable energy applications

Since the 1990’s, mobile computing has transformed its penetration from niche markets and early prototypes to ubiquity. Personal Digital Assistants (PDAs) evolved from GRiD’s PalmPad and Apple’s Newton in 1993 to the Palm, Handspring, and Microsoft-based models that support the multi-billion dollar industry today. While BellSouth/IBM’s Simon may have been the only mobile phone to offer e-mail connectivity in 1994, almost every modern mobile phone provides data services today. Portable digital music players have replaced cassette and CD-based systems, and these “MP3 players” are evolving into portable repositories for music videos, movies, photos, and personal information such as e-mail. Laptops, which were massive and inconvenient briefcase devices in the late 1980’s, now outsell desktops. Yet all these devices still have a common, difficult problem to overcome: power. This chapter will review trends in mobile computing over the past decade and describe how batteries affect design tradeoffs for mobile device manufacturers. This analysis leads to an interesting question: is there an alternative to batteries? Although the answer has many components that range from power management through energy storage [142], the bulk of this chapter will overview the history and state-of-the-art in harvesting power from the user to support body-worn mobile electronics.

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Human Generated Power for Mobile Electronics

Optimal design of small ΔT thermoelectric generation systems

A key technical challenge for high-altitude (near-space) concepts is autonomous station keeping, or the ability to remain fixed over a geo-location in the presence of winds. Although operational altitudes of 65,000 ft. altitude and above are above weather (i.e., storms, rain), winds still exist. And to station keep in the presence of these winds requires propulsive power. This paper focuses on the analysis of the station keeping performance of a notional solar-powered airship operating at an altitude around 65,000. The vehicle has a lifting-gas volume of 6.1 million ft 3 , is 450 ft in length, and is solar-electric powered with the entire upper surface covered by solar cells. Electric motors and propellers provide propulsion, additional on-board power is required for the payload and auxiliary equipment, and batteries are used for power storage. In this paper, the aerodynamic drag of the vehicle is estimated, the wind environment is characterized, and the solar-power available is determined for several geo-locations and time of year. This power available is then compared to the power required for station keeping in the presence of winds. It is shown that due to diurnal solar variations and season winds a large airship may be unable to meet station-keeping performance requirements in certain months of the year due to power limitations

Near-space station-keeping performance of a large high-altitude notional airship

Optimized Thermal Design of Small ΔT Thermoelectric Generators

A simple method to formulate an explicit expression for the roots of any analytic transcendental function is presented. The method is based on Cauchy's integral theorem and uses only basic concepts of complex integration. One convenient method for numerically evaluating the exact expression is presented. The application of both the formulation and evaluation of the exact expression is illustrated for several classical root finding problems.

James W. Stevens

Papers

Optimal design of small ΔT thermoelectric generation systems

Near-space station-keeping performance of a large high-altitude notional airship

Optimized Thermal Design of Small ΔT Thermoelectric Generators

Explicit Solutions for Transcendental Equations

Optimal placement depth for air–ground heat transfer systems