Human powered electronics and energy generation

¶ … Marketing a Human-Powered Electricity Generating Device

Given the pending power doom, there aren't nearly as many mad scientists out there figuring out alternatives to the battery as one would wish. -- Steve Morgensterndan Clinton and Suzanne Kantrakirschner, 2004

The proliferation of electronic-powered mobile devices such as cell phones, personal digital assistants, and iPods continues to increase and current signs all indicate that these trends will continue well into the future. Indeed, children, adolescents and adults are all embracing mobile technology in major ways. For example, Shuler recently observed that, "Mobile devices are part of the fabric of children's lives today; they are here to stay. Sesame [Street] introduced children to the educational potential of television. A new generation of mobile media content can become a force for learning and discovery in the next decade" (2009, p. 12). Likewise, according to Murphy, "A growing number of researchers are engaging mobile devices as search tools. Smartphones, cell phones, and other mobile technologies are now commonly among the first places people turn when seeking information" (2010, p. 14). The introduction of e-book readers such as Kindle and Nook have added to the proliferation of battery-powered handheld devices in recent years as well (Ardito 2009).

The explosive growth in the use of mobile electric-powered devices is attributable in large part to the fact that these devices have continually incorporated new advanced features that provide improved communication and entertainment capabilities. For instance, Ruiz-Martinez, Sanchez-Martinez, Martinez-Montesinos and Gomez-Skarmeta (2007) note that among these innovations include the ability to download information, send e-mail and instant messaging, use video telephony, and so forth. These authors add that in recent years, the "computation and storage capabilities offered by these handsets have been improved considerably in order to provide these advanced features" (Ruiz-Martinez et al. 2007, p. 94).

Moreover, Ruiz-Martinez and his associates suggest that the proliferation of mobile devices represents an enormous market already, and devices that can contribute to their usefulness are in high demand. In this regard, Ruiz-Martinez et al. emphasize that, "As a consequence of its growth and to these advanced features, today the development of new services for these mobile devices constitutes one of the most important business markets because any service developed could, potentially, be offered to any person in the world" (2007, p. 94). Clearly, identifying new devices for a potential market of several billion or so consumers is a worthwhile enterprise. In this regard, one of the common features of all such mobile devices is the need for battery power, and while technical innovations have also improved the life of batteries in recent years (Ukens 2001), this ongoing requirement for power represents a fundamental fly in the mobile device ointment, an issues that also represents the focus of this study which is discussed further below.

Statement of the Problem

Today, developing the power requirement for wireless and portable devices has assumed new relevance and importance. In recent years, innovations in energy storage capabilities have improved in substantive ways; these innovations, though, have failed to keep pace with the concomitant developments in memory storage, microprocessors, and wireless technology applications (Yildiz 2009). Consequently, the search for alternative energy sources that can substitute for conventional batteries has received a growing amount of attention. According to Yildiz, "Power scavenging may enable wireless and portable electronic devices to be completely self-sustaining, so that battery maintenance can be eventually removed. Researchers have performed many studies in alternative energy sources that could provide small amounts of electricity to electronic devices" (2009, p. 2007).

One such approach has included human-powered energy harvesting drawing on the natural movements of the human foot using shoe inserts to generate power for a wireless transceiver that was also mounted on the shoe sole (Yildiz 2009). Research has continued to address other applications of these shoe-mounted electric generators to identify methods of transmitting power from the shoe insert generator to where the power is needed such as a handheld electric-powered mobile device. The advantages of achieving breakthroughs in this area are clear because such devices would be able to passively harvest the natural movements of the owners of these devices to supplement or perhaps even replace the ubiquitous batteries that are currently needed to keep them working. These types of energy-harvesting devices are deemed passive in that no discernible additional effort is required to generate power; by contrast, there are also active human-powered energy harvesting devices that do require a purposeful action on the part of humans that are not part of their natural movements such as self-powered products developed by FreePlay that are fueled by a constant-force spring that must be wound up in order to operate the device (FreePlay Energy 2007). The utility of these human-powered energy-harvesting devices, though, remains largely conjectural with respect to providing sufficient wattage to power typical hand-held battery-powered devices, a problem that directly relates to the purposes of this study which is discussed further below.

Purpose of Study

The purpose of this study was to develop possible improvements on a power-generating system. The device/system includes a rotary arm that extends down from the sole of a shoe which ultimately drives a pair of small electrical generator through a steeped up gearbox. The research will be focused on the possible improvement of a magnetic device due to its potential robustness, simplicity and efficiency. Research was also carried out on piezoelectric energy, electrostatic energy and electromagnetic energy as a method of energy harvesting, their respective characteristic, operating principle and areas of operating. Research was also conducted concerning how the solution (see Figures 1 through 4 below) can be improve and what needs to be improved to increase its efficiency and output.

Figures 1 through 4: Prototype of the Human-Power Energy-Harvesting Device

The project involved identifying opportunities for improving a magnetic device and where possible effect improvements to its performance. The system includes a rotary arm extending down from the sole which ultimately drove a pair of small electrical generator through a stepped up gearbox. A one way clutch mechanism was used to transmit to the gearbox. This allow for additional spin following the initial impact of a step, also preventing lockup due to rotary inertia impact in the gear. The entire generator system is to fit in the sole of a standard running shoe with the rotary arm compressing once during each heel strike.

This entailed a permanent magnet coil setup whether it will be through rotary or linear means. Various concepts that were explored also include adding mechanical energy storage such as spring and flywheels. In addition, the method of extended energy storage, such as flywheels or springs, would be taken into consideration for use with generation source. While it was desired that this device produce close to a watt power, its integration into a standard shoe required special care. The priority was to constrain the power generating to module to fit seamlessly into the sole of a shoe, and then optimize the design to produce the greatest amount of output power. In addition to this purpose, the study also investigated research work carried out on other forms of established energy harvesting from vibration-based sources with focus on piezoelectric devices and electromagnetic generators of similar characteristics. In particular, the characteristics that were examined for these energy harvesting techniques included durability, power output, viability and commercial practicality as alternative power sources for powering devices with low power requirements.

Importance of Study

According to Heath, Herman, Lugo and Reeves (2005), one of the basic limitations of all mobile devices is their inherent reliance on battery power which can fail unexpectedly. Furthermore, particularly power-hungry mobile devices such as laptop computers require significant amounts of battery power to remain operable. In this regard, Gulati, Sawhney and Paoni report that even small mobile devices such as PDAs and wireless handsets have significant power constraints. "Without a grounded power connection," Gulati and his colleagues note, "these devices rely on a limited supply of battery power" (2003, p. 136). It may be possible, though, to address this need by developing an alternative, efficient energy-harvesting device that harvests the natural movements of humans as they go about their day-to-day activities.

Scope of Study

The scope of the study extends to the improvements that are needed to make the device commercially viable, including identifying the following:

1. What the problem is

2. What needs to be improve

3. Why it should be improve

4. How it can be improve

5. Dimension of spring

6. Force

7. Measurements and calculations

8. Electric losses

9. Spring loss

10. Friction

Rationale of Study

At present, it is possible to harvest power from a variety of energy sources, including mechanical vibrations, light, acoustic, electromagnetic sources, air flow, heat, and temperature variations (Yildiz 2009). Generally speaking, energy harvesting is defined as the conversion of ambient energy into some level of usable electrical energy (Yildiz 2009). Compared to conventional energy storage methods such as batteries, these alternative energy-harvesting sources represent an abundant source of energy (Yildiz 2009). To achieve the level of efficiency needed to generate sufficient amounts of power that are required by most of today's handheld electric-powered devices, though, will require further refinements of the solution's prototype.

Overview of Study

This study used a five-chapter format to achieve the above-stated research purpose. Chapter one of the study was used to introduce the topics under consideration, provide a statement of the problem, the purpose and importance of the study, as well as its scope and rationale. Chapter two provides a critical review of the relevant and peer-reviewed literature, and chapter three more fully describes the study's methodology, including a description of the study approach, the data-gathering method and the database of study consulted. Chapter four is comprised of an analysis of the data developed during the research process and chapter five presents the study's conclusions, a summary of the research and recommendations for improvements to the device prototyped and envisioned herein.

Chapter 2: Review of Related Literature

It is reasonable to suggest that all battery-powered handheld device users have experienced battery failure at a critical juncture, whether it is making an important or even emergency call on a cell phone, uploading an assignment to school, or downloading critically important corporate data on a personal digital assistance, tablet computer or similar devices. In this regard, Clinton and Kantrakirschner ask, "Why is it that more and more we find ourselves pushing the 'on' button and watching the sad spectacle of nothing going on?" (2004, p. 58). The reason for this failure, of course, is the limited amount of power that conventional batteries are capable of providing, with some of the more power-hungry devices such as multifunction cell phones, laptop and notebook computers that require battery replacements after just an hour's use (Clinton & Kantrakirschner 2004). As an example of such energy-intensive devices, Clinton and Kantrakirschner cite the Nokia 7700 which provides the following features:

1. A 65,546-color touch screen with 640x320-pixel resolution,

2. A Web browser;

3. Audio and video playback;

4. FM radio;

5. Built-in camera;

6. Voice recording;

7. Bluetooth connectivity;

8. Personal-information-management software, word processing, spreadsheet and presentation viewers.

This veritable "Swiss army knife" of mobile devices was engineered to provide between just 3 and 4 hours of telephone use only, and this performance is severely diminished if any of the other features are used (Clinton & Kantrakirschner 2004). According to a senior analyst for the technology consulting firm IDC, "Everybody wants more in the way of functionality, everybody wants more in the way of capabilities. They wish their iPod had a color screen. Vendors are trying to pack in more processing power; better, brighter, deeper displays; better audio capability; 3-D accelerators for graphics; more storage. And the reality is, battery life is extremely limited" (quoted in Clinton & Kantrakirschner 2004, at p. 60). Not surprisingly, researchers have been actively involved in seeking improvements in conventional battery design and performance, as well as reducing the energy requirements for existing devices. To date, at least some progress has been made as can be seen from the power requirements needed for three-megapixel digital camera model shown in Figure 5 below.

Figure 5. Average Power Requirements for 3MP Digicams: 2002-2004

Source: Based on tabular data in Clinton & Kantrakirschner 2004, p. 60

Other improvements in performance have also been developed in screen displays and hard drives for mobile computers, but the fact remains that while this research continues, the marketplace is being flooded with other multi-feature devices that remain energy-intensive and require frequent battery replacements. For instance, a recent report from Denison (2011) emphasizes that, "As the technology built into battery powered devices like laptops and cell phones advances, so does their demand for power. it's great that your cell phone can now act as a fully functional GPS device and HD video player, but it starts looking a lot less attractive when its battery life is knocked out in a matter of minutes" (p. 2).

While these multi-feature devices continue to be improved in their performance, the constant addition of yet more functionalities has created a Catch-22 cycle wherein researchers have been more efficient in incorporating additional features in hand-held mobile devices than they have in the battery technology that is required to power them (Yildiz 2009). According to this authority, "The critical long-term solution should therefore be independent of the limited energy available during the functioning or operating of such devices" (Yildiz 2009, p. 4). There are some potentially long-term solutions available, though, and Table 1 below compares the estimated power and challenges of various ambient energy sources in a recent study by Yildiz, Zhu, Pecen, and Guo (2007).

Table 1

Comparison of Power Density of Energy Harvesting Methods

Energy Source

Power Density & Performance

Source of Information

Acoustic Noise

0.003 ?W/

0.96 ?W/

(Rabaey, Ammer, Da Silva Jr.,

Patel, & Roundy, 2000)

Temperature Variation

10 ?W/cm3

(Roundy, Steingart, Frechette,

Wright, Rabaey, 2004)

Ambient Radio Frequency

1 ?W/cm2

(Yeatman, 2004)

Ambient Light

100 mW/cm2 (direct sun)

100 _W/cm2 (illuminated office)

(Yildiz 2009)

Thermoelectric

60 _W/cm2

(Stevens, 1999)

Vibration

(micro generator)

4 _W/cm3 (human motion -- Hz)

800 _W/cm3 (machines -- kHz)

(Mitcheson, Green, Yeatman, & Holmes, 2004)

Vibrations (Piezoelectric)

200 ?W/cm3

(Roundy, Wright, & Pister, 2002)

Airflow

1 ?W/cm2

(Holmes, 2004)

Push buttons

50 _J/N

(Paradiso & Feldmeier, 2001)

Shoe Inserts

330 ?W/cm2

(Shenck & Paradiso, 2001)

Hand generators

30 W/kg

(Starner & Paradiso, 2004)

Heel strike

7 W/cm2

(Yaglioglu, 2002)

(Shenck & Paradiso, 2001)

The stated values in Table 1 above were based on data presented in archived studies, textbooks, as well as empirical research conducted by Yildez et al. (2007). While this comparison is exhaustive, the comparisons do confirm that a wide array of potential alternatives to conventional batteries is available (Yildez et al. 2009).

Although a wide range of energy harvesting techniques are available, most are inadequate for the power-hungry mobile devices that are currently on the market, and all signs indicate that these devices will continue to incorporate yet further features in the future, making an alternative energy source all the more important. At present, there is no single energy-harvesting method available that is capable of generating sufficient power for every application, and the choice of method must be based on the type of application that is intended. Some of the currently available energy-harvesting methods include those summarized in Table 2 below:

Table 2

Currently available energy-harvesting sources

Source

Description

Human Body:

Mechanical and thermal (heat variations) energy can be generated from a human or animal body by actions such as walking and running.

Natural Energy:

Wind, water flow, ocean waves, and solar energy can provide limitless energy availability from the environment.

Mechanical Energy:

Vibrations from machines, mechanical stress, strain from high-pressure motors, manufacturing machines, and waste rotations can be captured and used as ambient mechanical energy sources.

Thermal Energy:

Waste heat energy variations from furnaces, heaters, and friction sources.

Light Energy:

This source can be divided into two categories of energy: indoor room light and outdoor sunlight energy. Light energy can be captured via photo sensors, photo diodes, and solar photovoltaic (PV) panels.

Electromagnetic Energy:

Inductors, coils, and transformers can be considered as ambient energy sources, depending on how much energy is needed for the application.

Source: Yildiz 2009

Figure 6 below shows a block diagram of general ambient energy-harvesting systems developed by Yildiz (2009). The first row of Figure 6 indicates the energy-harvesting sources; the second row of Figure 6 indicates actual implementation and tools that are employed to harvest the energy from the source; and the third row of Figure 6 indicates the energy-harvesting techniques used with each source.

Figure 6. Ambient Energy Systems

Source: Yildiz 2009

Taken together, it is clear that a significant problem has been created by the introduction of a wide range of energy-hungry mobile wireless devices in recent years, and the research was consistent in showing that these trends are expected to continue well into the foreseeable future. At the same time, despite ongoing intensive research, conventional battery technology remains relatively stagnated, suggesting that things are going to get worse before they get better unless and until a viable alternative power source can be developed to help power these mobile devices. To help address this need, the solution proposed herein may help fill the energy gap that will continue to widen and the methodology by which this project was developed is discussed further below.

Chapter 3: Methodology

Description of the Study Approach

This study used a literature review as its study approach. According to Fraenkel and Wallen, "researchers usually dig into the literature to find out what has already been written about the topic they are interested in investigating. Both the opinions of experts in the field and other research studies are of interest. Such reading is referred to as a review of the literature" (2001, p. 48). This approach is consistent with the guidance provided by numerous researchers who emphasize the need to review what is known about a given topic before developing conclusions and formulating opinions (Neuman 2003). For example, according to Gratton and Jones (2003), a review of the relevant literature is an essential task in all types of research. "No matter how original you think the research question may be," Gratton and Jones emphasize, "it is almost certain that your work will be building on the work of others. It is here that the review of such existing work is important. A literature review is the background to the research, where it is important to demonstrate a clear understanding of the relevant theories and concepts, the results of past research into the area, the types of methodologies and research designs employed in such research, and areas where the literature is deficient" (p. 51). In addition, a properly conducted literature review can also serve to identify any gaps in the existing body of knowledge. In this regard, Wood and Ellis (2003) identified the following as important outcomes of a well conducted literature review:

1. It helps describe a topic of interest and refine either research questions or directions in which to look;

2. It presents a clear description and evaluation of the theories and concepts that have informed research into the topic of interest;

3. It clarifies the relationship to previous research and highlights where new research may contribute by identifying research possibilities which have been overlooked so far in the literature;

4. It provides insights into the topic of interest that are both methodological and substantive;

5. It demonstrates powers of critical analysis by, for instance, exposing taken for granted assumptions underpinning previous research and identifying the possibilities of replacing them with alternative assumptions;

6. It justifies any new research through a coherent critique of what has gone before and demonstrates why new research is both timely and important.

Similarly, Silverman (2005, p. 300) suggests that a well-conducted literature review should seek to answer the following questions:

1. What do we know about the topic?

2. What do we have to say critically about what is already known?

3. Has anyone else ever done anything exactly the same?

4. Has anyone else done anything that is related?

5. Where does your work fit in with what has gone before?

6. Why is your research worth doing in the light of what has already been done?

Data-gathering Method and Database of Study

The data-gathering method proceeded in a step-wise fashion, beginning with a general examination of the relevant literature concerning the proliferation of battery-powered hand-held devices, the limitations and constraints involved with current battery technology, and extending to various energy-harvesting techniques. The database of study consulted included public and university libraries, as well as reliable online research resources such as EBSCO, Questia and Google Scholar.

Chapter 4: Data Analysis

In a study conducted to test the feasibility and reliability of the different ambient vibration energy sources by Marzencki (2005), three different vibration energy sources (electrostatic, electromagnetic, and piezoelectric) were investigated and compared according to their complexity, energy density, size, and encountered problems. The study is summarized in Table 3 below.

Table 3

Comparison of Vibration Energy-Harvesting Techniques

Electrostatic

Electromagnetic

Piezoelectric

Complexity of process flow

Low

Very High

High

Low

Very high

High

Energy density

4 mJ cm-3

24.8 mJ cm-3

35.4 mJ cm-3

4 mJ cm-3

24.8 mJ cm-3

35.4 mJ cm-3

Current size

Integrated

Macro

Macro

Problems

Very high voltage and need of adding charge source

Very low output voltages

Low output voltages

A comparison of piezoelectric, electrostatic and electromagnetic energy with respect to their respective viability for energy harvesting, their typical characteristics, operating principles and areas of operations is provided in Table 4 below.

Table 4

Comparison of Piezoelectric, Electrostatic and Electromagnetic Energy Sources

Piezoelectric Energy

Electrostatic Energy

Electromagnetic Energy

Viability for energy harvesting

Piezoelectric ceramics can transform a mechanical stimulus into an electric charge (Stix & Lacob 1999, p. 199).

Electrostatic produces higher and more practical output voltage levels than the electromagnetic method, with moderate power density (Yildiz 2009).

The induced voltage is inherently small and therefore must be increased to become a viable source of energy (Kulah & Najafi 2004).