Marketing a human-powered electricity generating device for mobile technology

¶ … 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.

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).

Typical characteristics

Piezoelectric ceramics tend to be brittle and do not respond to lots of movements, making them less useful than other materials where a mechanical response is required (Stix & Lacob 1999, p. 199).

A varactor, or variable capacitor, which is initially charged, will separate its plates by vibrations; in this way, mechanical energy is transformed into electrical energy (Yildiz 2009).

This technique uses a magnetic field to convert mechanical energy to electrical energy (Amirtharajah & Chandrakasan 1998).

Operating principle

The production of electric charges on the faces of certain asymmetric crystals when they are subjected to mechanical stress (Michels 1956, p. 678). The piezoelectric effect occurs when pressure is applied to a polarized crystal, resulting in a mechanical deformation that produces an electric charge (i.e., a current). A piezoelectric accelerometer contains a mass mounted between two piezoelectric crystals. As the unit accelerates, the mass is pushed in the direction opposite the acceleration, producing a pressure on the crystal. The pressure on the crystal produces a voltage proportional to the amount of force applied, providing a measure of the amount of acceleration (Barfield & Caudell 2001, p. 87).

This method depends on the variable capacitance of vibration-dependent varactors (Meninger, Mur-Miranda, Amirtharajah, Chandrakasan, & Lang 2001).

A coil attached to the oscillating mass is made to pass through a magnetic field, which is established by a stationary magnet, to produce electric energy. The coil travels through a varying amount of magnetic flux, inducing a voltage according to Faraday's law (Yildiz 2009).

Areas of operation

Piezoelectric materials are now being integrated into a wide range of products, such as a smart pack in a pair of skis that converts vibrations into electricity to provide better control on fast downhill runs (Stix & Lacob 1999, p. 199).

Constant voltage or constant current achieves the conversion through two different mechanisms. For example, the voltage across a variable capacitor is kept steady as its capacitance alters after a primary charge. As a result, the plates split and the capacitance is reduced, until the charge is driven out of the device. The driven energy then can be stored in an energy pool or used to charge a battery, generating the needed voltage source. The most striking feature of this method is its IC-compatible nature, given that MEMS (Micro-electro-mechanical system) variable capacitors are fabricated through relatively well-known silicon micro-machining techniques (Yildiz 2009).

Techniques to increase the induced voltage include using a transformer, increasing the number of turns of the coil, or increasing the permanent magnetic field (Torres & Rincon-Mora 2005). Each of these parameters, though, is limited by the size constraints of the microchip as well as its material properties (Yildiz 2009).

Chapter 5: Summary, Conclusion and Recommendations

Summary

The research showed that while mobile handheld electric-powered devices continue to proliferate in a dazzling array of configurations with ever-increasing functionality, the technology that provides fuel for these devices has not kept pace. Currently available batteries are either relatively expensive one-time use versions that require frequent replacement or even more expensive rechargeable batteries that have limited lifespans and require lengthy recharging periods. While the search for improved battery technology solutions continues, the research also showed that a number of approaches to harvesting energy in other ways have been developed over the years, including mechanical energy and mechanical vibrations, electromagnetic, piezoelectric, pyroelectric, and electrostatic methods. Each of this energy-harvesting approaches has its respective strengths and weaknesses, but the research indicated that human-powered mechanical energy harvesting represents a potentially viable method of harvesting sufficient energy to power many of the electric-powered mobile handheld devices currently in use, and with some refinements and improvements in design, these devices, such as the solution presented herein, could be capable of generating even larger amounts of electricity.

Conclusion

Testing of the device indicated that the in-shoe mounted devices are capable of generating an approximate average of 59 mW of average power, and 1.6 watts of peak power. In its current configuration, the power output is promising but remains inadequate for the applications for which it is needed. Testing did confirm, though, that relatively large amounts of peak power could be produced, through the use of traditional rotary generators situated in the heel of a shoe. It may therefore be possible to extend the energy-collection period through the use of mechanical energy storage systems that could produce an additional watt of power with a spring, and 250 mW with flywheels. This could be accomplished through the use of components that will nest within the shoe sole.

Recommendations

Based on the improvements that are needed to bring this device to commercial viability, the specific components that will require further refinement include the gearbox, the generator motor selection, linear vibration system, and the rotary configuration. The most promising refinement would likely involve the incorporation of an additional energy storage device such as a flywheel or torsional spring. Each of these additions could provide additional energy production, but each has its own unique constraints that would have to be addressed to satisfy the dimensions of the in-shoe mounting and ensure they were sufficiently rugged to withstand normal wear-and-tear. Finally, it may be possible to integrate a piezoelectric ceramic into this configuration to help amplify the power generation capability, but further innovations in this technology will likely be required to overcome the existing brittleness of these materials before they will be viable for such applications.