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class="style6">HELPLINE: </span>(610) 362-1320<br> <span class="style6">WEBSITE: </span><a href="http://www.empf.org">www.empf.org</a><br> <a href="http://www.aciusa.org">www.aciusa.org</a></div></td> </tr> </table> <p>&nbsp;</p> <p><br> <br> </p> <div align="center"> <p align="center" class="style7">Michael D. Frederickson<br> <strong><em>EMPF Director </em></strong><br> <br> Barry Thaler, PhD.<br> bthaler@aciusa.org <br> <strong><em>Empfasis Technical Editor<br> </em></strong><br> Paul Bratt<br> pbratt@aciusa.org <br> <strong><em>Empfasis Editor</em></strong><br> </p> <p align="center" class="style7"><img src="http://www.empf.org/empfasis/archive/images/iab_sm.gif" alt="IAB" width="100" height="52"><br> <span class="style9">Industrial Advisory Board</span><br> <span class="style14"><em>Gerald R. Aschoff</em>, The Boeing Company<br> <em>Dennis M. Kox</em>, Raytheon<br> <em>Gregory X. Krieger</em>, BAE Systems<br> <em>Edward A. Morris</em>, Lockheed Martin<br> <em>Jane Krueger </em>, Rockwell Collins<br> <em>Gary Kirchner</em>, Honeywell<br> <em>Andrew Paradise</em>, Northrop Grumman<br> <em>Richard Kidwell </em>, ITT Industries</span></p> </div> <p align="center" class="style7"><br> </p> </div> </td> </tr> </table> </div></td> <!-- InstanceBeginEditable name="Body1" --><td width="70%" rowspan="2" valign="top"><div class="body_style" id="body_content"> <p align=center><img src="images/energy.gif" alt="title"></p> <p class="body_text"><span class="style20">W</span>ireless sensor networks can be used by the warfighter to enhance wide area surveillance and situation understanding. Through coordinated monitoring of environmental conditions such as temperature, pressure, sound, or vibration, sensors can provide significant battlefield information. Wireless sensors can also be used for condition-based maintenance (CBM) on Navy ships. The EMPF has recently evaluated several advanced CBM sensor technologies installed in DDG 1000 switchgear at the Land Based Test Site (LBTS) located at the Naval Surface Warfare Center (NSWC) - Philadelphia. By combining these sensor outputs with wireless transmitters powered by harvested energy, the shipwide Integrated Condition Assessment System (ICAS) can be updated using an open architecture standard. Inline with the Navy ManTech s affordability initiatives, locations that are hazardous, restricted, or previously inaccessible can be now be monitored with reduced manpower and without the installation costs of wiring.</p> <p>The ability to deploy a large quantity of sensors over a wide area battlefield or throughout a naval ship requires a major reduction in sensor size, weight, and power (SWaP). Sensors both depend on batteries for power and are limited by their battery life. Manufacturers have also learned to design sensors that can harvest energy from their surroundings. A vibration harvesting sensor near a motor, a thermal harvester on the side of an electronics rack, or nanofibers woven into the knees and elbows of the warfighter s clothing can all generate sufficient power to operate a sensor. In addition, the sensor integrated circuits are becoming smaller, more sensitive, and require less power for their own use.</p> <p>Energy harvesting is a process where unused thermal or mechanical energy is captured and converted into electrical energy. Some of the technologies available for this conversion are thermoelectric, piezoelectric, capacitive, radio frequency (RF), solar, and inductive coupling. A comparison of the power produced using different energy harvesting techniques is presented in Table 1-1.</p> <p align="center"><img src="images/table1-1.gif"></p> <p><b>Thermoelectric Effect</b></p> <p>Thermal gradients are one of the oldest techniques for generating electricity. A simple thermocouple is a junction of two dissimilar wires with a temperature difference between the junction and the wire ends. The core of a thermoelectric generator (TEG) consists of an n-type and p-type semiconductor connected by a metal plate2. By connecting many PN junctions in series electrically and in parallel thermally, a large voltage output can be produced that is proportional to the heat flow (Figure 1-1). </p> <p align="center"><img src="images/fig1-1.gif"></p> <p>A thermoelectric generator converts heat flow (Q) into electrical power (P) with efficiency (hð) (eq. 1). Since the heat flow is proportional to the temperature difference (eq. 2), power output is proportional to the DðT maintained across the TEG. </p> <p align="center"><img src="images/table1-2.gif"></p> <p>The TEG can be directly connected to the wireless sensor if the heat source is stable or coupled to a small battery as a trickle charger. With commercially available sizes less than 2 mm (Figure 1-2), they can provide clean energy for long operating lifetimes using no moving parts and no consumable materials. TEGs can be placed on equipment, structures, or even the human body and can generate sufficient energy as long as a temperature gradient exists. A heat flow path must be maintained to provide thermoelectric power. Simple placement within a heated zone may initially generate power but will quickly stop when both sides reach the same temperature and heat flow stops.</p> <p align="center"><img src="images/fig1-2.gif"></p> <p><b>Piezoelectric Effect</b></p> <p>Some materials can generate electricity when strained. This reversible effect is typically observed in crystals and certain ceramics and is caused by the existence of dipole moments. These dipoles can be asymmetric ions on a crystal lattice or molecular groups in a polymer. During mechanical stress, the dipole moving closer or further apart generates a high voltage (e.g., 500 lbf on 1 cm3 of quartz can generate >10,000 volts). By loading the piezoelectric material in the longitudinal, transverse, or shear directions, a sensor can be made that detects vibrations, sound, or strain and then powers another sensor or transmitter (Figure 1-3). This type of device is small, highly reliable over a wide temperature range, inexpensive, and requires no maintenance or battery replacement. </p> <p align="center"><img src="images/fig1-3.gif"></p> <p><b>Capacitive (Electrostatic) Energy Harvesting</b></p> <p>Capacitive or electrostatic or harvesting is based on separating the plates of a charged variable capacitor (varactor) using vibrations and converting mechanical into electrical energy. </p> <p><b>RF Energy Harvesting</b></p> <p>Low level environmental RF energy can be harvested by using a broadband receiving antenna and diode rectifier coupled to a high efficiency power processor. At intervals when sufficient energy is available, the device can power a wireless sensor with a demonstrated efficiency of 20%.<sup>4</sup></p> <p><b>Solar Energy</b></p> <p>The photoelectric effect is a property of some materials to release electrons when exposed to light. These free electrons can be captured and used as a source of power for many applications. By coupling a solar panel with harvesting circuitry to ensure operation near the maximum power point, reliable power can be provided to a sensor node such as the Heliomote (Figure 1-4). </p> <p align="center"><img src="images/fig1-4.gif"></p> <p><b>Inductive Coupling</b></p> <p>The concept of electromagnetic induction holds that a time varying electric current flowing through one wire can induce current to flow in another nearby wire. A simple inductive device can send power through the air a short distance. By placing a small secondary coil within a sensor, a powered coil nearby creates a magnetic field that induces current to flow through the sensor and recharge its battery. Through magnetic resonance techniques, the distance between the two coils can be greatly increased. By properly "tuning" the receiving coil to match the powered coil, the receiving device can be safely powered across the room or on different floors. </p> <p>Energy harvesting technology is now certainly ready for the prime time. By combining this technology with a wireless sensor network, both wide area and narrow field sensors can provide the data needed to detect threats more accurately and for longer periods of time across larger areas. Better interfaces between warfighter and sensors can greatly enhance the awareness and understanding of battlefield threats. </p> <p>For more information about the installation and operation of wireless sensor networks, please read the articles "Tech Tips: Sensor Installation" and "Wireless Sensor Networks Explained" appearing elsewhere in this issue of Empfasis. For more information about energy harvesting, please contact the EMPF at 610.362.1320, via email at helpline@empf.org or visit the website at www.empf.org.</p> <p>References</p> <ul style="list-style-type: decimal"> <li>Raghunathan, Vijay, Aman Kansal, Jason Hsu, Jonathan Friedman, and Mani Srivastava. "Design Considerations for Solar Energy Harvesting Wireless Embedded Systems." The Fourth International Conference on Information Processing in Sensor Networks (IPSN 2005). Los Angeles. Apr. 2005. Web. http://www.stanford.edu/class/cs240e/papers/kansal_spots05.pdf </li> <li>Magill, Paul A. "Thermal Harvesting and Storage: a Heavenly Match." Hearst Electronic Products (2010). Web. http://www2.electronicproducts.com/Thermal_harvesting_and_storage_a_heavenly_match-article-fapo_Nextreme_AltEnergy_feb2010-html.aspx</li> <li>Bratt, Paul. "Thermal Interface Materials Testing." SMTA - The Surface Mount Technology Association. San Diego. 4 Oct. 2009. Web. http://www.smta.org/knowledge/proceedings_abstract.cfm?PROC_ID=2814</li> <li>Hagerty, Joseph A., Tian Zhao, Regan Zane, and Zoya Popovic. "Efficient Broadband RF Energy Harvesting for Wireless Sensors." 30th Annual GOMACTech Conference. Las Vegas. Apr. 2005. Web. http://ecee.colorado.edu/copec/paper_archives/efficientbroadbandrf_apr2005.pdf</li> </ul> <p class="body_text"><img src="../../archive/updated/pbratt.gif"></p> </div> </td> <!-- InstanceEndEditable --> </tr> <tr> </tr> </table> <br> <table width="100%" border="0"> <tr> <td colspan="2"><div align="center"> <p><em>The EMPF is a U.S. Navy-sponsored National Electronics Manufacturing Center of Excellence focused on the development,<br> application, and transfer of new electronics manufacturing technology by partnering with industry,<br> academia, and government centers and laboratories in the U.S</em></p> </div></td> </tr> <tr> <td class="footer">ACI Technologies, Inc - - <a href="http://www.aciusa.org">www.aciusa.org</a> - - (610)362-1200</td> <td><div align="right"><a href="http://www.onr.navy.mil/Science-Technology/Directorates/Transition/Manufacturing-ManTech.aspx"><img src="http://www.empf.org/empfasis/archive/images/mantech.gif" width="144" height="42" border="0"></a></div></td> </tr> </table> <div align="right"> <!-- Start of StatCounter Code --> <script type="text/javascript" language="javascript"> var sc_project=350643; var sc_partition=1; </script> <script type="text/javascript" language="javascript" src="http://www.statcounter.com/counter/counter.js"></script> <noscript> <a href="http://www.statcounter.com/free_hit_counter.html" target="_blank"><img src="http://c2.statcounter.com/counter.php?sc_project=350643&amp;amp;java=0" alt="hit counter" border="0"></a> </noscript> <a href="http://www.empf.org/sitemap.htm"><em>[site map] </em></a> <!-- End of StatCounter Code --> <!-- Start of StatCounter Code --> <script type="text/javascript" language="javascript"> var sc_project=1902214; var sc_invisible=1; var sc_partition=17; var sc_security="759b802c"; </script> <script type="text/javascript" language="javascript" src="http://www.statcounter.com/counter/counter.js"></script><noscript><a href="http://www.statcounter.com/" target="_blank"><img src="http://c18.statcounter.com/counter.php?sc_project=1902214&java=0&security=759b802c&invisible=1" alt="website statistics" border="0"></a> </noscript> <!-- End of StatCounter Code --> </div> </body> <!-- InstanceEnd --></html>