{"id":4862,"date":"2015-06-24T05:40:27","date_gmt":"2015-06-24T05:40:27","guid":{"rendered":"http:\/\/revoscience.com\/en\/?p=4862"},"modified":"2015-06-24T05:40:27","modified_gmt":"2015-06-24T05:40:27","slug":"toward-tiny-solar-powered-sensors","status":"publish","type":"post","link":"https:\/\/www.revoscience.com\/en\/toward-tiny-solar-powered-sensors\/","title":{"rendered":"Toward tiny, solar-powered sensors"},"content":{"rendered":"

New ultralow-power circuit improves efficiency of energy harvesting to more than 80 percent.<\/strong><\/em><\/span><\/p>\n

\"The<\/a>
The MIT researchers’ prototype for a chip measuring 3 millimeters by 3 millimeters. Courtesy of the researchers<\/figcaption><\/figure>\n

CAMBRIDGE, Mass<\/strong>\u00a0—\u00a0The latest buzz in the information technology industry regards \u201cthe Internet of things\u201d \u2014 the idea that vehicles, appliances, civil-engineering structures, manufacturing equipment, and even livestock would have their own embedded sensors that report information directly to networked servers, aiding with maintenance and the coordination of tasks.<\/span><\/p>\n

Realizing that vision, however, will require extremely low-power sensors that can run for months without battery changes \u2014 or, even better, that can extract energy from the environment to recharge.<\/span><\/p>\n

Last week, at the Symposia on VLSI Technology and Circuits, MIT researchers presented a new power converter chip that can harvest more than 80 percent of the energy trickling into it, even at the extremely low power levels characteristic of tiny solar cells. Previous experimental ultralow-power converters had efficiencies of only 40 or 50 percent.<\/span><\/p>\n

Moreover, the researchers\u2019 chip achieves those efficiency improvements while assuming additional responsibilities. Where its predecessors could use a solar cell to either charge a battery or directly power a device, this new chip can do both, and it can power the device directly from the battery.<\/span><\/p>\n

All of those operations also share a single inductor \u2014 the chip\u2019s main electrical component \u2014 which saves on circuit board space but increases the circuit complexity even further. Nonetheless, the chip\u2019s power consumption remains low.<\/span><\/p>\n

\u201cWe still want to have battery-charging capability, and we still want to provide a regulated output voltage,\u201d says Dina Reda El-Damak, an MIT graduate student in electrical engineering and computer science and first author on the new paper. \u201cWe need to regulate the input to extract the maximum power, and we really want to do all these tasks with inductor sharing and see which operational mode is the best. And we want to do it without compromising the performance, at\u00a0 very limited input power levels \u2014 10 nanowatts to 1 microwatt \u2014 for the Internet of things.\u201d<\/span><\/p>\n

Ups and downs<\/strong><\/span><\/p>\n

The circuit\u2019s chief function is to regulate the voltages between the solar cell, the battery, and the device the cell is powering. If the battery operates for too long at a voltage that\u2019s either too high or too low, for instance, its chemical reactants break down, and it loses the ability to hold a charge.<\/span><\/p>\n

To control the current flow across their chip, El-Damak and her advisor, Anantha\u00a0 Chandrakasan, the Joseph F. and Nancy P. Keithley Professor in Electrical Engineering, use an inductor, which is a wire wound into a coil. When a current passes through an inductor, it generates a magnetic field, which in turn resists any change in the current.<\/span><\/p>\n

Throwing switches in the inductor\u2019s path causes it to alternately charge and discharge, so that the current flowing through it\u00a0continuously ramps up and then drops back down to zero. Keeping a lid on the current improves the circuit\u2019s efficiency, since the rate at which it dissipates energy as heat is proportional to the square of the current.<\/span><\/p>\n

Once the current drops to zero, however, the switches in the inductor\u2019s path need to be thrown immediately; otherwise, current could begin to flow through the circuit in the wrong direction, which would drastically diminish its efficiency. The complication is that the rate at which the current rises and falls depends on the voltage generated by the solar cell, which is highly variable. So the timing of the switch throws has to vary, too.<\/span><\/p>\n

Electric hourglass<\/strong><\/span><\/p>\n

To control the switches\u2019 timing, El-Damak and Chandrakasan use an electrical component called a capacitor, which can store electrical charge. The higher the current, the more rapidly the capacitor fills. When it\u2019s full, the circuit stops charging the inductor.<\/span><\/p>\n

The rate at which the current drops off, however, depends on the output voltage, whose regulation is the very purpose of the chip. Since that voltage is fixed, the variation in timing has to come from variation in capacitance. El-Damak and Chandrakasan thus equip their chip with a bank of capacitors of different sizes. As the current drops, it charges a subset of those capacitors, whose selection is determined by the solar cell\u2019s voltage. Once again, when the capacitor fills, the switches in the inductor\u2019s path are flipped.<\/span><\/p>\n","protected":false},"excerpt":{"rendered":"

New ultralow-power circuit improves efficiency of energy harvesting to more than 80 percent. CAMBRIDGE, Mass\u00a0—\u00a0The latest buzz in the information technology industry regards \u201cthe Internet of things\u201d \u2014 the idea that vehicles, appliances, civil-engineering structures, manufacturing equipment, and even livestock would have their own embedded sensors that report information directly to networked servers, aiding with […]<\/p>\n","protected":false},"author":6,"featured_media":4863,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[14],"tags":[],"class_list":["post-4862","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-innovation"],"featured_image_urls":{"full":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2015\/06\/MIT-PowerHarvest-1.jpg",639,426,false],"thumbnail":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2015\/06\/MIT-PowerHarvest-1-150x150.jpg",150,150,true],"medium":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2015\/06\/MIT-PowerHarvest-1-300x200.jpg",300,200,true],"medium_large":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2015\/06\/MIT-PowerHarvest-1.jpg",639,426,false],"large":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2015\/06\/MIT-PowerHarvest-1.jpg",639,426,false],"1536x1536":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2015\/06\/MIT-PowerHarvest-1.jpg",639,426,false],"2048x2048":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2015\/06\/MIT-PowerHarvest-1.jpg",639,426,false],"ultp_layout_landscape_large":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2015\/06\/MIT-PowerHarvest-1.jpg",639,426,false],"ultp_layout_landscape":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2015\/06\/MIT-PowerHarvest-1.jpg",639,426,false],"ultp_layout_portrait":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2015\/06\/MIT-PowerHarvest-1.jpg",600,400,false],"ultp_layout_square":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2015\/06\/MIT-PowerHarvest-1.jpg",600,400,false],"newspaper-x-single-post":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2015\/06\/MIT-PowerHarvest-1.jpg",639,426,false],"newspaper-x-recent-post-big":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2015\/06\/MIT-PowerHarvest-1.jpg",540,360,false],"newspaper-x-recent-post-list-image":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2015\/06\/MIT-PowerHarvest-1.jpg",95,63,false],"web-stories-poster-portrait":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2015\/06\/MIT-PowerHarvest-1.jpg",639,426,false],"web-stories-publisher-logo":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2015\/06\/MIT-PowerHarvest-1.jpg",96,64,false],"web-stories-thumbnail":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2015\/06\/MIT-PowerHarvest-1.jpg",150,100,false]},"author_info":{"info":["Amrita Tuladhar"]},"category_info":"Innovation<\/a>","tag_info":"Innovation","comment_count":"0","_links":{"self":[{"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/posts\/4862","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/users\/6"}],"replies":[{"embeddable":true,"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/comments?post=4862"}],"version-history":[{"count":0,"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/posts\/4862\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/media\/4863"}],"wp:attachment":[{"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/media?parent=4862"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/categories?post=4862"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/tags?post=4862"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}