Issue link: https://cp.revolio.com/i/763374
18 ista views • December 2016 • www.ista.org Application of a Triboelectric Energy Harvester in Transport Packaging > CONTINUED FROM FRONT COVER affecting packaging, reported by the FDA in 2006, is that "US businesses lose up to $250 billion of profit due to the counterfeit drug trade every year" [2]. Together, these two trends increase the use of small electronic devices in packaging today. Some examples of smart packaging include smart labeling, oxygen and moisture control, counterfeit prevention, and vibration and shock monitoring of unit loads in distribution. Small electronic devices used to prevent counterfeiting are RFID tags, designated product codes ("track-and-trace"), and GPS units. This increasing use of electronic devices in packaging is expected to continue as capabilities increase and size and cost of these devices decrease. All of the technology advancements above have one major limitation in common: they use batteries as their power source. The necessity of replacing or recharging batteries results in limiting run times and requires additional costs when batteries must be replaced. Also progressing at an incredible rate, over the last few years, is the development and implementation of energy harvesters for real-world applications. Surprisingly, these trends have developed independently of one another, and as yet, no energy harvesting methods have been applied to address the power needs of smart packages in packaged product distribution. This paper summarizes the findings of a study of an energy harvester applied to charging small energy cells for a myriad of applications, and validated in a package distribution application. A triboelectric energy harvester is developed, and its response to shock and vibration inputs is explored. Energy Harvesting Methods There are four ambient energy sources available for energy harvesting in our environment. These are: mechanical energy, such as vibration, shock, and deformation of materials; thermal energy sources in the form of temperature gradients; radiant energy, such as the solar and infrared radiation, as well as radio waves; and chemical energy sources from chemical reactions and biochemical processes [3]. There are energy harvesting methods that are used for every one of these sources, most of which require specialized materials and processes. The environment often limits the method of energy harvesting to be used for an application, as these ambient sources are not present in every location, or during every season of the year. For the purpose of harvesting ambient mechanical energy, vibration energy harvesting methods are the most promising [3, 4]. There are a number of energy harvesting methods that may be used for harvesting mechanical vibration energy. The three most common methods are electrostatic, electromagnetic, and piezoelectric energy harvesting [4, 5]. Recently, a fourth category, triboelectric energy harvesting, has emerged. Electrostatic Energy Harvesting Electrostatic energy harvesting generally uses a structures that are composed of two metal capacitor plates that are isolated from one another by air, a vacuum, or some other type of insulator [6]. These two capacitor plates are electrically charged with equal, but opposite charges. Physical separation of these plates after charging results in a change in the charge that is present in the system. Electrostatic energy harvesters are typically intricate metal structures that are attached to a battery for the purpose of charging the capacitor plates [5]. For this reason, electrostatic energy harvesting is not an ideal method for application in packaging distribution. Electromagnetic Energy Harvesting Electromagnetic energy harvesting can be applied to multiple ambient energy sources, the most common of which are vibration and radio waves. The operating principle of this method is that changes in an electromagnetic field can cause a potential difference in energy, which can then be collected. In the case of vibration, the physical movement of a magnet and a charged coil past one another causes a change in the electromagnetic field [6]. Using vibration or physical motion to cause this interactive motion of the magnet and coil to occur many times per second can generate large amounts of electricity over time. As is the case with electrostatic energy harvesting, electromagnetic energy harvesting uses many materials that are difficult to integrate into a packaging system. Piezoelectric Energy Harvesting The most common of these methods, and the method that has received the most attention in research is piezoelectric energy harvesting [4]. The piezoelectric effect is a phenomenon in which certain materials become electrically polarized in response to applied mechanical strain. Many materials exhibit this behavior, all of which fall into four main categories: single crystal, such as quartz; piezoceramics, such as lead zirconate titanate (PZT); thin film, such as sputtered zinc oxide; and polymeric materials, including PVDF and many other polymers [6]. Recently, a fifth category has emerged, forced piezoelectric materials. This category uses mostly polymers that have been treated, usually with corona discharge treatment, causing them to exhibit strong piezoelectric responses [5]. Piezoelectric energy harvesting has been thoroughly explored by the scientific community. It is possible to use polymeric and thin-film materials in many geometries and structures, and therefore piezoelectric energy harvesting has potential in the context of packaging applications.