• Journal of Semiconductor Engineering
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• v.1 no.1
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• pp.13-30
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• 2020

Radio frequency (RF) energy harvesting technology have become a reliable and promising alternative to extend the lifetime of power-constrained wireless networks by eliminating the need for batteries. This emerging technology enables the low-power wireless devices to be self-sustaining and eco-friendly by scavenging RF energy from ambient environment or dedicated energy sources. These attributes make RF energy harvesting technology feasible and attractive to an extended range of applications. However, despite being the most reliable energy harvesting technology, there are several challenges (especially power conversion efficiency, output DC voltage and sensitivity) poised for the implementation of RF energy harvesting systems. In this article, a detailed literature on RF energy harvesting technology has been surveyed to provide guidance for RF energy harvesters design. Since signal strength of the received RF power is limited and weak, high efficiency state-of-the-art RF energy harvesters are required to design for providing sufficient DC supply voltage to wireless networks. Therefore, various designs and their trade-offs with comprehensive analysis for RF energy harvesters have been discussed. This paper can serve as a good reference for the researchers to catch new research topics in the field of RF energy harvesting.

• Journal of Sensor Science and Technology
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• v.29 no.5
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• pp.293-302
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• 2020

Food safety has emerged as a growing concern for human health in recent times. Consuming contaminated food may lead to serious health problems, and therefore, a system for monitoring food freshness that is both non-detrimental to the quality of food and highly accurate is required to ensure that only high-quality fresh food packages are provided to the customers. This paper proposes a method to monitor and detect food quality using a compact smart sensor tag. The smart tag is composed of three ultra-low-power sensors, which monitor four major indicators of food freshness: temperature, humidity, and the concentrations of ammonia and hydrogen sulfide gases. An RF energy scavenging circuit is integrated into the smart sensor tag to harvest energy from radio waves at a high frequency of 13.56 MHz to supply sufficient power to the tag. Experimental results show that the proposed energy harvester can efficiently obtain energy at a distance of approximately 40 cm from a 4 W reader. In addition, the proposed smart sensor tag can operate without any battery, thereby eliminating the requirement of frequent battery replacement and consequently decreasing the cost. Meanwhile, the freshness of preserved pork is continuously monitored under two conditions--room temperature and refrigerator temperature--both of which are the most common temperatures under which food is generally stored. The food-monitoring experiments are conducted over a period of one week using the proposed battery-less tag. Based on the experimental results, the food assessment is classified into four categories: fresh, normal, low, and spoiled.

• Journal of the Institute of Convergence Signal Processing
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• v.19 no.3
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• pp.89-96
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• 2018

This study aims to develop a fully passive smart sensing tag utilizing RF (Radio Frequency) energy harvesting technology at UHF (Ultra High Frequency) band of 915MHz. To optimize the power collected under various radiated conditions, an efficient energy harvesting module exploiting a boost circuit with maximum power point tracking (MPPT) is employed. Specifically, the proposed tag features two orthogonal antennas to enhance its capability of both energy scavenging and data transmissions. The experimental result shows that the developed smart sensor tag can scavenge an RF input power of as low as 0.19mW at a distance of 4 meters for a 3.6Vdc output. Furthermore, the proposed smart sensor tag performs the feasibility of completely autonomous monitoring food freshness at 2 meters with a low-power sensor array.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.219-219
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• 2008

Energy harvesting from the environment has been of great interest as a standalone power source of wireless sensor nodes for ubiquitous sensor networks (USN). There are several power generating methods such as thermal gradients, solar cell, energy produced by human action, mechanical vibration energy, and so on. Most of all, mechanical vibration is easily accessible and has no limitation of weather and environment of outdoor or indoor. In particular, the piezoelectric energy harvesting from ambient vibration sources has attracted attention because it has a relative high power density comparing with other energy scavenging methods. Through recent advances in low power consumption RF transmitters and sensors, it is possible to adopt a micro-power energy harvesting system realized by MEMS technology for the system-on-chip. However, the MEMS energy harvesting system hassome drawbacks such as a high natural frequency over 300 Hz and a small power generation due to a small dimension. To overcome these limitations, we devised a novel power generator with a spiral spring structure. In this case, the energy harvester has a lower natural frequency under 200 Hz than a normal cantilever structure. Moreover, it has higher an energy conversion efficient because shear mode ($d_{15}$) is much larger than 33 mode ($d_{33}$) and the energy conversion efficiency is proportional to the piezoelectric constant (d). We expect the spiral type MEMS power generator would be a good candidate as a standalone power generator for USN.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2010.03a
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• pp.7-7
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• 2010

Energy harvesting from the environment has been of great interest as a standalone power source of wireless sensor nodes for Ubiquitous Sensor Networks(USN). In particular, the piezoelectric energy harvesting from ambient vibration sources has intensively researched because it has a relatively high power density comparing with other energy scavenging methods. Through recent advances in low power consumption RF transmitters and sensors, it is possible to adopt a micro-power energy harvesting system realized by MEMS technology for the system-on-chip. However, the MEMS energy harvesting system has some drawbacks such as a high natural frequency over 300 Hz and a small power generation due to a small dimension. To overcome these limitations, we devised a novel power generator with a spiral spring structure as shown in the figure. The natural frequency of a cantilever could be decreased to the usable frequency region (under 300 Hz) because the natural frequency depends on the length of a cantilever. In this study, the natural frequency of the energy harvester was a lower than a normal cantilever structure and sufficiently controllable in 50 - 200 Hz frequency region as adjusting weight of a proof mass. Moreover, the MEMS energy harvester had a high energy conversion efficiency using a shear mode ($d_{15}$) is much larger than a 33 mode ($d_{33}$) and the energy conversion efficiency is proportional to the piezoelectric constant (d). We expect the spiral type MEMS power generator would be a good candidate for a standalone power generator for USN.