Microwave absorption in radar stealth technology is faced with challenges in terms of its effectiveness in low-frequency regions.Herein,we report a new laser-based method for producing an ultrawideband metamaterial-ba...Microwave absorption in radar stealth technology is faced with challenges in terms of its effectiveness in low-frequency regions.Herein,we report a new laser-based method for producing an ultrawideband metamaterial-based microwave absorber with a highly uniform sheet resistance and negative magnetic permeability at resonant frequencies,which results in a wide bandwidth in the L-to S-band.Control of the electrical sheet resistance uniformity has been achieved with less than 5%deviation at 400Ωsq^(-1)and 6%deviation at 120Ωsq^(-1),resulting in a microwave absorption coefficient between 97.2%and 97.7%within a1.56–18.3 GHz bandwidth for incident angles of 0°–40°,and there is no need for providing energy or an electrical power source during the operation.Porous N-and S-doped turbostratic graphene 2D patterns with embedded magnetic nanoparticles were produced simultaneously on a polyethylene terephthalate substrate via laser direct writing.The proposed low-frequency,wideband,wide-incident-angle,and high-electromagnetic-absorption microwave absorber can potentially be used in aviation,electromagnetic interference(EMI)suppression,and 5G applications.展开更多
A detailed design methodology of a micro-scale 2-DOF energy harvesting device that can harvest human motion energy of low frequency and wide bandwidth is developed. Based on the concept of the 2-DOF vibration absorber...A detailed design methodology of a micro-scale 2-DOF energy harvesting device that can harvest human motion energy of low frequency and wide bandwidth is developed. Based on the concept of the 2-DOF vibration absorber, device parameters are selected to harvest energy at low frequency of 1-10 Hz and wide bandwidth with ±20% of the mean frequency, which matches the human motion. The device dimensions are limited to 40 × 30 × 10 mm3 to fit with the human wrist size. Then, a finite element model is developed to investigate the system performance with the selected parameters. When subjected to harmonic excitation of 1 g, the proposed 2-DOF device is able to provide a power of at least 10 μW in between the two close resonant peaks of 4 Hz and 6 Hz, which is the target frequency range. The device shows very high power per square frequency compared with the reported harvesters.展开更多
In this paper,a piezoelectric energy harvester based on spiral-shaped polyvinylidene fluoride(PVDF)cantilever is designed and fabricated for harvesting low frequency vibration energy in the environment.In this design,...In this paper,a piezoelectric energy harvester based on spiral-shaped polyvinylidene fluoride(PVDF)cantilever is designed and fabricated for harvesting low frequency vibration energy in the environment.In this design,the spiral-shaped PVDF cantilever is major for lowering the resonant frequency by increasing the length of the cantilever;Copper and silicon proof masses on both sides are working on further decreasing the resonant frequency and widen its bandwidth.Due to the high flexibility of the PVDF cantilever,this device is extremely sensitive to vibration and can harvest weak vibration energy.Both simulation and experimental results have approved that this device can operate at very low frequency which is about 20 Hz and can effectively harvest energy from 15–50 Hz.The peak of the output voltage can reach 1.8 V with the acceleration of 0.2 g.This is a promising harvester for powering the wireless sensors in the future.展开更多
文摘Microwave absorption in radar stealth technology is faced with challenges in terms of its effectiveness in low-frequency regions.Herein,we report a new laser-based method for producing an ultrawideband metamaterial-based microwave absorber with a highly uniform sheet resistance and negative magnetic permeability at resonant frequencies,which results in a wide bandwidth in the L-to S-band.Control of the electrical sheet resistance uniformity has been achieved with less than 5%deviation at 400Ωsq^(-1)and 6%deviation at 120Ωsq^(-1),resulting in a microwave absorption coefficient between 97.2%and 97.7%within a1.56–18.3 GHz bandwidth for incident angles of 0°–40°,and there is no need for providing energy or an electrical power source during the operation.Porous N-and S-doped turbostratic graphene 2D patterns with embedded magnetic nanoparticles were produced simultaneously on a polyethylene terephthalate substrate via laser direct writing.The proposed low-frequency,wideband,wide-incident-angle,and high-electromagnetic-absorption microwave absorber can potentially be used in aviation,electromagnetic interference(EMI)suppression,and 5G applications.
文摘A detailed design methodology of a micro-scale 2-DOF energy harvesting device that can harvest human motion energy of low frequency and wide bandwidth is developed. Based on the concept of the 2-DOF vibration absorber, device parameters are selected to harvest energy at low frequency of 1-10 Hz and wide bandwidth with ±20% of the mean frequency, which matches the human motion. The device dimensions are limited to 40 × 30 × 10 mm3 to fit with the human wrist size. Then, a finite element model is developed to investigate the system performance with the selected parameters. When subjected to harmonic excitation of 1 g, the proposed 2-DOF device is able to provide a power of at least 10 μW in between the two close resonant peaks of 4 Hz and 6 Hz, which is the target frequency range. The device shows very high power per square frequency compared with the reported harvesters.
基金supported by the National Natural Science Foundation of China(Grant Nos.61176103,91023045 and 91323304)National Ph.D.Foundation Project(Grant No.20110001110103)Global Research Outreach Program of Samsung Advanced Institute of Technology
文摘In this paper,a piezoelectric energy harvester based on spiral-shaped polyvinylidene fluoride(PVDF)cantilever is designed and fabricated for harvesting low frequency vibration energy in the environment.In this design,the spiral-shaped PVDF cantilever is major for lowering the resonant frequency by increasing the length of the cantilever;Copper and silicon proof masses on both sides are working on further decreasing the resonant frequency and widen its bandwidth.Due to the high flexibility of the PVDF cantilever,this device is extremely sensitive to vibration and can harvest weak vibration energy.Both simulation and experimental results have approved that this device can operate at very low frequency which is about 20 Hz and can effectively harvest energy from 15–50 Hz.The peak of the output voltage can reach 1.8 V with the acceleration of 0.2 g.This is a promising harvester for powering the wireless sensors in the future.
