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Three-dimensional magnetic cloak working from d.c. to 250 kHz.

Zhu J, Jiang W, Liu Y, Yin G, Yuan J, He S, Ma Y - Nat Commun (2015)

Bottom Line: In this work, we vastly develop the bilayer approach to create a three-dimensional magnetic cloak able to work in both static and dynamic fields.Under the quasi-static approximation, we demonstrate a perfect magnetic cloaking device with a large frequency band from 0 to 250 kHz.The practical potential of our device is experimentally verified by using a commercial metal detector, which may lead us to having a real cloaking application where the dynamic magnetic field can be manipulated in desired ways.

View Article: PubMed Central - PubMed

Affiliation: State Key Lab of Modern Optical Instrumentation, Centre for Optical and Electromagnetic Research, College of Optical Science and Engineering, Zhejiang University, Hangzhou 310058, China.

ABSTRACT
Invisible cloaking is one of the major outcomes of the metamaterial research, but the practical potential, in particular for high frequencies (for example, microwave to visible light), is fatally challenged by the complex material properties they usually demand. On the other hand, it will be advantageous and also technologically instrumental to design cloaking devices for applications at low frequencies where electromagnetic components are favourably uncoupled. In this work, we vastly develop the bilayer approach to create a three-dimensional magnetic cloak able to work in both static and dynamic fields. Under the quasi-static approximation, we demonstrate a perfect magnetic cloaking device with a large frequency band from 0 to 250 kHz. The practical potential of our device is experimentally verified by using a commercial metal detector, which may lead us to having a real cloaking application where the dynamic magnetic field can be manipulated in desired ways.

No MeSH data available.


Related in: MedlinePlus

Measurement results for dynamic field.This displays the measured relative change of the z-component magnetic field intensity at a fixed point x=y=0 and z=R3+5 mm when the operating frequency varies from 5 Hz to 250 kHz. Here the magnetic field amplitude we apply is smaller than 1 mT. The measured induction voltage signal is nearly a purely imaginary number due to the low loss features of our ingredient materials used for the device. The uncertainty error arising mainly from the background noise becomes manifest at lower frequencies, especially below 50 Hz, because the measured signal decreases (and gets closer to the noise level) as the measurement frequency decreases. The samples of FM and SC shells only have nearly constant values around 6 and 7%, respectively, while the bilayer structure has almost zero relative change in the measurement band. The inset plots the real permeability spectrum of the FM material measured at room temperature, from 100 Hz to 250 kHz. The diluted composite has a negligible loss tangent (<0.01). The permeability spectrum at 77 K is estimated by multiplying by a factor proportional to the increase of the saturation magnetization due to the reduction in temperature. The minimum resolvable voltage of our lock-in amplifier is dependent on the operation frequency. The error bars in the figure are calculated by dividing the resolution with the measured sample voltage.
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f4: Measurement results for dynamic field.This displays the measured relative change of the z-component magnetic field intensity at a fixed point x=y=0 and z=R3+5 mm when the operating frequency varies from 5 Hz to 250 kHz. Here the magnetic field amplitude we apply is smaller than 1 mT. The measured induction voltage signal is nearly a purely imaginary number due to the low loss features of our ingredient materials used for the device. The uncertainty error arising mainly from the background noise becomes manifest at lower frequencies, especially below 50 Hz, because the measured signal decreases (and gets closer to the noise level) as the measurement frequency decreases. The samples of FM and SC shells only have nearly constant values around 6 and 7%, respectively, while the bilayer structure has almost zero relative change in the measurement band. The inset plots the real permeability spectrum of the FM material measured at room temperature, from 100 Hz to 250 kHz. The diluted composite has a negligible loss tangent (<0.01). The permeability spectrum at 77 K is estimated by multiplying by a factor proportional to the increase of the saturation magnetization due to the reduction in temperature. The minimum resolvable voltage of our lock-in amplifier is dependent on the operation frequency. The error bars in the figure are calculated by dividing the resolution with the measured sample voltage.

Mentions: For dynamic field measurement, we use a pair of custom-made Helmholtz coils with proper inductance. A Stanford signal generator is used to excite the coils, and the z-component magnetic field near the sample is inductively measured through a small copper loop connected to a lock-in amplifier. The field strength exposed to the sample is <1 mT, and the measurement frequency varies from 5 Hz to 250 kHz to suit the band of our lock-in amplifier. Figure 4 gives the measured relative change of the z-component magnetic field intensity at a fixed point x=y=0 and z0=R3+h (h=5 mm) for various samples. For the dynamic case, the magnitude of the induced voltage has been used to evaluate the relative change of the magnetic field component. As discussed later, the ingredient FM and SC materials we used have very low losses in the operation state. The induced complex voltage signals are nearly pure imaginary numbers in the measurement frequency band, that is, a phase difference around 90°. (with ±0.5° fluctuation) from the source current of the exciting coil. The influence of the real part of the measured signal is practically neglected in our consideration. From the curves, we see that the dynamic responses of these samples are nearly independent of the operating frequency. The inset of Fig. 4 shows the measured room temperature permeability spectrum of our FM composite from 100 Hz to 250 kHz. A nearly constant permeability around 1.54 is observed, which is essential for the large bandwidth of our cloaking device. Permeability at the working temperature (77 K) is estimated by multiplying the ratio of the saturation magnetization measured at these two different temperatures. Fine tuning of the composition in experiment is carried out till the lowest field perturbation is achieved. The measured relative changes of the z-component magnetic field intensity for the SC and FM shells only remain at about 6% and 7%, respectively, while that for the bilayer sample is desirably diminished to nearly zero (absolute amplitude <0.2%). Note the measurement at low frequencies (<50 Hz) has an increased uncertainty error due to the fact that the measured induction signal is proportional to the operation frequency and the influence of the background noise becomes more obvious at lower frequencies. However it will not impact the conclusion that the measured results verify the dynamic cloaking performance of our device from low frequency up to 250 kHz, where the quasi-static approximation works fairly well. In addition, we did check the field disturbance at places much closer to the sample surface, that is, at smaller h, and found the relative change of the z-component magnetic field increases slightly with fluctuation varying from 0.2% at h=5 mm to 0.3% at h=0. This also demonstrated the advantage of the 3D cloaking topology.


Three-dimensional magnetic cloak working from d.c. to 250 kHz.

Zhu J, Jiang W, Liu Y, Yin G, Yuan J, He S, Ma Y - Nat Commun (2015)

Measurement results for dynamic field.This displays the measured relative change of the z-component magnetic field intensity at a fixed point x=y=0 and z=R3+5 mm when the operating frequency varies from 5 Hz to 250 kHz. Here the magnetic field amplitude we apply is smaller than 1 mT. The measured induction voltage signal is nearly a purely imaginary number due to the low loss features of our ingredient materials used for the device. The uncertainty error arising mainly from the background noise becomes manifest at lower frequencies, especially below 50 Hz, because the measured signal decreases (and gets closer to the noise level) as the measurement frequency decreases. The samples of FM and SC shells only have nearly constant values around 6 and 7%, respectively, while the bilayer structure has almost zero relative change in the measurement band. The inset plots the real permeability spectrum of the FM material measured at room temperature, from 100 Hz to 250 kHz. The diluted composite has a negligible loss tangent (<0.01). The permeability spectrum at 77 K is estimated by multiplying by a factor proportional to the increase of the saturation magnetization due to the reduction in temperature. The minimum resolvable voltage of our lock-in amplifier is dependent on the operation frequency. The error bars in the figure are calculated by dividing the resolution with the measured sample voltage.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4696515&req=5

f4: Measurement results for dynamic field.This displays the measured relative change of the z-component magnetic field intensity at a fixed point x=y=0 and z=R3+5 mm when the operating frequency varies from 5 Hz to 250 kHz. Here the magnetic field amplitude we apply is smaller than 1 mT. The measured induction voltage signal is nearly a purely imaginary number due to the low loss features of our ingredient materials used for the device. The uncertainty error arising mainly from the background noise becomes manifest at lower frequencies, especially below 50 Hz, because the measured signal decreases (and gets closer to the noise level) as the measurement frequency decreases. The samples of FM and SC shells only have nearly constant values around 6 and 7%, respectively, while the bilayer structure has almost zero relative change in the measurement band. The inset plots the real permeability spectrum of the FM material measured at room temperature, from 100 Hz to 250 kHz. The diluted composite has a negligible loss tangent (<0.01). The permeability spectrum at 77 K is estimated by multiplying by a factor proportional to the increase of the saturation magnetization due to the reduction in temperature. The minimum resolvable voltage of our lock-in amplifier is dependent on the operation frequency. The error bars in the figure are calculated by dividing the resolution with the measured sample voltage.
Mentions: For dynamic field measurement, we use a pair of custom-made Helmholtz coils with proper inductance. A Stanford signal generator is used to excite the coils, and the z-component magnetic field near the sample is inductively measured through a small copper loop connected to a lock-in amplifier. The field strength exposed to the sample is <1 mT, and the measurement frequency varies from 5 Hz to 250 kHz to suit the band of our lock-in amplifier. Figure 4 gives the measured relative change of the z-component magnetic field intensity at a fixed point x=y=0 and z0=R3+h (h=5 mm) for various samples. For the dynamic case, the magnitude of the induced voltage has been used to evaluate the relative change of the magnetic field component. As discussed later, the ingredient FM and SC materials we used have very low losses in the operation state. The induced complex voltage signals are nearly pure imaginary numbers in the measurement frequency band, that is, a phase difference around 90°. (with ±0.5° fluctuation) from the source current of the exciting coil. The influence of the real part of the measured signal is practically neglected in our consideration. From the curves, we see that the dynamic responses of these samples are nearly independent of the operating frequency. The inset of Fig. 4 shows the measured room temperature permeability spectrum of our FM composite from 100 Hz to 250 kHz. A nearly constant permeability around 1.54 is observed, which is essential for the large bandwidth of our cloaking device. Permeability at the working temperature (77 K) is estimated by multiplying the ratio of the saturation magnetization measured at these two different temperatures. Fine tuning of the composition in experiment is carried out till the lowest field perturbation is achieved. The measured relative changes of the z-component magnetic field intensity for the SC and FM shells only remain at about 6% and 7%, respectively, while that for the bilayer sample is desirably diminished to nearly zero (absolute amplitude <0.2%). Note the measurement at low frequencies (<50 Hz) has an increased uncertainty error due to the fact that the measured induction signal is proportional to the operation frequency and the influence of the background noise becomes more obvious at lower frequencies. However it will not impact the conclusion that the measured results verify the dynamic cloaking performance of our device from low frequency up to 250 kHz, where the quasi-static approximation works fairly well. In addition, we did check the field disturbance at places much closer to the sample surface, that is, at smaller h, and found the relative change of the z-component magnetic field increases slightly with fluctuation varying from 0.2% at h=5 mm to 0.3% at h=0. This also demonstrated the advantage of the 3D cloaking topology.

Bottom Line: In this work, we vastly develop the bilayer approach to create a three-dimensional magnetic cloak able to work in both static and dynamic fields.Under the quasi-static approximation, we demonstrate a perfect magnetic cloaking device with a large frequency band from 0 to 250 kHz.The practical potential of our device is experimentally verified by using a commercial metal detector, which may lead us to having a real cloaking application where the dynamic magnetic field can be manipulated in desired ways.

View Article: PubMed Central - PubMed

Affiliation: State Key Lab of Modern Optical Instrumentation, Centre for Optical and Electromagnetic Research, College of Optical Science and Engineering, Zhejiang University, Hangzhou 310058, China.

ABSTRACT
Invisible cloaking is one of the major outcomes of the metamaterial research, but the practical potential, in particular for high frequencies (for example, microwave to visible light), is fatally challenged by the complex material properties they usually demand. On the other hand, it will be advantageous and also technologically instrumental to design cloaking devices for applications at low frequencies where electromagnetic components are favourably uncoupled. In this work, we vastly develop the bilayer approach to create a three-dimensional magnetic cloak able to work in both static and dynamic fields. Under the quasi-static approximation, we demonstrate a perfect magnetic cloaking device with a large frequency band from 0 to 250 kHz. The practical potential of our device is experimentally verified by using a commercial metal detector, which may lead us to having a real cloaking application where the dynamic magnetic field can be manipulated in desired ways.

No MeSH data available.


Related in: MedlinePlus