The theory of shielded loop resonators

Harpen, Michael D.

doi:10.1002/mrm.1910320615

Cited by 19 publications

(29 citation statements)

References 8 publications

(10 reference statements)

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“…A shielded loop is a coaxial, electrically-small loop antenna with a primarily magnetic response [33], [34]. The central conductor is left open circuited at the termination point of the loop to provide a resonance (see Fig.…”

Section: Analysis Of Coupled Shielded Loop Resonatorsmentioning

confidence: 99%

Comprehensive Analysis and Measurement of Frequency-Tuned and Impedance-Tuned Wireless Non-Radiative Power-Transfer Systems

Heebl

Thomas

Penno

et al. 2014

IEEE Antennas Propag. Mag.

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Abstract-This paper theoretically and experimentally investigates frequency-tuned and impedance-tuned wireless nonradiative power transfer (WNPT) systems. Closed-form expressions for the efficiencies of both systems, as a function of frequency and system (circuit) parameters, are presented. In the frequency-tuned system, the operating frequency is adjusted to compensate for changes in mutual inductance that occur for variations of transmitter and receiver loop positions. Frequencytuning is employed for a range of distances over which the loops are strongly coupled. In contrast, the impedance-tuned system employs varactor-based matching networks to compensate for changes in mutual inductance and achieve a simultaneous conjugate impedance match over a range of distances. The frequencytuned system is simpler to implement, while the impedance-tuned system is more complex but can achieve higher efficiencies. Both of the experimental WNPT systems studied employ resonant shielded loops as transmitting and receiving devices.

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Section: Analysis Of Coupled Shielded Loop Resonatorsmentioning

confidence: 99%

Comprehensive Analysis and Measurement of Frequency-Tuned and Impedance-Tuned Wireless Non-Radiative Power-Transfer Systems

Heebl

Thomas

Penno

et al. 2014

IEEE Antennas Propag. Mag.

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“…Their simple geometry allows the elements of their circuit model to be derived analytically. They also exhibit a predominantly magnetic response [18], which eliminates the electric dipole effect observed in the initial demonstration of WNPT [1].…”

Section: Resonant Shielded Loops For Wnptmentioning

confidence: 98%

“…The probe, sensor and power meter can be modeled as a series circuit. Then the found in (17) is given by (18) where R is the 50 sensor input resistance, P is the measured power in Watts, and and are the measured inductance and resistance of the isolated probe.…”

Section: Magnetic Field Measurementsmentioning

confidence: 99%

“…Theoretical and experimental magnetic field strength between the single-turn shielded loops along their axis. The theoretical curve was generated using (1a) in [32] and the experimental field was calculated from power measurements using (17) and (18). The input power was 17 dBm (0.05 W) and the received power was approximately 13 dBm (0.02 W).…”

Section: Enhanced Performance With the Ten-turn Coil Systemmentioning

confidence: 99%

“…Driver and load loops used in earlier WNPT systems [1], [11], [23], [24] are not needed in the proposed designs. Additionally, since shielded loops have a predominantly magnetic response [18], they eliminate the electric dipole moment of earlier open-circuited helical structures used for WNPT [1]. Finally, the shielded loop systems are geometrically simple and can be characterized analytically.…”

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confidence: 99%

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A Power Link Study of Wireless Non-Radiative Power Transfer Systems Using Resonant Shielded Loops

Thomas

Heebl

Pfeiffer

et al. 2012

IEEE Trans. Circuits Syst. I

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This paper discusses the use of magnetically coupled resonators for midrange wireless non-radiative power transfer (WNPT). A quasi-static (circuit) model is developed to establish key measures of performance and to aid in design. The use of directly fed, resonant shielded loops for WNPT is also proposed for the first time. Two experimental WNPT systems employing shielded loops are reported. A comprehensive experimental study is performed, and the performance of the WNPT systems shows close agreement with analytical predictions and developed circuit models. With a single-turn system of loop radius 10.7 cm, power transfer efficiency of 41.8% is achieved at a loop separation of 35 cm (3.3 loop radii). When the number of turns is increased to ten, a power transfer efficiency of 36.5% is achieved at a loop separation of 56 cm (5.3 loop radii). Measured magnetic field levels in the vicinity of the WNPT systems are shown to closely agree with analytical field values.Index Terms-Mutual inductance, non-radiative power transfer, resonant magnetic coupling, shielded loops, wireless power.

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Wearable Coaxially‐Shielded Metamaterial for Magnetic Resonance Imaging

Zhu,

Wu,

Anderson

et al. 2024

Advanced Materials

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Recent advancements in metamaterials have yielded the possibility of a wireless solution to improve signal‐to‐noise ratio (SNR) in magnetic resonance imaging (MRI). Unlike traditional closely packed local coil arrays with rigid designs and numerous components, these lightweight, cost‐effective metamaterials eliminate the need for radio frequency cabling, baluns, adapters, and interfaces. However, their clinical adoption has been limited by their low sensitivity, bulky physical footprint, and limited, specific use cases. Herein, we introduce a wearable metamaterial developed using commercially available coaxial cable, designed for a 3.0 T MRI system. This metamaterial inherits the coaxially‐shielded structure of its constituent cable, confining the electric field within and mitigating coupling to its surroundings. This ensures safer clinical adoption, lower signal loss, and resistance to frequency shifts. Weighing only 50 g, the metamaterial maximizes its sensitivity by conforming to the anatomical region of interest. MRI images acquired using this metamaterial with various pulse sequences achieve an SNR comparable or even surpass that of a state‐of‐the‐art 16‐channel knee coil. This work introduces a novel paradigm for constructing metamaterials in the MRI environment, paving the way for the development of next‐generation wireless MRI technology.This article is protected by copyright. All rights reserved

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The theory of shielded loop resonators

Cited by 19 publications

References 8 publications

Comprehensive Analysis and Measurement of Frequency-Tuned and Impedance-Tuned Wireless Non-Radiative Power-Transfer Systems

Comprehensive Analysis and Measurement of Frequency-Tuned and Impedance-Tuned Wireless Non-Radiative Power-Transfer Systems

A Power Link Study of Wireless Non-Radiative Power Transfer Systems Using Resonant Shielded Loops

Wearable Coaxially‐Shielded Metamaterial for Magnetic Resonance Imaging

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