Analysis of the Impedance Behaviour for Broadband Dipoles in Proximity of a Body Tissue: Approach by Using Antenna Equivalent Circuits

Tuovinen, Tommi; Berg, Markus; Iinatti, and Jari

doi:10.2528/pierb14021902

Cited by 8 publications

(7 citation statements)

References 28 publications

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“…In the proximity of tissues, the resonance frequencies are detuned downwards according to perturbation theory [72]. As shown in a recent study [73], below ≈1 mm distance between the antenna and the body, the dominating mechanism is caused by the parasitic inductance with very low contribution from the capacitive coupling. For example, for the fiber loop antenna the measured impedance (Z loop = 60.4 + j8.26) has a higher inductive component comparing to the one in the dipole antenna impedance (Z dipole = 52.5 + j0.14) and the spiral antenna (Z spiral = 46.09 − j16), which increases in the proximity of the phantom, and demonstrates a greater frequency shift than the fiber dipole antenna.…”

Section: Influence Of Conductive Medium: Frequency Shifts and Mechanimentioning

confidence: 90%

New Generation Wearable Antenna Based on Multimaterial Fiber for Wireless Communication and Real-Time Breath Detection

et al. 2018

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Smart textiles and wearable antennas along with broadband mobile technologies have empowered the wearable sensors for significant impact on the future of digital health care. Despite the recent development in this field, challenges related to lack of accuracy, reliability, user’s comfort, rigid form and challenges in data analysis and interpretation have limited their wide-scale application. Therefore, the necessity of developing a new reliable and user friendly approach to face these problems is more than urgent. In this paper, a new generation of wearable antenna is presented, and its potential use as a contactless and non-invasive sensor for human breath detection is demonstrated. The antenna is made from multimaterial fiber designed for short-range wireless network applications at 2.4 GHz frequency. The used composite metal-glass-polymer fibers permits their integration into a textile without compromising comfort or restricting movement of the user due to their high flexibility, and shield efficiently the antenna from the environmental perturbation. The multimaterial fiber approach provided a good radio-frequency emissive properties, while preserving the mechanical and cosmetic properties of the garments. With a smart textile featuring a spiral shape fiber antenna placed on a human chest, a significant shift of the operating frequency of the antenna was observed during the breathing process. The frequency shift is caused by the deformation of the antenna geometry due to the chest expansion, and to the modification of the dielectric properties of the chest during the breath. We demonstrate experimentally that the standard wireless networks, which measure the received signal strength indicator (RSSI) via standard Bluetooth protocol, can be used to reliably detect human breathing and estimate the breathing rate in real time. The mobile platform takes the form of a wearable stretching T-shirt featuring a sensor and a detection base station. The sensor is formed by a spiral-shaped antenna connected to a compact Bluetooth transmitter. Breathing patterns were recorded in the case of female and male volunteers. Although the chest anatomy of females and males is different compared, the sensor’s flexibility allowed recording successfully a breathing rate of 0.3 Hz for the female and 0.5 Hz for the male, which corresponds to a breathing rate of 21 breaths per minutes (bpm) and 30 bpm, respectively.

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Section: Influence Of Conductive Medium: Frequency Shifts and Mechanimentioning

confidence: 90%

New Generation Wearable Antenna Based on Multimaterial Fiber for Wireless Communication and Real-Time Breath Detection

et al. 2018

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“…For the unloaded coil, the subject can be assumed as a zero‐conductivity material employed in the coil, and the subject resistance is assumed infinite large to represent this case. For the coil loaded with the lossy subject, the subject is assumed as a material with non‐zero conductivity, and it introduces a parasitic resistance with a certain value to the coil resistance 26,27 …”

Section: Theorymentioning

confidence: 99%

“…For the coil loaded with the lossy subject, the subject is assumed as a material with non-zero conductivity, and it introduces a parasitic resistance with a certain value to the coil resistance. 26,27 The power source part is composed of an ideal voltage source and a resistor with transmission line resistance. The magnitude of the voltage is V s , and the transmission line resistance is Z 0 .…”

Section: Theorymentioning

confidence: 99%

Individualized and accurate SAR characterization method based on equivalent circuit model for MRI system

Jiang¹,

Yang²,

Wang³

2022

Magnetic Resonance in Med

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Purpose To protect patients from RF heating in MRI scan, this work proposes an accurate and patient‐specific whole‐body specific absorption rate (SAR) characterization method based on an equivalent circuit model. Compared to the standard pulse energy method defined in NEMA MS 8‐2016, this method avoids the complexity of integrating flux loops and has the potential to be easily implemented in MRI scanners. Theory and Methods In this study, we use an equivalent parallel circuit to model the power distribution on the transmit coil and subject. The coil and subject equivalent resistances are fitted by the frequency response functions of reflection coefficient and are thereafter used to calculate the power ratio between them. To assess the accuracy of this method, we measured the subject absorbed power of 2 phantoms and 5 volunteers and compared it with the standard pulse energy method with flux loops. Results The resistances, resonant frequencies, and quality factors of the transmit coil are fitted with the equivalent circuit model in both unloaded and loaded conditions. Whole‐body SAR of 5 volunteers is measured at 2 different landmarks. In addition, the relationship between SAR and the working frequencies of the transmit coil is measured and analyzed. The subject absorbed power measured by the proposed method demonstrates good accuracy (RMS error and maximum error of 3.77% and 9.47%, respectively) relative to the flux loop method. Conclusion The equivalent circuit model‐based method enables individualized, accurate, and simplified SAR characterization for clinical applications and research with moderate implementation complexity.

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“…The similar tissue definitions are used for the whole body model as for the rectangular and cylindrical phantoms. The on-body operation is depicted in comparison with a planar UWB dipole [22], which is a relevant example of the antenna owning a dominant tangential polarization with a body surface. The E-field distributions are demonstrated along a body model by following the comparison of radiation pattern shape.…”

Section: Performance Close To a Whole Bodymentioning

confidence: 99%

Towards high on-body sensor node performance with the 3D antennas for IR-UWB WBANs

Tuovinen

Berg

Hämäläinen

et al. 2015

2015 9th International Symposium on Medical Information and Communication Technology (ISMICT)

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The present paper examines on-body performance in the range of wireless body area network (WBAN) antennas by investigating a channel path gain, the applicability for launching creeping waves and a radiation pattern shape in the proximity of human tissues. The focus of the study is to compare the performance of the designed 3D antennas with an example of a planar antenna, of which the majority of the wearable radiators are comprised in the open literature. The designed antennas are optimized for the impulse radio ultra wideband (IR-UWB) WBANs and targeted for on-body sensor node purposes. The radiator structures have low profiles in the fundamental modes as λ/7 (discone), λ/10 (monopole with a bent ground) and λ/5 (monopole with a cylindrical ground). The antennas cover the Federal Communications Commission (FCC) UWB regulations. It was demonstrated that the 3D antennas can efficiently launch body's surface wave propagation along a body surface in the longitudinal direction and around a body. The improvement of several tens of decibels over a planar antenna is able to obtain by the proper on-body design with a dominant normal polarization.

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Analysis of the Impedance Behaviour for Broadband Dipoles in Proximity of a Body Tissue: Approach by Using Antenna Equivalent Circuits

Cited by 8 publications

References 28 publications

New Generation Wearable Antenna Based on Multimaterial Fiber for Wireless Communication and Real-Time Breath Detection

New Generation Wearable Antenna Based on Multimaterial Fiber for Wireless Communication and Real-Time Breath Detection

Individualized and accurate SAR characterization method based on equivalent circuit model for MRI system

Towards high on-body sensor node performance with the 3D antennas for IR-UWB WBANs

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