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Sensors 2018, 18(2), 636; https://doi.org/10.3390/s18020636

Split-Ring Resonator Sensor Penetration Depth Assessment Using In Vivo Microwave Reflectivity and Ultrasound Measurements for Lower Extremity Trauma Rehabilitation

1
Microwaves in Medical Engineering Group, Solid State Electronics, Department of Engineering Sciences, Angstrom Laboratory, Uppsala University, Box 534, SE 75121 Uppsala, Sweden
2
Department of Electronics and Communication, Amrita School of Engineering, Amrita Vishwa Vidyapeetham, Bengaluru , 560035, India
3
Department of surgery, Maastricht University Medical Center, PO Box 5800 6202 AZ Maastricht, The Netherlands
*
Authors to whom correspondence should be addressed.
Received: 12 January 2018 / Revised: 14 February 2018 / Accepted: 19 February 2018 / Published: 21 February 2018
(This article belongs to the Special Issue Non-Invasive Biomedical Sensors)
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Abstract

In recent research, microwave sensors have been used to follow up the recovery of lower extremity trauma patients. This is done mainly by monitoring the changes of dielectric properties of lower limb tissues such as skin, fat, muscle, and bone. As part of the characterization of the microwave sensor, it is crucial to assess the signal penetration in in vivo tissues. This work presents a new approach for investigating the penetration depth of planar microwave sensors based on the Split-Ring Resonator in the in vivo context of the femoral area. This approach is based on the optimization of a 3D simulation model using the platform of CST Microwave Studio and consisting of a sensor of the considered type and a multilayered material representing the femoral area. The geometry of the layered material is built based on information from ultrasound images and includes mainly the thicknesses of skin, fat, and muscle tissues. The optimization target is the measured S11 parameters at the sensor connector and the fitting parameters are the permittivity of each layer of the material. Four positions in the femoral area (two at distal and two at thigh) in four volunteers are considered for the in vivo study. The penetration depths are finally calculated with the help of the electric field distribution in simulations of the optimized model for each one of the 16 considered positions. The numerical results show that positions at the thigh contribute the highest penetration values of up to 17.5 mm. This finding has a high significance in planning in vitro penetration depth measurements and other tests that are going to be performed in the future. View Full-Text
Keywords: Microwave measurement; ultrasound measurement; split-ring resonator; penetration depth; human lower extremity; sensor; model optimization; multilayered material; electric field distribution Microwave measurement; ultrasound measurement; split-ring resonator; penetration depth; human lower extremity; sensor; model optimization; multilayered material; electric field distribution
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Mohd Shah, S.R.; Velander, J.; Mathur, P.; Perez, M.D.; Asan, N.B.; Kurup, D.G.; Blokhuis, T.J.; Augustine, R. Split-Ring Resonator Sensor Penetration Depth Assessment Using In Vivo Microwave Reflectivity and Ultrasound Measurements for Lower Extremity Trauma Rehabilitation. Sensors 2018, 18, 636.

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