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

Syaiful Redzwan Mohd Shah; Jacob Velander; Parul Mathur; Mauricio D Perez; Noor Badariah Asan; Dhanesh G Kurup; Taco J Blokhuis; Robin Augustine

doi:10.3390/s18020636

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

Sensors (Basel). 2018 Feb 21;18(2):636. doi: 10.3390/s18020636.

Authors

Syaiful Redzwan Mohd Shah¹, Jacob Velander², Parul Mathur³, Mauricio D Perez⁴, Noor Badariah Asan⁵, Dhanesh G Kurup⁶, Taco J Blokhuis⁷, Robin Augustine⁸

Affiliations

¹ Microwaves in Medical Engineering Group, Solid State Electronics, Department of Engineering Sciences, Angstrom Laboratory, Uppsala University, Box 534, SE 75121 Uppsala, Sweden. Syaiful.Redzwan@Angstrom.uu.se.
² Microwaves in Medical Engineering Group, Solid State Electronics, Department of Engineering Sciences, Angstrom Laboratory, Uppsala University, Box 534, SE 75121 Uppsala, Sweden. Jacob.Velander@angstrom.uu.se.
³ Department of Electronics and Communication, Amrita School of Engineering, Amrita Vishwa Vidyapeetham, Bengaluru , 560035, India. p_mathur@blr.amrita.edu.
⁴ Microwaves in Medical Engineering Group, Solid State Electronics, Department of Engineering Sciences, Angstrom Laboratory, Uppsala University, Box 534, SE 75121 Uppsala, Sweden. mauriciodavidperez@gmail.com.
⁵ Microwaves in Medical Engineering Group, Solid State Electronics, Department of Engineering Sciences, Angstrom Laboratory, Uppsala University, Box 534, SE 75121 Uppsala, Sweden. noorbadariah.asan@angstrom.uu.se.
⁶ Department of Electronics and Communication, Amrita School of Engineering, Amrita Vishwa Vidyapeetham, Bengaluru , 560035, India. dg_kurup@blr.amrita.edu.
⁷ Department of surgery, Maastricht University Medical Center, PO Box 5800 6202 AZ Maastricht, The Netherlands. taco.blokhuis@mumc.nl.
⁸ Microwaves in Medical Engineering Group, Solid State Electronics, Department of Engineering Sciences, Angstrom Laboratory, Uppsala University, Box 534, SE 75121 Uppsala, Sweden. Robin.Augustine@Angstrom.uu.se.

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.

Keywords: Microwave measurement; electric field distribution; human lower extremity; model optimization; multilayered material; penetration depth; sensor; split-ring resonator; ultrasound measurement.