Human Body Effects on RF Electronics
Alam, Shahed (2013)
Alam, Shahed
2013
Master's Degree Programme in Electrical Engineering
Tieto- ja sähkötekniikan tiedekunta - Faculty of Computing and Electrical Engineering
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Hyväksymispäivämäärä
2013-08-14
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi:tty-201308211290
https://urn.fi/URN:NBN:fi:tty-201308211290
Tiivistelmä
Wireless sensors require radio frequency (RF) circuits to operate at close proximity to the human body. For successful design of body worn applications of electronics the study of the effect of human body on RF interconnects and simple RF circuits has been undertaken through measurements and simulations in the frequency band of 50 MHz to 9 GHz. Coplanar waveguide (CPW) transmission lines are adopted to commence the investigation. The fact that in CPW structures the ground resides in the same plane as the signal trace enables the fabrication of thin structures apt for constructing. The test structures have been fabricated using inkjet technology which being an additive and low temperature process enables the printing of transmission lines and circuit structures at which in turn enables the fabrication of test structures on thin flexible Polyethylene naphthalate (PEN) substrate. In order to discern the effect of muscle on the RF interconnections, distributed parameters, effective relative permittivity, effective loss tangent, attenuation constant and characteristic impedance are extracted using a multiline extraction process. The extraction method was also used to successfully separate the dielectric and conductor losses.
The simulations have been performed using the AWR Microwave Office commercial RF simulator. The validity of the simulations and measurements has been assessed with the agreement of the simulations with measurements. It is deduced from simulations and measurements that above 1 mm distance the losses become equal to that of free space and at 0.5 mm gap losses are close to free space as well. However, when the distance is less than 0.5 mm the losses are significant. In order to mitigate the effect of body on RF interconnects narrow gap width and center line width should be used above 4 GHz. Bending the RF interconnects did not produce any significant change in the scattering parameters of the coplanar wave guide transmission lines, illustrating that bends do not detune the circuit performance considerably.
The effect of body on the RF circuits is analyzed using simple RF circuits of different sizes. Multiline Thru-Reflect-Line calibration has been used to extract scattering parameters of the discrete components used in the circuits. The on body simulations with AWR library components and extracted discrete component values reveal that as the length of the circuit is increased the measured components provided better convergence with measured results. The experiments performed illustrate that body has significant effect on the RF interconnects and RF circuits and the effects needs to be taken in account for proper performance of the RF circuits. The findings from the investigations are used to attain guidelines for body worn electronics design.
The simulations have been performed using the AWR Microwave Office commercial RF simulator. The validity of the simulations and measurements has been assessed with the agreement of the simulations with measurements. It is deduced from simulations and measurements that above 1 mm distance the losses become equal to that of free space and at 0.5 mm gap losses are close to free space as well. However, when the distance is less than 0.5 mm the losses are significant. In order to mitigate the effect of body on RF interconnects narrow gap width and center line width should be used above 4 GHz. Bending the RF interconnects did not produce any significant change in the scattering parameters of the coplanar wave guide transmission lines, illustrating that bends do not detune the circuit performance considerably.
The effect of body on the RF circuits is analyzed using simple RF circuits of different sizes. Multiline Thru-Reflect-Line calibration has been used to extract scattering parameters of the discrete components used in the circuits. The on body simulations with AWR library components and extracted discrete component values reveal that as the length of the circuit is increased the measured components provided better convergence with measured results. The experiments performed illustrate that body has significant effect on the RF interconnects and RF circuits and the effects needs to be taken in account for proper performance of the RF circuits. The findings from the investigations are used to attain guidelines for body worn electronics design.