Liton Chandra Paul

An investigation of SAR inside human heart for antenna directivity, surface current variations and effect on antenna frequency in presence of heart

In this work, the impact of human heart on an 800 MHz inset fed rectangular microstrip patch antenna characteristics were investigated using CST Microwave Studio. The antenna was simulated over a mimic human heart muscle and the distance between them was varied to analyze the changes in Specific Absorption Rate (SAR) upon antenna performance parameters (specifically, directivity & surface current) for discreet and waveguide port feeding. The results exhibited that the center frequency of the antenna was shifted to lower value and an increase in SAR values when the antenna was closer to heart for both the feeding techniques. However, the discrete port had more values of SAR than the waveguide port but for both cases SAR decreased with the increment of antenna distance from heart. SAR values for up to 4 mm distance in between the antenna and human heart did not satisfy IEEE and ICNIRP standards. For increasing surface current, the SAR values decreases due to less penetration of flux inside the tissue for both feeding techniques. Increasing directivity resulted decrement of SAR values due to the fact that more reflection of the wave from the tissue happened for more directivity. This work demonstrates how mobile phone antennas of GSM band affect human heart and how human heart affects antenna resonance frequency when mobile phones are kept in chest pocket.

Total efficiency comparison of different shaped microstrip patch antennas having Defected Ground Structure

In this paper, 15 different shaped (E, F, inverted F, G, H, I, L, inverted L, S, T, inverted T, U, inverted U, W and inverted W) conventional microstrip patch antennas along with a dumbbell (H) shaped Defected Ground Structure (DGS) in each are designed and simulated at 2.4 GHz operating frequency using CST Microwave Studio Suite. The efficiency of microstrip patch antennas are compared in terms of surface wave concept and the antenna with H shaped patch exhibiting total efficiency of -2.546 dB is found most efficient. The implementation of this work is highly anticipated to be employed for designing hybrid shaped patches for WLAN, wireless network (Wi-Fi and Bluetooth), nonstandard RF remote, ISM band applications.

Effect of human body on an 800 MHz inset fed rectangular microstrip patch antenna characteristics

This work demonstrates the impact of human body on an 800 MHz inset fed rectangular microstrip patch antenna characteristics. The antenna was simulated over a human phantom model consisting human thigh muscle using CST Microwave Studio. The distance between the antenna and human thigh muscle was varied to analyze the changes in antenna performance for waveguide port feeding. The results exhibited significant changes in antenna characteristics, especially the shifting of center frequency to a lower value due to the human body. Specific Absorption Rate (SAR) was studied as well to illustrate how on-body communication or mobile phone antennas of GSM band might affect human body when mobile phones are kept in pants pocket.

Nonlinear adaptive backstepping controller design for grid currents regulation of a CSI based PV system with external disturbances

In this paper, a nonlinear adaptive controller for regulating the grid of a current source inverter (CSI) based three-phase grid-connected photovoltaic (PV) system is proposed. The proposed control structure is composed with an outer control loop-responsible for controlling the DC-side inductor current and the inner current control loop-responsible for controlling injected current into the utility grid. The proposed adaptive controller is designed recursively by considering external disturbances within the system and these unknown external disturbances are estimated through the adaption laws. The overall stability of the whole CSI based three-phase grid-connected PV system is verified by formulating the control Lyapunov functions (CLFs) at different stages throughout the design process of the proposed controller. Finally, the performance of the designed controller is tested on a similar CSI based three-phase grid-connected PV system under different atmospheric conditions. Simulation results demonstrate that the proposed control scheme can effectively meet the desired control objectives as compared to the existing controller in terms of settling time and power quality.

Robust adaptive backstepping controller design for PWM based DC-DC buck converter based on projection method

DC-DC power converter is a most important power source for driving a DC system in contemporary power electronic systems. However, owing to the time-varying and nonlinear characteristics of load resistance, it is often very challenging issue to ensure the stability of such converters. This paper is concerned about the regulation of the output voltage of a DC-DC buck converter using a nonlinear robust adaptive technique. The proposed controller is designed recursively based on the Lyapunov theory where the load resistance is considered as an unknown parameter. This unknown load resistance is estimated through the parameter adaptation law based on the projection method. Note that the projection method is a robustness augmentation technique that bounds the unknown parameter variations in a convex set which confirm through the formulation of control Lyapunov functions (CLFs) at different stages. The advantages of the proposed controller are that it can provide robust performance against external turbulence and also conquer the over-parameterization difficulty. At last the usefulness of the designed controller is verified through simulation results and compared with an existing controller. From the simulation results, it is obvious that the designed controller provides a significant performance improvement than the existing controller in terms of settling time and fast tracking desired output voltage.

Nonlinear adaptive backstepping controller design for trajectory flight control of UAHs

Considering the external disturbances, this paper proposes a new control approach, with the intention of improving the trajectory flight control in the longitudinal-lateral trajectory plane with constant altitude, to design a nonlinear adaptive controller for an unmanned autonomous helicopter (UAH). The unknown external disturbances are considered within the system model and estimated through adaption laws and incorporated with the control law to attest the robustness property of the intended control scheme. The designed controller is able to provide the robustness property against external turbulences as well as can overcome the over-parameterization problem which generally emerges in some conventional adaptive methods. To prove the convergence of longitudinal and lateral dynamics to a desired equilibrium point, in every stage of the design procedure a control Lyapunov function (CLF) is formulated and stability of the whole system is proved through the negative definiteness of the derivative of CLF. Finally, the performance of the proposed controller is verified in a MATLAB/SIMULINK model in the presence of external turbulence into the system. The robustness of the proposed controller, in terms of rejecting external disturbances, is illustrated through the simulation results.

Adaptive controller design for speed control of DC motors driven by a DC-DC buck converter

A nonlinear adaptive controller for controlling the desired velocity of DC motors driven by DC-DC buck converters is proposed in this paper. The proposed controller is designed recursively based on the control Lyapunov function (CLF) to assure the desired control performance under varying the load torque of the DC motor as well as by considering the system parameters as unknown. These unknown parameters along with unknown load torque are estimated using the adaptation laws and incorporated in the control law to enhance the robustness of the proposed controller. To prove the speculative stability of the whole system, the CLFs are formulated at different stages during the design process of the controller. Another key attribute of the proposed adaptive control scheme is that it can overwhelm the over-parameterization problems of unknown parameters which generally come out in some conformist adaptive backstepping methods. Finally, the helpfulness of the proposed control scheme is demonstrated through the computer simulation results and performance of the designed controller is also compared with an existing adaptive backstepping controller.

RF absorption in biological tissue at varying distances and angles and rapport to tissue impedance

Exposure of the general public to low-level RF fields causes direct or indirect coupling of the fields in the human body. Due to this coupling, there is an induction of the fields inside the body tissue that causes currents in the tissue while the tissue absorbs RF power. In this work, the RF absorption by a biological tissue was measured by using an antenna trainer in a laboratory set up by varying distances and angles of RF radiation source. Using the detector current, the absorbed power by the tissue as well as the incident component of Electric field upon the receiving antenna was calculated with and without the tissue. From calculating rms value of the field, the voltage inside the tissue was estimated. Using the absorbed power and voltage inside the tissue, the impedance inside the tissue was calculated. Results indicated that the more impedance values inside the tissue incur more absorption of RF power. The more dominant effects for angles than the distances were obtained for absorbed power by the tissue.

Robust nonlinear adaptive backstepping controller design for unmanned autonomous vehicles

A robust nonlinear adaptive controller design for unmanned autonomous vehicles (UAVs) for controlling the hovering flight is presented. The controller is premeditated recursively based on the control Lyapunov theory where the mass of the UAV in the model is considered as anonymous parameter. To illustrate the forcefulness property of the designed controller, the effects of external disturbances are also considered in the UAV dynamical model throughout the devise of the controller. The unknown parameter (mass) is estimated using the adaptation law and incorporated in the final control law and then the overall immovability of the UAV system is confirmed by forming the negative semi-definiteness of Lyapunov functions. Note that the designed controller is adaptive to the mysterious parameter of the UAV and robust to external disturbances. Finally, the designed controller performance is experienced using a MATLAB simulation model under hovering flight condition and the performance is also compared with an existing nonlinear robust adaptive backstepping controller. The simulation results illustrate the sturdiness of the designed controller as compared to the existing nonlinear robust controller in terms of declining exterior wind gusts.