Browsing by Author "Sandeep Kumar"

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Design and Development of Bio-Compatible Miniaturized Antenna for Wireless Neural Monitoring
(National Institute of Technology Karnataka, Surathkal, 2024) Gopavajhula, Suryachand ,D.; Sandeep Kumar; V.Narasimhadhan A.
The findings of various investigations have unveiled that chronic diseases are the primary factor contributing to mortality among the elderly population worldwide. Consequently, there is a need to revamp public healthcare systems using emerging technology to address this issue. Swift diagnosis and perpetual monitoring of patients is best possible solution especially in the case of chronic diseases. But it is impractical for patient to visit diagnostic centres on a regular basis for continuous monitoring. The inclusion of body area networks (BAN) functioning within the vicinity of patients could provide a way to meet such demand. BAN networks contain implantable medical devices (IMDs) and external interrogator units which coordinate with IMDs in the collection of data. IMDs through sensors for the acquisition of various physiological parameters of the patients through deployment near or even inside the patient’s body in a few cases. However, powering such devices with minimal discomfort to patients is a tough ask for researchers. Hence, main focus of this research work is to design and develop an antenna for passive neural monitoring with the implant using mixer which operates with no power. The proposed antenna aids in making the the implant size smaller to enhance the patient’s comfort. Firstly, a comprehensive literature survey was undertaken to explore the different methodologies proposed by researchers for the implementation of an antenna in neural implants. Various approaches to power the implant, including the utilization of power cables, batteries, and RF power harvesting, passive monitoring using microwave back scattering were studied. Among these, the microwave back scattering technique, employing an Anti Parallel Diode Pair (APDP), emerged as the preferred choice due to its ability to make the harmonic mixer fully passive, thereby reducing the overall power requirement of the implant. In order to effectively work with the harmonic mixer, the antenna needs to resonate at harmonic frequencies. The key attributes of a neural implant antenna were identified as dual band operability, low profile, compact size, and bio-compatibility. Secondly, a Vivaldi antenna was developed to operate in two frequency bands with harmonic resonant frequencies, resulting in a highly directive end fire radiation pattern. However, in order to achieve these desired characteristics, the antenna had a maximum dimension of 35 mm. To address this limitation, a miniaturized antenna was designed using a modified micro-strip patch structure. This new design had a compact size of 15.5 mm x 13 mm while still achieving the optimum frequency and radiation characteristics. Due to its smaller size, the peak gain of the antenna in the lower and higher resonant bands was only 0.98 and 1.09 dB, respectively. As a result, further refinement of the antenna design was necessary. Thirdly, a tiny hat-shaped antenna with a defected ground was developed to meet the specific requirements of a neural implant antenna. To ensure its bio-compatibility, the antenna was covered with a dielectric polymer material (PDMS) and its performance was evaluated in both in-vitro and in-vivo setups during experimentation. The antenna exhibited an impedance bandwidth of 1.15 GHz, supporting high data rates, and achieved a directive gain of 1.29 dB at 3.84 GHz and 1.39 dB at 7.68 GHz. Finally, a miniature antenna measuring 9 mm x 11 mm was designed with elliptical resonators to enable dual-band functionality. The two elliptical resonators allowed the antenna to receive at 7.15 GHz and transmit at 14.3 GHz. The antenna’s impedance bandwidths of 1 GHz and 1.45 GHz facilitated communication at higher data rates. With peak gain values of 1.7 dBi and 2.2 dBi, the link budget was calculated considering data rates of 1 Mbps and 20 Mbps. To evaluate the Specific Absorption Rate, the antenna was simulated within a six-layer head model with a penetration depth of 10 mm. The performance metrics were compared, leading to necessary modifications to enhance the antenna’s capability and overall implant performance.
Robust Design Approach Towards GaN HEMT RF Front End Amplifier for High Power Transceivers
(National Institute of Technology Karnataka, Surathkal, 2024) Gupta, Manishankar Prasad; Sandeep Kumar
This research work focuses on the design and implementation of Gallium Nitride High Electron Mobility Transistor (GaN HEMT) based Microwave Low Noise Amplifiers (LNAs) and Power Amplifiers (PAs) with novel techniques for modern wireless broadband and dual-band communications. The Low Noise Amplifiers account for the majority of the system’s Noise Figure, while Power Amplifiers account for most of the high output power. As a result, front-end designs are being researched to improve the device’s signal to noise ratio (SNR) with highly linear output power. The primary objective of the proposed front-end is to produce low NF, small and large signal flat gain, excellent linearity, high efficiency, and high i/o power while minimum power consumption at the ultra-high frequency to microwave bands of operation. Firstly, a performance analysis of the GaN HEMT based low noise amplifier (LNA) using even-odd mode matching techniques has been developed. The proposed GaN LNA circuit provides a high input/output (i/o) power, and ultra-low noise over wideband ranging from 0.5 to 2.7 GHz with fractional impedance bandwidth of 138%. The proposed LNA circuit with the incorporation of input/output broadband stages relaxes 50Ω matching constraints and achieves high input and output power with good stability. The proposed LNA achieves a simulated/measured gain of 16dB/17dB. An ultra-low noise figure of 0.6 dB flat is achieved over a wideband. In addition, the high output power is achieved at 40dBm while input power is 25dBm. The fabricated GaN HEMT LNA circuit has consumed power of 120 mW. The area of the fabricated RF GaN HEMT LNA is 32 × 26 mm2 . Secondly, a GaN HEMT device to circuit approach towards LNA using defective ground bias (DGB) technique has been developed. This is the first MMIC GaN HEMT LNA design to offer dual-bands of operation in both L and S-bands to the author’s best knowledge. The proposed 0.15-μm GaN HEMT device is fabricated using slot radiation phenomenon, which achieved a high output power of 20W. To achieve an optimal noise, high i/o power, and almost flat gain at both L and S-band, the defective ground structure of bias topologies is modelled and optimized. An artificial ground defect is created to offer resonant properties, which utilizes frequency-selective properties to improve the performance of the LNA circuit. The dedicated LNA shows the benefits of compact size, extremely low noise figure of 0.74/1.6 dB, and high output power of 44 dBm. The compact GaN HEMT LNA could overcome the weak signal strength received by RF receivers for modern wireless communication systems. Thirdly, a high efficiency Rat-Race coupler (RRC) based compact GaN HEMT PA design over broadband has been developed. The RRC integrated PA design is proposed for the first time as per author best knowledge. The design methodology used a higher order two open stubs and a rat-race coupler (RRC) at i/o sections to control harmonics impedances. As a proof of concept, a PA is fabricated using a monolithic microwave integrated circuit (MMIC) with 0.15 μm gallium nitride high electron mobility transistor (GaN HEMT) process. The measured result shows that the designed PA achieves a flat power added efficiency (PAE) of 65% - 74 %, output power (Pout) of 44.8 dBm - 46 dBm, and drain efficiency (DE) of 72% - 85 %, over a record wide frequency of 1.8 GHz - 3.6 GHz, which is the highest one among all reported harmonic tuned PAs. Finally, a highly stable PA with three operating bandwidth points has been presented. A unique multi-harmonics-controlled network with three-paths impedance matching structure and proper bias topologies are combined to achieve excellent performance in terms of operating bandwidth, efficiency, and high i/o power. A buffer stage of impedance matching is generated by proposed three paths to reducing the harmonics, promoting the targeted fundamental bandwidth. To verify the methodology, a wideband PA is implemented with a 25-W wolfspeed Cree model CG2H40025F GaN HEMT device. The implemented PA is simulated and post-simulated, which provide a fractional bandwidth of 67 % over the frequency of 2 to 4 GHz, with DE of 54-65 %, PAE of 47-52 %, saturated output power of 43.1-44.6 dBm, and a gain of 7.1-9.5 dB. The above results show that PA realized by the proposed novel method is suitable for modern wireless applications. All the proposed GaN HEMT LNAs and PAs are fabricated using a MIC/MMIC process under the supply of 28V. The design of experiment (DoE) and statistical analysis are additional novel contributions towards robust proposed front-end amplifiers in this work. DoE is a new analysis technique to find the individual device parameter’s contribution to the final gain, NF, and return loss. Statistical analysis is also performed to find the yield so that the robustness of the proposed designs is satisfied. A novel harmonically controlled impedance matching techniques are used to design and analyze PAs.