P. P. Sarkar

Solution Treatment and Aging of Thick Rings from Titanium Alloy TI6AL4V

Rings from titanium alloy Ti6Al4V used for making pressure vessels for launch vehicles are studied after annealing and after solution treatment and aging. The mechanical characteristics of the rings after quenching and aging do not always have the specified values, especially in thicker sections. The studied rings are of two sizes and have a final wall thickness of 30.5 and 17.5 mm. The effect of the temperatures of solution treatment and aging, of the quenching rate, and of the section thickness on the mechanical properties is studied, and the process is updated to provide the required properties.

Processing and Characterization of Superinvar for Space Application

Material with ultra-low coefficient of thermal expansion (CTE) is required for mounting camera and other optical elements in satellite systems. Invar (64 Fe 36Ni) has been the work-horse material for this purpose. In recent years, modified version of conventional invar i.e. Superinvar with 5% cobalt (replacing 5% nickel) is being used to further bring down the errors in camera mountings due to thermal expansion. Processing of this alloy poses many challenges due to its requirement of ultra-low CTE. In the present work, melting and thermomechanical processing parameters were selected to meet the specified requirement of the alloy. The alloy was melted through vacuum induction melting process to obtain uniform and homogeneous chemistry and properties. Virgin raw material was used to achieve lowest carbon and manganese contents. Chemical composition thus obtained is found to be within the specification. Material was hot worked to refine the microstructure. Three different sizes of forged blocks were produced. Hot worked material was heat treated to obtain desirable and stable microstructure. Heat treatment cycle for stabilization was selected and used to retain carbon in the solution and minimize temporal growth. Mechanical properties (tensile strength and modulus of elasticity) and physical properties (CTE, thermal conductivity) were evaluated. Properties were found to be meeting the specification. It is observed that the material shows uniform single phase austenitic microstructure. The paper presents details of the process selection and challenges in processing of this alloy to obtain the targeted CTE < 0.6x10-6 per °C in the temperature range of 25°C to 150°C along with other desired mechanical properties.

Suppression and controlling of higher order modes in microstrip antenna with composite resonator

Suppression of higher order harmonic modes of the resonating frequency in a microstrip antenna has been proposed in the paper. Controlling harmonics in the microstrip antenna has been implemented by integrating composite resonators at the microstrip feed line which resulted in elimination of higher order modes occurring between the fundamental resonating frequency and the second harmonics of the microstrip antenna. The integration of the composite resonator in the microstrip feed line to suppress and control the higher order modes is the prime novelty of the paper.

Design and analysis of compact triangular microstrip antennas integrated with novel defective ground structure

In this paper triangular microstrip antenna with a novel defective ground structure are proposed. Without the defective ground structure (DGS) the structures are found to be resonant at 5.2 GHz. When the DGS are introduced a frequency shift of 5.2 GHz to 1.8 GHz is observed. The main essence of this paper is the miniaturization of the antenna.

Elimination of higher order modes in wearable microstrip antenna

Reduction of higher order harmonic modes of the fundamental operating frequency in a wearable microstrip antenna has been proposed. Controlling harmonics in the microstrip antenna has been implemented by integrating simple I shaped resonator at the microstrip feed line. As a result higher order modes occurring between the fundamental resonating frequency and the second harmonics of the wearable microstrip antenna have been successfully suppressed.