Srikanta Pal

Defect identification in friction stir welding using discrete wavelet analysis

Detection of fault occurred during friction stir welding.Analyzed using discrete wavelet transform on force and torque signals.Provides plot of frequency spectra vs. time with varying resolution.Variance and square of errors of detail coefficients of transformed signal are obtained to localize the defected zone. This article discusses on the detection of fault occurred during friction stir welding using discrete wavelet transform on force and torque signals. The work pieces used were AA1100 aluminum alloys of thickness 2.5mm. The plates were 200mm in length and 80mm in width. Presence of defect in welding causes sudden change in force signals (Z-load), thus it is easier to detect such abrupt changes in a signal using discrete wavelet transform. Statistical features like variance and square of errors of detail coefficients are implemented to localize the defective zone properly as it shows better variations (in defective area) than the detail coefficient itself.

A simple tuning method for high temperature superconducting microstrip filters

In this paper we report a simple tuning methodology of high temperature superconducting (HTS) microstrip filters. In order to establish this new tuning approach a 5 pole lumped element HTS bandpass filter, centre frequency 800 MHz, narrowband (bandwidth, 7.6 MHz), is designed and fabricated on a 2 inch (diameter) YBa2Cu3O6.94 thin film of thickness 700 nm and lanthanum aluminate (LaAlO3) substrate of 0.5 mm thickness. The filter was etched using conventional photolithography and a wet chemical etching process. The 5 pole lumped element filter is tested in an integrated RF-cryocooler measurement system at 65 K and also in liquid nitrogen (77 K). We demonstrate a 19.3 MHz downward shift of the centre frequency of the 5 pole filter response. This is achieved by overlaying two layers of thin dielectric tape (PTFE) (50.0 µ mt hickness, permittivity 3.2) ove rt he conducting patterned part of the filter surface. A full wave electromagnetic analysis of the dielectric environment of this tuning arrangement matches the measured response closely. To improve the passband response, the filter is tuned in liquid nitrogen, placing pieces of sapphire rods over the resonators of the filter layout.

Compact parallel coupled HTS microstrip bandpass filters for wireless communications

A practical design methodology for a compact parallel-coupled microstrip bandpass filter structure with steep attenuation is introduced using a computer-aided full-wave electromagnetic (EM) simulation based on the method of moments. The structure consists of an array of fully aligned half-wavelength spiral-meander-line resonators. Aimed at the application in the front-end receiver of digital cellular communication service, a 12-pole high-temperature superconductor filter with 2.27% fractional bandwidth (FBW) at 883.0 MHz was designed. In order to utilize the limited wafer area further, a 15-pole filter with 803.0-MHz center frequency, 2.25% FBW is precisely designed with greater EM simulation effort. Both the filters are fabricated using thallium-barium-calcium-copper-oxide thin films on a 2-in lanthanum-aluminate (LaAlO/sub 3/) wafer. The S-parameter measurements show a good agreement with the simulated results. At 70 K, the 12-pole filter shows less than 0.4-dB insertion loss, 0.3-dB passband ripple, and better than 12-dB return loss, and the 15-pole filter shows 0.25-dB insertion loss, 0.2-dB passband ripple, and better than 15-dB return loss. Out-of-band rejection for both the filters at 3 MHz below the passband edges is more than 60.0 dB. In order to estimate the power-handling capability of the filters, third-order intermodulation distortion was measured. A sensitivity analysis for the observed frequency shift in the filters is reported, which also shows very similar parametric dependence in both the filters. Also from this analysis, an approach for using the same deign in 0.5% FBW applications is discussed.

A compact, higher order, high temperature superconductor microstrip bandpass filter on a two-inch lanthanum aluminate substrate for personal communication service applications

A practical design methodology for a compact parallel-coupled microstrip bandpass filter structure with steep attenuation is introduced using a computer-aided full wave electromagnetic simulation based on the method of moments. The structure consists of an array of fully aligned half-wavelength spiral meander line resonators. Aimed at application in the front-end receiver of digital cellular communication service, a 12-pole high temperature superconductor filter with 2.27% fractional bandwidth at 883.0 MHz was designed. The filter is fabricated using thallium–barium–calcium–copper oxide (TBCCO) thin films on a two-inch lanthanum aluminate (LaAlO3) wafer. The S-parameter measurements show a good agreement with the simulated results. At 70 K, the 12-pole filter shows less than 0.4 dB insertion loss, 0.3 dB passband ripple, better than 12 dB return loss. The out of band rejection at 3 MHz below the passband edges is more than 60.0 dB. In order to estimate the power handling capability of the filter, the third-order intermodulation distortion was measured. A sensitivity analysis for the observed frequency shift in the filter is reported. Also from this analysis an approach for using the same design in 0.5% FBW applications is discussed.

A Quality of Service assured & faired MAC protocol for Mobile Adhoc Network

Mobile Adhoc Network (MANET) is a collection of mobile nodes with dynamic topology. Such networks are of interest because they do not require any prior investment in fixed infrastructure. Instead, the network nodes agree to relay each others packets and hence act as routers and automatically form their own cooperative infrastructure. The primary responsibility of a medium access control (MAC) protocol in Adhoc Network is the distributed arbitration for the shared channel for transmission of packets. The performance of Adhoc Network depends upon the sincerity of the MAC protocol. The MAC protocol of this type of network should be distributed, faired & free from hidden and exposed terminal problem. It should also support real-time traffic, transmission power control & be compatible with directional antennas. Researchers have proposed many MAC protocol for MANET, but none of them are simultaneously distributed, faired and support Quality of Service besides being distributed. In this paper a new MAC protocol has been proposed which supports quality of service and exhibit fairness and workable in a multihop environment.

Planar UWB Filter with Multiple Notched Band and Stopband with Improved Rejection Level

Abstract Analysis and realization of a microstrip-based planar ultra-wideband (UWB) filter with integrated multiple notch elimination property and simultaneously extended upper stopband is proposed. Initially, a UWB filter based on back-to-back microstrip-to-CPW technology is designed. Later, multiple spiral defected ground structures (DGS) are embedded to obtain multiple passband notches. Further, double equilateral U (DEU)-type DGS are used to improve upon the rejection level in upper stopband. The multiple passband notches are results of embedded spiral-shaped DGS (SDGS), while extended upper stopband is the outcome of suppressed higher-order spurious harmonics. The flexible dual-attenuation poles of DEU-shaped DGS suppress the stopband harmonics and widen the stopband. An approximate lumped equivalent circuit model of the proposed filter is modelled. The filter is compact and its layout measures 25.26 mm × 11.01 mm. The measured result is in good agreement with the full-wave electromagnetic (EM) simulation and circuit simulation.

EPCM – an efficient power controlled MAC protocol for mobile ad hoc network

To reduce interference and to save a significant amount of energy, a control of transmission power is employed in Mobile Ad hoc Network. Many researchers have reported numerous transmission power control schemes to achieve the objective. Some of those techniques use higher transmission power for control packets (Request To Send/Clear To Send) and lesser power for Data and ACK packets. These schemes, though save some amount of energy, achieve least aggregate throughput due to poor spatial reuse and hidden terminal interference. In this paper, an efficient Power Controlled Medium Access Control (EPCM) scheme is evinced, which uses uniform interference aware and minimum transmission power for both Control and Data packet. The performance of EPCM is evaluated and compared with three reported Medium Access Control protocols which are based on transmission power control schemes and is observed that the proposed protocol achieves better throughput and minimal energy consumption while avoiding the hidden terminal problem.

A faired quality of service assured MAC protocol for Mobile Adhoc Network

The primary responsibility of a medium access control (MAC) protocol in Adhoc Network is the distributed arbitration for the shared channel for transmission of packets. The performance of Adhoc Network depends upon the sincerity of the MAC protocol. The MAC protocol of this type of network should be distributed, faired & free from hidden and exposed terminal problem. It should also support real-time traffic, transmission power control & be compatible with directional antennas. Researchers have proposed many MAC protocol for MANET, but none of them are simultaneously distributed, faired and support Quality of Service besides being distributed. This paper proposes a new MAC protocol which is based on IEEE 802.11will address the QoS, fairness and multihop capability. Simulation was carried out to support quality of service from simulation it is observed that high prioritized traffics have larger throughput and transmission capability as comapared to the low prioritized traffics.

A Compact UWB Filter with Notched Band and Suppressed Stopband Using DGS

AbstractA microstrip-based Ultra-Wideband Bandpass Alter with a controllable notch and suppressed stopband is proposed. Dumbbell-shaped defected ground structure (DGS) etched in the ground and the double equilateral-U (DEU) DGS units under the input and output feeding lines provide the controllable notch and suppressed stopband, respectively. For optimum design of both the DGS (Dumbbell and DEU), a notch at WLAN frequency of 5.8 GHz and simultaneous stopband till 18 GHz is reported. Experimental results are in favor of the simulated data.

High Performance Wide Stopband Lowpass Filter Using Complementary Split Ring Resonators as Defected Ground Plane

A novel design of a wide stopband, microstrip technology based low pass filter using defected ground plane is reported in this paper. The filter structure has varied dimensions of periodic complementary square split ring resonator (CSSRR) in the ground plane. The periodic arrangement of non-uniformly spaced CSSRR units in the defected ground structure (DGS) provides sharp cutoff frequency and wide stopband behavior. The optimized design has stop bandwidth (2 to 8 GHz) around four times the cutoff frequency. Improvement in stop bandwidth of CSSRR based design is compared with that of the square-split-ring-resonator (SSRR) and non-uniformly Dumbbell shaped DGS resonator based design. An improved Slow-wave factor is found as compared to Dumbbell shaped DGS.