Search results

A new process called direct ceramic machining was successfully applied for the fabrication of dental restorations and technical components. It uses prefabricated, easy to machine ceramic blanks. The shape of a ceramic component is machined with enlarged contours to compensate for the sintering shrinkage. Afterwards the machined component is sintered to full density and thereby shrinks to its final dimensions. Technical components from 5 to 100 mm in size possessing features of 1/10th mm to several millimeters and dental restorations were fabricated sucessfully, and thus demonstrate the capability for rapid production of ceramic functional prototypes. The dimensional accuracy is about 20 μm with a relative accuracy of 0.1 per cent of the component's length. Thus accurate net‐shape of the components could be achieved without hard machining.

The purpose of this paper is to present the high-frequency performance of 0.13-μm n-type metal-oxide-semiconductor (NMOS) transistors with various multi-finger configurations for implementation in millimeter-wave (mm-wave) frequency.

A folded-like double-gate transistor layout is designed to enable the transistor to work in the mm-wave region. Different sizes of transistors with variation in finger width (W_F ) and number of fingers (N_F ) were fabricated to determine the optimum size of the transistor. The extrinsic parasitic elements of selected transistors were extracted and investigated. The radio frequency (RF) performance of these samples were then analyzed and compared.

The proposed layout performed well with the highest maximum oscillation frequency (f_max ) achieved at 122 GHz. Based on the comparison done, the optimum W_F obtained for the layout is at 2.0 μm. It is found that the extrinsic parasitic capacitance is more dominant than the parasitic resistance in affecting the f_max . In s-parameter analysis, it is observed that the transistor with the least N_F has smaller variance in small-signal gain throughout the measurement frequency. The maximum stable gain for the samples is also found to be roughly similar and independent of N_F .

A new layout structure for an NMOS transistor that works in mm-wave frequency is proposed. Experimental analyses presented here cover for both N_F and W_F , unlike others which focus on either N_F or W_F only.

This paper aims to propose a laser micro-machined 4 × 4 elements microstrip array antenna suitable for 5 G millimeter wave (mm-wave) applications. Each patch element of the array is excited with same amplitude and phase that is achieved with proper novel impedance matching stub. The proposed antenna achieves a simulated gain of 13.15 dBi and a measured return loss of −24.80 dB at 28.73 GHz with a total bandwidth of 7.48 GHz. The designed antenna is directional with a directivity of 15.1 dBi at 28.73 GHz, whereas fabricated on a low cost FR4 substrate with a substrate thickness of 0.074 λ mm. The antenna is realized with an aperture size of 2.24λ × 3.26λ.

The antenna structure starts from the design of single element called unit cell. The single element is designed using the transmission line model equations of a rectangular patch. To design a 28 GHz microstrip patch antenna, a dielectric material with lower permittivity and having thickness (h) less than 1 mm is required. This specification gives better gain and efficiency by reducing surface waves and mutual coupling between elements. The inset width is optimized to achieve the minimum reflection coefficient (S11). The single element has been arranged with a minimum spacing of λ/2 (5.3571 mm) in an H plane and E plane. It is connected using the microstrip lines with proper impedance matching. The four 2 × 2-sub array cell subsystems are connected with a corporate feed together formed the 4 × 4-array cell. Rectangular planar array method is used to arrange the elements in the 4 × 4 array cell.

The design concept is simple which includes the combination of corporate feed and insect feed. It is compact in size and easy to fabricate. The bandwidth of fabricated prototype antenna array is achieved as 7.48 GHz from 24.98 GHz to 32.46 GHz. The mutual coupling is very less though the antenna array is placed with minimum spacing between adjacent elements. This is because of the microstrip feeding structure with minimum phase shift. The gain can be further enhanced with increasing number of array element and proper designing of feed line. Owing to the advantages of low profile, wide bandwidth and high gain, the designed array will be potentially useful in 5 G wireless communications.

The measured antenna offers bandwidth 7.48 GHz (24.98 GHz-32.46 GHz) with centered frequency 28.73 GHz. The agreement between simulated and measured results is good. The VSWR is observed 0.32 < 2, offers good impedance matching and low mutual coupling. It gives better E-Field and H-field radiation patterns of the 4 × 4 array antenna structure at 28 GHz. The total gain of 13.14 dBi is achieved at the center frequency. The total efficiency of 63.42 per cent is achieved with FR4 substrate.

The aim of this paper is to optimize the machining parameters to obtain the smallest average surface roughness values during drilling of the carbon fiber-reinforced polymer (CFRP) composite material with abrasive water jet (AWJ) and analyze the damage of the delamination.

CFRP composite material had been fabricated having fiber orientations frequently used in the aerospace industry (0°/45°/90°/−45°). Three different stand-off distances (1, 2 and 3 mm), three different water pressures (1,800, 2,800 and 3,800 bar) and three different hole diameters (4, 8 and 12 mm) were selected as processing parameters. The average surface roughness values were obtained, and delamination damage was then analyzed using Taguchi optimization. Drilling experiments were performed using the Taguchi L₂₇ orthogonal array via Minitab 17 software. The signal/noise ratio was taken into account in the evaluation of the test results. Using the Taguchi method, the control factors giving the mean surface roughness values were determined. Analysis of variance was performed using the experimental results, and the effect levels of the control factors on the average surface roughness were found.

It was found that water pressure and hole diameter had a higher effect on average surface roughness, while water pressure and stand-off distance were effective on delamination.

Owing to their excellent thermal and mechanical properties, the CFRP composite materials show greater potential for their applications in aircraft and aerospace industry.

The novel approach is to reduce cost and spent time using Taguchi optimization as a result of AWJ drilling the material in this fiber orientation ([0°/45°/90°/−45°]_s, which is often used in the aerospace industry).

In this paper, a flexible solution for part feeding in assembly is analysed for its suitability to feed small parts with typical dimensions between 0.5 and 5.0 mm. The feeding concept is based on a tooling plate, which vibrates to separate and reorient the parts. A vision system is used to determine the position of parts in a correct orientation. A robot picks these parts and assembles them. The conditions for a successful reorientation of parts are studied. The influence of adhesive forces on the ability to re‐orientate is investigated. A prototype is built to determine empirically the magnitude of the adhesive forces and the influence of these forces on the feeding process.

The effect of increasing lip thickness (LT) and Mach number on subsonic co-flowing Jet (CFJ) decay at subsonic and correctly expanded sonic Mach numbers has been analysed experimentally and numerically in this study. This study aims to a critical LT below which mixing enhances and above which mixing inhibits.

LT is the distance, separating the primary nozzle and the secondary duct, present in the co-flowing nozzle. The CFJ with LT ranging from 2 mm to 150 mm at jet exit Mach numbers of 0.6, 0.8 and 1.0 were studied in detail. The CFJ with 2 mm LT is used for comparison. Centreline total pressure decay, centreline static pressure decay and near field flow behaviour were analysed.

The result shows that the mixing enhances until a critical limit and a further increase in the LT does not show any variation in the jet mixing. Beyond this critical limit, the secondary jet has a detrimental effect on the primary jet, which deteriorates the process of mixing. The CFJ within the critical limit experiences a significantly higher mixing. The effect of the increase in the Mach number has marginal variation in the total pressure and significant variation in static pressure along the jet axis.

In this study, the velocity ratio (VR) is maintained constant and the bypass ratio (BR) was varied from low value to very high values for subsonic and correctly expanded sonic. Presently, commercial aircraft engine operates under these Mach numbers and low to ultra-high BR. Hence, the present study becomes essential.

This is the first effort to find the critical value of LT for a constant VR for a Mach number range of 0.6 to 1.0, compressible CFJ. The CFJs with constant VR of unity and varying LT, in these Mach number range, have not been studied in the past.

Meal left after extraction of microalgae functional compounds is not finding its application in food. Hence, present study was aimed for the development of the cookies supplemented with meal of microalgae Chlorella sp. (Abca-17) obtained after solvent extraction of chlorophyll.

Cookies were prepared by substituting refined wheat flour (RWF) with microalgae meal (MM) at incorporation levels of 3, 6, 9 and 12 per cent. The effect of replacement of RWF with MM was analyzed on the pasting properties of the flour blends and physical, chemical, sensory and textural characteristics of the cookies.

MM exhibited high water and oil absorption capacity of 0.8 g/g and 1.2 g/g, respectively. Weight and thickness of the cookies increased, whereas the diameter, spread ratio and spread factor decreased with the increased proportion of meal in flour blends. The moisture and ash content (0.8-2.0 per cent) of the cookies increased, whereas fat content showed no pronounced variation. Sensory evaluation of cookies revealed no significant difference at 6 per cent level of incorporation and further supplementation resulted in dark colour and increased hardness. Texture profile analysis of cookies also revealed that the peak positive force for breaking the cookies increased (3115.6-7372.1 N) with increase in the level of incorporation of meal.

MM can be used in the development of the cookies at level of incorporation of 6 per cent and presents novice approach for utilization of bioprocessing waste.

The present study is a pioneer effort in demonstration of utilization of MM as alternate food ingredient. MM of Chlorella sp. (Abca-17) was characterized as food ingredient using physicochemical analysis and model food system using cookies.

The purpose of this paper is to evaluate the model of a rear pressure bulkhead with different design optimizations to meet the pressurized cabin requirements of an aircraft.

This paper presents the results of the static analysis of a dome-shaped rear pressure bulkhead model designed in Catia-v5. Numerical analysis of model meshed in hyper-mesh and solved using Opti-Struct for iterative design optimizations.

All the iterative models are analyzed at 9 Psi. Rear pressure bulkhead designed with L-section stringer shows better results than the model optimized with T-section stringer for the same thickness. The model optimized with L-shaped stinger also reduces the weight of the bulkhead without affecting the structural integrity.

It has been concluded in this paper that the selection of specific shapes of the stringers shows a significant influence on weight reduction.

This paper provides a topical, technical insight into the design and development of a rear pressure bulkhead. It also outlines the future development of dome-shaped rear pressure bulkhead.

To report on the evaluation of error of a face matching system consisting of a 3D sensor for obtaining the surface of the face, and a two‐stage matching algorithm that matches the sensed surface to a model surface.

Rigid mannikin face that was, otherwise, fairly realistic was obtained, and several sensing and matching experiments were performed. Pose position, lighting and face color were controlled.

The combined sensor‐matching system typically reported correct face surface matches with trimmed RMS error of 0.5 mm or less for a generous volume of parameters, including roll, pitch, yaw, position, lighting, and facecolor. Error accelerated beyond this “approximately frontal” set of parameters. Mannikin results are compared to results with thousands of cases of real faces. The sensor accuracy is not a limiting component of the system, but supports the application well.

The sensor supports the application well (except for the current cost). Equal error rates achieved appear to be practical for face verification.

No similar report is known for sensing faces.

A fiber Bragg grating (FBG) sensor was designed to measure the door gap of automobile bodies.

The gap sensor was designed through a combination of the sliding wedge and cantilever beam, involving a magnetic force installation and arc structure of the force transmission point. Moreover, the sliding block adopted an anti-magnetic and wear-resistant material and the temperature compensation of the two FBGs was conducted. The magnetic force and contact stress of the sensor were examined to ensure that the sensor exhibited a certain magnetic attraction force and fatigue life. The performance of the gap sensor was examined experimentally.

The sensor could measure gaps with dimensions of 5 mm to 11 mm, with a sensitivity and measurement accuracy of 150.9 pm/mm and 0.0063% F.S., respectively. Moreover, the sensor exhibited a small gap sensitivity, with a repeatability error of 0.15%, anti-creep properties and magnetic interference abilities.

The sensor is compact and easy to install, as well as use for multiple sensor locations, with a maximum size of 43 mm, a mass of 26 g and installation type of magnetic suction. It can be used for high-precision static and dynamic measurements of the door inner clearance with a resolution of 0.013 mm to improve the efficiency of internal clearance on-line analysis and assembly quality inspection.