Air-Coupled Reception of a Slow Ultrasonic A0 Mode Wave Propagating in Thin Plastic Film

At low frequencies, in thin plates the phase velocity of the guided A0 mode can become slower than that of the ultrasound velocity in air. Such waves do not excite leaky waves in the surrounding air, and therefore, it is impossible to excite and receive them by conventional air-coupled methods. The objective of this research was the development of an air-coupled technique for the reception of slow A0 mode in thin plastic films. This study demonstrates the feasibility of picking up a subsonic A0 mode in plastic films by air-coupled ultrasonic arrays. The air-coupled reception was based on an evanescent wave in air accompanying the propagating A0 mode in a film. The efficiency of the reception was enhanced by using a virtual array which was arranged from the data collected by a single air-coupled receiver. The signals measured at the points corresponding to the positions of the phase-matched array were recorded and processed. The transmitting array excited not only the A0 mode in the film, but also a direct wave in air. This wave propagated at ultrasound velocity in air and was faster than the evanescent wave. For efficient reception of the A0 mode, the additional signal-processing procedure based on the application of the 2D Fourier transform in a spatial–temporal domain. The obtained results can be useful for the development of novel air-coupled ultrasonic non-destructive testing techniques.

Design of Reconfigurable Stacked Patch Microstrip Antenna (RSPMA) at 1.8 GHz and 2.3 GHz

This paper presents a Reconfigurable Stacked Patch Microstrip Antenna (RSPMA) uses a combination of aperture coupled technique and stacked patch technology for reducing feigned radiation patterns. This RSPMA consists of three FR-4 substrate layers with 4.7 mm thickness each and 3 mm thick of an air-filled substrate between stacked patches and the ground plane. The top patches are rectangular shaped with a T-shaped hole at the center and the bottom patches are T-shaped, both etched on top of substrate 1 and substrate 2 respectively act as a radiating element. Two H-shape designs of aperture slots of different sizes on the ground plane are positioned at the center of the ground plane with reference to the top patches and bottom patches. A copper strip is used as an ideal RF switch is implemented at the feed line network for the ON and OFF mode. Thus, by adjusting the switch mode, the resonance frequencies can be varied, thus frequency reconfigurable is achieved. The activation of the selected aperture slots will produce waves and radiates the signal to the radiating layers of the patch antenna. Hence, two different frequencies, either at 1.8 GHz or 2.3 GHz were achieved through the RSPMA with the gain of 3.691 dB and 2.291 dB, respectively. The antenna designed was simulated using CST Microwave Studio at an operating frequency of 1 GHz to 2.7 GHz. The RSPMA is said to be potentially beneficial to the wireless communication system.

Textile-Based Antenna using Aperture-Coupled Technique for Global Positioning System (GPS) Application

This paper presents a preliminary design of a textile antenna using aperturecoupled technique for Global Positioning System (GPS) application. Mostly used in wearable application, textile materials are suitable to be applied as the antenna substrates due to the flexibility and conformability characteristic. In this paper, felt material with the relative permittivity, εr1 of 0.76 and thickness of 2.69 mm is chosen as the substrate, and is attached to a pure copper layer as the conductive material with the thickness of 0.07 mm. Meanwhile, the textile material used as the feed substrate is fleece with the thickness of 0.69 mm with the relative permittivity εr2 of 0.91. The design procedure is discussed and the simulated data using the CST Microwave Studio software is further analysed in terms of the return loss, gain, directivity and radiation pattern.

A Linearity Improved 10-bit 120-MS/s 1.5 mW SAR ADC with High-Speed and Low-Noise Dynamic Comparator Technique

This paper presents a linearity improved 10-bit 120-MS/s successive approximation register (SAR) analog-to-digital converter (ADC) with high-speed and low-noise dynamic comparator. A gate cross-coupled technique is introduced in boost sampling switch, the clock feedthrough effect is compensated without extra auxiliary switch and the linearity of sampling switch is enhanced. Further, substrate voltage boost technique is proposed, the absolute values of threshold voltage and equivalent impedances of MOSFETs are both depressed. Consequently, the delay of comparator is also reduced. Moreover, the reduction of threshold voltages for input MOSFETs could bring higher transconductance and lower equivalent input noise. To demonstrate the proposed techniques, a design of SAR ADC is fabricated in 65-nm CMOS technology, consuming 1.5[Formula: see text]mW from 1[Formula: see text]V power supply with a SNDR [Formula: see text][Formula: see text]dB and SFDR [Formula: see text][Formula: see text]dB. The proposed ADC core occupies an active area of 0.021[Formula: see text]mm2, and the corresponding FoM is 24.4 fJ/conversion-step with Nyquist frequency.

Nonlinear Aerodynamic Damping in a Highly Loaded Vibrating Compressor Cascade

A numerical aeroelastic study of a 2D linear compressor cascade based on the non-rotating annular compressor cascade with a NACA3506 profile was performed using a one-way coupled technique (prescribed-motion approach). Subsonic and transonic flow conditions with strong shocks in the blade passage were imposed. Using a nonlinear harmonic balance solver, unsteady simulations were performed by enforcing one blade oscillation motion. For each blade structural mode, the blade deflection amplitude was varied and its influence on the blade aerodynamic response was determined in terms of aerodynamic damping. The blade modes investigated consisted of one pitching and two heaving oscillation motion. In transonic flows and for the three structural modes investigated, the cascade shows nonlinear aerodynamic responses depending on the vibration amplitude. The results presented in this work show that nonlinear frequency domain methods are able to capture the blade nonlinear aeroelastic behavior coming from amplitude-dependent aerodynamic responses.

An Integrated DEM-FEM Model for Shot Peening Applications

Shot peening is a commonly used technique for improving the fatigue life of machine components by inducing compressive residual stresses in the surface layers. This process involves plastically deforming the surface layers by impacting with spherical particles at high speeds. The induced residual compressive stresses resist crack propagation and thus increase the fatigue life. The intensity of shot peening, measured using the Almen test, is an essential quantity for ensuring shot peening effectiveness and repeatability. It depends on various process parameters such as the shot speed, shot size, shot material, impact direction, and flow rate. In this study, a novel computational model is developed to simulate the Almen intensity tests on a Type-C strip accurately. The model uses a coupled technique based on the discrete element method (DEM) and the conventional finite element method (FEM). The predicted Almen intensity values agree with analytically calculated values. Results from the parametric studies conducted to analyze the influence of various parameters on the Almen intensity indicate that many different combinations of these parameters can obtain a given Almen intensity although the residual stress fields may vary.