Gas ultrasonic flowmeters are widely used in natural gas measurement. In order to achieve high accuracy, it is meaningful to study interaction mechanism between flow field and acoustic field. In this study, effects of non-ideal flow on ultrasonic propagation are discussed. Firstly, a flow-acoustic coupling model is established based on COMSOL and its feasibility is verified by experiments. In order to be more in line with actual working condition, flow field is obtained by CFD simulation instead of theoretical formula calculation. Secondly, with this method, two typical non-ideal flows which often exist in real application are mainly analysed, including vortices near transducers and bend flows. The acoustic trajectory offsets, transit time, sound pressure and measurement errors are compared with results of ideal flow field. It is shown that errors will increase 10% caused by vortices near transducers, and increase 13% caused by bend flows. Besides, when passing through vortices near transducers with negative flow, trajectory offsets are opposite to flow direction. Finally, some suggestions for flowmeter design are proposed to improve measurement performance of gas ultrasonic flowmeter.

The detection method of partial discharge (PD) ultrasonic array signals is a new method that applies array sensors and array signals process technique to the PD detection. Moreover, the technique has high signal-to-noise ratio and high reliability. Compared with a full array sensor, degree reduction array sensor is a sparse array detection system, which has advantages of simple structure, low cost, and meeting most needs of engineering. However, these existed degree reduction algorithms of sparse optimal design are relatively complicated, affecting the success rate and the accuracy of detection. Therefore, this study proposes a method, which is the optimal design of the PD ultrasonic array sensor based on genetic algorithm dimension reduction technique. First, a two-dimensional (2D) plane circular array search is changed into a corresponding 1D linear search, and the genetic algorithm performs the linear search. Then, a circular array structure is restored to calculate the array performance. Finally, an optimal sparse structure of the circular PD ultrasonic array sensor is obtained under multiple constraints. The simulated results and the experimental studies are carried out to verify the validity and effectiveness of the proposed approach.

Multiple Helmholtz resonance apertures are proposed to enhance the output pressure of air-coupled capacitive micromachined ultrasonic transducers (CMUTs) for non-contact ultrasound imaging applications. The methodologies of defining the design parameters of CMUTs and the resonant apertures on the membrane of CMUTs are discussed. In comparing certain configurations of resonant apertures with conventional CMUTs, simulation results show that a prospective improvement of output pressure (up to 32.1%) can be achieved.

Stress and residual stress are two crucial factors which play important roles in mechanical performance of materials, including fatigue and creep, hence measuring them is highly in demand. Pulse eddy current (PEC) and ultrasonic testing (UT) are two non-destructive tests (NDT) which are nominated to measure stresses and residual stresses by numerous scholars. However, both techniques suffer from lack of accuracy and reliability. One technique to tackle these challenges is data fusion, which has numerous approaches. This study introduces a promising one called neural network data fusion, which shows effective performance. First, stresses are simulated in an aluminium alloy 2024 specimen and then PEC and UT signals related to stresses are acquired and processed. Afterward, useful information obtained is fused using artificial neural network procedure and stresses are estimated by fused data. Finally, the accuracy of fused data are compared with PEC and UT information and results show the capability of neural network data fusion to improve stress measurement accuracy.

Guided wave has been utilised in various manners for non-destructive evaluation and testing. The dispersion and attenuation characteristics of guided wave restrict and complicate the accurate estimation of echo propagation distance. The study focuses on how to reduce the estimation error of propagation distance caused by these characteristics. The propagation of guided wave with attenuation and dispersion characteristics is analytically modelled in general cases. The flight-time compensation technique is developed based on the analytical model of wave propagation and the algorithm of chirplet matching pursuit. Numerical simulations are given to verify the efficacy of the developed compensation method. Finally, this study demonstrates the use of experimentally measured data for echoes identification and propagation distance estimation.

The quality of focusing in high-frequency ultrasound imaging is significantly affected by the length of the depth of field (DOF). A dual-concentric transducer combined with a phase-apodisation scheme is presented to achieve the extended DOF maintaining signal-to-noise ratio. As a preliminary study, computational simulation by using a Field-II program is conducted to demonstrate the feasibility. A dual-concentric transducer is composed of a disc- and a ring-type element with confocal apertures. When two input signals with 0° and 180° phases are simultaneously applied to the inner and outer elements, a bifocal-zone is generated in the axial direction. The overall − 6 dB DOF is 40% longer compared with a single element transducer. Thus, the proposed scheme can be a potential approach to increase the DOF for high-frequency ultrasound imaging.

Knowing the wind speed and direction in an electrical power generating wind farm is an important factor in its management. A measuring device for this function with no moving parts is desirable to reduce maintenance due to wear of the mechanical parts. Ultrasonic measuring techniques can be employed in such a device to fulfill this requirement by measuring the time it takes for a signal to propagate from an emitter to a receiver sensor. Wind in the direction of the sound wave, or against it will affect the travel time of the sound wave and the wind speed can be extracted from these Time Of Flight (TOF) measurements. Commonly used narrowband ultrasonic transducers have the disadvantage of generating a long oscillating signal where the start of the received signal has a very small amplitude and cannot be directly detected and flagged with a simple threshold circuit. The present paper describes a method where two signal bursts of different frequencies within the bandwidth of the transducers are used to obtain the TOF. The phase difference between the emitted and the received signal is measured at two frequencies and the results are then combined to give the TOF. The wind direction can be obtained with an additional measurement in the orthogonal direction by a second pair of sensors.

This paper presents an ultra-fast CMOS Data- Acquisition system. It has been developed predominately for use in Optical Scanning Acoustic Microscopy, and it is also applicable in RF transceiver systems. The key modules of this system include a sub- sampling sample-and-hold amplifier, and a pulse generator, which is based on a 2.6 GHz PLL with quadrature outputs and provides control signals for the SHA. The DAQ system is implemented in a standard 0.35 μm CMOS process, and achieves 10.2 G Sample/s sampling rate for the 80 MHz periodic laser input. (8 pages)

A 2.4 GHz range surface acoustic wave (SAW)-based pressure sensor was fabricated on a 41° YX LiNbO₃ substrate for a mechanical compression force measurement. For the first time, fabricated sensors were characterised wirelessly using the network analyser. Electron beam lithography was used for fine line patterning. Metal ground shielding was covered all over the cavity to reduce a coupling loss of the propagating SAW to the surrounding atmosphere. Equivalent circuit model and finite element methods were used to determine optimal design parameters. The three sharp peaks were obtained from three reflectors. As a mechanical force was applied to the piezoelectric diaphragm, the diaphragm was bended, resulting in the phase shifts of the reflected peaks. Obtained sensitivity was 2.9°/kPa.

A 2D ultrasound field imaging system that uses a CCD array to map the optical output of a planar Fabry-Perot polymer film sensing interferometer is described. This system enables ultrasound fields to be rapidly mapped over a 6.6×4.7 mm aperture with spatial and temporal resolutions of the order of 10 µm and 10 ns, respectively. The concept was successfully demonstrated by imaging the acoustic field at the focus of a pulsed 5 MHz PZT ultrasound transducer. The technique offers an alternative to piezoelectric-based methods for high-resolution biomedical and industrial ultrasonic imaging and field characterisation applications.