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A balanced armature receiver (BAR) as a special type of electromagnetic acoustic transducers plays a significant role in reproduction of music and speech, active noise control in modern hearing aid and in contemporary in-ear monitors. This paper aims to present a static analysis of the balanced armature receiver based on the lumped network approach (LNA) and the finite element method (FEM).

In this paper, the LNA and two-dimensional FEM are applied to model deflections of the BAR’s armature from the equilibrium position. Results of calculations are compared with measurements.

The derived analytical formulas and developed procedure allow for calculation of the armature deflection.

Comparing to the previous papers, the reluctance’s nonlinearity of the armature has been considered.

The aim of this paper is to better understand the generation and transmission mechanism of the electromagnetic acoustic transducer (EMAT).

A semi-analytical method was used to calculate the Lorentz force. Both the hypothetical magnetic field mirror method and the diffusion equation were adopted to solve the eddy current distribution by variables separation method in time domain. A three-dimension magnetostatic finite element model was used to calculate the static magnetic field and the relative permeability. And an experimental platform with a piezoelectric probe to generate and an EMAT to receive, the ultrasonic wave was set up to verify the distribution of the Lorentz force.

The Lorentz force at different time and in different positions of the steel plate can be easily calculated. The experimental results show a good agreement with the analytical results.

The accurate prediction of the Lorentz force provides an insight into the physical phenomenon of EMAT and a powerful tool to design optimum EMAT.

A report from a seminar on advanced sensing held on 9th November 1993 as part of the DTI Advanced Sensors Technology Programme [ASTTP]. The first subject covered was multiplexing for control systems and looked at the present diversity of bus systems supporting field devices from the viewpoint of sensor manufacturers, users and researchers. Another presentation relating to multiplexing of sensors, looked at a project for water quality measurement. The second topic was sensing in relation to non‐destructive testing, dealing mainly with new market opportunities in the food industry, the aircraft industry and civil engineering.

The purpose of this paper is to provide an insight on the use of robots in a range of industrial test and inspection applications.

Following a brief introduction, this discusses robotic test and inspection products and practices in the following applications: pipelines, storage tanks, bridges, marine uses, green energy generation and aerospace. Finally, concluding comments are drawn.

This shows that robotic test and inspection practices are being used in a wide range of applications across a diversity of industries. This reflects the many operational and economic benefits arising from their use which include the ability to automate certain laborious manual methods; operation in hazardous locations; uses in inaccessible environments such as within pipelines; the ability to deploy several different techniques simultaneously and thus detect multiple potential defects; reduced workforce costs; and, very often, more rapid testing and greater data acquisition rates than are possible with human operators.

This illustrates the increasingly important role played by robotic technologies in industrial test and inspection practices.

Island attack and defense, emergency rescue, scientific research, civilian fisheries and other fields are inseparable from timely, high-quality underwater communications. However light and other electromagnetic waves are severely attenuated in water, acoustic is currently the only energy carrier that can transmit signals over long distances in water. However, the complex water environment and serious interference bring serious challenges to underwater activities using underwater acoustic sensors-hydroacoustic transducers. Thus, this paper aims to develop a class of high reception sensitivity hydroacoustic transducer structures to provide research and utilization ideas for related scholars.

The electromechanical coupling coefficient is improved by converting the thickness vibration mode of the piezoelectric ceramic into the longitudinal vibration mode of the piezoelectric pillars array, and no polymer is added between the piezoelectric pillars array to reduce lateral coupling as well as internal friction, which can thus reduce the energy losses. Radial stacking in parallel can also enhance the charge generated through the positive piezoelectric effect. The optimal parameters of the structure are determined by equivalent circuit method and finite element analysis, and a hydroacoustic transducer of this structure is fabricated finally.

According to the standard test procedure, the hydroacoustic transducer was tested in water. The tests show that the conductance curve of the stacked high-sensitivity hydroacoustic transducer tested in the air is in good agreement with the simulation results. The resonant frequency is about 118 kHz, and the receiver sensitivity is −166 dB. The stacked material hydroacoustic transducer is in the high-frequency range and has a much higher sensitivity (−166 dB) than many types of hydroacoustic transducers fabricated by piezoelectric ceramic (less than −200 dB).

Although the stacked high-sensitivity hydroacoustic transducer that the authors have fabricated has a performance improvement, it has a limitation. The hollow design of the pillar arrays increases the reception stress on each pillar, and the imposed pressure comes from water also increases simultaneously, so the depth of water that the stacked high-sensitivity hydroacoustic transducer can operate in may be slightly shallower than that made of a pure piezoelectric ceramic block or a piezoelectric ceramic material with polymer added. This will be a problem to be solved in a future deployment.

Whether it is marine scientific research or in various fields such as civil recreation and fishing, hydroacoustic communication and necessary underwater exploration are indispensable for acoustic waves. The hydroacoustic transducer is the sensor that sends and receives sound waves, so a lot of water equipment, such as yachts, sonar buoys, and so on, cannot be separated from the hydroacoustic transducer. In addition, the complexity of the water environment also requires a good performance of the hydroacoustic transducer to facilitate the convenience and effectiveness of subsequent signal processing. Therefore, hydroacoustic transducers have great market and commercial value.

Hydroacoustic transducers are not only of great commercial value but also have a significant impact on the military as well as on people’s livelihood. As we all know, in the area of submarine communication and underwater exploration, sonar is the main force. The performance of the hydroacoustic transducer directly affects the performance of the hydroacoustic signal processing system, and ultimately directly determines the success or failure of the mission. In addition, the large-scale replacement of hydroacoustic transducers on equipment requires the concerted efforts of a large number of practitioners, such as material scientists, structural scientists, mathematicians and so on. Therefore, the rise of hydroacoustic transducers has given rise to a large number of learning positions as well as employment positions.

To enhance the reception sensitivity of the hydroacoustic transducer, the authors have optimized the existing hydroacoustic transducer materials and structures to propose a stacked sensitive element, which can effectively enhance the electromechanical conversion coefficient of the piezoelectric material. Furthermore, the authors have manufactured a hydroacoustic transducer using the proposed stacked sensitive element. The test results of the hydroacoustic transducer also show that the designed stacked sensitive element is of great help to enhance the reception sensitivity of the hydroacoustic transducer.

Wireless sensor networks (WSN), as a solution for buried water pipe monitoring, face a new set of challenges compared to traditional application for above-ground infrastructure monitoring. One of the main challenges for underground WSN deployment is the limited range (less than 3 m) at which reliable wireless underground communication can be achieved using radio signal propagation through the soil. To overcome this challenge, the purpose of this paper is to investigate a new approach for wireless underground communication using acoustic signal propagation along a buried water pipe.

An acoustic communication system was developed based on the requirements of low cost (tens of pounds at most), low power supply capacity (in the order of 1 W-h) and miniature (centimetre scale) size for a wireless communication node. The developed system was further tested along a buried steel pipe in poorly graded SAND and a buried medium density polyethylene (MDPE) pipe in well graded SAND.

With predicted acoustic attenuation of 1.3 dB/m and 2.1 dB/m along the buried steel and MDPE pipes, respectively, reliable acoustic communication is possible up to 17 m for the buried steel pipe and 11 m for the buried MDPE pipe.

Although an important first step, more research is needed to validate the acoustic communication system along a wider water distribution pipe network.

This paper shows the possibility of achieving reliable wireless underground communication along a buried water pipe (especially non-metallic material ones) using low-frequency acoustic propagation along the pipe wall.

Quantitatively detecting surface defects in a circular annulus with high levels of accuracy and efficiency has been paid more attention by researchers. The purpose of this study is to investigate the theoretical dispersion equations for circumferential guided waves and then develop an efficient technique for accurate reconstruction of defects in pipes.

The methodology applied to determine defects in pipelines includes four steps. First, the theoretical work is carried out by developing the appropriate dispersion equations for circumferential guided waves in a pipe. In this phase, formulations of strain-displacement relations are derived in a general equidistant surface coordinate. Following that, a semi-analytical finite element method (SAFEM) is applied to solve the dispersion equations. Then, the scattered fields in a circular annulus are calculated using the developed hybrid finite element method and simulation results are in accord with the law of conservation of energy. Finally, the quantitative detection of Fourier transform (QDFT) approach is further enhanced to efficiently reconstruct the defects in the circular annuli, which have been widely used for engineering applications.

Results obtained from four numerical examples of flaw detection problems demonstrate the correctness of the developed QDFT approach in terms of accuracy and efficiency. Reconstruction of circumferential surface defects using the extended QDFT method can be performed without involving the analytical formulations. Therefore, the streamlined process of inspecting surface defects is well established and this leads to the reduced time in practical engineering tests.

In this paper, the general dispersion equations for circumferential ultrasonic guided waves have been derived using an equidistant surface coordinate and solved by the SAFEM technique to discover the relationship between wavenumber of a wave and its frequency. To reconstruct defects with high levels of accuracy and efficiency, the QDFT approach has been further enhanced to inspect defects in the annular structure.

This study aims to understand the influence of megasonic (MS)-assisted agitation on printed circuit boards (PCBs) electroplated using copper (Cu) electrolyte solutions to improve plating efficiencies through enhanced ion transportation.

The impact of MS-assisted agitation on topographical properties of the electroplated surfaces was studied through a design of experiments by measuring surface roughness, which is characterised by values of the parameter Ra as measured by white light phase shifting interferometry and high-resolution scanning electron microscopy.

An increase in Ra from 400 to 760 nm after plating was recorded for an increase in acoustic power from 45 to 450 W. Roughening increased because of micro-bubble cavitation energy and was supported through direct imaging of the cavitation. Current thieving effect by the MS transducer induced low currents, leading to large Cu grain frosting and reduction in the board quality. Current thieving was negated in plating trials through specific placement of transducer. Wavy electroplated surfaces, due to surface acoustic waves, were also observed to reduce the uniformity of the deposit.

The formation of unstable transient cavitation and variation of the topology of the Cu surface are unwanted phenomena. Further plating studies using MS agitation are needed, along with fundamental simulations, to determine how the effects can be reduced or prevented.

This study can help identify manufacturing settings required for high-quality MS-assisted plating and promote areas for further investigation, leading to the development of an MS plating manufacturing technique.

This study quantifies the topographical changes to a PCB surface in response to MS agitation and evidence for deposited Cu artefacts due to acoustic effects.

Electrical properties of biological tissues are known to be sensitive to physiological and pathological conditions of living organisms. For instance, human breast cancer or liver tumor cells have a significantly higher electrical conductivity than a healthy tissue. The paper aims to the new recently developed magnetoacoustic tomography with magnetic induction (MAT-MI) which can be deployed for electrical conductivity imaging of low-conductivity objects. Solving a test problem by using an analytical method is a useful exercise to check the validity of the more complex numerical finite element models. Such test problems are discussed in Chapter 3. The detailed analysis of an electromagnetic induction in low-conductivity objects is very important for the next steps in the tomographic process of image reconstruction. Finally, the image reconstruction examples for object’s complex shapes’ have been analyzed. The Lorentz force divergence reconstruction has been achieved with the help of time reversal algorithm.

In given arrangements the magnetic field and eddy current vectors satisfy the Maxwell partial differential equations. Applying the separation of variables method analytical solutions are obtained for an infinitely long conducting cylindrical segment in transient magnetic field. A special case for such a configuration is an infinitely long cylinder with longitudinal crack. The analytical solutions are compared with those obtained by using numerical procedures. For complex shapes of the object, the MAT-MI images have been calculated with the help of the finite element method and time reversal algorithm.

The finite element model developed for a MAT-MI forward problem has been validated by analytical formulas. Based on such a confirmation, the MAT-MI complex model has been defined and solved. The conditions allowing successful MAT-MI image reconstruction have been provided taking into account different conductivity distribution. For given object’s parameters, the minimum number of measuring points allowing successful reconstruction has been determined.

A simple test example has been proposed for MAT-MI forward problem. Analytical closed-form solutions have been used to check the validity of the made in-house finite element software. More complex forward and inverse problems have been solved using the software.