Wave propagation in 0-3/3-3 connectivity composites with complex microstructure

This work presents a study of the properties of particulate composites. The whole range of particle volume fraction (0-1) and ideal 0-3, 3-3 and intermediate 0-3/3-3 connectivities are analysed. Two different approaches to produce a realistic model of the complex microstructure of the composites are considered. The first one is based on a random location of mono-dispersed particles in the matrix; while the second incorporates a size distribution of the particles based on experimental measurements. Different particle shapes are also considered. A commercial finite element package was used to study the propagation of acoustic plane waves through the composite materials. Due to the complexity of the problem, and as a first step, a two-dimensional model was adopted. The results obtained for the velocity of sound propagation from the finite element technique are compared with those from other theoretical approaches and with experimental data. The study validates the use of this technique to model acoustic wave propagation in 0-3/3-3 connectivity composites. In addition, the finite element calculations, along with the detailed description of the microstructure of the composite, provide valuable information about the micromechanics of the sample and the influence of the microstructure on macroscopic properties.

Diffusable growth factors induce bladder smooth muscle differentiation

Bladder smooth muscle differentiation is dependent on the presence of bladder epithelium. Previously, we have shown that direct contact between the epithelium and bladder mesenchyme (BLM) is necessary for this interaction. In this study, we tested the hypothesis that bladder smooth muscle can be induced via diffusable growth factors. Fourteen-day embryonic rat bladders were separated into bladder mesenchyme (prior to smooth muscle differentiation) and epithelium by enzymatic digestion and microdissection. Six in vitro experiments were performed with either direct cellular contact or no contact (1) 14-d embryonic bladder mesenchyme (BLM) alone (control), (Contact) (2) 14-d embryonic bladders intact (control), (3) 14-d embryonic bladder mesenchyme combined with BPH-1 cells (an epithelial prostate cell line) in direct contact, (4) 14-d embryonic bladder mesenchyme with recombined bladder epithelium (BLE) in direct contact, (No Contact) (5) 14-d embryonic bladder mesenchyme with BPH-1 prostatic epithelial cells cocultured in type 1 collagen gel on the bottom of the well, and (6) 14-d embryonic bladder mesenchyme with BPH-1 epithelium cultured in a monolayer on a transwell filter. In each case the bladder tissue was cultured on Millicell-CM 0.4-microm membranes for 7 d in plastic wells using serum free medium. Growth was assessed by observing the size of the bladder organoids in histologic cross section as well as the vertical height obtained in vitro. Immunohistochemical analysis of the tissue explants was performed to assess cellular differentiation with markers for smooth muscle alpha-actin and pancytokeratin to detect epithelial cells. Control (1) bladder mesenchyme grown alone did not exhibit growth or smooth muscle and epithelial differentiation. Contact experiments (2) intact embryonic bladder, (3) embryonic bladder mesenchyme recombined with BPH-1 cells, and (4) embryonic bladder mesenchyme recombined with urothelium each exhibited excellent growth and bladder smooth muscle and epithelial differentiation. Both noncontact experiments (5) and (6) exhibited growth as well as bladder smooth muscle and epithelial differentiation but to a subjectively lesser degree than the contact experiments. Direct contact of the epithelium with bladder mesenchyme provides the optimal environment for growth and smooth muscle differentiation. Smooth muscle growth and differentiation can also occur without direct cell to cell contact and is not specific to urothelium. This data supports the hypothesis that epithelium produces diffusable growth factors that induce bladder smooth muscle.

Domestic and personal accidents. Prevention in the absence of professional supervision

This paper provides a review of a selection of recent papers, most of which derive from presentations given at the 4th World Conference on Injury Prevention and Control or the 6th International Conference on Product Safety Research, both of which took place in Amsterdam in May 1998. What all the accidents studied in these papers have in common is the absence of professional supervision. Everyone immediately involved in the incident--whether as injured party, unintended cause or informal supervisor is an 'amateur'. It is proposed that the term 'domestic and personal accidents' should be used to describe this group of accidents, the study of which has been neglected in comparison to transport and occupational injuries. It is argued that domestic and personal activities are more heterogeneous than ones with an element of professional supervision and are therefore more difficult to prevent. Nevertheless examples are given of where 'horizontal' approaches to analysis and prevention of these accidents have proved possible.

Beam profile measurements and simulations for ultrasonic transducers operating in air

This paper outlines a method that has been implemented to predict and measure the acoustic radiation generated by ultrasonic transducers operating into air in continuous wave mode. Commencing with both arbitrary surface displacement data and radiating aperture, the transmitted pressure beam profile is obtained and includes simulation of propagation channel attenuation and where necessary, the directional response of any ultrasonic receiver. The surface displacement data may be derived directly, from laser measurement of the vibrating surface, or indirectly, from finite element modeling of the transducer configuration. To validate the approach and to provide experimental measurement of transducer beam profiles, a vibration-free, draft-proof scanning system that has been installed within an environmentally controlled laboratory is described. A comparison of experimental and simulated results for piezoelectric composite, piezoelectric polymer, and electrostatic transducers is then presented to demonstrate some quite different airborne ultrasonic beam-profile characteristics. Good agreement between theory and experiment is obtained. The results are compared with those expected from a classical aperture diffraction approach and the reasons for any significant differences are explained.

The radiation field characteristics of piezoelectric polymer membrane transducers when operating into air

This paper describes the evaluation of the radiation field characteristics of PVDF membrane transducers, whereby the active area is defined by an appropriate electrode pattern when operating into air. Measurement, including conventional scanning of the fields and laser vibrometry, is supplemented by finite element modeling over the frequency range 500 kHz to 1.1 MHz. Contrary to expectation, the surface displacements are nonuniform, giving rise to premature axial focusing of the field. This is shown to be caused by generation of the zero order symmetrical Lamb wave, arising from the electric field discontinuity at the electrode boundary of the transducer.

Investigation into the effects of modification of the passive phase for improved manufacture of 1-3 connectivity piezocomposite transducers

The 1-3 connectivity composite transducers comprise active piezoceramic pillars within a passive polymer matrix. The first stage in manufacturing the 1-3 material is to produce a bristle block (comprising a solid stock of active material with protruding pillars) by injection moulding or by dicing a piece of ceramic using precision sawing equipment. The bristle block is filled with a reactive polymer liquid that produces the passive polymer phase, and the filled block is machined to the desired dimensions. For optimum performance, the polymer phase should have complementary interaction with the ceramic phase as well as imparting dimensional stability. Epoxy-based polymers are the most usual passive materials because of their low viscosity in the uncured state and solvent resistance, coupled with their excellent adhesive, mechanical, and electrical properties. However, the curing of epoxy resins results in shrinkage of the polymer matrix and internal stress within the passive phase. This can lead to prestressing of the active ceramic material, distortion of pillars, reduction in the parallelism between the sides of pillars, acid, in certain circumstances, warpage of transducers. This is particularly evident when the solid stock in the bristle block is relatively thin. This paper reports the in situ modification of epoxy in the bristle block by UV-based low temperature polymerization of acrylate monomers within the epoxy matrix prior to polymerization of the epoxy resin. Internal stress measurements are presented to quantify the influence of this modification via a reduction of internal stress within the polymer matrix. Results from finite element analysis emphasise the conclusions of the experimental work, and examples of manufactured devices are presented. Composite transducer performance is assessed by laser measurement of surface displacement profiles, and a 50% improvement in surface displacement magnitude was observed for the modified devices.

Ultrasonic arrays for monitoring cracks in an industrial plant at high temperatures

A piezoelectric linear array structure has been designed to operate at temperatures up to 400 degrees C for nondestructive testing of steel components of a hot industrial plant. It is intended that these arrays be fixed permanently to the test subject so that known defects can be monitored by comparing measurements taken over a period of time without needing to shut down the plant. The arrays are used in pairs: the transmitter is a phased array producing a variable angle steered beam, and a second array is used for receiving. The defect can be identified from a series of scans collected from individual elements of the second array. A simple monolithic array structure was used, based on a single crystal of lithium niobate and operating in the frequency range 3 to 5 MHz. Prototype devices have 64 elements on a 0.5 mm pitch. Simulated defects in steel blocks have been scanned at high temperatures to illustrate the arrays' capability for nondestructive testing. The results suggest an accuracy better than 1 mm in finding the location of crack tips.

Generation and reception of ultrasonic guided waves in composite plates using conformable piezoelectric transmitters and optical-fiber detectors

A condition monitoring nondestructive evaluation (NDE) system, combining the generation of ultrasonic Lamb waves in thin composite plates and their subsequent detection using an embedded optical fiber system is described. The acoustic source is of low profile with respect to the composite plate thickness, surface conformable, and able to efficiently launch a known Lamb wave mode, at operating frequencies between 100 and 500 kHz, over typical propagation distances of 100 to 500 mm. It incorporates both piezocomposite technology and interdigital design techniques to generate the fundamental symmetrical Lamb wave mode in both metallic and carbon-fiber composite plates. Linear systems and finite element modeling techniques have been used to evaluate the operation of the transducer structure, and this is supplemented by experimental verification of the simulated data. An optical fiber, either bonded to the surface or embedded across the length of the composite plate samples, is used to detect the propagating ultrasonic Lamb waves. Single mode silica fiber has been used in conjunction with a portable 633 nm Mach-Zehnder interferometer for signal demodulation and subsequent data acquisition. This hybrid system is shown to generate and detect the fundamental symmetrical Lamb wave (s(0)) in both carbon-fiber and glass-fiber reinforced composite plates. Importantly, the system signal-to-noise ratio (SNR) associated with the acoustic source compares favorably with s(0) Lamb wave generation using a conventional transducer and angled perspex wedge arrangement.

Development of a PVDF membrane hydrophone for use in air-coupled ultrasonic transducer calibration

This work describes the use of a polyvinylidene fluoride (PVDF) membrane hydrophone for application in air-coupled transducer calibration. A one-dimensional theoretical analysis is used to demonstrate the potential and performance of PVDF as a hydrophone material over the frequency range 100 kHz to 5 MHz included in the evaluation is the influence of deposited metallic electrode layers on the sensitivity of the material. Experimental validation over the restricted range 400 kHz to 1 MHz is provided by a coplanar 0.028 mm thick membrane hydrophone in conjunction with a custom built 1-3 piezocomposite transmitter. Calibration of the membrane hydrophone is performed by employing a standard hydrophone that has been calibrated to a primary standard in a water medium. Justification for such an approach is presented within the theoretical analysis which provides a close correlation with experimental data. The generation of Lamb waves at critical angles in the PVDF and their subsequent influence on the directional response of membrane hydrophones operating in air is also addressed. A method for partial suppression of the Lamb waves, based around perforation of the membrane (either in whole or in part), is evaluated experimentally with reasonable results.

Unidimensional modeling of multi-layered piezoelectric transducer structures

Multi-layered transducer structures offer the potential of improved performance in terms of increased transmit sensitivity, greater bandwidth, and enhanced reception characteristics. Unfortunately, the successful design of such devices is often difficult, owing to the complex interaction between the active piezoelectric layers and passive intermediate interface layers. Furthermore, in many practical applications, the loading effects imposed by the electrical drive circuitry often limit the performance improvements that may be physically realized. This paper describes the development of a comprehensive, unidimensional modeling approach. This model may be employed to facilitate the analysis and subsequent optimization of laminated transducer assemblies. The devices currently under consideration include both piezoceramic and piezopolymer configurations, as well as alternative piezocomposite designs. The effects of varying bondline thickness and the introduction of passive interface layers are examined, as is the influence of the electrical load circuitry on overall system response. The ability to accurately predict the response of stacked piezoelectric structures is demonstrated through extensive comparison of experimental and theoretical responses. This paper concludes by highlighting the important role that modeling plays in the design, fabrication, and optimization of complex multi-layered transducer assemblies.

Surface-bonded and embedded optical fibers as ultrasonic sensors

The effectiveness of surface-bonded and embedded optical fibers for the detection of ultrasonic Lamb waves in 2-3-mm-thick steel, carbon-fiber-reinforced plastic (CFRP) and glass-reinforced plastic (GRP) plates are compared. A novel integrating ultrasonic sensor was achieved using the signal arm of an actively stabilized 633-nm homodyne Mach-Zehnder fiber interferometer which was either bonded directly to the plate surface or spliced to single-mode fibers embedded within a composite plate during manufacture. An embedded fiber is shown to be about 20 times more sensitive to Lamb wave motions than a surface-bonded fiber. However, the latter may be more practical.

Risk of injury per hour of exposure to consumer products

The aim of this study was to determine and compare the risk of injury per hour of use for a range of consumer products. Exposure data was derived from interviewing a large sample of adults about their use of 76 common kitchen, do-it-yourself and household products. This was combined with hospital sample data for injuries involving each product, to yield the risk-of-injury-per-hour-of-use. Powered cutting equipment, access equipment (ladders and scaffolding) and products with sharp blades were shown to have a comparatively high risk, along with cycles, sunbeds, creosote, cement, car jacks and exercise weights. Perceived risk was shown to be a poor basis for priority setting, but a practical guide to priority for preventive action can be provided by "mapping" products on a plot of the risk of injury per hour of use vs the total medical costs of such accidents.

Air-coupled piezoelectric detection of laser-generated ultrasound

A pulsed laser has been used to generate ultrasonic transients in samples of metal and fiber-reinforced polymer composite material. These have been detected using an air-coupled piezoelectric transducer. It is demonstrated that such a transduction system can be used for longitudinal waves in bulk material, Rayleigh waves at solid surfaces and Lamb waves in thin plates.

The human cytomegalovirus 86K immediate early (IE) 2 protein requires the basic region of the TATA-box binding protein (TBP) for binding, and interacts with TBP and transcription factor TFIIB via regions of IE2 required for transcriptional regulation

The 86K immediate early (IE) 2 protein of human cytomegalovirus trans-activates a number of homologous and heterologous promoters, including the cellular promoter for the 70K heat-shock protein (hsp70), and the human immunodeficiency virus long terminal repeat. We have previously shown that IE2 trans-activates these two promoters in a TATA-dependent manner, and that IE2 is able to form a direct contact with TATA-box binding protein (TBP) in vitro. We now show that IE2 binds to the basic repeat region of TBP. In addition IE2 can contact a second general transcription factor, TFIIB. We have mapped the TBP- and TFIIB-binding regions within IE2 and show that these regions overlap, and also lie within parts of the protein previously identified as being required for the trans-activation and autoregulation functions of IE2.

An intelligent ultrasonic inspection system for flooded member detection in offshore structures

An ultrasonic system for automatic underwater inspection of steel jacket offshore installation is described. It is based on the unambiguous detection of water ingress in normally sealed tubular members, thereby providing an indication of through-wall structural failure. A novel transducer design, based on a dual frequency array of 1-3 connectivity thickness drive transducers, is used to provide the required sensitivity and act also as an environmental monitor for input to an expert system, which performs automatic data analysis. Although intended primarily for operation on a remotely operated vehicle, the system may be employed satisfactorily by a driver. A series of test trials is described, and the prototype is shown to perform very well for all intended modes of operation.

Theoretical and experimental evaluation of a two-dimensional composite matrix array

A theoretical and experimental performance appraisal of a two-dimensional, ceramic-epoxy composite matrix array employing 1-3 connectivity is presented. The linear systems approach is used for temporal and spatial simulation of array performance, with specific regard to three-dimensional synthetic aperture imaging in a fluid load medium. Manufacture and experimental evaluation of a prototype array structure, operating at 1.2 MHz and comprising 100 elements arranged as a 10 by 10 matrix, is described. Close agreement between theory and experiment is obtained, providing a clear indication that the low crosstalk, uniformity, and wideband characteristics of composite array elements offer excellent prospects for such imaging applications.

Finite-element analysis of 1-3 composite transducers

The vibrational and electromechanical characteristics of a wide range of 1-3 composite structures, comprising ceramic pillars aligned within a polymer phase, are considered using finite-element analysis. The influence of pillar geometry, ceramic volume fraction, and pillar orientation is described in terms of overall transduction efficiency. It is shown that the finite-element method provides a versatile means of analysis and the results obtained permit a set of useful design guidelines to be developed. In general, a small pillar aspect ratio and a relatively high volume fraction provides the most satisfactory performance, in terms of electromechanical efficiency and uniformity of thickness dilation.