A wireless ultrasonic NDT sensor system

Ultrasonic condition monitoring technologies have been traditionally utilized in industrial and construction environments where structural integrity is of concern. Such techniques include active systems with either single or multiple transmit-receiver combinations used to obtain defect positioning and magnitude. Active sensors are implemented in two ways; in a thickness operation mode, or as an area-mapping tool operating over longer distances. In addition, passive ultrasonic receivers can be employed to detect and record acoustic emission activity. Existing equipment requires cabling for such systems leading to expensive, complicated installations. This work describes the development and operation of a system that combines these existing ultrasonic technologies with modern wireless techniques within a miniaturized, battery-operated design. A completely wireless sensor has been designed that can independently record and analyze ultrasonic signals. Integrated into the sensor are custom ultrasonic transducers, associated analogue drive and receive electronics, and a Texas Instruments Digital Signal Processor (DSP) used to both control the system and implement the signal processing routines. BlueTooth wireless communication is used for connection to a central observation station, from where network operation can be controlled. Extending battery life is of prime importance and the device employs several strategies to do this. Low voltage transducer excitation suffers from poor signal-to-noise ratios, which can be enhanced by signal processing routines implemented on the DSP. Routines investigated include averaging, digital filtering and pulse compression

Investigating the thermal stability of 1-3 piezoelectric composite transducers by varying the thermal conductivity and glass transition temperature of the polymeric filler material

The thermal behaviour of a number of 1-3 piezoelectric composite transducers is discussed. In particular, devices manufactured from a polymer filler with a relatively high glass to rubber transition temperature (T-g), and from polymer systems with increased thermal conductivity, are evaluated. The mechanical properties of the various filler materials were obtained via ultrasonic measurements, with the thermal properties extracted using dynamic mechanical thermal analysis (dmta), differential scanning calorimetry (dsc) and laserflash studies. A range of ultrasonic transducers were then constructed and their thermal stability studied using a combination of impedance analysis and laser surface displacement measurement

A wireless ultrasonic sensor network for the in-situ NDE of structures

This paper looks at a wireless ultrasonic sensor network for the in-situ NDE of structure

A wireless sensor network of permanently installed structural integrity monitors

Structural integrity monitoring (SIM) involving a large numbers of distributed sensors is of increasing importance to a wide range of industries. Compact sensor packages combining ultrasonic transducers with local sensor and communications control functions and signal processing have been designed using modern miniaturization techniques. Autonomous wireless devices powered by on-board batteries can extract top-up energy derived from the sensor environment. Applications to date include erosion or corrosion monitors via ultrasonic thickness measurement devices, area mapping array sensors and time-of-flight diffraction (TOFD) technique transducers for defect monitoring. Formation or propagation of defects can also be monitored with passive acoustic emission (AE) sensors.The project concepts and early prototyping were presented at QNDE 2003. This paper highlights further progress towards a distributed wireless ultrasonic sensor network and presents results of TOFD and thickness measurement tests. Signal processing techniques including averaging, finite impulse response (FIR) filtering and pulse compression have been employed to improve signal-to-noise ratio (SNR), to extend battery power and to address time resolution issues. Field trials in a hostile industrial environment with metallic obstructions in the form of pipe-work, ducting, stairs, beams and floors have been performed and methods of extracting environmental energy have been tested. ©2005 American Institute of Physic

A cellular system for wireless structural integrity monitoring

Installation and maintenance costs, and improved reliability of structural integrity monitoring in industrial applications demanding a large number of sensors applied to the structure can be achieved using wireless links between the sensors. This paper describes a wireless network system designed to interconnect a variety of ultrasonic transducers. Miniaturized wireless-coupled sensors which incorporate the sensor drive electronics, a DSP and Bluetooth communication module have been developed, initially for thickness measurement but capable of being reconfigured for time-of-flight crack monitoring, large area mapping using Lamb wave arrays and passive acoustic emission sensing. A networked system capable of inter-sensor and base station communications in an industrial environment is in progress and preliminary results obtained are presented

A wideband ultrasonic test system for characterisation of particulate systems in the linear and non-linear regimes

This paper describes the development, characterisation and application of a versatile acoustic test cell for the derivation of through-transmission and backscattered ultrasonic signals from particulate suspensions. The test cell comprises a chamber for the mixture within a larger water tank, with fixtures for ultrasonic transducers at either end of the tank. The mixing chamber has wideband membrane hydrophones at the entrance and exit of the acoustic path. A range of broadband ultrasonic transmitters permits operation over the excitation frequency range 150 kHz – 10 MHz. Importantly, this configuration permits detection of the fundamental operating frequency and its sub- and superharmonics for both backscatter and through-transmission measurements from a single transducer excitation. The methodology employs coded excitation waveforms in the form of wideband chirps coupled with matched filtering of the received waveforms to enhance SNR and time resolution, and extract specific spectral information. For the linear analysis, through-transmission signal amplitudes provide a measure of attenuation and arrival times determine acoustic velocity. Spectral content of backscattered signals is used to identify non-linear characteristics, which are analysed for information related directly to the mixture properties. The particulate systems evaluated were glass beads, biomedical contrast agents and Avicel. Results have been achieved when operating in the linear regime, which compare well with published data, and with good scatterers in the non-linear regime, to which preliminary characterization of particle concentration has been applied

Embedded ultrasonic transducer design and wireless communication for intelligent monitoring of structures

This paper describes a wireless demonstrator system designed for generation and detection of fundamental symmetrical Lamb waves (So) characterized by high velocity and low attenuation. The demonstrator comprises two piezoceramic transducers embedded within an epoxy plate, drive and pre-amplification electronics, a microcontroller and a communications interface. This arrangement can be configured to operate in an active pitch-catch or pulse-echo interrogation mode or as a passive acoustic emission (AE) sensor. The history of AE incidents, for example, may then be transmitted by Wireless link

Political fragmentation and projected tax revenues: evidence from Flemish municipalities

Revenue projections, Forecast accuracy, Local taxation, Flemish municipalities, Government fragmentation, D72, H72, H79,