David Gareth John

The propagation and attenuation of medium-frequency ultrasonic waves in concrete: a signal analytical approach

The manner in which medium-frequency ultrasonic pulses travelling through concrete are generated, received, digitized and analysed is described. Due to the highly attenuating nature of this medium and its differential effects on the frequency composition of broad-band signals, signal analysis was performed by partitioning the signal into discrete windows in the time domain, corresponding to the emergence of individual wave phenomena within the medium. These windows were then transformed to the frequency domain for subsequent filtering and interpretation. Experimentation combined with theoretical modelling has shown that the appearance and decay of discrete frequency bands depends on both the composition of the concrete, termed the resonance phase, and its external importance with respect to the ultrasonic inspection of concrete and other such inhomogeneous materials.

Digital deconvolution analysis of ultrasonic signals influenced by the presence of longitudinally aligned steel cables in pre-stressed concrete

Several experiments are described in which ultrasonic signals were transmitted and received through concrete containing steel rods and cables. Details of how the signals were processed to extract information relating to the condition of the steel itself are presented. In particular, the method deconvolution is employed in a manner which allows the impulse response and frequency response of the embedded steel alone to be uniquely isolated from the effects of the surrounding concrete, whilst still allowing the transducers to be mounted on the surface of the concrete.

An ultrasonic inspection system capable of detecting voids and corroded steel components embedded in prestressed concrete structures : Colloquium on Measurements, Modelling and Imaging for Non-Destructive Testing, London (United Kingdom), 27 Mar. 1991. pp. 4/1–4/3. IEE (1991) Digest No. 1991/054

An ultrasonic system has been developed which detect voids, voids in ducts, major cable breaks and severe corrosion damage. Transducers are employed that generate a broad range of frequencies. The system operates by investigating the changes that occur in the different frequency bands as the signal traverses through the concrete. The central hypothesis of the signal processing methodology is that different wavelengths will be reflected with different energies depending upon the size, geometry and acoustic impedance of the defect encountered. By partitioning the reflected signal into discrete frequency bands and by comparing the magnitudes of their energies, it is possible to derive information relating to the position, size and nature of the defect.

An ultrasonic inspection system capable of detecting voids and corroded steel components embedded in prestressed concrete structures

An ultrasonic system has been developed which detect voids, voids in ducts, major cable breaks and severe corrosion damage. Transducers are employed that generate a broad range of frequencies. The system operates by investigating the changes that occur in the different frequency bands as the signal traverses through the concrete. The central hypothesis of the signal processing methodology is that different wavelengths will be reflected with different energies depending upon the size, geometry and acoustic impedance of the defect encountered. By partitioning the reflected signal into discrete frequency bands and by comparing the magnitudes of their energies, it is possible to derive information relating to the position, size and nature of the defect.