Figure 4 - uploaded by Raied Al-Lashi
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The quantisation process. The horizontal axis represents the input signal amplitude and the vertical axis represents the digitised result.
Source publication
This paper describes a system for ultrasonic wave attenuation
measurements which is based on pseudo-random binary codes as
transmission signals combined with on-the-fly correlation for received
signal detection. The apparatus can receive signals in the nanovolt
range against a noise background in the order of hundreds of microvolts
and an analogue...
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Citations
... This coded information is used to modulate the original transmission signal and obtain a phase-modulated transmission. There are several other prevalent codes, such as Golay codes [23,24] and Barker codes; however, this paper solely deals with pseudo-random codes, which are randomly generated code streams of 1 and −1, as shown in Figure 3(a). The proposed application, using transmit-receive information encoding with a gap sequence (as described in the following section) is unaffected by merit factor variations as defined by Isla and Celga [21] . ...
High-power ultrasonic non-destructive evaluation (NDE) poses significant threats to intrinsic safety. It may lead to hazards in critical industrial applications, especially in oil & gas refineries, high-energy material technologies and the aerospace and aviation industries. Typically, industries employ various certifications and undertake several safety protocols to suppress the likelihood of industrial hazards. In order to satisfy safety standards for operating high-power equipment close to potential explosives and inflammable substances, industries direct large sums of investment into making these inspection systems intrinsically safe by designing complex structures and devising procedures to isolate such equipment from the system or process entirely. However, the uncertainty regarding the effectiveness of such protective measures results in a persisting difficulty in obtaining plant safety certifications and approvals. In this paper, the application of a coded excitation method to make inspection systems intrinsically safe and easily certifiable is explored. Using a pulse compression-based signal processing technique called coded excitation, it has been made possible to achieve non-contact transduction (electromagnetic acoustic transduction and air-coupled transduction) in transmitreceive mode with excitation as low as 0.5 V pp (peak-to-peak supply voltage). This work reports on the application of coded excitation in bringing down the transduction power requirements for guided ultrasonic wave inspection, thereby making it possible to formulate new inspection applications at very low power, particularly in safety-critical industries.
... Coded excitations have shown considerable potential in medical imaging and radar, but only a few applications have been reported for non-destructive testing (NDT) (1)(2)(3) . Ultrasonic flowmeters use time-of-flight (TOF) between a pair of transducers, have the advantage of no moving parts, and can measure both high and low extremes of flow (4) . ...
Coded excitation techniques have been widely used in radar and sonar for improved resolution and noise performance. Whilst becoming more common in medical ultrasound, only few industrial applications have been reported. We present some results from work looking at air-coupled phased arrays aiming at improved air flow speed measurements. The high insertion loss for air-coupled transducers means that coded excitation is desirable and needs to be investigated for arrays. Transducer sensitivity is often optimised at the expense of bandwidth, which can compromise the benefits of coded excitation and this relationship has been examined. The paper reports on the relative performance of Golay codes, and examines the trade-offs with transducer bandwidth.
... Meanwhile, certain defect of composite laminates also applicable to detect significantly by using air-coupled non-contact transducer but limit to some dimension [5]. Since the SNR approach used as one of measurable parameters to determine the inspection quality of ultrasonic measurement, several works has been done included pipeline inspection [6], aluminium buffer rods in molten bath [7] and in composite material inspection [8]. However, pre-processing work like signal filtering and smoothing are required to enhance the SNR for better flaw signal detection. ...
In ultrasonic non-destructive tests, transducer is one of the most part need to determine carefully. The attenuation behaviour of transducer will impact overall ultrasonic measurement accuracy base on signal processing analysis. In normal applications, ultrasonic inspector relies on transducer calibration result produced by the manufacturer where there are no doubts to question the accuracy of measurement results. However, the attenuation behaviour of transducer can be defined based on signal-to-noise ratio (SNR) value. In this paper, the attenuation behaviour of ultrasonic transducer was investigated based on SNR value through signal filtering approach. Since the detection of flaw in composite laminates using ultrasonic non-destructive testing (NDT) approach is highly complex due to noise occurrences, several types of filter were applied and compared each other in order to propose the suggested filter base on SNR result. A 2.25 MHz single crystal immersion transducer is used to perform ultrasonic scanning for composite laminates material which is thickness up to 7.4 mm with scanning rate 7.50 mm/sec under lab condition. As a comparison result, when applying discrete wavelet transform (DWT) de-noising approach, SNR was enhanced and caused defect detection was easily identified.
... In those cases, the information has been shown to be recovered using quantization levels that are not much bigger Manuscript than the signal itself [4], [6], [10], [15]- [17]-the explanation of how this is possible was attributed to the effect of dithering [18]- [20]. Of particular interest is [6], where it was reported that the information can be recovered using binary (1-b) quantization only. ...
Low-power excitation and/or low sensitivity transducers, such as electromagnetic acoustic transducers (EMATs), piezoelectric paints, air-coupled transducers, or small elements of dense arrays may produce signals below the noise threshold at the receiver. The information from those noisy signals can be recovered after averaging or pulse-compression using binary (one-bit) quantisation only without experiencing significant losses. Hence, no analog-to-digital converter is required, which reduces the data trhoughput and makes the electronics faster, more compact and energy efficient. All this is especially attractive for applications that require arrays with many channels and high sampling rates, where the sampling rate can be as high as the system clock. In this paper, the theory of binary quantisation is reviewed, mainly from previous work on wireless sensor networks, and the signal-to-noise ratio (SNR) of the input signals under which binary quantisation is of practical interest for ultrasound applications is investigated. The main findings are that in most practical cases binary quantisation can be used with small errors when the input SNR is in the order of 8 dB or less. Moreover, the maximum SNR after binary quantisation and averaging can be estimated as 10 log10 N 2 dB, where N is the number of averages.
