Ultrasonic signals

A novel approach for suppression of grain noise in ultrasonic signals, based on noncoherent detector statistics and signal entropy, is presented. The performance of the technique is demonstrated using ultrasonic B-scans from samples with coarse material structure. 

In the near future the technique will be further evaluated using ultrasonic signals from natural defects, e.g., fatigue cracks. The performance measure and the parameter optimization procedure wilt also be refined in order to obtain a computationally efficient implementation, easy to use for a trained operator. 

Nielsen, S.A. and Bj0rn0, L. (1997). Bistatic circular array imaging with gated ultrasonic signals. Acoustical Imaging, Vol. 23 (In press). 

Fig. 5 (a) Ultrasonic signal overlapped by a thermal component (observation time of 100 iis), (b) Low frequency ultrasonic signal filtered (observation time of 10 ns). 

Software allows to work in the mode of the ordinary ultrasonic flaw detector, to record and look through earlier recorded data files, to measures parameters of ultrasonic signals, to transmit through the buffer of the exchange the arrays for the further processing by different applications of Windows. 

Special constructions use also ultrasonic signal devices to measure values for the height of fluids or solids in high-pressure apparatus. 

Microwaves and Radar yes yes liquids, powders, granular solids. Action very similar to ultrasonic signals. Has been employed for discrete sensing. Pulsed energy used in transmitted or reflected inodes. Transmitter and receiver can be mounted outside the vessel. Very useful for determining mean levels io closed vessels under difficult conditions, e.g. in cases of high turbulence, in the presence of vapour or condensate, or where there is encrustation of surfaces with deposits. Typical accuracies are of the order of 0.2 per cent FSD 1. 

Devices such as ultrasonic flow equipment use the Doppler frequency shift of ultrasonic signals reflected from discontinuities in the fluid stream to obtain flow measurements. These discontinuities can be suspended solids, bubbles, or interfaces generated by turbulent eddies in the flow stream. The sensor is mounted on the outside of the pipe, and an ultrasonic beam from a piezoelectric crystal is transmitted through the pipe wall into the fluid at an angle to the flow stream. Signals reflected off flow disturbances are detected by a second piezoelectric crystal located in the same sensor. Transmitted and reflected signals are compared in an electrical circuit, and the corresponding frequency shift is proportional to the flow velocity. 

Uses Doppler frequency shift of ultrasonic signals reflected off discontinuities in fluid... 

Contact pulse echo—the ultrasonic signal is transmitted and received by a single unit. 

Immersion method—the assembly is immersed in a tank or water, and the water acts as a coupling mechanism for the ultrasonic signal. 

Bonded structures that are ultrasonically tested by the immersion methods often use a C-scan recorder to record the test. This recorder is an electric device that accepts signals from the pulser-receiver and prints out a plan view of the part. The ultrasonic search unit is automatically scanned over the part. The ultrasonic signals for bond or unbond are detected from built-in reference standards. C-scan NDT techniques are used extensively by aircraft manufacturers to inspect bonded parts. 

This definition of CBCs was established by Della Roy and Rustum Roy [6,20,21]. While Della Roy emphasized formation of modified conventional hydraulic cements, Rusmm Roy used CBC to mean formation of more general ceramics made at room temperature by techniques such as ultrasonic signals in aqueous phosphate systems. We extend this generalization further to include all inorganic materials that are consolidated into a hard mass by chemical reactions and not by sintering. 

P. L. Edwards, Ultrasonic Signal Distortion and its Effects on Velocity Measurements in Dispersive Constant-Group-Velocity Media , J. Acoust. Soc. Am. 1983, 73, 1608. 

The most commonly employed US transducers are thin platelets of piezoelectric (mainly ceramic) materials with metallic electrodes on both surfaces (see Section 1.4). Such transducers have resonance frequencies determined by the interference of the ultrasonic signals created at both surfaces and internal reflections. The interferences cause distortions (broadening) in the echo pattern in pulse-echo measurements. The resonances also introduce phase shifts in the signals and lead to restrictions in the bandwidth. The frequency range can be expanded by using concave, cylindrical or spherical piezotransducers. 

Shade, R.E., Furgason, E.S., and Murdock, L.L. 1990. Detection of hidden infestations by feeding-generated ultrasonic signals. Am. Entomol. 36, 231-234. 

Before the tensile test the samples were investigated by ultrasonic transmission measurements as described in Section 25.2. The peak power of the RF-car-rier pulse (again 10-30 cycles, center frequency 2.25 MHz) was swept from 0 up to 3.6 kW and back to zero. The transmitted ultrasonic signal was detected by a broadband receiver probe, recorded, and Fourier-transformed. The dependence of the resulting amplitude and phase spectra on the transmitting pulse power was recorded. Figs. 25.11 and 25.12 show the results obtained for two of the specimens, one with a weak and one with a strong bond of 5.5 and... 

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