Position echo

Given these data, some advocates then suggest that it is self-evident that schools should expand what they do related to mental health. This position echoes the call of many others who have recognized that schools provide an important venue for enhancing the health status of children and adolescents. Such a view is well articulated, for instance, in an Institute of Medicine report (Allensworth et al., 1997) and in initiatives funded by the federal government designed to foster coordinated school health programs and mh in schools (Adelman et al., 1999 Marx, Wooley, Northrop, 1998 Weist, 1999). 

The main goal of ultrasonic grain noise suppression in material flaw detection is to improve the perceptual possibilities of the operator to observe defect echoes. The suppression is defined as perceptually ideal when a received signal (or image) which contains echoes buried in noise is filtered to yield nonzero values only at the positions of the defect echoes. 

Figure I represents a two-dimensional damage distribution of an impact in a 0/90° CFRP laminate of 3 mm thickness. Unlike in ultrasonic testing, which is usually the standard method for this problem, there is no shadowing effect on the successive layers by delamination echos. With the method of X-ray refraction the exact concentration of debonded fibers can be calculated for each position averaged over the wall thickness. Additionally the refraction allows the selection of the fiber orientation. The presented X-ray refraction topograph detects selectively debonded fibers of the 90° direction.

Fig. 6. Test with one segment of 6 sector transducer in pulse-echo mode on aluminium plate, (a) no defect (b) defect simulated with mercury droplet (c) defect position.

The comparison between the experimental and computed Bscan is realised on the segmented data (figure 3). Although the multiple reflections from the front to the backwall are not predicted, it can be concluded that, for this specific configuration, a good agreement is achieved. For all the principal echoes, the amplitude and position is correctly predicted. 

Subsequently, we suspected the duct s grid system to be positioned at 3,60m. We, therefore, concentrated our tests on these areas. At all new positions tested elear echo-signals were found (see Scans in Fig. 8). This resulted in 7 ducts localized around the circumference. In most cases the drilling instantly hit the duets, heneeforth all duets were found. 

The transducer parameters (position, frequency, diameter) are optimised in order to obtain a sound beam which enables a good echo from the crack. 

The control of the airborne sound location system, the coupling monitor and the real-time evaluation of all signals, including the echo indications from the ultrasonic instrument, is carried out on two additional boards in the PC. The graphic user interface (under Windows 95), including online help, enables an easy operation of the system. The evaluation program links all echo indications in real time with the probe position and displays them in a graphic repre-... 

The exact position of reflectors within the weld volume is calculated by means of the known probe position plus weld geometry and transferred to a true-to-scale representation of the weld (top view and side view). Repeated scanning of the same zone only overwrites the stored indications in cases where they reach a higher echo amplitude. The scanning movement of the probe is recorded in the sketch at the top, however, only if the coupling is adequate and the probe is situated within the permissible rotation angle. 

Fig.3 shows the defect position on the bonding interface and the model of the reflective echo. The defects are exists on each bonding surface as(ii) (iv), is no exist as (i). 

Fig.7 shows the relation between the echo height F/B and the defect area s ratio Sr/So, when the ultrasonic wave is input from FCD500 side. This Sr/So is the ratio of the defect area Sr to the beam irradiational area So. Moreover, // X of (a) (b) (c) (d) are the value at the position where the echo height F/B is changed in Fig.5. And, the defect position of (i) (iv) in figure is shown the each position of Fig.3 respectively. Moreover, each curves are calculation values respectively, and this is described later. There has two case that F/T) of (a) (d) is changed by the defect position. The first case, F/B are increased as defect area s ratio Sr/So increases. The second case, F/B are increased after decrases as Sr/So increases. And defect area s ratio Sr/So to which F/B decreases is different according to the defect position...

Fig.9 shows the relation between the echo height F/B and the defect area s ratio Sr/So, when the ultrasonic wave is input from SUS304 side. As for each curves are similar to Fig.7. The tendency F/B are increased as Sr/So increases, or are increased after decrases as Sr/So increases by the defect position.

During the attenuation measurements. Transducer 1 was excited with a narrowband tone burst with center frequency 18 MHz, see Figure 1 for a schematic setup. The amplitude of the sound pressure was measured at Tranducer 2 by means of an amplitude peak detector. A reference amplitude, Are/, was measured outside the object as shown at the right hand side of Figure 1. The object was scanned in the j y-plane and for every position, (x, y), the attenuation, a x, y), was calculated as the quotient (in db) between the amplitude at Transducer 2, A[x, y), and Are/, i.e., a(x,y) = lOlogm Pulse echo measurements and preprocessing... 

The PE data was obtained by repeating the scanning of the object, now measuring the received echo at Transducer 1. For every position, (x, y), an A-scan was obtained from which we extracted the back wall echo by means of a time gate. This back wall echo is denoted s(x, y). Note that s x, y) is a time signal that can be written s(f, x, y) where t is the time index. One example of such a back wall echo is shown in Figure 2. 

The echo phase does not depend on the initial position of the nuclei, only on their displacement, vA, occurring in the interval between the gradient pulses. Analysis of the phase of the echo yields a measure of flow velocity in a bulk sample. Spatial resolution is easily obtained by the incorporation of additional imaging gradients. 

As the spins precess in the equatorial plane, they also undergo random relaxation processes that disturb their movement and prevent them from coming together fiilly realigned. The longer the time i between the pulses the more spins lose coherence and consequently the weaker the echo. The decay rate of the two-pulse echo amplitude is described by the phase memory time, which is the time span during which a spin can remember its position in the dephased pattern after the first MW pulse. Tyy is related to the homogeneous linewidth of the individual spin packets and is usually only a few microseconds, even at low temperatures. 

Figure Bl.15.16. Two-pulse ESE signal intensity of the chemically reduced ubiqumone-10 cofactor in photosynthetic bacterial reaction centres at 115 K. MW frequency is 95.1 GHz. One dimension is the magnetic field value Bq, the other dimension is the pulse separation x. The echo decay fiinction is anisotropic with respect to the spectral position.

In most ultrasonic tests, the significant echo signal often is the one having the maximum ampHtude. This ampHtude is affected by the selection of the beam angle, and the position and direction from which it interrogates the flaw. The depth of flaws is often deterrnined to considerable precision by the transit time of the pulses within the test material. The relative reflecting power of discontinuities is deterrnined by comparison of the test signal with echoes from artificial discontinuities such as flat-bottomed holes, side-drilled holes, and notches in reference test blocks. This technique provides some standardized tests for sound beam attenuation and ultrasonic equipment beam spread. 

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