Representative Transducers

The VIGRAL approach represents the reflecting surface of a defect as an ensemble of virtual point sources. At every measurement point of the B-Scan, the detecting transducer responds... 

Under ideal conditions (e.g., point sources producing spherical waves and no multiple reflections) a rectified backscattered signal represents line integrals of the ultrasonic reflectivity over concentric arcs centered at the transducer position. To reconstruct the reflection tomo-... 

We first supposed that the field radiated into the piece by the transducer is known, thanks to the Champ-Sons model. Then, the main approximation used consists in making far field assumptions in the beam defect interaction area. In the case of a focused transducer we assume that the incident wavefronts on the defect are plane. This is equivalent to say that the defect is located in or near the transducer focal area and that a defect located outside this zone does not cause a significant echo. In the case of planar contact transducer, the incident wavefronts on the defect are assumed to be spherical The incident field on the defect is therefore approximated by the product of a spatial function gfp,0,z)describing the amplitude distribution in the beam and a time-delayed waveform < ) ft) representing the plane or spherical propagation in the beam. The incident field on the defect can therefore be approximated for ... 

G = current-to-pressure transducer(I/P) H = actuator and I = final control element. Some devices combine A, B, and C, and (--) represents the line... 

Increasingly, the word sensor is used interchangeably with, or in place of, the word transducer to represent the conversion of one type of energy into another. The word actuator, however, refers to a distinctly different set of devices capable of activating a device upon receiving an appropriate signal. Sensors and actuators may be found as part of a system on a single piece of siUcon. 

Pneumatic signals are represented by solid hnes that are cross-hatched intermittently. The signal from the I/P transducer to the pneumatic positioning valve is pneumatic. 

The data acquired using broadband data is limited to a value that represents the total energy that is being generated by the machine-train at the measurement point location and in the direction opposite the transducer. Most programs trend and compare the recorded value at a single point and disregard the other measurement points on the common-shaft. 

Chemokines are small chemotactic cytokines that act as important messenger molecules between cells of the immune system. Chemokines produce their effects by activating a family of G-protein-coupled receptors. Chemokine receptors are all seven-transmembrane glycoproteins that are structurally related. They may be characterized into those that bind to specific ligands, or those that bind several chemokine ligands. There are also virally encoded (viral) chemokine receptors that represent shared receptors that have been transduced into the viral genome during evolutionary history (Premack and SchaU 1996). 

Mossbauer spectra are usually recorded in transmission geometry, whereby the sample, representing the absorber, contains the stable Mossbauer isotope, i.e., it is not radioactive. A scheme of a typical spectrometer setup is depicted in Fig. 3.1. The radioactive Mossbauer source is attached to the electro-mechanical velocity transducer, or Mossbauer drive, which is moved in a controlled manner for the modulation of the emitted y-radiation by the Doppler effect. The Mossbauer drive is powered by the electronic drive control unit according to a reference voltage (Fr), provided by the digital function generator. Most Mossbauer spectrometers are operated in constant-acceleration mode, in which the drive velocity is linearly swept up and down, either in a saw-tooth or in a triangular mode. In either case. 

The experimental design for the photoacoustic experiment is relatively simple. The apparatus is quite similar to that employed for nanosecond absorption spectroscopy with the major difference being that a piezoelectric transducer is used to monitor the acoustic waves rather than a photomultiplier tube to analyze the incident light. A representative schematic for PAC is shown in Fig. 2. 

---