Electromagnetic transducer

Jacobson et al. (1966, 1967) studied gastric secretion in relation to mucosal blood flow by an antipyrine clearance technique in conscious dogs with vagally denervated gastric fundic (Heidenhain) pouches. A vagally denervated fundic pouch is so constructed that the entire arterial blood supply is delivered by the splenic artery. A non-cannulating transducer (electromagnetic flowmeter) and a hydraulic occluder were implanted on the vessel. 

The electromagnetic field created by the transducer propagates through the examined material as a wave with the length... 

Shear Horizontal (SH) waves generated by Electromagnetic Acoustic Transducer (EMAT) have been used for sizing fatigue cracks and machined notches in steels by Time-of-Flight Diffraction (TOED) method. The used EMATs have been Phased Array-Probes and have been operated by State-of-the-art PC based phased array systems. Test and system parameters have been optimised to maximise defect detection and signal processing methods have been applied to improve accuracy in the transit time measurements. 

The first detector for optical spectroscopy was the human eye, which, of course, is limited both by its accuracy and its limited sensitivity to electromagnetic radiation. Modern detectors use a sensitive transducer to convert a signal consisting of photons into an easily measured electrical signal. Ideally the detector s signal, S, should be a linear function of the electromagnetic radiation s power, P,... 

Multiplying the transmittance by 100 gives the percent transmittance (%T), which varies between 100% (no absorption) and 0% (complete absorption). All methods of detection, whether the human eye or a modern photoelectric transducer, measure the transmittance of electromagnetic radiation. 

The important characteristics of a transducer used in conjunction with an electronic measurement system are accuracy, susceptibility, frequency, impedance and, if appropriate, the method of excitation. The transducer is likely to be the least accurate component in the system, and it should be calibrated (and recalibrated) at frequent intervals. It is likely to be subject to a range of different physical conditions, some of which it is there to detect and others by which it should remain unaffected (for example, a pressure transducer should be unaffected by any changes in temperature which it might be called upon to experience). Some types of transducer are not suitable for use under D.C. conditions and all will have an upper limit of frequency at which accuracy is acceptable. Many types of transducer are also affected by stray electromagnetic fields. 

The use of electromagnetic acoustic transducers (EMAT) obviates the coupling problems already referred to, and has been applied successfully to the inspection of boiler tubes. Ultrasonic time of flight diffraction (TOFD), developed by the Harwell Laboratory" , is utilised to fingerprint flaws (cracks) in process plant. Subsequent examination at, say, six month intervals can indicate any growth or extension of the crack. It is claimed that changes in crack height of 0-5 mm or less be estimated. 

Cardiac output can be measured using dye- or thermal-dilution techniques or by placement of an electromagnetic flow probe around the pulmonary artery. Insertion of a pressure transducer or fluid-filled catheter into the pulmonary artery and pulmonary vein allows for the calculation of pulmonary vascular resistance. The measurement of flow through the proximal aorta may also be useful but does not include coronary blood flow and as such is not equivalent to... 

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