Volume 119, Issue 5, May 2006
Index of content:
- ULTRASONICS, QUANTUM ACOUSTICS, AND PHYSICAL EFFECTS OF SOUND 
Detailed study of a traveling wave thermoacoustic refrigerator driven by a traveling wave thermoacoustic engine119(2006); http://dx.doi.org/10.1121/1.2184267View Description Hide Description
Thermoacoustic systems have very attractive features and possible wide applications in many areas, especially for cooling purposes. Inventions of traveling wave thermoacoustic engines and traveling wave thermoacoustic refrigerators with work recovery capability have greatly improved the thermodynamic efficiencies of the thermoacoustic systems. To fully utilize the advantages of traveling wave systems, a traveling wave work-recoverable thermoacoustic refrigerator has been designed and built that is driven by a traveling wave thermoacoustic engine, which is aimed at domestic refrigeration purposes. So far, the lowest temperature of and cooling power at are obtained by the system with helium gas and working frequency. Heat input into the system is . Simulations based on linear thermoacoustic theory have also been done for comparison with experimental results, which shows reasonable agreement within a certain pressure wave amplitude range and cold end temperature range. The comparisons meanwhile imply some serious loss mechanism inside the traveling wave thermoacoustic refrigerator.
119(2006); http://dx.doi.org/10.1121/1.2184288View Description Hide Description
Electromagnetic acoustic transducers (EMATs) generate ultrasonic waves in metals through an electromagnetic coupling mechanism. A concept for EMAT generation, using a coil alone without a permanent magnet, but with a pulse generator and a sample, is introduced. A simplified equivalent coil circuit is given and has been validated by experimental measurements. Such an equivalent circuit can be used for variations in excitation current calculations, which have often been neglected in previous publications in this area but have proved to be of great importance in considering the efficiency and frequency characteristics of ultrasonic generation. The equivalent coilinductance is dependent on the distance between the coil and the sample, due to coil interactions with eddycurrents and the Ampere current of the magnetization mechanism. Analytical solution for an annular coil above metal samples is given, and the influences of the lift-off, coil radius, material magnetic permeability and electrical conductivity on the equivalent coilinductance are discussed. Experimental measurements agree well with predictions.