A specially designed resistometer was constructed, and the lethal effect on Yersinia enterocolitica of ultrasonic waves (UW) at different static pressures (manosonication [MS]) and of combined heat-UW under pressure treatments (manothermosonication [MTS]) was investigated. During MS treatments at 30 degrees C and 200 kPa, the increase in the amplitude of UW of 20 kHz from 21 to 150 mum exponentially decreased decimal reduction time values (D(MS)) from 4 to 0.37 min. When pressure was increased from 0 to 600 kPa at a constant amplitude (150 mum) and temperature (30 degrees C), D(MS) values decreased from 1.52 to 0.20 min. The magnitude of this decrease in D(MS) declined progressively as pressure was increased. The influence of pressure on D(MS) values was greater with increased amplitude of UW. Pressure alone of as much as 600 kPa did not influence the heat resistance of Y. enterocolitica (D(60) = 0.094; z = 5.65). At temperatures of as much as 58 degrees C, the lethality of UW under pressure was greater than that of heat treatment alone at the same temperature. At higher temperatures, this difference disappeared. Heat and UW under pressure seemed to act independently. The lethality of MTS treatments appeared to result from the added effects of UW under pressure and the lethal effect of heat. The individual contributions of heat and of UW under pressure to the total lethal effect of MTS depended on temperature. The inactivating effect of UW was not due to titanium particles eroded from the sonication horn. The addition to the MS media of cysteamine did not increase the resistance of Y. enterocolitica to MS treatment. MS treatment caused cell disruption.

Influence of temperature and pressure on the lethality of ultrasound.

1 Introduction- 2 Ionizing Radiation Computed Tomography- 3 Thermal Imaging- 4 Microwave Imaging- 5 Ultrasonic Imaging- 6 Nuclear Magnetic Resonance- 7 Neutron Imaging- References- List of Notations- Color Plates

Nondestructive Characterization and Imaging of Wood

Review of air-coupled ultrasonic materials characterization.

In recent years, several new NDE applications of air-coupled, as opposed to liquid-coupled, ultrasonics have been seriously pursued. The applications range from through transmission testing of aerospace laminates and various honeycomb or foam filled materials, and solar cells, to pulse-echo flaw detection in plastic electronic packaging materials and in-line inspection of large-diameter gas pipelines. Most of the new applications have been made possible by major advances in component technologies: transducers, preamplifiers, pulsers, signal-conditioning, and impedance matching and noise-matching circuits. In this paper, we describe the transducer types and circuit topologies that are especially suitable for applications in the 20 kHz to 20 MHz frequency region. We also address the important key differences between air-coupled and liquid-coupled inspection configurations. In particular, we focus on the practical advantages and limitations that arise from the fact that gases and liquids exhibit substantially different specific densities and sound speeds.

NDE applications of air-coupled ultrasonic transducers

The inactivation of Bacillus subtilis spores by ultrasonic treatments under static pressure (Mano-Sonication, MS) and a combined MS/heat treatment (Mano-Thermo-Sonication) was investigated. The sporicidal effect of MS treatments depended on static pressure, amplitude of ultrasonic waves and treatment temperature. At 70 degrees C, pressure increments up to 500 kPa caused progressively more inactivation. An MS treatment at 500 kPa and 117 microns of amplitude for 12 min inactivated approximately 99% of the B. subtilis spore population. Over 500 kPa, further increments in pressure did not increase the percentage of inactivation. In the range 90-150 microns, an exponential relationship was observed between the amplitude of ultrasonic waves under pressure and the number of survivors. While an MS treatment (20 kHz, 300 kPa, 70 degrees C, 12 min) at 90 microns inactivated 75% of the B. subtilis spore population, the same treatment at 150 microns inactivated 99.9% of this population. The MS treatments at temperatures higher than 70 degrees C (MTS) led to more spore inactivation. In the range 70-90 degrees C, the combination of heat with an MS treatment (20 kHz, 300 kPa, 117 microns, 6 min) had a synergistic effect on spore inactivation. The inactivating effect of ultrasound was due neither to titanium particles eroded from the sonication tip, nor to free radicals released during ultrasonic treatment. The MS treatments sensitized spores of B. subtilis to lysozyme.

P. Heikkila

Papers

Plate wave resonance — a contactless test method