Generación de ondas de Lamb en estructuras tipo placa mediante cerámicas piezoeléctricas

[EN] In this work, Lamb waves have been generated in a thin aluminum plate by bonding a piezoceramic actuator onto the plate. The acoustic pressure immediately above the plate was measured by a needle hydrophone, coupled to the plate through a thin oil layer, across several centimeters. Use of a 2D FFT algorithm then provides the dispersion curves which compare well to the analytical solution calculated using the dispersion equation. Next, the Lamb modes were selectively reinforced or cancelled by bonding another piezoceramic to the plate at an appropriate location. If the second actuator is excited in phase with the first one the symmetric mode, S0, can be reinforced whereas the antisymmetric mode, A0, is partially cancelled. If the two actuators are excited out of phase, the A0 mode is then enhanced respect to the S0 mode.[ES] En este trabajo se han utilizado cerámicas piezoeléctricas para generar ondas de Lamb en estructuras tipo placa. Se midió la presión acústica a lo largo de unos centímetros de la placa mediante un hidrófono acoplado a ésta mediante una fina capa de aceite. Aplicando a esta información la trasformada bidimensional de Fourier se obtuvieron las curvas de dispersión experimentales y se compararon con las obtenidas teóricamente. A continuación, los modos de Lamb se reforzaron o cancelaron pegando otra cerámica en la placa en la posición adecuada. Al excitar la segunda cerámica en fase con la primera amplificamos el modo simétrico, S0, mientras que el modo antisimétrico, A0, se ve parcialmente cancelado. Excitando las dos cerámicas en contrafase, reforzamos el modo antisimétrico, A0, respecto del simétrico, S0.Support from the CICYT, grant DPI2004-06756-C03-01, is acknowledged.Peer reviewe

Effect on comfort of administering bubble-humidified or dry oxygen: the Oxyrea non-inferiority randomized study.

The clinical interest of using bubble humidification of oxygen remains controversial. This study was designed to further explore whether delivering dry oxygen instead of bubble-moistened oxygen had an impact on discomfort of ICU patients. This randomized multicenter non-inferiority open trial included patients admitted in intensive care unit and receiving oxygen. Any patient receiving non-humidified oxygen (between 0 and 15 L/min) for less than 2 h could participate in the study. Randomization was stratified based on the flow rate at inclusion (less or more than 4 L/min). Discomfort was assessed 6-8 and 24 h after inclusion using a dedicated 15-item scale (quoted from 0 to 150). Three hundred and fifty-four ICU patients receiving non-humidified oxygen were randomized either in the humidified (HO) (n = 172), using bubble humidifiers, or in the non-humidified (NHO) (n = 182) arms. In modified intention-to-treat analysis at H6-H8, the 15-item score was 26.6 ± 19.4 and 29.8 ± 23.4 in the HO and NHO groups, respectively. The absolute difference between scores in both groups was 3.2 [90% CI 0.0; + 6.5] for a non-inferiority margin of 5.3, meaning that the non-inferiority analysis was not conclusive. This was also true for the subgroups of patients receiving either less or more than 4 L/min of oxygen. At H24, using NHO was not inferior compared to HO in the general population and in the subgroup of patients receiving 4 L/min or less of oxygen. However, for patients receiving more than 4 L/min, a post hoc superiority analysis suggested that patients receiving dry oxygen were less comfortable. Oxygen therapy-related discomfort was low. Dry oxygen could not be demonstrated as non-inferior compared to bubble-moistened oxygen after 6-8 h of oxygen administration. At 24 h, dry oxygen was non-inferior compared to bubble-humidified oxygen for flows below 4 L/min

Generación de ondas de Lamb en estructuras tipo placa mediante cerámicas piezoeléctricas

[EN] In this work, Lamb waves have been generated in a thin aluminum plate by bonding a piezoceramic actuator onto the plate. The acoustic pressure immediately above the plate was measured by a needle hydrophone, coupled to the plate through a thin oil layer, across several centimeters. Use of a 2D FFT algorithm then provides the dispersion curves which compare well to the analytical solution calculated using the dispersion equation. Next, the Lamb modes were selectively reinforced or cancelled by bonding another piezoceramic to the plate at an appropriate location. If the second actuator is excited in phase with the first one the symmetric mode, S0, can be reinforced whereas the antisymmetric mode, A0, is partially cancelled. If the two actuators are excited out of phase, the A0 mode is then enhanced respect to the S0 mode.[ES] En este trabajo se han utilizado cerámicas piezoeléctricas para generar ondas de Lamb en estructuras tipo placa. Se midió la presión acústica a lo largo de unos centímetros de la placa mediante un hidrófono acoplado a ésta mediante una fina capa de aceite. Aplicando a esta información la trasformada bidimensional de Fourier se obtuvieron las curvas de dispersión experimentales y se compararon con las obtenidas teóricamente. A continuación, los modos de Lamb se reforzaron o cancelaron pegando otra cerámica en la placa en la posición adecuada. Al excitar la segunda cerámica en fase con la primera amplificamos el modo simétrico, S0, mientras que el modo antisimétrico, A0, se ve parcialmente cancelado. Excitando las dos cerámicas en contrafase, reforzamos el modo antisimétrico, A0, respecto del simétrico, S0.Support from the CICYT, grant DPI2004-06756-C03-01, is acknowledged.Peer reviewe

Lamb waves generation in plates using glued piezoceramics

In this work, Lamb waves have been generated in a thin aluminum plate by bonding a piezoceramic actuator onto the plate. The acoustic pressure immediately above the plate was measured by a needle hydrophone, coupled to the plate through a thin oil layer, across several centimeters. Use of a 2D FFT algorithm then provides the dispersion curves which compare well to the analytical solution calculated using the dispersion equation. Next, the Lamb modes were selectively reinforced or cancelled by bonding another piezoceramic to the plate at an appropriate location. If the second actuator is excited in phase with the first one the symmetric mode, S0, can be reinforced whereas the antisymmetric mode, A0, is partially cancelled. If the two actuators are excited out of phase, the A0 mode is then enhanced respect to the S0 mode.<br><br>En este trabajo se han utilizado cerámicas piezoeléctricas para generar ondas de Lamb en estructuras tipo placa. Se midió la presión acústica a lo largo de unos centímetros de la placa mediante un hidrófono acoplado a ésta mediante una fina capa de aceite. Aplicando a esta información la trasformada bidimensional de Fourier se obtuvieron las curvas de dispersión experimentales y se compararon con las obtenidas teóricamente. A continuación, los modos de Lamb se reforzaron o cancelaron pegando otra cerámica en la placa en la posición adecuada. Al excitar la segunda cerámica en fase con la primera amplificamos el modo simétrico, S0, mientras que el modo antisimétrico, A0, se ve parcialmente cancelado. Excitando las dos cerámicas en contrafase, reforzamos el modo antisimétrico, A0, respecto del simétrico, S0