J. Adamowski - Academia.edu (original) (raw)
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A dropped object was used as a source of an impulsive concentric wave.A wave generator was used t... more A dropped object was used as a source of an impulsive concentric wave.A wave generator was used to create reversed wave in the time reversal experiments.A set of wave probes measures the convergence of waves in the middle of the tank.The wave propagation was disturbed by a reflective wall inside the tank.Time reversal technique can be used to concentrate back water waves.Offshore structures design and validation currently involves complex numerical simulations and experimental verifications using reduced models. These experiments are usually conducted in ocean wave tanks. The wave focalization using time reversal is a well-known technique in the field of acoustics. It was proved using several physical waves, but was not experimentally tested in ocean wave in the scale of a wave tank. For this purpose, the tank of the University of São Paulo was used for these experiments. The tank has 148 flaps equipped with wave probes for control feedback of active wave absorption. Hence, the waves can be recorded and re-emitted by the flaps. The time reversal technique is here experimentally evaluated in order to generate focused waves in water tests. First, a small object dropping into the tank water acts as a source of impulsive wave for time reversal experiments. In a second experiment, a reflective wall is introduced into the tank, in order to distort the wave propagation and generate wave reverberations. The results show the ability of the time reversal technique to focalize impulsive waves back at the origin, even in the case of obstacles to the wave propagation.
IEEE Transactions on Industry Applications, 2000
The optimal operation of an oil well requires the periodic measurement of temperature and pressur... more The optimal operation of an oil well requires the periodic measurement of temperature and pressure at the downhole. In this paper, acoustic waves are used to transmit data to the surface through the pipeline column of the well, making up a wireless transmission system. Binary data is transmitted in two frequencies, using frequency-shift keying modulation. Such transmission faces problems with noise, attenuation, and, at pipeline joints, multiple reflections and nonlinear distortion. Hence, conventional demodulation techniques do not work well in this case. The neural network presented here classifies signals received by the receiver to estimate transmitted data, using a linear-vector-quantization-based network, with the help of a preprocessing procedure that transforms time-domain incoming signals in three-dimensional images. The results have been successfully verified. The neural network estimation principles presented in this paper can be easily applied to other patterns and time-domain recognition applications.
Ultrasonics, 2010
The therapeutic ultrasound (US) is one of the resources mostly used by physiotherapists; however ... more The therapeutic ultrasound (US) is one of the resources mostly used by physiotherapists; however the use of uncalibrated equipments results in inefficient or even harmful therapies to the patient. In this direction, the objective of this study was to evaluate the performance and the procedures of utilization and maintenance of US in use in clinics and Physical-therapy offices. A questionnaire with questions related to the procedures applied in service during the use of therapeutic ultrasound was applied to physiotherapists. The performance of 31 equipments of 6 different brands and 13 different models was evaluated according to the IEC 61689 norm. The parameters measured were: acoustic power; effective radiating area (AER); non-uniformity ratio of the beam (RBN); maximum effective intensity; acoustic frequency of operation, modulation factor and wave form on pulsate mode. As for the questionnaires, it was evident that the professionals are not concerned about the calibration of the equipment. The results demonstrated that only 32.3% of the equipments were in accordance with the norms for the variables power and effective radiation area. The frequency analysis indicated that 20% of the 3 MHz transducers and 12.5% of the 1 MHz contemplated the norms. In the pulsate mode, 12.7% presented relation rest/duration inside allowed limits. A great variation of the ultrasonic field was observed on the obtained images, which presented beams not centered, sometimes with bifurcation of its apex. The results allow concluding that, although used in therapeutic sessions with the population, none of the equipments presents all the analyzed variables inside technical norms.
A dropped object was used as a source of an impulsive concentric wave.A wave generator was used t... more A dropped object was used as a source of an impulsive concentric wave.A wave generator was used to create reversed wave in the time reversal experiments.A set of wave probes measures the convergence of waves in the middle of the tank.The wave propagation was disturbed by a reflective wall inside the tank.Time reversal technique can be used to concentrate back water waves.Offshore structures design and validation currently involves complex numerical simulations and experimental verifications using reduced models. These experiments are usually conducted in ocean wave tanks. The wave focalization using time reversal is a well-known technique in the field of acoustics. It was proved using several physical waves, but was not experimentally tested in ocean wave in the scale of a wave tank. For this purpose, the tank of the University of São Paulo was used for these experiments. The tank has 148 flaps equipped with wave probes for control feedback of active wave absorption. Hence, the waves can be recorded and re-emitted by the flaps. The time reversal technique is here experimentally evaluated in order to generate focused waves in water tests. First, a small object dropping into the tank water acts as a source of impulsive wave for time reversal experiments. In a second experiment, a reflective wall is introduced into the tank, in order to distort the wave propagation and generate wave reverberations. The results show the ability of the time reversal technique to focalize impulsive waves back at the origin, even in the case of obstacles to the wave propagation.
IEEE Transactions on Industry Applications, 2000
The optimal operation of an oil well requires the periodic measurement of temperature and pressur... more The optimal operation of an oil well requires the periodic measurement of temperature and pressure at the downhole. In this paper, acoustic waves are used to transmit data to the surface through the pipeline column of the well, making up a wireless transmission system. Binary data is transmitted in two frequencies, using frequency-shift keying modulation. Such transmission faces problems with noise, attenuation, and, at pipeline joints, multiple reflections and nonlinear distortion. Hence, conventional demodulation techniques do not work well in this case. The neural network presented here classifies signals received by the receiver to estimate transmitted data, using a linear-vector-quantization-based network, with the help of a preprocessing procedure that transforms time-domain incoming signals in three-dimensional images. The results have been successfully verified. The neural network estimation principles presented in this paper can be easily applied to other patterns and time-domain recognition applications.
Ultrasonics, 2010
The therapeutic ultrasound (US) is one of the resources mostly used by physiotherapists; however ... more The therapeutic ultrasound (US) is one of the resources mostly used by physiotherapists; however the use of uncalibrated equipments results in inefficient or even harmful therapies to the patient. In this direction, the objective of this study was to evaluate the performance and the procedures of utilization and maintenance of US in use in clinics and Physical-therapy offices. A questionnaire with questions related to the procedures applied in service during the use of therapeutic ultrasound was applied to physiotherapists. The performance of 31 equipments of 6 different brands and 13 different models was evaluated according to the IEC 61689 norm. The parameters measured were: acoustic power; effective radiating area (AER); non-uniformity ratio of the beam (RBN); maximum effective intensity; acoustic frequency of operation, modulation factor and wave form on pulsate mode. As for the questionnaires, it was evident that the professionals are not concerned about the calibration of the equipment. The results demonstrated that only 32.3% of the equipments were in accordance with the norms for the variables power and effective radiation area. The frequency analysis indicated that 20% of the 3 MHz transducers and 12.5% of the 1 MHz contemplated the norms. In the pulsate mode, 12.7% presented relation rest/duration inside allowed limits. A great variation of the ultrasonic field was observed on the obtained images, which presented beams not centered, sometimes with bifurcation of its apex. The results allow concluding that, although used in therapeutic sessions with the population, none of the equipments presents all the analyzed variables inside technical norms.