1,220 research outputs found
An Ultrasonic analog for a laser
We report measurements on ultrasonic systems analogous to random lasers. One
system entails unstable ultrasonic feedback between distinct transducers,
another involves a piezoelectric device that emits spontaneously and by
stimulation. Both systems are found to exhibit behaviors similar to those of
lasers. Over a wide range of parameters we observe narrow single emission
lines, sensitivity to linear cavity properties, complex multi-mode emissions,
and line narrowing
Entrainment and stimulated emission of auto-oscillators in an acoustic cavity
We report theory, measurements and numerical simulations on nonlinear
piezoelectric ultrasonic devices with stable limit cycles. The devices are
shown to exhibit behavior familiar from the theory of coupled auto-oscillators.
Frequency of auto-oscillation is affected by the presence of an acoustic cavity
as these spontaneously emitting devices adjust their frequency to the spectrum
of the acoustic cavity. Also, the auto-oscillation is shown to be entrained by
an applied field; the oscillator synchronizes to an incident wave at a
frequency close to the natural frequency of the limit cycle. It is further
shown that synchronization occurs here with a phase that can, depending on
details, correspond to stimulated emission: the power emission from the
oscillator is augmented by the incident field. These behaviors are essential to
eventual design of an ultrasonic system that would consist of a number of such
devices entrained to their mutual field, a system that would be an analog to a
laser. A prototype laser is constructed
Coherent backscattering of ultrasound without a source
Coherent backscattering is due to constructive interferences of reciprocal
paths and leads to an enhancement of the intensity of a multiply scattered
field near its source. To observe this enhancement an array of receivers is
conventionally placed close to the source. Our approach here is different. In a
first experiment, we recover the coherent backscattering effect (CBE) within an
array of sources and a distant receiver using time correlation of diffuse
fields. The enhancement cone has an excellent spatial resolution. The dynamics
of the enhancement factor is studied in a second experiment using correlation
of thermal phonons at the same ultrasonic frequencies, without any active
source
Overture Patriotic
https://digitalcommons.library.umaine.edu/mmb-ps/3177/thumbnail.jp
Melodies Of Scotland : Overture
https://digitalcommons.library.umaine.edu/mmb-ps/1805/thumbnail.jp
Adoration : A Meditation
https://digitalcommons.library.umaine.edu/mmb-ps/2183/thumbnail.jp
Overture Patriotic
https://digitalcommons.library.umaine.edu/mmb-ps/1570/thumbnail.jp
The Role of State Committees in Developing a Conservation Education Program *
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72361/1/j.1949-8594.1959.tb08233.x.pd
Energy Spectrum Evolution of a Diffuse Field in Elastic Body Caused by Weak Nonlinearity
We study the evolution of diffuse elastodynamic spectral energy density under
the influence of weak nonlinearity. It is shown that the rate of change of this
quantity is given by a convolution of the linear energy at two frequencies.
Quantitative estimates are given for sample aluminum and fused silica blocks of
experimental interest.Comment: 9 pages, 3 figures; revised for better presentatio
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