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Acoustic Phase Conjugation
Acoustic phase conjugation is a set of techniques meant to perform phase conjugation on acoustic waves. Techniques Acoustic phase conjugation can appear in a solid when the sound velocity is modulated by an electromagnetic field. The generation of the conjugate wave can be seen as the decay of a photon into two phonons, as seen on the diagram. The two phonons have opposite wave vectors k and -k (they will propagate in opposite directions) and a frequency two time smaller than that of the photon. Parametric pumping techniques can be performed in several media: * In piezoelectric crystals, a nonlinear piezoelectric effect will produce a modulation of fractions of a percent. * In magnetic crystals, a modulation of dozens of percent can be reached through the magneto-acoustic coupling, which can be improved by combining the magnetostriction and spin reorientation transition effects or using the magnetoacoustic resonance. A "supercritical" or "giant" amplification, up to 80 dB, can be ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Phase Conjugation
Phase conjugation is a physical transformation of a wave field where the resulting field has a reversed propagation direction but keeps its amplitudes and phases. Description It is distinguished from Time Reversal Signal Processing by the fact that phase conjugation uses a holographic or parametric pumping whereas time reversal records and re-emits the signal using transducers. * Holographic pumping makes the incident wave interact with a pump wave of the same frequency and records its amplitude-phase distribution. Then, a second pump wave reads the recorded signal and produces the conjugate wave. All those waves have the same frequency. * In parametric pumping, the parameters of the medium are modulated by the pump wave at double frequency. The interaction of this perturbation with the incident wave will produce the conjugate wave. Both techniques allow an amplification of the conjugate wave compared to the incident wave. As in time reversal, the wave re-emitted by a phase conj ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Acoustic Wave
Acoustic waves are a type of energy propagation through a medium by means of adiabatic loading and unloading. Important quantities for describing acoustic waves are acoustic pressure, particle velocity, particle displacement and acoustic intensity. Acoustic waves travel with a characteristic acoustic velocity that depends on the medium they're passing through. Some examples of acoustic waves are audible sound from a speaker (waves traveling through air at the speed of sound), seismic waves (ground vibrations traveling through the earth), or ultrasound used for medical imaging (waves traveling through the body). Wave properties Acoustic wave equation The acoustic wave equation describes the propagation of sound waves. The acoustic wave equation for sound pressure in one dimension is given by - = 0 where *p is sound pressure in Pa *x is position in the direction of propagation of the wave, in m *c is speed of sound in m/s *t is time in s The wave equation for particl ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lithotripsy
Lithotripsy is a non-invasive procedure involving the physical destruction of hardened masses like kidney stones, bezoars or gallstones. The term is derived from the Greek words meaning "breaking (or pulverizing) stones" ( litho- + τρίψω ripso. Uses Lithotripsy is a non-invasive procedure used to break up hardened masses like kidney stones, bezoars or gallstones. Contraindications "Commonly cited absolute contraindications to SWL include pregnancy, coagulopathy or use of platelet aggregation inhibitors, aortic aneurysms, severe untreated hypertension, and untreated urinary tract infections Techniques * Extracorporeal shock wave therapy * Intracorporeal (endoscopic lithotripsy): ** Laser lithotripsy : effective for larger stones (> 2 cm) with good stone-free and complication rates. ** Electrohydraulic lithotripsy ** Mechanical lithotripsy ** Ultrasonic lithotripsy : safer for small stones (<10 mm) History Surgery was the only method to remo ...[...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hyperthermia Therapy
Hyperthermia therapy ''(or hyperthermia, or thermotherapy)'' is a type of medical treatment in which body tissue is exposed to temperatures above body temperature, in the region of 40–45 °C (104–113 °F). Hyperthermia is usually applied as an adjuvant to radiotherapy or chemotherapy, to which it works as a sensitizer, in an effort to treat cancer. Hyperthermia uses higher temperatures than diathermy and lower temperatures than ablation. When combined with radiation therapy, it can be called thermoradiotherapy. Definition Hyperthermia is defined as supra-normal body temperatures. There is no consensus as to what is the safest or most effective target temperature for the whole body. During treatment the body temperature reaches a level between . However, other researchers define hyperthermia between (Europe, USA) to near (Japan, Russia). Types * ''Local hyperthermia'' heats a very small area and is typically used for cancers near or on the skin or near natu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Institut D'électronique De Microélectronique Et De Nanotechnologie
The Institute of Electronics, Microelectronics and Nanotechnology or IEMN (''Institut d'électronique de microélectronique et de nanotechnologie'' in French) is a research institute of University of Lille, CNRS and École Centrale de Lille (UMR CNRS 8520). IEMN research activities The main research focus are in six major scientific areas : * Materials and Nanostructures Physics, * Microtechnologies - Microsystems, * Micro and optoelectronics, * Communication circuits and systems, * Acoustics, * Instrumentation. With 200 permanent researchers and 100 doctoral students for a total staff of more than 500, IEMN focuses on the following research area : physics of matter, nanostructures, microsystems and microtechnologies, microwave components and microelectronic circuits, RF and microwave circuits, digital communications, optoelectronics and photonic circuits, acoustic and ultrasonic sensors, microwave instrumentation. IEMN labs sites * IEMN central laboratory : The 12,00 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Echogenicity
Echogenicity (misspelled sometimes as echogenecity) or echogeneity is the ability to bounce an echo, e.g. return the signal in ultrasound examinations. In other words, echogenicity is higher when the surface bouncing the sound echo reflects increased sound waves. Tissues that have higher echogenicity are called "hyperechogenic" and are usually represented with lighter colors on images in medical ultrasonography. In contrast, tissues with lower echogenicity are called "hypoechogenic" and are usually represented with darker colors. Areas that lack echogenicity are called "anechogenic" and are usually displayed as completely dark. Microbubbles Echogenicity can be increased by intravenously administering gas-filled microbubble contrast agent to the systemic circulation, with the procedure being called contrast-enhanced ultrasound. This is because microbubbles have a high degree of echogenicity. When gas bubbles are caught in an ultrasonic frequency field, they compress, oscillate, and ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Velocimetry
Velocimetry is the measurement of the velocity of fluids. This is a task often taken for granted, and involves far more complex processes than one might expect. It is often used to solve fluid dynamics problems, study fluid networks, in industrial and process control applications, as well as in the creation of new kinds of fluid flow sensors. Methods of velocimetry include particle image velocimetry and particle tracking velocimetry, Molecular tagging velocimetry, laser-based interferometry, ultrasonic Doppler methods, Doppler sensors, and new signal processing methodologies. In general, velocity measurements are made in the Lagrangian or Eulerian frames of reference (see Lagrangian and Eulerian coordinates). Lagrangian methods assign a velocity to a volume of fluid at a given time, whereas Eulerian methods assign a velocity to a volume of the measurement domain at a given time. A classic example of the distinction is particle tracking velocimetry, where the idea is to find th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Doppler Effect
The Doppler effect or Doppler shift (or simply Doppler, when in context) is the change in frequency of a wave in relation to an observer who is moving relative to the wave source. It is named after the Austrian physicist Christian Doppler, who described the phenomenon in 1842. A common example of Doppler shift is the change of pitch heard when a vehicle sounding a horn approaches and recedes from an observer. Compared to the emitted frequency, the received frequency is higher during the approach, identical at the instant of passing by, and lower during the recession. The reason for the Doppler effect is that when the source of the waves is moving towards the observer, each successive wave crest is emitted from a position closer to the observer than the crest of the previous wave. Therefore, each wave takes slightly less time to reach the observer than the previous wave. Hence, the time between the arrivals of successive wave crests at the observer is reduced, causing an increa ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Phase Conjugation
Phase conjugation is a physical transformation of a wave field where the resulting field has a reversed propagation direction but keeps its amplitudes and phases. Description It is distinguished from Time Reversal Signal Processing by the fact that phase conjugation uses a holographic or parametric pumping whereas time reversal records and re-emits the signal using transducers. * Holographic pumping makes the incident wave interact with a pump wave of the same frequency and records its amplitude-phase distribution. Then, a second pump wave reads the recorded signal and produces the conjugate wave. All those waves have the same frequency. * In parametric pumping, the parameters of the medium are modulated by the pump wave at double frequency. The interaction of this perturbation with the incident wave will produce the conjugate wave. Both techniques allow an amplification of the conjugate wave compared to the incident wave. As in time reversal, the wave re-emitted by a phase conj ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Optical Phase Conjugation
Nonlinear optics (NLO) is the branch of optics that describes the behaviour of light in ''nonlinear media'', that is, media in which the polarization density P responds non-linearly to the electric field E of the light. The non-linearity is typically observed only at very high light intensities (when the electric field of the light is >108 V/m and thus comparable to the atomic electric field of ~1011 V/m) such as those provided by lasers. Above the Schwinger limit, the vacuum itself is expected to become nonlinear. In nonlinear optics, the superposition principle no longer holds. History The first nonlinear optical effect to be predicted was two-photon absorption, by Maria Goeppert Mayer for her PhD in 1931, but it remained an unexplored theoretical curiosity until 1961 and the almost simultaneous observation of two-photon absorption at Bell Labs and the discovery of second-harmonic generation by Peter Franken ''et al.'' at University of Michigan, both shortly after the constru ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Time Reversal Signal Processing
Time Reversal Signal Processing has three main uses: creating an optimal carrier signal for communication, reconstructing a source event, and focusing high-energy waves to a point in space. A Time Reversal Mirror (TRM) is a device that can focus waves using the time reversal method. TRMs are also known as time reversal mirror arrays since they are usually arrays of transducers. TRM are well-known and have been used for decades in the optical domain. They are also used in the ultrasonic domain. Overview If the source is passive, i.e. some type of isolated reflector, an iterative technique can be used to focus energy on it. The TRM transmits a plane wave which travels toward the target and is reflected off it. The reflected wave returns to the TRM, where it looks as if the target has emitted a (weak) signal. The TRM reverses and retransmits the signal as usual, and a more focused wave travels toward the target. As the process is repeated, the waves become more and more focused on ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
