Nta ntawm Ultrasound

 The propagation laws of ultrasonic waves in the medium such as reflection, refraction, diffraction, and scattering are not fundamentally different from the laws of (audible) sound waves. But the wavelength of ultrasound is very short, only a few centimeters, or even a few thousandths of a millimeter. Compared with (audible) sound waves, ultrasound has many exotic properties:

1. Lub wavelength ntawm ultrasonic nthwv dej yog luv heev, thiab qhov luaj li cas ntawm qhov kev cuam tshuam ib txwm muaj ntau zaus ntau dua li lub wavelength ntawm ultrasonic yoj, yog li lub peev xwm diffraction ntawm ultrasonic yoj tsis zoo, tab sis nws muaj peev xwm propagate nyob rau hauv ib tug directional. ncaj kab nyob rau hauv ib tug homogeneous nruab nrab. cov yam ntxwv tau hais ntau dua. Yog li ntawd, thaum lub ultrasonic yoj propagates, lub directionality yog muaj zog, thiab lub zog yog yooj yim mus mloog.

2. Ultrasound tuaj yeem nthuav tawm hauv ntau hom xov xwm sib txawv thiab tuaj yeem taug kev deb txaus.

3. Kev sib cuam tshuam ntawm ultrasound thiab lub suab kis tau tus mob nruab nrab yog nruab nrab, thiab nws yog ib qho yooj yim los nqa cov ntaub ntawv hais txog lub xeev ntawm lub suab kis tau tus mob nruab nrab (kev kuaj mob lossis cuam tshuam rau lub suab kis nruab nrab). Ultrasound yog ib hom nthwv dej, uas tuaj yeem siv los ua tus nqa khoom lossis nruab nrab rau kev tshawb nrhiav thiab thauj cov ntaub ntawv (xws li B-ultrasound siv rau kev kuaj mob); ultrasound kuj yog ib daim ntawv ntawm lub zog, thaum nws siv ntau tshaj ib tug tej yam nqi, nws muaj peev xwm kis tau thiab qhov nruab nrab los ntawm lub ultrasonic yoj yog kis interacts, cuam tshuam, alters thiab rhuav tshem lub xeev, cov khoom thiab cov qauv ntawm lub tom kawg (siv rau kev kho mob). .

Lub ultrasonic yoj cuam tshuam nrog nruab nrab thaum lub sij hawm propagation txheej txheem, thiab cov theem thiab amplitude hloov, uas yuav hloov lub xeev, muaj pes tsawg leeg, qauv, muaj nuj nqi thiab cov khoom ntawm nruab nrab. Hom kev hloov no yog hu ua cov nyhuv ultrasonic. Kev sib cuam tshuam ntawm ultrasonic thiab nruab nrab tuaj yeem muab faib ua thermal mechanism, mechanical mechanism thiab cavitation mechanism.

(1) Thermal mechanism: Thaum lub ultrasonic yoj propagates nyob rau hauv nruab nrab, nws vibration zog yog tsis tu ncua absorbed los ntawm nruab nrab thiab hloov mus rau hauv tshav kub, uas ua rau kom qhov kub ntawm qhov nruab nrab. Cov nyhuv no ntawm kev nce qhov kub ntawm qhov nruab nrab yog hu ua thermal mechanism ntawm ultrasound. (2) Mechanical mechanism: Thaum qhov zaus tsawg, qhov nqus coefficient me me, thiab lub sijhawm ua haujlwm ultrasonic luv luv, cov nyhuv ultrasonic tsis nrog pom tseeb thermal nyhuv. Lub sijhawm no, cov nyhuv ultrasonic tuaj yeem raug ntaus nqi rau cov neeg kho tshuab, uas yog, cov nyhuv ultrasonic pib los ntawm kev koom tes ntawm cov neeg kho tshuab kom muaj nuj nqis characterizing lub suab teb. Ultrasound kuj yog ib hom kev sib kis ntawm txhua yam zog, thiab tsis xws li keeb kwm kev hloov chaw, kev vibration tshaj tawm, acceleration thiab suab siab nyob rau hauv lub fluctuation txheej txheem yuav qhia tau cov nyhuv ultrasonic.

(3) Cavitation mechanism: Ib lub ntsiab mechanisms ntawm ultrasonic sonochemical teebmeem yog acoustic cavitation (xws li tsim, loj hlob thiab vau ntawm npuas, thiab lwm yam). Qhov tshwm sim muaj xws li ob yam, uas yog, qhov muaj zog ultrasound ua npuas hauv cov kua thiab qhov tshwj xeeb txav ntawm cov npuas nyob rau hauv qhov kev txiav txim ntawm muaj zog ultrasound.

Ultrasound is a high{{0}}frequency mechanical wave with the characteristics of concentrated energy and strong penetrating power. Ultrasound is composed of a series of dense and dense longitudinal waves, and propagates around through the liquid medium. When the acoustic energy is high enough, the attraction between molecules in the liquid phase is broken during the loose half-cycle, forming a cavitation nucleus. The lifetime of the cavitation nucleus is about 0.1μs, it can generate a local high temperature and high pressure environment of about 4000-6000 K and 100MPa at the moment of explosion, and generate a microjet with a speed of about 110m/s with a strong impact force, this phenomenon is called Ultrasonic cavitation.