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# Physics Test #1

### PHYSICS TEST #1

Question | Answer |
---|---|

SPECULAR REFLECTIONS | MIRROR LIKE REFLECTIONS, REFLECTED BACK IN THE SAME ANGLE AS THE INCIDENT ANGLE, OR ORIGINAL ANGLE.OCCUR WHEN: 1. WL IS SMALLER THAN BOUNDARY. 2. THE BOUNDARY IS SMOOTH. |

NON-SPECULAR (DIFFUSE)REFLECTIONS | SOUND REFLECTED BACK IN MANY ANGLES RATHER THAN JUST ORIGINAL ANGLE LIKE WITH SPECULAR REFLECTION.OCCURS WHEN WL IS LARGER THAN BOUNDARY 2. THE BOUNDARY IS NOT SMOOTH. |

REFRACTION | CHANGE IN DIRECTION OF THE SOUND WAVE DUE TO A CHANGE IN ITS PROPAGATION SPEED. DUE TO CHANGE IN MEDIUM. |

ATTENUATION | WEAKENING OF A SOUND BEAM AS IT PROPAGATES 1. ABSORPTION (GREATEST) 2.REFLECTION 3. SCATTERING |

ATTENUATION COEFFICIENT | AMT OF ATTENUATION PER CM OR PATH LENGTH. 3dB = .5 or 50%-10dB = .1 or 10%-20db = .01 or 1% |

WAVELENGTH | THE LENGTH OF SPACE 1 CYCLE TAKES UP. |

DUTY FACTOR | AMOUNT OF TIME PW IS ACTUALLY ON. UNIT LESS. EXPRESSED IN # OR % |

PROPAGATION SPEED | SPEED AT WHICH A SOUND WAVES TRAVELS THRU A MEDIUM. ONLY DEPENDENT ON THE MEDIUM. |

SHEAR WAVES | PARTICLE MOTION RUNS PERPENDICULAR TO NORMAL VALUE. |

LONGITUDINAL WAVE | PARTICLE MOTION RUNS PARALLEL TO NORMAL VALUE |

RANGE OF FREQUENCIES | 2-15 MHZ BELOW OR ABOVE RESOLUTION IS TOO POOR |

PERIOD | TIME FOR ONE CYCLE TO OCCUR |

FREQUENCY | # OF COMPLETE CYCLES PER SEC |

DECIBEL | ATTENUATION UNIT UNIT OF COMPARISON |

INTENSITIES | SATA (LOWEST) SPTP (HIGHEST) SPTA (MACHINE) THE BIGGER THE SOUND WAVE, THE STRONGER IT IS. |

RANGE EQUATION | DISTANCE THE MEDIUM IS FROM THE TRANSDUCER. NEED: DISTANCE AND DIRECTION |

RAYLEIGH SCATTERING | OCCURS WHEN PARTICLES ARE SMALLER THAN THE WAVELENGTH HITTING THE BOUNDARY.THE INTENSITY OF THE SCATTERED SOUND DEPENDS ON THE FREQ TO THE 4TH POWER. IF THERE IS AN INCREASE IN FREQ, THEN THERE IS AN INCREaSE IN SCATTER. |

CW VS. PW | PW IS PULSES OF SOUND WAVES VERSES ONE CONTINUOUS SOUND WAVE. |

ACOUSTIC VARIABLES | DENSITY (KG/M3), PARTICLE MOTION (MM), PRESSURE (Pa), & TEMP (DEGREES) |

NORMAL INCIDENCE | SOUND HITS BOUNDARY AT A 90 DEGREE ANGLE |

OBLIQUE INCIDENCE | SOUND HITS BOUNDARY AT ANY OTHER ANGLE THAN 90 DEGREES. |

DENSITY | Kg/m3 THE CONCENTRATION OF MATTER |

SNELL'S LAW (LAW OF REFRACTION) | WHEN WAVE HITS A DIFFERENT MEDIUM THAT HAS A DIFFERENT PS MAKES THE SOUND WAVE CHANGE SHAPE. |

SCATTERING | THE REDIRECTION OF SOUND IN MAY DIRECTIONS BY: ROUGH SURFACES, HETEROGENEOUS MEDIA (EX. BLOOD) |

BACKSCATTER | SCATTERED SOUND THAT GETS BACK TO THE TRANSDUCER. |

IMPORTANCE OF SCATTERING | IT ALLOWS THE TISSUE PARENCHYMA AND TISSUE INTERFACE TO BE SEEN. HELPS TO MAKE IMAGING LESS DEPENDENT ON SCANNING ANGLE. |

MEGA | MILLION |

MILLI | THOUSANDS |

PROPAGATION SPEEDS | SOFT TISSUE 1540M/S OR 1.54MM/US AIR 331 M/S BONE 3-4,000 M/S |

TYPICAL DUTY FACTORS | 0.1% OR 1.0% |

ACOUSTIC IMPEDANCE | THE EFFECT THE SOUND HAS ON THE MEDIUM. Z=DENSITY (KG/M3) X PS(M/S) |

UNITS | PRESSURE (Pa) DENSITY (Kg/m3) TEMP (DEGREES) PARTICLE MOTION (MM) |

POWER | THE RATE AT WHICH ENERGY IS TRANSFERRED. |

PRF (KHz) | pulsed rep freq. # of pulses occuring in 1 sec. |

PRP (MILLISECONDS) | PULSE REP PERIOD THE TIME FROM BEGIN OF ONE PULSE TO BEGIN OF NEXT PULSE. |

DF (UNIT-LESS) | DUTY FACTOR FRACTION OF TIME PW IS ACTUALLY ON. |

PD (MICROSECONDS) | PULSED DURATION TIME IT TAKES FOR ONE PULSE TO OCCUR |

SPL | SPATIAL PULSE LENGTH THE SPACE ONE COMPLETE PULSE TAKES UP. |

IMPEDANCE FORMULA | |

PERIOD FORMULA | |

WAVELENGTH FORMULA | |

PRP FORMULA | |

ACOUSTIC IMPEDANCE FORMULA | |

4 STEP FORMULA | |

INTENSITY FORMULAS | |

DECIBELS |