Physics 5 PDF - Physical Characteristics of Sound

# Physical characteristics of sound ## Physics of vocal and hearing apparatus of humans: - Psychophysical parameters of sound - This looks at how sound is detected, the characteristics are: - Pitch - subjected determined by human ear based on frequency and intensity - Timber -...

# Physical characteristics of sound ## Physics of vocal and hearing apparatus of humans: - Psychophysical parameters of sound - This looks at how sound is detected, the characteristics are: - Pitch - subjected determined by human ear based on frequency and intensity - Timber - determined by spectral composition - Loudness level - evaluation of the degree of sound pressure - The range of hearing is somewhat between 16-20 and 20 kHz. Waves with a frequency above that is called ultrasound and those with a frequency below is called infrasound. - Psychophysical characteristics are measurements of sounds perceived by the human ear. - The hearing threshold starts at the lowest level of loudness, 10^-12 W/m^2. - Measuring the lower limit of hearing is one of the tests in audiology which determines the individual range of hearing. - The measuring of hearing threshold is called audiometry. - Sound pitch - is measured in the unit octave. It depends mainly of frequency, intensity and spectral composition. - Timber - is determined by the spectral composition of the sound depending on the number and intensity of the overtones (harmonics). Two tones can have the same frequency but different perceived sound because of the presence of different amounts of the various harmonics. - Loudness level - is used to evaluate the volume as stronger or weaker. - If the frequency is f=1kHz then k=1. K is a coefficient of the function of frequency and intensity. - The formula for loudness level is: Г = KL = klg 1/10 ## Audiometry - Audiometry is the test on a person's ability to hear different frequencies. - Results are plotted on an audiogram with the contours joining values at the same loudness. ## Frequency resolution, Binaural effect - Frequency resolution is the distance in Hz between two adjacent data points, this is calculated by: Sampling frequency/Number of samples acquired. - The binaural effect is an auditory illusion perceived when two different pure tone waves are heard together (with less than 40 Hz between the wavelengths). The effect makes the brain think that the tone is pulsating when in fact it is a steady sound and it is the brain creating the pulse. ## Physical and vocal apparatus of humans: - Vocal cords cause vibrations in air, the length of the cords is varied by muscles which alters the frequency of the sound. - There are three resonance cavities that assist in developing the sound - The vocal cords have a range between 300 - 3000 Hz. ## Acoustic methods in medical diagnosis: - Auscultation: The Latin for 'listening', usually with a stethoscope for examining the lungs and circulatory system as well as gastrointestinal system. - Percussion: Tapping the body to determine density, can detect fluids and gasses in intestine, liver and lung. - Ultrasound: Covered in next point ## Noise Protection - This helps protect the hairs in our ears which cannot grow back once damaged. - Based on two principles, that of absorption of sound and the increasing of distance between source and person. - **Definition of:** - Threshold of hearing - minimum sound tone that can be heard - Threshold of pain - maximum sound tone that can be heard without pain - Auditory filed - the space or range within which stimuli will be perceived as sound ## Level of intensity - Intensity = Sound power/Area. Sound intensity level = 10 log (Intensity/reference intensity) ## Level of loudness - Loudness = constant log (intensity/reference intensity) ## Noise protection - Intensity = Original intensity x constant absorption coefficient x distance # Ultrasound ## Properties of ultrasound. Piezo effect and reverse piezo effect. Physical principles of echography. Effect of Doppler and Doppler sonography. Medical applications of ultrasound. - Waves with frequencies above 20kHz are beyond the range of human detection and are called ultrasound. - In medicine ultrasound is used as a frequency of sound pulse directed into the body and reflected from boundaries and interfaces between organs and other structures and lesions are then detected. For example, tumors or a growing fetus. ## Piezoeffect and reverse piezoeffect - Piezoeffect is making an electrical charge at the surface of the piezocrystal during its deformation. - from the 32 crystal (like quartz, turmalin etc) there are 20 possibilities of this effect. - Reverse piezoeffect is the deformation of a whole piezocrystal because of an external electrical field. - Usually frequencies in the range of 1 to 10 MHz are used. - When a source of sound is moving towards and observer, the pitch is higher than when the source is at rest. When the source of sound is travelling away from the observer, the pitch is lower. This is known as the Doppler effect. It can also occur as the observer is moving and the source is at rest and for other types of waves such as light waves. - The observed frequency of the wave f' will be f'= f/(1+vsound/vsource). - The source also receives the echoes and the sound waves vibrate the transducer to turn the vibrations into electrical pulses that travel to the scanner where they are processed and turned into a digital image. - The image is formed based on how long it took to receive the echo and the strength of the echo, allowing it to locate and determine the intensity of of pixel. ## Effect of Doppler and doppler sonography - A Doppler ultrasound test uses reflected sound waves to see how blood flows through a blood vessel. - a handheld device is passed lightly over the skin above a blood vessel (transducer) sends and receives sound waves that are amplified through a microphone (sound waves bounce off solid objects eg blood cells) - The movement of blood cells causes a change in the pitch of the reflected sound waves. - If source and receiver get closer to each other the frequency gets higher. - Source is approaching (received signal is greater) v>vo - Source is moving away (received signal is less than emitted)v>vo - Receiver is approaching (received signal is greater)v>vo - Reiceiver is moving away (received signal decreases)v<vo - This is called the Doppler effect. - small angle of transducer means less risk for miscalculation. - (When 90 degrees the effect disappears, 0 degrees is the best). - FD= Vo/2v x cos(0) - We calculate in MHz because of the size of the red blood cells. - speed of sound through tissue is 1500 m/s. - FD (Doppler frequency); - 0 (is the angle between axis of transducer and axis of blood vessel); - v (transducer received waves with this frequency); - vo (source (eg. Blood cells) emits waves with this frequency); - c (speed of sound) - Registered frequency = source frequency (Velocity of propagation + velocity/velocity of propagation - velocity) - Doppler sonography takes advantage of the doppler effect to measure the velocity of blood cells in vessels. It measures the 'doppler shift', or the difference between transmitted and received frequencies, and as such calculate the velocity of the blood flow. The equation is: - Doppler shift = Reflected frequency - Transmitted frequency = 2. Transmitted frequency. Velocity.cos(angle)/Velocity of sound in tissue - From this we can work out max, min and average velocity of blood flow, dispersion and of velocities and resistance of blood vessels to blood flow. - Sonography is for the brain, echocardiography for the heart (some method different region) ## Medical applications of ultrasound - Used to heat joints - Used to view internal organs - View blood flow - Increase diffusion rate through cellular membranes - Object sterilziation