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Noninvasive Diagnosis Using Sounds Originating from within the Body
Published in Robert B. Northrop, Non-Invasive Instrumentation and Measurement in Medical Diagnosis, 2017
Laennec's original stethoscope was a hollow wooden cylinder with a funnel-like termination (a bell, or inverse horn) at the end that touched the patient. The distal end fitted into the doctor's ear canal. In its modern form, the stethoscope has two types of chest pieces: A shallow bell (for acoustic impedance matching), and a stiff, vibrating diaphragm (over a small bell chamber) that makes direct contact with the skin. The latter form is called a cardiology stethoscope. The chest piece (at the apexes of the bells) is attached to two, flexible tubes, 25–30 cm in length, which, in turn, connect to two metal ear tubes that insert into the clinician's ears. The ear tubes are spring-loaded to hold them in the ears. The flexible tubes can be neoprene, plastic, or even latex. Their material and dimensions will affect the frequency response of acoustic transmission from the body surface to the ears. The frequency response of the acoustic transmission of modern, acoustic stethoscopes has been measured by several workers (Jacobson and Webster 1977, Korhonen et al. 1996, Riederer and Backman 1998). Figure 3.1 illustrates the magnitude of the acoustic transmission in dB: 20 log10 (rms sound pressure out/rms sound pressure in). The trace with one major peak is for the diaphragm-type, cardiology chest piece alone (no tubes or earpieces). The single peak at ∼800 Hz may be due to diaphragm mechanical resonance, or a series Helmholz resonance involving the bell chamber. The acoustic transmission of the same chest piece, given tubes, and earpieces shows multiple peaks due to transmission line-type resonances of the tubes. Note that the peaks do not appear to be related as simple harmonics.
Basic Design of Ultrasonic Transducers
Published in Dale Ensminger, Leonard J. Bond, Ultrasonics, 2011
Dale Ensminger, Leonard J. Bond
These “special” transducers include those designed (1) to provide coupling of ultrasonic energy into an object without directly contacting the surface of the object and (2) to generate ultrasonic energy at high frequency in an acoustic transmission line by methods that convert almost all the electrical energy into ultrasonic energy with very little loss due to heat dissipation or energy reflection toward the source. Examples of the former type are noncontacting transducers used in the inspection of certain materials. Examples of the latter type include SAW devices and resistive layer types.
Focused Beam Acoustic Microscopy
Published in J. David, N. Cheeke, Fundamentals and Applications of Ultrasonic Waves, 2017
SAM imaging of microelectronic devices has recently been improved by the development of a new technique called dry-contact acoustic imaging [41]. Some ultrasonic techniques require immersion of the sample, and this is not desirable for IC packages and indeed for some materials such as composites. In the dry-contact approach, a thin layer of plastic is held in place over the chip sample to screen it from the water coupling fluid. Focused transducers were used at 30 MHz with a focal length of 19.7 mm and 50 and 100 MHz with a focal length of 12.7 mm. Plastic films made of either polyvinylidene chloride (PVDC), polyvinyl chloride (PVC), or silicon rubber were held onto the surface by evacuating the air between film and surface with a rotary pump. The surface roughness of a given sample was specified by two parameters, β the height of the roughness and γ its spatial distribution. Reflection spectra using water as a coupling fluid showed broad peaks for the three transducers at approximately 24, 32, and 37 MHz, with the immersion peaks significantly lower. This shows that the layer acts as an acoustic matching layer between the water and the silicon. Several applications were made to device imaging: (1) observation of delaminations in a dual in-line package, where the defect was observed in both immersion and dry-contact, and (2) inspection of solder joints in ball grid array (BGA) in fixing a silicon chip to a printed circuit board. In this case, the defect could not be observed by immersion at 50 MHz, whereas the dry-contact method was successful at both 50 and 100 MHz [42]. All of the dry contact results could be explained by taking into account the acoustic transmission and reflection coefficients at the various interfaces in the system as well as the attenuation in the plastic sheets.
Acoustic behaviour of textile structures
Published in Textile Progress, 2021
Parikshit Paul, Rajesh Mishra, B. K. Behera
The acoustic properties of materials can be placed into the three categories of propagation, absorption, and scattering, which can be related to measurable quantities, namely airflow resistance, acoustic transmission loss, acoustic absorption coefficient, and acoustic scattering coefficient. The sound wave interacts with the object surface and may be absorbed, transmitted, reflected, refracted, or diffracted from the surface depending on the surface type (Raichel, 2006).