Acoustic impedance measurements-correction for probe geometry mismatch.
نویسندگان
چکیده
The effect of evanescent mode generation, due to geometrical mismatch, in acoustic impedance measurements is investigated. The particular geometry considered is that of a impedance probe with an annular flow port and a central microphone, but the techniques are applicable to other geometries. It is found that the imaginary part of the measured impedance error is proportional to frequency, and that the sign of the error is positive for measurements made on tubes with diameter much larger than that of the inlet port, but negative for tubes with diameter close to that of the inlet. The result is a distortion of the measured frequencies of the impedance minima of the duct while the maxima are largely unaffected. There is, in addition, a real resistive component to the error that varies approximately as the square root of the frequency. Experiment confirms the results of the analysis and calculations, and a calibration procedure is proposed that allows impedance probes that have been calibrated on a semi-infinite tube of one diameter to be employed for measurements on components with an inlet duct of some very different diameter.
منابع مشابه
The influence of acoustic impedance mismatch on post-stenotic pulsed-Doppler ultrasound measurements in a coronary artery model.
Acoustic impedance mismatch at the fluid-wall interface was shown to affect the spectra from an intravascular Doppler device in an in vitro model with a diameter typical of human coronary arteries. Measurements were obtained first under Poiseuille flow conditions with impedance mismatches of 0%, 7% and 12%, and then under stenosed conditions for the 0% and 7% mismatch cases. For the zero mismat...
متن کاملCalibration of the two microphone transfer function method by determining the hard wall impedance at shifted reference sections
In many acoustic simulations, particularly when using lumped parameter models or electrical analog circuits, the acoustic impedance of a component needs to be determined accurately. A widely used acoustic impedance measurement method is the ”two microphone transfer function method”, which is standardized in ISO-10534-2. When the acoustic impedance is needed over a wide frequency band with a hig...
متن کاملHow to make the reconstruction of obstacles more (or less) accurate from exterior measurements
In this paper, we deal with the acoustic inverse scattering problem for detecting obstacles from the far field data. The complex obstacle is characterized by its shape, its type of boundary conditions and the boundary coefficients (surface impedance). We particularly show how one can use the boundary coefficient, distributed on the surface of the obstacle, to design obstacles which can be recon...
متن کاملAn Ultrasonic Wheel Probe Al Terna Tive to Liquid Coupling
Unfortunately, transmission of ultrasound between the transducer and the testpiece across an air gap is very inefficient because of the large acoustic impedance mismatch between air and solid materials [1]. This means that the ultrasound is almost totally reflected at the transducer-air boundary in transmission and at the testpiece-air boundary in reception. This problem is generally overcome b...
متن کاملFeasibility Study of a New Model for the Thermal Boundary Resistance at an Interface of Solid Thin Films
The thermal boundary resistance (TBR) is still a challengeable subject since its mechanism to explain quantitatively is not clear in spite of its importance. We performed non-equilibrium molecular dynamic (NEMD) simulation to evaluate TBR at an epitaxial solid interface composed of two different materials. Solid argon is selected as a simulation material since it is a non-conductor electrically...
متن کاملذخیره در منابع من
با ذخیره ی این منبع در منابع من، دسترسی به آن را برای استفاده های بعدی آسان تر کنید
برای دانلود متن کامل این مقاله و بیش از 32 میلیون مقاله دیگر ابتدا ثبت نام کنید
ثبت ناماگر عضو سایت هستید لطفا وارد حساب کاربری خود شوید
ورودعنوان ژورنال:
- The Journal of the Acoustical Society of America
دوره 117 5 شماره
صفحات -
تاریخ انتشار 2005