Three perforate-over-honeycomb liner configurations, one uniform and two with spanwise variable impedance, are evaluated based on tests conducted in the NASA Grazing Flow Impedance Tube (GFIT) with a plane-wave source. Although the GFIT is only 2” wide, spanwise impedance variability clearly affects the measured acoustic pressure field, such that three-dimensional (3D) propagation codes are req...

The use of acoustics to determine the pore properties of soils, such as porosity, permeability, and tortuosity, is well established. A theoretical surface impedance and complex bulk wavenumber was developed by K. Attenborough for porous media that incorporated the soil pore properties as parameters [J. Acoust. Soc. Am. 73, 785-799 (1983)]. Acoustic level difference measurements were used as a n...

This paper presents the effects of a wall impedance on the propagation of higher-order modes in a three-dimensional vocal-tract model. This model is constructed using an asymmetrically connected structure of rectangular acoustic tubes, and can parametrically represent acoustic characteristics in higher frequencies where the assumption of the plane wave propagation does not hold. The propagation...

Nowadays lots of applications in telecommunications require a wide bandwidth to transmit more information and improve the quality on the transmission of this information. In order to guarantee this condition low losses systems are designed; these losses can be classified in dissipation losses and mismatch losses. There are different classic methods for impedance matching, but they reach the imp...

The first transistor-based impedance matching circuit for radio-frequency (RF) applications is introduced in this paper. It adapts arbitrary output impedances of RF blocks to desired values between 50 and 250 , from 0 to 5GHz, while occupying only 0.005mm2 of circuit area in a 0.35μm SiGe BiCMOS process. Its superiority over traditional passive-element networks can be resumed by the following f...

Performance of a helical antenna designed for 2.4-GHz WLAN is experimentally investigated in terms of impedance matching. A section of the helical wire near the antenna feed point is replaced by a simple triangular copper strip. By deploying such technique, impedance matching can be achieved. Overall return loss is below −14 dB across entire WLAN frequency range. Moreover, overall return loss d...

Recently, spiral inductors have widely been used in the design of matching circuits of a wireless transceiver. However, such elements usually have low quality factor (Q) and may encounter the self-resonance in microwave-frequency band which permits its use in higher frequencies, and on the other hand, they occupy the large on-chip space. This paper presents a new design theory for the impedance...

Perforates are for instance used in mufflers for automotive applications and in acoustic liners for aircraft engines. In these applications they are often exposed to high level acoustic excitation in combination with grazing or bias flow. The paper is based on an experimental study of the nonlinear properties of these types of samples without mean grazing or bias flow as well as on a study of a...

We report a composite waveguide fabricated by attaching a coupling aperture to a waveguide. The acoustic impedance of the composite waveguide can be regulated by merely controlling its coupling vibrations, depending on its structure size. By changing the size to adjust the acoustic impedance of the composite waveguide at an impedance-mismatched fluidic interface, tunable sound transmission at t...