ABSTRACT
This letter proposes a method of designing unidirectional acoustic probes with flexible directivity patterns using two acoustic particle velocity sensors. The closed-form weighting vector of this two-sensor array is accurately derived by finding the minimum mean square error approximation to a desired directivity pattern that is expressed in a general form. Different unidirectional acoustic probes can be obtained by properly selecting the desired directivity pattern, and the previously proposed particle velocity gradient-based design approach can be thought of as a special case of the proposed method. Simulations and experimental results demonstrate the good performance of the proposed method.
ABSTRACT
This paper presents the foundations of a unidirectional acoustic probe based on the particle velocity gradient. Highly directional characteristics play a key role in reducing the influence of undesired acoustic sources. These characteristics can be achieved by using multiple acoustic sensors in a spatial gradient arrangement. Two particle velocity sensors possessing the figure eight directivity pattern were used in a first-order gradient configuration to yield a unidirectional probe that can reject most excitations originating from both sides and the rear. The effects of key parameters are thoroughly discussed, and the proposed theory is validated in practice.
ABSTRACT
The received Doppler signal of a stationary sensor, as emitted by a transiting acoustic source, is used to estimate source motion parameters, including speed, closest distance, rest frequency, and closest point of approach (CPA) time. First, the instantaneous frequency, amplitude, and CPA time are accurately estimated by the polynomial chirplet transform of the Doppler signal. Thereafter, the three other source motion parameters are obtained with a simplified amplitude-weighted nonlinear least squares method. The proposed scheme is successfully applied to the analysis of the characteristics of a moving truck.
