In a recent work, the beamsteering characteristics of parametric loudspeakers were validated in an experiment. It was shown that based on the product directivity model, the locations and amplitudes of the mainlobe and grating lobes could be predicted within acceptable errors. However, the measured amplitudes of sidelobes have not been able to match the theoretical results accurately. In this paper, the original theories behind the product directivity model are revisited, and three modified product directivity models are proposed: (i) the advanced product directivity model, (ii) the exponential product directivity model, and (iii) the combined product directivity model. The proposed product directivity models take the radii of equivalent Gaussian sources into account and obtain better predictions of sidelobes for the difference frequency waves. From the comparison between measurement results and numerical solutions, all the proposed models outperform the original product directivity model in terms of selected sidelobe predictions by about 10 dB.

/pdf/product-directivity-models-for-parametric-loudspeakers-448kdum531.pdf

Product directivity models for parametric loudspeakers

As a sound transmitting device based on the nonlinear acoustic theory, parametric acoustic array (PAA) is able to generate high directivity and low frequency broadband signals with a small aperture transducer. Due to its predominant technical advantages, PAA has been widely used in a variety of application scenarios of underwater acoustic engineering, such as sub-bottom profile measurement, underwater acoustic communication, and detection of buried targets. In this review paper, we examine some of the important advances in the PAA since it was first proposed by Westervelt in 1963. These advances include theoretical modelling for the PAA, signal processing methods, design considerations and implementation issues, and applications of the PAA in underwater acoustic engineering. Moreover, we highlight some technical challenges which impede further development of the PAA, and correspondingly give a glimpse on its possible extension in the future. This article provides a comprehensive overview of some important works of the PAA and serves as a quick tutorial reference to readers who are interested to further explore and extend this technology, and bring this technology to other application areas.

https://www.mdpi.com/1424-8220/20/7/2148/pdf

Parametric Acoustic Array and Its Application in Underwater Acoustic Engineering

Broadband parametric acoustic arrays appear to offer advantages for shallow water sub-bottom profiling. In this paper, the performance of a broadband parametric acoustic array system was experimentally evaluated. In tank experiments using the nonlinear parabolic wave (KZK) equation, the directivity, source level, parametric acoustic array length, and penetration depth were evaluated. Based on Berktay’s far-field solution, the system’s emission signal was designed. According to sea trials of the broadband parametric acoustic array system as designed, a clear sub-bottom profile was obtained. Moreover, buried pipelines in the seabed were effectively detected, verifying the system’s effectiveness.

/pdf/experimental-study-of-a-broadband-parametric-acoustic-array-o6s5fbbsbn.pdf

Experimental Study of a Broadband Parametric Acoustic Array for Sub-Bottom Profiling in Shallow Water

/pdf/investigation-of-the-steerable-parametric-loudspeaker-based-5gsx10yyus.pdf

Investigation of the steerable parametric loudspeaker based on phased array techniques

A modulation method of parametric array for underwater acoustic communication

본 논문에서는 적응형 걸음걸이 검출 알고리즘과 검출된 신호로부터 단일 발자국의 움직임을 분류하는 알고리즘을 제안한다. 제안된 단일 발자국 기반 알고리즘은 기존의 연속된 발자국 신호를 이용한 분류 방식이 아니기 때문에 전체적인 움직임뿐만 아니라 개별적이고 불규칙한 움직임도 검출 및 분류 가능하다. 분류를 위해 사용된 특징벡터는 발자국 신호의 푸리에 스펙트럼, CWT의 스펙트럼, AR 모델링 스펙트럼과 AR 스펙트로그램 영상으로부터 얻어진 벡터이다. SVM을 이용하여 단일 발자국의 움직임을 분류한 결과 AR 스펙트로그램으로 얻어진 특징벡터를 사용할 경우 90% 이상 분류 성능을 얻었다.

/pdf/footstep-detection-and-classification-algorithms-based-30uzdohu0o.pdf

Footstep Detection and Classification Algorithms based Seismic Sensor

The parametric array is a nonlinear conversion process that generates a narrow beam of low-frequency sound using small aperture. It can be applied to underwater communication between two nodes with known locations, since the highly directional sound beam may provide such benefits as privacy, no interference due to the multi-path. The difference frequency wave (DFW) from the parametric array shows small side lobes and extraordinary directivity. The shortcoming of the DFW generated by the parametric array may be its low sound pressure level relative to that of the directly generated sound beams. In this study, we designed and fabricated a multi-resonance transducer as a parametric array source and evaluated its feasibility as a transmitter. For that purpose, we determined the proper design parameters for midrange communication. We selected 10 kHz as the communication frequency and then determined the primary frequencies as 100 and 110 kHz. We composed the source transducer using the two kinds of unit transducers. The fabricated transducer array and the developed operating techniques enabled us to successfully transmit letters, words, and drawings inside the water tank. By testing the characteristics, we confirmed that the developed operating scheme and transducer can be used for underwater communication. [Work supported by ADD (UD130007DD).]

Development of a multi-resonance transducer for highly directional underwater communication

Digital acoustic signal processing can be applied to sonar and acoustic communications. Especially, transmitting acoustic signal to the desired direction has many applications in military and industry fields. In this paper, we present a steerable digital communication system using parametric array transducers. To evaluate the proposed system, we build digital communication system by using transducer array, power amplifier and Labview software. The Labview software is composed of two parts. The first part is designed to generate beam to the desired direction by changing parameters such as number of sensors, complex weight of each sensor, type of transmit data and etc. The second part is to generate modulated signal of ASK, FSK and PSK, and to demodulate the received signals. With laboratory experiments, we verify the performance of the proposed communication system. Experimental results show that the system can be used to mitigate multipath effect in shallow water and can achieve high data-rate transmission

Digital communication system using beamsteering for difference frequency in a parametric array

In this paper, we present novel analysis results of sonar communication using parametric array. We consider transducer diameter, primary frequency, difference frequency and acoustic power as analysis parameters of communication performance. We calculate theoretical BER(Bit Error Rate) and channel capacity of MIMO(Multi Input and Multi Output) communication system. By considering practical parameters, we obtain optimum difference frequency generation condition. The obtained primary frequency is 560 kHz, difference frequency 45kHz and acoustic power is 28.05Watt. For BER of , the range gain of parametric array communication is 3.35km compared to primary frequency communication. For channel capacity of 10bps/Hz, the SISO and MIMO communication range of parametric array communication are 3.8km and 3.98km respectively, while primary frequency communication range is 0.83km.

Analysis of Highly Directional Sonar Communication System

We propose adaptive detection algorithm to reduce a false alarm by considering the characteristics of the random noise on the detection system based on a seismic sensor. The proposed algorithm consists of the first step detection using kernel function and the second step detection using detection classes. Kernel function of the first step detection is obtained from the threshold of the Neyman-Pearon decision criterion using the probability density functions varied along the noise from the measured signal. The second step detector consists of 4 step detection class by calculating the occupancy time of the footstep using the first detected samples. In order to verify performance of the proposed algorithm, the detection of the footsteps using measured signal of targets (walking and running) are performed experimentally. The detection results are compared with a fixed threshold detector. The first step detection result has the high detection performance of 95% up to 10m area. Also, the false alarm probability is decreased from 40% to 20% when it is compared with the fixed threshold detector. By applying the detection class(second step detector), it is greatly reduced to less than 4%.

Target Detection Algorithm Based on Seismic Sensor for Adaptation of Background Noise

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