Guojun Zhang

Design, fabrication, and preliminary characterization of a novel MEMS bionic vector hydrophone

According to the auditory principle of fishs lateral line organ, a novel microelectromechanical systems (MEMS) bionic vector hydrophone used for obtaining vector information of underwater sound field is introduced in this paper. It is desirable that the application of MEMS-based piezoresistive effect and bionics structure may improve the low-frequency sensitivity of the vector hydrophone as well as its miniaturization. The bionic structure consists of two parts: high-precision four-beam microstructure and rigid plastic cylinder which is fixed at the center of the microstructure. The piezoresistor located at the beam is simulated to the hair cell of lateral line and the rigid plastic cylinder is simulated to stereocilia. When the plastic cylinder is stimulated by sound, the piezoresistor transforms the resultant strain into a differential voltage output signal via the Wheatstone bridge circuit. Microfabrication technology has been employed for the fabrication of the microstructure and measurement results are given. The experiment results show that the receiving sensitivity of the hydrophone is -197.7dB (0dB=1V/@mPa). The novel hydrophone not only possesses satisfactory directional pattern as well as miniature structure, but also has good low-frequency characteristics, and satisfies the requirements for low-frequency acoustic measurement.

“Lollipop-shaped” high-sensitivity Microelectromechanical Systems vector hydrophone based on Parylene encapsulation

This paper presents methods of promoting the sensitivity of Microelectromechanical Systems (MEMS) vector hydrophone by increasing the sensing area of cilium and perfect insulative Parylene membrane. First, a low-density sphere is integrated with the cilium to compose a “lollipop shape,” which can considerably increase the sensing area. A mathematic model on the sensitivity of the “lollipop-shaped” MEMS vector hydrophone is presented, and the influences of different structural parameters on the sensitivity are analyzed via simulation. Second, the MEMS vector hydrophone is encapsulated through the conformal deposition of insulative Parylene membrane, which enables underwater acoustic monitoring without any typed sound-transparent encapsulation. Finally, the characterization results demonstrate that the sensitivity reaches up to −183u2009dB (500u2009Hzu20090dB at 1u2009V/ μPa), which is increased by more than 10 dB, comparing with the previous cilium-shaped MEMS vector hydrophone. Besides, the frequency response takes on a ...

Root-MUSIC Algorithm with Real-Valued Eigendecomposition for Acoustic Vector Sensor Array

According to the Root-MUSIC algorithm for acoustic pressure sensor array, we put forward a new Root-MUSIC algorithm with real-valued eigen decomposition for acoustic vector sensor array. By way of recomposing the covariance matrix of vector sensor array and selecting appropriate lead orientation vector via spatial spectrum of array signal, we successfully evaluate the Direction of Arriva(DOA). Theory analysis and simulation experiment of an uniform line array show the performance of the new Root-MUSIC algorithm with real-valued eigen decomposition for acoustic vector sensor is better than the traditional Root-MUSIC algorithm with real-valued eigen decomposition in low SNR and few snapshots, and the calculations of new algorithm is small than the tradtional MUSIC algorithm.

Wide-frequency-bandwidth whisker-inspired MEMS vector hydrophone encapsulated with parylene

In order to eliminate polyurethane hat resonance frequency intervention and reduce fluid influence, a whisker-inspired MEMS vector hydrophone (WIVH) encapsulated with parylene is proposed to broaden frequency bandwidth and improve sensitivity-frequency response performance, compared to the lateral line-inspired MEMS vector hydrophone (LLIVH). Parylene that is conformally deposited on the device surface replaces polyurethane encapsulating hat and silicone oil existing in current encapsulation technology. The main advantage of WIVH as demonstrated by modelling and characterization is the enhanced bandwidth response, which is the critical factor in hydrophone design. Acoustic pressure gradient properties of the WIVH and LLIVH are analyzed to demonstrate the influence of the polyurethane hat. The interactions of the parylene membrane with fluid and the influences on vibrating performance are also investigated. Resonance measurement and sensitivity-frequency response analysis demonstrate the frequency bandwidth of the WIVH could be extended twice compared to that of the LLIVH. Moreover, the WIVH is proved to act as a typical pressure gradient hydrophone with an increment of 6 dB per octave in the linear region.

Development of cup-shaped micro-electromechanical systems-based vector hydrophone

Similar to the vital performance factors, the receiving sensitivity and the bandwidth exist interactively in the micro-electromechanical systems (MEMS)-based vector hydrophones. Some existing methods can improve the sensitivity of the hydrophone, but these improvements are usually gained at a cost of the bandwidth. However, the cup-shaped MEMS vector hydrophone that is presented in this paper can improve its sensitivity while retaining a sufficient bandwidth. The cup-shaped structure acts as a new sensing unit in the MEMS vector hydrophone, replacing the bionic columnar hair that was previously used for sensing. The relationships between the parameters of the cup-shaped structure and the sensitivity of the vector hydrophone were determined by a theoretical deduction. In addition, simulation analyses were performed, and optimized structural parameters were obtained in this work. ANSYS 15.0 simulation was used to derive the optimum characteristics for the cup-shaped structure. The results of the calibration experiments showed that the sensitivity reached up to −188.5u2009dB (gain of 40u2009dB, 1u2009kHz, 0 dB@1 V/μPa), and the bandwidth was in the 20u2009Hz–1u2009kHz range, which is sufficient for an underwater acoustic detection at low frequencies. This work has, thus, proved that the cup-shaped vector hydrophone has superior properties for the engineering applications.

Spatial smoothing algorithm based on acoustic vector sensor array

Spatial smoothing algorithm is an effective means of decoherence, this array of sound scalar in the traditional spatial smoothing algorithm is proposed based on a vector array of space forward, backward and bi-directional smoothing algorithm, combined with vector array MUSIC algorithm to solve vector array DOA of coherent sound source is estimated, simulation experiments show that the vector array of spatial smoothing algorithm is no ambiguity about the advantages side, in the low SNR and small snapshot of the situation is better than the distinguished array of sound scalar performance.

Self-adapting root-MUSIC algorithm and its real-valued formulation for acoustic vector sensor array

In this paper, based on the root-MUSIC algorithm for acoustic pressure sensor array, a new self-adapting root-MUSIC algorithm for acoustic vector sensor array is proposed by self-adaptive selecting the lead orientation vector, and its real-valued formulation by Forward-Backward(FB) smoothing and real-valued inverse covariance matrix is also proposed, which can reduce the computational complexity and distinguish the coherent signals. The simulation experiment results show the better performance of two new algorithm with low Signal-to-Noise (SNR) in direction of arrival (DOA) estimation than traditional MUSIC algorithm, and the experiment results using MEMS vector hydrophone array in lake trails show the engineering practicability of two new algorithms.

The Application of an Ultrasound Tomography Algorithm in a Novel Ring 3D Ultrasound Imaging System

Currently, breast cancer is one of the most common cancers in women all over the world. A novel 3D breast ultrasound imaging ring system using the linear array transducer is proposed to decrease costs, reduce processing difficulties, and improve patient comfort as compared to modern day breast screening systems. The 1 × 128 Piezoelectric Micromachined Ultrasonic Transducer (PMUT) linear array is placed 90 degrees cross-vertically. The transducer surrounds the mammary gland, which allows for non-contact detection. Once the experimental platform is built, the breast model is placed through the electric rotary table opening and into a water tank that is at a constant temperature of 32 °C. The electric rotary table performs a 360° scan either automatically or mechanically. Pulse echo signals are captured through a circular scanning method at discrete angles. Subsequently, an ultrasonic tomography algorithm is designed, and a horizontal slice imaging is realized. The experimental results indicate that the preliminary detection of mass is realized by using this ring system. Circular scanning imaging is obtained by using a rotatable linear array instead of a cylindrical array, which allows the size and location of the mass to be recognized. The resolution of breast imaging is improved through the adjustment of the angle interval (>0.05°) and multiple slices are gained through different transducer array elements (1 × 128). These results validate the feasibility of the system design as well as the algorithm, and encourage us to implement our concept with a clinical study in the future.

Design and analysis of a multiple sensor units vector hydrophone

Inspired by the hairy structure of fish neuromast, a multiple sensor units (multi-unit) vector hydrophone is proposed in the paper, which integrates multiple sensor units on one chip according to bionics. Its sensitivity and signal noise ratio (SNR) are theoretically analyzed compared with the hydrophone which has only one sensor unit. In order to verify the correctness of the theory, a 4-unit vector hydrophone has been fabricated. For experiments, the comparative calibration experiment is used to validate the theoretical analysis of sensitivity and fast fourier transform algorithm (FFT) is used to process the experiment data to verify the theoretical analysis of SNR. The results show that the sensitivity of the 4-unit hydrophone is improved by 11.8 dB and the SNR is improved by 1.9 dB on average, which is correlated with the theoretical analysis.

Design and measurement of a 32-element CMUT linear array for underwater imaging

Ultrasonic sensor has been widely used, ranging from underwater communication to many aspects, such as medical imaging and therapy. Compared with the traditional piezoelectric sensors, Capacitive micro-machined ultrasonic transducer(CMUT) have advantages of wide band, easy to integration, good consistency and low cost, which make it a research hotspot in the field of ultrasound. As the core of the whole ultrasonic imaging system, the design and fabrication of CMUT play an important role. According to the requirements of underwater imaging, in order to improve the imaging target and the array directivity, the geometric parameters of the array are optimized.