In this paper, the resistive switching and neuromorphic behaviour of memristive devices based on parylene, a polymer both low-cost and safe for the human body, is comprehensively studied. The Metal/Parylene/ITO sandwich structures were prepared by means of the standard gas phase surface polymerization method with different top active metal electrodes (Ag, Al, Cu or Ti of ~500 nm thickness). These organic memristive devices exhibit excellent performance: low switching voltage (down to 1 V), large OFF/ON resistance ratio (up to 104), retention (≥104 s) and high multilevel resistance switching (at least 16 stable resistive states in the case of Cu electrodes). We have experimentally shown that parylene-based memristive elements can be trained by a biologically inspired spike-timing-dependent plasticity (STDP) mechanism. The obtained results have been used to implement a simple neuromorphic network model of classical conditioning. The described advantages allow considering parylene-based organic memristors as prospective devices for hardware realization of spiking artificial neuron networks capable of supervised and unsupervised learning and suitable for biomedical applications.

/pdf/parylene-based-memristive-devices-with-multilevel-resistive-vqpgjipvl0.pdf

Parylene Based Memristive Devices with Multilevel Resistive Switching for Neuromorphic Applications

Detecting low-frequency underwater acoustic signals can be a challenge for marine applications. Inspired by the notably strong response of the auditory organs of pectis jellyfish to ultralow frequencies, a kind of otolith-inspired vector hydrophone (OVH) is developed, enabled by hollow buoyant spheres atop cilia. Full parametric analysis is performed to optimize the cilium structure in order to balance the resonance frequency and sensitivity. After the structural parameters of the OVH are determined, the stress distributions of various vector hydrophones are simulated and analyzed. The shock resistance of the OVH is also investigated. Finally, the OVH is fabricated and calibrated. The receiving sensitivity of the OVH is measured to be as high as −202.1 dB@100 Hz (0 dB@1 V/μPa), and the average equivalent pressure sensitivity over the frequency range of interest of the OVH reaches −173.8 dB when the frequency ranges from 20 to 200 Hz. The 3 dB polar width of the directivity pattern for the OVH is measured as 87°. Moreover, the OVH is demonstrated to operate under 10 MPa hydrostatic pressure. These results show that the OVH is promising in low-frequency underwater acoustic detection. Jellyfish sensory organs offer the inspiration for a new sensor design that can sensitively detect low-frequency sounds underwater. These capabilities are particularly for the long-range detection of submarines, which produce faint sound signatures in the 5–200 Hertz range. Researchers have struggled to develop compact ‘hydrophone’ devices that can sensitively capture such frequencies underwater, but Wendong Zhang of the North University of China and colleagues have identified a promising solution. Modeled on the pectis jellyfish auditory organ, this system features an otolith-like structure mounted on a cross-beam that produces a piezoresisitive signal in response to vibrations. Based on this concept, the researchers fabricated a device that effectively detects very faint sounds in the 20–200 Hertz range at depths of at least 1000 meters, highlighting the potential of such ‘otolith-inspired MEMS vector hydrophone’ devices.

/pdf/design-and-implementation-of-a-jellyfish-otolith-inspired-15dk5s2hhs.pdf

Design and implementation of a jellyfish otolith-inspired MEMS vector hydrophone for low-frequency detection.

This paper presents a comprehensive review of hydrophones, their design considerations, physical aspects, and structures by reviewing many publications that have been published over the last two decades. The investigation of the fundamental aspects and essential considerations of hydrophones in the literature are distributed in different papers and have not been brought together in a conclusive manner. This paper has collected and classified all the information about hydrophones including the parameters that affect their performance as well as their features. We have categorized the hydrophones according to their mechanism of operation, structure design, frequency response, and application. The literature has been summarized in a way that enables the readers' easy referral to appropriate designs for their desired application scenarios.

Hydrophones, fundamental features, design considerations, and various structures: A review

In this paper, the resistive switching and neuromorphic behavior of memristive devices based on parylene, a polymer both low-cost and safe for the human body, is comprehensively studied. The Metal/Parylene/ITO sandwich structures were prepared by means of the standard gas phase surface polymerization method with different top active metal electrodes (Ag, Al, Cu or Ti of about 500 nm thickness). These organic memristive devices exhibit excellent performance: low switching voltage (down to 1 V), large OFF/ON resistance ratio (about 10^3), retention (> 10^4 s) and high multilevel resistance switching (at least 16 stable resistive states in the case of Cu electrodes). We have experimentally shown that parylene-based memristive elements can be trained by a biologically inspired spike-timing-dependent plasticity (STDP) mechanism. The obtained results have been used to implement a simple neuromorphic network model of classical conditioning. The described advantages allow considering parylene-based organic memristors as prospective devices for hardware realization of spiking artificial neuron networks capable of supervised and unsupervised learning and suitable for biomedical applications.

/pdf/parylene-based-memristive-devices-with-multilevel-resistive-1nqlnv5lip.pdf

In the present paper, guided four beam (G4B) piezoelectric transducers with enhanced sensitivities have been designed. Based on the suggested G4B structures, piezoelectric energy harvesters (PEHs) ...

Performance enhancement of MEMS-guided four beam piezoelectric transducers for energy harvesting and acceleration sensing

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.

http://iopscience.iop.org/article/10.1088/0022-3727/49/7/07LT02/pdf

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

The invention relates to a vector hydrophone and specifically relates to a high-sensitivity resonant MEMS (Micro Electro Mechanical System) vector hydrophone structure. The high-sensitivity resonant MEMS vector hydrophone structure is used for solving the problems of poor antijamming capability and low sensitivity of the existing vector hydrophone. The high-sensitivity resonant MEMS vector hydrophone structure comprises a four-beam arm silicon microstructure, a micro cylindrical body, a central connector, driving electrodes and detection electrodes, wherein the four-beam arm silicon microstructure and the central connector are located in the same plane; the lower end of the micro cylindrical body is vertically fixed in the center of the upper surface of the central connector; eight driving electrodes and eight detection electrodes are arranged; the first driving electrode is paved on the left front part of the upper surface of the front beam arm of the four-beam arm silicon microstructure, while the second driving electrode is paved on the left rear part of the upper surface of the front beam arm of the four-beam arm silicon microstructure. The high-sensitivity resonant MEMS vector hydrophone structure is applicable to accurate positioning and measurement of underwater acoustic pressure signals.

High-sensitivity resonant MEMS vector hydrophone structure

The invention discloses a nanometer electromechanical vector hydrophone suitable for deep water. The nanometer electromechanical vector hydrophone further improves the sealing property, the high hydrostatic pressure resistance, the environmental suitability, the reliability and the similar indexes of an MEMS vector hydrophone. The nanometer electromechanical vector hydrophone comprises a stainless steel circuit tube shell, a necking tube shell, a fixed disc and an insulated annular tray, wherein the insulated annular tray is provided with a lug boss, the lug boss is provided with a round PCB board and a detecting chip, the insulated annular tray is formed with a sealing screw hole and a signal screw hole and is firmly connected with an acoustic cap, the acoustic cap is filled with silicon oil and antifoaming agent, and a support frame is arranged in the acoustic cap. The nanometer electromechanical vector hydrophone prevents the acoustic cap from deformation under high pressure and bubbles, enables the acoustic cap to be resistant to high hydrostatic pressure, and improves the environmental suitability, the underwater sound signal testing reliability, practicability, stability and so on. Under the high pressure, the internal pressure and the external pressure of the acoustic cap are balanced so as to bear the high hydrostatic pressure; the hydrostatic pressure resistance test proves that the nanometer electromechanical vector hydrophone is capable of working normally under the hydraulic pressure more than or equal to 20 Mpa.

Nanometer electromechanical vector hydrophone suitable for deep water

The invention provides a brand-new electronic stethoscope, in particular to a visual electronic stethoscope based on an MEMS (micro-electro-mechanical system) acoustic sensor. The visual electronic stethoscope comprises an acoustic-transmission polyurethane cap, a shell and a cover, wherein the shell is filled with insulation silicone oil. An MEMS acoustic sensor microstructure is fixed in the shell, a signal processing circuit board compartment and a lithium battery compartment are arranged on the outer surface of the bottom of the shell, the cover is provided with a liquid crystal screen and a plurality of function selection keys, a signal processing circuit board is mounted in the signal processing circuit board compartment and is connected with the liquid crystal screen and the MEMS acoustic sensor microstructure, and control modules are arranged on the signal processing circuit board. The electronic stethoscope based on the MEMS acoustic sensor has the advantages of small size, visualization, detection sensitivity, low cost and capabilities of being processed in batches and achieving waveform display by wireless transmission to a computer end, thereby being more accurate, visual and convenient than a traditional stethoscope in heart rate detection.

Visual electronic stethoscope based on MEMS (micro-electro-mechanical system) acoustic sensor

The invention provides a neutral buoyancy type MEMS vector hydrophone, wherein the detection ability of a NEMS vector hydrophone for weak acoustical signals in the water is significantly improved The neutral buoyancy type MEMS vector hydrophone comprises a stainless steel circuit shell, a necked shell, a fixed disc, and an insulated annular tray with a boss The boss is provided thereon with a circular PCB board and a detection chip The detection chip comprises a four-beam micro-structure, a sensitive cylinder body and a buoyancy ball The insulated annular tray is provided with a sealed screw hole and a signal screw hole A sound transmission cap arranged on the insulated annular tray and internally filled with the silicon oil is fixedly connected with the insulated annular tray The sound transmission cap is made of latex and super elastic materials A support frame is arranged in the sound transmission cap According to the technical scheme of the neutral buoyancy type MEMS vector hydrophone, the sensitivity of the NEMS vector hydrophone and the depths of directive pits are greatly increased on the premise that the frequency band of the hydrophone is not influenced at all Therefore, a good prospect is provided for the application and development of hydrophones

Neutral buoyancy type MEMS vector hydrophone

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