Since most of the contact conduction type of heart sound sensors don’t take into account the acoustic signal attenuation problem caused by the heart sound signal transmitting to a sensor whose filling materials’ impedance is different to human soft tissue, the signal-to-noise ratio (SNR) of the heart sound sensors is not very well. Human heart is immersed in blood. If the sensor’s core sensitive element can be immersed in fluid, the attenuation of heart sound signal may be decreased greatly. Inspired by the principle of hydroacoustic signal’s detection, this paper proposes the design of heart sound sensor based on the bionic vector hydrophone. Then theoretical analysis and finite element method (FEM) simulation about the sensor have been carried out. Combined sensitivity with resonant frequency, the optimum dimension of the sensor’s structure has been determined. The sensor’s micro-structure has been fabricated by using Micro-Electro-Mechanical System (MEMS) technology and coupling encapsulated by choosing a kind of medical coupling agent as the filling material. Finally, the performance of the proposed sensor is tested. The fact is that the proposed sensor can work well with either healthy people or patients with heart disease. The obtained data clearly show that: the SNR of the proposed heart sound sensor is superior to 3200-type of 3M Littmann 8.2 dB.
Implantable brain–computer interface (BCI) devices are an effective tool to decipher fundamental brain mechanisms and treat neural diseases. However, traditional neural implants with rigid or bulky cross-sections cause trauma and decrease the quality of the neuronal signal. Here, we propose a MEMS-fabricated flexible interface device for BCI applications. The microdevice with a thin film substrate can be readily reduced to submicron scale for low-invasive implantation. An elaborate silicon shuttle with an improved structure is designed to reliably implant the flexible device into brain tissue. The flexible substrate is temporarily bonded to the silicon shuttle by polyethylene glycol. On the flexible substrate, eight electrodes with different diameters are distributed evenly for local field potential and neural spike recording, both of which are modified by Pt-black to enhance the charge storage capacity and reduce the impedance. The mechanical and electrochemical characteristics of this interface were investigated in vitro. In vivo, the small cross-section of the device promises reduced trauma, and the neuronal signals can still be recorded one month after implantation, demonstrating the promise of this kind of flexible BCI device as a low-invasive tool for brain–computer communication.
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