The Design And Research Of The Portable Bioelectricity Sensor

The Bio-potential, as affirmed to be closely related to many functions of human body, has been widely used in clinical diagnosis, monitoring and the prevention of disease, etc. Because the amplitude of bioelectricity is very weak and the amplitude of many presented jamming signals are relatively often too large, biological signals can be got only through the special bioelectricity sensors. Generally, bioelectricity sensor changes the biological electrical signals into electrical signal of the circuit by two steps.1) Acquisition:The variation of the weak potential, which is flooded with many background noises, is collected on the human body surface through the electrode; then, the detected potential changes would transmit to the next amplifier circuit.2) Conditioning:The primary interface circuit will pick up the weak input signal contaminating with noise and carry out the required conditioning stages, such as amplification, filtering, analogue to digital converting, and impedance matching, so that the raw signal displaying and storage can be done for further processing.Recently, the research in the portable equipment and the brain computer interface (BCI) of bio-potentials has been booming around the world.. However, most commercial available devices are criticized for bulky in size and picky to the working environment. It is thus imperative to develop the dedicated bioelectrical sensing devices to be suited for the new requirement. The aim of this study is to design and implement a prototype of a portable bioelectrical sensor, which is integrated with electrodes with the main expectation of lower power consumption, high amplification gain, appropriate anti-interface ability, and easy-to-mount etc.Traditional way of using wet-electrodes is a complex procedures in placing them, including skin-abrasion, electrical gel pasting, and tap fixing, which make the recording annoying. Recent development attempt to overcome such flaws with new manufacturing technology, such as active electrodes and dry electrodes.The success of these new-generation electrodes depends largely on the rapid advance in the microelectronics. More applications of the bioelectrical sensors are found in an unconstrained condition for the data collection. Unlike the specially designed laboratory in hospitals, the proposed design of a preamplifier focus on three aspects:1) strong anti-interference ability;2) lower power consumption;3) easy interfacing with electrodes and condition circuits.To reduce the induced noises during signal transmission along the electrode cables, it is based on the active electrode structure, which is composed of a silver electrodes array with lmm in diameter and a low-cost op-amp TLC272. For the preamplifier circuit, it contains two low power consumption chips, instrumentation amplifier AD623and TLC1078/1079, to ensure the whole circuit is energy efficient. The first stage amplification, using an AC coupling method, is designed to reach at1000times voltage gain by an instrumentation amplifier AD623with high noise attenuation. Right Leg drive circuit (Driven Right Leg circuit, DRL) can drive the human body potential to the half the power supply voltage to meet the needs of the single power supply. Simulation by Pspice shows that the scheme has wider band and higher amplification gain compared with other several types of amplification scheme. Its common mode rejection ratio in frequency50Hz can reach more than120dB and the μV level signals can be amplified to10000times. The ECG signal acquisition tests (magnified1000times) in the practical circuit showed that, an ECG waveform of standard I guide league can be clear and obvious observed through the common oscilloscope without any skin treatment. For simulated weak signal (μV level) acquisition test (10000times gain), we can also observe a clear signal, suggesting a satisfied performance in a bad electromagnetic environment. For the digital part, we chose STM23chip to be an AD converter and the lower controller for communication with the host computer. The software in the host computer was programmed in LabVIEW, mainly for the display function.