As one of the most popular research hotspot of lab-on-chip, digital microfluidic (DMF) technology based on the principle of electrowetting has unique advantages of high-precision, low cost and programmable control. However, due to the limitation of electrodes number, the throughput is hard to further upgrade. Therefore, active matrix electrowetting-on-dielectric (AM-EWOD) technology is a solution to acquire larger scale of driving electrodes. However, the process of manufacturing of AM-EWOD based on thin-film-transistor (TFT) is complex and expensive. Besides, the driving voltage of DMF chip is usually much higher than that of common display products.In this paper, a solution for mass production of AM-EWOD based on amorphous silicon (a-Si) is provided. Samples of 32 × 32 matrix AM-EWOD chips was designed and manufactured. A boost circuit was integrated into the pixel, which can raise the pixel voltage up by about 50%. Customized designed Printed Circuit Board (PCB) was used to supply the timing signals and driving voltage to make the motion of droplets programmable. The process of moving, mixing and generation of droplets was demonstrated.The minimum voltage in need was about 20 V and a velocity of up to 96 mm/s was achieved. Such an DMF device with large-scale matrix and low driving voltage will be very suitable for POCT applications.
In underwater acoustic communications (UAC), signal synchronization plays a key role in the performance. It is usually performed using a known preamble transmitted prior to the data. However, the underwater acoustic (UWA) channel is characterized as time-varying and frequency-varying, which makes the preamble fluctuated as well as the transmitted data. Thus, it contains uncertainty to set a constant threshold for synchronization by using information (e.g., Doppler shift) extracted from the preamble. In this paper, we propose an adaptive scheme for UAC synchronization. The scheme uses the symmetrical triangular linear frequency modulation (STLFM) signal to design a fractional Fourier transform (FrFT)-based detection algorithm. It establishes the frame synchronization by detecting the deviation of the two energy peaks which usually emerge in their ''optimal'' FrFT domain in pairs. Instead of detecting the absolute peaks, the proposed method performs an initial synchronization and a precise correction based on the relative positional relationship and amplitude attenuation of the two peaks, which makes full use of the two peaks of the STLFM signal in the FRFT domain. The effectiveness of the scheme has been verified by simulations and field works. The results suggest that it is able to peak the time-varying signal amplitude for each frame in UWA channels. Besides, the proposed scheme performs better accuracy and stability in the frame synchronization compared to the traditional LFM method, which is shown as three times less detection error and five-to-ten times dropping of mean square error. INDEX TERMS STLFM (symmetrical triangular linear frequency modulation), FrFT (fractional fourier transform), underwater acoustic communication, frame synchronization.
Underwater acoustic (UWA) channels are characterized by narrow-band, time-varying, and strong multipath interference. At the same time, Doppler effect also has a significant impact in UWA communications due to low sound speed in water. Therefore, traditional wireless multiple access technology cannot be used directly underwater. However, by combining some existing technologies in underwater communications, the traditional multiple access method can be improved to enable underwater multiple access. In this paper, we introduced chirp signals as carriers, which is widely used in UWA communications. Combined with code division multiple access (CDMA) and orthogonal frequency division multiple access (OFDMA) techniques, a multi-carrier chirp signal based CDMA method is proposed, which improves the reliability and spectrum efficiency of underwater multiple access. The simulation results show that the proposed method has good Bit error rate (BER) performance. Further, the method is also able to achieve good BER performance under the influence of Doppler effect because chirp signals is capable of resisting Doppler effects.
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