Ultra weak signal detection method using active noise control system

在使用无电磁屏蔽的超灵敏传感器进行测量时，消除大量的环境噪声是非常重要的。本课题旨在通过有源噪声控制(ANC)来降低环境噪声对传感器的输入。测量系统采用超导量子干涉仪(SQUID)作为传感器，在低频区以超导量子干涉器件(SQUID)作为传感器进行无损检测。使用负反馈环路组合来尝试噪声消除。为了防止信号衰减，该反馈环路包含低通滤波器(LPF)。首先利用低通滤波提取较大的低频噪声。然后，具有反相分量的信号被反馈到补偿电路。最后，用补偿磁场抵消磁场。这种ANC系统使得利用机械臂进行扫描测量成为可能，而在没有ANC系统的情况下，钢样的噪声很大。为了获得较高的检测灵敏度，选择最佳的低通滤波特性是非常重要的。另一方面，ANC系统试图降低MHz射频区域的环境噪声，即所谓的射频干扰(RFI)。首先，设计了包括相位和幅度控制电路的ANC系统，以允许针对MHz区域的噪声波精确地调整反相波的相位和幅度。ANC系统将该正弦波抑制到白噪声水平约54分贝。其次，研究了采用数字信号处理技术实现高速处理的MHz射频干扰有源噪声控制系统的可行性。该系统有效地抑制了MHZ正弦波。降低量约为40分贝。

It is important to remove large environmental noise in measurement using hypersensitive sensors without electromagnetic shielding. This research topic has aimed to decrease the environmental noise input to the sensor by active noise control (ANC). The target frequency regions were several hundreds Hz or less and the MHz region.In the low frequency region, the measurement system assumed the nondestructive testing using the superconducting quantum interference device (SQUID) magnetometer as a sensor. The noise cancellation was attempted using the negative feedback loop composition. To prevent the signal from attenuating, this feedback loop contains the low pass filter (LPF). The large low-frequency noise was extracted by the LPF firstly. Then a signal with an antiphase component was fed back to a compensation circuit. Finally, the magnetic field was canceled by the compensation magnetic field. This ANC system made scanning measurement using robot-arms become possible, while the large noise was observed in the case of steel sample without the ANC system. It is important to choose the optimum characteristics of the LPF in order to get high sensitivity of detection.On the other hand, the environmental noise in the MHz radio-frequency region, so-called radio frequency interference (RFI) was attempted to be reduced by the ANC system. Firstly, the ANC system including a phase and amplitude control circuit has been designed to allow precise adjustments of the phase and the amplitude of the anti-phase wave against the noise waves in the MHz region. The ANC system suppressed this sinusoidal wave to the white noise level by about 54 dB. Next, the feasibility of the ANC system for MHz RFI that used the digital signal processing was studied for high speed processing. This ANC system suppressed the MHz sinusoidal waves effectively. The amount of reduction was about 40 dB.