Ultra weak signal detection method using active noise control system

在无电磁屏蔽的超灵敏传感器测量中，消除大的环境噪声是非常重要的。本研究课题的目的是通过有源噪声控制（ANC）来降低输入到传感器的环境噪声。目标频率区域为几百Hz以下和MHz区域，在低频区域，采用超导量子干涉仪（SQUID）作为传感器进行无损检测。尝试使用负反馈回路成分来消除噪声。为了防止信号衰减，该反馈环路包含低通滤波器（LPF）。首先利用低通滤波器提取低频大噪声;然后将具有反相分量的信号反馈到补偿电路。最后，通过补偿磁场来抵消磁场。该ANC系统使机械臂扫描测量成为可能，而在没有ANC系统的情况下，钢样品的情况下观察到大的噪声。为了获得高的检测灵敏度，选择最佳的LPF特性是很重要的。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，ANC系统包括相位和幅度控制电路，其被设计为允许针对MHz区域中的噪声波精确地调节反相波的相位和幅度。ANC系统将该正弦波抑制到白色噪声水平约54 dB。其次，研究了采用数字信号处理的MHz RFI有源噪声控制系统的高速处理的可行性。该ANC系统有效地抑制了MHz正弦波。降低量约为40 dB。

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.