Ultra weak signal detection method using active noise control system

在使用无电磁屏蔽的超敏传感器进行测量时，去除较大的环境噪声是非常重要的。本课题旨在通过主动噪声控制（ANC）来降低传感器的环境噪声输入。目标频率区域为几百赫兹或更少，以及MHz区域。在低频区域，测量系统采用超导量子干涉装置（SQUID）磁强计作为传感器进行无损检测。尝试使用负反馈环路组合进行噪声消除。为了防止信号衰减，这个反馈环路包含低通滤波器（LPF）。LPF首先提取出较大的低频噪声。然后将含有反相分量的信号反馈到补偿电路中。最后，磁场被补偿磁场抵消。该系统使机械臂扫描测量成为可能，而在没有ANC系统的钢样品中观察到较大的噪声。为了获得较高的检测灵敏度，选择最佳的LPF特性是非常重要的。另一方面，在MHz射频区域的环境噪声，即所谓的射频干扰（RFI），试图通过ANC系统来减少。首先，设计了包括相位和幅度控制电路的ANC系统，以允许在MHz区域精确调整反相位波的相位和幅度，以对抗噪声波。ANC系统将该正弦波抑制到白噪声水平约54 dB。其次，研究了采用数字信号处理技术实现高速处理的MHz RFI ANC系统的可行性。该系统有效地抑制了MHz正弦波。减少量约为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.