Durdaut Phillip, Müller Cai, Kittmann Anne, Schell Viktor, Bahr Andreas, Quandt Eckhard, Knöchel Reinhard, Höft Michael, McCord Jeffrey
Microwave Engineering, Institute of Electrical Engineering and Information Technology, Faculty of Engineering, Kiel University, Kaiserstr. 2, 24143 Kiel, Germany.
Nanoscale Magnetic Materials and Magnetic Domains, Institute for Materials Science, Faculty of Engineering, Kiel University, Kaiserstr. 2, 24143 Kiel, Germany.
Sensors (Basel). 2021 Aug 21;21(16):5631. doi: 10.3390/s21165631.
Surface acoustic wave (SAW) sensors for the detection of magnetic fields are currently being studied scientifically in many ways, especially since both their sensitivity as well as their detectivity could be significantly improved by the utilization of shear horizontal surface acoustic waves, i.e., Love waves, instead of Rayleigh waves. By now, low-frequency limits of detection (LOD) below 100 pT/Hz can be achieved. However, the LOD can only be further improved by gaining a deep understanding of the existing sensor-intrinsic noise sources and their impact on the sensor's overall performance. This paper reports on a comprehensive study of the inherent noise of SAW delay line magnetic field sensors. In addition to the noise, however, the sensitivity is of importance, since both quantities are equally important for the LOD. Following the necessary explanations of the electrical and magnetic sensor properties, a further focus is on the losses within the sensor, since these are closely linked to the noise. The considered parameters are in particular the ambient magnetic bias field and the input power of the sensor. Depending on the sensor's operating point, various noise mechanisms contribute to f0 white phase noise, f-1 flicker phase noise, and f-2 random walk of phase. Flicker phase noise due to magnetic hysteresis losses, i.e. random fluctuations of the magnetization, is usually dominant under typical operating conditions. Noise characteristics are related to the overall magnetic and magnetic domain behavior. Both calculations and measurements show that the LOD cannot be further improved by increasing the sensitivity. Instead, the losses occurring in the magnetic material need to be decreased.
用于磁场检测的表面声波（SAW）传感器目前正受到多方面的科学研究，特别是因为通过利用水平剪切表面声波，即乐甫波，而非瑞利波，可以显著提高其灵敏度和探测能力。目前，已能实现低于100 pT/Hz的低频检测限（LOD）。然而，只有深入了解现有的传感器固有噪声源及其对传感器整体性能的影响，才能进一步提高检测限。本文报道了对SAW延迟线磁场传感器固有噪声的全面研究。然而，除了噪声外，灵敏度也很重要，因为这两个量对检测限同样重要。在对传感器的电学和磁学特性进行必要解释之后，进一步关注的重点是传感器内部的损耗，因为这些损耗与噪声密切相关。所考虑的参数尤其包括环境磁偏置场和传感器的输入功率。根据传感器的工作点，各种噪声机制会对f0白相噪声、f - 1闪烁相噪声和f - 2相位随机游走产生影响。在典型工作条件下，由磁滞损耗引起的闪烁相噪声，即磁化强度的随机波动，通常占主导地位。噪声特性与整体磁学和磁畴行为有关。计算和测量结果均表明，不能通过提高灵敏度来进一步改善检测限。相反，需要降低磁性材料中发生的损耗。
