The accurate sensing of the location of specific objects in an indoor setting is critical for applications including robotic feedback control and non-intrusive structural integrity monitoring. Current optical and ultrasound approaches often suffer from insufficient accuracy, obstruction by other objects, and ambiguous identification. Alternatively, conventional radar-like radio-frequency (RF) methods can suffer from problems such as multipath ambiguity, small time of flight, and limited item recognition. Attachment of a passive RF identification (RFID) tag can provide a unique marker by modulating the backscattering signal, but current systems struggle with high interference and noise, and thus have poor ranging accuracy. Here we show that a 1 GHz harmonic RFID system can provide a ranging resolution of less than 50 micrometres with a sampling rate of greater than 1 kHz. The fundamental limits on ranging precision in our system are traced to the phase noise of the RF source and the aperture jitter of the data converter. The small passive tag required for the approach can be embedded in indoor or underwater objects, as well as within building structures.

在室内环境中准确感测特定对象的位置对于包括机器人反馈控制和非侵入式结构完整性监控在内的应用至关重要。当前的光学和超声方法经常遭受精度不足，被其他物体阻碍以及模棱两可的识别的困扰。或者，常规的类似雷达的射频（RF）方法可能会遇到诸如多路径歧义，飞行时间短和物品识别受限等问题。无源RF识别（RFID）标签的附着可以通过调制反向散射信号来提供唯一的标记，但是当前的系统在高干扰和高噪声的情况下苦苦挣扎，因此测距精度很差。在这里，我们表明1 GHz谐波RFID系统可以提供小于50微米的测距分辨率和大于1 kHz的采样率。我们系统中测距精度的基本限制可追溯到RF源的相位噪声和数据转换器的孔径抖动。该方法所需的小型无源标签可以嵌入室内或水下物体以及建筑结构中。