在不期望导线连接和电池更换的限制腔内,电阻变化的无线测量是特别期望的。与电容或电感传感器相比,电阻式换能器具有更好的可用性,其电阻变化可以通过电桥直接转换为可检测的电压。然而,在无电池平台上无线操作电桥,需要多级电路将直流信号转换为无线信号,使整个系统在不使用复杂集成电路的情况下难以小型化。或者,电阻换能器可以结合到无源LC谐振器中,以通过反向散射方法进行非接触式表征。这个设计,然而,在近场之外是无效的,它需要对谐振器的频率响应曲线进行复杂的线形分析。这里,我们将大大提高电阻传感器的远程检测能力,通过电感耦合它与参数谐振器。通过外部天线的无线泵浦电源激活后,参数谐振器可以自振荡并发出强振荡信号。温度引起的电阻变化被转换为振荡信号的线性频移,可以在传感器自身尺寸的20倍的大距离间隔内检测到。每0.1°C的温度变化可以转换为8kHz的频移,该频移大约比振荡峰的线宽大三倍。该传感器在25°C至41°C之间保持良好的线性度,为生理监测提供足够的范围。总之,我们制造了一个电阻到频率转换器,用于通过无线供电的参数振荡器远程检测电阻变化。除了这个用于温度传感的概念验证演示之外,电阻频率转换的一般概念将提高用于生理和环境监测的各种电阻传感器的远程可检测性。
Wireless measurement of resistance variation is particularly desirable inside confined cavities where wire connection and battery replacement are undesirable. Compared to capacitive or inductive transducers, resistive transducers have better availability, whose resistance changes can be directly converted into detectable voltages by electric bridges. However, to wirelessly operate electric bridges on batteryless platforms, multistage circuits are required to convert dc signals into wireless signals, making the whole system hard to miniaturize without using complicated integrated circuits. Alternatively, resistive transducers can be incorporated into passive L C resonators for contactless characterization by the backscattering method. This design, however, is ineffective beyond the near field, and it requires complicated line shape analysis of resonators\' frequency response curves. Here, we will significantly improve the remote detectability of a resistive transducer, by inductively coupling it with a parametric resonator. Upon activation by wireless pumping power with an external antenna, the parametric resonator can self-oscillate and emit strong oscillation signals. The temperature-induced resistance change is converted into linear frequency shifts of the oscillation signal that can be detected over large distance separations for up to 20-fold the sensor\'s own dimension. Every 0.1 °C of temperature change can be converted into 8 kHz of frequency shift that is approximately threefold larger than the linewidth of oscillation peak. This sensor maintains good linearity between 25 °C and 41 °C, providing enough range for physiological monitoring. In conclusion, we have fabricated a resistance-to-frequency converter for remote detection of resistance changes via a wirelessly powered parametric oscillator. Besides this proof-of-concept demonstration for temperature sensing, the general concept of resistance-to-frequency conversion will improve the remote detectability of a broad range of resistive transducers for physiological and environmental monitoring.