Ultra-Low-Power IM3 Backscatter Passive Sensing System for IoT Applications

HUANG Ruiyang; WU Pengde

doi:10.11999/JEIT250787

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HUANG Ruiyang, WU Pengde. Ultra-Low-Power IM3 Backscatter Passive Sensing System for IoT Applications[J]. Journal of Electronics & Information Technology. doi: 10.11999/JEIT250787

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HUANG Ruiyang, WU Pengde. Ultra-Low-Power IM3 Backscatter Passive Sensing System for IoT Applications[J]. Journal of Electronics & Information Technology. doi: 10.11999/JEIT250787

HUANG Ruiyang, WU Pengde. Ultra-Low-Power IM3 Backscatter Passive Sensing System for IoT Applications[J]. Journal of Electronics & Information Technology. doi: 10.11999/JEIT250787

Citation:

HUANG Ruiyang, WU Pengde. Ultra-Low-Power IM3 Backscatter Passive Sensing System for IoT Applications[J]. Journal of Electronics & Information Technology. doi: 10.11999/JEIT250787

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Ultra-Low-Power IM3 Backscatter Passive Sensing System for IoT Applications

doi: 10.11999/JEIT250787 cstr: 32379.14.JEIT250787

College of Electronics and Information Engineering, Hangzhou Dianzi University, Hangzhou 310018, China

Accepted Date: 2025-12-01
Rev Recd Date: 2025-12-01

Available Online: 2025-12-09

Abstract

Abstract

Objective With the advancement of wireless communication and electronic manufacturing, the Internet of Things (IoT) has progressed remarkably, healthcare, agriculture, logistics, and other fields. The exponential growth of IoT devices brings significant challenges: billions of devices demand enormous cumulative energy, and traditional battery-powered devices require frequent charging, increasing operational costs and exacerbating electronic waste. Thus, innovative energy-saving solutions are crucial for IoT’s sustainable development. Core strategies to address energy and lifecycle constraints involve enhancing energy supply and reducing device power consumption. Energy harvesting (EH) technology enables devices to collect and store solar, thermal, kinetic, and radio frequency (RF) energy for Ambient IoT (AmIoT) applications. However, existing EH technologies have limitations: conventional IoT devices (especially active RF components) consume high power, and insufficient EH efficiency may hinder real-time data transmission. To tackle these issues, this paper proposes a novel IM3 backscatter passive sensing system for direct analog sensing transmission without compromising RF energy harvesting efficiency. Methods The third-order intermodulation (IM3) signal is a nonlinear distortion product generated when two fundamental frequency tones are processed by nonlinear devices (e.g., transistors, diodes) in communication systems, with frequencies of 2f₁-f₂ and 2f₂-f₁. The core innovation of this work is establishing a controllable functional relationship between sensor information and IM3 signal frequencies, enabling information encoding via IM3 frequencies. A key regulatory component is an embedded impedance module—designed as a parallel resonant tank with resistors, inductors, and capacitors—integrated into the rectifier circuit. Tuning the tank’s resonant frequency selectively adjusts the conversion efficiency from fundamental tones to IM3 signals: aligning with a target IM3 frequency introduces a high-impedance load, reducing that IM3 component’s efficiency, while other IM3 signals remain unaffected. Sensor information dynamically adjusts the module’s resonant frequency by converting the information into a DC voltage applied to a voltage-controlled varactor. By linking sensor information to impedance states, impedance states to IM3 conversion efficiency, and IM3 frequency characteristics to sensor information, the system achieves novel passive sensing. Results and Discussions A rectifying transmitter operating in the UHF 900 MHz band was designed and fabricated (Fig. 8). One signal source was fixed at 910.5 MHz, and the other cyclically scanned 917–920 MHz, generating IM3 signals in the 923.5–929.5 MHz range. Both sources had an output power of 0 dBm, with DC voltage as the transmitted sensor information. Experimental results show a power trough in the backscattered IM3 spectrum; as the DC voltage varies 0–5 V, the trough position shifts accordingly (Fig. 9), with an attenuation of over 10 dB throughout, ensuring good resolution (related to the varactor diode’s capacitance ratio). Additionally, the embedded impedance module has little impact on RF-DC efficiency (Fig. 10): at fixed DC voltage, efficiency decreases by 5 basis points at the modulation frequency, independent of input power; under fixed input power, different sampled voltages cause ～5 basis points efficiency reduction at different frequencies. These results confirm the rectifier circuit’s stable efficiency, meeting low-power data transmission requirements. Conclusions This paper proposes a novel passive sensing system based on backscattered third-order intermodulation (IM3) signals, enabling simultaneous efficient radio frequency (RF) energy harvesting and sensing readout. It reveals the regulation mechanism between difference-frequency embedded impedance module and backscattered IM3 intensity. Controlled by sensing information, the module correlates sensing data with IM3 intensity for passive readout. Experimental results show the embedded impedance reduces target frequency IM3 intensity by over 10 dB and the RF-DC efficiency decreases by only 5 percentage points during readout. The microwave anechoic chamber tests confirm the error between IM3-parsed bias voltage and measured value is stably within 5%, indicating good stability. This system breaks the coordinated energy-information transmission bottleneck, providing battery-free communication for passive sensor nodes. It extends device lifespan and reduces maintenance costs in ultra-low-power scenarios like wireless sensor networks and implantable medical devices, with significant engineering application value.
- Passive sensing,
- Simultaneous Wireless Information and Power Transfer(SWIPT),
- RF Energy harvesting,
- Low-power,
- the Third Order Intermodulation(IM3)

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References(22)

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