Multi-hop Passive RFID Systems


    This invention relates to radio frequency power transfer circuits and, more specifically, to passive tag transponder circuits of radio-frequency identification (RFID) systems, with applications in tag-to-tag (T2T) communication systems. The proposed architecture eliminates the interference generated by a reader’s continuous wave (CW) on other communicating tags by separating the CW frequency from the tags’ communicating frequency. The frequency of the received CW is passively doubled through a rectifier, while the output power of the rectified waveform is maximized - accomplished through the appropriate design of the CW waveform. These advantages facilitate the use of passive RFID tags for large-area applications, previously requiring larger number of readers or restricted to more costly active RFID tags. 


Technical Summary:

    A new communication networked tag scheme is proposed to overcome the limited interrogation reader’s range. In particular, direct T2T communications may be concatenated to form a multi-hop path between a reader and its target tag. In each of these hops, the receiving tag decodes the backscattered signal from the sending tag and forwards the information to the subsequent tag, or the reader. Such a backscattering operation, referred to as “turbo backscattering”, extends the coverage area of the reader by at least two orders of magnitude over the traditional direct reader’s interrogation scheme. 

    A variety of interference scenarios are discussed along with proposed solutions for this new communication scheme. One such method involves a way to optimize the transmitted power waveform, as to maximize the backscattered power and separate it from the ambient radio-frequency (RF) signals. Potential interferences from the higher harmonics of the continuous wave (CW) are also eliminated when the impinging CW is modified by passing through the rectifier network.

    Another implementation problem of T2T RFID systems is that a tag’s received signal backscattered from another tag can be interfered by a much stronger CW from the reader. One proposed solution involves shifting the frequency of the CW when it is backscattered by a tag, so that the received signal at the tag totally avoids the CW interference. A scheme for frequency shifting is used to achieve this, wherein the CW waveform is rectified, doubling its fundamental frequency. To optimize the conversion efficiency of the rectifier network, a particular waveform design for the CW is proposed.


Figure 1: Passive tag transponder design.


Value Proposition:

    Through both an appropriate design of the readers’ waveforms and the separation of passive tag powering and communication systems, the proposed architecture eliminates the readers’ interference on tags’ communications and maximizes the power delivered to the tags. This solution also allows novel networked RFID tag architectures, which extend the coverage area of RFID systems.



  • Sensor Network Systems – Internet of Things (IoT)
  • Medical Devices – Implantable or skin-mounted tags with an external reader
  • Structural Health Monitoring – Passive monitoring of large-scale structures for potential failure
  • Warehouse Management – Real-time inventory analytics
  • Future Grocery Stores – Whole-cart scanning for checkout
  • Farming Technology- Livestock/agriculture monitoring, soil sensors, animal tags, etc.


Key Benefits:

  • Efficient – Rectified waveform maximizes backscattered power transfer with an improved conversion efficiency
  • Increased Coverage - Increases coverage area by over two orders of magnitude and/or reduces required number of readers
  • Low-Cost – Use of passive tags decreases cost compared to traditional RFID systems, requires less readers for the same coverage area



Zygmunt Haas, Ph.D. - Profile

Zhong Zheng


IP Status: Patent pending.

Licensing Opportunity: This technology is available for exclusive or non-exclusive licensing.

ID Number: MP-17003


Patent Information:
For Information, Contact:
OTC Licensing
Zygmunt Haas
Zhong Zheng
Engineering & Physical Sciences
Internet of Things (IoT)
Signal Processing
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