Harmonic Transponder Interrogation for Isolating Bidirectional Link Loss
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Solution Overview
Problem
Existing methods struggle to isolate forward and reverse link losses in harmonic transponders embedded in mediums with varying dielectric properties, making it difficult to accurately measure environmental parameters such as soil moisture and multipath characteristics in wireless communication channels.
Innovation Solution
A method involving the transmission of two closely spaced frequencies to a nonlinear frequency-multiplying transponder, analyzing backscattered signals for intermodulation distortion products, and determining the operating point to isolate link losses using over-the-air techniques.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If harmonic transponders are used to measure environmental conditions in embedded applications, then measurement capability is provided, but isolation of forward and reverse link losses from overall bidirectional link loss becomes difficult
Solution Approach 1:
The patent segments the bidirectional link loss measurement into separate forward and reverse link loss components by using two different interrogation frequencies (f1 and f2) that map to different harmonic frequencies (2f1 and 2f2). This allows independent measurement of forward link loss at frequency f1 and reverse link loss at frequency f2, resolving the difficulty of isolating individual loss components from the combined bidirectional measurement.
Solution Approach 2:
The patent introduces a frequency dimension by using multiple interrogation frequencies simultaneously. By measuring at both f1 and f2, the system creates separate measurement channels that allow mathematical separation of forward and reverse link losses, transforming a single-dimensional measurement problem into a multi-dimensional solution space where loss isolation becomes possible.
2Duration of action of stationary object
If passive wireless sensors are deployed for extended periods in environments where battery replacement is not tenable, then long-term monitoring capability is achieved, but device complexity and power management become more difficult
Solution Approach 1:
The patent employs periodic action by using periodic interrogation signals at multiple frequencies to excite the harmonic transponder. The transponder responds with harmonic signals that can be detected periodically, enabling long-term monitoring without requiring continuous high-power operation. This periodic excitation and response mechanism allows extended deployment while maintaining manageable power consumption through efficient harmonic frequency utilization.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables accurate determination of bidirectional losses and environmental conditions by leveraging intermodulation distortion products and AM characteristics, allowing for precise measurement of soil moisture and multipath characteristics.
Implementation Method 1
Harmonic transponders receive a signal from an interrogator, typically, at a single frequency, f0. As illustrated in FIG. 1—Top, this signal is rectified using a diode. By way of example, in the case of a pure sinusoid input (interrogation signal) with a single fixed frequency that has a certain period in time over which the shape repeats, the output from the diode is the rectified sinusoid, e.g., only the positive portion of the signal, that also repeats with the same period. Rectification is a nonlinear operation and as a result, the signal reradiated (i.e., backscattered) to the interrogator consists of harmonics of the input frequency.
Implementation Method 2
this signal is rectified using a diode. By way of example, in the case of a pure sinusoid input (interrogation signal) with a single fixed frequency that has a certain period in time over which the shape repeats, the output from the diode is the rectified sinusoid, e.g., only the positive portion of the signal
Implementation Method 3
the signal reradiated (i.e., backscattered) to the interrogator consists of harmonics of the input frequency
Data Source
AI summary
Aspects of the present disclosure include systems and methods for determining the loss of an unknown channel through remote wireless interrogation of a nonlinear transponder. The transponder's nonlinearity is leveraged to ascertain an operating point of the nonlinear transponder. In some examples the operating point is determined by interrogating a nonlinear transponder with an interrogation signal containing two closely spaced frequencies and measuring intermodulation distortion and/or other components of a return signal that nonlinear transponder backscatters. In some examples, an operating point is determined by interrogating the transponder with an amplitude-modulated interrogation signal, comprising a carrier frequency modulated with at least one second frequency and measuring components of a return signal backscattered by the nonlinear transponder. With an operating point determined, channel losses and material properties of an environment in which the transponder is located, among other things, can be determined.