Backscatter Device Using CSS Modulation and Impedance Switching
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Solution Overview
Problem
Current backscatter technologies face limitations in range and robustness, particularly in healthcare and wearable applications due to signal attenuation by the human body and high power requirements, making them unsuitable for wide-area connectivity and cost-effective embedding in objects.
Innovation Solution
The development of backscatter devices that utilize chirp spread spectrum modulation and impedance switching to generate and transmit signals, capable of suppressing harmonics and achieving long-range communication, enabling wide-area connectivity through devices like dermal patches and contact lenses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional radio technologies are used to provide reliable coverage and long ranges, then communication reliability is improved, but cost and power requirements become prohibitive for embedding into objects at scale
Solution Approach 1:
The patent replaces traditional active radio transmission with passive backscatter modulation. Instead of generating RF signals through power-hungry oscillators and amplifiers, the tag modulates incident RF signals by dynamically switching its antenna impedance between matched and mismatched states, achieving communication without a local RF signal source
Solution Approach 2:
The backscatter tag creates a copy of the incident RF signal and modulates it with data information. The incident signal serves as a template, and the tag reflects a modified version carrying encoded data, eliminating the need for the tag to generate its own high-power carrier signal
2Use of energy by moving object
If traditional backscatter technologies are used to reduce power consumption and cost, then power requirements are reduced, but range and robustness are limited due to signal attenuation
Solution Approach 1:
The patent employs dynamic impedance switching of the backscatter antenna between matched and mismatched states to encode binary data. This dynamic modulation of the scattered signal amplitude creates detectable transitions that enhance signal robustness against attenuation, allowing reliable communication over extended ranges while maintaining passive operation
Solution Approach 2:
The system performs preliminary signal processing at the reader side, including bandpass filtering to isolate the backscatter signal from noise and interference, and correlation detection to decode the modulated data. These preliminary actions enhance signal robustness before final detection, compensating for attenuation effects
3Device complexity
If simple impedance switching is used in backscatter devices, then device complexity is reduced, but harmonic components in the backscatter signal are not suppressed
Solution Approach 1:
The patent applies different impedance values to different portions of the modulating signal to selectively suppress harmonic components. By using multiple distinct impedance states (beyond simple matched/mismatched switching), the system creates a non-uniform impedance profile that cancels out harmonic frequencies while maintaining the fundamental signal, thus suppressing harmful harmonics without significantly increasing device complexity
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
These devices provide reliable, low-power, and cost-effective long-range communication, overcoming previous limitations by using chirp spread spectrum modulation and impedance switching to enhance signal strength and reduce interference, facilitating applications in smart cities, precision agriculture, and medical devices.
Implementation Method 1
an antenna configured to backscatter a carrier signal having a first frequency
Implementation Method 2
the first frequency is mixed with the square wave to transmit a chirp spread spectrum signal
Implementation Method 3
a switch coupled to the antenna, the switch configured to control an impedance of the backscatter device
Implementation Method 4
the variable oscillator comprises a voltage controlled oscillator. In some examples, a backscatter device may include a digital to analog converter coupled to the baseband circuitry and the voltage controlled oscillator
Data Source
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AI summary
Examples of backscatter systems, device, and techniques are described herein. Example backscatter devices may utilize CSS modulation to provide backscatter signals including CSS signals (e.g., LoRa packets). Utilizing CSS modulation may advantageously allow for backscatter communication over wide areas. Examples of backscatter devices described herein may toggle the impedance of the backscatter device between multiple (e.g., eight) impedances to reduce and/or eliminate higher order harmonic components in the backscatter signal (e.g., third and fifth harmonic components).