SAW Sensor Code and Time Diversity for Interference
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Solution Overview
Problem
Existing wireless surface acoustic wave (SAW) sensor systems face challenges in distinguishing between multiple sensors due to interference from random RF propagation delays and changes in sensed parameters, making it difficult to achieve robust and reliable demodulation of multiple signals without interchannel interference.
Innovation Solution
The use of a combination of code diversity and time diversity, where different pedestal delays in SAW sensors allow for the reuse of codes in different time slots, enabling the differentiation of multiple sensors by introducing discrete variations in pedestal and differential delays, and employing a time integrating correlator system to process signals effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If orthogonal frequency coded (OFC) sensors are used to provide codes that are inherently orthogonal, then sensor discrimination should be improved, but in practice random RF propagation delays and changes in delay due to the sensed parameter produce non-orthogonal interfering signals
Solution Approach 1:
The patent applies dynamics by making the code assignment dynamic rather than static. Sensors are assigned codes based on their measured parameter values, creating a dynamic code assignment system that adapts to changing conditions. This resolves the orthogonality problem because the code assignment changes with the sensed parameter, maintaining distinguishability even as conditions vary.
Solution Approach 2:
The patent changes the parameter being measured from the raw sensor reading to a derived parameter (the measured value itself) that determines code assignment. By using the measured parameter value to select the code, the system transforms the problem of maintaining orthogonality under varying conditions into a controlled code selection process where each code is optimized for its specific parameter range.
2Productivity
If a broadcast interrogation signal is used to interrogate multiple SAW sensors simultaneously, then the system capacity is improved, but the response signals from multiple sensors arrive at varying times causing signal resolution difficulties
Solution Approach 1:
The patent adds a new dimension to signal differentiation by using code domain separation in addition to time domain separation. Instead of relying solely on time differences, the system assigns different codes to sensors based on their parameter values, creating a code dimension for discrimination. This resolves the signal resolution problem while maintaining high system capacity.
Solution Approach 2:
The patent segments the code space into multiple code groups, each assigned to sensors with specific parameter ranges. This segmentation allows the system to handle multiple sensors simultaneously by dividing them into distinguishable groups, resolving the signal resolution issue while preserving broadcast capability for high system capacity.
3Measurement precision
If single frequency reflective tag sensors are used with start and stop reflectors, then identification of individual sensors is improved, but the signals from multiple sensors cannot be adequately resolved when they respond simultaneously
Solution Approach 1:
The patent merges code division multiple access (CDMA) principles with time division multiple access (TDMA) by using both coded reflections and time-based separation. Sensors reflect with unique codes determined by their parameter values, and the system processes responses in time windows, combining both approaches to achieve both precise identification and multi-sensor resolution simultaneously.
Solution Approach 2:
The patent adds the code dimension to the traditional time-based single frequency tag system. Instead of relying solely on time position for identification, the system embeds code information in the reflected signal based on sensor parameter values, creating an additional dimension for sensor differentiation that enables simultaneous resolution of multiple sensors.
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
This approach allows for the simultaneous interrogation of multiple SAW sensors, increasing the number of sensors that can be identified and measured within a system, while maintaining reliable signal processing and reducing interference, thereby enhancing the system's capacity and accuracy.
Implementation Method 1
the sensor acts as a passive reflector for the radio frequency (RF) interrogation signal
Implementation Method 2
wireless sensor system utilizing purely passive sensors such as acoustic wave (or surface acoustic wave—SAW) sensors
Implementation Method 3
employing a time integrating correlator system to process signals effectively
Data Source
AI summary
An apparatus and method for distinguishing between sensors that are to be wirelessly detected is provided. An interrogator device uses different, distinct time delays in the sensing signals when interrogating the sensors. The sensors are provided with different distinct pedestal delays. Sensors that have the same pedestal delay as the delay selected by the interrogator are detected by the interrogator whereas other sensors with different pedestal delays are not sensed. Multiple sensors with a given pedestal delay are provided with different codes so as to be distinguished from one another by the interrogator. The interrogator uses a signal that is transmitted to the sensor and returned by the sensor for combination and integration with the reference signal that has been processed by a function. The sensor may be a surface acoustic wave device having a differential impulse response with a power spectral density consisting of lobes. The power spectral density of the differential response is used to determine the value of the sensed parameter or parameters.