Implanted Sensor RF Communication via Phase Locked Loop Frequency Lock
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Solution Overview
Problem
Current methods for communicating with implanted wireless sensors, such as those monitoring abdominal aortic aneurysm pressure, are inefficient in terms of energy usage and prone to errors due to environmental variations and false locking issues, particularly in low-power environments.
Innovation Solution
A system that uses a low duty cycle, gated burst of RF energy to determine the resonant frequency of an implanted LC resonant circuit sensor, employing phase locked loops to adjust the energizing signal's phase and frequency, and incorporates frequency and phase dithering to prevent false locks and switching transients, while considering environmental factors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a transmission signal having multiple frequencies is used to determine resonant frequency, then the resonant frequency can be determined, but the energy in frequency bands outside the resonant frequency is wasted, resulting in increased power consumption, size, and thermal requirements
Solution Approach 1:
The patent applies periodic action by using a single-frequency transmitted signal that is modulated in a periodic manner (e.g., pulse modulation or frequency modulation) to encode information about the resonant frequency. The receiver detects these periodic variations to determine the resonant frequency without requiring multiple frequency components simultaneously, thereby reducing power consumption while maintaining measurement precision.
Solution Approach 2:
The patent utilizes parameter changes by varying the phase or frequency of the transmitted signal in a controlled manner to probe the resonant characteristics of the implanted sensor. By systematically changing these parameters and observing the response, the system determines the resonant frequency without needing to transmit across multiple frequency bands, thus reducing energy waste.
2Measurement precision
If multiple frequencies are transmitted to determine resonant frequency, then measurement can be performed, but electromagnetic interference with other signals increases
Solution Approach 1:
The patent employs periodic modulation of a single-frequency signal to convey resonant frequency information. This approach concentrates the signal energy at one frequency while using time-domain periodic variations to encode the measurement data, thereby minimizing electromagnetic interference with other signals compared to transmitting multiple frequency components simultaneously.
Solution Approach 2:
The patent uses an intermediary modulation scheme where the resonant frequency information is embedded in the temporal or phase characteristics of a single-frequency carrier signal. This intermediary representation allows the system to convey measurement data without directly transmitting multiple frequencies, thus reducing electromagnetic interference while maintaining measurement capability.
3Speed
If the sensor signal is detected quickly, then the weak signal can be captured before dissipation, but the system must operate in a low power environment with constrained energy resources
Solution Approach 1:
The patent applies periodic action by using pulsed or modulated transmission signals that activate the sensor and receiver in periodic cycles. This allows the system to detect the weak sensor signal quickly during the active period while maintaining low power consumption during the inactive periods between cycles, effectively balancing speed and energy efficiency.
Solution Approach 2:
The patent employs preliminary action by pre-conditioning the sensor and receiver systems during low-power intervals, such as calibrating or preparing the detection circuitry before the actual measurement cycle. This allows the system to be ready for rapid signal detection when needed without requiring continuous high-power operation, thus achieving fast detection with minimal overall energy consumption.
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 accurate, energy-efficient communication with implanted sensors, reducing the risk of false locks and environmental interference, enabling reliable monitoring of physical parameters like pressure with minimal power consumption.
Implementation Method 1
The system energizes the sensor with a low duty cycle, gated burst of RF energy... The energizing signal induces a current in the sensor which is maximized when the energizing frequency is the same as the resonant frequency of the sensor
Implementation Method 2
the sensors utilize an inductive-capacitive ('LC') resonant circuit with a variable capacitor. The capacitance of the circuit varies with the pressure of the environment in which the sensor is located and thus, the resonant frequency of the circuit varies as the pressure varies
Implementation Method 3
the resonant frequency of the circuit can be used to calculate pressure
Data Source
AI summary
The present invention determines the resonant frequency of a sensor by adjusting the phase and frequency of an energizing signal until the frequency of the energizing signal matches the resonant frequency of the sensor. The system energizes the sensor with a low duty cycle, gated burst of RF energy having a predetermined frequency or set of frequencies and a predetermined amplitude. The energizing signal is coupled to the sensor via magnetic coupling and induces a current in the sensor which oscillates at the resonant frequency of the sensor. The system receives the ring down response of the sensor via magnetic coupling and determines the resonant frequency of the sensor, which is used to calculate the measured physical parameter. The system uses a pair of phase locked loops to adjust the phase and the frequency of the energizing signal.