Phase Difference Locked Loop for Remote Physiological Detection
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Solution Overview
Problem
Existing radar systems face challenges in accurately detecting small physiological changes in humans due to non-linear responses in motion signals and temperature-dependent signal drift, making it difficult to remotely measure stress and viability levels with sufficient fidelity.
Innovation Solution
A phase difference locked loop circuit is employed, using two receivers out of phase by less than a wavelength to generate an error signal, which is used to correct frequency and reduce distortion and drift, allowing for accurate detection of motion and physiological changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If radar systems are used to detect small physiological changes remotely, then non-contact measurement capability is improved, but measurement precision deteriorates due to non-linear response in derived motion signals and temperature-dependent signal drift
Solution Approach 1:
The patent implements a feedback mechanism where the phase difference between signals from two receivers is continuously monitored and used to generate an error signal. This error signal is fed back to a voltage-controlled oscillator to adjust the transmitted frequency, thereby compensating for temperature drift and maintaining measurement precision without requiring physical contact with the subject
Solution Approach 2:
The patent changes the operating frequency parameter dynamically by using a voltage-controlled oscillator that adjusts frequency based on temperature conditions and phase difference measurements. This allows the system to adapt to temperature variations and maintain optimal detection accuracy for physiological changes while operating remotely
2Measurement precision
If temperature compensation is implemented to reduce signal drift, then measurement precision is improved, but device complexity increases due to additional temperature sensing and control circuitry
Solution Approach 1:
The patent combines the temperature compensation function with the existing phase difference measurement system by using the same two-receiver configuration for both physiological detection and temperature drift compensation. The phase difference signal serves dual purposes: detecting physiological motion and generating error signals for temperature compensation, thereby reducing overall system complexity
Solution Approach 2:
The system uses its own received signals to generate temperature compensation without requiring external temperature sensors or separate compensation mechanisms. The phase difference between the two receivers provides inherent information about both physiological motion and temperature-induced frequency drift, allowing the system to self-correct
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 solution enables precise detection of heart rate variability and other physiological signals, reducing noise and temperature-related drift, thereby improving the accuracy of remote stress and viability assessments.
Implementation Method 1
a first receiver for receiving the reflected transmitted carrier signal; a second receiver for receiving the reflected transmitted carrier signal
Implementation Method 2
a second receiver for receiving the reflected transmitted carrier signal, the second receiver being placed out of phase by less than a wavelength of the carrier signal from the first receiver; means for subtracting the carrier signal received by the second receiver from the carrier signal received by the first receiver to produce an error signal
Implementation Method 3
a voltage control oscillator operatively connected to the transmitting diode for controlling the frequency of the carrier signal; the frequency control forcing the error signal to zero
Data Source
AI summary
An apparatus for sensing motion having a transmitter for transmitting a carrier signal; a frequency control connected to the transmitter for controlling the frequency of the carrier signal; a first receiver for receiving the reflected transmitted carrier signal; a second receiver for receiving the reflected transmitted carrier signal, the second receiver being placed out of phase by less than a wavelength of the carrier signal from the first receiver; means for subtracting the carrier signal received by the second receiver from the carrier signal received by the first receiver to produce an error signal; wherein when motion is sensed by the apparatus, the error signal moves from zero thereby causing a corrective signal to be generated and sent to the frequency control, the frequency control forcing the error signal to zero.