Range-Gated RF Sensor Circuit for Stable Physiological Sensing
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Solution Overview
Problem
Existing radio frequency sensors for detecting physiological characteristics face issues with false triggers due to high sensitivity at close ranges and difficulty in sensing objects at medium ranges, along with challenges in regulatory compliance and interference.
Innovation Solution
A digital radio frequency motion sensor with a microcontroller-based circuit design that generates pulsed RF signals for range gating, using a dielectric resonator oscillator for stable frequency and a switched circuit for pulsed RF oscillation, enabling improved oscillator frequency stability and fast switching characteristics while adhering to regulatory requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If continuous wave Doppler radar is used to detect moving objects, then the sensor can receive signals from both near and far objects, but this leads to false triggers due to motion artefact interference and high sensitivity at close range
Solution Approach 1:
The patent applies periodic pulsed transmission instead of continuous wave transmission. The radar transmits periodic pulses with controlled width and repetition frequency, enabling range gating to distinguish between near and far objects. This periodic action allows the system to selectively detect targets within specific distance ranges while filtering out unwanted reflections from other ranges, thereby reducing false triggers while maintaining versatile detection capability
Solution Approach 2:
The patent segments the detection space into distinct range gates by using pulsed transmission with specific pulse widths. Each pulse width corresponds to a specific range gate, allowing the sensor to focus detection on particular distance intervals. This segmentation separates near-range and far-range detection into different time windows, eliminating interference between them and reducing false triggers
2Measurement precision
If pulse width is reduced to improve range gating precision, then the sensing region becomes narrower, but this makes it difficult to sense objects at medium ranges
Solution Approach 1:
The patent implements dynamic pulse width modulation where the pulse width varies over time according to a predetermined pattern. This allows the range gate to dynamically expand and contract, enabling precise measurement at certain ranges while maintaining sensitivity at medium ranges at other times. The dynamic adjustment optimizes both precision and versatility across different operating conditions
Solution Approach 2:
The patent uses periodic variation of pulse width with predetermined frequency and duty cycle. This periodic modulation creates time-varying range gates that can precisely target specific distances during certain phases while maintaining broader coverage during other phases, thus achieving both high precision and medium range sensing capability
3Speed
If fast switching is implemented to improve range gating response, then the sensor can better define sensing regions, but this challenges oscillator frequency stability
Solution Approach 1:
The patent applies preliminary action by pre-charging capacitor circuits before the actual switching event. This prepares the circuit in advance with stored energy, enabling extremely fast switching transitions without disturbing the oscillator's frequency stability. The preliminary charging of switching capacitors allows the radar to achieve fast range gating response while maintaining stable carrier frequency
Solution Approach 2:
The patent introduces intermediary capacitor circuits as buffers between the switching control and the oscillator. These intermediary elements absorb the switching transients and isolate them from the oscillator, allowing fast switching for range gating while protecting the oscillator frequency from instability. The intermediary capacitors act as shock absorbers for electrical transients
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
The solution effectively reduces false triggers, enhances range gating precision, and ensures regulatory compliance, allowing for accurate detection of physiological characteristics with reduced interference and improved sensor reliability.
Implementation Method 1
an oscillator, such as a dielectric resonator, configured to generate a stable radio frequency oscillating signal
Implementation Method 2
Continuous wave (CW) Doppler radar motion sensors emit a continuous wave radio frequency (RF) carrier signal and mix the transmitted RF signal with the return echoes to produce a difference frequency equal to the Doppler shift produced by a moving target
Implementation Method 3
a switched circuit coupled to the pulse generator and the oscillator. The switch circuit may be configured to generate a pulsed radio frequency oscillating signal having a dominant frequency derived from the oscillator
Data Source
AI summary
A digitally implemented radio frequency sensor for physiology sensing may be configured to generate oscillation signals for emitting radio frequency pulses for range gated sensing. The sensor may include a radio frequency transmitter configured to emit the pulses and a receiver configured to receive reflected ones of the emitted radio frequency pulses under control of a microcontroller. The received pulses may be processed by the microcontroller to detect physiology characteristics such as motion, sleep, respiration and/or heartbeat. The microcontroller may be configured to generate timing pulses such as with a pulse generator for transmission of radio frequency sensing pulses. The microprocessor may sample received signals, such as in phase and quadrature phase analogue signals, to implement digital demodulation and baseband filtering of the received signals.