Methods and systems for electromagnetic near-field coherent sensing
The present disclosure may be embodied as methods and/or systems for non-contact measuring of an on-body and/or inside-body motion of an individual. A sensing signal is provided within a near-field coupling range of a motion to be measured. In this way, a measurement signal may be generated as the sensing signal modulated by the motion. The sensing signal may be an ID-modulated signal. In some embodiments, the sensing signal is a backscattered RFID link provided a wireless tag. A downlink signal may be provided to power the wireless tag. The sensing signal may be a harmonic of the downlink signal. The measurement signal is detected. The motion is measured based on the measurement signal. The measurement signal may be detected as far-field radiation after transmission through a source of the motion. The measurement signal may be detected as reflected from a source of the motion as antenna reflection.
1. A method for non-contact measuring of an on-body and/or inside-body motion of an individual using a near-field coherent sensing system (NCS), comprising:
disposing a first near-field antenna within a first near-field coupling range of a first motion to be measured;
outputting, via the NCS with the first near-field antenna, a first sensing signal within the near-field coupling range of the first motion to be measured to generate a first measurement signal that is modulated by the first motion;
detecting the first measurement signal; and
measuring the first motion based on the first measurement signal;
wherein the first near-field coupling range is less than about one wavelength of the first near-field antenna, and wherein the first measurement signal comprises an interference result of the first sensing signal and a first backscattered signal that is modulated by the first motion.
2. The method of claim 1 , wherein the first sensing signal is an ID-modulated signal or is an active radio link or a backscattered RFID link.
3. The method of claim 2 , further comprising:
disposing a second near-field antenna within a second near-field coupling range of a second motion to be measured;
outputting, via the NCS with the second near-field antenna, a second sensing signal within the second near-field coupling range of the second motion to be measured to generate a second measurement signal that is modulated by the second motion;
detecting the second measurement signal; and
measuring the second motion based on the second measurement signal,
wherein the second near-field coupling range is less than about one wavelength of the second near-field antenna, and wherein the second measurement signal comprises an interference result of the second sensing signal and a second backscattered signal that is modulated by the second motion.
4. The method of claim 3 , further comprising measuring a derivative value based on the synchronized measured first motion and second motion.
5. The method of claim 1 , wherein the first sensing signal is provided by a wireless tag, and wherein the method includes providing a downlink signal to power the wireless tag.
6. The method of claim 1 , wherein the first sensing signal is a harmonic signal at a frequency of 2f of a downlink signal at a frequency of f, or a harmonic signal at a frequency of 2f of a source signal at a frequency of f.
7. The method of claim 1 , wherein the first measurement signal is detected far-field radiation after transmission through a source of the first motion or is detected as reflected from a source of the first motion as antenna reflection.
8. The method of claim 1 , wherein measuring the first motion further comprises filtering the first measurement signal to obtain a first motion signal through timing and waveforms.
9. The method of claim 1 , wherein the first sensing signal and the first measurement signal are propagated far field a distance greater than about one wavelength of the first near-field antenna.
10. The method of claim 1 , wherein the first sensing signal is generated using a downlink signal received by a passive harmonic generator.
11. The method of claim 10 , wherein a frequency of the first sensing signal generated by the passive harmonic generator is a harmonic of a frequency of the downlink signal received by the passive harmonic generator.
12. The method of claim 1 , wherein the method further comprising:
coupling a radio frequency signal having a fundamental frequency to a harmonic generator and;
generating the first sensing signal having a harmonic frequency by the harmonic generator.
13. The method of claim 12 , wherein the radio frequency signal at the fundamental frequency of f is coupled to the harmonic generator by an RF cable or a wireless link.
14. The method of claim 1 , further comprising:
coupling a signal at a fundamental frequency of f to a harmonic generator to generate a harmonic signal having a frequency of 2f;
coupling the generated harmonic signal at the frequency of 2f to the first near-field antenna for emitting the harmonic signal as the first sensing signal;
receiving one or more signals directly propagated from one or more antennas comprising the first sensing signal directly propagated from the first near-field antenna and the reflections of one or more signals modulated by one or more motions comprising the reflection of the first sensing signal modulated by the first motion; and
collecting the received signals comprising the first measurement signal by a harmonic reader to demodulate the received signals.
15. The method of claim 14 , wherein the harmonic reader comprises a Tx chain and an Rx chain sharing the same RF clock source such that the harmonic reader is configured to function as a coherent harmonic transceiver.
16. The method of claim 1 , further comprising collecting one or more RF signals by a harmonic reader, wherein the collected signals comprise one or more backscattered RF signals modulated by one or more motions and wherein the one or more motions comprise:
i) one or more movements inside a body to modulate one or more sensing signals in a differential-mode modulation to form differential interference with one or more directly emitted sensing signals in the near-field; and
ii) one or more movements on a surface of the body to modulate one or more sensing signals in a common-mode modulation.
17. The method of claim 16 , further comprising passing collected signals through one or more filters to:
i) demodulate the differential-mode modulation and the common-mode modulation; and
ii) filter the first measurement signal and optionally a second measurement signal to obtain a corresponding first motion signal and optionally a second motion signal.
18. The method of claim 1 , wherein the first near-field antenna is configured to be disposed within the first near-field coupling range of a heart motion, a pulse, a respiration motion, a bowel motion, or an eye motion to form a differential-mode modulation of the first sensing signal, and wherein information of the differential-mode modulation is collected and separated from common-mode modulation by one or more filters.