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 near-field coherent sensing system for measuring motion of an individual, comprising:
a first tag comprising a first signal source for generating a first sensing signal using a downlink signal received by the first tag and a first near-field antenna in electrical communication with the first signal source, wherein the first near-field antenna is configured to be disposed within a first near-field coupling range of a first motion to be measured to generate a first measurement signal as the first sensing signal is modulated by the first motion; and
a receiver for detecting 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 a frequency of the first sensing signal generated by the first signal source is a harmonic of a frequency of the downlink signal received by the first tag.
2. The system of claim 1 , wherein the first motion a heart motion, a pulse, a respiration motion, a bowel motion, or an eye motion.
3. The system of claim 1 , wherein the first sensing signal is an ID-modulated wave, an active radio link, or a backscattering RFID link.
4. The system of claim 1 , where the receiver is a part of the first tag.
5. The system of claim 1 , wherein the frequency of the first sensing signal is the first harmonic of the frequency of the downlink signal.
6. The system of claim 1 , wherein the first tag modulates the downlink signal with an orthogonal ID, such that the first sensing signal is a CDMA signal.
7. The system of claim 1 , further comprising a filter in communication with the receiver, wherein the filter is configured to demodulate and filter the first measurement signal to obtain a first motion signal.
8. The system of claim 7 , wherein the filter is a processor programmed to sample, demodulate, and filter the first measurement signal to derive motion.
9. The system of claim 1 , further comprising:
a second tag comprising a second signal source for generating a second sensing signal and a second near-field antenna in electrical communication with the second signal source, wherein the second near-field antenna is configured to be disposed within a second near-field coupling range of a second motion to be measured to generate a second measurement signal as the second sensing signal is modulated by the second motion; and
wherein the receiver is further configured to detect the second measurement signal,
wherein the second near-field coupling range is less than about one wavelength of the second near-field antenna.
10. The system of claim 9 , further comprising a processor for measuring a derivative value based on the detected first and second measurement signals.
11. The system of claim 10 , wherein the derivative value is a blood pressure.
12. The system of claim 1 , wherein the frequency of the first sensing signal is the second harmonic of the frequency of the downlink signal or the third harmonic of the frequency of the downlink signal.
13. The system of claim 1 , wherein the first tag is configured to be integrated into a fabric.
14. The system of claim 1 , wherein the receiver is configured to isolate a differential mode and a common mode from the first measurement signal and the first sensing signal.
15. The system of claim 1 , wherein the first tag is configured to be disposed in water.
16. The system of claim 1 , wherein the first near-field antenna comprises (i) a first antenna of the first tag configured to receive the downlink signal from a reader and (ii) a second antenna configured to backscatter an uplink signal to the reader of the first tag.
17. The system of claim 16 , wherein the first antenna of the first tag is configured to harvest energy from the downlink signal to provide power to the first tag.
18. The system of claim 17 , wherein the first tag further comprises:
a microcontroller;
a charge pump configured to harvest a first portion of energy from the downlink signal to operate an RF receiver and the microcontroller; and
a nonlinear transmission line configured to couple a second portion of energy from the downlink signal for harmonic generation and backscattering through the second antenna of the first tag.
19. The system of claim 16 , wherein the first antenna of the first tag and the second antenna of the first tag are mounted to a printed circuit board of the first tag.
20. The system of claim 1 , further comprising a reader comprising a far-field antenna, disposed at a far-field distance from the first tag, configured to receive a harmonic signal from the first near-field antenna of the first tag.