Tiny mmWave sensor for smart farming

Tiny mmWave sensor for smart farming

Technology News |
By Nick Flaherty

Researchers at the University of California, Davis, have developed a proof-of-concept sensor for millimeter wave (mmWave) radar sensor.

The 100mW 39GHz sensor uses an innovative Doppler-based noise cancelling scheme to detect movement down to a resoltuion of 4μm and vibrations down to 39nm.

The development is part of an ongoing project funded by the Foundation for Food & Agriculture Research, or FFAR, to develop a low-cost sensor capable of tracking the water status of individual plants.

The sensors, the size of a grain of rice, are built on a 65nm CMOS chi.

Conventional Doppler radar suffers from detection nulls, at which the receiver detection gain drops to zero. Quadrature demodulation for either carrier frequency or intermediate frequency (IF) is necessary to alleviate nulls but still induces nonlinear detection gain that needs to be compensated through digital signal processing (DSP).

The Doppler radar topology achieves ultrahigh displacement range accuracy and sensitivity and to eliminate detection nulls without using quadrature demodulation.

An edge-driven phase demodulator (EDPD) processes the rectified square-wave intermediate signal and converts displacement/vibration to a true-dc/baseband signal with a constant gain. Coherent demodulation and signal generation through common-referenced subsampling phase-locked loops (SSPLLs) allow the radar to achieve 4μm static range accuracy and 39nm vibrational (at 10 kHz) range sensitivity in measurement.

“It seemed really impossible because the noise levels that we were looking at were required to be so low that almost no signal source could actually handle it,” said Professor Omeed Momeni and his lab in the Department of Electrical and Computer Engineering who led the project.

The prototype succeeded because it allowed them to handle the volume of noise their sensor received like a simple arithmetic problem. They subtracted the unnecessary noise while maintaining the sensitivity of their measurement and the integrity of their data.

With this technique, the millimeter wave sensor could detect all the information it needed without becoming drowned out by noise. This innovation powered the sensor’s high accuracy rates.

Outside of the FFAR project, they think it has promise for detecting the structural integrity of buildings and improving virtual reality.




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