Autonomous vehicles relying on light-based image sensors often struggle to see through blinding conditions such as fog. Sub-terahertz wavelengths, which are between microwave and infrared radiation on the electromagnetic spectrum, can be detected through fog and dust clouds with ease, whereas the infrared-based LiDAR imaging systems used in autonomous vehicles struggle. To detect objects, a sub-terahertz imaging system sends an initial signal through a transmitter; a receiver then measures the absorption and reflection of the rebounding sub-terahertz wavelengths. That sends a signal to a processor that recreates an image of the object.

The chip leverages sub-terahertz wavelengths for object recognition, which could be combined with light-based image sensors to help steer driverless cars through fog. (Credit: MIT)

Implementing sub-terahertz sensors into driverless cars is challenging. Sensitive, accurate object-recognition requires a strong output baseband signal from receiver to processor. Traditional systems, made of discrete components that produce such signals, are large and expensive. Smaller, on-chip sensor arrays exist, but they produce weak signals.

A two-dimensional, sub-terahertz-radiation receiving system array on a chip was developed that could help steer driverless cars when traditional methods fail. The array is orders of magnitude more sensitive, meaning it can better capture and interpret sub-terahertz wavelengths in the presence of a lot of signal noise.

To achieve this, researchers developed a scheme of independent signal-mixing pixels — called heterodyne detectors — that are usually very difficult to densely integrate into chips. They drastically shrank the size of the heterodyne detectors so that many of them can fit into a chip. The trick was to create a compact, multipurpose component that can simultaneously down-mix input signals, synchronize the pixel array, and produce strong output baseband signals.

A prototype was built that has a 32-pixel array integrated on a 1.2-square-millimeter device. The pixels are approximately 4,300 times more sensitive than the pixels in today's best on-chip sub-terahertz array sensors. The chip could potentially provide “electric eyes” in driverless cars and autonomous robots.

The researchers incorporated into their chip a component called a phase-locked loop that locks the sub-terahertz frequency of all 32 local oscillation signals to a stable, low-frequency reference. Because the pixels are coupled, their local oscillation signals all share identical, high-stability phase and frequency. This ensures that meaningful information can be extracted from the output baseband signals. This entire architecture minimizes signal loss and maximizes control.

For more information, contact Abby Abazorius at This email address is being protected from spambots. You need JavaScript enabled to view it.; 617-253-2709.

Tech Briefs Magazine

This article first appeared in the August, 2019 issue of Tech Briefs Magazine.

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