Sending Strong Signals

Wireless signals are not just for communication — they are also useful for sensing applications, such as those needed in medical imaging or object tracking. But electromagnetic radiation is not all the same, of course. If you want to transfer a large amount of data very quickly, or develop a sensing system with exceptionally high resolution, then higher frequency radiation is what you are looking for. Because of their shorter wavelengths, terahertz waves, for instance, can encode a lot of information in just a brief transmission.

However, generating terahertz waves from a tiny silicon chip is quite difficult and inefficient. Yet miniaturizing the technology is necessary before it can be incorporated into electronic devices or larger, high-precision arrays of sensing units. Because of the way that terahertz waves interact with silicon, they cannot be effectively transmitted by a traditional chip without the use of a silicon lens. But these lenses are expensive and bulky, which prevents them from being integrated into high-density clusters of transmitters.

These problems may soon be a thing of the past, as researchers from MIT have developed a novel solution that eliminates the need for silicon lenses while significantly improving the efficiency of terahertz wave generation. By designing a terahertz amplifier-multiplier system and using a specially engineered dielectric sheet, the team has created a compact, scalable chip that produces high-power terahertz signals.

Are you picking up what I'm putting down?

One of the biggest obstacles in terahertz chip technology is the difference in dielectric properties between silicon and air. When terahertz waves try to exit a conventional chip, most of the signal is reflected at the silicon-air boundary, leading to significant power loss.

To address this, the team turned to an electromechanical concept known as “matching,” which aims to equalize the dielectric constants of different materials to reduce reflection. They accomplished this by affixing a thin sheet of patterned material to the back of the chip. This sheet, which has a dielectric constant between that of silicon and air, allows terahertz waves to be transmitted more efficiently rather than being reflected back into the chip.

Using a commercially available low-cost substrate, the researchers refined the dielectric properties by precisely punching tiny holes into the sheet with a laser cutter. By controlling the hole density, they were able to fine-tune the dielectric constant to the ideal value needed for efficient terahertz transmission.

Now you're playing with power

In addition to the dielectric sheet, the team also used advanced transistors developed by Intel, which offer higher frequency limits and improved power handling compared to traditional CMOS transistors. These high-performance components, combined with the new transmission method, allowed the researchers to achieve a peak radiation power of 11.1 decibel-milliwatts — one of the best performances recorded among state-of-the-art terahertz devices.

This new chip design opens the door for practical applications in areas where high-resolution sensing and data transmission are needed. For example, terahertz waves could be used in security scanners that detect hidden objects with greater accuracy, or in environmental monitoring systems that identify airborne pollutants in real time.