A joint research team from Institute of Science Tokyo (Science Tokyo) and Hiroshima University has successfully improved the performance of terahertz-band communication devices using a mechanical tuning technique based on a microactuator.
Terahertz waves exceeding 100 GHz offer the potential to utilize extremely wide frequency bandwidths for communication, and research and development in this field has been accelerating worldwide. In Japan, in addition to ongoing studies in the 300 GHz band, active research in the 150 GHz band has recently gained momentum. However, as the frequency increases, the wavelength becomes shorter, making the impact of unavoidable mechanical fabrication errors more significant. These errors can greatly affect the performance of the communication modules.
To address this challenge, the research team applied a microactuator capable of sub-micrometer precision to terahertz-band components such as the waveguide transitions that connect antennas and chips. This approach aimed to compensate for performance degradation caused by mechanical inaccuracies. A reflective surface inside a waveguide transition was constructed using a flexible conductive membrane, and its position was controlled by the microactuator. As a result, the team demonstrated that the reflection and transmission characteristics of the waveguide transition could be precisely tuned at 250 GHz.
Terahertz frequencies above 100 GHz offer extremely wide bandwidths suitable for next-generation wireless communications, and research toward their practical use is ongoing worldwide. In particular, the 150 GHz and 300 GHz bands are actively being studied in Japan due to their relatively low atmospheric attenuation, which enables stable signal propagation.
However, at such high frequencies, mechanical fabrication errors—typically around ±50 μm—can no longer be ignored. While this level of error is negligible for conventional sub-6 GHz modules, it becomes several percent of the wavelength at 300 GHz, where the wavelength is about 1 mm. These errors can significantly impact the performance of devices, especially those connecting the chip to the antenna, and therefore require compensation mechanisms. Moreover, since 300 GHz exceeds the maximum operating frequency of standard CMOS transistors, it is difficult to implement active tuning circuits or electronic switches, highlighting the need for alternative approaches.
A joint research team from Institute of Science Tokyo (Science Tokyo) and Hiroshima University has developed a mechanical tuning method using microactuators to improve the performance of terahertz communication devices.
Inspired by optical cameras, which adjust focus by moving lenses to maximize the received light intensity from a specific distance, the researchers applied a similar concept to terahertz devices. As a demonstration, they introduced a mechanical tuning structure into a waveguide transition that connected an antenna to a chip. A flexible, conductive membrane was used as a movable backshort (reflector) within the waveguide, and its position was precisely controlled using an impact-drive microactuator with sub-micron accuracy. The actuator drove a slider element that pushed the membrane, enabling high-precision adjustment of the reflector's position. As a result, the team successfully demonstrated impedance tuning of a 250 GHz waveguide transition, validating the effectiveness of mechanical tuning as a method of compensating for fabrication-induced performance variation.
