The world’s smallest ultrasonic detector is created

Researchers at Helmholtz Zentrum München and the Technical University of Munich (TUM) have developed the world’s smallest ultrasonic detector. It is based on miniature photonic circuits on a silicon chip. The novelty is reported by the journal Nature.

The ultrasonic detector is 100 times smaller than the average human hair, but it can visualize details that were previously inaccessible to observation. New Ultra-High Resolution Imaging Aids Scientific Research

Since the development of medical ultrasound imaging in the 1950s, the mainstream technology for detecting ultrasonic waves has primarily focused on the use of piezoelectric detectors that convert the pressure of ultrasonic waves into electrical voltage. The image resolution achieved with ultrasound depends on the size of the piezoelectric detector used. Decreasing this size results in a higher resolution. However, a further decrease in the size of piezoelectric detectors sharply reduces their sensitivity, making them unsuitable for practical use.

Silicon photonics technology is widely used to miniaturize optical components and pack them tightly on a small surface of a silicon chip. Although silicon does not exhibit piezoelectricity, its ability to confine light to less than optical wavelength has already been widely used to develop miniature photonic circuits.

Researchers at Helmholtz Zentrum Munchen and TUM took advantage of these miniature photonic circuits to create the world’s smallest ultrasonic detector: the Silicon Waveguide Reference Detector, or SWED. Instead of detecting voltage from piezoelectric crystals, SWED monitors changes in the intensity of light propagating through miniature photonic circuits.

“This is the first time that a smaller blood cell detector has been used to detect ultrasound using silicon photonics technology,” explains Rami Schneiderman, SWED developer. “If the piezoelectric detector were downsized to the SWED scale, it would be 100 million times less sensitive.”

“The degree to which we were able to miniaturize the new detector while maintaining high sensitivity through the use of silicon photonics was simply breathtaking,” emphasizes Professor Vasilis Ntsiahristos, research team leader. The SWED is about half a micron (= 0.0005 millimeters). This size corresponds to an area that is at least 10,000 times smaller than the smallest piezoelectric detectors used in clinical imaging applications. SWED is also up to 200 times smaller than the ultrasound wavelength used, which means it can be used to render parts as small as one micrometer, resulting in so-called ultra-high resolution imaging.

“The detector was originally developed to improve the performance of optoacoustic imaging, which is the main focus of our research at Helmholtz Zentrum München and TUM. However, we now foresee its application in the broader field of sensing and visualization, ”concludes Ntsiahristos.