by John R. Fischer
, Senior Reporter | September 22, 2020
Researchers at Helmholtz Zentrum München and the Technical University of Munich have developed what they claim is the world’s smallest ultrasound detector.
At a size 100 times smaller than an average human hair, the silicon waveguide-etalon detector (SWED) enables super-resolution imaging by visualizing features much smaller than previously thought possible. And while primarily designed for optoacoustic applications, the detectors could be used in broader fields such as sensing and imaging.
"Optoaocustic imaging is an optical imaging method that is insensitive to photon scattering, enabling deep imaging inside tissues," SWED developer Rami Shnaiderman, a researcher at the Institute of Medical and Biological Imaging at Helmholtz Zentrum Munich and the chair of biological imaging at the Technical University of Munich, told HCB News. "This approach resolves the absorption of light on the basis of detection of ultrasound waves emitted from absorbers. The resolution of such images strongly depends on the size of the ultrasound detector employed."
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Core detection technology for ultrasound usually consists of piezoelectric detectors, which convert the pressure from ultrasound waves into electric voltage. The smaller the piezoelectric detector is, the higher the image resolution. Reducing its size also enables smaller, densely packed, one- or two-dimensional arrays and an improved ability to distinguish features in the imaged tissue or material. Further reducing the size, however, impairs its sensitivity to the point where it is unusable for practical applications.
That’s why researchers at both organizations used silicon photonics technology instead to build detectors, with the technology able to confine light in dimensions smaller than optical wavelength. Instead of recording voltage from piezoelectric crystals, the SWED monitors changes in light intensity propagating through the miniaturized photonic circuits. It has already been widely exploited for development of miniaturized photonic circuits and is already widely used to miniaturize optical components and densely pack them on the small surface of a silicon chip.
Smaller than a human blood cell, the SWED is an on-chip that is about half a micron, which corresponds to an area that is at least 10,000 times smaller than the smallest piezoelectric detectors employed in clinical applications. It improves image resolution, enables new discoveries by observations of smaller pathological features, and is 200 times smaller than the ultrasound wavelength employed, meaning that it can visualize features that are smaller than one micrometer, leading to what is called super-resolution imaging.