Since the development of medical ultrasound imaging in the 1950s, the main technology for measuring ultrasound waves has been based on the use of piezoelectric detectors, which convert the pressure of ultrasound waves into electrical voltage. The imaging resolution achieved with ultrasound depends on the size of the piezoelectric detector used.
Reducing its size leads to higher resolution and enables the production of smaller, more densely populated one- or two-dimensional ultrasound arrays that can better distinguish features in the imaged tissue or material. However, further reducing the size of piezoelectric detectors significantly reduces their sensitivity. This makes them unsuitable for practical applications.
Silicon photonics technology is often used to miniaturize optical components in order to densely populate the small surface area of a silicon chip. While silicon does not exhibit piezoelectricity, its ability to capture light at dimensions smaller than its optical wavelength has already been widely used to develop miniaturized optical circuits.
Researchers at Helmholtz Zentrum München and TUM have taken advantage of these miniaturized optical circuits to build the world's smallest ultrasonic detector: the Silicon Waveguide Etalon Detector, or SWED for short. Instead of recording the voltage of piezoelectric crystals, the SWED monitors the changes in light intensity propagating through the miniaturized optical circuits.
The new detector is smaller than a blood cell and never before has such a small detector been used to measure ultrasound using silicon photonics technology. If a piezoelectric detector were scaled down to the size of SWED, it would be 100 million times less sensitive.
The size of SWED is about half a micrometer. The detector was originally developed to improve the performance of optoacoustic imaging - a key area of research at Helmholtz Zentrum München and TUM. Now, however, there are much broader application possibilities in the field of sensor technology and imaging.
Source: TUM
