»FEMUT« – New Opportunities for Ultrasound Examinations

Innovative Frequency-Encoded Volume Imaging Using 3D Laser-Induced Fabricated Capacitive Ultrasound Transducers

Ultrasound delivers images with resolutions down to the submillimeter range in real time – this is why the technology is one of the most widely used diagnostic imaging methods in medicine worldwide. Our team of the department »Materials Characterization and Testing« is working on the further development of the ultrasound method together with the Fraunhofer Institute for Biomedical Engineering IBMT in the project »FEMUT« (Innovative frequency-encoded volume imaging using 3D laser-induced manufactured capacitive ultrasound transducers).

Ultrasonic Systems to Become Cheaper to Manufacture

Through »FEMUT«, Dr. Erik Waller's team is developing a new manufacturing method for ultrasonic sensors using 3D printing. The advantage: The flexible process produces ultrasonic sensors quickly and cost-effectively on any substrate, for example on glass fiber end facets.

Modern systems work with a large number of regularly arranged ultrasonic transducers made of piezoelectric ceramic rods. Piezoelectric materials are suitable for making sensors because they generate electrical charges when subjected to pressure, shear stress or bending. The individual transducers must be individually controlled for imaging. Until now, a medical ultrasound sensor has consisted of hundreds of elements with always the same vibration characteristics; the associated electronics have just as many channels – this makes the systems complex and expensive. 

The approach pursued in the FEMUT project is to get by with just one electronic channel: Ultrasonic transducers that vibrate at different frequencies and that can be flexibly manufactured using 3D laser printing make it possible. This approach requires new scanning algorithms based on »Compressed Sensing«. This refers to a signal processing technique that quickly captures and reconstructs signals.

New Algorithms and Manufacturing Techniques

In the project »FEMUT« new algorithms as well as fabrication techniques are developed to use broadband ultrasound transducers as CMUT (micromachined capacitive ultrasound transducer) with a small number of elements and only one electronic channel for imaging for the first time.

The solution idea is to use frequency coding instead of time coding. Until now, conventional ultrasound transducers have been based on time coding of the sound fields with an upstream phase plate. The FEMUT approach aims to enable locally defined frequency coding in the sound field for the first time using an additive manufacturing process. 

Different frequencies make it possible to control an entire sound field with different frequencies rather than individual elements. For this purpose, the corresponding sound field has to be designed by means of new algorithms. This task lies with the Fraunhofer Institute for Biomedical Engineering IBMT.

Fraunhofer ITWM Manufactures Prototypes

At Fraunhofer ITWM, on the other hand, the task is to manufacture – initially – prototypes. Using 3D printing, a designed can be produced, tested, and optimized on conductive substrates within hours. 

The specific technological goal of the project is the development of a CMUT-based ultrasound transducer for frequency-based imaging for use in medical diagnostics. The extremely simplified technology should then allow use in minimally invasive endoscopes, for example.