06/5 WIPSS - polymer - EMPA

		Cross section of the WIPSS: It is expected that the echo of the empty micro channel is much stronger than that of the filled channel. Evaluation of the reflected ultrasound energy yielded promising results with regard to the read-out accuracy.

The subproject's aim is the development of an adequate ultrasound system which performs the read-out process of an implantable passive strain sensor (WIPSS). The sensor is currently being designed by Prof. Hierold's group at the ETH Zurich. It consists of a micro channel, which is filled with a certain amount of fluid depending on the load that interacts with the sensor. Thus, a read-out system must be able to measure the amount of fluid/air in the micro channel in order to compute the actual load.

Achieving high read-out accuracy is a challenging task, considering the sensor's small lateral dimensions as well as all the negative effects of human tissue on sound propagation. Therefore a novel method is proposed that evaluates the total amount of ultrasound energy which is reflected by the micro channel. The method presumes a describable relation between the micro channel's fill level and the reflected energy. Since the sensor can be covered by thick layers of highly inhomogeneous human tissue, proper weighting of the ultrasound signals is required.

Compared to a conventional ultrasound imaging method, evaluation of the echo energy has several advantages: As the new technique does not involve the acquisition of high resolution 3D data, the operating frequency can be lowered, which in turn ensures high penetration depth of the ultrasound beam. It is expected that the tissue's properties and the insonification angle have only little influence on the read-out accuracy. With regard to its future application, it is envisaged that the read-out method can be implemented in a conventional 3D ultrasound scanner.