Session: 01-08-01: Passive, Semi-Active, and Active Noise and Vibration Control

Paper Number: 165066

Characterization and Modeling of Ultrasonic Backscatter Communication During Misalignment 

BACKGROUND: Implantable medical devices (IMD) are used to monitor injuries and facilitate patient recovery. These devices need to be powered and must be able to communicate externally. Wireless power and communication methods provide easy, consistent and safe ways to interact with IMDs. A common method chosen is radio frequency (RF) inductive coupling, however its depth and power transfer capabilities are limited. An alternative method is ultrasound. Ultrasound has low tissue attenuation, allowing high tissue penetration and larger limits for power transfer without excessive tissue heating. In addition, for a device of the same size, ultrasound devices can transfer more power at a greater depth than RF devices.

To communicate from an implant, a secondary transducer can be used to form the communication link; however, IMDs are being designed smaller and thus require more power efficiency. A method that accommodates both these aspects is ultrasound backscatter communication which reflects the initial transferred power wave using the implant’s receiving transducer. By changing the implant’s impedance, the reflected wave can be modulated to contain information that is decoded by the transmitter. This method reduces the number of transducers needed as well as the power consumed.

Communication links work best when transducers are perfectly aligned; however, when a device is implanted in a patient, it can no longer be seen. With lack of sight for aligning an implant with an external device, it is necessary to develop a robust backscatter communication method. The goal of this paper is to characterize the behavior of ultrasonic backscatter communication when transmission and implant transducers are misaligned.

METHODS: This study used two identical 1 MHz lead zirconate titanate disc transducers separated by 100 mm in a tank of deionized water. Various planar and angular misalignment configurations were tested. The angular testing involved changing both the transmission and implant angles, and then the voltages across the transmission and implant transducers were recorded. A continuous 20-volt peak-to-peak sine wave was transmitted to an implant, which is then manipulated to transmit the backscatter communication signal using impedance modulation.

RESULTS: The largest recorded voltages occurred when the transducers were aligned concentrically and in parallel. For all misalignments, the backscatter communication magnitude decreased linearly with both angular and planar misalignment. For angular misalignment, the limit of power received was 15° while the limit for backscatter communication was 10°. For planar misalignment, power ceased at 20 mm and backscatter communication ceased at 12.5 mm.

CONCLUSIONS: Backscatter communication linearly decreases as misalignment increases. Communication ceases when the transducers are either 12.5 mm planarly misaligned or when angularly misaligned by 10°.

Presenting Author: Kaleb Mcgillivray-Seaton University of Canterbury

Presenting Author Biography: Kaleb graduated from the University of Canterbury New Zealand in 2021 with a Bachelor of Mechatronics Engineering (with Honors) degree and a certificate in Biomedical Engineering. In the summer of 2022, Kaleb completed a research project reviewing power and communication system for implantable sensors under the supervision of Associate Professor Deborah Munro. From this, he established his research objectives for his Ph.D. His doctoral research focuses on developing ultrasound transducer designs for omnidirectional, wireless communication with implants in the body.

Authors:

Kaleb Mcgillivray-Seaton University of Canterbury
Deborah Munro University of Canterbury