Session: 01-06-02: New Advances in Acoustics and Vibration: AI and Machine Learning, New Methods and Materials

Paper Number: 143324

143324 - Validation of Gelatin Layering for Ultrasound Power Transfer and Backscatter Communication 

BACKGROUND: The human body is a complex system with many functions, and researchers are designing sensors to be placed within the body to monitor these functions. These new devices aim to collect data in real-time with minimal invasiveness by using wireless power and communication methods. Current choices for wireless systems typically involve radio frequency (RF) inductive coupling, but there are drawbacks. RF signals have strong attenuation within the human body which leads to low tissue penetration and lower power transfer. It is possible to increase power transfer by increasing the output; however, there are strict regulations on the transferable power levels. An alternative wireless power and communication method is ultrasound. Ultrasound has low tissue attenuation, thus a high tissue penetration depth, and it can deliver more power for the same size device.

However, ultrasound requires a medium to propagate through, such as human tissue, which is built from layers of skin, fat, and muscle. Across the body, and between people, the thickness of these layers varies. The properties of the tissues, including elasticity, density, and temperature, effect sound wave propagation and calculation of a material’s speed of sound and acoustic attenuation.

When testing ultrasonic devices, an alternative to human tissue is typically used. Common substitutes are animal tissue, castor oil, or water. The drawback of using animal tissue is that its properties change with time due to drying and decay. Water and castor oil properties are similar to average tissue layer properties but not individual layers. Their speed of sound and density are lower than that of muscle or skin and higher than fat. Thus, current substitutes lose the nuisances of reflections and refractions that occur in a heterogenous material. An alternative is to use a gelatin simulant of human tissue that is molded into slabs and stacked. Changing the material of the layers thus creates a heterogenous testing material with varying thicknesses. The goal of this research was to validate a protocol for stacked gelatin slabs as a substitute for human tissue.

METHODS: This study used Humimic Medical gelatin #0, which simulates fat. The slabs were 75x75 mm with thicknesses of 10, 20, and 50 mm. The ultrasound transducers were 1 MHz lead zirconate titanate discs, and a signal generator was used to drive them. The “implanted” transducer was connected to a 240 kΩ resistor. Voltages across the transmission transducer and implanted transducer were recorded with and without water between the slabs.

RESULTS: Without water between layers, the implant had almost no voltage; the slab stacks with water were much higher and had acceptable performance for both when water was only between gelatin layers and when only on the transducer-gelatin boundary. Stacked slabs had lower performance and voltage output than when a singular gelatin slab was used. Results were also found to be comparable with fresh porcine tissue.

CONCLUSIONS: The Humimic gelatin is a promising test material. Water added between layers increased acoustic cohesion between layers, but using a single stack produced better signal transfer.

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