Adjustable Wave Tube Stand for Acoustic Reflection Technique Biomedical Engineering Design December 12, 2007 Team Members Ryan Carroll – Team Leader Benjamin Engel – BSAC Andrew Bremer – BWIG Jeremy Glynn – Communications Clients – Erin Douglass MS-CCC-SLP, Dr. Houri Vorperian, Ph.D. Vocal Tract Development Lab University of Wisconsin - Madison Dr. Willis Tompkins, Ph.D. Biomedical Engineering Department University of Wisconsin Madison Abstract Acoustic reflection technique is a non-invasive method of measuring vocal tract anatomy. It is useful in studying a number of conditions including sleep apnea and speech disorders. Current studies at the Vocal Tract Lab of the University of Wisconsin seek to compare acoustic reflection technique data with information from medical imaging studies. The current protocol for Acoustic Reflection Technique calls for the wave tube device to be held in the hands of a researcher throughout the duration of the scans. This is inducing variability in the data. For this reason it has been proposed to design an adjustable stand for the acoustic reflection wave tube device in an effort to improve accuracy and repeatability of scans. Several designs were considered and evaluated. The final design incorporates a miniature adjustable boom stand attached to a custom high density polyethylene base that is used to hold the wave tube device. This design also features rubber strapping and a silicone lining to firmly hold the wave tube in place. Further development of this device may include modifications made to improve the range of possible test subjects as well as a counterweight system to prevent tipping under all circumstances.2 Table of Contents Background Information……………………………………………………………….3 Problem Statement……………………………………………………………………..5 Motivation……………………………………………………………………………...6 Design Specifications…………………………………………………………………..7 Design Evaluation by Component……………………………………………………..9 - Fastening Mechanism………………………………………………………….10 - Gripping Mechanism…………………………………………………………..11 - Base Material…………………………………...……………………………...13 - Method of Adjustment………………………………………………………….14 - Joints…………………………………………………………………………...15 Final Design……………………………………………………………………………16 - Adjustable Stand……………………………………………………………….16 - Stand Modifications……………………………………………………………18 - HDPE Base……………………………………………………………………19 - Fastening Mechanisms…………………………………………………………19 Prototype Testing………………………………………………………………………21 Ethical Considerations…………………………………………………………………23 Future Work…………………………………………………………………………....23 References……………………………………………………………………………...26 Appendix A: Product Design Specification……………………………………………273 Figure 1 – Acoustic Reflection Technique Echogram Background Information Acoustic reflection technique is a non-invasive method of measuring vocal tract anatomy, more specifically the volume of the human vocal tract. The underlying principle of acoustic reflection technique is rather simple; however it relies on a number of assumptions as well as difficult computational algorithms. As sound waves propagate through an enclosed tube and come across changes in cross sectional area, part of the sound is reflected while the rest of the sound continues to propagate until it comes in contact with a surface. Acoustic reflection technique takes advantage of this physical property of sound by measuring certain characteristics of sound waves emanating from a human vocal tract. The process of acoustic reflection technique requires a patient to exhale into a device known as a wave tube. This wave tube contains a mouthpiece that prevents loss of sound waves to the outside environment. The tube is also equipped with a sensitive microphone capable of measuring the amplitude of both incident and reflected sound waves that it receives. This information, coupled with the speed of the sound pulse, as well as the amount of time it takes for the wave to travel, allows for the computation of a series of cross sectional areas along the length of the human vocal tract. Often these cross sectional areas are plotted against their distance from a Distance (cm) Area (cm2)4 fixed point on the human body, most often the teeth or inlet of the mouth. This representation is known as an airway echogram (Figure 1). These cross sectional areas are then combined along the length of the vocal tract to gain information about the volume of the vocal tract [1]. Difficulty in computing the cross sectional areas arise due to the occurrence of multiple reflections and multiple arrival times. Fortunately a number of studies have addressed this issue, as the propagation of waves had incredible implications in many other devices. One of the major assumptions made with the acoustic reflection technique is that there exists a rather uniform gas composition within the human vocal tract; this is not always the case. Since acoustic reflection technique is based partially off of the speed of sound there exists error within the method because computation of the speed of a propagating wave depends on the gas composition within the vocal tract. Under normal conditions it had been shown that this error is negligible. Another assumption made with acoustic reflection technique is that the propagation of sound waves is one dimensional. That is to say that as sound emanates from a source it travels as a planar wave front. In measuring the human vocal tract, it is safe to state that this assumption is withheld throughout the
View Full Document