Masters Theses

Date of Award

3-1986

Degree Type

Thesis

Degree Name

Master of Science

Major

Engineering Science

Major Professor

Jack Wasserman

Abstract

Measurement of the electrical properties of mechanically stressed bone has been done since 1957. The inconsistency of the results thus far, however, indicate a need not only for the development of a more refined method of measuring these properties, but also for determination of potential noise sources which can mask the desired signals. In the past, three amplification methods have been used to measure the electrical response of bone: current amplification, voltage amplification, and charge amplification. Of the three, the voltage amplifier has been the most popular, mainly because of its ease of use. In an earlier thesis, Simpson (1980) studied the properties of all three types of amplifiers and then developed voltage and current amplifiers suitable for the task of measuring the electrical response of mechanically stressed bone.

For this study, prototypes were built and tested, and a suitable system was developed to incorporate both a current and voltage amplifier for the measurement and study of the electrical response of mechanically stressed bone samples subject to cantilever beam bending. The impact loading system used a weighted plunger to provide end loading of the bone samples. This system was also able to measure the mechanical deflection of the bone directly using an optical probe, allowing for the study of the correlation of voltage and current generation with the mechanical deflection of the bone. The results were recorded and studied on a Hewlett-Packard 5420B Digital Signal Analyzer. Testing was conducted to determine potential noise sources, isolate the causes, and reduce or eliminate them.

Three sources of noise were found; 1) 60 Hz, 2) static electricity, and 3) mechanical vibration. Grounding removed the 60 Hz noise. Static electricity and mechanically induced vibration produced signals that were typical of the signals produced by normal bending of bone.

Static electricity was produced by motion of the plunger within the plunger guide just before impact with the bone samples. Static electricity may be reduced by avoiding the use of sliding surfaces for plunger guides near the bone samples.

Vibration induced signals were caused mostly by movement of the cable between the electrode leads from the bone sample and the inputs to the amplifiers. It was found that these noise signals can be reduced by designing a more rigid mounting for the bone samples, and either reducing the length of the cabling between the bone samples and amplifier or designing a "hybrid" amplifier that can be mounted adjacent to the bone samples.

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