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UW-Madison BME 400 - Automated Device to Measure Forces and Frequency of Vibrations in Mosquito Bites

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Department of Biomedical EngineeringProblem StatementBackground on MosquitoesPrior WorkDevice Components and CriteriaPotential SolutionsSensor: A major change that may improve the sensor lies in the amplifier circuit. Piezoelectric amplifiers generally use a charge amplifier circuit, shown below, rather than a standard instrumentation amplifier, such as is being used currently. The single-ended charge amplifier will have to be modified into a differential amplifier, but this does not present much of a problem. This adjustment could improve the low frequency performance of the sensor, as well as the common mode rejection. Changes in the layout of the sensor as well as the methods of construction could greatly improve its robustness.Preliminary TestingFuture WorkPhysical CharacteristicsElectrical Aspects of the DesignOperational CharacteristicsProduction CharacteristicsMiscellaneousAutomated Device to Measure Forcesand Frequency of Vibrations inMosquito BitesKevin Brosche and Jake FealaDepartment of Biomedical EngineeringBME 400 – Capstone Design Client:Professor Amit LalDepartment of Electrical EngineeringAdvisors:Professors Willis Tompkins and Mitchell TylerDepartment of Biomedical EngineeringProblem StatementTo design an automated device to sense and quantify forces and vibrations present in mosquito bites. The motivation for building a device that does this is to examine how mosquitoes use their proboscis to bite in a way that is often virtually undetectable to humans. The long-term goal is to design a needle that mimics this behavior in order to minimize discomfort in blood and fluid sampling.Background on MosquitoesMosquitoes will be the test subjects for this research. Therefore it is essential to understand their anatomy and behavior, and in particular, what attracts them.There are more than 2400 species of mosquitoes, about 150 of which originate in North America. Commonly regarded as one of nature’s biggest pests, the mosquito has spawned a multi-billion dollar industry in repellents to keep them away, as well as attractants to attract and eliminate them. Unlike most insects, light has no significant attractive effect on mosquitoes (Becker et. al,1995), rather mosquitoes respond primarily to chemical attractants to locate their prey. Because attracting mosquitoes to our device is critical to obtaining results, we have extensively researched major mosquito attractants. Carbon Dioxide (CO2) exhaled duringbreathing is commonly regarded as the primary attractant for almost all mosquito species.In addition, numerous studies cite sweat extracts or chemicals exhaled in breathing as long-range attractants. 1-octen-3-ol and lactic acid are among the most rigorously studied and have been shown to act synergistically with CO2 to increase mosquito response (Kline et. al 1990, Healy & Copeland 1995). Female mosquitoes are the only blood-sucking, or “host-seeking” mosquitoes; males lackthe proboscis that is used to penetrate the skin. It has been hypothesized that during bites,mosquitoes vibrate their proboscis. Sonic vibrations may alter the Young’s modulus (stiffness) of the skin as perceived by the proboscis, by the same physical concept that can make a liquid seem “hard” if its surface is struck by a fast-moving object. Therefore, less force would be required in puncturing the skin, and a smaller area on the skin would be deformed during the process. This may be one reason a mosquito’s bite oftentimes goes undetected by pain receptors in the skin. Preliminary research shows vibrations in the range of 200-400 Hz may be produced during bites. Prior WorkA preliminary prototype has been designed that uses piezoelectric film (PVDF) to sense extremely small forces produced by the mosquito’s proboscis. The current device has promise, but lacks the accuracy and consistency needed to draw conclusions from the data. Constant monitoring is necessary to operate this prototype, which requires hours of attention to capture a few bites. A self-contained, automated unit would greatly acceleratethis research. The current sensor is shown below. It will be described in the next sectionDevice Components and CriteriaPhysical Environment: The device needs to be self-contained. This means that all the electrical components and battery need to fit in a compact box that eventually may be placed outdoors. For this reason the box must be watertight and designed to withstand moderate environmental elements. Chemical / Biological / Physical Attractants: Some method of attracting mosquitoes and inducing them to bite is required. The device must attract mosquitoes in the vicinity of the box and persuade them to bite a sensor. The device should utilize one or more knownmosquito attractants, including: - dark colors - CO2- 1-octen-3-ol- heat - lactic acid - sweat- moisture - acetone - “host odors” (natural skin scent)These attractant methods have different effects at different ranges; testing will be necessary to find the optimum combination. Previous work found the most success witha combination of heat applied directly beneath the sensor, CO2, and skin scent rubbed on the sensor just before introducing it to the mosquito. Of the other attractants, only 1-octen-3-ol has been tried, albeit unsuccessfully when used on Anopheles mosquitoes. However, this may have to do with the way in which it was applied rather than its attractive promise.Photodiode / Motion Sensor: Could be used to detect the presence of mosquitoes in the test chamber and activate the electronics for the possibility of a bite. This is not a requirement, but it could be very helpful for both conserving power and collecting only relevant data.Sensor: The sensor will build on previous work with piezoelectric polyvinyl diflouride (PVDF) film. Two identical PVDF squares were mounted on a circuit board, below smallholes in a copper plate, with room to vibrate in the z direction as shown below. The active and ground electrodes (copper traces on a printed circuit board) were then connected to an AD620 in-amp which acted as a differential preamplifier for the signal before being filtered and amplified on a different board, then sent to a computer for processing. The amplifier must have very high gain and common-mode rejection ratio toaccurately pick up the miniscule signals created by the mosquito bites. Also, a high pass filter is necessary to attenuate the high DC offsets and low


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UW-Madison BME 400 - Automated Device to Measure Forces and Frequency of Vibrations in Mosquito Bites

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