TuftsUniversity
College of Engineering
Department of Electrical and Computer Engineering
EE97/98 Senior Design
Fall/Spring 2007
Handheld Magnetic and Dielectric Susceptometer
Project Proposal
Name:Samuel MacNaughton
ChandlerDowns
Dante DeMeo
Introduction: We plan to design and develop a handheld magnetic and dielectric susceptometer operable at room temperature for use in sensor applications. Materials can be identified by the unique characteristics of magnetic susceptibility and dielectric susceptance. The original design for the coil of the magnetic susceptometer will come from Professor Sameer Sonkusale and graduate student KyoungchulPark. Once we refine and test this design, a dielectric susceptometer module will be added to increase the range of our sensing capabilities. Emphasis will be placed on making this sensor handheld and operable at room temperatures, for now it takes up several cubic feet of space on a lab bench. A handheld susceptometer would have market appealbecause it will increase the affordability and usability of the device.
There are a myriad of possible applications for such a sensing device, includingpollutant and contaminant testing, material identification and especially medicine. This device could revolutionize the medical industry by producing a method for the instant detection of disease. Recent developments in nanoparticle technology have yielded paramagnetic particles which can attached to antibodies to produce an effective tag with a unique electromagnetic signature. The susceptometer would be able to recognize a pathogen by the unique electromagnetic signature of its antibody. The current industry standard uses similar techniques except with fluorescent or chemical tags. Detecting the fluorescent or chemical signature is time and labor intensive, as well as more expensive than the magnetic and dielectric alternative. Outside of medicine, potential magnetic and dielectric sensor applications include environmental pollutant testing, composition testing, and quality engineering.
Problem: The current optical and chemical techniques for detecting pathogens and pollutants are time, space and labor intensive. Magnetic susceptibility can use paramagnetic materials to detect and find these substances instantly, inexpensively and portably.
Mission Statement: To design and develop a handheld magnetic and dielectric susceptometer operable at room temperature for commercial and medical use in sensor applications by April 2007.
Expected Outcome: To build a portable, working prototype of a device capable of sweeping a wide frequency range to find the characteristic resonant frequency of a paramagnetic sample at room temperature.
Background Information:
Magnetic Susceptibility and its Measurement
Magnetic Susceptibility (represented as a Greek chi, χ) is a measure of a material’s reaction to an applied magnetic field. It is the magnetic analogue of the electric dielectric permittivity constant. At the atomic level, the magnetic moments of the electrons in their orbits can interfere either constructively or destructively by aligning parallel or antiparallel with an applied magnetic field. Most of our knowledge of paramagnetism stems from the research of Pierre Curie in the early 20th century. Recent developments in nanotechnology allow for the development and creation of paramagnetic particles that are small enough to be used inside a body, while also not interfering with the metabolism. These nanomaterials may be used as tags for the detection of pathogens, antigens, or an unlimited number of other potential hazards.
In general materials can be placed into three categories regarding their susceptibility: diamagnetic, paramagnetic, and ferromagnetic. Diamagnetic materials slightly weaken the applied field and are characterized by a negative susceptibility, while paramagnetic materials amplify the field and have a positive susceptibility. Ferromagnets amplify the applied field to a much greater extent and have a susceptibility that is many orders of magnitude larger. Our susceptometer will be applied to paramagnets, which constitute the vast majority of materials. All further information regarding susceptibility can be assumed to be paramagnetism specific.
There are two important differences between paramagnetic and ferromagnetic substances: Paramagnetic susceptibility is temperature dependent, and paramagnetic substances do not exhibit hysteresis. The relationship between temperature and susceptibility is given by the Curie-Weiss law shown in Equation 1. Our susceptometer will operate at a temperature much greater than the critical temperature (Tc). The fact that paramagnetic substances do not exhibit hysteresis simply makes analysis much easier.
Magnetic susceptibility generally has dimensions of volume over mass, and, for paramagnetic materials, magnetic susceptibility is generally of the order of 10-6 cm3/g. Placing a paramagnetic substance in a sinusoidally varying magnetic field effectively creates a driven harmonic oscillator on the molecular scale. This driven harmonic oscillator will have one resonant frequency that is explicitly dependant on the susceptance of the material. At this frequency the magnetic field will either significantly decrease or, more often, dramatically increase.
Due to the precession of atomic magnetic moments in an applied magnetic field, magnetic susceptibility is actually a complex figure having both a real and imaginary component. The real component can be separated by multiplying the signal by itself (with no phase delay) and then filtering the high frequency components. The imaginary component can be isolated through the same process with a 90° phase shift in the multiplier stage.
Where C is a material constant related to the number and magnitude of the individual magnetic moments in the atomic structure, and Tc is the critical temperature where the material loses its ferromagnetic properties and becomes paramagnetic.
Equation 1
where , N = number of turns, A = cross-sectional area, l = length.
Equation 2
Schedule / Milestones:
Task / Start Date / Duration (Weeks) / Scheduled Finish DateSign-up Sheet / 9/7/2007 / 2 / 9/21/2007
High level circuit design / 9/21/2007 / 3 / 10/12/2007
Project Proposal / 9/28/2007 / 1 / 10/5/2007
Component Selection and Acquisition / 10/12/2007 / 9 / 12/14/2007
System Engineering Diagram / 10/5/2007 / 1 / 10/12/2007
Risk Assesment / 10/19/2007 / 3 / 11/9/2007
Project Plan / 10/26/2007 / 2 / 11/7/2007
Design Specs / 9/21/2007 / 12 / 12/14/2007
Circuit Construction / 12/14/2007 / 8 / 2/8/2008
Breadboard / Labview Tests / 1/25/2008 / 3 / 2/15/2008
Reassesment of circuit / 2/15/2008 / 3 / 3/7/2008
Design of PCB / 3/7/2008 / 2 / 3/21/2008
Computer Modelling / 3/7/2008 / 2 / 3/21/2008
Creation of PCB / 3/21/2008 / 1 / 3/28/2008
Working Prototype / 3/28/2008 / 3 / 4/18/2008
Final Testing / 4/18/2008 / 1 / 4/25/2008
Final Report / 4/18/2008 / 2 / 5/1/2008
Major Milestones:
10/5Project Proposal
11/7Project Plan
12/14Design Specs
2/15Final Testing / Beta Prototype
4/25Working Prototype Presentation
5/1Final Report
Risks and Contingencies
There are a number of risks involved in the design of this device which must be planned for in order for the project to be successful. One source of risk is the overall sensitivity of the device after it is constructed. If the signal from the input coil is too weak, then the subsequent modulesare not equipped to separate the desired signal from the inherent noise of the circuit. We can mitigate this risk by producing a number of different coils, each having a different geometry, and presumably different sensitivities. If we find that a coil geometry does not meet the desired sensitivity specifications, we can move on to another design. Additionally, by creating a second ‘control’ coil with no sample within it, we can use differential amplifying between the two to get a more sensitive overall design with a drawback of increased complexity.
Electrical and magnetic noise pose the greatest risk in the project. Peaks created by electrical and magnetic noise can mask the true peak observed at the resonant frequency of the sample. We can mitigate this risk by implementing magnetic and electrical shielding and choosing parts exclusively based on their noise to gain ratio. Should too much noise still be present, we would need to develop another module in our output stage devoted to noise reduction and removal.
The current source also poses some risk. As mentioned before, it must be extremely low noise. It must also function at very low frequencies with very little change in magnitude. We can mitigate the risk of gain in the current source by building a negative impedance component alongside the current source. If the range of the current source turns out to be irreparably limited, we can increase the sensitivity proportionally to maintain the value of the product.
References:
Griffiths, David J. Introduction to Electrodynamics. 3rd ed. UpperSaddleRiver: Prentice Hall, 1999.
Park, Kiyoung.
Sonkusale, Sameer. Project Advisor
1