This report summarizes the successful validation of the printed circuit board (PCB) designed for
the purpose of signal transduction from a quartz crystal microbalance (QCM) and interfacing the
signal with a computer. In the first phase of the project, the team was requested to optimize the
circuitboard design and print the board. The second phase of the project which is the focus of
this report included assembling the board with the necessary components and executing the
requested validation test, listed bellowed, s to ensure all design requirements were met:
1) Initial Validation for Stability
2) Nonanethiol Monolayer Formation Validation Test
3) Ethanol Monolayer Protected Cluster (MPC) Validation Test
4) Stability of the QCM in Water
The design requirements for the QCM-PCB system, determined in phase I of the project, are
summarized as such:
1) Stability over a 30 minute timespan less than 5 Hz deviation
2) Low noise (Less than 1 Hz from the standard baseline)
3) Ability to operate at 5 MHz in air (which is the resonance frequency of the material)
4) Ability to maintain operation in water.
This report begins by producing the data from the validation tests and interpreting the data.
Whether the test was successful is evaluated in the context of the experimental conditions. Modes
of failure and deviations from the experimental plan are also discussed. In summary, the QCM-
PCB system surpassed the design requirements when operating in air. It was stable, sensitive, and
accurate, thereby passing the design criteria #1, 2, and 3. However, problems were encountered in
the circuit design that disallowed testing in water. Recommendations on ways to surpass this
problem are included.
Finally, recommendations for the modes of failure encountered and recommendations for the next
steps in developing this PCM-QCM product are discussed. From the perspective of this industry
research team, it was determined that the best course of action with regards to water-performance
was to contract out the circuit issue to a company with greater expertise. Reasoning behind this
recommendation is included in the report. PCB Construction and Initial Validation
The PCB was soldered and constructed according to requirements, with only one minor issue
with regards to the circuit design. The inductor connected in series with the resistor over the
QCM had a self-resonance frequency (SRF) of 0.1 MHz, when it was actually required to operate
at 5MHz (the resonance frequency of the crystal). This design failure disallowed the PCB from
making correct readings in air. However, it was identified that this portion of the circuit
(including the variable resistor) was built into the PCB with the purpose of allowing operation of
the QCM in water. Further, it was identified that if these components were bypassed the PCB
would still work in air. Therefore, a wire was soldered to bypass these two components,
essentially removing them from the system and connecting the two nodes.
As a result of this alteration, the QCM was able to give the expected reading (~5MHz) and with
superior stability. Figure 1a below shows the stability of the device over 42 minutes. The jumps
and the beginning and end of the stability test are a result of vibrations from the handling of the
device and QCM, and are unrelated to the stability of the QCM during testing. Figure 1b
eliminates these jumps caused by handling and magnifies the data obtained when the QCM was
undisturbed. As can be seen, the maximum change over 42 minutes is 3 Hz with the overall noise
in the circuit being ~ 0.5Hz or less. This is incredibly stable and justified the continuation of the
project to the next validation tests.
Figure 1a. Stability test showing the PCB operatinFigure 1b. Data from Figure 1a, magnified and
with the QCM and left in air for 42 minutes. rescaled to better show stability and noise.Nonanethiol Validation Testing
The data obtained in this test was good enough to justify continuing to the last validation test.
The data of this test justified the performance of the device, but was hindered by environmental
conditions, hence the last validation test was required to ensure the PCBs performance.
The following is a brief description of the testing procedure: The gold disc of the QCM was
cleaned thoroughly with pirhanna solution, air dried, and immediately installed into the
instrument. The QCM was immediately put to use to avoid contamination and allowed to sit in a
fumehood enclosure for 5 minutes to allow the signal to stabilize, after which a vial containing
nonanethiol was opened under the QCM crystal. Given the volatility of nonanethiol, a monolayer
immediately forms on everything in the enclosure, including the gold surface of the QCM. The
monolayer changes the frequency of the crystal almost instantaneously by 7.13Hz, which should
be easily identifiable seeing that the noise is less than 0.5Hz and the crystal is stable within a 3Hz
range over 42 minutes.
The data is seen in Figure 2. The thiol