Spectrophotometer 01 Design Description Document
UNIVERSITY OF ROCHESTER
Design Description
Document
Smartphone Spectrophotometer
Elie Glik, Carol Xu
Customer:
Engineers:
Advisor committee:
Per A
Elie Glik, Carol Xu
Tom Brown, Jim Zavislan
Document Number: 01
Date:
7/31/2017
Revision Level:
A
Authentication Block
This is a computer generated document and the electronic
master is the official revision. This paper copy is
authenticated for the following purpose only:
A self-powered spectrophotometer attachment to a modern day smartphone camera to allow spectral
response data for lab and commercial purposes. Students in small limited budget labs may use this
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Spectrophotometer 01 Design Description Document
device along with their smartphone to identify light sources, measure chemical concentrations, or
compare solutions.
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Spectrophotometer 01 Design Description Document
Contents
Product Requirement Document .................................................................................................................. 4
System Block Diagram................................................................................................................................... 4
Optical Design 1 ........................................................................................................................................ 4
Optical Design 2 ........................................................................................................................................ 7
Mechanical housing for optics .................................................................................................................. 8
Mechanical attachment ............................................................................................................................ 8
Software Interface .................................................................................................................................... 8
Test Plan / Validation .................................................................................................................................... 9
Risk Assessment .......................................................................................................................................... 10
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Spectrophotometer 01 Design Description Document
Product Requirement Document
(See digital document 1)
Product Requirements Document
Cellphone spectrophotometer
Customer:
Engineers:
Advisor committee:
Per A
Elie Glik, Carol Xu
Tom Brown, Jim Zavislan
Contents
Vision ............................................................................................................................................................. 2
Environment.................................................................................................................................................. 2
Regulations and Risk Factors......................................................................................................................... 2
Product Requirement Document .................................................................................................................. 3
System Block Diagram
1)
2)
3)
4)
An optical system for dispersing the incoming light and directing it into the cellphone
A mechanical housing for the optics
A mechanical attachment for the device to a smartphone
Software interacting with the smartphone
Optical Design 1
This is the chosen design, but still needs to be verified and validated
Overview:
A single diffraction grating of specified lines/mm will be illuminated with a ray angle such that there is a
specific illuminated area. This light from the 1st order will then be redirected and focused into the
camera. Additionally, the light from the 0th order will be partially allowed to hit the camera system,
allowing the target to be capture as well.
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Spectrophotometer 01 Design Description Document
Cellphone
Camera
Slit
Diffraction grating
Figure 1a – Optical Design 1
st
Slit
1 order image
Cellphone
Camera
Prism/ Grating
th
0 order image
Figure 2 –Optical Design 1b- Shows another optical design with order 0 being visible as well as using a prism.
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Spectrophotometer 01 Design Description Document
Figure 3 – Shows the result on the detector with 2 visible orders. For order 0 the object of interest (OOI) can be visible as well
as its spectrum. This will be convenient in making sure that the OOI is being measured.
From the iPhone5 specification1 F/2.4 | Focal length= 4.10mm
According to the equation for imaging system
∆ℎ = 𝑓 ∗ 𝑡𝑎𝑛∆𝜃
𝑓 = 4.1𝑚𝑚, ∆ℎ = 𝑠𝑒𝑛𝑠𝑜𝑟 𝑙𝑒𝑛𝑔𝑡ℎ ∗ %𝑢𝑠𝑒𝑑 = 4.569𝑚𝑚 ∗ 0.75 =3.427mm
∆𝜃 = tan−1
∆ℎ
= tan−1 0.8359 = 0.6963
𝑓
= 𝜃𝑚𝑎𝑥 − 𝜃𝑚𝑖𝑛
According to the equation for grating angle
𝑚𝜆 = 𝑑𝑠𝑖𝑛𝜃
We take m=1 since we use the first order of diffraction
𝜆 = 𝑑𝑠𝑖𝑛𝜃
In the experiment we conducted, the wavelength range for iPhone 5 is 402.4nm to 688.54 nm
So 𝜆𝑚𝑎𝑥 = 688.54𝑛𝑚, 𝜆𝑚𝑖𝑛 = 402.4𝑛𝑚
sin 𝜃𝑚𝑎𝑥 =
𝜆𝑚𝑎𝑥
𝑑
sin 𝜃𝑚𝑖𝑛 =
𝜆𝑚𝑖𝑛
𝑑
So
1
http://www.anandtech.com/show/7329/some-thoughts-about-the-iphone-5s-cameraimprovementsv
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sin 𝜃𝑚𝑖𝑛 sin 𝜃𝑚𝑎𝑥
=
𝜆𝑚𝑖𝑛
𝜆𝑚𝑎𝑥
𝜃𝑚𝑎𝑥 − 𝜃𝑚𝑖𝑛 = 0.6963
Solve for 𝜃𝑚𝑖𝑛 =0.5966rad; 𝜃𝑚𝑎𝑥 = 1.2919𝑟𝑎𝑑
d=𝝀𝒎𝒂𝒙 /𝜽𝒎𝒂𝒙 = 𝟕𝟏𝟔. 𝟐𝟑𝒏𝒎
Groove Density= 1396/mm
Resolution Validation: CCD for iPhone camera=3264x2448pixel with 1.5um/pixel
𝐷𝑏𝑒𝑡𝑤𝑒𝑒𝑛 𝑑𝑙𝑖𝑛𝑒
∗ 𝑃𝑖𝑥𝑒𝑙 ∗ 𝐴𝑎𝑟𝑒𝑎 𝑢𝑠𝑒𝑑 =
𝐷𝑡𝑜𝑡𝑎𝑙 𝑟𝑎𝑛𝑔𝑒
=
0.7𝑛𝑚
∗ 2448𝑝𝑖𝑥𝑒𝑙 ∗ 0.75 = 𝟒. 𝟒𝟗𝒑𝒊𝒙𝒆𝒍
286.14𝑛𝑚
Product: http://www.thorlabs.com/thorproduct.cfm?partnumber=GH13-12V
With 1200 groove density.
Characteristic
Lines/mm grating
Area of grating filled
Distance from grating to lens
system
Percent of detector filed
Number of pixels used for the dline
Expression
Ex1
1200/mm
1.16mm
?
?
80%
80%
4.5
Based on this design, it is possible to resolve the d-line with 4.5 pixels of resolution, and by using a
standard grating of 1200 lines/mm. The Optical Design 1a and 1b are similar in setup, but 1b requires
more complexity since it is able to show the 0th order for using purposes.
Optical Design 2
Overview:
Using a pinhole, diffracted light will enter the system. It will then go through two or more diffraction
gratings where the first order of each of them will be focused onto the cellphone’s camera lens, while
insuring that both spectrums are imaged separately. The result may look something like this on the
image:
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Figure 4 – a white light source imaged with several diffraction gratings
Based on the calculations for design 1, it is possible to image the d-line with just one diffraction grating,
simplifying the system. Therefore, this design is no longer being pursued.
Note: If after verification mistakes were overlooked in design 1, this design will be used as reference.
Mechanical housing for optics
The goal is to 3D print this housing to provide a rigid outside body. The components will slip in and out,
and then be held together by a top plate.
Mechanical attachment
There are a few options to pursue before deciding on one (in order of interest)
1. Permanently adhere the device to a case
2. Build a case such that the device can rigidly slip in and out (on rails)
3. Assemble the device to a commercial cellphone car mount, such that the same device can
mount to any smartphone within a size range
In all cases, vital factors determined experimentally:
a. Device attachment needs to be rigid
b. Device needs to be rigid in order not to change spacing from sample to sample
c. Smartphone compatibility of plug and play is desired
Software Interface
There are a couple possibilities that still need to be investigated. The first is using a webapp where the
photo is uploaded through the smartphone’s browser to a site where the diffracted system is measured
against a calibration. The second option is to build an app for android and iOS to calculate and calibrate
the whole solution. The third option, is to mix said options together by building an app to assist with the
capturing and uploaded process to the webapp.
The following site was found and will be attempted to be used to upload captured samples and receive
computed results. http://spectralworkbench.org/
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The basic process for using the site is as follows: A spectral image is taken of a known source, such as a
specified LED, arc lamp, or CFL source, and then is uploaded to the site through the upload GUI. A
calibration is then created by the software matching up peak bands. Next, a sample is taken, and
uploaded. The sample is analyzed and the results are returned, relative to the calibration.
Test Plan / Validation
The test plan consists of multiple parts:
1. Test the proof of concept (POC)
Testing the POC will involve a stable setup where the optical design is validated. A CFL bulb will be
provided as the calibration, and d-line doublet will be used as the test subject. After a spectrum of
the CFL is produced, its peaks will be identified manually. Calibration of the optics and alignment will
be done manually (or with some aid from computational means). This will establish a baseline for
the doublet test subject. The input light will be replaced and a spectrum will be produced and
analyzed with the CFL reference.
If the doublet is resolvable after 5 iterations, and the accuracy is to the specification in the PRD, then
this concludes the first phase of validating.
2. Test the prototype
Similar to above, the prototype will be tested with the d-line doublet. The prototype will be subject
to the next test criteria:
a. drop test
A drop from 2 ft above an optical table
b. calibration routine
The device will be calibrated with a known spectrum
c. shake test
After the device is attached to the smartphone, (and calibrated) some light shaking will be
applied. The doublet needs to be able to be resolved again without recalibrating
d. switch to a different cellphone model
The smartphone will be replaced with another cellphone model, and the above repeated
(excluding the drop test).
3. Test the manufactured product
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The final product also needs to be tested. A similar test will be performed as with the prototype, but
on a random distribution of samples from the manufactured products. Depending on the advice
from the manufacturer, and further research, an adequate sample size will need to be selected to
have a 99% reliability over all the products. There should be no Dead Upon Opening (DUO) products.
Risk Assessment
The largest amount of risk is optical alignment. The product might work under certain highly controlled
circumstances, but then fail to meet the resolution and accuracy specifications. With this in mind, the
product will be constructed so that it is rigid, and its mounting is rigid. Calibration will be at minimum
easy to do. Ideally, the system will be able to calibrate itself, taking small random adjustments into
consideration when matching up the sample to the calibration.
Auto calibration might be achieved through a reticle, which the software can measure the deviation
from the known reticle position in the calibration routine. This may provide (less than calibration
accuracy) but still help in mitigating the error from misalignment.
The second largest risk is creating a 3D printed product where the optical components can be slotted in,
and where the alignment, and spacing is correct.
The next largest risk is profile size. Ideally this device will be small enough to clip onto the cellphone and
be easy enough to swap in and out to carry.
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