Inexpensive chip-based device may transform spectrometry

http://news.mit.edu/2018/inexpensive-chip-device-spectrometry-1023

by charlysl • 8 years ago

83 30 8 years ago

news.mit.edu

rfinney• 8 years ago

Open access Nature Communications paper : https://www.nature.com/articles/s41467-018-06773-2 High-performance and scalable on-chip digital Fourier transform spectroscopy

Here we demonstrate a transformative on-chip digital Fourier transform spectrometer that acquires high-resolution spectra via time-domain modulation of a reconfigurable Mach-Zehnder interferometer. The device, fabricated and packaged using industry-standard silicon photonics technology, claims the multiplex advantage to dramatically boost the signal-to-noise ratio and unprecedented scalability capable of addressing exponentially increasing numbers of spectral channels.

starshadowx22• 8 years ago

FTIR devices seem to cost around 50000 right now, would this be something that would lower that cost?

FTIRs are definitely in demand with harm reduction groups both in cities and for drug testing at music festivals. If we could get these at lower costs it would honestly save lives.

mediaman• 8 years ago

How is FTIR used for drug testing? Is it used to test for contamination based on the spectrum profile?

nikmobi• 8 years ago

Not an expert, but if you can test for contamination why wouldn't you be able to test for the drugs themselves?

Raman spectroscopy[1] is one that I know of that is frequently used to determine chemical composition. Spectroscopy in general still amazes me.

[1] https://en.wikipedia.org/wiki/Raman_spectroscopy#Application...

dejv4• 8 years ago

Peaks of each chemical is unique so you can scan database of known chemicals and compare.

You can even measure the amounts of various chemicals in solution, but that would require complex calibration. In this case you are basically writing ML system that is trying to fit various peak heights/areas to amount of compound.

starshadowx22• 8 years ago

This doesn't really explain how but it does talk about the uses of an FTIR in a drug checking, harm reduction situation.

https://globalnews.ca/news/4540315/new-drug-checking-machine...

somebodynew• 8 years ago

A very simple refractive IR spectrometer is possible for under $1000 if you can live with 2-10μm range. I don't have a full write up yet but the basic design is an MLX90614 thermopile scanning infrared light generated by nichrome wire, focused with a zinc selenide CO2 laser lens (the ones without an AR coating are better but harder to find), and separated by a silicon prism which is essentially just a chunk of a broken silicon boule. It's very difficult to find transparent materials in this wavelength range, especially when you're limited to cheap goods mass-produced for some other application. Signal noise and speed will be much worse than a modern FTIR but it's usable when calibrated.

dejv4• 8 years ago

It might work for qualitative measurement (what is the solution you are measuring), but this kind of instrument will not be performant enough to do qualitative analysis. Once you want to measure amounts the FTIR is probably the only way to go, especially with more complex solutions.

dejv4• 8 years ago

There is Neospectra [1] company that produces FTIR-on-chip modules. Performance is not that great compared to research grade FTIR, but the price is a lot less.

[1] https://www.neospectra.com/

analog313• 8 years ago

I help design spectrometers. Every once in a while, a new idea for a mini spectrometer floats across my desk. Many of the ideas are based on silicon IC fabrication technologies or micromachining.

The drawback is the same in every case: The sheer amount of light that can pass through the optics of a spectrometer depends on its size. This in turn affects what signal-to-noise ratio can be realized.

These devices are certainly interesting, and performance is relative to requirements, so a novel application could make use of whatever sensitivity is made available by a particular device. But a tiny spectrometer isn't likely to be a drop-in replacement for a big one unless the big one is overkill for its application.

Still, I read these articles with interest, because my "size matters" rule is somewhat ad hoc, and there might be a factor that I'm overlooking.

DenisM• 8 years ago

Maybe you can help me with this... I want to measure the quality of light in my home and office. CRI seems to be the right metric, and it seems that the cheapest option is a $2000 (Sekonic) hand-held device. Are there cheaper options? I don't need much precision, just enough info to understand that these lightbulbs over here are much better than those other lightbulbs over there.

I am puzzled as to why it has to be so expensive. I would think one can put a prism, project the light over the surface of a black-and-white CCD sensor and measure the light intensity along the length, giving a reasonably good idea of how much energy is deposited into each wavelength range. I feel like one of these can be made for $20 in parts?

danielvf3• 8 years ago

You can get a plastic DSLR camera body cap for less than 50 cents each (ebay from China). This cap goes where the lens would attach the camera when you don't have a lens on. Sometimes I cut a hole in the center of a cap and make really hacky camera "lenses" for fun. You could put a prism on the outside of a cap.

You would then need to calibrate your new spectra-cam on something with a known radiation (usually just find a good blackbody radiator.) You can't just convert to black and white without calibration because the RGB sensors on the camera are going to have their own sensitivity to different wavelengths. This would be an awesome project!

I write firmware for high end professional LED lights, and have a $3K spectrometer on my desk. Here are things I've learned:

1. CRI is simply a bad formula to judge light quality overall and gives almost meaningless results at lower color temperature levels.

2. There are lots of fantastic python modules for working with spectrograph and light data.

3. One awful thing cheap LED lights do is blink slowly to control their voltage. This is at least as bad a poor CRI for aggravating your eyes. (Sometimes you can see this just by using slow motion video on your phone)

analog313• 8 years ago

Here are some brief thoughts. It turns out that monochrome CCD's can be a bit pricey because they are sold in lower volumes than color chips. Where you might find one is in the video security market, since they are often used with illumination from infrared LED's to do covert monitoring.

On the other hand, you could achieve pretty decent "monochrome" behavior by just summing the three color channels of a RGB camera, at least in the visible range of wavelengths. With that issue settled, you could figure out a way to produce a rainbow spectrum by hook or crook, such as a cheap prism from Surplus Shed (if they have one in stock -- they are a great source of bargain optics) and some lenses. For intensity calibration, a plain tungsten lamp would suffice for home experimentation. They operate very close to their rated color temperature. For wavelength calibration, one idea is to see if there are useful visible lines in the mercury emission spectrum (don't remember) which are emitted by a regular fluorescent lamp. Also, colored LED's at room temperature run pretty close to their rated peak wavelengths.

milleramp2• 8 years ago

This spectrometer is inexpensive: https://publiclab.org/wiki/desktop-spectrometry-kit-3-0 The problem is calibration, you would need to calibrate with sources like lasers or fluorescent light with known spectral peaks. Then you could use the spectrum to calculate CRI. You are just calculating cri (which has its own issues), so even with a crude device some spectral error is ok.

milleramp2• 8 years ago

There is also this: https://nanolambda.myshopify.com/ Not sure how accurate the calibration is but a nice little device.

darkmighty• 8 years ago

This works remarkably well:

http://sci-toys.com/scitoys/scitoys/light/cd_spectroscope/sp...

https://lavinia.as.arizona.edu/~mhammer/outreach/cdSpectrome...

(diffraction spectrometer from used CDs!), very easy to make, and it costs ~$0.

It has enough resolution to distinguish individual lines of fluorescent lamps (by using a narrow aperture). Highly recommended (very nice as an educational tool also, to impress folk with the hidden spectra of light around us ;) ).

softgrow• 8 years ago

If you are wanting an inexpensive spectrometer, then Public Labs has instructions on how to build one using an old DVD as a diffraction grating https://publiclab.org/wiki/spectrometry

I got a kit as a present and really enjoyed it.

dejv4• 8 years ago

It depends on what you want this spectrometer to do. Public Lab spectrometer is interesting and cheap, but the performance is very very limited.

If you need something better you can search eBay for used (scanning) monochromators. Next step is to check Ocean Optics or Hamamatsu catalogs: they have good line of products, but those are in 1000 USD+ range.

keithnz• 8 years ago

This is cool, a while back when I used to do fruit sorting machines, we used a spectrometer for working out the sugar content of fruit.

Nothing quite like setting up the machine to siphon off the biggest sweetest peach you can find at one of the largest peach farms in the world. best. peach. ever. :)

Inexpensive chip-based device may transform spectrometry

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