It is common to design custom arrangements of sources and detectors for fNIRS experiments. This is to ensure that the target brain regions are adequately sampled for the given experiment, constrained by the number of sources and detectors provided by the given fNIRS instrument. AtlasViewer provides a convenient tool for designing a custom array of sources and detectors and evaluating that the target brain regions are being sampled by those sources and detectors. Further, the file generated by AtlasViewer can then be used to generate a ninjaCap STL file for a given head circumference that can then be 3D printed, providing grommets in the designed locations for attaching fNIRS sources and detectors. Further, grommets can be placed at designed locations for attaching EEG electrodes.

Grommets presently exist for placing sources and detectors for the ninjaNIRS21 system and the NIRSport2 system from NIRx. A grommet exists the actiCAP slim/snap electrodes used with, for instance, the BrainVision LiveAmp EEG system. Landmark “grommets” can also be placed that are convenient, for instance, for marking ‘Cz’ or other 10-20 locations on the cap. Custom grommets can be added following the instructions given here.

The instructions for how to design your array of sources and detectors in AtlasViewer is here. The interface is a convenient 3D interface that allows you to point and click positions on the scalp to create new markers and then assign them as sources, detectors, or auxiliary locations that can be used for other purposes such as electrodes, accelerometers or landmark positions. The distances between markers can be specified. Individual markers can be anchored at specific locations allowing the other markers to “spring relax” on the scalp to obtain the specified distances between the markers.

Generating your STL file

The tool for converting your file into an STL file is provided through the BIDS-fNIRS Cloud Server. You must log in to this server with your login and password for the server. You will see the tool for generating your ninjaCap on the left hand side panel once you log in. Note that while this server is hosted under, your login and password is unique for

If you would like the non-profit Neuluce to print your cap for you, please access the order form here. Note that Neuluce is the non-profit organization which pays the bills for the openfnirs server and host.

Please visit the Hardware Forum to discuss ninjaCap and post any questions you may have.


You can click most images in the first and second column to download the and STL files respectively.

You also need chinstrap to hold the cap on the head firmly. Please download chinstrap stl file here.

These are the files for our first whole head probe.

Whole head high density design

These are the files for our second whole head probe designed in 2023. This version also has a neck strap along with a chinstrap.

Latest whole head high density design

These files are for our frontal high density probe.

Frontal HD probe design

These files are for our frontal sparse density probe.

Frontal SD probe design