Project data
Authors Chris Shaw
Ajseidl
Kemyszka
Export to Open Know How Manifest
Page data
Part of MY3701
Type Project
Keywords 3-D printing, Piezoresistive, Helmets, Impact Sensors
SDGs Sustainable Development Goals SDG09 Industry innovation and infrastructure
Published by Chris Shaw
Ajseidl
Kemyszka
Pedro Kracht
Published 2013
Affiliations MTU
Page views 1,861
Location data
Location Michigan, USA

To create a full model of a 3-D printable piezoresistive sensor in order to detect the amount of impact that an athlete receives during a collision to monitor the possibility of a concussion.

With professional sporting leagues such as the National Football League (NFL) and National Hockey League (NHL) adding an emphasis on player safety, especially with head injuries, it is important to have a quick and reliable way to determine the amount of force a helmet receives during a collision. This information can help determine if the player sustained a concussion and if they should be taken out of the game to protect themselves. The data that is gathered throughout games can also be accumulated and help to try and make rules that help determine if new rules are necessary to protect players in the future.

The typical acceleration that is required to sustain a concussion is about 95 g-forces.[1] Which is substantially lower than the average football player receives during a hit, with a value of 103 g-forces. Luckily most of the force of the hit can be spread around most of the body, but when the large majority of the force is directed at the head, it is necessary to make sure the players who got hit have experienced a safe amount of force to head. This is why a sensor to monitor the impact would be a great idea to improve the health and safety of the players.

Literature and Product Research

The use of Polyvinylidene Fluoride (PVDF) as a material for pressure sensitive piezoresistive equipment has become a popular choice in the bio-medical research industry. A popular application found for Polyvinylidene Fluoride pressure sensitive films is to create a pressure sensitive 'Smart Catheter'[2]

Another use of pressure sensitive PVDF sensors were found for the use of heartbeat monitor,[3] which is similar to the semiconductor layout we will use for our own project.

Polyvinylidene Fluoride (or PVDF) Piezoresistive Sensors are a popular choice in the field of polymer based Piezoelectric semiconductors. They are used and other applications in which the detection of impacts beyond a specific threshold may be detrimental to the integrity of the product. Although PVDF film sensors were found in many biomedical research applications (heart monitors, catheters, etc.) There were no found markets in which they are currently being sold to the public. However, other pressure sensitive adhesive strips using silicon as a base material were found for retail over the internet, with the most common being a basic deformation-sensitive adhesive strip. The price found for a basic version of this product was $7.50,[4] with everything included, except the circuitry to detect the current variations caused from impact or deformation. With this price, it seems very viable to implement several of these sensors within helmets, especially with the high cost lawsuits being passed over head to head collisions. It is believed that the polymer version of these sensors will have the possibility to be competitive with the Si-based sensor price range, as listed in the B.O.M. in the Materials section of the page. Design Due to the Piezoelectric nature of PVDF once polarized, the design of a pressure sensor using this material is fairly simple, with it's step by step design process outlined in the "3-D Printing" section below The creation of a circuit to allow this piezo-resistive material to successfully be monitored and recorded can be seen below; (This excludes the computer software capable of compiling the data for analysis) Figure 2: Elementary circuit design for PVDF pressure sensor The circuit uses one resistor, one voltage amplifier, one capacitor, all linked around a PVFD film and excited with a power source of two 3 Volt batteries. The circuitry concept was inspired by the layout used for the heartbeat monitor source, and was re created using Dia. • From the below dimensions used in OpenSCAD, the capacitance of the 25 micron thick PVDF layer can be determined using the following equation: $\displaystyle{ C=*epsilon*(A/t) }$ [5] with epsilon being permittivity: relative(12 for PVDF)*space($\displaystyle{ 8.854*10^-12 F/m }$) A = active area of film electrodes = 32mm x 13mm t = film thickness = 25um with a resulting PVDF film capacitance of: $\displaystyle{ C=((12)*(8.854*10^-12))*((32*10^-3)m * (13*10^-3)m/(25*10^-6)m) = 1.768 nF }$ A 3-D model of the project was created on OpenSCAD to give a visual representation of the final product. Below is the OpenSCAD code (in mm) and STL Link: cube([23,19,1]); translate([27,0,0])cube([23,19,1]); color([0,0,1])translate([9,3,1]) cube([32,13,.025]); color([0,1,1])translate([0,0,1.025]) cube([23,19,3]); color([0,1,1])translate([27,0,1.025]) cube([23,19,3]); color([0,1,1])translate([23,0,1.025]) cube([4,2,0.5]); color([0,1,1])translate([23,17,1.025]) cube([4,2,0.5]); Materials There are four main materials that will be used to create the sensor, they are: Polyvinylidene fluoride (PVDF), Mylar (which is the brand name of polyethylene terephthalate), Polydimethylsiloxane (PDMS) and silver paste. PVDF is the material that is used as the semiconductor and is highly piezoelectric[6] making it a very desirable material to be used for pressure sensor applications. It has a melting temperature of 160oC[7] PVDF is compared below to some other commonly used 3D printing inks. These inks all use the extrusion deposition technique, which is the most common technique used for reprap 3D printers. The material is wound around a coil and then heated up and melts. It is then sent through a nozzle and the material is then deposited layer by layer in both the vertical and horizontal directions creating the part that is desired. Silver paste was chosen as the metal electrode because of its capabilities to stand up to high voltages and continue to work with voltage spikes.[8] The capabilities to work through voltage spikes will be important since there will be numerous incidents within a single game where the player will experience some force in the head. Material Melting Temperature (oC) Polyvinylidene Flouride 160 Polycarbonate (PC)[9] 155 Polylactic Acid [10] 150-160 Polyethylene terephthalate (PET)[11] 250-260 The complete list of materials that are required in order to make the sensor is shown below, along with links to the MSDS pages for each of the materials and bulk material pricing. Material Health Fire Reactivity Personal Protection Cost PVDF MSDS[12] 0 1 0 A$208.00per 100g[13]
Mylar MSDS[14] 1 1 0 $1.69 per 100g[15] PDMS MSDS[16] 2 1 0 J$48.4 per 100mL[17]
Silver Paste MSDS[18] 2 1 0 $172.00 per 25g[19] Cost Material Cost per part ($)
Polyvinylidene Flouride $0.39 Mylar$0.04
PDMS $1.22 Silver Paste$3.21

Conclusion

Although all of the aspects for creating an accurate PVDF, Piezo-resistive, impact monitoring sensor with circuitry for helmets and other impact applications have not been fully explored during the duration of this research, I feel it is a very viable, cost effective, 3-D printable concept which could be created and applied to impact sports for concussion monitoring, and other impact sensitive applications in the future.

Resources

1. http://www.sciencedaily.com/releases/2010/06/100624092526.htm
2. Tushar Sharmaa, Sang-Soo Jea, Brijesh Gillb, John X.J. Zhanga, (2012), Patterning piezoelectric thin film PVDF–TrFE based pressure sensor for catheter application, http://www.sciencedirect.com/science/article/pii/S0924424711005012
3. Yi-Yuan Chiua, 1, Wan-Ying Linb, 1, Hsin-Yao Wangb, Song-Bin Huanga, Min-Hsien Wua, (2013), Development of a piezoelectric polyvinylidene fluoride (PVDF) polymer-based sensor patch for simultaneous heartbeat and respiration monitoring, http://www.sciencedirect.com/science/article/pii/S0924424712006310
5. Measurement Specialties, Inc. (1999), Piezo Film Sensors Technical Manual, http://web.archive.org/web/20140611234057/http://resenv.media.mit.edu/classes/MAS836/Readings/MSI-techman.pdf source
6. "PVDF Properties." http://www.polymerprocessing.com/polymers/PVDF.html
7. "Piezo Film Sensors Technical Manual" pg 13 http://web.archive.org/web/20140611234057/http://resenv.media.mit.edu/classes/MAS836/Readings/MSI-techman.pdf
8. "Polycarbonate." http://en.wikipedia.org/wiki/Polycarbonate
9. "Polyactic Acid" http://en.wikipedia.org/wiki/Polylactic_acid
10. "Polyethylene terephthalate" http://en.wikipedia.org/wiki/Polyethylene_terephthalate
11. "PVDF MSDS." dotmar.com.au. N.p., n.d. Web. 12 Oct. 2013. <http://web.archive.org/web/20160311173948/http://www.dotmar.com.au/images/stories/pdfs/symalit_pvdf.pdf>.
12. "Polyvinylidenefluoride - Granule ." www.goodfellow.com. N.p., n.d. Web. 12 Oct. 2013. <http://www.goodfellow.com/catalogue/GFCat4I.php?ewd_token=xS9p6K0dbfBNkirTPct21RMqoC2Tg0&n=Ez90cHNg4TJ3PIQNCnXKlGI7kUSCOG>.
13. "PVDF MSDS." dupont.com N.p., n.d. Web. 12 Oct. 2013. <http://msds.dupont.com/msds/pdfs/EN/PEN_09004a2f8002e2ee.pdf>.
14. www.amazon.com. N.p., n.d. Web. 12 Oct. 2013. <http://www.amazon.com/CAP-mil-Mylar-Reflective-Film/dp/B0001WW40Q>.
15. "PDMS MSDS." www.sciencelab.com N.p., n.d. Web. 12 Oct. 2013. <http://web.archive.org/web/20181206204848/http://www.sciencelab.com:80/msds.php?msdsId=9924928>.
16. www.amapolymer.com. N.p., n.d. Web. 12 Oct. 2013. <http://web.archive.org/web/20120704093433/http://www.ampolymer.com:80/Standards/PDS.html>.
17. "Silver Paste MSDS." www.sciencelab.com N.p., n.d. Web. 13 Oct. 2013. <http://www.sigmaaldrich.com/MSDS/MSDS/DisplayMSDSPage.do?country=US&language=en&productNumber=735825&brand=ALDRICH&PageToGoToURL=http%3A%2F%2Fwww.sigmaaldrich.com%2Fcatalog%2Fproduct%2Faldrich%2F735825%3Flang%3Den>.
18. www.sigmaaldrich.com. N.p., n.d. Web. 13 Oct. 2013. <http://web.archive.org/web/20210122034836/https://www.sigmaaldrich.com/catalog/product/aldrich/735825?lang=en&region=US>.
19. BYU PDMS N.p., n.d. Web. 16 Oct. 2013. <http://www.photonics.byu.edu/PDMS.phtml>.
20. Micron Printing Web. 16 Oct. 2013. <http://forums.reprap.org/read.php?279,186168,186168>.
21. Review of In-situ Fabrication Methods of Piezoelectric Wafer Active Sensor for Sensing and Actuation Applications Web. 16 Oct. 2013. <http://www.me.sc.edu/research/lamss/pdf/conferences/c111_spie2005_5765-04.pdf>.
22. RecycleBot http://reprap.org/wiki/Recyclebot
23. Characterization, Performance and Optimization of PVDF as a Piezoelectric Film for Advanced Space Mirror Concepts http://prod.sandia.gov/techlib/access-control.cgi/2005/056846.pdf
24. Yi-Yuan Chiua, 1, Wan-Ying Linb, 1, Hsin-Yao Wangb, Song-Bin Huanga, Min-Hsien Wua, (2013), Development of a piezoelectric polyvinylidene fluoride (PVDF) polymer-based sensor patch for simultaneous heartbeat and respiration monitoring, http://www.sciencedirect.com/science/article/pii/S0924424712006310
25. http://en.wikipedia.org/wiki/Work_function

Contact Info

Chris Shaw - Email: cjshaw@mtu.edu

Alex Seidl - Email: ajseidl@mtu.edu

Kyle Myszka - Email: kemyszka@mtu.edu