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Michael Marchev
05

PublishedJune 2023 – August 2023

Northeastern University Center for STEM Education logo

To evaluate the population variation in head-to-helmet contact forces in helmet users.

Role
Research Assistant & Co-author
Organization
Northeastern University Center for STEM Education / Young Scholars’ Program
Timeline
June 2023 – August 2023
Tools
Force sensitive resistors, Arduino Mega, Digital force gauge, Caliper stand, Custom chinstrap tension gauges
Team
University research group, Young Scholars’ Program
Project type
Research · Experimental Mechanics · Biomedical Engineering · Finite Element Analysis
Measurement system diagram: a helmet interior with its seven instrumented pads labelled, a detail of the chinstrap tension gauges, and the chinstrap system laid flat.
05.0 — MEASUREMENT SYSTEMMeasurement system diagram. A: Helmet with force sensitive resistor notation marked in red, other key features marked in blue. B: Detail of the chinstrap tension gauges. C: Detail of the helmet chinstrap system, aligned to correspond to the helmet shown in A

Specifications

Publication
Annals of Biomedical Engineering 53, 946–955 (2025)
Article
Measurement and Assessment of Head-to-Helmet Contact Forces
Helmets
Four sizes of Kevlar composite helmet, seven interior pads each
Sensors
A force sensitive resistor on each pad; custom chinstrap tension gauges
Volunteers
89 (25 female, 64 male)
My contribution
Methodology, validation, investigation

Focus areas

  • Methodology
  • Validation
  • Investigation
  • Research
  • Experimental Design
  • Medical / Human-Centered Design
01

Measurement system

A force sensitive resistor (FSR) (Adafruit Industries, LLC. New York, NY) was installed on each pad. To mount each FSR, a flexible rim was created around the perimeter of the sensor using electrical tape. The rim was sewn onto the cloth exterior of the padding, which allowed the sensors to flex and conform to the shape of the pad. Measurements were recorded using an Arduino Mega microcontroller.

To measure the tension in the chinstrap, a custom mechanical force gauge was developed which replaced the original adjustment buckles in the chinstrap.

Three foam helmet pads — circular, trapezoidal and oval — each with a square force sensitive resistor sewn on with electrical tape.
05.1 — INSTRUMENTED PADSOregon Aero foam liner pads instrumented with contact pressure sensors. Left to right: Circular top pad, Trapezoidal front/back pad, oval side pad
02

Calibration

Because flexure in the FSR was observed to change the measured force value, the pressure measurement on the surface of the pad was calibrated with the FSR and pad installed in the helmet.

A digital force gauge (Imada, Inc., Northbrook, IL) was used to measure the force applied to the FSR. A curved force applicator was fitted to the force gauge to emulate the curvature of the head. The force gauge was mounted on a caliper stand (Mitutoyo America Corp., Holyoke, MA) which was used to apply variable compression to the padding. A cubic spline was found to have the lowest RMS error when fitting the data so was used to relate the FSR analog value to sensor force.

CAD of a disc-shaped force applicator with a curved underside and a keyhole slot, in isometric and side views.
05.2 — FORCE APPLICATORForce applicator used to emulate contact with the curved surface of the head
Scatter plot of applied force against sensor reading, with a cubic spline fit rising steeply above a reading of about 700.
05.3 — CALIBRATION CURVECalibration curve for helmet FSRs
03

Results

The majority of forces measured on any individual pad were between 0 and 5 N. However, some users exhibited pressure points with forces as high as 30 N. The contact force distribution is non-uniform across the interior of the helmet, with the largest force concentrated at the front.

Box plots of contact force by pad position for female and male volunteers, in three wearing configurations; the front pad carries the largest forces.
05.4 — CONTACT FORCE BY PADContact force distributions for each pad for A no-chinstrap B user-comfort and C fixed-tension conditions. F=Front, FL=Front Left, BL=Back Left, B=Back, BR=Back Right, FR=Front Right, T=Top
04

Publication

Jennings, T., Tillman, A., Mukasa, D., Marchev, M., Müftü, S., Amini, R. Measurement and Assessment of Head-to-Helmet Contact Forces. Ann Biomed Eng 53, 946–955 (2025). https://doi.org/10.1007/s10439-025-03677-3

Author contributions: Michael Marchev contributed toward methodology, validation, and investigation.

Text and figures on this page are from the article and its supplementary material, published open access under a Creative Commons Attribution 4.0 International License (https://creativecommons.org/licenses/by/4.0/). Figures were resized.

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