The Vector-corrected Network Analyser (VNA) has been an indispensable tool for many decades in the field of RF and microwave engineering where the availability of calibrated and traceable results is taken for granted. However, calibrated and traceable measurements are not so easily available in the acoustic domain. In an effort to allow such measurements, a dual-port acoustic vector network analyser (AVNA) has been designed and built. The calibration of this test and measurement system hinges on the repeatability of the uncalibrated system and its acoustic waveguide joints. The first generation of acoustic waveguide joints have been 3D printed with a high precision printer and designed to include alignment pins, O-rings, and a reinforcing 'clip' system to allow for a consistent bolt torque without damaging the plastic waveguide. We show that the resulting variation in measurements between cycles of disassembly and reassembly is acceptably small and will allow for calibration of the system. Three-dimensional printed titanium joints show increased rigidity and ease of use but similar repeatability.

BACKGROUND: Manual wheelchair users are at a high risk of repetitive strain injuries, carpal tunnel syndrome, and rotator cuff tears due to propelling their wheelchair for mobility. Rolling resistance (RR) is one of the key forces that leads to increased propulsion forces and risk of injuries. OBJECTIVE: To better understand the factors contributing to RR, we iteratively designed, developed, and validated a drum-based testing machine and test method. METHODS: As part of the validation of the system, we tested and compared 4 manual wheelchair wheels under a range of conditions including camber, toe in/out, tire pressure, surfaces, and speed. A treadmill was employed to simulate flat ground RR. RESULTS: A machine was effectively design, developed, and tested to measure RR. Tire type, surfaces, and toe were found to be the largest contributors to RR. Comparison of the drum-based system to flat ground revealed that an offset can be used to calculate overground RR from drum measurements. CONCLUSIONS: Ongoing work includes performing a comprehensive analysis of the degree to which each factor contributes to RR of commonly used casters and rear-wheels so that the wheelchair sector can work to reduce RR and the associated risk of repetitive strain injuries.