Regulatory Compliance News

ISED Issues Technical Guidance on Curve-Fitting Methods for Nerve Stimulation Evaluations

Innovation, Science and Economic Development Canada (ISED) released Notice 2024-DRS0004, establishing detailed technical guidelines on the application of curve-fitting techniques during nerve stimulation compliance assessments. The notice clarifies regulatory expectations for radio apparatus operating between 3 kHz and 10 MHz under section 5.3.1 of RSS-102.NS.MEAS and section 7.1.1 of SPR-002. By formalizing these analytical protocols, ISED provides test laboratories and device manufacturers with a standardized methodology to extrapolate exposure levels at touch position (0 mm) without requiring explicit pre-approval inquiries, addressing recurring reporting deficiencies observed in equipment certification filings.

The updated guidelines outline a precise four-step evaluation process for assessing magnetic (H-field) and electric (E-field) exposure, covering initial Maximum Field Strength (MFS) identification, data collection, mathematical curve-fitting, and statistical result validation. Rather than assuming the geometric center of a transmitting element or coil yields peak emissions, testing personnel must map field distributions across multiple evaluation planes to pinpoint the actual MFS coordinates. Data collection mandates a minimum of ten measurement sample points, primarily collected at distances exceeding 1.7 times the probe sensor dimensions, while maintaining perpendicular orientation to the measurement plane.

To ensure mathematical accuracy and prevent overfitting, the notice requires applicants to evaluate at least three distinct regression models—such as linear, quadratic, or higher-order polynomial functions—and select the model that yields the lowest standard error of the regression at a minimum 95% confidence level. These detailed curve-fitting analyses, along with complete descriptions of transmitting coil geometries and operational configurations, must be fully documented within radio frequency exposure compliance reports. This technical clarification supports Canada’s broader human exposure framework under RSS-102 Issue 6, ensuring robust biological safety evaluations for wireless power transfer systems and low-frequency radio devices entering the Canadian market.