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Palomar Medical Technologies was developing a handheld mass-market laser hair removal system and required a reliable way to control laser exposure time as the device moved over a user’s skin. Various speed-sensing technologies were tested and rejected. The most promising technique used two capacitance-based fingerprint identification chips to take a rapid succession of images that were processed by a Digital Signal Processor (DSP) to detect speed of movement.
The system had to fit in a tight handpiece together with the Fingerprint ID Sensors and optics. The Fingerprint ID sensors were mounted on flexible circuit boards to ensure good signal integrity and minimize the packaged size. All handpiece electronics had to be squeezed on a single 1.2” x 1.6” board. The power supply subsystem was initially mounted separately, in a base station, but was later incorporated into the handpiece. The system had to take minimal power, as there was no airflow and no space for adding a fan. The correlation-based speed detection software required significant processing capability.