Capacitive switch technology deployed in medical ultrasound

Roughly the footprint of a smart phone, Vscan provides doctors with an instant, non-invasive look inside the body.  This technology lets doctors visualise inside the patient with ease, with excellent imaging with abdominal, cardiac and obstetric presets.  With each image captured, a visual representation is generated; this can help doctors identify issues and better triage patients to help avoid sometimes unnecessary delays and costly diagnostic testing.

Portability based on small size and low weight, ease of use and aesthetics were key design criteria for GE Healthcare when developing Vscan. A navigation wheel UI was therefore integrated into the design to allow the device to be used in one hand and managed with a thumb.

When Molex first visited GE Healthcare to discuss the project, the development team had already found an initial solution for the UI.  This solution was based on a rigid PCB (Printed Circuit Board) with metal spring fingers directing the capacitive signals inside the device.  During this early development phase an inherent weakness of this design was discovered; the open structure would lead to difficulty in protecting the unit from EMI/EMC issues.

Molex proposed a one-piece solution utilising a Flexible Printed Circuit (FPC), complete with the capacitive IC and all associated components, combined with the graphic overlay, metal domes and silicone rubber actuators.  This solution allowed the UI to be mounted externally, with the tail of the FPC to be inserted into a small opening in the top housing.  This design not only simplified assembly – reducing it to merely peeling off the backing paper from the adhesive mounting and placing the UI in the correct location on the front housing – but left only a small opening in the housing making it easier to deal with EMI/EMC.

While fully flexible in choice of capacitive controllers, for this solution Molex used Cypress Semiconductor’s CapSense PSoC chip architecture, which replaces dozens of mechanical switches and controls with an elegant touch-sensitive interface.  It uses an electrical field to detect the presence of a human finger or other conducting object as switch activation.  When a conductive object enters the field, the switch recognises a change in the capacitance indicating an actuation.

This technology is resistant to contaminants, which makes this user interface more robust to wear and tear and reliable than its mechanical counterparts.  In addition, Molex’s ability to seal the capacitive switch design was an excellent solution for resistance to the sterilising solutions used in the medical environment.