Feature: Medical


Figure 1: CBT device design. (a) Concept of a wearable thermal device applied to the forehead to estimate human core body temperature; (b) The CBT patch; (c) Human tissue side of the flexible CBT patch; (d) Side view


Rigid-flex circuit design for wearable temperature sensor applications


• Design a reliable rigid-flex printed circuit board for remote patient monitoring applications;


By Marc Smith, Principal Engineer, Analog Devices


H


ere we will discuss generic design guidelines for a core body temperature (CBT) sensor measurement device, which can also be applied to multiple temperature sensing applications requiring high accuracy (± 0.1°C). Te implementation was a joint development between


Texas A&M University and Analog Devices (ADI). Tese design considerations will help the designer to:


• Recognise the design challenges, trade-offs and mitigation techniques associated with the development of an accurate CBT sensing device;


20 March 2024 www.electronicsworld.co.uk


• Apply design guidelines for heat flow and mechanical structure considerations and for rigid-flex PCB manufacturing.


CBT device overview Te CBT patch was developed as a flexible wearable thermal sensing device that accurately estimates human core body temperature (Figure 1a); see its main components in Figure 1b. Te device comprises four temperature sensors (MAX30208)


separated by materials with different thermal conductivities, to accurately quantify CBT. Te temperature sensors are powered by 1.8V, and use little power. One sensor is located at the centre of the PCB, one at the middle, one at the edge, and a fourth one sits on the tip of a circuit finger, which bends toward the centre of the PCB – see Figure 1c. Te CBT patch can monitor patients in pre-, post- or operative surgery settings, where typical ambient temperature is between


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