Figure 4.

Closed-loop photothermal control and blood flow monitoring with a wireless patch

(A) Image of the optoelectronic patch attached to the lower back. The patch is wirelessly powered by a transmitter at a distance of 4 cm.

(B) Infrared thermal image of the activated patch during wireless powering. Dotted white circle indicates the position of the LED array.

(C) Image of the patch attached to the arm.

(D) Infrared thermal image of the activated patch on the wrist.

(E) Schematic of the closed-loop control algorithm.

(F) Skin temperature with and without closed-loop control using the setup in (A). The yellow dotted line indicates the target temperature of 36.2°C

(G) Schematic of the sensor placement along the radial artery using the setup in (C). The sensors are placed on the skin directly over the artery with spacing d_s=10 mm.

(H) Temperature as a function of time from each sensor when the LED array is activated for 120 s.