They have those with radiant heat that, for the life of me, I cannot remember the name.
I've been playing around with an idea the past few years I'd like to try with a small group of chicks like that...been thinking about making a loosely stuffed fleece "hen" with a wire rectangular or oval-shaped structuring that could be bent to simulate a mother hen huddled over chicks. The fleece would/could radiate their own body warmth back to them and they could come and go under it as they please. It would have folds and lumps that hang down and loosely brush the ground to provide pockets where chicks could huddle together. The whole thing would be removable from the wire and be washable.
Still wanna try it to see if it would work.....
I'd love to see it if you ever try. Sounds intriguing.