The curled metal fixtures set to go up on a handful of Michigan Avenue light poles later this summer may look like delicate pieces of sculpture, but researchers say they’ll provide a big step forward in the way Chicago understands itself by observing the city’s people and surroundings. The smooth, perforated sheaths of metal are decorative, but their job is to protect and conceal a system of data-collection sensors that will measure air quality, light intensity, sound volume, heat, precipitation and wind. The sensors will also count people by measuring wireless signals on mobile devices. Some experts caution that efforts like the one launching here to collect data from people and their surroundings pose concerns of a Big Brother intrusion into personal privacy. In particular, sensors collecting cellphone data make privacy proponents nervous.