Is This Possible?

Try goggle sometime: http://www.bing.com/search?q=rfid+temperature+sensor&src=IE-TopResult&FORM=IETR02&conversationid=

No reason why not. A similar system is installed in new cars, only the sensor reads tire pressure instead of temperature.

I thought the pressure sensors used some form of micro-power capture from the spinning of the tires.

Regardless of how tire pressure sensors work it is entirely possible for an RF power source to power some sensor.

OK, maybe a better example is an RFID tag which would incorporate a temperature sensor. The tag circuitry is powered from RF energy transmitted by the reader.

https://en.wikipedia.org/wiki/Radio-frequency_identification

Why not, have a friend that has a medical device to reduce pain in his back. It is charged with an external device. The device in his back sends statis of the device back to the external device for the doctor to reveiw. Also send info on the batterys state of charge while he is charging it.

There is key point everybody (including myself) is implying but not stating. The amount of power needed to read temperature and resend that information back to a NFC interface is so small that the interface can provide all of the needed power and still be inside the NFC standard power levels. One can also be clever and harvest wasted power from alternate sources, too.

Do you live under a rock?

http://rfmicron.com/

http://www.rfwirelesssensors.com/

1 - Yes

2 - pretty small, probably starts with something about the length of a credit card

There are a number of sensors now that are about the size of a grain of sand. I think temperature sensors were first to reach this size. Come to think of it, I used thermistors not much larger than that well over 50 years ago.

There are cameras that can transmit from inside the human body which are capsules relatively easily swallowed. That, of course, must include the camera, circuitry to decode the signals from the camera and transmit the information, as well as a power source. So your credit card size is way too big...

Yes, but who can afford these mini, or micro sensors?

Passive RFID chips are as low as 7¢ each, and active ones start at $25, according to one article I saw. Mass production can lower these costs. "They" are finding ways to 3D print circuits and components, so I expect the active costs to drop dramatically in the next few years.

There are a lot of devices coming out that use the computing and transmit/recieve capabilities of smartphones to reduce the cost of the devices, like my "FLIR One" IR camera, that reduced the price from several thousand dollars to $250.

After thinking a bit more about it, one limiting factor on size would be the coil or antenna used to absorb the activating energy from the reader, but a postage stamp size should easily do that. I can also easily imagine a device that would use an LED or laser to send the activating energy to a light receptor of some kind, and such a receptor could probably be a few mm across, making a postage stamp seem large.

It all sounds appealing. Does it make an experimenter's job easier? I suspect it might as long as he is a programming genius, or do these devices set themselves up automatically, like a new piece of hardware acquiring a driver?

Any device to be used with a smartphone will indeed require someone to program an "app", but in many cases that programming will be done by someone associated with the construction of the device. The device itself will also require programming to respond appropriately to the phone.

All of the programming I did was before the common availability of smartphones, and I was never an expert in anything beyond BASIC, but there are so many open source routines available now that I don't think it would require a "programming genius" to create one of these devices.

I suspect that the genius required is in the miniaturization...

I was thinking along the lines of my current project, instead of using wired sensors to Arduino board. I expect the difficulty might be in keeping all probes in range for RFID communication with the board.

Wow!

I just copied "NFC Technology" directly from your post and pasted it into the Google search box and Voilla!, up comes a quite in-depth Wiki article about just that!

Just think! You could have had your question answered without having to wait for any replies from us.

Rail lines have been doing this for 40 years. Engine radiates RF down to the ground. Module on the ground rectifies the RF and powers up. Module transmits info to engine. Engine records info.

The size will likely be entirely dependent on the energy requirements and the frequency of energy transfer [antenna required].