Likely working like a linear loaded quarter wave or possibly half wave.
Certainly a nearfield situtation, but vulnerable to hacking from the general area to include the next room over, or from just outside. Boo.
I also question the choice of frequency band, you should tell your son to investigate carefully on this issue, also I hope he is aware of the problems incurred by hackers with these types of devices.
An Insulin Pump hacked to turn on and keep pumping can and will kill the user.
There are also the "inadvertent" situations to consider carefully here. For example, RF interference from another device should never be able to activate - or inactivate - the medical device.
System design should then be governed by factors that pay attention to absolute failsafe, to include both hardware and software design. And, of course, RF considerations suc as frequency band, modulation scheme, password encryption and protection, this is not a trivial matter.
I am assuming that it is very likely that your son is in development to answer these problems, as not only Insulin Pumps, but Pacemakers have recently been in the news as being unsecured in several ways. http://www.technewsdaily.com/7696-firewall-prevent-pacemaker-hacking.html
Websearch can bring up a whole lot more, including the findings at the last hacker's convention, in which not only the basic and rather easy radio comm situation, but the bad situation of passwording which blames both users for picking easy to crack passwords as well as designers for not encrypting same or using better programming schemes.