Look at iOS Troubleshooting Wi-Fi networks and connections http://support.apple.com/kb/TS1398
iPad: Issues connecting to Wi-Fi networks http://support.apple.com/kb/ts3304
iOS: Recommended settings for Wi-Fi routers and access points http://support.apple.com/kb/HT4199
Additional things to try.
Try this first. Turn Off your iPad. Then turn Off (disconnect power cord) the wireless router & then back On. Now boot your iPad. Hopefully it will see the WiFi.
Go to Settings>Wi-Fi and turn Off. Then while at Settings>Wi-Fi, turn back On and chose a Network.
Change the channel on your wireless router. Instructions at http://macintoshhowto.com/advanced/how-to-get-a-good-range-on-your-wireless-netw ork.html
Another thing to try - Go into your router security settings and change from WEP to WPA with AES.
How to Quickly Fix iPad 3 Wi-Fi Reception Problems
If none of the above suggestions work, look at this link.
iPad Wi-Fi Problems: Comprehensive List of Fixes
Fix iPad Wifi Connection and Signal Issues http://www.youtube.com/watch?v=uwWtIG5jUxE
If any of the above solutions work, please post back what solved your problem. It will help others with the same problem.
Did any one face with the same issues intermittently? Are there any hardware issues reported with Ipad2 and wi-fi module?
Can it be a hardware issue as the internet connection loss is getting more frequent day by day, but there have been no any changes within the wi-fi access point settings since I launched my wi-fi router first ?
Thanks Texas Mac Ma, I'm battling with this issue almost a year and tried all these solutions they solve the issue intermittently, currently I have WPA2 with AES router settings, static IP.
In order to renew the connection only 2 things help: 1st - leave the device for a few days and it will restore the connection itself. 2nd - find another wi-fi network which it connects just fine and after that it can connect to my network also fine and works for a few more days until the next connection lost.
Reboot/restrart, toggle of services ... nothing helps at the moment