Converting 100mV AC to 1V DC
We might need more information from you about what kind of signal this sensor is actually outputting. By 100mV AC, do you simply mean that the sensor is giving an analog signal output that has an amplitude of 100mV? Or, do you mean that your sensor is outputting an AC signal (like a sine wave with a fixed frequency) and the amplitude of this wave changes over time, depending on what is sensed?

If the case is the latter, as I suspect given the information you've provided, here's a solution that I'd go with:

First, AC couple your signal so that your 100mV swing will be centered around 0V (GND). This can be done easily by placing a capacitor in series with your output signal. 

Now, your signal is centered around 0V and has a 50mV swing on each side for a total of a 100mV swing. You're going to want to amplify this signal to have a total 1V swing, so amplify the signal to get a 500mV swing on each side using an op-amp, bringing your signal to a range of -500mV to 500mV. Now, just add in a DC bias using a resistive divider or other means of 500mV, and your signal will now be your same AC signal from 0-1V. 

Note: if you don't have a negative supply for your op-amp, you'll want to do the math and add a bias to your signal before amplifying it. This thread might help: Single supply op-amp audio amplifier

To get the DC level from this, you can low-pass filter your signal to smooth out the AC waveform and get a level that you can feed into your ADC. Rather than do the math, I prefer to mess around with the capacitor values (goes between the output and GND) and scope the output till I get a response that I like.

Good luck with your project!