Increasing the sensitivity of an ultrasonic sensor

Is it possible to increase the sensitivity of an ultrasonic sensor? Like this one http://www.sparkfun.com/commerce/product_info.php?products_id=8504?

I am making a circuit with a friend and we need extremely high precision position measurement. We are using an electromagnet and positioning a metallic object below it. We don't want to pulse the current on and off, but it seems like this might be necessary. I was thinking of using a digital potentiometer, but I haven't been able to find one in a good range. Anything from 0 - 1000 ohms would be what we want, but I haven't found a pot with such a range. Ideally the voltage would be kept constant, and current could be adjusted. We might have to try to pulse it, but finer control would be had with variable current. I assume it's possible as power supplies can supply C @ CV.

i dont know about the ultrasonic sensor, but why not use pulse width modulation to control the current?

We will, but we need to know where exactly the item is, as the PWM duty will be dependent on its position.

I am having the same issue, with the ping sensor. How does one get a more precise measurement?

I think we are going to scrap the US and use an IR sensor, I believe they might be slightly more precise in measurement, except they have a logarithmic voltage return :(.