User:Pranav Rathi/Notebook/OT/2011/10/11/Device for studying acoustic and mechanical noise in optical setups

Introduction

All optical setups are subjected to the mechanical and airborne acoustic noise generated by various electronic and mechanical devices such as computers and air-vents in a lab. Optical setups such as optical tweezers are very sensitive to these noises. Optical tweezers like ours is so sensitive that it almost woke like a microphone. Currently it is reading all kinds of mechanical and airborne noises which are very troublesome for DNA unzipping and overstretching experiments. So I had to do a full scale investigation of these noises[[1]]. To do it I had to create this device: I named it Acoustic & Mechanical Noise Reader (AMNR). This device is nothing but a condenser microphone inside the ear-plug of a stethoscope. But it is so sensitive that it can read the mechanical noise up to -95DB (believe it or not), and it just uses a regular computer sound card with a Lab View V9 program. This whole setup has three parts; AMNR, noise investigator and helper program and, tone generator and speaker.

The whole purpose of this device is following:

• Identify the airborne noise frequencies around the tweezers and their source.
• Identify the mechanical noise (vibrations) frequencies in the optical table and their source.
• Help me chose and design the right setup (stages and sample holders) on the microscope.
• Help me in designing and searching ways to isolate the optical trap form acoustic and mechanical noise.

Most of this I discussed in the “Noise issue with the optical tweezers’’ page of my note book[[2]]. In this page I will just discuss the construction and demonstration briefly.

Hardware

The hardware is pretty simple:

1. Classic ll S.E. stethoscope by 3M Littmann. This is one of the best in the market used by cardiologists, with nominal price.
2. Condenser microphone. Omnidirectional mic with frequency response 50Hz to 1.5kHz.
3. 3.5mm headphone lead.
4. Investigator and helper Lab View V9. Link to download: [3].
5. Tone generator Lab View V9. Link to download:[4].
6. 5.25" speaker by Virtual Reality Sounds Labs. The speaker has frequency response from 100Hz to 20kHz, which is more than enough for me.

I do not know any specifications of the sound-card and external amplifier i am using to generate the tone of different frequencies.

Demonstration

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