Synthetic Beam Chopper

Summary

A new system of signal modulation and lock-in amplification has been developed at Vanderbilt University. The invention serves as a low cost alternative to current mechanical beam choppers and lock-in amplifiers, with lower limits of detection, decreased need for mechanical precision, and improved accuracy.

Addressed Need

• Analog lock-in amplifiers exhibit error due to: drift, offset, gain, duty cycle, and limited linearity and precision of analog multiplication techniques especially with significant noise

• Digital multiplication is error and drift free; however, accuracy, precision and sensitivity are limited due to the analog-to-digital conversion

• Lock-in amplifiers are unable to eliminate or compensate for effects of interference, creating a poor lower limit of detection

• Conventional rotational choppers create noise and error due to limitations in precision and accuracy of the fabrication and small imperfections or non-uniformities in shape and spacing

• Choppers are very expensive due to precision fabrication techniques, even though their failure rate is high.

Technology Description

The invention is a synthetic beam chopper to be used with lock-in amplification during signal detection. The chopper has a set of beam modulating features as well as a set of reference signal-generating features. These features rotate together as a unit creating a simple mechanical phase lock between the two signals. The reference signal-generating features provide an oversampled index for numerical representation of the modulation waveform of the beam. The invention is the first of its kind to optimize sampling by sampling at relative-prime frequencies. This method leads to an increase in effective precision and reduces crosstalk. This digital lock-in amplifier has several modes of operation that can all be calibrated and automated and also utilizes direct triggering and indexing.

Commercial Application

• An extension of traditional beam choppers used in spectrophotometers, ion and neutron spectrometers and other instruments

• Signal detection such as phase-sensitive detection using lock-in amplification

Unique Properties and Competitive Advantages

• Low cost alternative to existing mechanical beam choppers and lock-in amplifiers

• Lock-in measurement conditions nearly identical to actual measurement conditions

• Significant improvement in accuracy, precision, and the analog-to-digital conversion process

• Lower limits of detection

• Decreased need for mechanical precision

• Significant reduction of coherent interference effects and 1/f noise, which dominates many experimental systems at lower frequencies

• Simple, low-cost technique ready for commercial use with broad applications and implementations (eg: MEMS)

Intellectual Property Status

US utility patent 8,527,226 has been issued.

For more information go to: Shaver Publications

Inventors: 
Jesse Shaver
Licensing manager: 
Ashok Choudhury

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