System and method for characterizing a sample by low-frequency spectra

Abstract

A method and apparatus for interrogating a sample that exhibits molecular rotation are disclosed. In practicing the method, the sample is placed in a container having both magnetic and electromagnetic shielding, and Gaussian noise is injected into the sample. An electromagnetic time-domain signal composed of sample source radiation superimposed on the injected Guassian noise is detected, and this signal is used to generate a spectral plot that displays, at a selected power setting of the Gaussian noise source, low-frequency spectral components characteristic of the sample in a selected frequency range between DC and 50 kHz. In one embodiment, the spectral plot that is generated is a histogram of stochastic resonance events over the selected frequency range. From this spectrum, one or more low-frequency signal components that are characteristic of the sample being interrogated are identified.

1 - 22 . (canceled)  
   
   
       23 . Apparatus for interrogating a sample that exhibits low-frequency molecular motion, comprising: 
 a container adapted for receiving the sample, the container having both magnetic and electromagnetic shielding;    an adjustable-power source of Gaussian noise for directing Gaussian noise to the sample, with the sample in the container;    a detector for detecting an electromagnetic time-domain signal composed of sample source radiation superimposed with the directed Gaussian noise; and 
 an electronic computer adapted to receive the time-domain signal from the detector, and to process the signal to generate a spectral plot that displays, at a selected power setting of the Gaussian noise source, low-frequency spectral components characteristic of the sample in a selected frequency range between DC and 50 kHz.  
   
   
   
       24 . The apparatus of  claim 23 , wherein the electronic computer includes a signal analyzer that functions to (i) calculate a series of Fourier spectra of the time-domain signal over each of a plurality of defined time periods, in a selected frequency range between 100 Hz and 50 kHz, and (ii) average the Fourier spectra.  
   
   
       25 . The apparatus of  claim 24 , wherein the calculating includes calculating at least five Fourier spectra, each taken over a 1-5 second time-domain interval.  
   
   
       26 . The apparatus of  claim 23 , wherein the source of Gaussian noise includes an adjustable-power Gaussian noise generator and a Helmholz coil which is contained within the magnetic electromagnetic shielding, and which receives a selected noise output signal from the noise generator in a range 100 mV to 1 V.  
   
   
       27 . The apparatus of  claim 26 , wherein the generator is designed to inject Gaussian noise into the sample at a frequency between DC and 2 kHz.  
   
   
       28 . The apparatus of  claim 23 , wherein the detector is a second-derivative gradiometer which outputs a current signal, and a SQUID operatively connected to the gradiometer to convert the current signal to an amplified voltage signal.  
   
   
       29 . A method for interrogating a sample that exhibits low-frequency molecular motion, comprising: 
 placing the sample in a container having both magnetic and electromagnetic shielding, 
 injecting noise into the sample at a selected noise amplitude;  
 recording an electromagnetic time-domain signal composed of sample source radiation superimposed on the injected noise,  
 generating a spectral plot that contains, at a selected power setting of the noise source, low-frequency, sample-dependent spectral components characteristic of the sample in a selected frequency range between 100 and 50 kHz, and  
 repeating the injecting, recording and generating at different selected noise amplitudes until a plot showing a maximum or near maximum number of spectral components characteristic of the sample is generated.  
   
   
   
       30 . The method of  claim 29 , wherein the generating includes (i) calculating a series of Fourier spectra of the time-domain signal over each of a plurality of defined time periods, in a selected frequency range between 100 Hz and 50 kHz, and (ii) averaging the Fourier spectra.  
   
   
       31 . A method for interrogating a sample that exhibits low-frequency molecular motion, comprising: 
 receiving the sample;    magnetically and electromagnetically shielding the sample;    directing adjustable-power Gaussian noise to the sample;    detecting an electromagnetic time-domain signal composed of sample source radiation superimposed with the directed Gaussian noise; and    receiving the time-domain signal, and processing the signal to generate a spectral plot that displays, at a selected power setting of the Gaussian noise source, low-frequency spectral components characteristic of the sample in a selected frequency range between DC and 50 kHz.    
   
   
       32 . The method of  claim 31 , wherein the processing includes (i) calculating a series of Fourier spectra of the time-domain signal over each of a plurality of defined time periods, in a selected frequency range between 100 Hz and 50 kHz, and (ii) averaging the Fourier spectra.  
   
   
       33 . The method of  claim 32 , wherein the calculating includes calculating at least five Fourier spectra, each taken over a 1-5 second time-domain interval.  
   
   
       34 . The method of  claim 31 , wherein the directing Gaussian noise includes providing a Helmholz coil contained within magnetic electromagnetic shielding, which receives a selected noise output signal in a range 100 mV to 1 V.  
   
   
       35 . The method of  claim 34 , wherein the directing Gaussian noise includes injecting Gaussian noise into the sample at a frequency between DC and 2 kHz.  
   
   
       36 . The method of  claim 31 , wherein the detecting is performed using a second-derivative gradiometer which outputs a current signal, and a SQUID operatively connected to the gradiometer to convert the current signal to an amplified voltage signal.  
   
   
       37 . An apparatus for interrogating a sample that exhibits low-frequency molecular motion, comprising: 
 means for placing the sample in a container having both magnetic and electromagnetic shielding;    means for injecting noise into the sample at a selected noise amplitude;    means for recording an electromagnetic time-domain signal composed of sample source radiation superimposed on the injected noise;    means for generating a spectral plot that contains, at a selected power setting of the noise source, low-frequency, sample-dependent spectral components characteristic of the sample in a selected frequency range between 100 and 50 kHz; and,    means for repeating the injecting, recording and generating at different selected noise amplitudes until a plot showing a maximum or near maximum number of spectral components characteristic of the sample is generated.    
   
   
       38 . The apparatus of  claim 37 , wherein the means for generating includes means for calculating a series of Fourier spectra of the time-domain signal over each of a plurality of defined time periods, in a selected frequency range between 100 Hz and 50 kHz, and means for averaging the Fourier spectra.