Heath Scientific
Home About Technology Products Applications Events Contact Us
Technology: Ultrasonic HR-US 
  INTRODUCTION

The relationships between a material's properties and acoustical characteristics have been studied for a long time and ultrasonic techniques have been used in non-destructive testing and imaging for decades.
Ultrasound as an analytical tool has revolutionized diagnostics and medicine, but the application of ultrasound to material analysis has been held back by problems with ultrasonic design, electronics and size of sample handing, complicated measuring procedures and resolution. Recent advances in computing power and digital techniques have made it possible to design a versatile laboratory instrument with applications ranging from ceramics to polymer science to cell biology and emulsions. The high-resolution HR-US family of ultrasonic spectrometers recently launched by Ultrasonic Scientific is an example of this.


Most spectroscopists are accustomed to using electromagnetic waves in analysis (UV, VIS, IR, NMR etc.).
Ultrasonic spectroscopy is simply spectroscopy employing sound waves. In particular, it uses a high-frequency acoustical wave (similar or higher to those used by dolphins for communication and bats for
navigation). The wave probes intermolecular forces in materials. Oscillating compression (and
decompression) in the ultrasonic wave causes oscillation of molecular arrangements in the sample, which
responds by intermolecular attraction or repulsion. The amplitudes of deformations in the ultrasonic waves
employed in analytical ultrasound are extremely small, making ultrasonic analysis a non-destructive
technique.


Of course an ultrasonic wave, unlike its light counterpart, is able to propagate through opaque samples, in
fact through most materials. Another advantage is that it is relatively easy to change the wavelength of
ultrasonic wave: unlike optical techniques where the wave originates in a light source and therefore needs
special effort to get a required spectral purity, ultrasonic waves are synthesized electronically. Therefore a
typical ultrasonic spectrometer can cover a broad range of wavelengths (10 to 100 and even more times). It
could be described as probing the interior of the analyzed sample with a set of fingers, which differ in their
length by more than an order of magnitude!

 

ULTRASONIC PARAMETERS AND MEASURING PRINCIPLES
The two major parameters measured in high-resolution ultrasonic spectroscopy are the attenuation and the
velocity of the waves. Attenuation is determined by the energy losses in compressions and decompressions
in ultrasonic waves, which include absorption and scattering contributions. As measurements of attenuation
do not require high temperature stability of the sample, they can be performed in large samples. That is why
attenuation was the parameter responsible for the largest portion of past ultrasound applications in research, such as the kinetics of fast chemical reactions and particle sizing in emulsions and suspensions.


Ultrasonic velocity is determined by the density and the elasticity of the medium. This is extremely sensitive
to the molecular organization and intermolecular interactions in the sample and can be exploited in the
analysis of a broad range of molecular processes. However, its application requires high resolution of the
measurements, which cannot be achieved in large samples because of the difficulty of controlling the
temperature. It is because of the difficulty in resolving both sets of information that scientists tended to
belong to research groups working on the measurement of either attenuation or velocity and adjusted their
instruments for the best performance in the selected area.


The general principles of high-resolution ultrasonic measurements are shown in the Figure. The
generated electronic signal is transferred by the piezotransducer into the ultrasonic wave travelling through the sample. Another piezotransducer transfers the received ultrasonic wave into an electronic signal for
subsequent analysis.



The most widely used approach for the measurements of ultrasonic characteristics in the past was based on
the pulse technique. In this technique an ultrasonic pulse generated at a certain frequency is sent through a
sample and received either at the other end or, after the reflection from the wall of the container, back to the
source of ultrasound. Measurements of the amplitude of the wave in the pulse allow the determination of the
ultrasonic attenuation and the propagation time (or related parameters), which characterize the ultrasonic
velocity. The resolution of this technique is limited by the path length of the pulse, or by the size of the
sample.
The Ultrasonic Scientific HR-US spectrometer employs a novel principle where the path length of the
ultrasonic wave in the sample exceeds the size of the sample. The use of modern advances in ultrasonic
design, electronics and digital processing allow the attainment of ultrasonic measurements with record
resolution (down to 10 -5 % for ultrasonic velocity) in a broad range of the sample volumes, down to a single
droplet.

 

BENEFITS OF ULTRASONIC ANALYSIS
Most materials are ultrasonically transparent, allowing the analysis of a broad variety of sample types,
chemical reactions and processes. Ultrasonic analysis can now be easily performed in chemistry, physics,
biotechnology, pharmaceuticals, food, agriculture, environmental control, medicine, oil, petroleum and gas
industries.
As ultrasonic signals are generated electronically with the use of small piezotransducers, modern high-resolution
ultrasonic spectrometers do not have large actuators (as in dynamic rheology) or bulky light
sources and other optical parts. This permits the construction of robust and multipurpose instruments, which
perform a broad range of analytical functions and are equally in research, analytical, product development
and quality control laboratories and in process control analysis.
Our modern ultrasonic cells do not have any cavities or sharp corners allowing for easy filling, refilling,
cleaning and sterilization. They can accommodate even aggressive liquids such as strong acids or organic
solvents without evaporation in a course of measurements, sizes range from 4ml down to 30µl. Semi-solid
cells are also available for samples such as biological tissues, gels, toothpaste, cheeses, waxes, pastes, creams
and so forth.
The measurements are completely computer controlled and results are presented in a graphical and digital
format, which is compatible with Excel and most current data analysis software.
Users of high-resolution ultrasonic spectrometers can measure concentrations of components, transition
temperatures and temperature intervals, characterize the temperature stability and shelf life of their materials,
analyze enzymatic activities, sizes of particles in suspensions and emulsions, kinetics of sedimentation,
kinetics of chemical and physical processes in materials, stoichiometries and affinities in ligand binding and
other parameters of their samples.
Fast measurements allow the analysis of flowing samples and, coupled with the ability to perform
measurements on small volumes, make it possible to use high-resolution ultrasonic spectrometers in HPLC
and similar applications. Because the ultrasonic velocity and attenuation can be measured simultaneously at
different wavelengths as a function of time the instrument can be used for the analysis of the kinetics of
chemical reactions and processes, such as the analysis of enzymatic activity. The ability of ultrasound to
analyze opaque samples makes it possible to measure the speed of enzymatic reactions in aqueous solutions
as well as in blood or tomato juice, samples where traditional spectroscopy fails. It can analyses chemical
reactions, transitions and processes as fast as 10 -5 to 10 -7 seconds without optical markers, meaning that the
reaction or system can be studied in its natural state
The construction of modern ultrasonic cells allows controlled stirring of the sample, hence permitting
measurements under shear and measurements in sedimenting samples. It also allows the measurement of
ultrasonic velocity and ultrasonic attenuation in the course of titration, useful for the analysis of ligand
binding, adsorption of molecules on the surface of particles in colloid systems and complex formation
phenomenon.
The novel design of the Ultrasonic Scientific HR-US makes possible ultrasonic measurements in the
temperature ramp regime for analysis of heat stability, phase transitions, conformational transitions in
polymers and others. In addition the small sample requirement saves the cost of analysis, which is a key issue
in pharmaceutical, biotechnological and biomedical industries and research.
Finally, there is the impressive dynamic range allows the analysis of solutions of small concentration, down
to 0.3ppm (0,3µg/ml). At the other end of the scale the same instrument can be used for concentrated
mixtures and non-liquid samples such as biological tissues, hard gels, butter and others. Other techniques
such as differential scanning calorimetry would require two different devices for the same set of samples; a
high-resolution calorimeter for dilute solutions and another 'solid' calorimeter for concentrated samples.
In short HR-US 102 allows high-resolution measurements of the velocity and attenuation of acoustical waves
at high, ultrasonic frequencies propagating through materials. It provides fast, non-destructive analysis of a
wide spectrum of properties of materials. It combines simple sample handling with record precision, variety
of measuring regimes, small sample volume, convenience and exceptional simplicity of use.
   © Heath Scientific - Home to www.heathscientific.com