Multiple frequencies wave generation

Different from acoustic attenuation spectroscopy, in electroacoustic spectral analysis, sound waves are generated by an applied high frequency electric field across a colloidal suspension and subsequently detected. This is called the electrokinetic sonic amplitude effect (ESA) [38]. These sound waves arise because the alternating electric field pushes the suspended particle forwards and backwards. By measuring the magnitude and phase angle of the sound waves at multiple frequencies (typically from 1-10 MHz), the particle dynamic mobility, Pd, can be determined, provided the concentration and the density of the... 

The term sonochemistry indicates the use of sound waves to generate chemical and physical effects which can be harnessed in multiple applications (Fig. 1). Although such effects can be obtained at a wide range of frequencies, the word sonochemical is invariably linked to ultrasound, i.e. sound we cannot hear (typically above 20 kHz). Natural phenomena are good sources of both ultrasonic (e.g. animal communication or navigation) and infrasonic waves (such as earthquakes and tidal motion). Ultrasonics is currently of interest to lay people because of medical imaging, metal cleaning, industrial and dental drills and non-destructive material characterisation. 

To increase the active zones existing in the reactor, one can easily modify the position of the transducers (if multiple transducers have been used, which is likely to be the case at large-scale operation due to the fact that it is quite difficult to successfully operate a single transducer with very high power and frequency due to limitations in the material of construction of the transducers) so that the wave patterns generated by the individual transducers... 

This is a realistic situation because electrodes often generate a DC offset voltage V. Equation 8.24a shows that the fundamental frequency reappears, but does not contribute to a low-pass—filtered output signal. This is because we have a true sinus multiplication. If the reference signal is a square wave as it often is in simpler chopped phase sensitive rectifiers, the input DC appears also in the output as an error signal. 

The technical realization of this synchronized system is shown in Fig. 6.16a. The frequency Vs = /27t of the ultrasonic wave is chosen as an integer multiple v =q c I Id of the mode-locking frequency. A fast photodiode, which detects the mode-locked optical pulses, provides the trigger signal for the RF generator for the ultrasonic wave. This allows the adjustment of the phase of the ultrasonic wave in such a way that the arrival time of the mode-locked pulse in the cavity dumper coincides with its maximum extraction efficiency. During the ultrasonic pulse only one mode-locked pulse is extracted. The extraction repetition frequency Vq = (cjld jk can be chosen between 1 Hz to 4 MHz by selecting the repetition rate of the ultrasonic pulses [669]. 

---