Horn Design

The significance of the position at which the step is placed should be appreciated. It is always at the nodal point of the horn because at this point there is zero vibration (i. e. no stress). If the size reduction is not precisely at this null point stress will develop at this point. Fortunately however titanium has high tensile strength and so small errors in the position of constriction can be accommodated. 

These designs avoid the possible stress developed in stepped horns. The amplification factor for either a linear or an exponential horn is the ratio of the end diameters (not areas as with stepped). The linear taper is the easier design to manufacture but its potential magnification is normally restricted to a factor of approx. 4-fold. The exponential taper offers higher magnification factors than the linear taper. Its shape makes it more difficult to manufacture but the small diameter of the working end and its length make it particularly suited to micro applications. 

For the probe system, whatever design of horn is used, a large maximum power density can be achieved at the radiating tip. This can be of the order several hundred W cm . The working frequencies are normally of the order 20 - 40 kHz. A number of probe devices are commercially available and, up to a few years ago (before the advent of sonochemistry) were referred to as cell disrupters. The majority operate at 20 kHz and utilise a wide range of different metal probes. The advantages of the probe method of energy input are threefold  

However the probe, like the bath, does suffer from the same difficulty with respect to temperature control. This problem has been alleviated to some extent in modern instruments by the incorporation of a pulse mode of operation. Quite simply this consists of a timer attached to the amplifier which switches the power to the probe on and off repeatedly. The off time allows the system to cool between the pulses of sonication. The on time is represented as a fraction of the total time involved in the cycle (about 1 s) i. e. 100 % is continuous sonication while 50 % represents 0.5 s bursts of power every 0.5 s. 

This type of pulse operation should not be confused with duty cycle as used in medical ultrasound. In medical parlance the duty cycle refers to the on/off ratio for scanning which involves the emission of pulse of extremely short duration (e. g. 10 seconds) involving only a few cycles of ultrasound in the MHz range. It is in the longer off period that the echoes are detected. By way of contrast a chemical sonicator pulse of 0.5 s involves 10000 cycles at 20 kHz. 

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Horn design is a very important aspect of ultrasonic engineering. The vibrational amplitude of the piezoelectric crystal itself is normally so small that the intensity of sonication attainable by direct coupling of the transducer to the chemical system is not large enough to cause cavitation. The horn acts as an amplifier for the vibration of the transducer and the precise shape of the horn will determine the gain or mechanical amplification of the vibration. It is for this reason that it is sometimes referred to as a... 

Ultrasonic welding of parts fabricated from ABS, acetals, nylon, PPO, polycarbonate, polysulfone, and thermoplastic polyesters should be considered as early in the design of the part as possible. Very often, minor modifications in part design will make ultrasonic welding more convenient. The plastic resin manufacturer or ultrasonic equipment suppher can recommend best joint design and ultrasonic horn design. 

Bolometers have been produced in small arrays by simply mechanically placing them at the foci of an array of feed horns designed to channel far infrared radiation to them. Since bolometers are not as sensitive as other detectors and they are difficult to produce in large arrays, they are generally only used for far infrared astronomy where other detectors are not sensitive. They are operated at temperatures of 1 to 2 K or below in dewars containing liquid helium. 

Two major sources of ultrasound are employed, namely ultrasonic baths and ultrasonic immersion hom probes [79, 71]- The fonuer consists of fixed-frequency transducers beneath the exterior of the bath unit filled with water in which the electrochemical cell is then fixed. Alternatively, the metal bath is coated and directly employed as electrochemical cell, but m both cases the results strongly depend on the position and design of the set-up. The ultrasonic horn transducer, on the other hand, is a transducer provided with an electrically conducting tip (often Ti6A14V), which is inuuersed in a three-electrode thenuostatted cell to a depth of 1-2 cm directly facing the electrode surface. 

Eig. 9. A typical sonochemical apparatus with dkect immersion ultrasonic horn. Ultrasound can be easily introduced into a chemical reaction with good control of temperature and ambient atmosphere. The usual pie2oelectric ceramic is PZT, a lead 2kconate titanate ceramic. Similar designs for sealed... 

FS Horn, JJ Miskel. Enhanced drug dissolution rates for a series of drugs as a function of dosage form design. Lex Sci 8(1) 18-26, 1971. 

The cup-horn configuration, shown in Fig. 8, was originally designed for cell disruption but has been adopted for sonochemical studies as well (81). It has greater acoustic intensities, better frequency control, and potentially better thermostating than the cleaning bath. Again, however, it is very sensitive to the liquid levels and to shape of the reaction vessel. In addition, the reaction vessel faces a size restriction of 5 cm diameter. 

Fig. 8. Cup-horn sonicator. Modification of a design from Heat Systems-Ultrasonics, Inc. (81,82).

Fig. 9. Direct immersion ultrasonic horn equipped for inert atmosphere work. [Design of K. S. Susiick (183). ...

In many countries, water is not safe to drink. Untreated water is sometimes polluted with toxic chemicals. It may also carry numerous water-horne diseases, including typhoid fever, cholera, and dysentery. In Canada, the water that comes through your tap has heen through an elaborate purification process. This process is designed to remove solid particles and toxic chemicals, and to reduce the number of bacteria to safe levels. Adding chlorine to water is the most common way to destroy bacteria. 

A system for reporting fires and alerting the plant fire brigade and the municipal fire department should be provided. This system should be as simple as possible to minimize the potential for confusion in emergencies. The preferred design is a multiplex system that alarms in the control room or some other 24-hour constantly attended location and activates visual devices, such as strobes or beacons, and audible notification devices, such as a steam whistle, air horn, or tone generator. Complete systems are available from recognized vendors. 

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