Ultrasonic bathing system

An ultrasonic bathing system comprising a bathtub for containing a bathing fluid, an ultrasonic transducer mounted on said bath, means for energizing said transducer to generate ultrasonic waves in the bathing fluid at a power and frequency for providing a mechanical cleaning action, and means for pulsing said energizing means to provide bursts of constant amplitude waves having a mark-space ratio dependent on the required power level.

BACKGROUND OF THE INVENTION 
This invention relates to an ultrasonic bathing system. 
Ultrasonic bathing systems have been known for some time. One such system 
is described in U.S. Pat. No. 5,048,520 of Sep. 17, 1991. This patent 
claims to describe an ultrasonic bathing system employing a power level of 
between 0.1 and 5 watts per square centimeter at a time of less than 15 
minutes, with the frequency being swept through a predetermined sweep 
frequency band. The alleged reason for employing a swept frequency 
generator is that if a constant frequency is employed, standing waves will 
be set up within the bathtub and these will cause distributed regions of 
high and low intensity within the bathing fluid. 
The above patent makes several claims concerning the germicidal effects of 
ultrasonic systems and also the significance of cavitation about which the 
present applicants are skeptical. Nonetheless, it is believed that the 
establishment of ultrasonic waves within a bathing fluid can serve to 
exert a mechanical cleaning action on an immersed item, whether it be a 
mechanical component or a human body. The advantage of ultrasonic systems, 
as opposed to pumped flow systems, is that after each use the bathing 
fluid can be completely drained from the bathtub. There are no pipes 
connecting the bathtub to a pumping system that can serve to retain 
harmful bacteria. 
While ultrasonic bathing systems have certain advantages over conventional 
whirlpool systems, a problem remains as to how to adjust the power level 
of the ultrasonic energy within the bathing system without effecting the 
cleaning efficiency. If a conventional signal generator is employed and 
the power level turned down, this merely reduces the amplitude of the wave 
applied to the bathing system. 
Since the cleaning action of ultrasonic energy is dependent on the 
resulting mechanical agitation, the agitation caused by the wave is less 
at a lower amplitude and the cleaning efficiency suffers. Indeed, below 
certain power levels, the ultrasonic energy is really insufficient to 
create a mechanical cleaning action. Yet, there are many situations where 
it is desirable to reduce the overall power level. For example, elderly 
patients or patients with serious wounds may require more gentle treatment 
than patients having a stronger constitution. The problem is, that 
treatment at a reduced power level may in fact be no treatment at all if 
the mechanical agitation caused by the ultrasonic energy is insufficient 
to dislodge attached debris. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide an improved ultrasonic 
bathing system of simplified construction. 
According to the present invention there is provided an ultrasonic bathing 
system comprising a bathtub for containing a bathing fluid, an ultrasonic 
transducer mounted on said bath, means for energizing said transducer to 
generate ultrasonic waves in the bathing fluid at a power and frequency 
for providing a mechanical cleaning action, and means for pulsing said 
energizing means to provide bursts of constant amplitude waves having a 
mark-space ratio dependent on the required power level. 
In accordance with the invention, the power supplied to the bathtub can be 
varied by varying the mark-space ratio of the burst of ultrasonic energy. 
By ensuring that the frequency and amplitude of the waves are kept 
constant, a uniform cleaning action can be assured. 
The fact that the energy is supplied in bursts also helps to reduce the 
formation of standing waves within the bathtub, although at full power a 
continuous constant amplitude wave is supplied to the bathtub and the 
applicant has found that standing wave formation does not present a 
serious problem at such power levels.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to FIG. 1, a conventional bathtub 1 contains water 2 and is 
provided at one end with a standard faucet arrangement 3. The bath has a 
plug hole 4, but is otherwise closed and does not have water flow 
conduits, such as would be required in a whirlpool-type system. 
At one end of the bath, an aperture is formed in the bathtub and a steel 
plate forming part of an ultrasonic transducer 5 is firmly bolted around 
its periphery to the wall of the bathtub. The transducer 5 is connected to 
a control unit 6, which supplies constant amplitude ultrasonic energy to 
the transducer 5. In a manner that will be described, the ultrasonic 
energy supplied to the transducer can be supplied in the form of short 
duration bursts having a variable mark-space ratio so as to permit control 
of the mean power level supplied to the water. However, because the 
amplitude of the wave within the burst remains constant, the cleaning 
efficiency at reduced power levels is substantially unaffected. 
If a continuous wave were used, and the energy was varied by varying the 
amplitude of the wave, at low power levels there would be very little 
cleaning action because of the minimal agitation caused by the low 
amplitude wave. In other words, in accordance with the invention, it is 
more efficient to intersperse periods of constant high energy with period 
of zero energy, in order to reduce the mean power level, than to have a 
continuous supply of energy at a lower amplitude, which causes less 
agitation of the medium to be cleaned. 
FIG. 2 illustrates the control circuitry in more detail. The transducer 
plate 5 is attached to a transducer 7, which can be for example a 
transducer made by American Ultrasonics. 
This is connected to a American Ultrasonics 40 khz signal generator 8, 
which when energized produces a constant amplitude wave at 100.+-.10% 
volts for energizing the transducer 7. 
In order to regulate the power level, the 120 V, 60 hz, 2 amp main supply 
is fed to the signal generator 8 through a zero crossing power triac 9, 
type Motorola MAC 222. This is triggered from the control port of a 
microcomputer 10, type Motorola 68MC05C8P, which produces a train of 
pulses 11 having a repetition rate dependent on the desired output power 
level. The microcomputer is connected through a serial interface 11 to a 
double insulated user control panel. 
The train of output pulses 11 triggers the triac to allow selected portions 
of the mains voltage cycle through to the signal generator 8. In the 
illustrated example shown in FIG. 2, alternate half cycles pass through 
the triac 9, which causes the signal generator 8 to produce bursts of 
energy 13 during alternate half cycles. As a result, the mean power level 
supplied to the bath 2 is 50% of the power level supplied when a 
continuous wave is generated, but the amplitude within the burst remains 
constant so that the cleaning action is unaffected. 
In addition to controlling the power supply circuits to the transducer, the 
microcomputer 11 also controls the time of operation of the bath and 
displays information to the user in the bath water about the tub status, 
for example programming length of bath and power (duty cycle). 
The system in accordance with the invention provides a practical ultrasonic 
bathing system that requires the minimum number of components. The bathtub 
1 is essentially conventional with the exception of the transducer plate 
attached at one end. No special plumbing is required, as for instance 
would be the case with a whirlpool. 
The present invention provides convenient means of adjusting the mean power 
level of ultrasonic energy supplied to the bathtub without detrimentally 
effecting the cleaning action.