L. Feijs, P. Peters, F. Delbressine, and J. Hu, Sensor and System for Fluid Flow Simulation, the Netherlands 229336, 2008. FULLTEXT: PDF HTML REFERENCE: BibTeX EndNote



April 9, 2008

Loe Feijs, Peter Peters, Frank Delbressine, Jun Hu


To simulate a umbilical cord or another assembly of veins and or arteries used for training of medical workers, training for first aid tasks in areas such as surgery, obstetrics and acute care paramedics.  The invention simulates the effects and consequences of bending, blocking or otherwise obstructing the flow in a fluid channel such as typically but not exclusively the blood flow.


 The system contains a flexible tube the outside material and touch-related properties of which resemble the same of the real vessel that is being simulated. Those properties include the stiffness of the tube and its resistance against bending and twisting.  The system sends an acoustical signal into the tube from one end and receives the same signal at the other end. If the tube is being squeezed, this will be detected by a weakening or absence of the acoustical signal. The system can easily be made to have a very natural look and feel without any real fluid flowing around. This precisely satisfies the need for simulation purposes in medical training. The system is very robust in the sense that its operation does not depend critically on material properties, tube length, sensor tuning etcetera. Moreover the system is insensitive to external noise because the receiver contains a band pass filter for the acoustic signal used and thus rejects other frequencies. The system is cheap because all components are cheap, particularly the tube, the speaker, the microphone, the oscillator and the filter, none of which demand high precision components or fittings. The sender and the receiver need not be coupled, they each can run on their own power supply.


As shown in Figure A the system contains a signal source (1) producing a sine wave of 1700 Hz the signal of which is fed into a miniature loudspeaker (2) which is enclosed in a small box of plastic or any other material. The box contains a hole in which a flexible plastic or rubber tube (3) fits such that the sound of the loudspeaker will be conveyed by the tube. These components together will be called the sender. At the other end of the tube is an assembly called receiver which consists of a microphone (4), an electronic or digital filter (5) and a detection unit (6). The filter is a band pass filter amplifying the 1700 Hz signal but weakening signals of very different frequencies. The detector consists of a rectifier with low-pass filter of time constant of 1 second such that the amplitude envelope of the signal is obtained.  Said envelope signal goes to a comparison circuit with an adjustable threshold.

The frequency of 1700 Hz can equally well be higher or lower. Similarly the wave form can be a sine but other forms can be used as well. It is best to have a little bit of damping in the flexible tube, such as a soft material in one or two of the enclosing boxes or a well-chosen tube material, in order to prevent very sharp standing wave patterns. In our prototype, even without special measures we found the phenomenon of standing waves to cause no trouble at all.

The sender-tube-receiver system is part of a larger system which serves for purposes of medical training.

In one application shown in Figures B and C the flexible tube, perhaps together with other flexible tubes, forms a simulated umbilical cord connecting a mother manikin to a baby manikin. Of course the umbilical cord is connected to a kind of simulated placenta.

In Figure B item (1) is the said simulated placenta inside the simulated uterus (2) of the mother manikin, typically, but not exclusively, the sender. The other end, typically, but not exclusively, the receiver is connected to the baby manikin at the usual place of the belly button (3). The receiver is inside the baby manikin. The sender-tube-receiver subsystem will detect whether there is too much pressure on the umbilical cord, for example when it is squeezed between the baby and the delivery channel as shown in (4) or when there is a stretched twist (5) in the cord.

Figure C shows the larger system. The mother manikin (1) has an internal model (2), for example containing scripts, mathematical models, object-oriented models or any combination of those. Said model simulates bodily aspects of the mother, which may or may not be related to the blood flow simulated by the tube of the invention. Inside the mother manikin is a power supply (4) which feeds the sender (3). The baby manikin (5) contains its own power supply (6) which feeds the receiver and other equipment. The baby manikin has an internal model again being any combination of said modeling elements. The model controls output elements of the baby manikin, typically but not exclusively a simulated heart (9), a simulated skin color (10) or other bodily features (11). In a slightly different configuration the umbilical cord transports electric energy through the tube of the invention or any other tube so that either the mother or baby power supply becomes superfluous.

In another application shown in Figure D the flexible tube is inside a single manikin, for example, but not exclusively, a baby manikin. One or more of these tubes represent the arteries in the neck such that strangulation is detected by one or more instances of the sender-tube-receiver system of the invention. The sender is conveniently positioned in the head (1) of the manikin in which case the receiver is inside the torso (2). The tube is (3). A likely cause of strangulation is the umbilical cord (4) which may or may not be based on the invented sender-tube-receiver configuration.

The claim of this invention includes analog and digital generation and filtering. Figures E and F show the circuit diagrams of receiver and sender of one analog embodiment.


Dynamic childbirth simulators have been invented as early as 1974, see US3822486 Dynamic childbirth simulator for teaching maternity patient by Knapp et al. and the related US3797130, US3826019, US3824709. In US3822486 there is an umbilical cord and an amniotic sac but the cord only houses an electric conductor for a loudspeaker signal (no sound wave going through the cord).

More recent simulator-related inventions by Van Meurs et al. such as US6273728 Life support simulation system simulating human physiological parameters, are about the construction of manikins as a combination of a mathematical and a mechanical model. The idea of programmable behavior as such is already in the 1974 US3822486 but Van Meurs describes specific implementations. No special constructions of the umbilical cord are described in US6273728, let alone the acoustic sensor-tube-receiver system. Related inventions by the same authors are for example US5890908  Apparatus for and method of simulating the injection and volatilizing of a volatile drug, or US5772442 Apparatus and method for simulating bronchial resistance or dilation, none of which are either about the umbilical cord or other blood vessels simulated in the manner of the present invention.

Numerous inventions are done about the usage of sound waves and ultrasound waves for performing mechanical measurements such as measuring object positions or measuring existing flows in tubes.  To the best of our knowledge none of these is about getting an indication about the status of a tube which is simulated as if it would be carrying a fluid flow for training purposes.  For example: EP0292875 Automatic device to indicate the horizontal position or  US4722224 Ultrasonic sensor for the detection of gas bubbles. The usage of ultrasound reflection is also well-known, but it should be noted that in the present invention neither ultrasound nor reflection play a role.

Road tubes are used for traffic monitoring and other vehicle detection systems. An example is the product Total traffic counter of Scottech, 89 Colombo Street, Frankton, Hamilton, New Zealand, see www.trafficcount.co.nz. Such road tubes work with an air sensor, measuring the pulse when a vehicle passes. Somewhat similarly but for a different application, US5096329 Drunk driver detection system, uses hollow strips containing pressure chambers, the volume of which is reduced when a vehicle tire crosses or rides along on top of one of the strips. US2007090931 Pedestrian impact sensing apparatus for a vehicle bumper uses a flexible hollow tube and measures airflow to know crush rate.

The present invention remotely resembles JP61256213 Acoustic type edge sensor, but the latter invention is about detecting internal contamination of a tube near the edge of a fitting only, not even about bending and twisting. Moreover the latter invention uses resonance, unlike the present invention. Note that the present invention does no rely on standing waves, reflections, resonance etc., although there may or may not be standing waves in the flexible tube. In our experience the detection mechanism is fairly robust for the presence of standing waves.  The present invention also remotely resembles JP3279833 Tube leakage detector, but the latter invention is about detecting leaks, whereas the present invention is primarily intended for bending twisting, squeezing etc, although it could be configured to detect leaks as well.








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