Abstract:
A sensor is for continuous detection of minute changes of density in fluids and biological fluids, solids and semisolid bodies by use of a transducer. A method continuously detects changes of density of fluids or solids. The method can be carried out using the sensor.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention is related to a sensor for continuous detection of minute change of density in fluids and biological fluids, solids and semisolid bodies by a transducer. The transducer used may be of different types and a PZT (Piezo Electric) transducer is preferably used. The invention is also related to a method for determining minute changes in density of fluids and biological fluids by a transducer as well as the use of such a transducer. In connection with the present application the transducer is used to register the change of density as the change of the phase shift between the exited pulse train and its reflection in addition to the amplitude difference between the two pulse trains—ingoing train and reflected train. 
       BACKGROUND OF THE INVENTION 
       [0002]    Density, which is expressed as the relationship between mass and volume by the formulae p=m/V kg/m 3 , is normally settled by weighing a volume of the mass and divide this by the mass of the body. For a solid mass, its volume can be found by emerging the body in a liquid and measure the displacement of the liquid. 
         [0003]    However, the density of either liquids or bodies is dependent upon its volume at a set temperature. For example water has a density of 1000 kg/m 3  at 4° C., but as the volume increases by increasing temperature, the density is less than 1000 kg/m 3  as shown in the following calculations between 4 and 10° C.: 
         [0000]    
       
         
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                   
               
               
                   
                   
                 Expen- 
                 Volum change 
                   
                   
                 Differnce 
               
               
                   
                   
                 sion 
                 of water 
                   
                   
                 between 
               
               
                   
                   
                 coeffi- 
                 Vx = 
                   
                   
                 T x  and 
               
               
                 ° 
                 T x   
                 cient γ 
                 Vo*γ*(Tx − 
                 Mass 
                 Density 
                 274° K 
               
               
                 C. 
                 ° C. 
                 cm 3 /K 
                 T4) + Vo 
                 g 
                 ρ g/cm 3   
                 Δρ g/cm 3   
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 4 
                 274 
                 0.0002 
                 1 
                 1 
                 1.00000000 
                 0 
               
               
                 5 
                 275 
                 0.0002 
                 1.0002 
                 1 
                 0.99980004 
                 0.00019996 
               
               
                 6 
                 276 
                 0.0002 
                 1.0004 
                 1 
                 0.99960016 
                 0.00039984 
               
               
                 7 
                 277 
                 0.0002 
                 1.0006 
                 1 
                 0.99940036 
                 0.00059964 
               
               
                 8 
                 278 
                 0.0002 
                 1.0008 
                 1 
                 0.99920064 
                 0.00079936 
               
               
                 9 
                 279 
                 0.0002 
                 1.001 
                 1 
                 0.99900100 
                 0.00099900 
               
               
                 10 
                 280 
                 0.0002 
                 1.0012 
                 1 
                 0.99880144 
                 0.00119856 
               
               
                   
               
             
          
         
       
     
         [0004]    Normally these minute changes in the density are neglectible, but in special cases knowing the change of density is vital. One example is in order to monitor the change in body liquids which can change by changes of the solutes in the body liquid. One such solute can be alcohol, another one can be glucose and still another one can be related to dehydration, leading to concentrating of the solutes in the body liquid. As the volume of the liquids change by changing temperature, a temperature sensor monitors the temperature of the body/liquid and displays the density at the temperature at which the measurement was taken. As a further example fresh food may be mentioned, such as meat and fruit and so forth. Bacterial growth in the fresh food will effect a change of the density of the food, and the present invention could thus function as a quality control in this case. At present no means for easy determination of minute changes in density are available. 
       SUMMARY OF THE INVENTION 
       [0005]    In order to solve the above-mentioned technical problems, and provide the said means, the present invention provides a device for continuous detection of minute changes of density in fluids or solids, comprising a transducer generating pulse trains, a pulse transmitter, power input, signal analyzer and a read out unit. 
         [0006]    According to the present invention the transducer is selected from the group consisting of a PZ (Piezo Electric) transducer, a magnetic transducer, a sound transducer, a mechanical transducer and a pneumatic transducer. 
         [0007]    The transducer is preferably a piezo electric transducer. 
         [0008]    The pulses generated by the transducer are selected from the group consisting of sinus pulses, square pulses and step pulses. 
         [0009]    The pulses generated are preferably sinus pulses. 
         [0010]    The present invention also provides a method for continuous detection of changes of density of fluids or solids, comprising applying a fixed pulse train generated by a transducer to the surface of the body/liquid in question and monitoring the change in phase shift and amplitudes between the ingoing pulses and the reflected pulses. 
         [0011]    In a preferred embodiment of the method the transducer used is selected from the group consisting of a PZ (Piezo Electric) transducer, a magnetic transducer, a sound transducer, a mechanical transducer and a pneumatic transducer. 
         [0012]    The transducer used is preferable a PZ transducer. 
         [0013]    The pulse train generated in the method according to the invention is preferably selected from the group consisting of sinus pulses, square pulses and step pulses. 
         [0014]    In a preferred embodiment the pulse train is sinus pulses. 
         [0015]    The invention also relates to the use of the device for monitoring the change of density of body liquids caused by changes of solutes in said liquid. 
         [0016]    One body liquid of interest is glucose. 
         [0017]    Another body liquid of interest is alcohol. 
         [0018]    A further condition which may be monitored is dehydration. 
         [0019]    The present invention also relates to the monitoring of the change of density of beverages, such as wine or liquor. 
         [0020]    Another embodiment of the invention relates to the monitoring of the change of density of wood or wood products. 
         [0021]    A further embodiment of the invention relates to the monitoring the density of oil. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]      FIG. 1  shows a principle set-up of the device according to the invention. 
           [0023]      FIG. 2  is a graph showing phase delay as a function of increase in density difference. 
           [0024]      FIG. 3  shows an example of a simulation set-up. 
           [0025]      FIG. 4  shows an example of a test tensor. 
           [0026]      FIG. 5  is a graph showing an example of density as a function of phase delay at 20° C. 
           [0027]      FIG. 6  is a graph showing temperature vs phase delay for a silver container. 
           [0028]      FIG. 7  is a graph showing density vs phase delay for a silver container. 
           [0029]      FIG. 8  shows a graph illustrating temperature vs phase delay for steel container. 
           [0030]      FIG. 9  shows response signal after excitation. 
           [0031]      FIG. 10-18  show experimental measuring results with the present device on arm or stomach. The experimental results of the present invention (Mecsense) are correlated to convential blood sample measurements of glucose (Glucose). 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0032]    According to the present invention the detection of density changes, when using a PZ transducer, involves the detection and use of piezoelectric properties of the materials. 
         [0033]    The key element in the technique according to the invention is that once the piezoelectric element is excited and when the excitation force is stopped it experiences the response voltage due to the reverse piezoelectric effect. The inventors have found that this response contains information that is distinguishable for different density levels. 
         [0034]    Industrially it can be of interest to know the density of beverages at a set temperature of, such as for wine and liquor. Another example can be to monitor the moisture in for example wood, where the density of the wood and water gives the bulk density which will change depending on the water content. If the density is required at a given temperature, a mathematical algorithm compensates for the measured values if the temperature is higher/lower that the required temperature. The algorithm is based upon the following: 
         [0035]    The general formula for the density is: 
         [0000]      ρ o   =m/V   o  kg/m 3  
 
         [0000]    wherein m=the mass of the body and V o  is the volume of the body at a set temperature of t o . 
         [0036]    When the temperature increases/decreased from t o  to t x , the volume changes in accordance with: 
         [0000]        V   x   =V   o *γ*( T   x   ±T   o )* V   o   m   3  
       wherein γ is the expansion coefficient for the body/liquid in question and T x  is the temperature at the point of measurement.       
 
         [0038]    The density of the same mass is then: 
         [0000]      ρ x   =m/V   x  kg/m 3  
 
         [0000]    The difference in density is thus: 
         [0000]      Δρ=ρ o ±ρ x  kg/m 3  
 
         [0000]      Δρ= m *(1/ V   o ±1/( V   o *γ*( T   x   −T   o ))+ V   o  kg/m 3  
 
         [0000]    The following relationship exists between ρ o  and ρ x : 
         [0000]      ρ o =ρ x   *V   o   /V   x    kg/m   3  
 
         [0039]    Still another use of the invention is to monitor certain fluids in pipes, such as oil pipes whereby it is made possible to continuously monitor the real density of the oil at the actual temperature. This makes it possible to detect changes of the density caused both by the temperature and water and gas content in the oil. 
         [0040]    A special case within the oil industry is to measure the density of the oil to establish the API grade. Normally this is done by 15.56° C. By using the present invention it is possible to measure the density at any temperature by taking into account the increased volume (or decreased volume) at the temperature. 
         [0041]    The objective of the invention has been to find a simple principle which makes continuous monitoring of the changes of density “on site” without taking a sample of the object in question, possible. 
         [0042]    This is achieved by applying a fixed pulse train generated by a PTZ transducer to the surface of the body/liquid in question and monitoring the change in the phase shift and amplitudes between the ingoing pulses and the reflected pulses. 
         [0043]    The pulses used may be sinus pulses, square pulses or step pulses. The pulses may be generated electrically, mechanically, pneumatically or hydraulically. 
         [0044]    As indicated above, one possible use of the present invention would be to monitor changes in the glucose level in a human body. Different types of sensors for this purpose have already been described. Thus U.S. Pat. No. 5,119,819 discloses a method and apparatus for non-invasive monitoring of changes in blood glucose concentration in a tissue specimen. The sensor used is based on the measurement of velocity changes of reflected ultrasound over a fixed distance with frequencies approaching 7.5 MHz, and whereby the velocity difference is due to changes of glucose content in blood combined with temperature difference. The method is in fact not non-invasive as claimed, since the sensor is to be placed on the earlobe with a tube extending through the ear lobe with the ultrasound sender attached at one end and a reflector at the other end thereof. 
         [0045]    The objective with the invention has been to find a simple principle which continuous could monitor the changes of the density “on site” without taking a sample of the object in question. 
         [0046]    This is achieved by applying a fixed pulse train generated by a PTZ transducer to the surface of the body/liquid in question and monitoring the change in the phase shift and amplitudes between the ingoing pulses and the reflected pulses. 
         [0047]    In order to verify the principle, a mathematical simulation of the same has been performed, which gave the results as shown in the graph illustrated in  FIG. 2 . 
         [0048]    From  FIG. 2 , it can be observed that, however small, there is a non-linearity of 2.224% in the results; this can be explained by the noise in the software setup. 
         [0049]    The table below shows the computed phase delay between the densities in the region of interest, considering 999.80 kg/m 3  as reference. 
         [0000]    
       
         
               
             
               
               
               
             
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Density versus phase delay in ns. 
               
             
          
           
               
                 Nr 
                 Density (kg/m 3 ) 
                 Phase Delay Difference (ns) 
               
               
                   
               
             
          
           
               
                 1 
                 999.80-999.85 
                 8.27 
               
               
                 2 
                 999.80-999.90 
                 16.25 
               
               
                 3 
                 999.80-999.95 
                 24.27 
               
               
                 4 
                  999.80-1000.00 
                 33.20 
               
               
                   
               
             
          
         
       
     
         [0050]      FIG. 3  show the principle set up of the model. 
         [0051]    After the modeling confirmed the principle, a test structure was constructed as shown in the picture of  FIG. 4 . 
         [0052]    The sensor was hooked up to a pulse transmitter and an oscilloscope was applied to monitor as shown in the following block diagram. 

 
         [0053]    The following instruments were used for the experimental set-up: 
         [0000]    
       
         
               
               
               
               
             
               
               
               
               
             
           
               
                   
               
               
                 No. 
                 Equipment 
                 Details 
                 Description 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 1 
                 Transducer 
                 NCE51 Wrapped 
                 In contrast to the 
               
               
                   
                   
                 around electrode 
                 standard transducers 
               
               
                   
                   
                 (WAE) 1 MHz PZT 
                 with two terminals 
               
               
                   
                   
                   
                 on two ends, WAE 
               
               
                   
                   
                   
                 transducer was used 
               
               
                   
                   
                   
                 to have good contact 
               
               
                   
                   
                   
                 with water. 
               
               
                 2 
                 Function 
                 HP 33120A 15 MHz 
                 The function 
               
               
                   
                 Generator 
                 Function Generator 
                 generator was used to 
               
               
                   
                   
                   
                 supply the bursts of 1 
               
               
                   
                   
                   
                 MHz for 80 cycles at 
               
               
                   
                   
                   
                 10 Vpp. 
               
               
                 3 
                 Oscilloscope 
                 Agilent MSO925A 
                 This 20 G Sample/s 
               
               
                   
                   
                 2.5 GHz 
                 sampling rate scope to 
               
               
                   
                   
                   
                 8 bit resolution was 
               
               
                   
                   
                   
                 used to capture the 
               
               
                   
                   
                   
                 raw response from the 
               
               
                   
                   
                   
                 Transducer. 
               
               
                 4 
                 Source Meter 
                 Keithly 2410 Source 
                 The precision source 
               
               
                   
                   
                 Meter 
                 meter was used to 
               
               
                   
                   
                   
                 supply stable current 
               
               
                   
                   
                   
                 to the RTD 
               
               
                   
                   
                   
                 temperature sensor. 
               
               
                 5 
                 Multimeter 
                 Agilent 34410A 6 
                 The precision 
               
               
                   
                   
                 Digit Precision 
                 multimeter was used 
               
               
                   
                   
                 multimeter 
                 to observe the output 
               
               
                   
                   
                   
                 voltage from the 
               
               
                   
                   
                   
                 temperature sensor. 
               
               
                 6 
                 Temperature 
                 IST Innovative 
                  1/10 Din tolerance, 
               
               
                   
                 sensor 
                 technology PT100 
                 Platinum RTD sensor 
               
               
                   
                   
                   
                 was used with a 
               
               
                   
                   
                   
                 temperature 
               
               
                   
                   
                   
                 coefficient of 3850 
               
               
                   
                   
                   
                 ppm/° C. 
               
               
                 7 
                 Thermal 
                 Julabo F34 thermal 
                 This was used to 
               
               
                   
                 controller 
                 control pumping 
                 insure the temperature 
               
               
                   
                   
                 station 
                 stability of ±0.03° C. 
               
               
                 8 
                 Weighing 
                 Mettler Toledo 
                 This scale was used to 
               
               
                   
                 scale 
                 PB403-S 
                 dissolve salt in 
               
               
                   
                   
                   
                 distilled water, to a 
               
               
                   
                   
                   
                 milligram precision. 
               
               
                 9 
                 Purified 
                 18 Mohm Pure Water 
                 The highest standard 
               
               
                   
                 water 
                   
                 water was used to 
               
               
                   
                   
                   
                 ensure the fitting of 
               
               
                   
                   
                   
                 fresh water density to 
               
               
                   
                   
                   
                 temperature curve. 
               
               
                 10 
                 Salt 
                 Sodium Chloride 
                 96% pure laboratory 
               
               
                   
                   
                   
                 grade for making 
               
               
                   
                   
                   
                 different density 
               
               
                   
                   
                   
                 solutions. 
               
               
                 11 
                 Silver 
                 Ag925 
                 Water container made 
               
               
                   
                   
                   
                 of 92.5% pure silver 
               
               
                   
                   
                   
                 and 7.5% copper. 
               
               
                   
               
             
          
         
       
     
         [0054]    The experimental results are shown in the figures;  FIG. 5  presents the density Vs phase delay plot for the solutions where the experiments were carried out at a constant temperature of 20° C., and the input parameters were used from table  1 . All experiments were performed in a clean room, taking all possible precautions to minimize the environmental factors. 
         [0055]    The results from the second study are shown in the  FIGS. 6 and 7 , where the change in temperature is plotted against phase delay and change in density is plotted against phase delay, respectively. The tests were performed with water in a silver container. 
         [0056]    The results from the third study where a stainless steel container was used for water are shown in  FIG. 8 . This experiment was performed to establish the effect different materials have on the transducer output. The results show that different materials are not an influential factor on the response from the PZT. 
         [0057]    In the resultant figures the illustrated non linearity is the maximum point deviation of the measured data from the linear fit curve. 
         [0058]    Prior to the experimental verification of the principle, a test was carried out and where the graphs shown in  FIG. 9  shows the difference in phase delay and amplitude. 
         [0059]    As can be seen there is a distinct phase shift between the curves at different temperatures. Furthermore it can also be seen that there is a distinct difference in the amplitude between the different curves. 
         [0060]    The non-linearity from the theoretical linearity is caused by inaccuracy in the weighted salt to water. 
         [0061]    In all studies the PZT was excited for 80 μs at 1 MHz frequency and the analysis was carried out on the response signal for 20 μs. For the excitation the voltage used was 10 Vpp, same as the voltage used in the mathematical simulation. 
         [0062]    After verification of the principle, human trial were initiated with the sensor located in a housing and attached to the body by an elastic band. 
         [0063]    The tests were performed on a non-diabetci human who increased the glucose level by drinking half a litre of Coca Cola and eating a slice of bread. During the test, the blood sugar was tested by Abbot&#39;s Freestyle Lite invasive glucose meter every 10 minutes. 
         [0064]      FIG. 10-18  show experimental measuring results with the present device on arm or stomach. The experimental results of the present invention (Mecsense) are correlated to convential blood sample measurements of glucose (Glucose). The measurements shows glucose readings as a function of time. The deviations of the two different kinds of measurements are indicated as numerical values in mmol/l and in percentage. 
         [0065]    The invention makes it possible to show the development in the density over time, average values and how fast the density changes in either direction. 
         [0066]    As for the measurement of the glucose level in humans the question arises if other substances changes in parallel with the glucose, and if so, how they can be mitigated. 
         [0067]    Many substances in blood and tissue will change after a meal. Especially the heavy triglycerides could pose a challenge. Tissue buildup of proteins, extra cellular fluid and hormones could be another. So far these sources if error have been estimated to be in the magnitude of 1/10000 to 1/1000000 of the effect of density changes imposed by glucose. 
         [0068]    Calculations performed on the effect of alcohol show that this is neglectable. 
         [0069]    The density changes with temperature must be compensated for, since a 0.1° C. change in the temperature represents 0.35 mmol/liter glucose. 
         [0070]    We have found that glucose changes in tissue have emerged theoretically as a sole and reliable parameter of tissue density changes. 
       Medical Evaluation of Dehydration by Hospitalized Sick and Dehydrated Patients. 
       [0071]    By moderate dehydration (5-10%) the condition is often complicated, the heart frequency, blood pressure and heart function is modestly affected. Peripheral circulation may be reduced (capillary filling time &gt;3 sec.), diuresis is often low and consciousness may be reduced. By severe dehydration (&gt;10%) the patient will often have marked dehydration symptoms such as reduced consciousness, reduced skin turgor, dry mucosa, halonated eyes, tachycardia, weak pulse, tachypnea or Cheyne-Stokes respiration and oliguria and anuria. 
         [0072]    By light dehydration in medical terms of 5% (which is 3 kg water of minimum 100 kg body weight (60% water)) and after long and hard training or gasteroenthritis, the concentration will increase in the excess of 5%. How this affect the density has to be verified by calculation. For ordinary patients this is a situation where NIGM (Non Invasive Glucose Monitoring) is not used. However, contrary to changes of glucose level, dehydration is a slow process taking hours and days whereas glucose levels can change in minutes. Thus, if dehydration takes place, glucose variation in diabetics will fluctuate over and under the mean body density caused by dehydration. 
         [0073]    The invention is further more described in the following drawings. 
         [0074]      FIG. 1  shows a principle set-up of the invention. 1) shows the body to be measured, 2) shows the PZT transducer which are generating the pulse trains, 3) is the pulse transmitter sending the electrical pulses to the PZT transducer, 4) is the power input, 5) is signal analyzer and 6) is the read out unit showing the results either as digest, graphs or a combination of these. 7) is a temperature sensor which by a mathematical algorithm compensates for the temperature on the object measured. 
         [0075]    It is to be understood that other wiring diagrams can be applied with the objective to send a pulse train to the PZT transducer with a receiver of the reflected pulse train with an analyzer of the phase shift and difference in the amplitude.