M.J. Garcia-Hernandez

Ultrasonic monitoring of malolactic fermentation in red wines

The progress of malolactic fermentation in red wines has been monitored by using ultrasonic techniques. The evolution of ultrasonic velocity of a tone burst 1MHz longitudinal wave was measured, analyzed and compared to those parameters of oenological interest obtained simultaneously by analytical methods. Semi-industrial tanks were used during measurements pretending to be in real industrial conditions. Results showed that the ultrasonic velocity mainly changes as a result of the conversion by lactic acid bacteria of malic acid into lactic acid and CO2. Overall, the present study has demonstrated the potential of the ultrasonic technique in monitoring the malolactic fermentation process.

Ultrasonic Lamb wave NDE system using an air coupled concave array transducer

Rapid and non contact ultrasonic NDE techniques are of great industrial interest. This paper describes an air-coupled ultrasonic inspection system based on concave linear arrays working on pitch-catch configuration, The system has been designed for real-time characterisation of sheet and plate manufactured materials such as paper and resin-fibre composites. The proposed system is based on air-coupled Lamb wave excitation and reception that performs a rapid measurement of the optimum input angle of the incident beam impinging the material surface. No mechanical parts are used for tuning the plate wave excitation with the angle, doing that electronically by steering the acoustic beam. This solution increases the exploration velocity and the measurement repeatability and system reliability. The main contributions are related to the utilization of a 0.8 MHz ultrasonic air-coupled concave array transducer. This transducer, using only 32 elements, is able to generate a 2.5 square cm size flat wavefront, steering up to /spl plusmn/26 degrees with 1.6 degree resolution, keeping the distance of wave flight and the impact point constant. The angular resolution can be improved up to 0.2 degrees using a novel micro-deflection technique, without any increment of the system complexity.

Resizing buffer rods for ultrasound testing of food products with acoustic noise considerations

Buffer rods can be used to perform non-destructive and on-line analysis of food and beverage products. These rods, usually solid cylinders, can be long and heavy for certain applications. In this paper, a resizing analytic procedure is described. Buffer rods designed following this new procedure can be several times shorter than the conventionally designed ones, optimising thus their weight and cost. The signal to noise ratio (SNR) of the resized buffers is also studied in order to determine their practical usability. To this effect, simulations and experiments are conducted using metal and plastic buffer rod materials appropriate for food and beverage testing such as aluminium and polyethylene.

P3F-1 Lamb Wave Generation with an Air-Coupled Piezoelectric Array Using Different Square Chirp Modulation Schemes

This paper describes a new Lamb wave excitation technique using square chirp signals for air-coupled inspection of laminate materials in a non destructive testing system. The airborne ultrasonic waves are generated with an air-coupled ultrasonic plane array transducer with 15 active elements. Each array element is excited with a square chirp signal in order to apply pulse compression techniques. The advantages of using chirp signals are a greater SNR when using pulse compression (compared with burst or single pulse), a more precise time of flight calculation and a greater use of the transducer bandwidth. However, a decrease in the signal amplitude is expected due to the dispersion of the Lamb waves.

Linearity error in Clamp-on ultrasonic flowmeters due to the installation on pipes made of dispersive materials

This article analyses and explains the implications that dispersive materials have over the linearity in flow measurement when a Clamp-on ultrasonic flowmeter is used. This is of capital importance because dispersive materials are commonly used in the manufacture of transducer wedges and pipes. The evaluation of this phenomenon has been tested by experimental measurement. The used setup consisted of a water flow calibration facility where a commercial Clamp-on ultrasonic flowmeter was installed on it and its flow measurement was compared with a reference flowmeter. Two experiments have been conducted. A first experiment was performed to evaluate only the effect produced by the fact that the transducer wedge is made of dispersive material. For this reason, an ultrasonic flowmeter was installed on a pipe made of non-dispersive material, in this case, an INOX pipe. Linearity error introduced by the wedge was below 1%. This error complies with the accuracy specification of the ultrasonic flowmeter given by the manufacturer (±1.5%). Finally, a second experiment consisted of installing the ultrasonic flowmeter on a dispersive pipe (PVC pipe) in order to measure the worst condition (both materials, wedge and pipe, were dispersive). Under this condition, the linearity error was increased until it reaches a value of 6.4%. Moreover, in case of a dispersive material pipe, the bigger the pipe thickness is, the bigger non-linearity error is reached.

Temperature compensation of ultrasonic velocity during the malolactic fermentation process

Ultrasonic properties of materials present a strong dependence on temperature and in turn the ultrasonic velocity of propagation in the material under test. It is precisely for this reason that most ultrasonic measurements are often carried out with thermostated samples by using either water tanks or climate chambers. This approach is viable in a laboratory and when the measured or characterized samples are relatively small. However, this procedure is highly improbable to be applied when in situ measurements in industrial environments must be performed. This goes for the case of, for example, ultrasonic velocity measurements in wine while it is performing malolactic fermentation inside a tank of hundreds of thousands of litres. In this paper two different practical approaches to temperature compensation are studied. Then, the two temperature compensation methods are applied to the measured ultrasonic velocity values along a whole malolactic fermentation process. The results of each method are discussed.

Zero-Flow Offset Variation in Ultrasonic Clamp-On Flowmeters Due to Inhomogeneity and Nonlinearity of Pipe Materials

The objective of this paper is to measure the zero-flow offset variation in ultrasonic Clamp-on flowmeters produced by using pipes made of materials with a nonhomogeneous and nonlinear behavior. The evaluation of this phenomenon has been tested by the experimental measurement, the experiments consist of measuring the variation in the flow measurement when in “no-flow condition,” the transducers are moved along the pipe. Experimental results reveal that the reciprocity criterion is not fulfilled when nonhomogeneous and nonlinear pipe materials are used. Consequently, in these types of pipes materials, it is necessary to calibrate the offset when transducers are installed, and probably will need recalibration if the transducers are displaced to another position on the pipe. However, in installations, where it is not possible to stop flow in order to calibrate, the flowmeter will have an error in the measured value and this error will depend on the acoustic characteristics of the pipe material.

Effect of angle errors in conical tip buffer rods

Buffer rods are usually plastic or metallic solid cylinders of known acoustic properties, which are placed between the ultrasonic transducer and the sample under study. For some applications, the buffer rod end in contact with the sample under inspection is shaped in a form of a conical tip. If the cone angle is fixed to 45°, the components of the ultrasonic wave reflected at the buffer conical tip are received at the transducer in phase, forming thus a maximum amplitude signal. Otherwise, the components of the ultrasonic wave are received out of phase, composing thus a weaker signal. In this work, the effect of the buffer rod cone angle on the measurement signals has been studied by means of simulations and experiments. The simulations were performed using a two-dimensional finite differences tool and the measurements were conducted with the same operating conditions and buffer rod materials and dimensions than those defined for simulations. The influence of some aspects such as ultrasonic transducer operating frequency and diameter, and buffer rod material has also been analyzed.

Digital processing system for an air-coupled concave array NDT system

This work presents a processing subsystem for an air- coupled concave array NDT system, which uses Lamb waves. This processing system is able to equalize, delay and add the signals provided by a circular concave array used to receive Lamb waves in laminate materials, such as paper. A Field Programmable Gate Array (FPGA) is used in order to achieve shorter processing times and more flexibility than with DSP systems. The used array has circular concave shape and hence the delays used to get a plain wavefront are not lineal, thus a table with the delay values must be stored inside the FPGA. The Non-Destructive Testing is a growing field of interest for those industries where the high value of the developed components implies the need of a better quality control. In most of these cases the materials cannot be destroyed or altered, therefore a Non Destructive Test is needed. Ultrasonic testing is widely used to test a great variety of materials, but ultrasonic waves need a couplant to get a good transmission coefficient between the inspected material and the ultrasonic transducer. When air is used as couplant, new problems appear, like the higher attenuation that ultrasound suffers in this element. However, the greatest problem is the huge acoustic impedance mismatch that exists between air and the transducers. This mismatch, which is 40(PZT) to 0.006(Air), impedes a good transmission of the energy from the transducer to the inspected material. To improve the bad transmission coefficient, matching layers are included in the transducer (1) and improvements in the systems dynamic range are achieved (2). Lamb waves (3) are also widely used to inspect laminate materials. The main benefit which Lamb waves contribute in is the ability to inspect great portions of material in a short time, making them ideal for inspections where a great area has to be inspected. Moreover, the usefulness of Lamb waves in industrial applications where paper is tested has been demonstrated (4), (5). The usual way to produce a Lamb wave in a plate is to impact a plain wavefront with a certain angle respect to this plate. Lamb wave ultrasonic techniques are mostly based on the application of single element ultrasonic transducer with specific configurations, where the single element is specifically oriented to excite specific Lamb wave modes, see (6). The angular range where Lamb waves can be excited is very narrow in air (7), therefore a system that provides high angular resolution is needed. An array system would be a good solution to obtain this high angular resolution. It also has two main advantages, a transducer array will allow accurate beam steering, and the signal - to - noise ratio will improve. Furthermore, the array has a circular concave shape, so that it raises the angular steering margin of the array. The array used in this paper and its characteristics are deeply described in (8).

Design and implementation of an ultrasonic sensor for rapid monitoring of industrial malolactic fermentation of wines

ABSTRACT Ultrasound is an emerging technology that can be applied to monitor food processes. However, ultrasonic techniques are usually limited to research activities within a laboratory environment and they are not extensively used in industrial processes. The aim of this paper is to describe a novel ultrasonic sensor designed to monitor physical–chemical changes that occur in wines stored in industrial tanks. Essentially, the sensor consists of an ultrasonic transducer in contact with a buffer rod, mounted inside a stainless steel tube section. This structure allows the ultrasonic sensor to be directly installed in stainless steel tanks of an industrial plant. The operating principle of this design is based on the measurement of ultrasonic velocity of propagation. To test its proper operation, the sensor has been used to measure changes of concentration in aqueous samples and to monitor the progress of a malolactic fermentation of red wines in various commercial wineries. Results show the feasibility of using this sensor for monitoring malolactic fermentations in red wines placed in industrial tanks.