Frank Daschner

Composition of foods including added water using microwave dielectric spectra

Abstract The added water content of fresh and untreated pork, poultry, fish and prawns was adjusted either by dipping in polyphosphate and salt solutions of known concentrations for controlled periods, or by injection (pork) with polyphosphate and salt solutions. Mixtures were prepared from treated and untreated fish and other foods (milk and flour). Liquid uptake was determined by the weight gain of samples. The proximate composition of the samples was determined: water, fat, protein, NaCl and phosphorus (for polyphosphate content). Complex dielectric spectra of each product were measured at known temperatures and at 31 frequencies in the range 0.2–12 GHz using an automatic network analyser (ANA) and a 3.0 mm open-ended coaxial sensor. The spectra were subjected to various procedures. • Principal component analysis (PCA) using the individual complex components. • Regression of the composition data against the principal components to obtain prediction formulae for composition including liquid uptake (internal cross-validation). • Regression of the composition data against raw spectral data and against other composition variables to obtain similar formulae. In order to design a simpler instrument, the effect on accuracy was studied of reducing the number of frequencies in the spectrum and its range. The slight loss of accuracy engendered by using only five or six frequencies was acceptable. The accuracy of the method in predicting liquid uptake and composition was good. Using one of the compositional variables in the calibration made it equivalent to accuracy obtained by proximate analysis, which was the limiting factor. Measurements on solutions of glycerol, NaCl and water with precisely known composition demonstrated that the intrinsic accuracy of the instrument was far better. A prototype instrument was built and validated using samples of prawns and herring.

Resonant microwave sensors for instantaneous determination of moisture in foodstuffs

Abstract Open microwave resonators are very well suited for online moisture monitoring during the production of foodstuffs. In order to allow for rapid measurements, the required information is derived from the dielectric behaviour of the material. Unlike for example the method of Karl Fischer titration, the dielectric microwave method determines the moisture content indirectly and is thus dependent on density changes. The present paper outlines special features of open resonators for density independent moisture measurement. It is demonstrated, how unfavourable design of the window for coupling out the fringing field of the open resonator leads to non-linear behaviour of the characteristics of resonant frequency and reciprocal quality factor vs density and moisture changes. Several engineered open microwave moisture sensors are presented and discussed. More in detail, a surface sensor, a surface sensor equipped with a small container on top, a self contained hand-held surface moisture sensor and a grooving-probe as well as a multi-hole sensor are shown. The electronics and the signal processing of the sensors are briefly described. Finally experimental moisture measurements and a density independent calibration are given for rolled oats. Moisture measurements on whole kernels of oats, barley and wheat demonstrate the only weak dependence of the microwave moisture measurement approach on the special type of material.

Non-contacting determination of moisture content in bulk materials using sub-nanosecond UWB-pulses

This paper presents a new approach of noncontacting moisture determination in bulk materials utilizing time-domain transmissometry. The described method is independent of the mass per area of the material under test and does not suffer from measurement ambiguities, which are well known from frequency-domain methods. Ultra-wideband quasi-Gaussian monocycle pulses are applied with a cycle width of approximately 400 ps. The measurement signal is transmitted through the material over free space using double-ridged horn antennas. The received signal is acquired in the time domain and analyzed with different methods of data processing. The results obtained with multiple linear regression, principal component analysis, and artificial neural networks are compared with each other. Furthermore, a possible hardware implementation for a dedicated time-domain transmissometer is proposed based on a earlier developed time-domain reflectometer for the determination of food quality.This paper presents a new approach of noncontacting moisture determination in hulk materials, which is independent of the mass per area of the material. It also dues not suffer from measurement ambiguities, which are well known from frequency domain methods. UWB quasi ganssian monocycle pulses are applied with a cycle width of approximately 400ps. The measurement signal is transmitted through the material over free space. The received signal is acquired in the time-domain and analysed, using multivariate calibration techniques. Principal component analysis and principal component regression yield the best results. Two different types of antennas and their influence on the accuracy of the measurements are investigated.

Strongly frequency dependent focusing efficiency of a concave lens based on two-dimensional photonic crystals

Results of an experimental study of a concave lens based on a two-dimensional microwave photonic crystal with neff<1 are shown. We demonstrate that the lens focuses electromagnetic radiation for transverse electric (TE) and transverse magnetic (TM) polarizations. Intensity gains as high as 5.4 for TE polarization and 6.3 for TM polarization were achieved for definite frequencies lying in the explored interval from 6to15GHz, the smallest area of the focal spot being equal to 0.24λ2 and 1.02λ2 for TE and TM polarizations respectively. The proposed lens serves as a model system that can be scaled to THz and optical frequencies.

Optimization of the microwave determination of water in foods using principal component analysis

In this paper a method for determining the composition of foodstuffs from the measured microwave dielectric spectra using an open ended coaxial probe is presented. The dielectric spectra of several kinds of meat were collected in the range of 200 MHz to 12 GHz. The data are used to predict the composition of the materials applying principal component analysis and regression. Effects of the reduction of the used bandwidth on the performance are investigated. Optimal frequency ranges with respect to measurement accuracy and hardware effort for an instrument are defined.

UWB Free-Space Characterization and Shape Recognition of Dielectric Objects Using Statistical Methods

This paper presents a novel method for the free-space characterization and shape recognition of dielectric objects using multivariate calibration methods and linear discriminant analysis. The dimensions of the variously shaped objects are comparable with some of the transmitted wavelengths of the ultra-wideband (UWB) time-domain pulses used. A system illuminating the objects under test by a subnanosecond UWB pulse has been built. An array of receiving antennas receives the scattered pulses that contain information about the shape, the size, and the dielectric or related material properties of the objects. Multivariate analysis is applied to separate geometric effects from those due to the dielectric properties. Results are shown for two measurement series determining the amount of carbon and weight or the dielectric constant of the objects under test, independent of their shape, size, and orientation. Furthermore, a classification algorithm is applied, separating the objects into geometrical classes independent of all other varied parameters.

UWB-Sensors for Industrial Applications

Apart of the new perspectives ultra wideband technology opens in communications, it also permits the development of a new class of electromagnetic industrial sensors, which is based on multi-parameter measurements. This paper presents three versions of experimental UWB-sensors of the new kind and demonstrates their capabilities. A non-contacting free space sensor for determining the moisture content of granular materials, a contacting sensor for estimating the storage time and quality of foodstuffs, and a sensing system for detecting and locating foreign bodies in material streams are described. The fundamental system design for all sensors is quite similar and based on pulses with picosecond rise times. An engineered version of the sensor system is presented for the quality sensor.

Multiparameter microwave sensors for determining composition or condition of substances

A multiparameter microwave sensor is introduced that is capable of monitoring the percentage of constituents in composite dielectrics like foodstuffs. Results are demonstrated for so called artificial meat and for fish. The method applies principal component analysis (PCA) and principal component regression (PCR), both known from other disciplines like chemometrics. A prototype instrument operating in the frequency domain is presented showing excellent results. Also time domain measurements are suggested, which prove for the first time the applicability of the PCA and PCR signal processing scheme on short pulses with ps- and ns-risetimes.

Rapid monitoring of selected food properties using microwave dielectric spectra

In this paper, a novel microwave measurement approach is presented, which is capable of determining selected food properties from the dielectric spectrum. Such properties could be the water content, a possible amount of additionally added water, the content of conducting ions or the percentage of other constituents, having a noticeable influence on the effective complex permittivity versus frequency. The approach is based on measured dielectric data across a significant bandwidth of one or two octaves (or more), and on data analysis using the multi-variate statistical method of Principal Component Analysis (PCA) and Principal Component Regression (PCR). The prototype of a dedicated microwave instrument is described and as an experimental example the viability of the new approach is demonstrated by the exact determination of the percentage of deliberately added water in fruit juices.

Non-contacting moisture sensing using a dedicated UWB time domain instrument

Abstract This paper presents a method for the moisture determination of small and irregularly shaped objects independent from their shape and orientation. The objects under test are illuminated by UWB-pulses and the scattered pulses are received by an array of antennas. A dedicated measurement set-up and time domain transmission instrument is proposed. The scattered pulses contain information about the geometric as well as the dielectric properties. In order to separate this information multivariate calibration is applied. The time domain data is therefore subjected to principal component regression, partial least squares regression and an artificial neural network. All calibration methods deliver excellent performance. The moisture content of the objects can be determined with an accuracy of prediction of 0.69% while the range of moisture is within about 5% to 24%.