Identification of Concealed Insect Infestations Using a Passive Ultrasound Monitor

Concealed insect infestations in stored grain are responsible for large economic losses worldwide, and have traditionally been difficult to detect arid quantify. A simple method of infestation detection and quantification has been developed, taking advantage of the ultrasonic emissions generated by the feeding activity of the insects. The acoustic signals generated by the insects are characterized as bursts of energy in the frequency range of 5 to 75 kHz, varying with the variety of seed being examined. These signals can be detected reliably by monitoring the seeds for sounds in a frequency band between 30 and 50 kHz. The stage of development of an insect, and thus the amount of damage of which the insect is capable, can be predicted by studying a time series of these signals. A basic signal acquisition procedure has been developed which amplifies the variations in the pattern of acoustic signals associated with different stages of larval development for the cowpea weevil. A histogram is constructed to describe the time intervals between successive feeding events, and is compared to typical histograms associated with each stage of development. In over 80% of the cases, an acquired histogram from a cowpea weevil at a known stage of development was most similar to the typical histogram associated with insects at the same stage of development. Using this correlation to quantify an infestation could lead to a significant reduction in the use of pesticides for insect eradication

Pseudo-Random Codes for Single-Mode and Simultaneous Multi-Mode Operation in Ultrasonic Imaging Systems

Conventional pulse-echo imaging systems used in ultrasonics can become limited in average transmit power by transmitter, transducer, and medium peak-power limitations. In addition, imaging systems which use multi-element arrays are limited in speed by the necessity to transmit sequentially when scanning in more than one direction in order to avoid interfering echoes. A new system is studied which can overcome both the speed and power limitations by using correlation receivers and pseudo-random transmit codes. First, the performance of several single-mode correlation systems are compared to conventional pulse-echo systems in the presence of clutter and moving targets. The system which uses special pseudo-random codes called Golay codes is shown to provide the best overall performance. A multi-mode correlation system is then studied which images in many different modes (e.g. scan directions) simultaneously. This multi-mode system is studied under the effects of moving targets, clutter and background receiver noise. A comparison with the operation of Conventional sequentially-scanned phased array systems is made under a variety of signal-to-noise ratio (SNR) conditions and operating speeds to determine the optimal type of imaging system. Results indicate that under many conditions, a simultaneous multi-mode system can provide improved SNR and/or speed over conventional sequential multi-mode systems. The multi-mode system which uses Golay codes is shown to provide the best overall performanc

Adaptive Deconvolution to Improve Resolution

Deconvolution applied to ultrasonic flaw detection offers the possibility of greatly improved resolution through the elimination of the transducer response. Seydel has previously demonstrated that at least a modest increase in resolution is possible provided the signal-to-noise ratio of the signal being deconvolved is large enough. The random signal flaw detection system can be shown to be ideally suited to deconvolution since it provides enormous signal-to-noise ratio enhancement. Furthermore, the bandwidth compression inherent in this system allows A-D conversion of the output at a rate several orders of magnitude lower than the transmitted ultrasonic frequency. The computer program created to implement the deconvolution procedure also utilizes elementary pattern recognition techniques to deal with the remaining signal noise and ensure a good signal-tonoise ratio for the deconvolution output. The operation of this program was discussed and some preliminary results were presented which showed that at least a ten-fold increase in resolution is possible. At present this processing technique is restricted to a special class of targets, those composed of a series of plane surfaces

Deconvolution Processing for Flaw Signatures

The ultimate resolution of all ultrasonic flaw detection systems is limited by transducer response. Although the system output contains detailed information about the target structure, these details are masked by the system characteristics. Since the output can be described as the convolution of the target response and the impulse response of the system, it should- in principle - be possible to reverse this operation and extract the target response. In practice, it is found that the presence of even relatively small amounts of noise make the deconvolution process impossible. If, however, the flaw detection system has an extremely high output signal-to-noise ratio it is possible to use estimation techniques in the deconvolution process to achieve a good approximation to the actual target response. Results are presented that demonstrate these techniques applied to both simulated and experimental data. Coupling deconvolution processing with feature extraction is shown to yield an order of magnitude increase in range resolution

The Use of Noise Signals for Multi-Mode Beam Shaping

Noise as a transmitted signal has been used in radar, ultrasonic Doppler flow measurement, and ultrasonic flaw detection. In each of these applications, the unique properties of noise have mainly influenced the design and operation of the signal processing portions of the system in which it was used. Our present work shows that the use of noise as a transmitted signal may also benefit the properties of phased array transducers used in imaging systems. Some imaging systems excite the transducer array sequentially in several modes. The echoes resulting from each of the transmitted modes are stored separately and then processed together to yield an effective beam pattern which cannot be realized by any elementary mode of the array. Although phased arrays are frequently used to simultaneously receive in a number of modes, it has not, up to now, been possible for an array to transmit more than one mode at a time. A technique is described which allows several modes to be transmitted simultaneously from a transducer array. This is achieved by exciting each mode with its own independent random signal. The echoes corresponding to each transmitted signal can then be unambiguously identified by correlation with the desired reference signal. This technique generally leads to simplified system design and permits operation in real time. Preliminary results for a small random signal phased array system will be described

Random Noise Signal Processing

Pulse echo flaw detection systems have found extensive use in industry for quality control of many types of metal and ceramic components. The random signal flaw detection system described in this paper provides an increase in sensitivity of several orders of magnitude compared to conventional pulse echo systems. Following a review of the theory of system operation, we present some recently obtained results of our system on materials which are strongly sound absorbing, including ceramics, plastics and metals as well as material s which have large grains. In addition to detecting flaws in strongly absorbing materials we feel that this system might also be utilized as a way of estimating grain size, inclusion size or porosity

Beam Intensity Profiling Using Correlation Systems

Techniques are described in which the intensity distribution of an ultrasound beam is measured with high resolution by means of the radiation reflected from a target whose effective backscattering diameter is smaller than one wavelength. Correlation receivers are used to improve the signal-to-noise ratio of the echo. As the target is scanned across the beam, the phase of the reference signal applied to the correlation receiver must be adjusted to compensate for changes in the time of flight of the ultrasound echo. The broadband beam intensity mapping technique employs a noise signal in which phase compensation is adjusted manually. The other technique, which is used with narrow band signals, applies a phase quadrature technique to achieve phase compensation