Sound Wave Energy  

 

Discussion of energy alternatives usually focuses on energy generation to power our business, public, and personal enterprises. We hear much less about energy alternatives other than power generating ones. Developing sound wave energy technologies and applications deserve much more media attention than these have yet to receive.

 

I’ll try to summarize some of these technologies and applications of sound wave energy before turning to those being developed and used by the timber and forest products industry. First, let’s characterize sound wave energy sources based on the frequency ranges of the waves being generated. Infrasound is generally considered to be sound waves below 20 hertz and in the inaudible range for humans. Audible sound waves extend from about 20 to 20,000 hertz, while ultrasound waves are usually considered to be above 20,000 hertz.

 

A few of the applications of ultrasound energy are probably familiar to most people. We see films and TV shows in which SONAR (sound navigation and ranging) is used. Some of us have sonar devices for fishing purposes. Many couples view fetal images that technicians produce using ultrasound equipment. Commercially available medical ultrasound systems date back to the 1960s, and sonar devices were created and employed by militaries in World War I and II.       

 

Ultrasound energy applications are much more extensive. Among these are non-destructive testing for infrastructure safety inspections, wildlife and water quality monitoring, industrial cleaning of electronics, motion detection and proximity sensors for security purposes, location detection of people trapped in rubble after catastrophes, acoustic “tweezers” or levitation for manipulating very small objects, and virtual or augmented reality creation. Ultrasound technologies are advancing in the fields of sonogenetics (sound waves to control cellular activities) and phononic computing (information processing using crystals for sound wave connections instead of through traditional electron transfer).  

 

Many infrasound and audible sound wave technologies applications also exist. A few examples are natural disaster detection before and during volcanic eruptions, earthquakes and tsunamis, wind farm turbine performance and problem monitoring, and forensic sound analysis for criminal investigations. Researchers are exploring ways to use piezoelectric materials to harvest energy from ambient noise in urban environments or from vibrations generated by machinery. Piezoelectric material generates an electrical charge when subjected to pressure or mechanical stress such as sound. Conversely, applying electrical voltage to the material can cause it to deform slightly.

 

There are existing and potentially important new applications of sound wave energy for the timber industry. Some of these applications are still emerging technologies, and their widespread adoption will depend on overcoming challenges related to cost and scalability.

 

Using sound waves for more precise forest inventory is an area of ongoing research, but traditional methods are still more common. Acoustic emission is currently being used to assess tree health and detect internal decay. Research is ongoing to refine these techniques for early disease/pest detection. Sound wave scanning has potential for identifying and predicting wood quality and for assessing tree age (though this is more complex). Such methods are sometimes combined with other technologies for receiving a more complete analysis.

 

Ultrasonic inspection is being used for wood density measurement and defect detection. Acoustic sorting is also being explored, but it faces challenges in terms of speed and accuracy for widespread application. For wood treatment, work is underway to explore how acoustic waves can improve chemical penetration, but this is apparently not yet a standard practice. Ultrasonic drying is also an area of research, and its effectiveness and cost are being investigated.

 

Acoustic testing is being used by some manufacturers for quality control of engineered wood products. Acoustic monitoring for timber transport seems a less established practice but using it for condition assessment and moisture tracking could have considerable merit and might become more common.

 

Who seems to be leading the research thrust into sound wave technology for the timber industry? There appears to be a mix of academic and corporate players. Some of the key American academic institutions include Oregon State University, North Carolina State, and the University of Tennessee. Universities in Canada and Sweden are also actively involved in this research.

 

Several corporations committed to research and sound wave energy application for non-destructive testing of timber are FaKopp, James Instruments, Inc. and Proceq (now part of Screening Eagle Technologies). FaKopp develops and provides handheld devices for assessing standing timber and logs, and it has been exploring the use of ultrasonic technologies for wood defect detection and quality assessment in timber processing. James Instruments, Inc. and Proceq also offer various portable ultrasonic testing devices.