Volume 2/Number 1


Watermelon thumper Echoes UD success

The computer-controlled ripeness sensor ultimately could result in huge savings for the global watermelon industry, according to Ed Kee, a UD extension specialist, and William J. Watson, executive director of the National Watermelon Promotion Board, based in Orlando, Fla.

Worldwide, the industry is believed to generate more than 1.5 trillion pounds of fruit for sale annually in 90 countries on five continents, reports Watson. Farmers in Delaware grow some $6 million worth of watermelons yearly, Kee says.

Watson says he was thrilled to learn of the new UD ripeness sensor. "Among our members, the number one thing that keeps popping up is that there needs to be a device to help anyone harvesting or buying a watermelon to determine ripeness," he says. "This invention can only help the whole watermelon industry."

A prototype version of the UD device cranks out a ripeness reading in just 12 seconds. It's also durable, easy to use, weighs about 18 pounds and costs less than $1,100, Kee says.

"This is the first generation of a very promising new machine," Kee adds. "Down the road, we envision a hand-held microprocessor to replace the laptop computer we're currently using with the device." Such a device could prove essential for farmers, he says, and it might be handy for consumers, too.

Watermelon growers need an automatic ripeness sensor, Kee says, because "it's not at all unusual for a 40,000-pound truckload of watermelons to be rejected at the marketplace." An entire load can be rejected if 10 melons are green, he explains.

"If the melons were delivered from Delaware and rejected in Boston, for example, then the farmer pays the freight both ways, losing about $5,000 to $6,000 on a 40,000-pound truckload," Kee points out.


The UD watermelon ripeness sensor was developed by students Matt Behr of Towson, Md., Dave Bartoski of Camp Hill, Pa., Allan Cohen of Wyckoff, N.J. and Jason Firko of Claymont, Del., all EG '99, as part of a senior design class focusing on real industry problems and customers.

But, the technology isn't simply a student project, says UD faculty member James Glancey, who helps supervise student design teams, with colleague Michael Keefe, associate professor, and class coordinator Dick Wilkins, professor, both in mechanical engineering.

"These students have come up with a technology that's absolutely viable," says Glancey, an associate professor of bioresources engineering and mechanical engineering at UD. "It would be very useful to growers."

Delaware's watermelon harvest for 1997 came to 64,600,000 pounds, making it the nation's 12th largest watermelon-growing state, just behind Maryland, U.S. Department of Agriculture statistics show.

Other top watermelon states include California, Florida, Georgia, Texas, Arizona, Indiana, North Carolina, South Carolina, Missouri and Oklahoma. Worldwide, the United States ranks fourth in global watermelon production, behind China, Turkey and Iran.


How does the UD machine work? Its central feature is a platform where the watermelon rests. Sandwiched between the platform and the melon, a piece of foam rubber holds the fruit steady. A mallet attached to a metal arm protrudes from the right side of the machine, while a microphone sits close to the melon, on the left.

When Behr swings the metal arm, the mallet strikes the melon. The microphone picks up the sound and transfers it via electric signal to a laptop computer. The voltage signal is then converted into digital information, which is analyzed.

Because the hollow thunk of a ripe melon echoes, it produces an acoustical signal that shows up as a peak on the computer screen, which dies down gradually. On melons tested thus far, the frequency of the signal, when normalized using volume, has shown a promising correlation to the actual sugar content of the melon, according to Kee. (The size of the watermelon influences the frequency of its signal and, therefore, is taken into account during analysis, Behr notes.)

Melon characteristic frequencies have ranged from 100 to 250 hertz, corresponding to the desired sugar content of 8 to 12 percent. These findings will be put to the test this summer, as researchers investigate more melons.

The work remains preliminary, Kee emphasizes, but results so far are promising: "The device is fast, and it's user-friendly," Kee says. "The electronics are sealed to keep out the dirt. It's also durable and easy to maintain." It's reasonably priced, too, and comes with Velcro straps, so that the computer and the sensor can be carried conveniently into the field.