- The Washington Times - Wednesday, August 4, 2004

Just as the keening sound of a car alarm aims to keep burglars away from a vehicle, the manufacturers of ultrasonic pest-control devices aim to use sound to keep birds, rodents and other pests out of homes and businesses.

“It’s a really loud noise for them,” says Mark Schafer, treasurer and past president of the Ultrasonic Industry Association in Dayton, Ohio, and president of Sonic Tech Inc. in Ambler, Pa. “At first, it appears to work well. The pests are startled and flee.”

Just how well the devices work to keep unwelcome pests from homes and businesses is up for debate.

“All biological systems adapt to things like that,” says Mr. Schafer, who holds a doctorate in biomedical engineering.

The pests can learn to ignore the sound after seeing a lack of danger, he says.

In addition, the sound travels within “a limited range,” says Charles Kramer, supervisor of pest control and facilities management at the University of Maryland at College Park. “Their strength decreases exponentially.”

The ultrasonic pest-control devices generate sound at 20 to 80 kilohertz, above the range of human hearing. Rodents, birds and some insects can hear the higher frequencies.

Hertz is the unit that measures the frequency of vibrations and waves, such as radio and sound waves, in the electromagnetic spectrum. One hertz is equal to one cycle per second of each vibration or wave.

“The frequency is how many times the sound waves are vibrating back and forth per second,” Mr. Schafer says.

The frequency indicates the pitch, which ranges from a low pitch, or a slow wave, to a high pitch, or a fast wave.

Sound from ultrasonic pest-control devices is broadcast by what is essentially a miniature loudspeaker designed to operate at high-pitch frequencies. The “speaker,” a piezoelectric crystal in the device, is named after piezo, the Greek word for squeeze, for the movement it makes.

The piezoelectric crystal is designed to convert electrical energy from the wall outlet or battery into a vibration. The crystal takes in an alternating voltage and vibrates in response, expanding and contracting as it does so. As the crystal vibrates, it emits high-frequency sound waves that leave the unit and beam out in a wedge shape, similar to how a flashlight or lighthouse beams light.

“They design the front of these units like a loudspeaker to beam the sound as broadly as possible,” Mr. Schafer says.

The sound at the ultrasonic level is “fragile” and cannot travel around corners and through walls, says Craig Ashcraft, director of marketing for Sonic Technology Products Inc. in Grass Valley, Calif.

“If you put a piece of paper in front of [the device], it will block the sound. Anything will block the sound,” Mr. Ashcraft says.

For this reason, manufacturers recommend that ultrasonic pest-control devices be placed in open areas.

“To make them effective is the positioning. You want to put them where the frequency range can broaden out to the widest range,” says Tom Zauszniewski, sales representative for Fox International Ltd., a distributor for Applica Consumer Products that has warehouse headquarters in Ohio, New York and Texas.

A product called PestChaser, designed by Sonic Technology Products, aims to repel rodents by using a swept frequency that alternates between 32 and 62 kHz 80 times a minute.

“It’s not one solid tone. To a rodent, it sounds like a jackhammer, something they can’t get used to,” Mr. Ashcraft says.

The jackhammer noise, however, is “not 100 percent effective,” he adds.

“It takes a couple of weeks for them to realize the noise is not going away on its own,” he says. “There are some rodents, because the food source and shelter is so attractive, they are willing to live with that noise, but the percentage is so low.”

Mr. Ashcraft recommends using traps along with the units to remove any rodents that decide to stay, since the noise will confuse them and make them easier to capture, he says.

“If it doesn’t send the rodents out, what it does is set up a perimeter so new rodents won’t come in,” he says.

Chicago-based Bird-X Inc. produces a bird repeller that projects 360 degrees of ultrasonic waves from four piezo ceramic speakers in one unit or with one or more of the speakers functioning as satellites. The sound, in the 22 to 30 kHz range, alternates among the speakers according to how the user programs the device. The speakers face opposing directions to achieve the 360-degree coverage.

“It’s better to have a variety of ways to combat the pest bird,” says Mona Zemsky, marketing manager for Bird-X. “Nobody is surprised they are very stubborn. They will grasp at anything to stay. Give them something they can’t get used to.”

An important aspect of the devices, Ms. Zemsky says, is that they do not bother humans.

“They don’t have to worry about being bombarded with these noises, not that we live in a library, either. This just won’t add to the mix,” she says.

But this benefit is the reason the ultrasonic devices do not work, says Mr. Kramer of the University of Maryland.

“Typically, pests are not all that sensitive to sound,” he says.

Mr. Kramer recalls using ultrasonic bird chasers 20 years ago that pigeons sat on and used as “pigeon-go-round,” he says.

“Pests would not be called pests if they were easy to get rid of,” he says. “There is a rule of suspicion one has to use when looking at real easy, gimmicky things.”

Richard Kramer, technical director of the Tacoma Park company American Pest Management, agrees with Charles Kramer, to whom he is not related.

“It doesn’t affect any animals that I’m aware of,” he says. “It may disrupt their behavior for a very short period of time, but then they attenuate to something like that.”

The devices “work to a point,” says Pete Meister, a general manager for Applica Consumer Products in Miami Lakes, Fla., which owns Black & Decker and Weitech, two brands that carry ultrasonic pest-control devices. “If the temptation of food is greater than wanting to be away from the sound, they’ll come into your house [or business].”

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