The LTC3588-1 from Linear Technology is an ultralow quiescent current power supply designed specifically for energy harvesting and/or low current step-down applications.

Vibration energy harvesting is powering micro-circuits.

Alternative power sources could soon replace the limitations set by batteries; such as increased costs, limited space within products, and the ongoing maintenance associated with replacement and recharging.

One solution is the harvesting of kinetic energy or ambient vibrations to self-power micro-circuits found in various low-power applications by utilizing the piezo and reverse piezo effect.

Piezo & Reverse Piezo Effect

Piezo utilizes flexible ceramics that are electrically active. Tony Armstrong, director of product marketing at Linear Technology explains, “The piezoelectrical effect is reversible in that materials exhibiting the direct piezoelectric effect (the product of an electric potential when stress is applied) also exhibit the reverse piezoelectric effect (the production of stress and/or strain when an electric field is applied).”

By capturing ambient vibrations from the surrounding environment, a voltage and electric charge is generated (piezo effect). This electric charge is then utilized to self-power the micro-circuit device.

“It’s the Solid State effect,” explains David Henderson, co-CEO and CTO of New Scale Technologies. “A good example is the pushbutton on a PC. When the button is pushed you hear a beep which is generated from the vibration of the push, converting into electric energy and changing the shape of the ceramics; and thus creating the sound. The electric energy is then converted into acoustic sound.”

Henderson also provides another example in medical ultrasounds. He notes that the piezo (ceramics) emits the ultrasonic sounds, which in turn creates the reverse piezo effect by reverting the electricicty back to measure the image.

Optimizing Performance 

Figure 1: To create a voltage from vibration, it is necessary to use a piezo transducer, which has an electrical signal output that must be conditioned using a power conversion circuit.

The best way to optimize the performance of the piezo and reverse piezo effect is challenging, according to Henderson.

“You want to get the frequency up, which is difficult because most frequencies from the ambient vibrations are pretty low, between 10 and 20 Hz. The amount of energy is not enough to create larger frequencies, so batteries are better suited for larger applications.”

According to Armstrong, in order to optimize a piezo transducer, “an end user needs to characterize their source for vibration frequency and displacement.

Once these levels have been determined, a Piezo manufacturer can design the Piezo which is mechanically tuned to the specific vibration frequency and size it to provide the necessary amount of power.

The vibration in the piezo material activates the direct piezo effect which results in the accumulation of charge on the output capacitance of the device.”

Creating Voltage

The piezo ceramics are essential in creating the voltage from the vibrations that are useful in microcircuits. Both Henderson and Armstrong emphasize the importance of a capacitor which stores the mechanical energy created by the ambient vibrations.

“The vibrating device creates an AC signal that has to be rectified and stored into a battery or capacitor, which then converts the AC into a DC signal. The battery and capacitor is what drives the microcircuit,” says Henderson.

“In order to create a voltage from vibration,” says Armstrong, “it is necessary to use a piezo transducer [which has] an electrical signal [output] that needs to be conditioned using a power conversion circuit. Once enough vibration cycles have passed, the input capacitor of the conversion circuit has accumulated enough charge to reach UVLO rising of the conversion circuit, which turns on the buck converter to start charging the output capacitor.” (Figure 1)

Converting Into Electric Energy

The mechanical energy that is produced from the ambient vibrations passes through the piezo ceramics, which in turn, creates a voltage that assists in powering the device by dampening those same vibrations. The LTC3588-1 from Linear Technology Corporation is an ultralow quiescent current power supply designed specifically for energy harvesting and/or low current step-down applications.

“It can interface directly to a piezoelectric or alternative AC power source, rectify the voltage waveform and store harvested energy on to an external capacitor, bleed off any excess power via an internal shunt regulator and maintain a regulated output voltage be means of a nanopower high efficiency buck regulator,” says Armstrong.

Vibration Energy Harvesting can continue to self-power devices as long as some type of mechanical vibration source exists, making a great alternative to cut prices, space and maintenance generally found in battery operated devices.