Measuring the efficiency of piezo energy harvesters (PEHs) according to the definition constitutes a challenging task. The power consumption is often established in a simplified manner, by ignoring the mechanical losses and focusing exclusively on the mechanical power of the PEH. Generally, the input power is calculated from the PEH’s parameters. To improve the procedure, we have designed a method exploiting a measurement system that can directly establish the definition-based efficiency for different vibration amplitudes, frequencies, and resistance loads. Importantly, the parameters of the PEH need not be known. The input power is determined from the vibration source; therefore, the method is suitable for comparing different types of PEHs. The novel system exhibits a combined absolute uncertainty of less than 0.5% and allows quantifying the losses. The approach was tested with two commercially available PEHs, namely, a lead zirconate titanate (PZT) MIDE PPA-1011 and a polyvinylidene fluoride (PVDF) TE LDTM-028K. To facilitate comparison with the proposed efficiency, we calculated and measured the quantity also by using one of the standard options (simplified efficiency). The standard concept yields higher values, especially in PVDFs. The difference arises from the device’s low stiffness, which produces high displacement that is proportional to the losses. Simultaneously, the insufficient stiffness markedly reduces the PEH’s mechanical power. This effect cannot be detected via the standard techniques. We identified the main sources of loss in the damping of the movement by the surrounding air and thermal losses. The latter source is caused by internal and interlayer friction.

Systems for measurement power characteristics of piezo harvesters in dependence on a frequency and a load resistance are not commonly used due its complexity. Therefore, the parameters are usually measured manually near its resonant frequency. In some cases, it is convenient to measure the characteristics in a broader range of parameters. Then, in order to achieve more precise results and effective measurement we decided to develop our own measurement system. The system controls an effective value of vibrations, sets a frequency and a load resistance for measuring a power generated by a piezo harvester and measures a tip displacement of the harvester. These quantities are used for a characterisation of piezo harvesters. Moreover, the voltage and current on vibration exciter are measured to evaluate the overall efficiency of the harvester. The system was tested on a harvester MIDE PPA-1001 for various added weights and vibration levels from 0.1 to 0.5 g. The measured data analysed and the efficiency was calculated as a ratio between a vibration power consumed by the harvester and its electrical output. The evaluated overall efficiency varies between 10 and 15 % nearby its optimal working conditions.

This paper deals with a logarithmic and a linear chirp sine generation on a fixed-point FPGA mainly for vibration testing, nevertheless, the generator can also be used in other areas. A basic overview of the logarithmic chirp sine signal is provided. Then, methods of software signal generation as well as different hardware platforms are briefly described and their pros and cons are mentioned. A DDS generator on FPGA needs the phase difference between samples as an input. This generation for the logarithm chirp sine signal is presented, and its resolution, errors and limitations on fixed-point arithmetic are revealed. Our implementation runs on Compact RIO 9067, uses 32-bit fixed-point and is able to generate linear and logarithm chirp signals from 10 Hz to 7 kHz with a minimum chirp speed of 1 oct/min.